INFLUENCE OF MOISTURE CONTENT AND STORAGE TEMPERATURE ON THE PRODUCTION OF AFLATOXIN BY ASPERGILLUS FLAVUS EA-81 IN MAIZE AFTER EXPOSURE TO GAMMA RADIATION

The effect of gamma radiation on aflatoxin production by Aspergillus flavus EA-81 in maize with different initial moisture levels was determined over a 15-day period. The viability of A. flavus on maize decreased over time with increasing moisture contents and storage at 8C. After 45 days at 28C, levels of viable conidiospores of A. flavus increased from 4.5 × 10⁷ to about 3.0 × 10⁸ per gram of maize. Levels of aflatoxin B₁ produced by A. flavus were 10 μg kg^-1 in the maize stored at 8C after 45 days. Production of aflatoxin was highest at 40% moisture and 28C. Irradiation of 1.0 or 2.0 kGy greatly reduced the level of mold growth relative to unirradiated controls. A dose of 4.0 kGy eliminated all viable fungi. Aflatoxin B₁ production decreased with increased levels of irradiation and was negligible at 4.0 kGy. When maize was inoculated after irradiation and stored, the spore counts and aflatoxin levels were higher than in unirradiated and inoculated controls after 30 days. Apparently, the natural competitive microflora prevented growth and thus limited higher concentrations of aflatoxin in maize.     

The yeast flora of stored ready-to-use carrots and their role in spoilage

Spoilage of ready-to-use grated raw carrots packaged in polymeric films and stored at 10°C was investigated for involvement of yeasts. Cryptococcus albidus was only isolated during the first 3 days of storage, increasing to levels of 10⁵–10⁶g^-1. Candida lambica was more commonly isolated after 3–7 days of storage, and reached 10⁷–10⁸g^-1 after 12 days. Candida sake was present throughout storage, increasing from 10⁵–10⁶ after 3 days to 10⁷–10⁸ after 12 days. In some samples, Candida parapsilosis and Candida tropicalis were also isolated at levels similars to C. sake . All the yeasts isolated at the end of storage were fermentative species and their metabolism was characterized with a Warburg apparatus. Neither the number of yeasts nor the composition of the yeast flora were related to the deterioration of the product. Although Candida lambica inoculated on grated carrots caused spoilage after 12 days at 10°C, the high O₂ permeable film was most effective in reducing exudate.     

Microbiological study of semi-hard goat's milk cheese (Majorero)

The development of microbial flora in industrially produced semi-hard cheese made from pasteurized goat's milk was studied during manufacture and over a 90-day ripening period.
Estimates of total count, streptococci, lactobacilli, leuconostocs, coliforms, micrococci and staphylococci, Staphylococcus aureus and yeasts and moulds were carried out at various stages of the ripening process; streptococci and lactobacilli were identified by species.
Initially, the total count increased rapidly, primarily as a result of the growth of mesophilic lactic streptococci mainly Streptococcus lactis and Strep, cremoris. Subsequently, both these counts stabilized or decreased. Lactobacilli increased, and by the end of the ripening period were the predominant microorganisms. Most common were Lactobacillus casei var. casei. , especially at the end of storage; L. casei var. rhamnosus , L. casei var. plantarum and L. cellobiosus were also isolated. Leuconostocs were not found in any of the cheeses, and hence no eye formation took place. Coliforms, enterococci, yeasts and moulds remained below 10²–10³ c.f.u. g⁻¹. Maximum levels of micrococci and staphylococci were found after 15–30 days of ripening and decreased gradually towards the end of the ripening period. Neither the milk curd, nor cheese contained Staph. aureus.     

