40

M I C R O B I O L O G I C A L P R O B L E M S I N V O L V E D I N PACKAGED M E A T S

J O H N C. A Y R E S

DEPARThqENT O F D A I R Y AND FOOD I N D U S T R Y

1 O W A S T A T E UNl V E R S l T Y , A M E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

It has been known f o r many years t h a t f resh red meats develop maxi- mum sca r l e t red color (oxymyoglobin) when packaged i n f i l m s having high oxy- gen transmission r a t e s such a s a re provided by cel lulose acetate, polystyrene, and cellophane, but t ha t these meats have b e t t e r keeping qua l i t i e s when stored i n f i lms t h a t a re less permeable t o oxygen (Ramsbottom e t a l , 1951; Kraft and Ayres, 1952; Ramsbottom, 1954; Brissey, 1963). consumers have reacted unfavorably t o the color of incompletely oxygenated red meats. For t h i s reason, p l a s t i c s permitting some oxygen diffusion i n packaged f resh meats have been advocated, even though it i s recognized t h a t the desired color development i s at the expense of longer storage l i f e . On the other hand, cured meats most s a t i s f a c t o r i l y r e t a in the desired pink-red color of n i t r i c oxide myoglobin and myochromogen when the f i lm i n which they a r e packaged i s impermeable t o oxygen. In the presence of l i g h t , which be- haves as a ca ta lys t , these l a s t two pigments a re rapidly converted t o metmyo- globin and other oxidized pigments. It i s f o r t h i s purpose t h a t much e f f o r t i s being made t o package cured meat products i n f i lms im-permeable t o oxygen.

Unfortunately,

Several techniques have been developed f o r providing sa t i s fac tory gas and light relat ionships f o r packaged cured meats. commonly used are:

Among those most

I. Wax paperboard t r ays with transparent p l a s t i c windows. The f i l l i n i x Company developed t h i s type of container i n 1945 (viz Modern Packaging, 1945, 1951) t o block the entrance of l i g h t except when the meat was t o be viewed.

11. Entirely transparent packaging materials except f o r backing board o r metal disk support.

a. Compression and use of a s t re tchable f i lm such as polyethylene, rubber hydrochloride, e tc .

b. Gas flushing and pouch packaging. LSuggested i n the ea r ly 1950's by Ogilvy and A p e s (1951) and &af t and Ayres (1953) and i n general use since 1962.1

c. F i l m opaque t o W or with a W absorber. used comerc ia l ly .

A s yet not

d. Evacuation and use of:

1. Heat shrinkable f i l m .

2. Form f i t t i n g p l a s t i c s .

In the last f i v e years, packages having the contour of the products being packaged have gained i n popularity. materials a re qui te popular f o r products such a s wieners, sausages, e t c . The most successful of a l l packaging films a r e those t h a t f i t around the product and then can be evacuated and shrunk as i n the Cryovac process so that very l i t t l e , i f any, f r e e a i r remains.

These form-fit t ing

I n addition t o furnishing better color protection, these packaging innovations provide greater san i ta t ion i n the handling of meat products and thus improve the keeping qua l i ty of packaged meats. Neverthe- less, there are always a few bac ter ia t h a t a r e present and ult imately grow. The nature and extent of such pro l i fe ra t ion i s a matter of importance. I n the presence of proper moisture conditions, microorganisms i n i t i a l l y present on the meat grow rapidly even a t low temperatures. Unfortunately, there a r e many consumers who believe that cured meats packaged i n the newer types of transparent, c lose f i t t i n g materials have an unduly extended storage l i f e . To i l l u s t r a t e : one of our a s s i s t an t s wa8 searching i n t h e market f o r a package of wieners t ha t had not been i n the re f r igera ted display case longer than two hours and asked one of the clerks arranging meats i n a large supermarket. This employee indicated complete unconcern regarding the ages of t he packages and expressed the opinion tha t age was unimpor- t a n t because the meat was packaged i n these new types of packages and should keep.

It long has been recognized (Glage, 1901; Hichardson and Scherubel, 1909; Scott, 1936) t h a t bac t e r i a l slime i s produced only a t high humidity and tha t desiccation serves as a preventative. Bacter ia l slime develops a t 99% RH and above. A t 98qb RH, growth becomes v i s i b l e but colonies do not coalesce. A t 96 1/2-97$ RII, the number of bacteria/cm2 reaches lo9 without growth be- coming v i s i b l e t o the naked eye.

