Summer Milk Research Articles

693. A rejection test for raw milk

The determination of apparent lactic acid has been used as a basis for a rejection test for raw milk. The method consists of precipitation of milk proteins with barium chloride, sodium hydroxide and zinc sulphate, and the addition of ferric chloride to the filtrate to produce the yellow colour of ferric lactate. Lactic acid is not solely responsible for the production of the yellow colour, which, nevertheless, gives a good relationship with keeping quality of milk (measured as hours to the C.O.B. end-point at 22° C.) and the values have been expressed as ‘apparent lactic acid’.The relationship of winter and summer milks to keeping quality has been studied, and a value of 0·03% apparent lactic acid in milk is equivalent to an average keeping quality of 5¾ and 8½ hr. for winter and summer milks, respectively. A value of 0·03% is recommended as the earliest value of apparent lactic acid at which milk could be rejected.The apparent lactic acid in colostrum and late-lactation milk and in milk from cows suffering from mastitis has been determined, and only in late-lactation milk were the values found to be significantly higher than usual in fresh raw milk, and an inverse relationship between yield and apparent lactic acid is suggested.Permanent glass matching disks have been prepared for use in a Lovibond comparator. This permits the intensity of the yellow colour produced with 1% ferric chloride to be determined and the apparent lactic acid in milk estimated.Grateful acknowledgement is made to the management and staff of the Dairy Department of the Reading Co-operative Society and the Farmer's Clean Milk Dairy, Reading, and local milk producers for supplying samples for experiments; to the N.M.T.S. staff in Reading for help in finding suitable farmers, and to the Dairy Husbandry Department of the N.I.R.D. for information about and samples of abnormal and late-lactation milk. Our particular thanks are due Miss Marie Gruber for technical assistance, to Dr N. J. Berridge for the suggestion and help on the work on pH change as an indication of keeping quality (given in the appendix), and to Dr A. T. R. Mattick for the advice given in this work.

A NOTE ON THE SEASONAL VARIATIONS OF THE KEEPING QUALITY OF COMMERCIAL STERILIZED MILK

Summary:During a period of four years the keeping quality of milk commercially sterilized by a continuous automatic process has been recorded. The results indicate a marked seasonal variation, suggesting a relatively high incidence of aerobic spore‐formers in winter milk and a relatively low incidence in summer milk. Aerial contamination from dusty fodders is tentatively suggested as the dominant factor controlling this phenomenon.

HEAT RESISTANT BACTERIA IN RAW MILK:Part VI. The Seasonal Incidence of Thermoduric Organisms

SUMMARY(1) Thermoduric colony counts at 30°C. of farm milk supplies handled in unsterile as well as in sterilised utensils were generally higher in summer and autumn than in winter and spring.(2) The thermoduric organisms content of bulked raw tanker milk on despatch from country creameries was highest during July to October and lowest during December to February.(3) The magnitude of the thermoduric colony counts of Tuberculin Tested milk was associated with atmospheric temperature, the highest counts being recorded during warm days.(4) Some preliminary work on the bacterial content of milking machine clusters suggests that the thermoduric bacterial flora of dairy utensils is at its maximum in summer and early autumn.(5) High thermoduric counts are more common in milk with high total colony counts, so that a higher thermoduric content is to be generally expected in raw milk during warm weather when the latter is at its maximum.(6) Though thermoduric organisms are generally most abundant in raw milk in summer and early autumn, excessive thermoduric counts have been encountered during all seasons of the year and high counts may occur during cold weather when sterilisation of utensils is neglected.

The Determination of Linoleic Acid in Milk Fat

Summary A spectrophotometric method is described for the determination of linoleic acid in milk fat. Values are given for the linoleic acid and apparent linolenic acid content of samples of milk fat obtained from whey and from summer and winter milk.

