implementation of haccp to the dairy industry (1)

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IMPLEMENTATION OF HAZARD ANALYSIS CRITICALCONTROL POINT (HACCP) TO THE DAIRY INDUSTRY:CURRENT STATUS AND PERSPECTIVESD. K. SANDROU a & I. S. ARVANITOYANNIS ba Laboratory of Food Chemistry and Biochemistry, Department of Food Science andTechnology, School of Agriculture , Aristotle University of Thessaloniki , Box 265,Thessaloniki, Hellas, 54006, Greeceb Laboratory of Food Chemistry and Biochemistry, Department of Food Science andTechnology, School of Agriculture , Aristotle University of Thessaloniki , Box 265,Thessaloniki, Hellas, 54006, GreecePublished online: 05 Mar 2007.

To cite this article: D. K. SANDROU & I. S. ARVANITOYANNIS (2000) IMPLEMENTATION OF HAZARD ANALYSIS CRITICALCONTROL POINT (HACCP) TO THE DAIRY INDUSTRY: CURRENT STATUS AND PERSPECTIVES, Food Reviews International, 16:1,77-111, DOI: 10.1081/FRI-100100283

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Food Rev. Int., 16(1), 77111 (2000)

IMPLEMENTATION OF HAZARD ANALYSISCRITICAL CONTROL POINT (HACCP) TOTHE DAIRY INDUSTRY: CURRENT STATUSAND PERSPECTIVES

D. K. SANDROU and I. S. ARVANITOYANNIS*Laboratory of Food Chemistry and BiochemistryDepartment of Food Science and TechnologySchool of Agriculture Box 265Aristotle University of Thessaloniki54006 Thessaloniki, Hellas (Greece)

ABSTRACTThe dairy industry is confronted with new challenges because of thecontinuously increasing complexity of the ingredients/packaging mate-rials used and the technological advances/processes employed. The cur-rent structural development of the dairy industry means that any qualityfailures are bound to have more widespread consequences than previ-ously. Consequently, the role of preventive controls is becoming increas-ingly important. Implementation of Hazard Analysis Critical ControlPoint (HACCP) by the dairy industry is anticipated to enhance consumerconfidence in its products and reduce the existing barriers in interna-tional trade. This review discusses the implementation of HACCP prin-ciples throughout the production and distribution chain of milk and dairyproducts.

KEY WORDS: HACCP; Hazard analysis; Critical control point; Dairyindustry; Milk; Milk products

*To whom all correspondence should be addressed. Tel.: 1 30 31 998788. Fax: 1 30 31 998789. E-mail:[email protected]

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Copyright 2000 by Marcel Dekker, Inc. www.dekker.com

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78 SANDROU AND ARVANITOYANNIS

INTRODUCTION

Milk and dairy products have been implicated in main human diseases such as tuber-culosis because milk has always been considered one of the most perishable fooditems (ICMSF, 1988). The structural development of the dairy industry in most coun-tries, including the geographical expansion of milk products manufactured by largeproduction units, means that any quality failure will probably have more widespreadconsequences than previously (Burgess et al., 1994).

Results of the WHO surveillance program (WHO, 1992) indicate that the numberof causative agents of food-borne diseases continues to increase. End product testinghas been for many decades the most widely used tool to ensure food safety. However,there is a growing awareness that end product testing cannot by itself ensure thesafety of food (Heeschen, 1997). The best way to achieve disease reduction is throughimplementation of the preventive system of Hazard Analysis Critical Control Point(HACCP) from production to consumption of dairy products (Roberts, 1995).

However, prior to HACCP implementation, it was proved to be advantageouswhen several prerequisite programs such as Total Quality Management (TQM), Sta-tistical Process Control (SPQ), Just-in-Time (JIT), ISO 9000/ASQ 9000 and BS5750, and Good Manufacturing Practice (GMP) had already been in place (Hubbard,1996; Gould, 1994). TQM is a comprehensive approach to improving competitive-ness, effectiveness, and flexibility through planning, organizing, and understandingeach activity, and involving each individual at each level. Total quality results ineffective leadership (upper management) through commitment to constant improve-ment, a right first time philosophy, training people to understand customer-suppliedrelationships, managing systems, processes, and teamwork improvement, modernsupervision and training, and continuous education. The basis for the TQM modelimplementation resides on changes/improvement in culture, communication, andcommitment thus leading to enhancement of customer-supplied relationship (Oak-land, 1993; Ishikawa, 1989). It is vital for the company to communicate to any exter-nal supplier the purchasing organization policy on the quality of incoming goodsand services. Suppliers who incorporate a quality management system of ISO 9000/ASQ 9000 series or BS 5750 or SPC into their operations will be selected. JIT is aprogram directed toward ensuring that the right quantities are purchased or producedat the right time and that there is no waste, or in other words, high quality, low cost,minimum lead times and high flexibility (Hutchins, 1985; Sarv, 1992). The methodsto be adopted in order to reach these goals will comprise: TQM, focus on design,plant and equipment layout, set-up time reduction, lot or batch size reduction, work-in-progress and/or buffer stock reduction, and flexible workforce. In 1997, the Inter-national Organization for Standardization (ISO) launched the ISO 9000 series whichhad many similarities to the ASQ 9000 and was based upon the earlier developedBS 5750. The ISO 9000/ASQ 9000 requirements include:

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IMPLEMENTATION OF HACCP TO DAIRY INDUSTRY 79

Management responsibility (quality policy, organization chart, responsibilities);Quality system (quality plan and manual, operators skills and training);Quality control procedures, inspections, and checks;Contract review [customer requirements (quality and delivery date), differences be-

tween order/quotation];Design control (plan R&D, verification and identification of design outputs,

changes);Document control (quality and departmental manuals/service, list of approved sup-

pliers, purchasing specification, international/national standards);Purchasing (objective selection of subcontractors based on evidence/assessments);Identification/Traceability (from purchased materials to finished products);Process control (description of process/equipment);Checking/Inspecting incoming materials/services/equipment;Non-conforming products (documented system);Corrective action (failures, complaints from customers to suppliers);Quality records (to demonstrate compliance with own requirements);Quality system audits and reviews (internal, external);Training (identifying and reviewing training needs, carrying them, and keeping rec-

ords);Servicing (adequate resources, regular service);Statistical Techniques (Implementation of SPC)

Good Manufacturing Practices (GMPs) are an indispensable part of every foodquality system. They contain detailed requirements for avoiding the occurrence ofmishappenings in the following areas (Hubbard, 1996; Gould, 1994):Personnel (disease control, cleanliness, education, training, supervision);Plant and Grounds (storage and maintenance of equipment and materials, waste dis-

posal, appropriate building construction for ventilation, cleaning, lighting);Sanitary operations (special precautions for toxic agents, pest control, food contact

surfaces);Sanitary facilities and Control (water supply, toilet facilities, sewage and waste dis-

posal);Equipment and Utensils (design, materials, and workmanship should be cleanable);Processes and Control (sanitation in incoming materials, transporting, segregation,

manufacturing, packaging, and storing)HACCP is an internationally recognized process control system to assess hazards

and to establish safety control systems that focus on prevention (checking of CCPs)rather than relying on end product testing (Heeschen, 1997). Appropriate qualitativeand quantitative sampling aimed at getting a representative sample is a prerequisitefor excluding a typical source of analytical error (Leenheer, 1993). It provides plant

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management with specific controls and advice on how to operate their productionprocess at these points (Manis, 1995). Control is proactive since remedial actionsare taken in advance and deviations can be detected in time in order to take theappropriate steps aiming at reestablishing control (Notermans and Mead, 1996).HACCP can be characterized as a hierarchical control system and should be regu-larly reviewed to make the necessary changes if any modifications of the process/product are required (Dijkers et al., 1995; Mortimore and Wallace, 1995).

