food spoilage

Food spoilage

Definition

n Food spoilage can be defined as a disagreeable change in a food's normal state.

n NOT acceptable for human consumption and for food industrial usage

n Such changes can be detected by smell, taste, touch, or sight(disgusting).

n Food safety ↔ food quality

Classifications of food spoilage

n Stable or non perishable foods (sugar, flour, dry beans)

n Semi perishable foods Foods handled and stored properly → remain unspoiled for long period (potatoes, apples)

n Perishable foods Spoil readily without special preservative methods (fish, meat, eggs, milk)

Main causes of food spoilageq Physical changes n aw, temperature, mechanical effectsn Caused by the inappropriate transport, handling and storage

q Biological factorsn Microbiological

q bacteria, yeasts, moulds (most common)

n Macrobiologicalq rodents, insects, birds, parasites

q Chemical, biochemical factors

n non-microbial or enzymatic changes usually involving oxygen → oxidation processes (e.g., rancidity of fats and oils)

n activity of endogenous tissue enzymes (food of vegetable or animal origin)

Consequences/effectsof food spoilageq changes in nutritional value n Decomposition of proteins, carbohydrates,

vitaminsq changes in organoleptic features n colour, flavour, taste, consistency →

mucilaginous surface, unpleasant odour, q unwholesome effectsn Biogenic amines, toxins,n Metabolites of microorganismsn Pathogen microbes

Sources of microbial spoilagen Ubiquiter microorganismsq Can originate from: natural

habitat of microorganisms; e.g. soil, water, air,

n Special sources contaminationq Spoiled raw materialsq Food wasteq Biofilm on the surface of

equipmentsq Human → personal hygiene

Ubiquiter microorganisms

• natural habitat of microorganisms is the soil(except for pathogen bacteria)

• Way of contamination of animals and plants can be direct from soil or indirect by water or air

• Related microorganisms:– Gram (-): Pseudomonas, Acinetobacter, Alcaligenes,

Enterobacter spp.;– Gram (+): Micrococcus, Arthrobacter, Streptomyces

spp.;– Aerobic and anaerobic sporoforms: Bacillus,

Clostridium

Ubiquiter microorganisms

• Microorganisms can contaminate the surface of plant or fur and skin of animals

• These are not harmful for plants or animals, but after harvesting or slaughtering can cause spoilage during storage of products (Micrococcus, Lactobacillus spp.).

• Meat products also can be contaminated by microorganisms from mouth (Streptococcus spp.) or from the gastrointestinal tract (Bacteroides, Eubacterium, Clostridium spp)

Special sources contamination• Surfaces of equipment, instruments, utensils, the

wall and floor surfaces,– Inappropriate hygiene of plant → Food waste → resulting a

specified, adapted micro-flora typical to plant and products

• Spoiled raw material – Plant: mechanical lesions during the harvesting, transport

can enhance the penetration of microbes into the deeper tissues

– Animal: contaminated mainly during slaughter

• Rodents, insects (fly, fruit fly, bee, wasp) can contaminate the products during storage and processing

Characteristic of microorganisms

• Reproductive potential– Among optimal circumstances the fastest– The fastest growing microbe becomes dominant

(mainly bacteria, but …)• Metabolism, nutrient requirements

– Substrate → metabolism in cells → metabolites (useful or harmful)

– The process is influenced by the environment (presence/absence of oxygen, available nutrients)

Factors affecting microbial spoilagen Intrinsic factors of foodstuffsq Physical-chemical properties: aw,

redox circumstances, pH,q Chemical composition: Nutrient

materials, vitamins, inhibitorsq Biological structure

n Extrinsic factors of foodstuffsq Temperature, humidity, atmosphere

compositionq Processing effectsq Hygiene, cleaning, disinfections

n Implicit parameters q Interactions of microorganismsq Reproductive potential

Intrinsic factors – water activity• Water content of foods is quite high:

– Meat, egg: > 70%– Milk, fruits, vegetables: >80%

• For microbes only the free water is available (free water content is characterized by the aw)

• The minimal aw is the limit to microorganisms for growth/reproduction– Bacteria: highest water requirement (>0.91aw)– Yeasts: water requirement is lower than the bacteria

(≥0.88aw)– Moulds: low water requirement (>0.78aw)

Minimum water activity requirement of microorganisms

Group of microorganisms Minimum aw of growth_______________________________________________________

Most Gram-negative bacteria 0.97Most Gram-positive bacteria 0.90Halophilic bacteria 0.75