CHANGES IN PARBOILED ROUGH RICE CAUSED BY IMPROPER DRYING AND MICROBIAL INFECTION

Molds and bacteria contaminate parboiled rough rice when it is improperly dried or while awaiting drying due to humid rainy weather. When IR 20 parboiled rough rice was not dried for 7 days due to humid weather molds increased to 2.45 × 10⁷ per gram from 6 × 10⁴ per gram and bacteria increased to 75.9 × 10⁶ per gram from 5.1 × 10⁶ per gram observed initially. The milled rice yield decreased to 60.1% from 72.2% and the head rice yield decreased to 55.0% from 98.8% due to infection. The resultant bran contained only 12.1% oil compared to 31.9% in normally dried and milted paddy with about 40.0% free fatty acids in oil. The infection induced breakdown changes increased the levels of sugars, amino acids and polyphenols in grains which might cause kernel discolouration in the associated heat development during infection.     

Influence of pre-treatments on microbial load of stored dehydrated onion slices

Onions slices were pre-treated in potassium meta-bisulphite (KMS) and sodium chloride with different concentration levels to study the microbial load of tray and greenhouse-dried onion slices up to 6 months of storage. Data were analysed as per procedure of one-way classified anova using DMRT of AgRes statistical package for bacteria, yeast, fungi and Lactobacilli . Results revealed that in almost all samples, permissible levels of bacteria [18.33 × 10¹ colony-forming units (CFU) per gram], yeast (ND), fungi (0.5 × 10¹ CFU g⁻¹) and Lactobacilli (0.25 × 10¹ CFU g⁻¹) were observed after 5 months of storage. All the samples were also found to be free from Escherichia coli and no Mac Conkey growth was noticed. Onion slices pre-treated in 0.25% and 0.50% KMS and dried in tray and greenhouse, respectively, were found best after 6 months of storage period.     

RADIATION STERILIZATION OF SPICES FOR HOSPITAL FOOD SERVICES AND PATIENT CARE

A survey of the commercial spices used by food services in a typical hospital environment revealed high contamination with microorganisms, i.e., 10⁴ to 10⁷ counts per gram. The predominant microorganisms were as followed (in colony counts/gram): (1) heat-resistant bacterial spores in black pepper, 1 × 10⁷; thyme, 2 × 10⁶; anise, 7 × 10⁴; curry powder, 4 × 10⁵; poultry seasoning, 8 × 10⁴; pickling spice, cardamom, and cumin, 1.5–3 × 10⁴; (2) mixed populations of vegetative cells and bacterial spores in cumin, 1 × 10⁶; (3) molds in cream of tartar, 2 × 10⁴. Sterility of food may be important in a hospital setting, especially in the care of immunocompromised patients. To eliminate the organisms, we recommend radiation treatment, accompanied by appropriate microbiological quality control. On the basis of radiation survival data, the composite natural flora would be reduced to the level of "commercial sterility" (defined as less than 10 organisms per gram((Kiss 1982) by the following minimum radiation doses (in kGy): black pepper, 13; thyme, 13; cumin, 12; anise, 10; curry, 7.3; pickling spice, 7; poultry seasoning, 6; cardamom, 9.4; cream of tartar, 4. For practical purposes, two dose levels can be recommended for treatment of spices in the hospital environment, low = 6–10 kGy and high = 10–15 kGy.     

HEAT PASTEURIZATION OF CRAB AND SHRIMP FROM THE PACIFIC COAST OF THE UNITED STATES: PUBLIC HEALTH ASPECTS

ABSTRACT— A study of the potential public health hazard presented by coagulase-positive staphy-lococci, salmonellae and Clostridium botulinum in the meat of Dungeness crab and Pacific Coast shrimp pasteurized in flexible plastic containers revealed potentially toxinogenic staphylococci on the commercial nonpasteurized product, in 15% of the shrimp and 9% of the crab samples. No salmonellae or Cl. botulinum were isolated from, respectively. 26 and 54 samples of shrimp or 74 samples of crab. Pasteurization for 1 min at 180°F destroyed large inocula (10⁷ and 10⁸ cells) of staphylococci and salmonellae introduced into packages of the products, but processing for 5 min at 180°F allowed some members of an inoculum containing 10³ spores of Cl. botulinum type E to survive. While storage at 40°F prevented the growth on crab and shrimp meat of all staphylococci and salmonellae tested, it permitted growth and toxin formation by Cl. botulinum type E after 30–40 days. No toxin could be detected in packages inoculated with type A and proteolytic B spores and held at 50°F or lower. A 0.1% dip of sodium benzoate, with or without fumaric acid, did not prevent growth and toxinogenesis by Cl. botulinum types A, proteolytic B or E. It was concluded that for complete safety a holding temperature of 36°F or lower at all times would be required, but that it could not be expected to be maintained in commercial channels.     

