Microbial flora of technological interest in raw ovine milk during 6°C storage

Changes in the microbial flora of ovine milk of medium hygienic quality (initial mean total plate count 3.3  ×  10⁵ cfu/mL) were studied throughout refrigerated storage at 6°C. Total plate counts after 48 h of refrigerated storage (mean count 4.6  ×  10⁵ cfu/mL) were under the current standards in the European Union (EU) for raw ovine milk to be used for cheesemaking after heat treatment. However, after 96 h, mean total plate counts (1.6  ×  10⁷ cfu/mL) were above the standards. Lactococci were found at levels higher than Pseudomonas spp. in milk freshly drawn (54.5% and 3.5% of total plate count, respectively) and after 96 h at 6°C (47.9% and 33.9% of total plate count, respectively). Lactobacilli, enterococci, coliforms and thermodurics were found at values lower than lactococci and Pseudomonas spp., before and after refrigerated storage ( ≤  0.08% of the total plate count). A significant growth ( P  < 0.001) was detected for mesophiles, Pseudomonas spp. and lactococci after 96 h of refrigeration at 6°C; however, thermodurics, coliforms, lactobacilli and enterococci, showed no significant increase ( P  > 0.05). Presumptive Escherichia coli (β-glucuronidase-positive) underwent a decrease throughout storage at 6°C.     

Some virulence properties and characterization of motile Aeromonas species from milk and white cheese

Three hundred and thirty-eight samples of milk and milk products in Ankara were screened for the presence of motile Aeromonas species. The overall frequency of aeromonads in these samples was 27%. As expected, raw milk samples were more contaminated with aeromonads than were other products. Sixty-five (49.2%) of the 132 bulk raw milk samples were contaminated with aeromonads. In 35 of these samples, populations of aeromonads from 1.5 × 10² to 3.0 × 10³ cfu/mL were counted in ampicillin dextrin agar (ADA). Ten (40%) of the 25 raw milk samples sold in the street were contaminated with aeromonads. In eight of these samples, 1.2 × 10²−3.0 × 10³ cfu/mL were counted. Five (16%) of the 31 pasteurized milk and 12 (8%) of the 150 white cheese samples were contaminated with Aeromonas spp., but no countable aeromonads population was noted in ADA. The incidence of A. hydrophila, A. sobria and A. caviae in all samples was found to be 90.2%, 4.3% and 5.4%, respectively. The majority of the strains identified as A. hydrophila and A. sobria were able to produce haemolysin, protease and DNase, while strains identified as A. caviae were only positive for DNase. All isolated Aeromonas species ( A. hydrophila, A. sobria and A. caviae ) were positive for uptake of Congo red dye. Nevertheless, only strains identified as A. hydrophila and A. sobria showed a high rate of positive results when tested for the production of the Voges–Proskauer reaction and lysine decarboxylase. The results of this work show that motile Aeromonas spp., especially A. hydrophila , are frequently found in these samples. As these products are usually commonly consumed in Ankara, they can pose a risk especially for children, the elderly and immunocompromised individuals.     

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.     

The distribution of Enterobacteriaceae and some pathogenic micro-organisms in nonbranded white cheese samples sold in Ankara city

In this research, 75 samples of nonbranded white cheese, presented for sale in small markets from various regions and bazaars in Ankara, were studied. Eighty-six isolates, 71 of which are Gram-negative isolates and 15 of which are Gram-positive isolates, were obtained. These isolates were identified by using bioMérieux API20E and classical methods. Total mesophilic bacteria counts and total coliform bacteria counts were carried out for each white cheese sample. The total average mesophilic bacteria of 75 white cheese samples was 15.5 × 10⁵ cfu/g and the total average coliform bacteria were 13.6 × 10⁵ cfu/g.     

Characterization of Polysaccharide and Volatile Compounds Produced by Kefir Grains Grown in Soymilk

ABSTRACT: The characteristics of polysaccharides isolated from milk and soymilk kefir grains, and the composition of flavor and volatile compounds from soymilk kefir were investigated. Soymilk kefir grains revealed lower polysaccharide content than milk kefir grains, with a polysaccharide profile consisting primarily of glucose and galactose, with the former predominating. The apparent molecular weight of the polysaccharide was estimated at 1.7 × 10⁶ Da. In comparison to nonfermented soymilk, the concentrations of the key volatile compounds for soymilk kefir (such as acetaldehyde, acetone, diacetyl, and ethanol) increased, while n-hexanal concentration decreased. The acetaldehyde level for soymilk kefir was slightly higher, but levels for the other volatile compounds were lower than for milk kefir.     