There are seven HACCP principles that permit a systematic approach to dairyplant:

Hazard analysis associated with every step, raw material to consumption of the productCCP identification to control all hazards [microbiological (severe, moderate with

potential for wide dissemination and moderate with limited dissemination), physi-cal (extraneous material such as metal, glass, plastic, wood, etc.), and chemical(drug residues, pesticizers identified, toxins)

Limits for preventionMonitoring needsCorrective actions to be taken if monitoring identifies variation from established

limitsEffective record keepingProcedures to verify that HACCP is working

HACCP is a 12-step process that incorporates the above mentioned seven HACCPprinciples. In addition, management consent and team selection must be obtained,the dairy food and distribution method should be described as completely as possible,the intended use and intended users should be identified, a flow diagram of the prod-uct developed and verified, and a mechanism established for evaluation and revisionfor a HACCP plan once implemented. The dairy industry presents two distinguishingfeatures; its main raw material is a single, primary agricultural product which remainsbasically unchanged despite the various processes it goes through for controllingseveral potential microbiological hazards (van Schothorst and Kleiss, 1994). Byadopting a national or international standard of good dairy practices for the produc-tion of milk, many worries concerning potential chemical and microbial residuesleaving the production unit can be alleviated through documentation and education(Cullor, 1997). Of particular importance for the quality of raw milk is that dairyproducers and veterinarians can implement rapid testing assays as part of the on-farm HACCP programs in order to determine whether the critical limits for potentialfood-borne drug and chemical residues and infectious agents have been exceeded(Gardner, 1997; Bluthgen and Heeschen, 1997a; Bluthgen and Heeschen, 1997b;Darling et al., 1974).

This article will discuss the application of HACCP principles throughout the pro-duction and distribution chain of milk, cheese, yogurt, ice cream, cream, and butter.

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Furthermore, a brief discussion of the current status and perspectives of the dairyindustry will be given.

CURRENT STATUS OF HACCP IN THE DAIRY INDUSTRYProduction of Pasteurized Milk

Pasteurized milk is the largest selling milk in most industrialized countries becausethe consumption of raw milk carries the risk of infection by milk-borne pathogens,especially Salmonella (Small and Sharp, 1979) and Campylobacter (Heeschen, 1996;Potter et al., 1983; Summer, 1996). The International Dairy Federation has definedpasteurization as, A process applied to a product with the object of minimizingpossible health hazards arising from pathogenic microorganisms associated withmilk, by heat treatment, which is consistent with minimal chemical, physical andsensory changes in the product (Varnam and Sutherland, 1996; EEC 92/46, 1992;EEC 93/43, 1993; Mossel, 1981). However, in some countries, farms are still allowedto sell raw milk for household use. In the UK and several other countries, bottledraw milk can be directly delivered to customers provided that milk-producing cowshave been attested free from tuberculosis and brucellosis (Mossel et al., 1995).

The flow diagram for the manufacture of pasteurized milk is shown in Figure 1and the critical control points are indicated. Raw milk is a magnificent medium forthe growth of microorganisms which can be derived from the udder, the environment,

Figure 1. Flow diagram for the manufacture of pasteurized milk (Dijkers et al., 1995).

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the milk handling equipment, and the personnel (Mossel et al., 1995). Escherichiacoli, Staphylococcus aureus, Corynebacterium bovis, Streptococcus agalactiae, Str.dysgalactiae, and Str. uberis (Hahn, 1996) may cause under certain circumstancesmastitis, leading to significant economic losses (Elbers et al., 1998; Barkema et al.,1998). In winter months, feed and bedding are the main sources of thermoduricspoilage organisms, while milk handling equipment is the major source of Gram-negative, psychrotrophic spoilage bacteria. Employees suffering clinical symptomsof infection and feces may contaminate milk with Campylobacter and Salmo-nella.

In previous years, tuberculosis (Mossel et al., 1995) and brucellosis (Romero etal., 1995) caused by Mycobacterium bovis or M. tuberculosis and Brucella abortus,Br. melitensis or Br. suis were of major concern (Mossel et al., 1995). Cattle andsubsequently raw milk may be infected with Aeromonas, Campylobacter (Potter etal., 1983), Salmonella typhimurium, Listeria monocytogenes (Rocourt and Bille,1997; Santillan et al., 1997), Yersinia enterocolitica (Walker and Gilmour, 1986)and Coxiella burnetii (Mossel et al., 1995) from a number of sources such as non-potable water, pastures, feces, air, animals purchased from other herds, and buildings.Both milk composition and high temperatures support the growth of spoilage bacte-ria, such as Enterococcus, Streptococcus, Lactobacillus, Bacillus and members ofthe Enterobacteriaceae, despite the presence of anti-microbial systems in milk. Attemperatures above 7 C, the increase in Gram-negative psychrotrophic bacteria, es-pecially Pseudomonas and Alcaligenes, and production of lipolytic or proteolyticenzymes is rapid thus causing deleterious changes in milk and dairy products (Var-nam and Sutherland, 1996).

Antibiotics (Dasenbrock and LaCourse, 1998), mycotoxins (van Egmont et al.,1997), radioactive material, agricultural chemicals (Bluthgen and Heeschen, 1997b),polychlorinated biphenyls (Bluthgen et al., 1997), and poisonous plants may entermilk through intra-mammary therapy and through transfer from the feed or the envi-ronment. These substances may cause strong allergic reactions, carcinogenesis andstomach irritation to the consumer and they may adversely affect the technology ofdairy products (Troutt et al., 1995).

In conclusion, milk should only be accepted at the dairy plant when obtained fromanimals which:

Are not suffering from tuberculosis and brucellosis (Romero et al., 1995);Are free from contagious diseases (Heeschen, 1996; Troutt et al., 1995);Are not suffering from clinical mastitis (Mossel et al., 1995);Have not be treated with antibiotics unless milk has been obtained after expiration

of the retention period following veterinary treatment (Troutt et al., 1995);Are subjected to proper supervision and support from relevant authorities (Tschumi,

1997);Does not suffer from infections or tissue damages of the udder (Burgess et al., 1994)

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To ensure that milk-producing animals meet these standards and that their milk isof the expected high quality, adherence to good husbandry practices is essential(Heeschen, 1996; Leenheer, 1993). Pastures should be free of harmful substances,animal manure, and sewage sludge, while the supplied water should preferably beof potable quality. In order to avoid spread of infections within the herd, good hy-gienic status of animals should be maintained and quarantine of any incoming stockis necessary (Troutt et al., 1995). Scrupulous dairy hygiene can reduce the levels ofpsychrotrophs and thermodurics to the order of 35 3 103 cfus ml21 (van den Berg,1986). Total colony counts in raw milk within the range 12 3 105 can be easilyreached as well (Mossel et al., 1995). Cleaning the udder and the teats with appro-priate antiseptics before and after milking can minimize the hazards of tissue damageand infections during milking (Burgess et al., 1994). Farmers should be educated tomake the best use of antibiotics, conform to hygienic rules and avoid handling milkduring sickness (Mossel and Grun, 1971). Appropriate design and construction ofmilk handling equipment should reduce the risks of contamination of raw milk, whileits thorough cleaning and disinfection are necessary before use (ICMSF, 1998). Inrecent years, improved standards of housing and use of separate milking parlors havefurther reduced the risks of raw milk contamination. After milking, rapid cooling ofmilk to below 4 C within 4 h should follow, on-farm storage time should be limited,and temperature abuse should be avoided (Dijkers et al., 1995). As part of the on-farm HACCP programs, cost-effective, accurate, and reproducible tests that can de-termine the status of cows, milk and dairy environment are required (Reybroeck,1996). For infections and residues of low prevalence, testing strategies that are highlyspecific can help minimize false-positive results and excessive costs to the dairyindustry (Gardner, 1997). In the nearest future, on-farm procedures and in particularimplementation of HACCP (Troutt et al., 1995) that can monitor the presence ofemerging and reemerging human pathogens will definitely need to be established(Cullor, 1997).

