Influence of Bacillus spp. Enzymes on Ultra High Temperature-treated Milk Proteins

Abstract

A model case of long-life half-fat milk contamination with spores of 15 strains of B. licheniformis, B. subtilis a B. cereus isolated from farm environment and from raw milk was used to determine proteolysis by measuring the changes in milk protein contents. The methods of infrared spectroscopy, free tyrosine using Lowry's method according to Juffs and setting of decrease in casein fractions using the SDS-PAGE were employed. Under storage temperature of 4 o C no proteolysis was recorded. However, under storage temperature of 24 °C the following changes in comparison with initial values were recorded after 3 weeks: a decrease in protein contents from 34.60 g⋅1-1 to 29.46-32.86 g⋅l-1 and increased free tyrosine contents from 0.65 mg⋅ml-1 to 2.13-1.59 mg⋅ml-1 depending on Bacillus spp. type. It was detected that milk heating at a temperature of 100 o C for 10 min and at 135 o C for 5 s, respectively, the spores of resistant strains Bacillus licheniformis may survive and show proteolytic activity. When monitoring the reduction of casein fractions it was found that the κ-casein was the most quickly broken down to 7.43%. The values of β-casein dropped to 27.53% and α-casein to 43.95%. Under storage temperature of 4 °C the reduction of all casein fractions was lower. A reduction to 79.42% for κ-casein, 78.30% for β-casein and 85.71% for α-casein was recorded. The intensity of changes was dependent on species and strain of Bacillus spp. used, on storage temperature and heat inactivation of spores. The initial spore concentration made itself felt, too.

Physico-Chemical Changes, Microbiological Properties, and Storage Shelf Life of Cow and Goat Milk from Industrial High-Pressure Processing

“…Zajác et al [43] has reported the significant decrease in fat content of raw cow milk after 24 h of storage at a temperature of 4 • C to be due to the lipolysis of milk fat initiated by both indigenous milk lipases and also microbial lipases which usually grew in number during storage. Significant increase of free fatty acids as a consequence of lipolysis in UHT cow milk after three weeks of storage was also confirmed by Janstová et al [49]. These analyses have also shown that goat milk has relatively higher total protein and fat contents than cow milk.…”

Identification and Characterisation of Spore-Forming Bacteria in Bovine Raw Milk Collected from Four Dairy Farms in New Zealand

“…Spoilage and pathogenic spore-forming bacteria responsible for the safety and quality of milk products are found to be present in the farm environment [54][55][56][57]. These bacteria circulate in the farm environment and enter the raw milk via milking of dirty teats and udders [5,6,29].…”