Postharvest Microbiology of Farm-reared, Tropical Freshwater Prawn (Macrobrachium Rosenbergii)

ABSTRACT: The microbiological quality of farm-reared, tropical freshwater prawn ( Macrobrachium rosenbergii ) stored at 2 different temperatures was studied. The prawn muscle was found to have the initial bacterial load of 10⁴ cfu/g. The lactics and vibrios were in the range of 10² cfu/g, while the E. coli , aeromonads, staphylococci, anaerobes, and molds were in the level of 10¹ cfu/g. Salmonella and Vibrio cholerae were present in the prawn muscle. The prawn muscle held at room temperature (28 ± 2 °C) was organoleptically acceptable up to 8 h, when the bacterial load was more than 10⁶ cfu/g. However, the prawn muscle stored at freezer temperatures (−10 to −15 °C) was found to be in acceptable condition even after 30 d of storage and the bacterial load was fluctuating in the range of 10³ to 10⁴ cfu/g.     

Effect of Inoculation Level of Lactobacillus rhamnosus and Yogurt Cultures on Conjugated Linoleic Acid Content and Quality Attributes of Fermented Milk Products

ABSTRACT:  The effect of inoculation concentration of Lactobacillus rhamnosus and yogurt cultures and storage time on conjugated linoleic acid (CLA) content and quality attributes of fermented milk products was determined. Yogurt culture ( Lactobacillus bulgaricus and Streptococcus thermophilus, 1:1 ratio, YC ) , L. rhamnosus (LB), and LB co-cultured with yogurt culture, were inoculated at 10⁶, 10⁷, 10⁸ CFU/mL into a milk with hydrolyzed soy oil as the lipid source. CLA content, microbial counts, acidity, texture, and volatile flavor profile of the fermented milk products were stable during storage at 4 °C for 14 d. Total CLA contents ranged from 0.51 to 1.00 mg CLA/g lipid following 14 d of storage. Inoculation level of L. rhamnosus and yogurt cultures had no significant effect on CLA content and texture, but affected acidity and the volatile flavor profile of the fermented milk products. The fermented milk products produced by L. rhamnosus co-cultured with yogurt culture with 10⁷ CFU/mL total inoculation level resulted in a high CLA content and desirable quality characteristics. This research demonstrated that the optimal inoculation concentration and the combination of L. rhamnosus and yogurt cultures were important factors to produce fermented milk products with CLA content and acceptable quality attributes.     

EFFECT OF PENCILLIN ON FREE OR IMMOBILIZED LACTOCOCCI: MILK ACIDIFICATION AND RESIDUAL ANTIBIOTIC LEVEL

Five lactic acid cultures were added to milk containing penicillin, and the effect of immobilization on acidification and residual penicillin concentration were determined. Cells of Lactococcus lactis subsp . cremoris CRA-1 immobilized in calcium alginate beads were less sensitive to penicillin than free cells, and inhibition occurred later in the fermentation. The lactococci were less sensitive to penicillin when high cell densities were inoculated (10⁹ CFU/mL). There was a significant reduction of penicillin (up to 0.3 IU/mL) when milk was inoculated with high populations of Lac. cremoris and incubated at 30C for 6 h. The drop in penicillin concentration was not related to adsorption to the alginate or to the presence of β-lactamase on the cultures. When free cells of Lac. cremoris, Streptococcus salivarius subsp . thermophilus or Lactobacillus delbrueckii subsp . bulgaricus were added to milk containing antibiotics, and incubated at 4 or 10C for 48 h, significant reduction of penicillin levels did not occur in the contaminated milk. Milks containing more than 4 × 10⁶ lactococci CFU/mL can give false positive results in the antibiotic disk assay using Bacillus subtilis.     

