Cottage Cheese Samples Research Articles

<i>Listeria monocytogenes</i> and other Listeria species in retail meat and milk products in Addis Ababa, Ethiopia

Abstract Background: Listeriosis is one of the important emerging bacterial zoonotic infections worldwide. Among the different species of the genus Listeria, Listeria monocytogens is known to cause listeriosis in humans and animals. Information on the occurrence and distribution of Listeria monocytogenes and other Listeria species is very limited both in the veterinary and public health sectors in Ethiopia. Objectives: The present study was undertaken to determine the occurrence and distribution of Listeria monocytogenes and other Listeria species in retail meat and milk products in Addis Ababa, Ethiopia. Methods: A total of 316 food samples were collected using a cross-sectional study design from September 2003 to April 2004. The techniques recommended by the International standards Organization (ISO 11290-1, 1996) and the French Association for Standardization (AFNOR, 1993) were employed for the isolation and identification of Listeria species. Serotyping of Listeria monocytogenes was carried out at the French Authority for Food Safety (AFSSA), Ploufragan, France. Results: Out of the total of 316 samples examined, 103 (32.6%) were found to be positive for Listeria. Listeria species were isolated in 69.8% (37/53), 47.5% (29/61), 43.5% (20/46), 18.6%, (8/43), 15.4% (8.52) and 1.6% (1/61) of the pork, minced beef, ice cream, fish, chicken and cottage cheese samples respectively. Listeria monocytogenes was detected in 5.1% of the samples analysed. It was isolated mainly from ice cream (19.6%) and pork samples (7.5%) followed by minced beef (1.6%), fish (2.3%) and chicken samples (1.9%). The serotypes of Listeria monocytogenes identified belonged to 1/2b, 4b and 4e. In addition to Listeria monocytogenes, other Listeria species identified were Listeria (L). innocua (65%), L. seeligeri (8.7%), L. welshimeri (6.8, L.murrayi (L. ivanovii and L. grayi (each 0.9%). Conclusion: This study demonstrated the widespread occurrence and distribution of L. monocytogenes and other Listeria species in retail meat and milk products in Addis Ababa, Ethiopia. [Ethiop.J.Health Dev. 2004;18(3):208212]

Staphylococci plate counts in foods of milk origin

We have examined 35 samples of fine cottage cheese, 14 samples of whole winter “bryndza”, 29 samples of Ondava cheese, 18 samples of skim kephir milk, 18 samples of whole acidophilous milk, 5 samples of yoghurt milk with strawberry flavour and 50 samples of fresh butter (Rajo) for the presence of staphylococci focusing onStaphylococcus aureus. All samples intended for microbiological analysis were taken directly from market establishments. None of the examined samples of yoghurt milk complied with the Codex Alimentarius because they contained Staphylococcus aureus bacteria on the level of 100, 65, 5, 75, and 60 CFU/ml. The other analysed food products satisfied the current standards with regard to the presence of staphylococci.

Inhibition of Listeria monocytogenes in cottage cheese manufactured with a lacticin 3147-producing starter culture.

The efficacy of using a lacticin 3147-producing starter as a protective culture to improve the safety of cottage cheese was investigated. This involved the manufacture of cottage cheese using Lactococcus lactis DPC4268 (control) and L. lactis DPC4275, a bacteriocin-producing transconjugant strain derived from DPC4268. A number of Listeria monocytogenes strains, including a number of industrial isolates, were assayed for their sensitivity to lacticin 3147. These strains varied considerably with respect to their sensitivity to the bacteriocin. One of the more tolerant strains, Scott A, was used in the cottage cheese study; the cheese was subsequently inoculated with approximately 10(4) L. monocytogenes Scott A g-1. The bacteriocin concentration in the curd was measured at 2560 AU ml-1, and bacteriocin activity could be detected throughout the 1 week storage period. In cottage cheese samples held at 4 degrees C, there was at least a 99.9% reduction in the numbers of L. monocytogenes Scott A in the bacteriocin-containing cheese within 5 d, whereas in the control cheeses, numbers remained essentially unchanged. At higher storage temperatures, the kill rate was more rapid. These results demonstrate the effectiveness of lacticin 3147 as an inhibitor of L. monocytogenes in a food system where post-manufacture contamination by this organism could be problematic.