I. Fresh Meats

Fresh raw meats contain f a i r l y low s a l t concentrations so tha t they a r e i n equilibrium with a surrounding atmosphere of 99% re l a t ive humidity (Scott, 1936). In other words, their equilibrium re l a t ive humidity i s 99 or their average water content approximates a water a c t i v i t y (aw) value of .99 where the aw of pure water i s 1.00. If the atmosphere surrounding the meat is r e l a t ive ly dry, moisture d iss ipa tes from the surface and the outside layer becomes c rus t l ike or horny. ing" provides unfavorable conditions f o r bac te r i a l multiplication, the meat becomes excessively tough, undesirable i n appearance, and dark i n color and so the use of several of the more highly permeable p l a s t i c s such as cel lulose acetate , polystyrene, or p la in cellophane i s not recommended even though these films provide good oxygenation of the myoglobin t o oxymyoglobin.

While such surface dehydration or "case harden-

With r e l a t ive ly impermeable films, the a, value remains constant throughout the expected storage l i f e of the meat. Grganisms such a s Pseudomonas, Achromobacter, Salmonella and Shigella, a s w e l l as many other bacter ia , require very high water a c t i v i t i e s f o r multiplication. Scott (1957) has shown that Pseudomonas w i l l not produce slime a t a, l e s s than .98 and t h a t most of the bacter ia associated with the spoilage of meats w i l l not grow a t a, l e s s t h a t .96. Thus, it i s unlikely tha t f resh meat products could be stored a t a water a c t i v i t y low enough t o eliminate growth of such microorganisms.

42.

Organisms of possible public health significance i n f resh meats a r e exotic or, at most, play a very minor ro le . One report (Ayres and Adams, 1953) indicated t h a t the usual load of putrefactive anaerobic spores present i n packaged raw beef ranged between 0.7-6.0 per 100 g. while i n another invest igat ion (Steinkraus and Ayres, 1964) a mean spore count of 6.5 per gram of f resh beef trimmings was reported. According t o McKillop (1959), the most probable numbers of Clostridium perfringens i n uncooked meats i s approximately 0.03 per gram while - C. botulinum has not been i so la ted from f resh meats.

Various genera of the Enterobacteriaciae, including Salmonella, Paracolobactrum and Escherichia, have been repeatedly recovered from ground meats. Occasionally, coagulase posi t ive Staphylococci a l so have been found. In addition, t he recent incrimination of packaged smoked f i s h as the source of C. botulinum E has served a s a warning t o the en t i r e food packaging indGstry of the poten t ia l danger from pathogens when adequate safeguards i n san i ta t ion a re not practiced.

Since the ea r ly work of Glage i n 1901, there have been many s tudies confirming t h a t almost a l l of the microorganisms found on r a w meats a r e a t the surface and t h a t the in t e rna l f l e sh i s r e l a t ive ly f r e e of microorganisms. negl igible increase i n numbers of organisms i n the deep f lesh of beef stored f o r two weeks a t 5 O C . This l ed Noran (1935) t o conclude t h a t spoilage by bac ter ia i n the deeper pa r t s of the f l e sh i s unimportant compared with t h a t taking place a t the surface. Depending upon the tempera- t u r e of storage and the age of cut-up meats, bac t e r i a l p ro l i fe ra t ion serves as an indicator f o r the freshness of the meat. For example (Fig. l), s l iced beef i n i t i a l l y containing l e s s than 100 bacter ia per square centimeter of surface area keeps f o r nine t o t en days when stored a t 5OC, while steaks having an i n i t i a l load of 20,000 c rgan i sm develop off-odor within s i x days. Soon a f t e r the detection of off-odor, these meats become slimy. All too often, incipient s l i m e has been observed i n packaged meats, par t icu lar ly i n ground beef. handled, were i n the range of 75,000-150,000 per gram. A s meat i s cut and passed through the grinder, the load becomes redis t r ibuted. i s not cleaned immediately before re-use, l eve ls of a million o r more per gram may be expected. =aft and Ayres (1952) and Ayres (1960) r e fe r t o con- centrat ions ranging from 60-100 mill ion organisms per cm2 by the time tha t slime becomes manifest. There i s a t i m e lapse of only a few hours between recognition of off-odor and production of slime. t i m e consis ts almost e n t i r e l y of pseudomonads although, t o a l e s se r degree, Achromobacter, Micrococcus, and Flavobacterium may a l so be present. organisms a r e psychrotrophs and pe r s i s t even though the meat i s stored a t low temperatures.