Effect of technological parameters on the characteristics of kasseri cheese made from raw or pasteurized ewes' milk

Two groups of kasseri cheese (pasta filata type) were manufactured from raw or pasteurized ewes' milk, without starter cultures. Cheeses of each group were divided into two subgroups: the first was ripened and stored at 4°C and packaged in plastic film; the second ripened and stored at 15°C and coated with paraffin wax. Milk pasteurization and technological parameters had a significant effect on the pH ( P  < 0.05), while only technological parameters had an effect on the total solids content. At day 120, the range of mean cfu/g counts for the mesophilic aerobic flora was 9.5 × 10⁷−1.4 × 10⁸; for the thermophilic streptococci, the range was 2.6 × 10⁷−7.6 × 10⁷; and for the thermophilic bacilli, 9.8 × 10⁶−1.7 × 10⁷. Changes in the N fractions became significant after 30 days of ripening. For mature 120-day-old cheeses, the percentage of total N soluble at pH 4.6 was 22.7%–22.9% in raw milk cheeses and 19.0%–21.7% in pasteurized milk cheeses. The percentage of total N soluble at 12% TCA was 10.1%–12.2% in raw milk cheeses and 7.3%–11.5% in pasteurized milk cheeses; the percentages of total N soluble at 5% PTA were 3.1%–4.0% and 2.6%–3.6%, respectively. The residual α_s-casein percentages at day 120 ranged between 63% and 78% of the respective area at day 1; the residual β-casein ranged between 67% and 75%. There were some characteristic differences in the reverse phase-HPLC peptide profiles of the four cheeses. In general, the effect of the different ripening conditions was more pronounced in cheeses made from pasteurized milk.     

Microbiological and chemical characterization of Fiore Sardo, a traditional Sardinian cheese made from ewe's milk

The purpose of this study was to assess the chemical and microbial characteristics of 12 batches of artisanal Fiore Sardo, a protected designation of origin (PDO) hard cheese made from raw ewe's milk without addition of starters, during maturation. High standard deviations were observed for moisture percentage, total solids percentage and NaCl percentage content, possibly owing to differences in manufacturing processes and/or milk composition. Total mesophilic bacteria varied between 10 log₁₀ cfu/g in 48-h-old cheese samples and 3 log₁₀ cfu/g in 9-month-old samples. Total coliforms and staphylococci showed the highest counts at 48 h of ripening then decreased significantly, dropping to levels below 2 log₁₀ cfu/g at 3 months of maturation. Lactic acid bacteria and enterococci were the dominant micro-organisms throughout maturation. They were mainly represented by the species Lactococcus lactis ssp. lactis, Enterococcus faecium, Lactobacillus plantarum and Lactobacillus casei group. Low levels of yeasts were detected throughout the maturation period of the cheese. Debaryomyces hansenii and Kluyveromyces lactis var. lactis were the prevalent yeast species isolated.     

Investigation on culturable microflora in tibetan kefir grains from different areas of china

Four samples of Tibetan kefir grains (TK-ZJUJ 01-04) from Tibet and surrounding areas were investigated via phenotypic and genotypic methods to compare and analyze the diversity of culturable microflora among different origins. As a result, 4 genera of microorganisms from TK-ZJUJ01: Bacillus subtilis (2.9 × 10(7) cfu/mL), Lactococcus lactis (8.2 × 10(7) cfu/mL), Kluyveromyces marxianus (3.0 × 10(6) cfu/mL), Saccharomyces cerevisiae (9.0 × 10(6) cfu/mL); 4 genera from TK-ZJUJ02: Lactobacillus kefiri (1.0 × 10(8) cfu/mL), Pichia kudriavzevii (5.0 × 10(6) cfu/mL), K. marxianus (1.9 × 10(7) cfu/mL), Kazachstania unispora (6.2 × 10(7) cfu/mL); 6 genera from TK-ZJUJ03: Leuconostoc lactis (4.6 × 10(7) cfu/mL), L. lactis (3.0 × 10(7) cfu/mL), Lactobacillus plantarum (3.0 × 10(7) cfu/mL), K. unispora (3.0 × 10(6) cfu/mL), K. marxianus (2.0 × 10(6) cfu/mL), (1.7 × 10(7) cfu/mL); and 4 genera from TK-ZJUJ04: L. plantarum (1.8 × 10(7) cfu/mL), Acetobacter fabarum (5.0 × 10(6) cfu/mL), K. unispora (6.2 × 10(7) cfu/mL), Pichia guilliermondii (6.2 × 10(7) cfu/mL) were identified. Yeasts like P. kudriavzevii and P. guilliermondii isolated in this study were the first time reported in Tibetan kefir grains. For TK-ZJUJ 01-03, lactic acid bacteria were the major microorganisms, which accounted for more than 50% of all the microbial population, while for TK-ZJUJ04, the largest microbial group was yeasts which accounted for more than 50%. In a word, study of diversity and composition of microflora provided us theoretical foundation for further investigation and application of Tibetan kefir grains. Practical Application: This is the basic research in order to develop and industrialize a new kind of yogurt starter which is naturally formed microbiota with both lactic acid bacteria and yeasts in it.     