Effectiveness of Salt, pH, and Diacetyl as Inhibitors for Escherichia coli O157:H7 in Dairy Foods Stored at Refrigeration Temperatures

The behavior of Escherichia coli O157:H7 inoculated in 10% rehydrated nonfat dry milk adjusted to pH levels between 3.8 and 5.4 with lactic acid, salt levels of 0 to 6%, and diacetyl levels of 0, 5, and 10 μg/g was determined at 4 and 12°C. Cell populations were determined by surface plating on tryptic soy agar after 7 and 35 days of incubation. Survival was also determined using retad cultured dairy products. E. coli O157:H7 did not survive in skim milk at pH 3.8 and was reduced by 3 log cycles at pH 4.1, regardless of salt, diacetyl, and temperature levels. At pH levels above 4.4, survival was observed at lower salt concentrations for up to 35 days at both 12 and 4°C. The organism grew (up to a 2.2-log increase) at pH 5.0 at 2% salt levels after 35 days of storage at 12°C but not at 4°C. Diacetyl at a concentration of 10 ppm had no effect on survival and growth. In all but one case, E. coli O157:H7 was inactivated in yogurt, sour cream, and buttermilk at a rate similar to or greater than what was consistent with the acidified skim milk data. Also consistent with the skim milk data, growth occurred in two of the three cottage cheese samples at 12°C after 7 days but not after 35 days or at 4°C, when a 1- to 2-log decline was observed.

High-Sensitivity Dry Rehydratable Film Method for Enumeration of Coliforms in Dairy Products: Collaborative Study

A dry-film coliform count plate that is inoculated with 5 mL sample was compared with the Violet Red Bile Agar plate method in a collaborative study by 18 laboratories. Products analyzed were 2% milk, chocolate milk, cream, vanilla ice cream, cottage cheese, and cheese. Collaborators tested blind duplicate uninoculated samples and samples inoculated at low, medium, and high level. Significantly (P < 0.05) higher numbers of coliforms were recovered by the dry-film method from 2% milk samples at the 3 inoculum levels, the chocolate milk at the low- and high-inoculum levels, and the cream at the high-inoculum level. Significantly higher counts were obtained by the agar method for cottage cheese samples at the low-inoculum level. The repeatability standard deviation for the dry-film method was significantly higher for the high-inoculum level chocolate milk sample and the medium-inoculum level cottage cheese. The same statistic was significantly higher for the agar method at all 3 inoculum levels in the 2% milk and the medium-inoculum level cream. The high-sensitivity dry rehydratable film method for enumeration of coliforms in dairy products has been adopted first action by AOAC INTERNATIONAL.

Survival of Listeria monocytogenes in Cottage Cheese

Most studies on the behavior of Listeria monocytogenes in cheeses have focused on the soft, ripened types because of human listeriosis outbreaks linked to consumption of these foods, while observations in cottage cheese are limited and conflicting. Fresh market cottage cheese samples with and without sorbate, purchased in the United States and Canada, respectively, were contaminated with L. monocytogenes strain Scott A (103 CFU/g). Mean total plate counts/g, log10, in the fresh U.S. and Canadian cheeses were 3.54 and 5.22, respectively. After 24 days at 5°C, the respective numbers were 3.51 and 6.27. Mean pH values in the U.S. cheeses at freshness and after 24 days were 5.05 and 5.03, respectively, and values in the Canadian cheese were 4.89 and 4.77. Increases of >3 logs in cell numbers were seen at temperature abuse (10 and 20°C) in all cheese samples, although sorbate-containing cheese spoiled at a slower rate and samples were free of visible surface mold growth even after 21 days. Cottage cheese did not support growth of L. monocytogenes at any of the storage temperatures, and declines (0.35 and 0.81 log10, in sorbate-free and sorbate-containing cheese, respectively) were seen after 24 days at 5°C. Treatment with 3% sodium or calcium lactate did not affect listerial cell numbers. These findings demonstrate that sorbates in cottage cheese are effective as preservatives but not as antilisterials. Persistence of listeriae in cottage cheese emphasizes the need to prevent contamination during manufacturing and storage.