Most yeasts 0.88Osmophilic yeasts 0.62

Most filamentous fungi 0.80Xerotolerant fungi 0.71Xerophilic fungi 0.61Xeromyces bisporus 0.60

_______________________________________________________

Water activity of some foods

Food aw

Fresh vegetables, meat, milk, fish 0.98<Cooked meat, bread 0.95 – 0.98Cured meats, ham, cheese 0.91 – 0.95Dry cheese, salami 0.87 – 0.91Flour, rice, beans, cereals 0.80 – 0.87Jams 0.75 – 0.80Dried fruits, caramels 0.60 – 0.75Spices, milk powder 0.20 – 0.60

Intrinsic factors

n water activity „tolerance”: aw=0,7 → food is sufficiently protected from spoilage

n Microorganisms growing in the food change the level of available moisture by release of metabolic waterq moulds can destruct the tissues → water available to

yeasts and bacteria

Intrinsic factors – water activity• If we want to ensure the safe storage life the aw has to

be reduced under 0.7• Water content of dried foods belonging to aw of 0.7:

7-10Cocoa

7-10Milk powder (whole)10Skim milk powder

18-25Dehydrated fruits13-21Dehydrated stock12-22Dried/dehydrated vegetables

10Dried whole egg10Dried meat, fish

Maximal water content %Food

Factors affecting microbial spoilageIntrinsic factors of foodstuffs

Physical-chemical properties: aw, redox circumstances, pH,Chemical composition: Nutrient materials, vitamins, inhibitorsBiological structure

Extrinsic factors of foodstuffsTemperature, humidity, atmosphere composition

Processing effectsHygiene, cleaning, disinfections

Implicit parametersInteractions of microorganismsReproductive potential

Factors affecting the moisture/waterrequirements of organisms

n Nutritive properties of the substraten pHn Content of inhibitory substancesn Availability of free oxygenn Temperature

Influence of aw on the growth and toxin-production of moulds

Mycotoxin MicrobesMin. aw

GrowthToxin-

production

AphlatoxinAspergillus flavus 0,78-0,84 0,83-0,87

Ochratoxin Aspergillus ocraceusPenicillium cyclopium

0,770,82-0,85

0,850,87-0,90

Patulin Penicillium expansum, 0,81 0,95

Factors affecting microbial spoilage

n Intrinsic factors of foodstuffsq Physical-chemical properties: aw, redox

circumstances, pH,q Chemical composition: Nutrient materials, vitamins,

inhibitorsq Biological structure

n Extrinsic factors of foodstuffsq Temperature, humidity, atmosphere compositionq Processing effectsq Hygiene, cleaning, disinfections


Intrinsic factors: pH and buffering capacityn pH of foods: mostly acidic (pH=4-7)n Most of the bacteria are inhibited under pH 4n Yeast and moulds can tolerate the lower pH

Min. pH Opt. pH Max. pHMost of the bacteria

4-4.5 6.5-7 8-9

Acidophil bacteria (Lactobacillus spp, Acetobacter, spp., Clostridium butyricum,

3-4 5 6-9

Alkalinetolerant bacteria (Vibrio spp.) 5 7-8 10-11

Yeast 2.5-3 5 8-9

Mould 2 5 9-10

pH and buffering capacityn The pH of food can be effective also against the activity of

pathogensn pathogens:

q Staph. aureus → no toxin production < pH=4.5 q Salmonella no growth ≤ pH 3.8 ( pH 4.5)q Clostridium botulinum: no growth ≤ 4.5

n acids (non-dissociated form)→ antimicrobial effect, preservative function (e.g. benzoic acid, sorbic acid, )q ↔ spoilage (pickled cabbage, cucumber)

n meat ageing: mammals → pH=5,5q → DFD pH>6,0

n fish → pH 6,2-6,5n moulds: aphlatoxin ≤ 3,3 also!n high pH is also not tolerable for microbes, but: Pseudomonas, Vibrio

spp.n eggs → CO2 lost → pH≈9

Redox circumstances – redox potentialq Redox circumstances can be characterized by the redox

potential (Eh) depending on the presence/and concentration of oxidizing and reducing agents

q The Eh is also influenced by the redox-capacity of the product → resistance against the change of redox potential

q Also remarkable factor, that the product in what rate can be impregnated by air (minced meat)

q Redox potential requirements for microorganisms:q Aerobic microbes: ≥300mVq Anaerobic microbes: ≤-300mV

q Redox potential of foods:q Plant origin: 300-400mVq Meat, meat products, cheese: -20 to -200mV (e.g. minced

meat: -200 → +200mV

Composition of foods

q nutrients necessary for microbial growthq foods rich in protein → putrefactionq foods rich in carboydrates → fermentative

spoilageq Limiting factor:q vitamins → fruits low vitamin B content → mostly

moulds and yeasts, as spoilage organisms (they can synthetize them)

