UHT Sterilization Research Articles

Incorporation of Radiolabeled Whey Proteins into Casein Micelles by Heat Processing

Skim milk was heated at 70, 95, and 140°C to simulate the processes of pasteurization, forewarming, and UHT sterilization, and the specific interactions between α-lactalbumin or β-lactoglobulin and the caseins studied using tracer amounts of added 14C-labeled whey protein. Radioactivities of the whey and of the washed casein pellets from renneted skim milk were measured and the extent of the interaction estimated.Upon heating skim milk at 70°C for 45s, less than 2% β-lactoglobulin and less than .3% α-lactalbumin were incorporated into the curd. Heating at 95°C for .5 to 20min resulted in 58 to 85% of the β-lactoglobulin and 8 to 55% of the α-lactalbumin becoming associated with the curd. Heating at 140°C for 2 and 4s caused 43 and 54% of the β-lactoglobulin and 9 and 12% of the α-lactalbumin, respectively, to be bound to the curd fraction. The radiolabeling technique is very sensitive and useful for tracing low levels of interaction between whey proteins and casein in heated milk systems.

Iodine Content of Dairy Milk in France in 1983 and 1984

Iodine concentrations were determined in 848 samples of milk from tanks of 537 dairy factories collected in 1983 and 1984 during winter and summer. Industrial processing, like pasteurization, UHT sterilization and spray-drying, had no effect on iodine concentrations. Of the samples of bovine milk, 94.7% ranged between 10 to 250 μg/kg. Iodine in bovine milk averaged 97 and 93 μg/kg in the winter of 1983 and 1984, and 44 and 23 μg/kg in the summer of 1983 and 1984. The frequency of iodine concentrations above the 500 μg/kg limit was 0.5% in 1983 and 0.3% in 1984. Iodine in ovine milk varied from 116 to 1183 μg/kg. Of the ovine milk samples 53.3% were above 500 μg/kg. Thus the iodine content of milk, is not yet a health problem in France.

Synergistic effects of various lipases and phospholipase C on milk fat

SummaryThe enzyme, phospholipase C, from a number of psychrotrophs isolated from milk was shown to survive HTST pasteurization and UHT sterilization processes. The phospholipase C of Bacillus cereus was able to increase lipolytic activity of a commercial lipase preparation and native milk lipoprotein lipase in raw milk by making the substrate more susceptible to hydrolysis: phospholipase C had no effect on the lipase activity of a fluorescent Pseudornonas spp. The enhancement of lipolysis by phospholipase C was affected by pronase and papain, but not by trypsin. Homogenization of the raw milk had the same effect on lipolysis by lipoprotein lipase as addition of phospholipase C.

Effects of thermal industrial processing on acid-soluble nucleotides of milk

SUMMARYCommercial bulk milk contained, in its acid-soluble nucleotide fraction, small quantities of CMP and AMP as well as a high proportion of orotate (503±16 μg/g of total solids). These components were altered by thermal treatment during processing. Standard sterilization and spray drying of milk lowered significantly the CMP, AMP, and orotate concentrations. HTST pasteurization caused a slight decrease in CMP and AMP concentrations, but the orotate content remained unchanged. The UHT sterilization seemed to be the thermal treatment in which the acid-soluble nucleotides of milk underwent least change. It is therefore concluded that the decrease in concentration of the nucleotides of milk is more directly related to the time for which the milk remains at the processing temperature than to the temperature itself.

Effects of adding potassium iodate to milk before UHT treatment. ii. iodate-induced proteolysis during subsequent aseptic storage.

The addition of potassium iodate to milk at 9.1 mM before UHT treatment resulted in rapid breakdown of alpha s- and beta-casein during subsequent aseptic storage. Maximum rates of proteolysis were observed at storage temperatures of 37-45 degrees C, but the reaction was strongly inhibited by storage at 55 degrees C and by increased holding time at 140 degrees C during the UHT sterilization. Iodate-induced proteolysis of purified alpha s1-and beta-casein was detected only with solutions in the serum phase of raw milk; no proteolysis occurred with solutions in 0.1 M-phosphate buffer (pH 6.7) or in milk ultrafiltrate, irrespective of whether whey proteins and lactose were also added. Thus, it appears that iodate increased the activity of one or more proteolytic components which were present in milk and were unable to pass through an ultrafiltration membrane. However, it is unlikely that iodate acts by increasing the activity of proteinases produced by contaminant bacteria; the presence of iodate did not affect the activity of a proteolytic enzyme isolated from Pseudomonas fluorescens PM-1. Furthermore, iodate promoted protein breakdown during storage of milk drawn aseptically from the cow and subsequently UHT processed. It is suggested that iodate increased the activity of native milk proteinases, other than plasmin which was inactivated by UHT treatment, possibly by preventing thiol-disulphide exchange reactions during the heating process.