Optimization Process of Black Soybean Natto Using Response Surface Methodology

ABSTRACT:  Response surface methodology (RSM) was used to determine the optimum combinations of 3 factors, cooking time (40 to 120 min), inoculated bacteria populations (10¹ to 10⁹ cells/100 g), and fermentation time (12 to 36 h) for producing black soybean natto. All of the responses (hardness, viscosity, and trichloacetic acid-soluble nitrogen) were significantly affected by the 3 factors. Fermentation time was the most important factor affecting quality of black soybean natto. Optimum combinations were cooking time 110 min, inoculated bacteria populations 10² to 10⁴ cells/100 g, and fermentation time 30 to 33 h.     

ATTEMPTS TO UTILIZE BACTERIOPHAGE TO COMBAT SALMONELLA ENTERICA SEROVAR ENTEMTIDIS INFECTION IN CHICKENS

Bacteriophage capable of lysing a nalidixic acid-resistant Salmonella enterica serovar Enteritidis strain (Se E Nal^r) were tested for the ability to reduce cecal Salmonella counts in young chickens infected with the bacterium. Qualitative analysis of cloacal swabs suggested that phage treatment can possibly reduce shedding of Se E Nal^r, but average Se E Nal^r counts of between 10⁵ and 10⁷ cfu of Se E Nal^r per g of cecum were obtained even from phage-treated 14-day old birds and even when more than 10⁷ plaque forming units of phage were present per gram of cecal content. The average cecal Se E Nal^r counts were generally between 0.3 and 1.3 orders of magnitude lower in phage-treated chickens than in untreated controls birds. The difference in counts was statistically not significant in three animal trials, but significant in two trials using feed particles as delivery vehicles for the phage. Although some of the Se E Nal^r in the cecae of phage-treated chickens had developed resistance to some of the phage used, factors other than phage resistance must have contributed to the failure of the phage to substantially reduce Se E Nal^r counts.     

CHALLENGE STUDIES WITH PROTEOLYTIC CLOSTRIDIUM BOTULINUM IN YEAST AND CHEMICALLY LEAVENED CRUMPETS PACKAGED UNDER MODIFIED ATMOSPHERES

Challenge studies were done with proteolytic Clostridium botulinum (10³ spores/g) in yeast-and chemical-leavened crumpets (50-g) packaged in air with an ethanol vapor (2-G Ethicap®) generator or in 100% CO₂ and stored at ambient temperature (25C) for 30 days. Neurotoxin was detected in all gas- (CO₂) packaged crumpets after 5 days regardless of the method of leavening. While neurotoxin was delayed for 10 days in chemical-leavened Ethicap®-packaged crumpets, it was not detected in any similarly packaged yeast-leavened crumpets throughout storage. This inhibition of growth and neurotoxin production by C. botulinum was attributed to the production of ethanol by Saccharomyces cerevisiae in the yeast leavened crumpets, in conjunction with the ethanol vapor generated by the Ethicap® sachets (2-G), to levels to inhibitory to the growth of C. botulinum (>2.8% v/v). Subsequent challenge studies in sterile crumpets inoculated with either C. botulinum (10³ spores/g) or a co-inoculum of C. botulinum (10³ spores/g) and S. cerevisiae (10⁵ CFU/g) confirmed the significant role (p<0.001) of S. cerevisiae in enhancing the antibotulinal efficacy of ethanol vapor. These studies showed that the method of crumpet leavening could have a profound effect on the growth of and neurotoxin production by C. botulinum in crumpets packaged under modified atmospheres.     

