Raw Milk Supplies Research Articles

Extended storage of raw milk. i. effect on microbiological quality

Quality of industrial and fluid raw milk was assessed by Standard Plate Count (SPC),. Psychrotrophic Bacterial Count (PBC), proteolytic count, Tyrosine Value (TV) and lipase activity. Of the 360 milk samples tested, 78% had PBC of < 10,000/mL, 92%<50,000/mL and 8% > 100,000/mL. The same raw milk supplies showed SPC distribution of 63% < 10,000/mL, 86% < 50,000/mL and 14% > 100,000/mL. Wide variations in TV were obtained, ranging from 0.32mg/mL to 0.78mg/mL. Counts generally exceeded 106/mL before a definite increase in TV could be observed indicating that the application of this test as a sole indicator of microbiological quality would be limited.Examination of SPC and PBC for industrial milk samples showed that there was no significant (P=0.05) increase in counts during three-day holding periods in farm bulk tanks. Fluid milk samples which were pooled and stored at 4°C after every-other-day collection, were held for two additional days before any marked increase in bacterial count and TV occurred. It is suggested that under proper sanitation and storage conditions, raw milk may be held for up to four days before processing without sacrificing quality.

Importance and significance of raw milk quality to the liquid milk processor

The importance and significance of raw milk quality to the liquid milk processor are considered in the light of changing commercial pressures. The attributes the processor seeks in his raw milk supplies are examined, how he handles and processes this milk to ensure customer satisfaction and, finally, what improvements still need to be made in the quality field.

Isolation and identification of proteolytic psychrotrophic sporeforming bacteria from raw milk supplies at an experimental dairy in India

Of 51 samples of raw milk produced at the National Dairy Research Institute, 65% were found to contain proteolytic psychrotrophic sporeforming bacilli. The protease activity of 50 isolates selected ranged from 20 to 480 units/ml. Twenty/four per cent (12) of the total isolates exhibited enzyme activity in the range 51–100 units/ml, while 20% (10) had protease activity of more than 300 units/ml. Of the 50 isolates, 36% were Bacillus cereus, 20% B. polymyxa, 14% each B. laterosporus and B. circulans. 10% B. pumilus. 4% B. subtilis and 2% were identified as B. coagulans.

Subpasteurization Heat Treatment to Inactivate Lipase and Control Bacterial Growth in Raw Milk

Raw milk was heat-treated under subpasteurization and suprapasteurization conditions, cooled and stored for up to 72 h at 4.4 and 6.7°C. Milk lipase activity and bacteria counts were monitored in both unheated and heated milks. Inhibition of milk lipase activity ranged from 42 to 98% for treatments of 57.2°C for 10 sec to 73.9°C for 10 sec, respectively. The logs of Standard Plate Count after 72 h of storage at 6.7°C were 6.56, 4.86, 4.31, 4.00 and 2.82 for unheated and 10-sec heat treatments at 57.2, 65.6, 73.9 and 82.2°C, respectively. Psychrotrophic Bacteria Counts were also lower in the heated milks than in the unheated milk. The logs of Psychrotrophic Bacteria Counts after 72 h of storage at 6.7°C were 6.21, 2.45, 2.27, 1.33 and 1.00 for unheated and 10-sec heat treatments at 57.2, 65.6, 73.9 and 82.2°C, respectively. Heat treatment of raw milk supplies would result in limiting action of the milk lipase system and growth of bacteria.

Repeatability and Accuracy of Dye-Binding and Infra-Red Methods for Analyzing Protein and Other Milk Components

Udy and Pro-Milk Mark II dye-binding methods and the Milko-Scan 104 infra-red device were evaluated for accuracy and repeatability in the analysis of protein in raw milk supplies. The infra-red device was also evaluated for accuracy in determination of milkfat, lactose and solids-not-fat, and was compared with the Milko-Tester for fat analysis. Repeatability of the three methods was, in all instances, less than 0.05% for protein. Standard deviation of accuracy (σy,x) for protein (total nitrogen × 6.38) for the Udy Analyzer, Pro-Milk, and Milko-Scan units was 0.063, 0.062, and 0.067, respectively. Standard deviation of accuracy of the Milko-Scan rated against Mojonnier and Milko-Tester methods for milkfat was, respectively, 0.054 and 0.050. Compared with liquid chromatography lactose determination and Mojonnier solids-not-fat determination, the Milko-Scan showed a standard deviation of accuracy of 0.083 and 0.073, respectively.