The Relation of the Carotenoid and Vitamin A Content of Summer Milk to the Carotenoid Content of the Pasture Herbage

Summary Fluctuations in the vitamin A and carotenoid content of summer milk produced by three groups of cows were related to the fluctuations in the carotenoid content of the pasture herbage consumed during three pasture seasons. The three groups included cows pastured on bluegrass, one group with and one without supplemental hay, and another on legume mixtures, without supplemental hay. The data illustrate the following: (a) A closer relation exists between pasture carotenoids and milk carotenoids than between pasture carotenoids and milk vitamin A. (b) After the initial rise following the beginning of the pasture season, the fluctuations in milk carotenoids follow the changes in pasture carotenoids more closely when the pasture carotenoids level is below about 250 γ per g. than when it is higher, indicating a maximum response at this level, (c) Permanent bluegrass pasture, under weather and management conditions which favor rapid growth, often is equally as good a source of carotenoids as is a pasture consisting of legume mixtures. The superiority of legumes is evident during periods of drought.

The Influence of Tocopherols and Cod Liver Oil on the Stability of Milk

Summary A significant correlation was found between the tocopherol content of milk fat and the ability of milk to resist the reaction, involving ascorbic acid oxidation, which produces oxidized flavors. This might explain the differences between the stabilities of winter and summer milks.

The Antirachitic Value of Winter and Summer Milk Produced in Hawaii1

The Antirachitic Value of Winter and Summer Milk Produced in Hawaii1

The Ratio of Ascorbic, Nicotinic, and Pantothenic Acids, Riboflavin and Thiamin in Late Summer Milk

Summary Fifteen samples of late summer milk produced under typical modern dairy farm conditions, were assayed for ascorbic, nicotinic, and pantothenic acids, riboflavin, and thiamin. The average vitamin content of the milk was ascorbic acid 18.4 ± 0.69 mg., nicotinic acid 1.1 ± 0.10 mg., pantothenic acid 3.66 ± 0.31 mg., riboflavin 1.37 ± 0.08 mg., and thiamin 0.44 ± 0.04 mg. per liter. The ratio has been computed for each vitamin to the other four vitamins of the group. For instance, considered on the basis of the thiamin content of the milk, the ascorbic acid is 41.6 times, nicotinic 2.5, and riboflavin 3.3 times its thiamin content, whereas the recommended vitamin allowances for infants are in the ratio of ascorbic acid 75 times, nicotinic acid 10 times, and riboflavin 1.5 times that of thiamin. Hence the milk under consideration would have to be fortified with ascorbic and nicotinic acids to meet the recommended allowances for infant feeding.

Experiments with Greenmelk in Chicken Leukemia

GREENMELK is a commercial product containing a combination of succulent cereal grasses and buttermilk. It is recommended as a supplement to grain concentrates for mammals and poultry. It is reputed by its manufacturers to be rich in carotene, vitamins B1, C, E, riboflavin, summer milk factor, xanthophyll and chlorophyll. It contains, in young cereal grasses and buttermilk, two of nature’s best sources of vitamins, proteins and minerals.Greenmelk is produced by raising wheat, oats, and other cereal grasses on good soils, and, before the young shoots have jointed, the shoots are cut at the time when they are richest in desirable qualities of vitamin content. These young grasses are then mixed with buttermilk reputed to preserve their vitamin content and their most desirable feeding qualities. This process is believed to condense and pasteurize these food materials and make them particularly suitable for poultry feeding.The use of such materials is .

247. The problem of variations in the growth-promoting value of milk for rats

1. Three Shorthorn cows were grazed on the best available permanent pasture when the growth of grass was vigorous, and three other cows of similar lactational history continued to be stall-fed. At the time of the experiment they had been on winter rations for 6 months.2. By suitable blending of morning and evening milkings the fat content of the milk from both groups of cows was adjusted daily to a common level. A part of each milk was then holder-pasteurized.3. Four groups of specially prepared litter-mate male rats were fedad lib., for a period of 8 weeks, on raw and pasteurized milks, both being supplemented with minerals. There were no differences in appetite or gain in weight.4. In similar experiments sugar was added to the milks to double their caloric value. Again the growth and appetite of the animals were the same on the raw summer and “winter” milks. Pasteurization did not alter significantly the value of the milks, but the summer milk, whether raw or pasteurized, was superior to the pasteurized “winter” milk.5. Guinea-pigs receiving the raw mineralized milks alone or with sugar died within a comparatively short time. There was no difference in growth performance or time of survival between the summer and “winter” milk groups.6. These experiments give no indication of the presence of a specific new appetite or growth factor in pasture milk.