Thirty-six years ago, Koran and Smith (1929) reported a

I n i t i a l loads of f resh ly ground beef, even when careful ly

When the grinder

The resident f l o r a a t t h i s

These

11. Cured meats

A s indicated e a r l i e r , pigments i n these meats rapidly undergo deter iorat ion i n the presence of oxygen and l i g h t and so the industry has developed f i l m s and packaging equipment t h a t prevent the combined e f f e c t s of these deleter ious agents.

43, Fig. 1. E f fect o f i n i t i a l bacter ial populations

on storage 1 i f e o f sl iced and ground beef.

STORAGE TEMPERATURE 4.4O C

II I I I I I 0 2 4 6 8 IO I;

TIME IN DAYS

44.

Several s tudies have been made of the microbiology of vacuum- packed s l iced processed meats (Leistner, 1956, 1957; Allen and Foster, 1960; Brown and Schmucker, 1960; Ingram, 1960; Linderholm, 1960; A l m -- e t a l , 1961; Hansen and Riemann, 1962). While these packaging procedures were uniformly reported t o improve appearance and acceptabi l i ty , reports differed concerning the influence t h a t evacuation had on microbial p ro l i fe ra t ion . Ingram (1960) and Linderholm (1960) reported ins igni f icant differences i n t o t a l counts between stored vacuum-packed and nonvacuum products. t o Ingram, reducing the oxygen tension i n packaged Wiltshire bacon did not limit the r a t e of bac te r i a l multiplication since most of the micrococci derive "oxygen from n i t r a t e instead of air and the l a c t o b a c i l l i do not need it." i s m s a r e capable of growing e i t h e r aerobical ly or anaerobically but t h a t anaerobic packaging provides some extension of shelf l i f e due t o the inhibi- t i o n of growth of yeasts and mold and other aerobic microorganisms. t he other invest igators a t t r i bu ted differences i n dominant f l o r a t o vacuum- packaging. According t o A l m -- e t a1 (1961), t h i s s h i f t w a s from a mixture of Bacillus sp., Mcrococcus sp. and Lactobacillus sp. t o almost a pure cul+,ure of Lactobacillus sp. from heterofermentative organisms t o homofermentative Lactobacillus sp. Hansen (1960) and, l a t e r , Hansen and Riemann (1962) indicated t h a t the f l o r a i n vacuum-packed s l iced bacon held a t 2OoC sh i f ted from almost equal propor- t i ons of Lactobacillus (30), Streptococcus (30), and Micrococcus (40%) a t two days t o predominantly l a c t i c acid bac ter ia (70%) a t the expense of the streptococci (20%) and micrococci (19%), but with bacon held at 50C fo r s ix days, the f l o r a w a s const i tuted en t i r e ly of Lactobacil l i (75%) and Strep- tococci (25%) and a f t e r 24 days w a s i n t h i s same proportion.

Leistner (1957),

According

Likewise, Niven (1961) reported t h a t most cured meat spoilage organ-

However,

Similarly, Allen and Foster (1960) reported a change

The use of vacuum or gas packaging f o r f rankfurters has become increasingly popular during the past decade. made i n t h i s laboratory p r io r t o t h a t t i m e (Ogilvy, 1950; Ogilvy and Ayres, 1951, 1953), it w a s deemed important t o f ind i f there was a change i n the predominant f l o r a a s a result of the use of evacuation or gassing. A s may be seen i n Fig. 2, differences i n counts on frankfurters i n evacuated packages (dotted l i n e s ) were insuf f ic ien t t o conclude t h a t vacuum packing caused any reduction i n population. represent median values f o r f i v e separate determinations; the v e r t i c a l l i n e s represent ranges f o r each t e s t . ) wieners (containing added cerea l ) , while somewhat higher than those recorded i n a previous study f o r an a l l meat frankfurter (Ogilvy and A y r e s , 1953; v iz Fig. 3 were again qui te consistent, the usual surface load being within t h e range 7,000-25,000 per f rankfurter . During the first four days i n the re f r igera ted display case, these numbers remained a t about the same l e v e l but by the s ix th day, some of the samples had begun t o show evidence tha t t he resident f l o r a was increasing and counts were higher i n each subsequent t e s t . While there was a slight reduction i n numbers during the first three days of storage, it i s not known i f any significance can be attached t o t h i s phenomenon. It is qui te possible t h a t during handling and packaging a number of microorganisms t h a t were merely adventit ious contaminants may have come i n t o contact with the wiener surface and found the substrate unsuitable f o r growth.