Comparison of Code Date Reliability for Freshly Bottled Whole, Lowfat and Nonfat Fluid Milk

Whole, lowfat, and nonfat fluid milk samples were collected from dairy plants on the day of bottling and each set of the three types of milk was processed from the same raw milk supply. Bacterial analyses for total aerobic count and for specific degradative types were made immediately after collection. Samples were also stored at 1.7, 5.6 and 10.0 C to test for flavor deterioration. Total count of aerobic bacteria and of specific degradative types did not differ significantly among the three types of milk. Organoleptic analysis was made periodically to determine milk quality (flavor score) and defect (flavor). At any of the storage temperatures the keeping quality (days required from bottling to reach a flavor score of < 36) was unrelated to the length of time between bottling and last day of sale (code date) assigned by the processor. At 5.6- and 10.0-C storage, more whole milk samples were criticized for more serious flavor defects (e.g. putrid) than for the less serious ones (e.g. lacking freshness) found in the lower fat milks. Keeping quality of all three types of milks at 1.7- and 5.6-C storage could be predicted from keeping quality determined at 10.0 C with equations previously developed for whole milk.

ADVANCES IN THE MICROBIOLOGY OF MILK AND DAIRY PRODUCTS

The techniques of microbiology from the seventeenth century up to the present time are reviewed and the problems of disease in dairy herds with its effect on raw milk supplies assessed. Progress in the cleaning of milk vessels and sterilization is detailed and the history of pasteurization with its affect on the keeping quality of milk is shown. The introduction of starters in cheese manufacture during the last century is described and the important advances made are stressed.

Surveillance of Milk Products for Penicillin as Done by the Dairy Division of the U.S. Department of Agriculture

In 1974 a State regulatory agency found penicillin in an interstate shipment of nonfat dry milk (NDM). Food and Drug Administration checks in the source State showed that industry and regulatory follow up on offending producers was not always adequate to assure segregation of adulterated milk from use either in fluid or manufactured products. Other States reported the USDA their findings of penicillin-positive NDM. Dairy Division in March, 1975 inaugurated a penicillin surveillance program on NDM offered for official grading. Official grading is required for NDM purchased under the government price support program and by several commercial buyers. There was prompt action by industry to cooperate with State regulatory agencies in educational work with farmers and veterinarians to keep penicillin-positive milk from the market. Industry stepped up its testing of fluid and dry milk products. The results to date show much has been accomplished toward eliminating penicillin and other antibiotics from raw milk supplies and finished dairy products.

An Evaluation of Methods for Detecting and Comparative Incidence of Penicillin Residues in Different Types of Raw Milk Supplies

Over a one-month period, 288 samples of raw milk (equally divided among grade A, and manufacturing grade can and bulk milk producers) were tested by the disc assay and Delvotest P methods for penicillin residues. All positive samples were also checked by the Sarcina lutea cylinder plate method. The disc assay procedure detected one positive sample (0.34%), the Delvotest P method seven positive samples (2.4%) and one questionable (+/−) reaction. When applied to samples found positive by the Delvotest P procedure, the cylinder plate method identified as positive two samples. The Delvotest P method was found sensitive to 0.002 unit of penicillin. Hydrolytic rancidity (to acid degree values as high as 4.75) caused no false positive reactions. When applied to delactosed whey, false positive reactions did occur, as has been noted with other methods.

FACTORS INFLUENCING THE INCIDENCE OF B. CEREUS SPORES IN MILK

The many factors involved in the contamination of milk with B. cereus cells and the importance of minimizing the number of spores at the time of pasteurization are discussed. Methods of controlling the level of B. cereus spores and the use of heat in the cleaning and sterilizing operation are shown, and studies on the level of aerobic spores in raw milk supplies showing a seasonal effect evaluated.