When raw milk is pumped to the transfer tanker, an automatic pump stoppingabove 6 C should be used and this temperature should not be exceeded during trans-portation (Dijkers et al., 1995). Transportation time should be as short as possible,avoiding any unnecessary delays. Moreover, milk tankers should be cleaned anddisinfected at least daily, should be regularly inspected and maintained, and shouldnot be used for transport of any other materials in order to prevent microbiologicalor chemical recontamination of milk (Burgess et al., 1994). The tanker driver shouldnot suffer from infections, should conform to hygienic rules, and should not haveaccess to stables in order to avoid contamination of milk with pathogens of humanorigin.

Milk tankers should be cleaned and disinfected after discharging. Dischargingareas should have adequate drainage and should be easily rinsed to avoid accumula-tion of water and raw milk residues. Milk should be conveyed from the tanker intothe dairy building in closed hose or pipe systems. On receipt, raw milk should be

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subjected to the following controls by analytical laboratories performed accordingto Good Laboratory Practice (Broderick, 1993) for quality assessment:measurement of pH value and of titratable acidity;tests for sediment and antibiotic residues;measurement of temperature, which should not exceed 10 C;determination of its microbiological quality through validated rapid methods;determination of its composition;tests to ensure that milk has not been adulterated;somatic cell count

If milk is pasteurized within 4 h from the time of reception, it should be immediatelycooled and kept refrigerated at a temperature below 6 C to prevent the growth ofpathogens. If holding time is 34 days, the temperature should be kept below 3 Cand for 4 days a temperature of 2 C or below is required (ICMSF, 1988). To extendthe storage time of raw milk, thermization, cooling or addition of lactoperoxidaseor hydrogen peroxide is suggested (Varnam and Sutherland, 1996). Mixing storedraw milk with newly received raw milk should be strictly avoided and storage tanksshould be cleaned and disinfected prior to their filling with fresh raw milk (Burgesset al., 1994).

Standardization of fat to the specific concentration desired and size reduction offat globules to minimize creaming should always precede pasteurization. Homog-enizers can be incorporated in the pasteurizer and operate near pasteurization temper-ature, allowing the use of lower pressures and reducing microbiological contamina-tion. Visual inspection and microbiological tests should be used to verify the correctapplication of CIP and pressure settings should be periodically checked.

The next major step is pasteurization, the purpose of which is to increase productshelf-life and render raw milk safe by eliminating the hazards caused by the presenceof heat sensitive pathogenic microorganisms (van Schothorst and Kleiss, 1994; Jer-vis, 1994) The requirements for the successful operation of High Temperature ShortTime (HTST) pasteurization for commercially used are: Application of correct thermal process by means of:

an automatic safety system which prevents extreme temperatures (too low/high),a long, thin holding tube to minimize running period (Farrall, 1973),an automatic flow diversion device which ensures flow control and assurance (Dijk-

ers et al., 1995); Prevention of cross-contamination within pasteurizer by correct design of the

equipment and proper operating conditions; Cleanability of pasteurizer which can be achieved through:

use of the suitable type of stainless steel,

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correct design of the equipment to allow access to all of its parts during cleaning,proper training and motivation of personnel (ICMSF, 1988); Limitation of fouling by minimizing temperature difference between heating me-

dium and milk; Economic operation by using plate heat exchangers of large surface area and

through regeneration (Varnam and Sutherland, 1996)In order to verify that milk has been correctly pasteurized thermograph recordsshould be examined, while an alkaline phosphatase test can be additionally usedfor verifying whether pasteurization is adequate or whether milk has been cross-contaminated by raw milk (Harding, 1991). The possible sources of cross-contamina-tion of pasteurized milk are shown in Figure 2 (Burgess et al., 1994). Post-heatingrecontamination will turn pasteurized milk sour and sometimes even cause entericinfections (Mossel et al., 1995). It was previously claimed that the risks from recon-taminated heated products may be even greater than those from raw food becauseof the absence of a competing flora (Kraft et al., 1976). The sources on the rightside of Figure 2 are external to the factory and stand for items from which the factoryshould be protected, while the sources on the left side are those that originate frominside the factory and should be subjected to strict control programs. Air and peopleare shown in the center because they are potential contamination sources both insideand outside the factory (Burgess et al., 1994; Simonsen et al., 1987). Of particularimportance to the prevention of cross-contamination is the proper design and opera-tion of the equipment and the distinction between the areas, the equipment, and theCIP system used for raw and pasteurized milk (Mortimore and Wallace, 1995).

After pasteurization, milk should be rapidly cooled down to 4.5 C. A temperaturerise to over 5 C results in an alarm and if it cannot be stopped, the process shouldbe stopped at a temperature above 6 C (Dijkers et al., 1995). Although GMPs includethe necessary maintenance of the equipment, leaks in the barrier between milk andcooling fluid may eventually occur. To control the hazard of recontamination ofpasteurized milk, a slight over-pressure on the side of milk is exerted (van Schothorstand Kleiss, 1994).

Figure 2. Possible sources of cross contamination of pasteurized milk (Burgess et al., 1994).

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Packaged pasteurized milk is stored in refrigerating plants for 24 h at most, socontrol is just a matter of correct planning. Refrigerating plants should (IDF GroupD14/44, 1995):be carefully dimensioned;have automatic defrosters;achieve equal distribution and circulation of cold air;have adequate refrigerating capacity;provide sufficient ventilation and airing

Packaging of pasteurized milk prevents any microbiological, chemical, and physicalcontamination during storage, transport, and distribution provided that package in-tegrity is maintained (Jervis, 1994). Packages should be filled to the predeterminedvolume and seals should be carefully examined to prevent leakage and contamination(Smolander et al., 1997). Glass bottles should be either visually inspected or exam-ined by an automatic photoelectric cell device to ensure that they are adequatelycleaned and sanitized, while the quality assurance system of the supplier of the plas-tic-coated cardboard containers should be periodically audited to ensure their satis-factory bacteriological quality (Varnam and Sutherland, 1996; Graves et al., 1998).Packaged pasteurized milk is stored in refrigerating plants for 24 h at most andcontrol is just a matter of correct planning. Refrigerating plants should be carefullydimensioned, have adequate refrigerating capacity and automatic defrosters, and suf-ficient ventilation and airing and circulation of cold air (IDF Group D14/44, 1995).

During cold storage, air temperature should be controlled by an automatic controlloop in order to avoid rise in temperature over 6 C. For the same purpose, vehiclesused for the distribution of milk should have mechanical compressor units. Bothretailers and consumers should put milk into coolers and apply the first-in first-out(FIFO) management. Photodegradation of milk during storage is usually attributedto light transmittance (photooxidation), oxygen permeability of the packaging mate-rial as well as the storage temperature (Bosset et al., 1994). Since many nutrientscontained in milk are sensitive to light, i.e., vitamins A, B6, B12, D, and K, tocopherol,tryptophan, b -carotene, and unsaturated fatty acids, it is advisable to use opaque orstrong light scattering packaging materials (Shipe et al., 1978). Effective inspectionby public health inspectors plays an important monitoring role in the case of retailers,but cannot be applied to consumers (Dijkers et al., 1995).