Microbiological quality of ice creams commercialized in some cities in the state of Rio de Janeiro, Brazil

The microbiological quality of 60 ice cream samples of three commercial brands (A, B and C) of various flavours, commercialized in some towns in the State of Rio de Janeiro, Brazil, was evaluated. Total bacteria count (TCB), coliforms at 35°C (CT), coliforms at 44°C (CF) and presence of Staphylococcus aureus were performed on all samples. TCB ranged from 2.0 × 10 ² to 6.9 × 10 ⁵ cfu/mL, CT from < 3–≥ 2400 MPN/mL, CF from < 3–1100 MPN/mL and S. aureus from < 10–1.4 × 10 ⁶ cfu/mL. The level of bacterial contamination found in this study reflects the unhygienic conditions prevalent in manufacturing and storage of ice creams. Actions are thus necessary by the Brazilian regulatory agencies to require the ice cream processing plants to adopt quality guarantee systems, such as good manufacturing practices and hazard analysis and critical control points system.     

Microbiological, physicochemical, and sensory characteristics of kefir during storage

Changes in certain microbiological, physicochemical, and sensory parameters of kefir were studied during refrigerated storage. Kefir batches were prepared using 1% and 5% added kefir grains, and samples for analysis were taken 24 h after inoculation and then after 2, 7, 14, 21, and 28 days of storage at 5 ± 1 °C. After fermentation for 24 h after inoculation, lactobacilli and lactococci were present at levels of 10⁸ cfu/ml, and yeasts and acetic acid bacteria were present at levels of 10⁵ and 10⁶ cfu/ml, respectively. The lactic acid flora decreased by about 1.5 log units between days 7 and 14 and then stabilized at that level. Yeast and acetic acid bacterial counts, lactose, and pH all remained constant over the storage period, while the total fat content and dry matter decreased. The percentage inoculate did exert an influence, and the sample batches made using 1% added kefir grains had higher lactic acid bacterial counts, lactose, and pH, while the sample batches made using 5% added kefir grains had higher yeast and acetic acid bacterial counts and viscosity. The total fat and dry matter contents were similar in both sample batches. Sensory analysis of the kefir samples revealed maximum acceptability levels in the first 2 days 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%.     

Some chemical and microbiological properties of ghee produced in Eastern Anatolia

Some properties of 30 ghee samples produced in Eastern Anatolia in Turkey were evaluated. Lipolytic bacteria and yeast–mould counts ranged from undetectable to 9.9  ×  10⁵ and 6.9  ×  10⁵ cfu/g, respectively. Most of the samples showed higher free fatty acids (FFA) and peroxide values (PV) than the limits mentioned in International Dairy Federation standards. Storage at 5°C for 30 days was not sufficient to stop the lipolytic and yeast–mould growth and lipid oxidation of the samples. Ghee samples with considerably higher trans -C18 : 1 and trans -C18 : 2 fatty acids contents were considered to be adulterated with hydrogenated oils. It is recommended that specific attention should be given to technology transfer and the education of traditional dairy product manufacturers.     

GROWTH INHIBITION OF CLOSTRIDIUM PERFRINGENS VEGETATIVE CELLS AND SPORES USING CHICKEN IMMUNOGLOBULIN Y

Egg yolk antibody (IgY) was isolated by the water dilution method from the egg yolk of chickens immunized with Clostridium perfringens vegetative cells and spores. Specific binding activity of IgY against C. perfringens vegetative cells and spores remained relatively high during the immunization period (up to 9 weeks). The titer of specific IgY against C. perfringens spores was 1.4-fold less than that of specific IgY against C. perfringens vegetable cells. The specific IgY powder (10 µg/mL) was found to inhibit the growth of C. perfringens vegetative cells or C. perfringens spores in a liquid medium. The difference of C. perfringens vegetative cell growth between the treatment and control groups was 8.9  ×  10⁶ colony forming units (cfu)/mL at 8 h of incubation and 9.95  ×  10⁷ cfu/mL at 24 h of incubation. Significant cfu reductions in C. perfringens spores were also observed with specific IgY powder at 24 h of incubation.