Estimating Shelf-Life of Cottage Cheese Using Hazard Analysis

Cottage cheese samples were stored at three temperatures: 0, 4, and 7°C. Microbial counts, pH, percentage of free whey, and sensory characteristics were analyzed over time to determine the shelf-life. Weibull hazard analysis was used to fit the shelf-life data to different statistical models. From the Weibull graphs, cottage cheese stored at 4°C had a nominal shelf-life of 19 d, whereas cottage cheese stored at 7°C had a nominal shelf-life of 6.5 d. Physical and microbial measurements suggest different deterioration mechanisms that are dependent on storage temperature of the samples.

Sensory and Instrumental Analyses of Cottage Cheese Firmness

The firmness of 2% milk fat creamed cottage cheese was evaluated by sensory and instrumental analyses. Forty-one adult consumers evaluated the texture and overall acceptability of four cottage cheeses on a 9-point hedonic scale. They found no significant difference (p>0.05) among three of the samples in either texture or overall acceptability, while one sample was rated lower than the others. Instrumental measurement indicated a significant difference (p≤0.05) in curd firmness among the samples. A ten-member laboratory panel evaluated the degree of firmness of four cottage cheese samples using a 15cm line scale anchored from “soft” to “firm”. The panel was able to perceive a difference in firmness between samples corresponding to a 10% change in the instrumental reading. Results suggest that 2% milk fat creamed cottage cheese with a firmness between 25 and 35g/cm wire would find consumer acceptability.

Protein and Major Cations in California Cottage Cheese and Yogurt

To determine the concentrations of protein and major cations (calcium, potassium, magnesium, and sodium) in California cottage cheese and yogurt, 244 samples of cottage cheese and 52 samples of yogurt were collected from local retail stores. Mean concentrations of protein were 12.5% in cottage cheese and 4.50% in yogurt. Mean concentrations of calcium were 75.9 mg/100g in cottage cheese and 152.1 mg/100g in yogurt. Mean concentrations of potassium were 60 mg/100g in cottage cheese and 219 mg/100g in yogurt. Mean concentrations of magnesium were 10.8 mg/100g in cottage cheese and 19.7 mg/100g in yogurt. Mean concentrations of sodium were 393 mg/100g in cottage cheese and 65.8 mg/100g in yogurt. To measure the variation in concentrations of these constituents in cottage cheese due to time of year, samples of regular and lowfat cottage cheese were collected from a local plant each week for a year. Annual mean concentrations of protein, calcium, potassium, magnesium, and sodium were 12.37%, 92.9 mg/100g, 63.7 mg/100g, 13.4 mg/100g, and 417 mg/100g in regular cottage cheese and 12.58%, 106.9 mg/100g, 85.6 mg/100g, 15.3 mg/100g, and 420 mg/100g in lowfat cottage cheese. Differences between the means for regular and lowfat cottage cheese were statistically significant for all constituents except sodium. Time-of-year effects were significant for protein, calcium, potassium, and sodium.

The Calcium Content of Cottage Cheese Made by Culture and Direct Acidification

Using atomic emission spectrophotometry, the average calcium content of 29 market samples of cottage cheese made by the culture method was found to be 76.6 mg/100 g, and that of 18 market samples made by the direct acidification procedure was 91.2 mg/100 g. The average calcium content of 24 samples of lowfat cottage cheese was 87.5 mg/100 g and that of 23 samples of 4% cheese was 76.7 mg/100 g. Lowfat direct set cottage cheese had the most calcium, 102.3 mg/100 g. Curd made in the laboratory by the culture and direct acidification procedure showed no significant difference in calcium content.

Use of Sodium Substitutes in Cottage Cheese and Buttermilk

Twenty-four market samples of cottage cheese had an average sodium concentration of 4.91±1.20 mg/g. Two samples of cottage cheese formulated to contain 1.1% “Lite” and Zyest, and having sodium concentrations of 3.23 and 2.54 mg/g had significantly lower flavor scores than a sample containing 1.4% NaCl and having 6.25 mg of Na/g. The Standard Plate Counts and the yeast and mold counts on the cottage cheese after storing 10 d at 4°C were not different between samples containing salt, salt substitute or salt substitute plus a dry yeast preparation. Psychrotrophic bacteria were more numerous in the samples containing the yeast preparation. Four samples of buttermilk containing .015% “Zyest 45-F” and .25% NaCl, .25% “Lite” and .015% “Zyest 45-F”, .25% NaCl, or .25% “Lite” had comparable flavor scores. The sodium concentrations of the four samples were 1.096, .793, 1.125 and .771 mg/g, respectively. The growth of yeasts and molds in samples containing “Zyest 45-F” and “Lite” was slightly but not significantly greater than the other three samples. Psychrotrophic counts on buttermilk after 7 d of storage at 4°C were much lower than the original counts, but were not influenced by the additives used.