COMMERCIAL STERILIZATION AND ASEPTIC PACKAGING OF MILK PRODUCTS

Milk is nature's most nearly perfect food and to utilize its nutritive values milk must be free from all pathogenic microorganisms. Pathogenic bacteria present, if any, in raw milk supplies are destroyed by the pasteurization process. Milk and its fluid products, so treated, possess on an average of 7–10 days shelflife, which in modem sophisticated distribution systems, is not adequate. Commercial sterilization in conjunction with aseptic packaging extend the shelflife of milk products to 90+ days. These products, excellent in performance, are not yet popular in the dairy case but, if consistent efforts are continued for their promotion, will win consumer's confidence. Increasing application of the sterilization process in the dairy industry has prompted marketing of numerous types and brands of sterlilizing equipment. Every sterilization operation, due to differences in equipment and range of products manufactured, is faced with various problems in commercial applications of the process. Besides technical problems, label declaration and mode of distribution of these products cause legal complications in many areas of this country. Furthermore, no definition for commercially sterilized milk products aseptically packaged in flexible containers has been officially established by federal, state, and local regulatory agencies. Regardless of problems and challenges in commercial application of the sterilization process in the milk industry, potential opportunities in this country for milk products, thus processed, are great.

Proteolysis detection in milk. I. Interpretation of tyrosine value data for raw milk supplies in relation to natural variation, bacterial counts and other factors.

SummaryA method for detection of proteolysis in milk was evaluated. Amino acids and peptides soluble in trichloroacetic acid were estimated by the Lowry–Folin procedure with expression of results in terms of colour yield equivalent to that of tyrosine (the ‘tyrosine value’ (TV)). Some variables and alternatives in the method of estimation were investigated.TVs for milk freshly drawn from individual cows were extremely varied (0·31–0·92 mg/ml). TVs for samples of refrigerated milk from daily supply farms were in the range 0·40–0·58 mg/ml; no relationships between TV and bacterial counts were evident with these samples. With bulk refrigerated raw milk supplied to Brisbane for liquid consumption from country depots and local farms equipped with bulk vats, significant positive relationships were found between TV and total bacterial count (TBC) for supplies from some sources, but in no instance was a significant relationship found between TV and psychrotroph or proteolytic psychrotroph count. Significant positive relationships were found between TV of bulk milk supplies from some sources and atmospheric temperature, and between TBC of the supplies and atmospheric temperature. The significance of these various relationships for bulk milks is discussed.Natural variation in TV imposed limitations on reliability of the method to provide an index of proteolysis; in general the results indicated that its application was restricted to bulk milk cold-stored for at least 3 days.

QUALITY CONTROL COMMITTEE LABORATORY OF THE MINNEAPOLIS-ST. PAUL MARKET

The Quality Control Committee laboratory is a unique organization which was started approximately 32 years ago by Dr. Harold Macy of the University of Minnesota. The dairy industry operates a laboratory which does most of the official testing for the health agencies in the Minneapolis-St. Paul market. With higher costs of operations many health agencies are trying to find ways of saving money, and still have a satisfactory laboratory program to protect the public's health. Some health agencies are using industry laboratories, and the cost is passed on to the customer rather than the taxpayer.The laboratory functions are to evaluate the quality of the raw milk supply from 4238 Grade A producers, and the finished products from 17 processing plants. The laboratory also does the official butterfat testing for the Federal Milk Market Administrator for Order 68.This organization is supervised by a Steering Committee of nine individuals who represent the University of Minnesota; the producer cooperatives, who supply the raw milk; and the Grade A fluid milk processors from the Minneapolis-St. Paul market.All of the routine results from the laboratory are provided to the health agencies. The health agencies and laboratory manager have a close working relationship to coordinate the program. In order for an organization like this to work, it takes cooperation from all parties involved.