Inasmuch a s a study had been

(The points f o r each of the two curves

I n i t i a l counts of t he control

45.

W m 2

I- o a m L L 0

3t

Fig. 2. Changes i n b a c t e r i a l loads on vacuum packaged VS. conventional l y packaged f rankfur te rs .

- CONTROL PACKAGE

STORAGE TEMPERATURE 4.4"C

I I I I I J 0 2 4 6 8 IO 12 21

TIME IN DAYS

46.

Fig. 3. E f fec t o f carbon dioxide on growth o f micro- organi sms on frankfurters stored a t II.Ic°C.

[FROM OGILVY a AYRES(l953)l

I I I I I I 1 5 IO 15 20 25 30

TIME IN DAYS

47.

A s ea r ly as 1882, Kolbe recognized t h a t C02 in te r fe red with the normal development of micrcorganisms on meat. Since t h a t t i m e , many inves- t i g a t o r s have t r i e d t o account f o r t he inh ib i t ion of microorganisms by C02 (Frankel, 1889; Jacobs, 1920; Pruchas -- e t a l , 1922; Brown, 1922; Valley and Rettger, 1927; Ki l le f fe r , 1930; Tomkins, 1950; Moran, -- e t a l , 1932; Callow, 1932; Haines, 1933; Scott , 1938; Mallman -- e t a l , 1940; Golding, 1940, 1945; Ruyle e t al , 1946; Ogilvy and Ayres, 1951, 1953; Hays and Riester, 1958; Hays - e t - 9 a1 1959). Organisms o r ig ina l ly found on t h i s type of meat were predominantly G r a m pos i t ive types such as micrococci, b a c i l l i and sarcinae being most numerous with l ac tobac i l l i , G r a m negative bac ter ia , molds and yeasts being less com- monly encountered. and yeasts was progressively retarded while t h a t of t he l a c t i c ac id bac ter ia was not (Fig. 3 ) . w a s composed almost e n t i r e l y of Lactobacillaceae and Microbacterium. The product, while tar t , contained no organisms of public heal th significance.

Carbon dioxide improves the storage l i f e of f rankfur te rs .

A s t h e l e v e l of CO2 was raised, growth of molds, micrococci

I n atmospheres containing 50 t o 96% COzp t he surface f l o r a

Most cured meats contain su f f i c i en t sodium chloride, sugar and n i t r a t e - n i t r i t e t o reduce the water-act ivi ty t o a, = .90-.95. A s may be seen i n Fig. 4, Hansen and Riemann observed t h a t Clostridium botulinum requires an equilibrium r e l a t i v e humidity of 98 (aw = .98) f o r germination and does not grow below 94. packaged - t h i s organism does not pose a r e a l t h rea t . Danish invest igators reported t h a t Staphylococcus aureus grew readi ly a t a, values of .90-.95 and so was considered important as a possible pathogen. Cavett (1962) indicated t h a t the incidence of coagulase pos i t ive S. aureus was low i n vacuum packed s l i ced Wiltshire bacon but t h a t these organisms were occasionally detected. Large numbers of these organisms are occasionally recovered from f rankfur te rs (Plate 1). The majority of t h e S. aureus c e l l s present i n t h i s pa r t i cu la r p e t r i p l a t e were coagulase pos i t ive and conceivably cons t i tu te a r e a l danger.