Production of Ultra High Temperature (UHT) Milk

UHT milk, in contrast to pasteurized milk, has extended shelf life at ambient temper-atures, since the applied thermal process is capable of inactivating vegetative micro-organisms and spores. Although UHT eliminates almost all psychrotrophic organ-

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isms, the latter frequently produce lipases and proteases, which manage to survivebecause of their thermo-resistance. Survival of these enzymes is likely to lead torancidity and induce gelation of milk (Adams and Brawley, 1981; Keogh and Pet-tingill, 1982). UHT production requires the application and maintenance of sterileconditions from sterilization until aseptic packaging. The flow diagram for the pro-duction of UHT milk is shown in Figure 3. For the quality and safety aspects ofraw milk apply what have already been described for pasteurized milk.

UHT heating can be carried out by using either an indirect or direct method. Bothof them require the use of flow diversion devices and recording thermographs, similarto pasteurization. In the indirect method, milk is treated in tube or plate heat ex-changers and high operating pressures are employed to avoid milk boiling at hightemperatures. In direct heating, milk is preheated by a regenerative heat exchangerand then heated up to 140 C by mixing milk with superheated steam, either by injec-tion or infusion. Flash cooling is the last stage of direct heating and has three techno-logical objectives (Varnam and Sutherland, 1996):reduction of thermal damage;removal of water to restore milk to its original composition;removal of low molecular weight volatile compounds to improve product quality

Direct heated UHT milk is considered to be of higher quality than indirectly heatedUHT milk because the former is held for shorter times at higher temperatures thanthe latter. The critical aspects of UHT heat treatment are the flow rate, the pressure

Figure 3. Flow diagram for production of UHT milk in semi-rigid containers (ICMSF, 1988).

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and the temperature of milk and heating medium, the correct functioning of flowdiversion valve and the cleanliness and sterility of the equipment prior to the steriliza-tion treatment (ICMSF, 1988). Pasteurization is a CCP because it greatly increasesrefrigerated shelf-life. Fouling is also a significant problem in indirect plants, sinceit affects product quality and the economic operation of the plant. Deposits of milkon heat exchange surfaces can be minimized by reducing the temperature differencebetween heating medium and milk and by processing good quality milk, the pHvalue of which should be over 6.6 (Varnam and Sutherland, 1996).

Homogenization of milk is essential in order to avoid the occurrence of fat separa-tion and hardening during storage. Sterility of the homogenizer is critical to preventcontamination of direct heated milk and it must be designed and operated accordingto aseptic principles. Homogenization pressure and single or double stage operationof the homogenizer should also be considered. Cooling of UHT milk to room temper-ature is performed in plate or tube heat exchangers. The equipment should be prester-ilized, pinholes free and should have been suitably designed for aseptic operationand sufficient overpressure on the sterile side to prevent any recontamination of UHTmilk (ICMSF, 1988).

Sterilized milk is finally filled under aseptic conditions into presterilized flexiblecontainers (Holdsworth, 1992). Aseptic filling machines should be installed in a cleanarea, separated from other areas of the plant to minimize contamination of the equip-ment (David, 1992). Airflow, pressure, and relative humidity should be constantlykept under control. Packaging material and air or gases used for flushing packs shouldbe sterilized. The efficiency of packs and air sterilization should be verified withchallenge tests and the integrity of seals with non-destructive tests (Floros and Gna-nasekharan, 1992), dye tests, or microbiological challenge tests. Bacillus stearother-mophilus is commonly used as a challenge organism for milk sterilization, while thechoice of challenge organism for packaging material sterilization depends on themethod used for sterilization. Personnel should conform to hygienic rules and followmanufacturers instructions for control of the aseptic filling equipment.

A determining factor of quality end product (Scott and Bloomfield, 1990; Holds-worth, 1992), which should not be overlooked, is the maintenance of sterile condi-tions downstream of sterilization. Sterility can be achieved by circulating hot waterthrough the plant and by ensuring that the parts of the equipment in contact withmilk reach a temperature of 130 C and have been properly designed (Varnam andSutherland, 1996). The quality of the end product can be verified by means of properstatistical testing schemes (Broderick, 1993; Wagstaffe, 1993). Although, in theory,it is possible to sample even 100% of the production, usually the number of packsbeing tested is reduced down to 0.01% of packs in a batch. After the incubationperiod, packs are examined for swelling or coagulation, while destructive samplingmay reveal sensory defects. In cases of doubt, microbiological examinations and pHdetermination may also be carried out (ICMSF, 1988).

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Production of Spray Dried Milk

Since 1950, there have been 17 major food poisoning outbreaks due to milk powders.Two of them were caused by staphylococcal toxins and the rest, by Salmonella spp.(Shapton and Shapton, 1994). A simplified procedure of spray dried milk manufac-ture is shown in Figure 4. Raw milk should be of good microbiological quality andstored at low temperatures for limited time periods (Mossel et al., 1995). Standardiza-tion of milk should be conducted prior to pasteurization to avoid cross-contaminationbetween raw and pasteurized milk (Mossel et al., 1995). Temperature and holdingtime of milk and operation of CIP should be controlled to prevent mesophilic bacteriafrom growing and psychrophiles from producing heat-stable enzymes (Garcia Arn-esto and Sutherland, 1997; Adams and Brawley, 1981; Keogh and Pettingill, 1982).Prior to pasteurization, milk should also be clarified to remove undesired matter.Hygienic design and operation of the equipment, frequent disposal of sludge, andcleaning intervals of 36 h can be applied to minimize any potential microbiologicalhazards (ICMSF, 1988).

Pasteurization should be carried out prior to concentration, since there is no flowdiversion device for underheated milk in evaporators. During pasteurization, appro-priate operating conditions should be maintained and recontamination of pasteurizedmilk should be prevented (EHEDG, 1992), as has already been described. Conden-sation is usually carried out by evaporation, although reverse osmosis/ultrafiltrationor freeze concentration may be applied. Since operating conditions allow the growth

Figure 4. Flow diagram for production of spray dried milk (ICMSF, 1988).

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of thermophiles at certain stages of the evaporation and growth of Staphylococcusaureus in the final concentrate, the holding temperature before drying should beabove 55 C and holding time should be less than 4 h (Shapton and Shapton, 1994).The evaporator should be equipped with appropriate instrumentation to monitortemperature, vacuum, and product concentration. Employment of experienced andskilled staff is necessary at all times and cleaning and sanitizing treatments shouldbe implemented at regular intervals. Homogenization should be conducted at a tem-perature of 70 C to prevent the growth of both mesophilic organisms (Hammer etal., 1996) and thermophiles. The homogenizer should be regularly cleaned, sanitizedand even dismantled if deemed so, to minimize the probability of growth of meso-philes in wet residues (Hammer et al., 1996).

Concentrated milk enters the spray dryer through the atomizer and the viscosityof the milk feed affects the properties of the dried milk. Air within the drying cham-ber should comply with the following requirements:

Filtered to remove dust particles (Carminati, 1996). The air filtration system shouldbe of sufficient capacity and regularly maintained (Shapton and Shapton, 1994).

Good microbiological quality and even distribution within the chamber to avoid theformation of moisture pockets.

Unfiltered air from adjacent areas contaminated with Salmonella should not enterthe drying chamber. Slight overpressure of the air within the chamber can preventthe entrance of unfiltered air (ICMSF, 1988).

Relative humidity, entrance temperature, exit temperature, and movement of the airshould be constantly monitored (Mossel, 1975). The microbiological monitoringof air is essential and should be carried out by collecting the microorganisms byone of the following procedures (Mossel et al., 1995): absorption in a rich infusionbroth (Thorne et al., 1992) and direct isolation on a specific medium using a slitsampler (Quinn et al., 1980).