RELATIONSHIP BETWEEN THE KEEPING QUALITY PROPERTIES OF GRADE A RAW MILK AND STANDARD PLATE, THERMODURIC, AND COLIFORM COUNTS

SummaryThe usefulness of a keeping quality test for evaluating the quality of a Grade A raw milk supply has been investigated. One hundred bulk tank truck and 81 individual producer samples were examined for keeping quality properties (development of off-odor, “leathery-like” fat, or gas during storage at 20–21 C for 16 to 40 hours) and for standard plate count (SPC), thermoduric count (TC), and coliform count (CC). Multiple correlations observed between the keeping quality properties and the bacterial counts of the milk were: off-odor vs. SPC, TC, and CC, 0.46; “leathery-like” fat vs. SPC, TC, and CC, 0.42; gas vs. SPC, TC, and CC, 0.38; SPC vs. off-odor, “leathery-like” fat, and gas, 0.49; TC vs. off-odor, “leathery-like” fat, and gas, 0.33; and CC vs. off-odor, “leathery-like” fat, and gas, 0.53.Using 100,000/ml for SPC, 1,000/ml for TC and 1,000/ml for CC as upper limits for Grade A milk, over 75% of the samples exceeding one or more of these limits were detected by the keeping quality test after 16 hours incubation. Longer incubation periods resulted in the detection of higher percentages of samples which exceeded one or more of the bacterial standards. Based on results obtained, speed of obtaining results, and simplicity of the test, it is believed that this raw milk keeping quality test merits consideration as a supplement to other routine quality control procedures, particularly for plants having minimum laboratory facilities.

THE QUALITY OF RAW MILK FROM SELECTED OHIO MARKETS.: I. FLAVOR

SummaryAn 8-month survey was made on the flavor of raw milk supplies from four major Ohio markets. A total of 317 milk samples obtained from farm bulk tanks and from tank trucks were examined fresh and after storage at 38–40 F for 48 hours. Approximately 40% of the industrial producer's fresh milk supply had highly satisfactory flavor quality and the flavor of 10% of the shipments was completely undesirable. The combining of the producers' milk in the tank pick-up truck resulted in milk for the plants having a flavor that was neither very good nor very bad. The most common flavor defect was “feed” but other flavors frequently encountered were “cowy” and “rancid.” A significant flavor deterioration occurred in the raw milk during its storage for 48 hr at 38–40 F. The principal changes involved the development of such flavors as “rancid,” “unclean” and acid-associated flavors such as “malty.” The rancid flavor was a common defect in the milk after storage during the winter season, and unclean, musty, oily and the acid-associated flavors were frequently found in the milk after storage during the summer season. The results suggest the need for more adequate milk flavor control measures and that milk should be processed as soon as possible after reaching the plant if it is to possess the finest possible flavor.

‘BITTY’ CREAM: THE OCCURRENCE AND SIGNIFICANCE OF BACILLUS CEREUS SPORES IN RAW MILK SUPPLIES

SUMMARY: Methods for determining the Bacillus cereus content of milks and of rinses of dairy equipment are described and their limitations discussed. Milk samples from various sources were examined throughout the year for ‘bittiness’ as well as for B. cereus. The organism was not detected in all samples showing bittiness. There was a marked seasonal variation in the B. cereus index of raw milk supplies; maximum numbers were obtained from July to September and minimum numbers in April and May. Rinses of farm dairy equipment yielded few B. cereus spores but milk cans not uncommonly contained large numbers, especially in the summer months, when 10·5% of cans showed more than 5 × 103/can. Preliminary observations on other sources of B. cereus are described and some of the problems of the control of this organism in raw milk supplies are discussed.

Q fever in Great Britain; epidemiological information from a serological survey of healthy adults in Kent and East Anglia.