The Riboflavin Content of Cow's Milk

The riboflavin content of about 400 samples of milk was determined by the measurement of the intensity of fluorescence of an acetone filtrate by a photoelectric cell. The riboflavin ranged from .60 to 3.42mg. per liter. A negative skew correlation of −0.830 was found between riboflavin content and milk production. Commercial milk in summer contained about 20 per cent more riboflavin than winter milk. Cows, after being fed in winter on phosphoric acid grass silage, showed no increase in riboflavin when turned out on grass pasture.

235. The enrichment ofaerogenes-cloacaetypes in milk held at low temperatures: with observations on the relative rates of growth ofaerogenes-cloacaeandb. colitypes in milk at different temperatures

1. Seventy-five pure cultures of various types of coliform bacteria were grown in sterilized or partially sterilized milk for 24 hr. at 17° C. The cultures ofB. aerogenes, B. oxytocusandB. cloacaetypes as a rule multiplied much more rapidly than those of theB. colitypes. Similar results were obtained when twenty-nine cultures of various coliform types were grown in raw milk for 24 hr. at 17° C. There was generally little or no tendency to clumping of the organisms in the milk, even after 3 days' incubation at 17° C.2. Forty mixed cultures, each consisting of anaerogenes-cloacaetype and aB. coli, were grown in milk for 24 hr. at 17° C. In thirty-four instances theaerogenes-cloacaetype multiplied more rapidly than theB. coli.3. Twenty-one of these mixed cultures were also grown in milk for 24 hr. at 22, 30 and 37° C. At 22, as at 17° C, theaerogenes-cloacaetype multiplied as a rule more rapidly than theB. coli, while at 30 and 37°C. the reverse was the case.4. Twelve specimens of bovine faeces were inoculated into raw milk and the cultures kept at 17° C. for 36 hr.Aerogenes-cloacaetypes occurring in the faeces became enriched in the milk, the coliform flora of the milk at the end of the incubation period frequently consisting chiefly of these types.5. The greater incidence ofaerogenes-cloacaetypes in summer milk in Scotland as compared with winter milk, found in a previous investigation, may be explained by the fact that when milk is contaminated directly or indirectly with faeces, these types become enriched at the temperatures of holding commonly employed in summer. Such enrichment does not occur in winter, the holding temperature of the milk being as a rule so low that there is little or no proliferation of any coliform types. Consequently, the relative proportions of the various coliform types in winter milk tend to remain similar to those in the faeces.

Ascorbic Acid and Oxidized Flavor in Milk. I. Distribution of Ascorbic Acid and Occurrence of Oxidized Flavor in Commercial Grade a Raw, in Pasteurized Irradiated, and in Pasteurized Milk Throughout the Year

Summary Samples of commercial grade A raw, irradiated pasteurized, and regular pasteurized milk, taken daily, bi-weekly, or tri-weekly, at time of delivery throughout the year, were titrated daily for four days for ascorbic acid. The 2-6 dichlorophenolindophenol direct titration method of Sharp (6) was used in determining the ascorbic acid values. On the third day of titration the milk was examined for development of the oxidized flavor. The ascorbic acid content of winter milk was lower than that of spring, summer, or fall milk on the first, second, third or fourth day of storage. Summer milk under conditions of the study usually had more ascorbic acid than spring and fall milk under similar conditions of study, especially on the third and fourth days. Ascorbic acid values for spring and fall milk generally were between the summer and winter values, but varied as to the period of storage. The average first day values of ascorbic acid in the grade A milk studied were 6.0, 10.5, 8.8, and 7.7 milligrams per liter during winter, spring, summer and fall, respectively. Those for pasteurized irradiated milk were 7.2, 11.1, 14.2, and 10.9 milligrams per liter while those for regular pasteurized milk were 9.9, 12.9, 13.0 and 13.0 milligrams per liter during the same respective seasons. The rate of disappearance of ascorbic acid, calculated on the third day of titration, when the milk was examined for oxidized flavor, was greater in the winter than in the summer, being relatively greater in the irradiated and in the grade A milk than in the pasteurized milk. Conversely, the stability of ascorbic acid against oxidation was greater in summer than in winter milk. The stored irradiated milk had a strong oxidized flavor from late fall to early spring. The grade A raw milk had a less pronounced oxidized flavor during this period, but was yet troublesome, whereas no oxidized flavor was noted in the pasteurized milk throughout the year. The direct titration method of determining the ascorbic acid in milk was found to be very helpful in predicting the presence of a catalyst in commercial bottled milk.

