Influence of milk ultrafiltration on bacteriophages of lactic acid bacteria.

Bacteriophages added to whole milk were partially concentrated during ultrafiltration. At 4:1 retentate, phage had concentrated 2.4:1. Thermal destruction at 54 degrees C followed first order kinetics up to 6% protein, whereafter it deviated. When allowed to grow in retentate in the presence of appropriate host, 3.5 generations of phage appeared after 12 h at 22 degrees C compared with four generations in skim milk. In the presence of phage, lactic acid bacteria population increased to only 10(7) cfu/ml compared with 3 X 10(9) in their absence. Retentate starter prepared in the presence of phage was as active as skim milk starter prepared in the presence of phage.

Conversion of glucose in lactase-hydrolyzed whey permeate to fructose with immobilized glucose isomerase.

The maximum conversion of glucose to fructose in lactase-hydrolyzed whey permeate by glucose isomerase was approximately 52% at .1 g enzyme/ml substrate after 7 h incubation at 60 degrees C. Removal of minerals from the substrate was essential for enzyme activity. The dependence of the enzyme on Mg++ and Co++ for activity in the presence of high ash concentration was demonstrated. Optimum Mg++ and Co++ additions were 250 and 100 ppm, respectively. The isomerization reaction was enhanced more when both 100 ppm Mg++ and 50 ppm Co++ were added. Hydrolyzed isomerized lactose whey syrup with sweetness equivalent to sucrose was successfully produced through enzymatic isomerization of glucose in lactase-hydrolyzed whey permeate after supplementation with pure glucose. Fructose in hydrolyzed isomerized lactose whey syrup was effectively separated from other sugars by Dowex 1X8-200 anion exchange resin in the bisulfite form.

Removal of penicillin G from contaminated milk by ultrafiltration.

Penicillin G purposedly added to whole raw milk at concentrations from .05 to .20 IU/ml was removed to undetectable levels by a combination of ultrafiltrations and permeate washes. After penicillin removal, whole milk 3:1 vol/vol concentrated retentates were reconstituted to milk with antibiotic-free permeate with little change in composition and with very good to excellent flavor. Washing 3:1 vol/vol concentrated retentates from penicillin-contaminated milks with water also removed penicillin to an undetectable level but changed the composition of product, which displayed a flat flavor.

Growth of lactic acid bacteria in highly concentrated ultrafiltered skim milk retentates.

Buffer capacity of ultrafiltered skim milk retentates at various protein concentrations and growth of direct set, frozen concentrated lactic starter cultures in such retentates were studied. Maximum buffering occurred at approximately pH 5.1 to 5.3. An average .48% lactic acid concentration was required to reduce the pH of plain skim milk to 4.6 compared with 1.01% for skim milk retentates concentrated 2.3:1 and 1.14% for skim milk retentate concentrated 2.6:1. Skim milk retentates concentrated 4.3:1 and 5.8:1 were unable to attain pH 4.6 even when titratable acid was greater than 1.8%. Lactic acid required to reduce pH to 4.6 for the two lower concentrated retentates (2.3:1 and 2.6:1) were 1.85 and 2.45%. Time to attain pH 4.6 was a function of the bacterial cell concentration of the cultures and the total protein level of retentates. Starter organism growth was unaffected by high total solids or ash of retentates. Growth rate and lactose metabolism decreased markedly below pH 5.2 at which point bacterial population was 10(9) cfu/ml.

Histological and histochemical characterisation of mammary gland tissue of cows infected with foot-and-mouth disease by contact exposure.

Foot-and-mouth disease virus was observed to replicate in secretory epithelial cells of bovine mammary gland alveoli as a result of systemic infection initiated by exposure to infected animals. Viral antigens were demonstrated using fluorescent antibody and immunoperoxidase labelling techniques before the development of signs of clinical disease. In addition, labelled antigens were observed associated with cytoplasmic-like fragments in luminal membrane limited structures. Histologically, lesions of the alveolar secretory epithelium consisted of focal necrosis of these cells which eventually sloughed into the lumen.

Physicochemical transformation of milk components and release of foot-and-mouth disease virus.

Possible mechanisms for protective roles of milk components on foot-and-mouth disease virus present in the milk of infected cows were examined. Light scattering bands collected from Ficoll-sucrose gradient fractions of skim-milk contained membrane-limited structures but these were non-infectious for bovine kidney cells. Infectivity titres in buttermilk higher than those of the original cream or butter suggested association of virus with milk fat globules. Increased infectivity titres in skim-milk after treatment with SDS suggested release of virus particles from dissociated casein micelle subunits. Chelating agents, de-emulsifying agents and trypsin, which alter the structure of the individual milk components casein, lipid and milk fat globule membrane were without effect on infectivity titres.

