Cottage Cheese Samples Research Articles

Food-borne virus:detection in a model system.

The purpose of this study was to develop methods for detection and quantitation of food-borne virus. Samples (25 g) of cottage cheese, contaminated with various quantities of coxsackievirus type A9, comprised the model system. Two of the methods presented have at least a 50% probability of detecting virus at levels below 5 plaque-forming units/25-g sample. Noteworthy aspects of these methods include use of a glycine-NaOH buffer (pH 8.8) containing approximately 1 m MgCl(2) as the diluent in which the sample is slurried, treatment of the slurry with Freon TF and bentonite to facilitate centrifuge clarification, and concentration of the clarified sample extract by a two-stage process employing polyethylene glycol followed by ultracentrifugation. Virus in the final 0.5-ml sample concentrate was detected and quantitated by the plaque technique in rhesus monkey kidney cell cultures. Processing of the sample requires approximately 2 days, and the inoculated cultures may have to be observed for as long as 7 days thereafter. If these levels of sensitivity are desired, and if 12 samples per day are tested on a routine basis, the cost savings achieved by employing these methods rather than testing sample extracts without concentration may range from 75 to 90%.

Food-borne Virus: Detection in a Model System

The purpose of this study was to develop methods for detection and quantitation of food-borne virus. Samples (25 g) of cottage cheese, contaminated with various quantities of coxsackievirus type A9, comprised the model system. Two of the methods presented have at least a 50% probability of detecting virus at levels below 5 plaque-forming units/25-g sample. Noteworthy aspects of these methods include use of a glycine-NaOH buffer (pH 8.8) containing approximately 1 m MgCl(2) as the diluent in which the sample is slurried, treatment of the slurry with Freon TF and bentonite to facilitate centrifuge clarification, and concentration of the clarified sample extract by a two-stage process employing polyethylene glycol followed by ultracentrifugation. Virus in the final 0.5-ml sample concentrate was detected and quantitated by the plaque technique in rhesus monkey kidney cell cultures. Processing of the sample requires approximately 2 days, and the inoculated cultures may have to be observed for as long as 7 days thereafter. If these levels of sensitivity are desired, and if 12 samples per day are tested on a routine basis, the cost savings achieved by employing these methods rather than testing sample extracts without concentration may range from 75 to 90%.

Increases in Soluble Nitrogen and Bitter Flavor Development in Cottage Cheese

Factors affecting increases in soluble N (expressed as per cent of total nitrogen) and the relation, of these increases to bitter flavor development in Cottage cheese were investigated. Soluble N in fresh Cottage cheese curd made with cultures and rennet extract was significantly higher (P<0.01) than in curd made by direct acidification. Increases in soluble N by cultures and rennet extract were not associated with bitter flavor. Significantly higher (P<0.05) soluble N values for bitter market samples of Cottage cheese than for nonbitter Cottage cheese indicated that soluble N had increased in the bitter cheeses during storage and handling. Development of bitter flavor was associated with increases in soluble N and psychrophilic bacteria.

Consumer Preferences for Flavor in Creamed Cottage Cheese

A triangular test and a paired comparison test were used to determine, respectively, the difference threshold and preference for diacetyl in creamed Cottage cheese samples by a consumer panel. Creamed Cottage cheese of 4% fat and 80% moisture was used in the tests. Levels of diacetyl compared were 0.2 vs. 1.4, 0.2 vs. 2.2, 0.2 vs. 3.5, and 0.2 vs. 5.0ppm. The consumer panel could detect differences between samples when diacetyl content of the samples differed by 1.4ppm or more. Preference was for the creamed Cottage cheese containing the higher level of diacetyl. Sex, age, and like or dislike of creamed Cottage cheese did not affect the ability to detect differences between diacetyl levels. Sex and age did not affect the preference choice in the preference test. Both sexes and all age groups expressed a greater preference for the high diacetyl creamed Cottage cheese. Preference of those individuals who liked Cottage cheese was not significantly different from those individuals who disliked creamed Cottage cheese. However, those who disliked the product showed a slight preference for the samples with low levels of diacetyl.