Survival of Listeria monocytogenes During Manufacture and Storage of Cottage Cheese

Cottage cheese was made by the short-set procedure in pilot-plant-sized vats from pasteurized skim milk inoculated to contain 104 – 105Listeria monocytogenes (strains Scott A or V7)/ml. Half the curd from each trial (two trials with each strain of L. monocytogenes) was creamed and half remained uncreamed. Numbers of L. monocytogenes were determined by surface-plating samples diluted in Tryptose Broth (TB) on McBride's Listeria Agar (MLA). Initial TB dilutions were then stored at 3°C and plated on MLA after 2, 4, 6 and 8 weeks or until L. monocytogenes was recovered. Selected L. monocytogenes colonies from each sample were serologically confirmed. Results for both strains indicate that during manufacture, numbers of L. monocytogenes remained relatively constant until after cooking of curd was completed. All samples analyzed after cooking curd 30 min at 57.2°C (135°F) contained fewer viable L. monocytogenes than could be detected by our methods (10 or 100 CFU/g or ml). Both strains were recovered from cold-enrichment samples, indicating that small numbers of the organism survived the cheesemaking process. Using direct plating onto MLA, L. monocytogenes was recovered from 43 of 112 (38.4%) cottage cheese samples during storage at 3°C for up to 28 d. After cold-enrichment in TB for up to 8 weeks, 59 of 112 (52.7%) samples were positive for L. monocytogenes. Greater numbers of L. monocytogenes, particularly strain Scott A, were found in creamed rather than uncreamed cottage cheese; however, numbers seldom exceeded 100/g.

Sodium Concentration of Selected Dairy Products and Acceptability of a Sodium Substitute in Cottage Cheese

Twenty-five samples of cottage cheese collected from processors and local markets in Tennesse in a 2-day period contained an average of 4.57mg sodium/g. Samples collected over longer time had an average concentration of 3.78mg sodium/g, and lowfat cottage cheese had an average of 3.22 mg/g. Buttermilk contained an average of 1.14mg sodium/g; regular vanilla ice cream averaged .83 mg/g, and “no stabilizer added” vanilla ice cream had an average of .59 mg/g. Sodium in lowfat chocolate milk averaged .83 mg/g and French onion dip 5.33 mg/g. One brand of yogurt contained .76 mg/g and another brand 1.69 mg/g.A salt substitute containing equal concentrations of sodium chloride and potassium chloride was used in the creaming mixture for cottage cheese. Taste panel results showed that cottage cheese containing 1.26% sodium chloride, 1.26% salt substitute, or .63% of each had similar flavor scores.

Quantitative analysis of food products by pulsed nuclear magnetic resonance II. Simultaneous analysis of water and fat in milk powder and cottage cheese

SummaryA small process analyser employing the pulsed nuclear magnetic resonance technique has been used to determine both water and fat contents of milk powder and cottage cheese samples. The procedures used for establishing and eliminating cross-interferences in these analyses are described. For milk powders, water and fat contents in the ranges 1–5 and 0·5–25 % respectively were determined with standard deviations of 0·20 % water and 0·64 % fat. Cottage cheese samples with water and fat contents in the ranges 77–81 and 2–7 % respectively were determined with standard deviations of 0·30 % water and 0·16 % fat.

Quantitative analysis of food products by pulsed NMR

SummaryWater contents in the range 1–5% for skim milk powder and 77–81% for cottage cheese curds have been determined quantitatively by pulsed nuclear magnetic resonance methods. The procedures fro establishing optimum operating conditions for a commercial pulsed NMR process analyser are described, and temperature‐dependences of the analytical results are given. For skim milk powders, inegrated measurement times of 72 sec per sample gave a standard deviation of 0.2% water, while at the other end of the range the cottage cheese samples yielded 0.3% standard deviastion in the water content with measurement times of 10 sec per sample. The results demonstrate the versatility of the pulsed NMR technique for analysis of food products over a very wide range of water contents.