PRACTICAL APPLICATIONS

IgY antibody exerts an antimicrobial activity against pathogens by binding, immobilizing and consequently reducing or inhibiting the growth, replication or colony forming ability of pathogenic bacteria; thus, it is proved to be a viable alternative for antibiotics and preservatives. In this study, IgY against Clostridium perfringens can be used to replace chemical preservatives in food industries. Because IgY functions well at low temperature, it can be used to inhibit the growth of Clostridia which germinate in refrigerated storage conditions, thus preventing foodborne enterotoxicity caused by such bacteria. In practical applications, natural antimicrobial IgY antibody can be applied to meat products for the improvement of food safety.     

Microbial growth and colour of minimally processed shiitake mushroom stored at different temperatures

The effect of storage temperature on the microbiological and sensory characteristics of minimally processed shiitake was investigated. Shiitake mushrooms were washed, sanitised, packed in polystyrene trays, overwrapped with plastic film and stored at 7, 10 or 15 °C. Microbial counts, polyphenoloxidase activity, external lightness ( L* ) and acceptance tests were conducted. Mesophilic, aerobic psychrotrophic bacteria, yeasts and moulds predominated during storage. Pseudomonas was detected after 10 days' storage showing an increase of, approximately, 7 log cycles at 15 °C. Mushroom rejection occurred when the microbial population was lower than 10⁶ CFU g⁻¹, suggesting that, other factors, such as browning, affect mushroom spoilage more than microbial activity. Mushrooms treated with citric or ascorbic acids maintained high L * value during 10 days. The shelf life of minimally processed shiitake mushrooms was 10 days at 7 °C, but less than 5 days at 10 °C, and approximately 3 days at 15 °C.     

SHELF-LIFE OF FRESH FILLED PASTA. HAZARD ANALYSIS AND CRITICAL CONTROL POINTS OF THE MANUFACTURING PROCESS AND HOUSEHOLD PRACTICES

Hazard Analysis and Critical Control Point (HACCP) approach was used to assess the safety of a fresh filling pasta (ricotta-filled ravioli) manufacturing plant in La Plata region, Argentina. Household practices like cooking and holding meals before serving were also evaluated. Samples of ricotta, main raw material of the filling, showed colony counts of Enterobacteriaceae total microorganisms, molds and yeasts of (5 × 10³-1 × 10⁵), (1x10⁵−1x10⁸) and 1 × 10⁵ CFU/g, respectively. E. coli was also detected in one out of five samples, suggesting a hazardous condition of this raw material. Salmonella spp. was not isolated from any of the dough samples tested. Ricotta filling showed high colony counts of mesophilic microorganisms (6 × 10⁶ CFU/g), Enterobacteriaceae (1 × 10⁵ - 1 × 10⁶ CFU/g), while E. Coli was detected in 20% of the samples. Counts of B. cereus, S. aureus were less than 1 × 10² CFU/g in the analyzed materials. In the finished product (ricotta-filled ravioli), the colony counts of mesophilic microorganisms and Enterobacteriaceae were 3 × 10⁸ and 8 × 10⁵ CFU/g, respectively. Critical Control Points found were cooking and holding time before serving. The implementation of suggested corrections allowed the microbial quality of the final product (ricotta-filled ravioli) to be improved considerably. The growth of total microbial counts during refrigerated storage (0, 4, 8 and 10C) were measured and the shelf-life of ricotta and ricotta-filled ravioli was calculated.     