Use of Time-Temperature Indicators as Quality Control Devices for Market Milk.

i-Point TTM and 3M Monitormark time-temperature indicators were evaluated for their use as quality monitors for market milk. i-Point indicators exhibiting a life span of 10 d at 4.4°C. 8 d at 6.8°C and 6.5 d at 10°C and 3M Monitormark having a response temperature of 5°C and a 14 d maximum exposure time were selected. Fresh HTST pasteurized commercial market milk was stored at 4.4,6.8 or 10°C. Time temperature indicators, activated at the time of storage of milk were followed daily at the three storage temperatures for color development in i-Point TTM and index number in 3M Monitormark. Milks were evaluated for bacterial numbers and acceptability at selected time intervals. Milks generally remained acceptable approximately 4 d after the end of the life span of i-Point indicators at 10°C and more than 10 d at 4.4 °C. 3M Monitormark exhibited insensitivity in the temperature range of 4-10°C. This integration of time as well as temperature makes it possible to replace the sell-by-date on market milk with i-Point TTM indicator to more effectively monitor quality.

Cassava as a food.

This review has attempted to examine information pertaining to the role of cassava (Manihot esculenta) as a major food source for a large part of the world population, particularly the countries of South America, Africa, and Asia, where it is primarily a major source of energy for 300 to 500 million people. Its cultivation, usually on small farms with little technology, is estimated to cover on an annual basis about 11 million hectares providing about 105 million tons, more than half of which is consumed by humans. The importance of cassava as an energy source can be seen by its growing demand in the European economic community countries where it forms up to 60% of the balanced diets for swine. Cassava is one of the crops that converts the greatest amount of solar energy into soluble carbohydrates per unit of area, thus 1 kg of moisture-free cassava meal may yield up to about 3750 kcal which would mean that a yearly production of 15 tons of cassava meal per hectare would yield some 56 million kcal. The major limitations of cassava as food appear to be its poor protein content and quality and the rapid post harvest deterioration of its roots which usually prevents their storage in the fresh state for more than a few days. However, in addition to its use for culinary purposes, cassava finds application in industrial products such as an adhesive for laundry purposes, for manufacturing paper, alcohol, butanol, dextrin, adhesive tape, textile sizing, and glue.

Vesicular exocytosis of foot- and -mouth disease virus from mammary gland secretory epithelium of infected cows.

Foot-and-mouth disease virus particles were observed by electron microscopy in the cytoplasma of alveolar secretory cells of the bovine mammary gland after contact exposure of uninfected cows to pits with foot-and-mouth disease. Virus, contained in membrane-limited vesicles, was released from the basal and peranuclear portions of the cells into the intracellular and extracellular spaces by an exocytotic mechanism similar to that of the release of th milk-fat globule. Virus was released into the lumen from the apical portion of the cell both by membrane-limited vesicles and by the merocrinal exocytosis of casein-associated virus. The lytic release of virus was observed in 20% of the preparations observed.

Ultrafiltration of Skim Milk at High Temperature.

Raw skim milk was selectively concentrated at 60 C by ultrafiltration and diafiltration procedures in an Abcor UF-22S unit equipped with high flux membranes. The thermal effect on flux rate, microbiological quality of the retentate and whey protein denaturation were observed under this processing condition. The higher processing temperature increased flux rate, improved microbiological quality and expanded the possibility of denaturing whey proteins, particularly with diafiltration. Composition of the product was normal and alkaline phosphatase negative.

Mixed cultures of different yeasts species and yeasts with filamentous fungi in the SCP production. I. Production of single cell protein by mixed cultures Candida lipolytica and Candida tropicalis.

The aim of this study was to determine the application of mixed cultures Candida lipolytica and Candida tropicalis in the SCP production. N-paraffin fraction of crude oil and individual n-alkanes C:7--C:17 and glucose were used as carbon sources. The cultures were grown on laboratory scale in shaking flasks and in a 7 1 fermentor. It was found that the mixed cultures gave about 18% higher yield of biomass than the individual cultures.

Symptom response to lactose-reduced milk in lactose-intolerant adults.

The possible usefulness of low-lactose milk for those lactose-intolerant subjects who develop symptoms from milk consumption was investigated. In the first part of the study, 16 intolerant subjects (blood glucose rise less than 25 mg/100 ml) received low-lactose skim milk containing 15 g lactose (2.5 cups) and 7.5 g lactose (2.5 cups), regular skim milk containing 30 g lactose (2.5 cups), and all three milks plus a small breakfast. The low lactose milks produced significantly fewer symptoms. The food given with the milk had no significant effect on symptomatic response. The second group of 17 subjects received 25 g lactose in water (250 ml), skim milk (500 ml) and whole milk (500 ml); 10 g lactose in lactose-reduced skim (500 ml) and whole milk (500 ml) and whole milk (500 ml); and a placebo (250 ml). There was a significant positive relationship between amount of lactose consumed and symptom response. The form in which the lactose was administered (e.g., whole versus skim milk) was not significantly related to symptoms. It is concluded that in a symptomatic subjects a significantly greater quantity of low-lactose milk than regular milks can be consumed.