Psychrotrophic strains of Bacillus and Pseudomonas that demonstrated both proteolytic and lipolytic activity were incubated with Grade A milk. The yield of direct-acid cheese manufactured from inoculated milk decreased as psychrotrophic inoculation level increased. Yield reduction resulted from both lipid and protein degradation, and accounted for approximately 45 and 55% of the dry matter loss, respectively. Fat losses were observed from decreased milkfat tests and increased acid degree values. Protein losses were observed from increased non-protein nitrogen and whey nitrogen values. Therefore, cheese yield studies must involve assays of both protein and lipid on a dry matter basis. Acid degree values and fat disappearance in stored milk and total nitrogen in whey were the best indicators of reduction in yields. Although bacterial enumeration, titratable acidity and pH were not good indicators of yield, they may be important in determining when yield loss starts.
Human consumption of iodine has increased to amounts which are about equal to the upper safe level as set by the National Research Council. One of the major sources for the greater iodine consumption is an increase in the amount reported in milk and other dairy products. The mammary gland does not limit the amount of iodine secreted in milk as it does with many other elements. Increased use of organic iodine in feed has resulted in high levels in milk in some dairy herds. Most of the herds with levels above 1,000 μ g/liter were fed organic iodine above recommended levels as a prevention for foot rot. Iodine teat dips and udder washes can contribute additional iodine to the milk. In a few instances, the misuse of iodine sanitizers in the dairy industry has also contributed to increased milk iodine. If milk iodine levels are to be held at the present level or decreased, iodine feed supplementation and sanitizers must be used as currently recommended.
The variability of yield for Cheddar cheese manufactured in 7- and 390-kg-size vats and cottage and direct-acid-set cheese manufactured in 7-kg-size vats was compared. The direct-acid-set cheese had less variability than Cheddar or cottage cheese (% coefficient of variation was .91, 1.79 and 4.69, respectively) manufactured in 7-kg-size vats and Cheddar cheese manufactured in 360-kg-size vats (% coefficient of variation was .91 and 1.98, respectively). Cottage cheese had the largest variability between replications using small vats because of additional stirring and curd manipulation required in its manufacture. Therefore, when cheese variety is of no concern, the direct-acid-set cheese procedure would reduce variation between replication more than traditional Cheddar procedures when used in an experimental design. In addition, a greater number of vats of cheese could be manufactured per day using the small vat system.
Superoxide dismutase activity was shown to be present in bovine milk serum and was quantified by measuring the capacity of retentate from dialyzed milk serum to inhibit reduction of cytochrome c by xanthine-xanthine oxidase-generated superoxide anion. One unit of enzyme was defined as the quantity of superoxide dismutase which inhibits cytochrome c reduction by 20%. By this definition 19,500 units of enzyme were present per liter of retentate from dialyzed milk serum. This amount is equivalent to about 2.4 mg of purified bovine erythrocyte superoxide dismutase per liter. Polyacrylamide gel electrophoresis of a partially-purified superoxide dismutase from acid whey, followed by staining for enzymic activity, confirmed the presence of the enzyme in milk serum which was identical in electrophoretic properties to those of bovine erythrocyte copper-zinc superoxide dismutase. Pasteurization at 63 C for 30 min did not decrease superoxide dismutase activity in milk serum. Heating of purified bovine erythrocyte-superoxide dismutase at 100 C for 1 min resulted in almost complete loss of enzymic activity, whereas the partially-purified superoxide dismutase from acid whey still retained 40% of the original activity under these conditions. Bovine milk superoxide dismutase may be an important naturally-occurring antioxidant for increasing oxidative stability of milk and other dairy products.