Hence, f o r these meats - even though they may be vacuum or gas Cn the other hand, t he

It i s recognized t h a t recovery of such staphylococci - even from food implicated i n a food poisoning outbreak - i s only circumstant ia l evidence of t h e proper e t io log ica l agent ( H a l l e t al , 1963) and t h a t proof requires dem- onstrat ion of enterotoxin i n the food. S t i l l , coagulase pos i t ive staphylococci have often been associated with pyemic infec t ions and, therefore , t h e i r pres- ence i s viewed with grave suspicion. Since suf f ic ien t heat and s a l t s are applied during processing of most cured meats t o destroy almost a l l vegetative c e l l s , t he pr inc ipa l problem i s one involving subsequent contamination. Ultimate microbial populations d i r e c t l y r e f l e c t san i ta t ion during handling, packaging and storage. p o s s i b i l i t y of packing cooked ham with less than t en bac ter ia per s l i c e , but i n a study made by Miller (1960) of 113 r e t a i l packages of s l i ced cooked ham, counts ranging from fewer than 1000 t o more than 52 mil l ion per inch2 of surface area were recovered. t h a t are consumed shor t ly a f t e r heating or eaten without being cooked a re r a r e l y responsible f o r staphylococcal food poisoning; those generally involved have been heated before being subjected t o care less handling and inadequate r e f r ige ra t ion .

--

For example, Hansen and R i e m a n n (1962) indicated the

According t o Casman e t a1 (1963), meat products --

48 Fig. 4. Comparison of water a c t i v i t y values fo r various meats with those l imit ing the germination or growth of microorganisms.

D i s t i l l ed water

Fresh meat

Frankfurter

Sausage

Sliced pressed ham Salami Sliced bacon

Cured pork Fermented sausage

Smoked pork

Fermented sausage - with high salt content

1.0- (lowest aw permitting growth i n a r t i f i c i a l media)

Slime production

Bacillus mycoides

Clostridium botulinum (germination) Pseudomonas (growth) Bacillus cereus (germination)

Achromobacter (growth)

- 0.95 Salmonella newport, Bacil lus s u b t i l i s Bacil lus cereus (growth) Clostridium botulinum (growth)

Sarcina sp.

Micrococcus roseus - 0.90 Staphylococcus aureus (anaerobic)

Lower growth l imi t f o r several yeasts

Staphylococcus aureus (aerobic) Aspergillus niger

- 0.85

Aspergillus glaucus

- 0.80 Xeromyces

(From Hansen & Riemann, 1962; a l so data from Scott, 1957)

49.

I n conclusion, t h e length of storage l i f e expected f o r f resh or cured meats w i l l d i r e c t l y r e f l e c t t he san i ta t ion pract iced during handling, packaging and storage. qua l i t y of both products, but t h i s safeguard alone i s insu f f i c i en t t o prevent undesired bac ter io logica l and chemical changes. ment of air by C02 may have salutary act ion f o r cured meats but t he e f f ec t of water a c t i v i t y i s probably of more importance. Since such meats are r e l a t i v e l y f r e e of microorganisms immediately a f t e r cooking, t h e human fac to r i s of con- siderable consequence. appropriate f i l m s , packaging techniques, and storage temperatures; it should be possible t o extend the safe storage l i f e of cured meats. It j s advocated t h a t f r e sh meats be kept a t as low temperature and held f o r as short a time as possible .

Adequate r e f r ige ra t ion w i l l prolong the keeping

Evacuation and the replace-

With proper san i ta ry precautions and the use of

Reference s

1.

2.

3.

4.

5.

6 .

7 .

8 .

9.

10.

Allen, J. H. and Foster, E. M. Spoilage of vacuum-packed s l i ced processed meats during re f r igera ted storage. Food Research 25, 19 (1960).

Alm, F., Erichsen, I . , and Molin, N. The e f f ec t of vacuum packaging on some s l i ced processed meat products as judged by organoleptic and bacter iologic ana lys i s . Food Technol. - 15, 199 (1961).

Ayres, J. C. Temperature re la t ionships and some other cha rac t e r i s t i c s of the microbial f l o r a developing on re f r igera ted beef. Food Research - 25, 1 (1960).

Ayres, J. C . and Adams, A. T. Cccurrence and nature of bac te r ia i n canned beef. Food Technol. - 7, 318 (1953).

Brown, W. and i n various concentrations of oxygen and of carbon dioxide. Ann. Botany 2, 257.

On t h e germination and growth of fungi a t various temperatures

Brown, W. L. and Schmucker, M. L. The influence of low l e v e l gamma i r r ad ia t ion , a n t i b i o t i c treatment, storage temperature and vacuum packaging on f lavor and b a c t e r i a l changes i n cured bacon. Food Technol. - 14, 92 (1960).

Callow, E. H. Gas storage of pork and bacon. I. Preliminary experiments. J. Soc. Chem. Ind. (London) - 51, 116T. (1932).