Production of standard quality dried milk requires continuous control of milk dropletsize, temperature, and speed of circulating air. Precautions should be taken to preventcontamination of dried milk from raw milk, as well as to avoid growth of pathogenicorganisms in concentrated milk before drying. The various areas of the plant shouldbe separated as much as possible, especially the wet side of the plant from thepowder side to prevent cross-contamination (Varnam and Sutherland, 1996). Thedryer should be properly designed to allow dry cleaning and when water is used itsdesign should prevent accumulation of moisture. A strict control should be imposedon the personnel movement and employees should change clothes and shoes andwash their hands when enter the spray drying area (Scott and Bloomfield, 1990).Hot powder should be cooled with filtered air of high microbiological quality toavoid recontamination of the powder and the equipment should be always kept dryto prevent the growth of microorganisms (ICMSF, 1988). Moisture content of theend product should be measured to validate that the specified level is achieved, since

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localized high moisture content in milk powder allows mold growth and aflatoxinproduction (Shapton and Shapton, 1994; Richard et al., 1975). The sampling method-ology depends on the sample size and that microbial distribution is not homogeneousin milk powder.

Milk powder is transported to the filling station and is exposed to some extent toenvironmental air. The manufacturing area environment, plant, and equipment shouldbe properly designed, maintained, and cleaned according to good manufacturing anddistribution practices (GMDPs) (Espy, 1994). To verify that the Quality Assuranceprogram applies effective control, microbiological monitoring of environmental, andend-product samples with special reference to Salmonella are required. Packagingmaterial should be hygienically manufactured and should be properly stored to ex-clude pests and dust (Mossel et al., 1995). Packaging should provide the consumerwith sufficient information for safe storage and product reconstitution (Scott et al.,1982).

Manufacture of Plain Yogurt or with Fruit/Nut Puree

Yogurt is the most popular fermented milk product because of its extended shelflife and properties that contribute to the promotion of health. The quality of yogurtdepends on the type of raw material used, on the manufacturing procedure employedand on the proper functioning of the process equipment and process line (Rasic andKurmann, 1978). The flow diagram for yogurt manufacture with added fruit or nutpuree is shown in Figure 5. All stages upstream of cooling of heated milk shouldcomply with the requirements that have already been described for pasteurized milk.Stages requiring special attention and consideration during milk treatment are stan-dardization, homogenization, and the addition of stabilizer. These processes improvethe texture and mouth-feel, decrease susceptibility to syneresis, and reduce noduleformation. Trained and experienced personnel should supervise standardization andchemical analysis should be performed to ensure that legal requirements or consumerpreferences are met. Homogenization pressure should be constantly monitored andstabilizers should be purchased from approved suppliers meeting an accurate and upto date agreed specification.

Starter culture should have the following properties (Litopoulou-Tzanetaki, 1993):consist of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius

subsp. thermophilus in ratio of 1:1;be bacteriophage and contaminating bacteria free;grow fast and start acid production within 30 minutes of inoculation to cause rapid

drop in pH value;produce volatile flavor compounds and substances for preventing the growth of an-

tagonists, such as bacteriocins, nisin, and acetaldehyde.

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Figure 5. Flow diagram for the production of yogurt with fruit or nut puree (Shapton and Shapton,1994).

Well-trained employees should perform starter inoculation under hygienic conditionsin milk, which is penicillin free and sufficiently heated and rapidly cooled at a tem-perature of 43 C (Tamine and Robinson, 1985). Starter culture is usually added at2.53% thus permitting the completion of fermentation within 3 h. Throughout fer-mentation, temperature and acidity should be constantly measured (Rasic and Kur-mann, 1978).

Post-fermentation treatment of yogurt involves cooling, filling, and packaging.Cooling rate and temperature should be monitored in order to prevent syneresis ofthe end product. During handling, excessive agitation and shear stress of yogurt mustbe avoided because they can lead to reduction in viscosity and leakage of free whey(Varnam and Sutherland, 1996). After cooling, filling should follow immediatelyand, at this stage, fruit or nut puree should be added and evenly distributed in theyogurt. Fruit puree prevents the growth of pathogens because of its low pH value,but allows mycotoxin production. The applied heat treatment can destroy yeasts,spoilage organisms, and vegetative pathogens with the exception of spores of Clos-tridium botulinum. However, the low-pH value of 4.7 (Vasavada and White, 1979)prevents growth of Cl. botulinum and toxin production and cooling of puree inhibitsgrowth of survived microorganisms. Nut puree may carry toxins and pathogens ifa botulinum process of Fo 5 3 is not applied and the puree is held at ambient tempera-

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tures. Heat resistant aflatoxins may be present in puree if nuts became moist becauseof improper conditions of harvesting and storage. In order to control the quality ofthe puree, the following measures should be taken (Shapton and Shapton, 1994):

Regular auditing of suppliers to ensure their compliance with the product specifica-tions and HACCP implementation;

Statement of heat treatment protocol and puree formulation according to the supplier;Certificate of heat treatment and container integrity for each batch;Monitoring for aflatoxins in nuts before puree production.Yogurt is finally packaged in plastic pots capped with metal foil or plastic and stored

at low temperatures for a short time. To prolong the storage life of yogurt, asepticproduction lines and cultures with weak after-acidification ability can be used(Rasic and Kurmann, 1978).

Manufacture of Cream and Butter

Cream consists of a concentration of milk fat in milk with the fat mainly in formof globules and constituting the basis for butter production. Synoptical flow diagramsfor the manufacture of cream and butter are summarized in Figures 6 and 7. Rawmilk should be of the same quality that is required for pasteurized milk and shouldcomply with some additional requirements decisive to the quality of the end product(Kosinski, 1996; Mossel et al., 1995). Efficient separation requires the process of

Figure 6. Flow diagram for the production of pasteurized cream (Kosmidou and Arvanitoyannis,1998).

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Figure 7. Basic process for the manufacture of butter (Varnam and Sutherland, 1996).

milk within a short time from receipt and exclusion of air during pumping of milkby means of suitably designed equipment (Kosikowski and Mistry, 1997).

Prior to separation, it is essential that milk is heated to 55 C to inactivate naturallipases of milk that may cause rancidity. To achieve the desired fat content of creamduring standardization, determination of the fat content of whole milk is first requiredand then control of the flow of cream and skimmed milk in the separator by meansof special valves should be applied (Muir and Kjaerbye, 1996). The accuracy ofthis method depends on the calibration of flow meters, the standardized operatingconditions, and the experience and training of personnel. When composition of milkor operating conditions fluctuate, measurement of density is essential to the buildup of automatic control systems to maintain constant fat content in cream (Varnamand Sutherland, 1996).

During pasteurization of cream in tubular or plate heat exchangers, steam pressure,product flow rate and viscosity, and absence of fouling should be constantly con-trolled (Hinrichs and Kessler, 1996). A flow diversion valve should be fitted in the

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pasteurization plant to ensure that the specified pasteurization temperature of creamis reached. At regular intervals, the pasteurization unit, including homogenizer,should be cleaned and sterilized according to the instructions of the manufacturer(ICMSF, 1988). Homogenization is a CCP only if it is applied after heating becauseit involves the hazard of milk recontamination (Kosinski, 1996). Cooling shouldfollow immediately after heat treatment to prevent growth of heat resistant organismsand cooling equipment should be properly designed, maintained, and disinfected(Kosmidou and Arvanitoyannis, 1998).