INHIBITION OF STAPHYLOCOCCUS AUREUS AND BACILLUS CEREUS ON A VEGETARIAN FOOD TREATED WITH NISIN COMBINED WITH EITHER POTASSIUM SORBATE OR SODIUM BENZOATE

Various amounts of nisin (0, 10³ and 5 × 10³ IU/g) in combination with either potassium sorbate (0, 2, and 3%) or sodium benzoate (0, 0.06 and 0.12%) were tested for effectiveness in inhibiting growth of Staphylococcus aureus C10 and Bacillus cereus B7 inoculated on a vegetarian food. The strains used were isolated from vegetarian foods obtained commercially in Taiwan, and the test food, spice and dried bean curd, was selected for the study based on ability to support the growth of these organisms. After treatment with a preservative combination, the surfaces of sterilized food samples were inoculated, samples were stored in vacuum or nonvacuum packages at either 4C or 30C, and at appropriate times, tested for microbial growth. Growth of both isolates was unaffected by vacuum-packaging treatment; however, a bacteriostatic effect was found at 4C. Data indicated that during the 14-day storage at 4C, vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 0.12% sodium benzoate significantly (p < 0.05) decreased the counts of S. aureus C10 and B. cereus B7 by 2.61 and 3.02 log₁₀ CFU/g, respectively. In the vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 3% potassium sorbate, counts for C10 and B7 were decreased by 2.35 and 2.64 log₁₀ CFU/g, respectively. Thus, the combined treatment extended the shelf-life of the vegetarian food .     

Production of Enterotoxin-B in Cured Meats

SUMMARY— A variety of laboratory cured hams were inoculated with 10³−10⁶ cells of S. aureus strain S-6 and incubated at 10, 22 and 30°C anaerobically for up to 16 weeks. Enterotoxin-B was detected by gel-diffusion in hams with original pH over 5.30, up to 9.2% NaCl (brine) and 0.54 ppm undissociated nitrous acid. There was better toxin production at 30° than at 22° or 10°C. Toxin was detected at 10°C after at least 2 weeks incubation and in most samples after 8 weeks when pH was greater than 5.6. Toxic hams had more than 4 × 10⁶ cells/g. Contaminants were always less than 10⁵/g. Tween 80 inhibited toxin production at 30° but not at 10°C. Toxic hams looked normal even after 2 months incubation at 10°C.     

Control of Listeria monocytogenes in ready-to-eat meats containing sodium levulinate, sodium lactate, or a combination of sodium lactate and sodium diacetate

ABSTRACT:  This study investigated the use of sodium levulinate to prevent outgrowth of Listeria monocytogenes in refrigerated ready-to-eat (RTE) meat products. Turkey breast roll and bologna were formulated to contain 1%, 2%, or 3% (w/w) sodium levulinate, 2% sodium lactate, a 2% combination of sodium lactate and sodium diacetate (1.875% sodium lactate and 0.125% sodium diacetate), or no antimicrobial (control). Samples of the RTE products were sliced, inoculated with 10² to 10³ CFU/cm² of a 5-strain cocktail of L. monocytogenes , vacuum packaged, and stored at refrigeration temperature for 0 to 12 wk. Counts reached 10⁸ CFU/cm² on control turkey roll product after 8 wk, and over 10⁷ CFU/cm² on control bologna after 12 wk. Addition of 2% or more sodium levulinate to turkey roll and 1% or more sodium levulinate to bologna completely prevented growth of L. monocytogenes during 12 wk of refrigerated storage. A consumer taste panel with pathogen-free samples found no differences in the overall liking among the preparations of turkey roll or among preparations of bologna. These results show that sodium levulinate is at least as effective at inhibiting outgrowth of L. monocytogenes in RTE meat products as the current industry standards of lactate or lactate and diacetate, and levulinate addition does not alter the overall liking of the RTE meat products.     