Violet Red Bile 2 Agar for Stressed Coliforms1

Counts on a new, autoclave-sterilizable violet red bile (VRB-2) agar were compared with counts on freshly boiled VRB agar. Yields on VRB-2 agar averaged 217, 180, 130, and 112% of counts obtained on the control medium for samples of water, cottage cheese, frozen vegetables, and raw milk, respectively. The general principle used for the development of VRB-2 agar could be applied to many other kinds of selective plating media.

COTTAGE CHEESE SHELF LIFE AND SPECIAL GAS ATMOSPHERES

SUMMARY– Cottage cheese samples were stored at 3–4°C for 10–12 days in special all‐glass containers with purified carbon dioxide, nitrogen and air atmospheres. Shelf‐life quality of the cheese was measured by taste panel scoring and by bacterial counts of the top centimeter of product. Carbon dioxide slightly decreased the bacterial counts but it produced an acid or tart cheese. Nitrogen did not significantly decrease the bacterial counts nor affect the taste of the cheese.

FATE OF COLIFORMS IN YOGURT, BUTTERMILK, SOUR CREAM, AND COTTAGE CHEESE DURING REFRIGERATED STORAGE

Aerobacter (Enterobacter) aerogenes and Escherichia coli were inoculated separately into commercially produced samples of yogurt, buttermilk, sour cream, and cottage cheese. Inoculated products were stored at 7.2 C and were tested daily for up to 10 days to determine changes in numbers of coliforms and in pH values. The number of viable coliforms in yogurt declined dramatically and was markedly different from the initial value after only 24 hr of storage. Usually, survival of coliforms in yogurt did not exceed 3 days of holding. In buttermilk, most often a marked decline in numbers of coliforms was evident after 24 hr of storage. A substantial reduction in numbers (>50% of organisms present initially) of A. aerogenes B199 occurred in sour cream during the first 24 hr of storage, but a similar decline in numbers of E. coli and A. aerogenes FD was not evident until after 3 days of storage. Changes in numbers of E. coli and A. aerogenes in cottage cheese generally were not as rapid as in other products during the first days of storage. A few cottage cheese samples, however, did support rapid increases in test culture numbers. Because of the rapid decline in numbers of coliforms in yogurt, buttermilk, and sour cream, the provision in Standard Methods for the Examination of Dairy Products that permits examination of some of these products for up to 48 hr after manufacture seems inadvisable.

Microbial Flavor Defects in Dairy Products and Methods for Their Simulation. II. Fruity Flavor1,2

The history, nomenclature, and the mechanism involved in the development of the fruity defect caused by the metabolism of Pseudomonas fragi in dairy products are briefly reviewed. A flavor reference standard suitable for training judges of dairy products in recognition of this defect may be prepared by culturing an active strain of the organisms in pasteurized homogenized milk fortified with 0.1% ethanol. This defect may be more conveniently simulated in milk by addition of a mixture of pure ethyl butyrate and ethyl hexanoate in 1,2-propanediol to give concentrations of 0.35 and 0.50ppm of the respective esters. The same ester mixture may also be used in simulation of the fruity defect in Cottage cheese samples.

Sensory and Shelf-Life Evaluations of Cottage Cheese Treated with Potassium Sorbate

Cottage cheese samples containing 0.025 to 0.20% potassium sorbate were evaluated by as ensory panel of 18 judges, using the duo-trio test method or organoleptically in seven Cottage cheese plants. The samples were then stored at 4 or 7C and evaluated for shelf-life. The panel did not significantly detect 0.10% or less of potassium sorbate in Cottage cheese by taste or odor. The minimum levels of potassium sorbate detected in the Cottage cheese plants were 0.10% (four plants), 0.05% (two plants), and 0.025% (one plant). Shelf-life was extended in some experiments by 0.05% potassium sorbate and in all experiments by 0.10%. These amounts of potassium sorbate retarded growth of bacteria that produced fruity and putrid odors and slime in Cottage cheese at refrigeration temperatures and bacteria that produced sourness and molds.