Composition of foods - Inhibitory substances

n Originally presented in the food, added purposely or accidentally, or developed by growth of microorganisms or by processing methodsq Natural:n Lysozyme, lactoferrin, lactoperoxidase - fresh milk, n Lysozyme - egg whiten Benzoic acid - cranberries n Egg-white/albumen: avidin → neutralizes biotin →

no longer available for microorganisms → inhibition of bacterial growth

q antimicrobial substances (capsaicin, fitoncid)

Biological and physical structure of foods

q protection barriersq natural biological structures: shell, shell membraneq cuticle of intact plant organsq fresh meat: fascia → aw ↓ → against Gram-

psychrotropic bacteria can be effective protection (minced meat: lack of fascia → ↑ susceptibility)

Extrinsic factors: Storage temperaturen Most important extrinsic factorn spoilage microorganisms: -10°C → 80°Cn Under the minimum temperature growth stopn Above the maximum temperature microbes are

killedn Mesophiles: 5-45 °Cn Psychrotrophic: -5 - +35 °Cn Psycrophiles: -10 - +20 °Cn Thermotrophic: 20 - 50 °Cn Thermophiles: 40 – 80 °C

Extrinsic factors: Storage temperaturen most of the pathogens → mesophiles →↓

temperature markedly decrease their growth (except: Listeria monocytogenes, Yer. enterocolitica, Vib.parahaemolyticus, Cl. botulinum E, F, Francisellatularensis); (C. jejuni 30-46°C)

n at chilling temperature spoilage occurs earlier than any health hazard due to pathogensq Cl. botulinum: min. temperature for growth 10°Cq Staph. aureus: min. temperature for growth 7°Cq Salmonella: min. temperature for growth 5-6°C

Extrinsic factors: Storage temperaturen chill storage (5-7°C): pathogens will not destroyed

necessarily, but their growth will stop n psychrophilic and psychrotrophs still growingn stronger chilling (-1 → +2°C): also these organisms

almost entirely inhibitedn growth retarding/inhibiting effect of chilling supported by:

aw, pH, pO2n freezing: -18°C → growth of all microorganisms entirely

inhibited- most sensitive → Gram- bacteria, but survival of some pathogens may be important (e.g., Salmonella in frozen poultry)- activity of microbial enzymes → -30°C

n dominant spoilage flora of foods in relation to storage temperature

Extrinsic factors: Relative humidityn equilibrium between the moisture content of

the food and the air (if the packaging is not completely moisture proof)

n Fresh food can lost partly its water content during storage (e.g. fresh cheese → drier atmosphere → dry surface → flora shift towards moulds)

n Products with low aw in humid environment → adsorb moisture → go mouldy

n food materials inhibit water diffusion →equilibration nearly complete at the surface → interior unaffected

n → difference between the spoilage association → moulds on the surface, xerotrophic bacteria inside

Extrinsic factors: Relative humidity

n surface spoilage may also be complex → fatty tissues → water diffusion slow→n chill-stored meat dry → moulds and some yeasts may grown lean meat → bacteria → slimy

n chilled foods exposed to warm damp air → moisture condenses onto foods „sweating” → rapid bacterial growth → spoilage

Extrinsic factors: atmosphere composition

n O2 ↓ CO2↑→ inhibit the aerobe microbes and mouldsn (can be used in case of fruits/vegetables

storage – altogether with chilling)n Modified atmosphere packagingn Can be modified by passive or

active wayn Active: making vacuum in the package

or using oxygen adsorbentn Passive: caused by the respiration of

the product’s micro-floran (meat- lactobacillus)

Factors affecting microbial spoilagen Intrinsic factors of foodstuffsq Physical-chemical properties: aw, redox





Extrinsic factors: processingn Contaminated raw materials (always)n Washing, sorting, peeling, → decrease microbe

number or contaminationn Comminuting, mincing, +additives → increase

microbes number

n Chilled, minced meatq no fascia (low aw), high O2, high Eh → potential spoilage

caused by Pseudomonas-Acitenobacter-Alcaligenes is quite high

q Technological hygiene, cleaning, disinfection

Implicit parameters

n Growth/reproduction raten Generation time/reproduction circle: less than 1 hourn spoilage associations: dominant species → ↑ specific

growth raten under given conditions (temperature, aw, pH, Eh)n aw >0,98 + pH > 4.5 → necessarily bacterian marked differences among bacteria (e.g., Pseudomonas

and bacilli) grow much faster than Lactobacillaceae, these latter become dominant → the former inhibited (e.g., anaerobic conditions)