The effects of different incubation temperatures on the acetaldehyde content and viable bacteria counts of bio-yogurt made from ewe's milk

Yogurt and bio-yogurt were manufactured from ewe's milk using a starter culture and a probiotic culture. Incubation was carried out at 37°C and 42°C until pH 4.6 was reached and the yogurts were stored at 4 +1°C for 14 days. Analysis after 1, 7 and 14 days showed that incubation temperature and storage time significantly influenced overall properties of the samples. During the storage, whey separation and pH decreased, but titratable acidity, lactic acid and volatile fatty acid contents increased. Viable bacterial counts in all bio-yogurts were above 10⁷ cfu g⁻¹ at the end of storage.     

Viability of probiotic micro-organisms (Lactobacillus acidophilus La-5 and Bifidobacterium animalis subsp. lactis Bb-12) in ice cream

The purpose of this research was to determine the survival of two probiotic micro-organisms in ice creams (4% fat). The micro-organisms were Lactobacillus acidophilus La-5 and Bifidobacterium animalis subsp . lactis Bb-12 . To meet this objective, an ice cream mixture was formulated and subjected to three treatments. Treatment 1 was inoculated with L. acidophilus , treatment 2 with B. lactis and the third treatment was inoculated with a mixture of both bacteria inoculated in 1 : 1 proportions. The inoculation was with 4% culture for each treatment. The final products were stored at −25°C for 60 days. The ice cream inoculated with L. acidophilus had a final concentration of 2 × 10 ⁶ cfu/g and the survival rate was 87%. The treatment inoculated with B. lactis had a final concentration of 9 × 10 ⁶ cfu/g, with a logarithmic decrease of 10%. When both micro-organisms were inoculated together, the survival rate was 86%.     

BACTERIAL COUNTS AND RANCIDITY ESTIMATES OF STORED QUICK-SALTED FISH CAKES

Total plate, halophilic and staphylococcal counts were determined in quick-salted fish cakes after 0, 1, 2 and 3 months' storage without packaging at an ambient temperature of 35–40°C. A rancidity (thiobarbituric acid or TBA) index was also determined in sun-dried and tunnel-dried cakes, before and after desalting, stored under the same conditions for the same lengths of time. Species studied were skipjack, mullet, Spanish mackerel and shark from the Gulf of California. It was found that total plate and halophilic counts behaved similarly, initially increasing with time, passing through a maximum, and then decreasing. Counts increased with decreasing salt and increasing moisture contents of the cakes. Maximum counts obtained were of the order of 10⁶ per gram for cakes made from shark, while negative counts were obtained with cakes made from skipjack after 3 months. No growth of staphylococci was obtained at any time in any of the plated dilutions (10⁻¹ to 10⁻⁶). Rancidity of the cakes increased with time, depending upon the following factors: oil content of the species; degree of unsaturation of the oil; drying time of the cakes; presence or absence of hematin pigments; presence or absence of sunlight when drying. Some of the rancid components in the cakes were removed by desalting in boiling water. In a limited taste panel evaluation of the cakes, order of preference was found to correlate well with decreasing rancidity     

Quantitative changes in bacteria, amino acids and biogenic amines in sardine (Sardina pilchardus) stored at ambient temperature (25–28°C) and in ice

Freshly caught sardines contained high levels of bacteria located mainly on the skin and the gills. These bacteria invaded and grew rapidly in sardine muscle, reaching 5x10⁸ c.f.u. g^-1 and 6x10⁸ c.f.u. g^-1 respectively after 24h at ambient temperature and 8 days in ice.
Histidine, arginine, lysine, tyrosine and methionine levels decreased during storage. The other amino acids, except proline and taurine, accumulated in the fish muscle, indicating an extensive proteolysis.
Histamine, cadaverine and putrescine accumulated to levels of 2350ppm, 1050ppm and 300ppm respectively, after 24h storage at ambient temperature. Histamine and cadaverine reached similar levels after 8 days storage in ice, whereas putrescine formation was insignificant. Spermidine and spermine levels increased slightly under ambient conditions.
Salting the fish at 8% delayed bacterial and chemical changes but only in iced sardines.
The high content of free histidine found in sardines and the susceptibility of its muscle to histamine and cadaverine formation could explain its increasing implication in incidents of histamine poisoning.