Filling and packaging of cream should occur at a temperature below 7 C in anarea separated from the rest of the plant (Eyer et al., 1996; Taylor, 1975; Marcy andMossel, 1984). Temperature and filtration of air in the filling area should be con-trolled to prevent microbial contamination of cream (Carminati, 1996). Pumping ofcooled cream should be minimized and equipment should be properly designed andmaintained to avoid physical damage of cream (Varnam and Sutherland, 1996; Hin-richs and Kessler, 1996). Personnel hygiene and good handling practices are impor-tant for preventing inoculation of cream with undesirable microorganisms (Gerats,1987). Detailed methods and frequency of cleaning and tests for cleaning efficiencyshould be clearly specified (Blackwell, 1969). Upon receipt, packaging materialshould be visually tested for integrity and cleanness and stored in accordance withmanufacturers specifications (Eyer et al., 1996). Packages should be labeled KeepRefrigerated, properly coded, and include a use by date and the cream composi-tion. Distribution and storage of cream should be carried out under refrigerationtemperatures, should not be prolonged, and the first infirst out (FIFO) managementshould be applied (Muir and Kjaerbye, 1996).

To produce a high quality butter, it is essential to ensure correct treatment ofcream after separation since the temperature at which this process is carried outenhances microbiological growth (Woolfschoon, 1984). Heating of cream by directsteam injection in combination with vacuum deodorization should be avoided be-cause it causes high fat losses in buttermilk and deterioration of butter flavor (Varnamand Sutherland, 1996). Mixing of different quality creams should also be avoidedsince it can barely wipe out the defects of the used raw materials (Kosinski, 1996).

Aging consists of formation of a certain ratio of solid : liquid triglycerides thusinfluencing the consistency of the final product; the shape and the size of fat crystals,the losses of fat in buttermilk, and the performance of churning (Zerfiridis, 1996).To determine the correct method of aging the composition of fat, the season of theyear, the iodine value, and the refractive index should be considered. The optimumtemperaturetime combination and cooling rate should be applied with respect tothe fat content of cream and the melting and crystallization properties of fat (Muir,1996).

Cream is ripened by use of lactic cultures, such as Lactococcus lactis, Lc. crem-oris, Lc. diacetylactis, Leuconostoc citrovorum, Leuc. mesenteroides, and Leuc.cremoris (Litopoulou-Tzanetaki, 1993). Starter culture is usually added at 4% for

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developing the characteristic flavor of the product, for restraining the growth of pro-teolytic and lipolytic microorganisms, and for reducing the intensity of potentialflavor defects (Kosikowski and Mistry, 1997). Lactic cultures should be able to growfast, produce 1.52 mg/kg diacetyl, lower pH value at 4.75, and complete the fer-mentation within 1418 h. During ripening, cream temperature should be maintainedat 17 C, acidity and diacetyl level should be constantly monitored, and cream shouldbe slowly stirred (Hinrichs and Kessler, 1996).

Churning and working result in the conversion of cream to butter. The main factorsthat affect the efficiency of these operations and should be controlled are:

The size of fat globules;The fat content, the acidity, and the viscosity of cream;The operating temperature;The type, the rotation speed, the fullness, and the size of the buttermaker.

Churn hygiene can be substantially improved by replacing the construction materialwith stainless steel (Wolfschoon, 1984). During these operations, butter salting, anddrainage of buttermilk should also be carried out. Usage of the correct salt (NaCl)concentration and its even distribution throughout butter can contribute to the shelflife extension. Salt is the only preservative used and is also used to improve butterflavor. Sodium chloride should definitely be obtained from suppliers who conform tonecessary regulatory and microbiological specifications in order to prevent microbialcontamination of butter (Burgess et al., 1994). Insufficient drainage of buttermilkcan lead to excessive fat losses and to potential microbial spoilage of the end product.Before leaving the churn, butter should be compact with homogeneous and waxytexture and should have the required moisture content. Water content can be deter-mined either with dielectric instruments or with near-infrared analysis (Varnam andSutherland, 1996) and can be affected by the following factors (Jooste, 1974):concentration of unsatured fatty acids in cream;aging of cream;churning and working temperature;rotation speed of the buttermaker.

Packaging should protect butter from chemical, microbiological, and mechanical al-terations and should provide the consumer with a product of premium quality. Pack-aging material varies with respect to size of the pack and should be obtained fromsuppliers implementing a HACCP system and being frequently audited. Packagingmaterial should be water-resistant, should not allow moisture loss, should be lightand oxygen impermeable, should not enhance mold growth, and should not migrateto the butter compounds thus altering the organoleptic characteristics and the hy-gienic condition of the product (Kosmidou and Arvanitoyannis, 1998). After packag-

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ing, butter should be quickly cooled down to temperatures of -18 C for preservationand then stored in areas with controlled temperature and humidity of air and withgood air-filtration system (Jensen et al., 1983). Rework of butter should be performedto the correct extent and the performance of employed equipment should be moni-tored. Distribution and sale of butter at low temperatures is essential for the safepreservation of butter and for prolonging shelf life.

A common quality defect of butter is the development of rancidity and bitterness.It is usually caused by heat resistant lypolitic enzymes produced by Pseudomonasfluorenscens and Ps. fragi (Mossel et al., 1995). To prevent this defect, raw milkshould be stored at refrigeration temperatures, strict hygienic conditions should bemaintained during manufacture, and salt and moisture should be evenly distributedthroughout butter (Litopoulou-Tzanetaki, 1993; Kosinski, 1996). Finally, anothercommon problem is fat oxidation which is related to copper presence and to the useof unpasteurized cream (Wolfschoon, 1984; Barnes and Edwards, 1992). In general,the introduction of pasteurization for milk and cream managed to reduce the healthrisks from butter. However, health risks are likely to occur when butter is importedfrom areas not applying pasteurization or where severe recontamination is possible,e.g., L. monocytogenes. It is advisable to keep the pH # 4 in order to minimize thelikelihood of growth of E. coli and L. monocytogenes (Abbar and Mohamed, 1987;Massa et al., 1990).

Manufacture of Ice Cream

Ice cream and other whipped frozen dairy desserts are foams made up of air cellssurrounded by a partially frozen emulsion (Huang and Platt, 1995). Ice cream con-sists mainly of water, fat, and milk solidsnon-fat, in combination with sugars, emul-sifiers-stabilizers, colorings, flavorings, and fruits or nuts. The flow diagram for themanufacture of ice cream is synoptically shown in Figure 8. Whole fresh milk isthe most suitable source of fat and solidsnon-fat, although low acidity cream andspray dried skim milk powder are also necessary to accomplish the typical composi-tion of ice cream. All initial ingredients should be obtained from sources that complywith current legislation and should be regularly tested for their quality. Hermeticpackaging, correct storage conditions and, in some cases, heat treatment can maintainthe majority of their hygienic and physicochemical properties (Holdsworth, 1992).

The common procedure for mix preparation is to first add the liquid ingredientsto the mix vat or the pasteurizer, then the dry solids and after the mix has reachedthe temperature of 49 C, to add the sugar (Shapton and Shapton, 1994). Using thecorrect quantities of the ingredients necessitates calibrated measuring equipment andusing well-trained employees. Dry ingredients should be fully dispersed and all mate-rials should be dissolved before pasteurization temperature is reached (Varnam and

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Figure 8. Simplified HACCP flow chart for the production of a simple ice cream (Kosmidou andArvanitoyannis, 1998).

Sutherland, 1996). Homogenization breaks up and disperses fat globules, preventingfat separation and churning (Fletcher, 1997). The main benefits of homogenizationare:

ice cream becomes uniform with smooth and creamy texture;aging of mix can be shortened;reduction of stabilizer concentration.

At the beginning of each production run, the homogenizer should be inspectedfor cleanness and disinfection to ensure that the mix will not be heavily contaminated.