THE ENUMERATION OF PSYCHROPHILIC MICROORGANISMS IN DAIRY PRODUCTS

The eleventh edition of Standard Methods for the Examination of Dairy Products sanctions optional use of incubation temperatures and times (5–7 C for 7–10 days) for determination of the psychrophilic bacterial count of dairy products. This study shows that this 2 degree difference in incubation temperature, the 3 day difference in incubation time and a combination of these factors could be responsible for a significant variation in psychrophilic bacterial counts. A total of 67 raw milk, 58 pasteurized milk, 19 ice cream and eight cottage cheese samples were plated at 5 and 7 C for 7 and 10 days. Significantly higher counts were obtained after 10 days than after 7 days incubation at both temperatures; however, greater increases in counts resulted from raising the temperature from 5 to 7 C. Highest counts were obtained at 7 C for 10 days. A total of 559 isolates were picked from plates of 12 milk samples that had been incubated at 5 and 7 C for 7 days and 7 C for 10 days. Classification of the isolates indicated that variations in counts were due to differing abilities of organisms within genera to grow at low temperatures and not to preferential growth of different genera. Adoption of one incubation temperature and time for the determination of psychrophilic bacterial counts is recommended.

Modified Reduction Test to Predict the Shelf Life of Cottage Cheese

Summary One hundred and one commercial samples of Cottage cheese were subjected to a modified reduction test designed to measure the correlation between shelf life and the reduction time required for resazurin, methylene blue, and 2,3,5-triphenyl tetrazolium chloride (TTC). Prior to testing, the samples were neutralized to a pH of 6.5±0.5, bile salts No. 3 (Difco) were added to partially inhibit the Gram-positive lactic organisms, and trypticase soy broth was added to stimulate the growth of the psychrophiles. The reduction times varied from 1.3 to 40 hr., depending on the quality of the cheese and the type of dye used. The reduction times in hours at 24° C, plotted against keeping quality in days, gave correlation coefficients as follows: resazurin pink, 0.80; resazurin white, 0.77; methylene blue, 0.75; and TTC 0.74. Reduction to resazurin pink gave the most rapid results as well as the highest correlation. The correlations between shelf life and initial psychrophile and total count were -0.67 and -0.78, respectively. The test is useful for identifying Cottage cheese with a short shelf life. Nineteen of 20 samples which developed an organoleptically detectable defect within two days when stored at 10° C., reduced resazurin to pink in 7.75 hr. or less, and all samples requiring more than 23 hr. to reduce resazurin retained their original organoleptic quality for six or more days.

Studies on Psychrophilic Bacteria. I. Distribution in Stored Commercial Dairy Products1,2

Summary Psychrophilic microorganisms capable of dominating the population in commercially pasteurized samples of milk, cream, chocolate drink, and cottage cheese after storage at 4° C. were isolated and characterized. Of 586 cultures, 70.6% were species of the genera Pseudomonas , 7.9% Alcaligenes , 9.2% Achromobacter , and 0.7% Flavobacterium ; 10.8% were coliform bacteria and 0.8% yeasts. Distribution among the products, and between summer and winter samplings, was substantially uniform. Some factors underlying the discrepancies evident in the literature on the nature and distribution of the psychrophilic microflora of dairy products are discussed.

Studies on the Flavor of Creamed Cottage Cheese

Summary The biacetyl contents of 41 samples of commercial creamed cottage cheese, obtained from retail stores, varied from 0 to 3.2 p.p.m.; 73.1% of samples contained less than 1.0 p.p.m. and 95.1% contained less than 2.0 p.p.m. When cottage cheese is manufactured by the long-set method, the maximum amount of biacetyl capable of being produced by a lactic culture is not attained at the time of cutting the curd (pH 4.7). During cottage cheese manufacture there is a partition of the milk constituents and flavor compounds. The whey fraction contains considerably more citric acid, lactose, biacetyl, and acetylmethylcarbinol than the curd. However, a proportionate amount of the biacetyl present at the time of cutting is retained by the cheese and the use of a culture producing considerable biacetyl results in cheese with a correspondingly higher biacetyl content. The addition of citric acid to a creaming mixture for cottage cheese did not result in an increased biacetyl content when the cheese was held at 45° F. The addition of both citric acid and lactic culture to a creaming mixture for cottage cheese increased the biacetyl content when the holding temperature was 45° F., but a sour flavor was evident after several days' storage.

A BACTERIOLOGICAL STUDY OF COTTAGE CHEESE WITH PARTICULAR REFERENCE TO PUBLIC HEALTH HAZARD

Bacterial contamination of public health significance was determined on 150 samples of market cottage cheese. The study was made over a period of one year, and the packaged cheese was obtained from eight different manufacturers.Line runs were made at the dairy plants to determine the exact areas of contamination in the manufacturing process.Various pathogenic organisms were introduced into cottage cheese to determine if cottage cheese would support the growth of such organisms or if it could act as a means of transmission of such pathogens.