Implicit parameters

n interactions → synergistic, antagonistic = competition (indifferent)

n interactions may be between spoilage and pathogen organisms and between spoilers

n mechanisms: q Utilization of nutrientsq Alteration of pH, q Alteration of redox potential, q Alteration of awq production metabolites (inhibitors, antibacterial

substances, Vitamin B, etc.)

Implicit parameters• public health importance: inhibition of

pathogens based on the antagonistic effects

Bacillus, Enterococcus, Lactobacillus, Micrococcus, Pseudomonas, Streptococcus

Staph. aureus

Enterococcus, Lactobacillus, Lactococcus

L. monocytogenes

Enterococcus, Lactobacillus, Pseudomonas

E. coli

Enterococcus, Lactobacillus, Micrococcus

Cl. botulinum, Cl. perfringens

Enterococcus, LactobacillusBacillus cereus

Microbe caused spoilage(inhibitor)

Pathogen (inhibited)

Special spoilage associations (micro-flora) of certain foodsn Non-heat treated productsq chilled fresh meat, fish, milk (rich in proteins, ↑aw,

pH>4.5):q psychrotrophic, rod-shaped Gram-negative bacteria,

(Pseudomonas-Acinetobacter-Alkaligenes) → slimeformation

q vegetables: Gram-negative bacteria (Pseudomonas, Erwinia) → which can break down cellulose and protein → rotting

q cured meat products without heat treatment (↑pH, ↓↓aw): moulds

q fermented foods (pH<4.5): yeasts, moulds, lactobacilli

Special spoilage associations (micro-flora) of certain foodsn Heat-treated foodsq pasteurized products (milk, ham, sausages):

thermotolerant streptococci (enterococci) and lactobacilli (aerobic and anaerobic spore-forming species → Bacillus, Clostridium)

q baked products: yeasts, moulds; bacteria: Bacillus spores → ropiness

n Dried foodsq Cereal flours, dried vegetables, fruits (↓↓aw): mouldsq Chocolate, candy (high carbohydrate content, ↓↓aw):

yeasts

Chemical, biochemical spoilage

n Oxidation (effect of oxygen, generally enhanced by light, temperature, metals)q Result: Taste, odour, colour changesn Pepper-faden Meat-greyn Rancidity of fats and oils

Rancidity of fatn Sign of rancidity: unpleasant, disgusting taste,

odour; n Lipid peroxidation – or autooxidationq Need 3 factors:n Oxygenn Substance that can be oxidated: fat contains

unsaturated fatty acidn Catalisator: light, high temperature, metal ions

n Fotooxidation → activate oxygenn Lard-fat heat treated at high temperature: 140 °C →

activate oxygenn Lipid peroxidation: alcohol, ketone, aldehide are

produced →unpleasant, strange odour, taste

Rancidity of fatn Inhibit the peroxidation:q decreased exposure to O2n Proper instrumentsn Cuttingn Short time

q Antioxidantsn Vitamin E, Cn Artificial antioxidants

q Lower temperaturen Lypolysis of triglycerides ↓

Rancidity of fat

n Ketone rancidityq Moulds in presence of oxygen and water can release

fatty acids from lipids → methylketone → unpleasant taste

q Hydrolytic rancidityq Enzymatic reactionsq Original enzymes, microbial enzymes

Enzymatic spoilagen Mainly not heat treated raw materialsn Plantsq Fruits, vegetables after harvesting →

polysaccharides decomposition → sweet taste decrease

q Protopectin decomposition → to soluble pectin → softening (over matured fruit)

q Mechanical effects: membrane damaged →polyphenols, oxidize enzymes released →enzymatic reactions → browning

Enzymatic spoilageq Meatn After slaughtering similar

biochemical reaction than in the liveanimal

n Glycogen decomposition →n final pH value

q Milkn Lipasen Cream, butter, sour creamn Can be deactivated by heat treatment

q Eggn Water amount decrease, weight loss,n Viscosity of white ↓, ovomucine

decomposition

food spoilage

Documents

disinfections implicit parameters

microorganisms reproductive potential

implicit parametersn

reproductive potential

low aw

redox potential

nutrient materials

redox circumstances