1. Eleven thousand two hundred and twenty-eight sera from persons, mostly blood donors, living in Kent and seven counties in East Anglia, have been tested and 379 (3·4%) found to have complement-fixing antibody toRickettsia burnetiat a serum titre of 1/10 or greater.2. A group of 396 donors in Kent and East Anglia, composed of 190 donors with antibody, and 206 donors from those without antibody to serve as controls, were interviewed, and an epidemiological history was obtained on the possible ways in which they had been exposed toR. burnetiduring the period 1942–53.3. A comparison of the epidemiological histories of the positive and negative donors showed that donors in Kent who had constant occupational exposure to cattle and sheep including unprocessed materials from them, or who had had a raw milk supply to their homes for all or part of the period 1942–53, more frequently had antibody than those donors without such qualities. In East Anglia the positive serological state among donors was associated only with the use of raw milk and not with occupational exposure to animals. There were suggestive findings among Kentish donors that those who visited farms or other potentially infectious places, either during the course of their job or during their leisure, also experienced greater risk of infection.4. In general, these findings of infection from occupational exposure, from visits to infectious localities, or from the use of raw milk in the home, confirmed the tentative epidemiological conclusions drawn from a previous investigation of patients with Q fever. It was not found in this survey, however, that residence near dairy farms, receipt of objects from potentially infectious localities, or contact with persons from such localities was associated with a special risk of infection.5. No association was found between the donors' serological state and the keeping of dogs, cats, poultry, pigs, rabbits, psittacine birds in the vicinity of the home or its infestation by mice, rats or mosquitoes.

The use of the milk ring test in a survey of the incidence of bovine brucellosis in southern Scotland.

A report is made of a total of 438 simultaneous blood serum and milk ring tests, and an attempt made to evaluate the milk ring test as a diagnostic aid in individual animals.The ring test has been used to test the bulk milk from some 370 herds providing the greater part of the raw milk supply for Edinburgh.The incidence of viable Br. abortus in raw milk samples taken in the Edinburgh area has been studied together with the ring test reaction of such samples.The survey has shown that:(1) The ring test is correct in some 93 % of cases in detecting cows whose blood serum will be found positive to the brucella agglutination test.(2) The ring test, if carefully carried out, is a simple time-saving and accurate screening test for detecting herds possibly infected with brucella.(3) A high proportion of herd milks (53 %) giving a positive reaction to the ring test is disclosed, and the probable effect of vaccination with strain 19 in giving rise to this figure is noted.(4) The relatively high incidence (at least 10·5%) of Br. abortus in Edinburgh milk supplies is noted.Thanks are tendered to Dr Bruhn of the Veterinary School, and Dr Bendtsen, Veterinary State Serum Institute, both of Copenhagen and to Dr Stableforth of the Ministry of Agriculture and Fisheries Laboratory at Weybridge, for providing samples of stained antigen. Thanks are also due to the Bacteriology Department, Edinburgh University, for providing material from guinea-pigs and for relevant information; to J. Norval, Esq., M.R.C.V.S., for permission to obtain samples from the slaughterhouse, and also to the dairies and farmers who granted facilities for taking samples and to Miss Elma Chapman for assistance in the laboratory studies and in taking samples.

Animal diseases of public health significance.

Excerpt The relation of disease in animals and man has been recognized for thousands of years. The earliest observations were recorded by the Egyptian physicians who administered to the ills of ani...

THERMODURIC ORGANISMS IN MILK. PART II. PRELIMINARY STUDIES ON TESTING TECHNIQUES

Summary:To define a suitable technique for estimating thermoduric bacteria in raw milk supplies, experiments were made to determine whether any difference could be detected between colony counts after laboratory pasteurization at 145 or 150° F. (62.8 or 65.5°) and whether colony counts are affected by temperature and period of storage of samples before laboratory pasteurization. Temperatures above 63.5±0.5° occasionally gave underestimates of the thermoduric population. Within limits time and temperature of storage generally had no effect on numbers of thermoduric bacteria and samples to be examined for thermoduric content can be aged at temperatures between 4 and 20° and examined at any time up to 24–26 hr.It is recommended that the pasteurizing bath shall be capable, under working load, of heating the samples to 63.5° within 5 min. To ensure this with certain types of bath it may be necessary to circulate the water, or to avoid overloading.A limited study of types of thermoduric organisms predominating after different incubation periods and temperatures of storage revealed that the type initially predominant was generally present in greatest numbers after the milk had been aged for 24 hr. Occasionally Gram‐positive sporing rods overgrew other types and some micrococci were not favoured by storage at 20°.