164. The nutritive value of milk supplemented with minerals as an exclusive diet for fats. Comparison of equal volumes of Summer and “winter” milk before and after laboratory pasteurization

Milk was obtained simultaneously from cows on early pasture and from stall-fed cows receiving winter rations. By suitable blending of the morning's and evening's milkings of each milk the fat content of the two milks was equalized daily. A part of each milk was then pasteurized in the laboratory by a “holder” method. The total nutritive value of the milk was measured on rats in two separate experiments. In one the milks, supplemented with iron, copper and manganese, were fed as an exclusive diet. The four types of milk were given to twelve groups of litter-mate male rats, the intake being equalized within each group. The experiment lasted 8 weeks, and at the end no difference was found in gain in weight, body length, general appearance of the rats or composition of the carcasses. The palatability of the milks as gauged by the refusals of the rats was investigated by various statistical methods, which showed that summer milk was probably more palatable than “winter” milk, but that pasteurization had no effect.In the second experiment the intake of milk was limited to 20 ml. daily, but the rats were given in addition unlimited access to a basal diet of casein, sugar and salts. This experiment was also carried out on groups of four litter mates (four groups of does and seven groups of bucks). After 8 weeks 5% brewer's yeast was added to the basal diet, resulting in a marked increase of the growth rate of all the groups. At the end of the 8 weeks, the gains in weight, intakes of basal diet, and gains per gram of solids ingested were compared. The only statistically significant differences were in favour of pasteurized summer milk when compared with summer raw and with “winter” pasteurized.

Further Studies on the Growth Promoting Factor Associated with Summer Milk: One Figure

Further Studies on the Growth Promoting Factor Associated with Summer Milk: One Figure

The source of vitamin D in summer milk

The source of vitamin D in summer milk

110. The Influence of High Environmental Temperature on the Secretion and Composition of Milk. A Preliminary Note

It is a well-established fact that during the summer months, particularly July and August, the chemical quality of milk tends to be poor. The samephenomenon has been reported in Germany (i) and in the United States of America(2, 3). The individual factor or factors responsible have not been thoroughly established, although the work of Ragsdale and Turner (4) andHays (5) shows clearly that the fat content of milk tends to be reduced as the environmental temperature increases. The extent of the summer depression in milk quality in this country is much greater during hot dry summers. Cranfield(6) and Golding et al. (7) found exceptionally poor-quality milk during the summers of 1929 and 1933 respectively. In both these years most cows were subjected to a higher temperature than usual and also to a variety of other unusual factors such as the changes in nutrition occasioned by dried-up pastures. The work reported here was planned in order to throw some light on the influence of temperature, and whether it may be considered solely responsible for low-quality summer milk or whether other factors such as nutritional ones may be partially responsible.

Cod liver oil in the winter feeding of milch cows

1. Further confirmation is presented in support of the relationship between the presence of vitamin A in the milk and its supply in the food.2. The influence of the supply of the vitamin A in the food on the quantity or fat content of the milk is uncertain, in any case it appears to be much less than that produced by turning the cows out to grass.3. The increase of the vitamin A-content of the milk produced by feeding cod liver oil is not accompanied by a rise in the lipochrome pigments as is the case when the cows are turned out to grass.4. Up to 4 ounces per day of a good quality cod liver oil produced no fishy flavour in the milk or butter of one cow, but further experiments appear desirable.5. Stall feeding even when ensilage was used causes the winter milk to be lower in vitamin-content than summer milk; this is mitigated by such restricted grass feeding as is possible in the south of England.