Casman, E. P., McCoy, D. W. and Brandly, P. J. Staphylococcal Growth and Enterotoxin Froduction i n N e a t . Appl. Microbiol. - 11, 1 (1963).

Cavett, J. J. The Microbiology of Vacuum Packed Sl iced Bacon. J. Appl. Bact. 25, 2 . (1962).

Frankel, C . Microorganismen.

Die Einwirkring der KohlensLure auf d i e Lebenstatigkirt der Z. f . Hyg. - 5, 332 (1889).

50.

11 *

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

Glage, F. Ueber d ie Bedeutung der Aromabakterium fir d ie Fleischhygiene. Z. Fleisch-u, Milchhyg. - 11, 131 (1901).

Gelding, N. S. The gas requirements of molds. 111. The e f f ec t of various concentrations of carbon dioxide on the growth of Penicillium rogueforti i n air . J. Dairy Sei. - 23, 891 (1940).

Golding, N. S. The gas requirements of molds. I V . A preliminary in- te rpre ta t ion of growth r a t e s of four common molds on the basis of absorbed gases. J. Dairy Sci. 737 (1945).

Haines, R. B. The influence of carbon dioxide on the r a t e of multiplica- t i o n of cer ta in bacter ia as judged by v i s i b l e counts. J. SOC. Chem. Ind. (London) 52, 13T. (1933).

H a l l , H. E., Angelotti, R. and Lewis, K. H. Quant i ta t ive detection of staphylococcal enterotoxin B i n food by gel-diffusion methods. Public Health Reports (U.S. ) - 78, 1089 (1963).

Hansen, N. H. Qual i ty deter iorat ion and bac te r i a l growth i n prepacked bacon. Publication No. 28, Danish Meat Research Ins t . (Roskilde) 1960.

Hansen, N. H. and Riemann, H. Mikrobiologische Beschaffenheit von vorverpacktem Fleisch and vorvepackten Fleischwaren. - 14, 861 (1962).

Fleischwirtschaft

Hays, G. R., Burroughs, J. D. and Warner, R. C. Microbiological aspects of pressure packaged foods. 11. The ef fec t of various gases. Food Technol. - 13, 567 (1959).

Hays, G. L. and Riester, D. W. Microbiological aspects of pressure packaged foods. Soap Chem. Special t ies 34, 113 (1958).

Ingram, M. Bacter ia l multiplication i n packed Wiltshire bacon. J. Appl. Bact. 23, 206 (1960).

Jacobs, M. H. To what extent a r e the physiological e f f ec t s of carbon dioxide due t o hydrogen ions? Am. J. Physiol. - 51, 321 (1920).

Kil le f fe r , D. H. Carbon dioxide preservation of meat and f i sh . Ind. Eng. Chem. - 22, 140 (1930).

Kolbe, H. Antiseptische Eigenschaften der Kohlensaure. J. Prakt. Chem. - 26, 249 (1882).

Kraft, A. A. and Apes , J. C. Post-mortem changes i n stored meats. IV. Effect of packaging materials on keeping qua l i ty of self-service meats. Food Technol. - 6, 8 (1952). Leistner, L. Die Neuzeitliche Verpackung i n der Fleischwirtschaft. I. Fleischwirtschaft - 8, 422 (1956). Leistner, L. Die Neuzeitliche Verpackung i n der Fleischwirtschaft . 11. Fleischwirtschaft - 9, 262 (1957).

51.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

Linderholm, K. G. Bakteriologiska och hygieniska undersokningar av vakuumforpackade charkuterivaror. 1 7 . (1960).

Nord. Hygienisk Tidskr. XLI ( 1 - 2 ) ,

Mallmann, W. L . , Zaikowski, L. and Ruster, M. The e f f ec t of carbon dioxide on bac ter ia with par t icu lar reference t o food poisoning organisms. Mich. Agr. Exp. Sta. Bull - 489 n.s. (1940).

McKillop, E. J. Bacter ia l contamination of hospi ta l food with special reference t o - C 1 . welchii. J. Hyg. 57, 31 (1959).

Miller, W. A. The microbiology of self-service, packaged square s l i c e s of cooked ham. J. Milk and Food Technol. - 23, 311 (1960).