EXAMINATION OF THE MICROBIAL STATUS OF SELECTED INDIGENOUS FERMENTED FOODS IN NIGERIA

Four Nigerian traditionally fermented foods (wara, nono, ogi and kununzaki) were evaluated for the presence of some microorganisms of public health concern. Among the dairy foods , Staphylococcus aureus and Klebsiella sp. were isolated from wara while Escherichia coli, Salmonella sp. and Klebsiella sp. were isolated from nono. The cereal-based fermented foods (ogi and kunu-zaki) contained Bacillus subtilis, E. coli, S. aureus, Klebsiella sp. and Enterococcus faecalis. The mesophilic aerobic counts were: 5 × 10⁵ for wara; nono, 1.53 × 10⁷; ogi, 3.6 × 10⁶ and kunu-zaki, 2.6 × 10⁶ cfu/mL. The enterobacteriaceae counts on nono, wara, ogi and kunu-zaki were 1.79 × 10⁷, 4.5 × 10⁵, 4.0 × 10⁵ and 1.2 × 10⁶ cfu/mL, respectively. No Vibrio count (detection limit: <10 cfu/mL) was recorded in all the food samples considered. The yeast and mold counts ranged from 1.0 × 10⁵– 3.31 × 10⁷ among the food products. The antimicrobial susceptibility patterns of the organisms isolated from dairy products (nono and wara) revealed that they were resistant to ampicillin (100%) and sensitive to gentamicin (100%) and nalidixic acid (100%). Most isolates from cereal based products (ogi and kunu-zaki) were 100% resistant to penicillin, ampicillin and chloramphenicol. This work highlights the need to maintain hygienic standards in the preparation of our locally fermented cereal and dairy foods.     

Viability of probiotic micro-organisms (Lactobacillus casei Shirota and Bifidobacterium animalis subspp. lactis) in a milk-based dessert with cranberry sauce

The objective of this study was to evaluate the survival of two probiotic micro-organisms, Lactobacillus casei Shirota and Bifidobacterium animalis subspp . lactis , in a milk-based dessert (2.7% fat) with cranberry sauce added. B. lactis had a final concentration of 1.99 × 10⁶ cfu/g after 21 days of study, with a logarithmic decrease of 8.87%. On other hand, L. casei Shirota had a final concentration of 2.05 × 10⁷ cfu/g at the end of the same period, a logarithmic decrease of 8.41%. Statistical analysis showed that significant differences existed between both micro-organisms and over various storage times, the more viable micro-organism being L. casei Shirota , which decreased less than one logarithmic cycle after 21 days.     

Reduced-fat Cheddar cheese from a mixture of cream and liquid milk protein concentrate

Reduced-fat Cheddar cheese (RFC) was manufactured from standardized milk (casein/fat, C/F ˜ 1.8), obtained by (1) mixing whole milk (WM) and skim milk (SM) (control) or (2) mixing liquid milk protein concentrate (LMPC) and 35% fat cream (experimental). The percentage yield, total solid (TS) and fat recoveries in the experimental RFC were 22.0, 63.0 and 89.5 compared to 9.0, 50.7 and 87.0 in the control RFC, respectively. The average % moisture, fat, protein, salt and lactose were 40.7, 15.3, 32.8, 1.4 and 0.07%, respectively, in the experimental cheese and 39.3, 15.4, 33.0, 1.3 and 0.10%, respectively, in the control cheese. No growth of nonstarter lactic acid bacteria (NSLAB) was detected in the control or the experimental cheeses up to 3 months of ripening. After 6 months of ripening, the experimental cheese had 10⁷ cfu NSLAB/g compared to 10⁶ cfu/g in the control. The control cheese had higher levels of water-soluble nitrogen (WSN) and total free amino acids after 6 months of ripening than the experimental cheese. Sensory analysis showed that the experimental cheeses had lower intensities of milk fat and fruity flavours and decreased bitterness but higher intensities of sulphur and brothy flavours than in the control cheese. The experimental cheeses were less mature compared to the control after 270 days of ripening. It can be concluded from the results of this study that LMPC can be used in the manufacture of RFC to improve yield, and fat and TS recovery. However, proteolysis in cheese made with LMPC and cream is slower than that made with WM and SM.     

QUANTITATIVE STUDIES OF PROTEOLYTIC AND LIPOLYTIC BACTERIA IN FROZEN MINCED BEEF AND HAMBURGER

Sixty frozen samples (30 hamburger patties and 30 minced meat) purchased from different retail markets in Ismailia, Egypt were examined for incidence of proteolytic and lipolytic bacteria. Mean values of proteolytic psychrophiles in the examined samples of hamburger and minced meat were 2×10⁵ and 6×10⁴, respectively. Lipolytic psychrophiles in hamburger were 8×10⁵ and 3×10⁵ in minced meat. Proteolytic mesophiles in hamburger and minced meat were 6×10⁵ and 5×10⁴, respectively. Mean values of lipolytic mesophiles were 5×10⁴ for hamburger and 5×10³ for minced meat. Proteolytic thermophiles in hamburger and minced meat were 3×10³ and 10³, respectively. Both proteolytic and lipolytic activities were exhibited by various bacteria that were identified.