Since even during pasteurization, ice cream protects microorganisms from de-struction, the American Public Health Association (APHA) suggested that theminimum temperature/time treatment of ice cream should be 70 C 3 30 min or80 C 3 25 sec (Litopoulou-Tzanetaki, 1993). The addition of nisin to ice cream hasbeen suggested in an attempt to minimize the survival of Listeria monocytogenes. Infact, the presence of nisin in the ice cream was shown to result in significant reductionin the cell population and, in particular, in the 3%-fat ice cream stored for morethan 3 months at -18 C (Dean and Zottola, 1996). Heat should be evenly transferredthroughout the mix and properly calibrated thermometers should constantly monitorthe pasteurization temperature. Fouling of heat exchangers is also a serious concern,but it can be minimized by adopting optimum cleaning procedures and by preventingthe incorporation of excessive air into the mix (Visser et al., 1997). Rapid cooling

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at temperatures below 5 C should follow pasteurization, otherwise the viscosity ofmix can increase considerably and melting of the ice cream will not be uniform(Zerfiridis, 1996). Low temperatures prevent the growth of microorganisms that cansurvive the pasteurization. Tempering usually lasts for 24 h at low temperatures andresults in solidification of fat, stabilization of water, hydration of proteins, and in-crease in viscosity. Texture and structure become smooth and both resistance tomelting and whipping capacity are improved. Temperature and mixing period shouldbe monitored to ensure that they are maintained below the predetermined limits. Thefunctions of freezing consist of freezing a portion of the water contained in the mixand incorporating air into the mix (Shapton and Shapton, 1994). To ensure adequatefreezing of the mix, the suitable type of freezer should be selected and its properand safe operation should be maintained. Ice cream should be transferred to thehardening room immediately after freezing where the appropriate combinationof temperature/time should be applied. Rapid hardening of ice cream is importantfor two reasons; first to prevent melting and formation of large ice crystals duringrefreezing and second to improve the sensory properties (e.g., texture and palatabil-ity) of the ice cream.

Packaging materials should be obtained from reputable suppliers and should beselected according to the intended product use and storage time. Films, foils, lami-nates, and paper should be selected in terms of their preventing moisture losses andtheir adequate flexibility to withstand the volume expansion of the ice cream (Bossetet al., 1994). Storage temperature should vary within the range -20 C to -25 C. Tem-perature fluctuations must be avoided since they can lead to migration and accumula-tion of water and to the formation of large crystals on refreezing (Varnam and Suther-land, 1996). GMP should be applied to prevent infestation of insects and rodents inthe freezing rooms, to control the humidity and the microbiological quality of theair to avoid corrosion on surfaces (Shapton and Shapton, 1994), and to prevent icecream shrinkage due to changes in altitude, temperature or pressure, heat shock,small ice crystals, and improper blending (Dubey and White, 1997).

Manufacture of Cheddar Cheese

Cheddar is one of the most important varieties of hard cheeses and the traditionalprocess for making Cheddar cheese is outlined in Figure 9. Salmonella (Hedberg etal., 1992), Listeria monocytogenes (Burow et al., 1996), and Escherichia coli (Mosselet al., 1995) are considered to be high risk threats to the cheese industry, whileStaphylococcus aureus (Tatini et al., 1971)is considered a low risk threat becausegrowth and toxin production in cheese are suppressed by using appropriate startercultures and employing acidity control (Johnson et al., 1990a). The following pro-cesses have been suggested in order to minimize pathogen numbers in cheese (John-son et al., 1990b):

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Figure 9. Flow diagram for production of Cheddar cheese (Kosikowski and Mistry, 1997).

Mastitis control by application of stricter regulatory programs (HACCP) and incen-tives for quality payment of raw milk (Abdul and Awaz, 1997; Mossel et al.,1995);

Reduction of farm environmental contamination;Cooling and thermization of raw milk (Heeschen, 1996);Bactofugation and microfiltration of raw milk (Langeveld, 1972);Heat treatment of raw milk. The National Cheese Institute has recommended that

the minimum heat treatment of milk for cheesemaking should be 64.4 C 3 16 sor equivalent with adequate process control (Johnson et al., 1990a);

Lactic cultures, bacteriocins, hydrogen peroxide, nitrate salts, and carbon dioxidecan be used as milk additives (Mehanna et al., 1998);

Alteration of the compositional properties of cheese;Exposure to high hydrostatic pressure (Hayakawa et al., 1994; Knorr, 1995).

The performed tests at raw milk receipt to ensure satisfactory quality of cheese-making milk consist of controlling (Wolfschoon, 1984): a) total count, b) somaticcells, c) spore-forming bacteria, d) antibiotic residues, e) temperature, f) acidity andpH, and g) casein:fat ratio, which should be 0.690.71 for cheddar and can beachieved with standardization.

After pasteurization, milk is cooled down to 30 C and lactic culture of Lactococ-cus lactis or Lc. cremoris is inoculated. The activity of starter culture should bedetermined before use and it should be able to start acid production within 3045min. Starter culture should also exhibit stability for aging (Haque et al., 1997) and

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Figure 10. Flow diagram for Feta cheese production (Mauropoulos and Arvanitoyannis, 1999).

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be free of bacteriophages (Canteri, 1997; Chopin, 1997). The lactic culture is impor-tant to cheddar manufacture because (Litopoulou-Tzanetaki, 1993):It causes sufficient acidification to inhibit growth of pathogens and to improve the

texture and consistency of cheese;It contributes to the formation of the typical Cheddar flavor by optimizing the pH

and Eh conditions for aroma initiating chemical reactions and by providing precur-sors for volatile compounds;

It facilitates the formation of curd by rennet, affects the degree of syneresis and thequantity of rennet retained by the curd.

Cheese vats should be cleaned and disinfected before starting production and theequipment should be checked for detergent or sanitizer residues because the lattercan inhibit starter activity (ICMSF, 1988). When acid development begins, rennetshould be added for coagulum formation. The rennet should be obtained from reputa-ble suppliers and added at the correct concentration. Excessive dosage of rennet isrelated to the bitter flavor in cheese since this enzyme has proteolytic activity oncaseins (Wolfschoon, 1984). Temperature of 41 C, pH of 5.7, and Ca12 presencewere shown to be the optimum conditions for rennet activity (Zerfiridis, 1994).

Heating at 38 C leads to curd shrinkage and to whey release and it should beterminated when the titratable acidity of whey reaches 0.140.16% (ICMSF, 1988).The subsequent procedures of draining and texturization should be performed byexperienced personnel at the correct time, to the proper extent, and at the appropriatetemperature (Varnam and Sutherland, 1996). The equipment should be well main-tained and disinfected to avoid both damaging and contamination of the curd (IDF,1997; Parmentier, 1997). It should be stressed that throughout cheese manufacturepH, acidity, moisture content, and consistency of the product should be constantlymonitored to verify that that all stages are carried out correctly. Salting affects ripen-ing, rind formation, flavor development, and preservation of cheese. Salt (NaCl)should be obtained from certified suppliers, should be of the suitable grade and purity,and should be evenly distributed in the curd to avoid discoloration of Cheddar. Saltconcentration should not exceed 2%, unless acidity development is either too rapidor too slow (Zerfiridis, 1994). Pressing completes the whey removal and contributesto curd compaction. Pressure should be gradually applied and not exceed 1.7 atm.Vacuum packaging in plastic films or cryovac and cooling of Cheddar should followpressing to avoid deformation of the blocks. Efficiency of the applied vacuum, sealintegrity, and potential packaging damage should be checked to prevent mold growthand spoilage (Mathlouthi et al., 1994). Aging usually lasts for 612 months at atemperature of 410 C, contributing to the development of the required organolepticcharacteristics and destruction of contaminating pathogens. If the pH of the freshproduct is not 5.25.3, it is possible that the fermentation has failed and the productshould be checked for Salmonella and Staphylococcus aureus (ICMSF, 1988). Ched-dar should be stored and distributed at refrigerating temperatures and the first in

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first out management should be applied. Packages should remain undamaged andprotected from mold growth to extend shelf life of the product.