Moran, T. Post-mortem and re f r igera t ion changes i n meat. J. SOC. Chem. Ind. 54, Pt. 2 t r ans . 149T (1935).

Moran, T. and Smith, E. C . Post-mortem changes i n animal t i s sues . The conditioning o r ripening of beef. Gr. B r i t . Dept. of Sci. and Ind. R e s . H. M. Stationery Office. Food Invest. Bd. Special Rept. - 36, (1929).

Moran, T. , Smith, E. C . and Tomkins, R. G. The inh ib i t ion of mould growth on meat by carbon dioxide. J. SOC. Chem. Ind. (London) - 51, 114T. (1932).

Ogilvy, W. S. Storage of meat i n carbon dioxide atmospheres a t tenperatures above freezing. (Unpublished Ph. D. t hes i s , Ames, Iowa, Iowa State Univ. Library) (19 50 ) . Ogilvy, W. S. and A p e s , J. C . Post-mortem changes i n stored meats. 111. The e f f e c t of atmxpk-eres containing carbon dioxide i n prolonging the storage l i f e of f rankfurters . Focd Technol. 5, ZOO (1951).

Ogilvy, W. S. and A p e s , J. C. Post-mortem changes i n stored meats. V. The e f f e c t of carbon dioxide on microbial growth on stored frankfurters and charac te r i s t ics of some microorganisms i so la ted from them. Food Research - 18, 121 (1953).

Prucha, M. J., Brannon, J. M. and h b r o s e , A. S. milk and milk products destroy bac ter ia? Univ. of Ill. Agr. Co l l . and Exp. Sta . Bull. - 256 (1922).

Ramsbottom, J. M. Meat-packaging c r i t e r i a . Modern Packaging (Feb.) (1954).

Does C 0 2 i n carbonated

Richardson, W. D. and Scherubel, E. F. The deter iorat ion and commercial preservation of f l e s h foods. Second paper - The storage of beef a t temperatures above t h e freezing point. J. Ind. Eng. Chem. - 1, 95 (1901).

Ruyle, E. H., Pearce, W. E. and Hayes, G. L. Prevention of mold i n k e t t l e d blueberr ies i n No. 10 cans. Food Research - 11, 274 (1946).

Scott, W. The grGwth of microorganisms on ox nuscle. 1. The influence of water content of substrate on rate of growth at -1OC. Australia J. Coun. Sc i . Ind. Research - 9, 177 (1936).

Scott, W. J. The growth of microorganisms on ox muscle. 111. The influence of 10 per cent carbon dioxide on r a t e s of growth a t -1OC. Austral ia J. Coun. Sci. Ind. Research - 11, 266 (1938).

52.

43. Scott, W. J. Water re la t ions of food spoilage microorganisms. Advances _.- i n Food Research - 7, 83. N. Y. 404 pp. (1957).

Academic Press Inc., New York,

44. Steinkraus, K. H. and A p e s , J. C. Incidence of putrefact ive anaerobic spores i n meat. J. Food Sci. - 29, 87 (1964).

45. Tomkins, R. G. Studies of the growth of moulds. Proc. Roy. SOC. (London) ser . B - 105, 375 (1930).

46. Valley, G. and Rettger, L. F. The influence of carbon dioxide on bacter ia . J. Bact. 7 14, 101 (1927).

47. Williams, 0. B. and Furnell, H. G. Spore germination, growth and spore formation by Clostridium botulinum i n r e l a t ion t o the water content of the substrate . Food Research - 18, 35 (1953).

NEIL WEBB: ....... i n introduction of Dr. H. E. Hall, who has prepared a paper for the group. -- A br i e f background on Dr. Hall, he spent 5 years i n the U. S. Army i n Cl in ica l bacteriology and from there he moved t o Boston City Hospital, a divis ion of Hartford University, working with Dr. Nax Finland. He came South t o Kentucky where he f inished h i s academic work Ph D i n 1955 and worked i n bac te r i a l a l l e r g i e s and as a research associate a t the University of Kentucky. laboratory technician i n Akron, Ohio working on c l i n i c a l mycology and bacteriology. After joining the Taft Center f o r sometime, he i s Acting Chief of the Food Microbiological Section a t the Robert A. T a f t Sanitary Engineering Center, Cincinnati, Ohio. It i s a pr iv i lege t o present Dr. H a l l .

He l a t e r worked a s a pr iva te

# # # # # # # # # # # # #