Manufacture of Feta Cheese

Feta is a traditional Greek cheese and representative of the white soft cheeses thatare ripened and kept in brine (Anifantakis, 1991a; Abou-Donia, 1991; Tamine andKirkegaard, 1991). The distinguishing characteristics of Feta are the creamy and richflavor, the soft texture with some irregular small mechanical openings, and the whitecolor and the rectangular shape (Zerfiridis, 1994; Tsotsanis, 1996).

Moisture content and minimum fat in dry matter of Feta should be 5256% and43%, respectively (Abd El-Salam et al., 1993; Vastardis and Anifantakis, 1992;Greek Codex of Foods and Drinks, 1998).

All stages upstream of cooling of heated milk should comply with the prescribedrequirements for pasteurized milk except for a few differences. It should be stressedthat the performed controls at the receipt of raw milk are (Mauropoulos and Arvani-toyannis, 1999): 1) acidity, 2) aerobic mesophilic count, 3) freezing point, and 4)antibiotic and metabolite residues. The used sheep milk for the production of goodquality Feta should have lower acidity than 0.23% and pH higher than 6.55 (Anifan-takis, 1991b). Sheep milk should also be standardized to a fat and casein content of5.8% and 4.6%, respectively (Greek Codex of Foods and Drinks, 1998).

The lactic cultures used for Feta are Lactobacillus bulgaricusStreptococcus ther-mophilus (1:1) (Pappas and Zerfiridis, 1989), Lactobacillus bulgaricusLactococcuslactis (3:1), and Lactobacillus caseiLactococcus lactis (1:1) (Abd El-Salam et al.,1993). Starter culture should be inoculated at 1% and should be left at 3234 C for1530 min (milk ripening). The activity of the lactic culture should be verified bymonitoring the acidity development in milk. Contamination with bacteriophages canalter the activity of the culture, while phage inhibitory media for starter growth canbe used to minimize the hazard of bacteriophages (Cogan and Hill, 1993). Prior torennet addition, the acidity of milk should be measured in order to control the quan-tity of rennet and the temperature of milk (Mehanna et al., 1998).

Dry-salting of Feta requires the use of corn-size granular salt, which is slowlydissolved and contributes to the drainage of the curd (Anifantakis, 1991a and 1991b).Salt should be evenly distributed in the mass of cheese. Within the first 24 h, salt-in-moisture should be 2.5% and pH 5.2 to ensure the safe preservation and normalripening of Feta (Pappas et al., 1996; Mehanna et al., 1998). During salting, Fetashould also be protected from flies because they lay their eggs on the cheese surfacecausing its spoilage within a few days (Zerfiridis, 1994). Further ripening is com-pleted at 5 C after 2 months (Tsotsanis, 1996). Ripening usually lasts for two weeksat 16 C and 85% relative humidity and is crucial to the development of the character-istic physicochemical and organoleptic properties of Feta. Ripening rooms should

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be separated from the rest of the plant, be equipped with air filtration system andthoroughly cleaned (Mauropoulos and Arvanitoyannis, 1999). By the end of the firstripening stage the pH should be 4.04.6 because lower values result in moistureloss, acidic taste, and limited compactness, while higher values lead to reduced shelflife (Anifantakis, 1991a).

Packaging of Feta is traditionally carried out in barrels, although nowadays tinsare mostly preferred. Tins are filled with 6% brine to cover the surface of the cheese,are hermetically sealed, and transferred to the refrigerator. Other types of conven-tional wrapping for soft cheeses can consist of waxed paper board (both sides)/regenerated cellulose or high density polyethylene (HDPE) or polyethylene tereph-thalate (PET) coated with hydrosorbent coating (Mathlouthi et al., 1994). Feta shouldnot be packaged and cooled unless it has reached a pH value of at least 4.6, otherwisethe cheese will convert into a soft, creamy mass similar to mud. Moreover, the de-struction of pathogens, such as coliforms, Salmonella, and Brucella is not feasibleduring ripening. Killing of Mycobacterium requires adequate pasteurization of milkand is not affected by pH value or salt concentration in cheese (Hammer et al.,1998). In the refrigerator, tins can swell if temperature exceeds 5 C or psychrotrophscontinue cheese fermentation. To prevent the swelling of tins, the temperature shouldbe constantly monitored and a small, easily covered hole should be made at thesurface of the tins to release the produced gases. The relative humidity in the refriger-ator should also be controlled to prevent tin rusting. Feta is safe for consumptiononly after 2 months ripening at 5 C and the first infirst out procedure should beapplied.

PERSPECTIVES

Several recent literature searches attempted by authors (Mortimore and Wallace,1995; Mossel et al., 1995; Harrigan and Park, 1991) have shown that despite theimpressively recorded progress regarding the reduction in incidences of microbialdiseases transmitted by food, food poisoning continues to be a visible and verylikely hazard. However, such a situation is both unethical and unacceptable becauseit could easily be restricted if not avoided by adopting HACCP and GMDPs (Mosselet al., 1995; Roberts, 1995; Leenheer, 1993). Most of the reported incidents are dueto to a synergistic action of several factors such as deficiencies in small catering andfood manufacturing companies, failure to control diseases transmitted by meat/dairyproducts, and lack/failure of the public to actively participate and to motivate boththemselves to adopt hygienic practices (treating, cooking, and storing foods) andgovernmental agencies to intervene via stricter legislation. Although ISO 9001/2implementation (Bolton, 1997) or other quality assurance system (Ishikawa, 1989)in conjunction with HACCP have managed to bring down the number of incidents,further work is urgently required (Tauxe, 1991; Lin et al., 1988a and b).

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Many retailing companies have already realized the importance of being providedwith goods manufactured by companies implementing the HACCP. Consequently,the retailing companies consider as a prerequisite the HACCP implementation bytheir suppliers. This seems to be a convincing and promising way to persuade allthe involved parties (raw material producer, manufacturer, retailer, and consumer)to adhere to HACCP and GMDPs. The consumer should understand that althoughthe so-called zero-defect food production is rather a non-realistic and illusory ap-proach, it is up to him to minimize the hazards originating from cross-contaminationand inappropriate storage. In fact, EEC favors the HACCP implementation by theEEC companies (EEC 93/43, 1993). Furthermore, the widespread use of refrigeratedpasteurized foods of extended durability (REPFED) meals has shown the importanceof strict temperature control both for pasteurization and thereafter (storage, distribu-tion). The financial factor (high hospitalization cost) is likely to play the most impor-tant role for motivating the government towards a legislation that companies shouldcomply with regarding the implementation of quality and safety assurance systems.

In general, there is great potential for further implementation of HACCP in con-junction with a quality assurance system (ISO 9001/2) for medium-small size foodcompanies. Introduction of Environmental Management System (EMS) and ISO14000 will be the basis for shielding the food production companies from environ-mental disasters.

ABBREVIATIONS

ASQ: American Standards Quality Control 9000BS 5750: British Standards 5750EMS: Environmental Management SystemGMDP: Good Manufacturing and Distribution PracticeGMP: Good Manufacturing PracticesHACCP: Hazard Analysis Critical Control PointICMSF: International Commission on Microbiological Specifications for FoodsIDF: International Dairy FederationISO: International Organization for StandardizationJIT: Just-in-timeSPC: Statistical Process ControlTQM: Total Quality ManagementWHO: World Health Organization

ACKNOWLEDGMENTS

The authors would like to thank Professor G. Zerfiridis for his useful and pertinentsuggestions.

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implementation of haccp to the dairy industry (1)

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