Type A and B bovine milks: Heat stability is driven by different physicochemical parameters

Characterization of variables related to high stability of raw cow milk

This research paper analyzes the stability of raw cow milk in the alcohol test and seeks to understand to know the factors that influence milk stability and the occurrence of unstable non-acid milk. Milk samples were collected from the cooling tanks of rural farmers in the state of Paraná twice in summer and twice in winter. The farms were classified according to the production system: pasture with supplementation and feedlot. The following variables were analyzed: stability in the alcohol test, titratable acidity, ionized calcium concentration (iCa), chemical composition of milk, somatic cell count and standard plate count. The results showed that milk stability was greater in winter vs. summer, when the milk contained higher iCa, and in the feedlot vs. pasture system. The Pearson Correlation between variables (ethanol stability, milk composition, iCa, cooling tank temperature, milk volume, number of milking, number of cows milked, fat/protein ratio, distance and travel time) were analyzed. Stability was negatively correlated with iCa concentration and positively with lactose content. Logistic regression of the risk of unstable non-acid milk at 72% alcohol (UNAM72) showed that only iCa and lactose were determinants, while evaluation of the same risk at 78% alcohol revealed iCa, titratable acidity, lactose and milk urea nitrogen as risk factors. Under the dairy farming conditions of Paraná state, the frequency of UNAM72 was low (12.16%) and was higher in summer and in pasture systems with supplementation. In conclusion, in dairy herds bred with high technological level, with adequate nutritional and health management, the frequency of UNAM is low and is related to nutritional management abnd, perhaps, heat stress, factors that alter iCa and lactose levels.

Identification and Activity Characterization of γ-Glutamyltransferase from Bovine Milk

It is well known that bovine milk contains γ-glutamyltransferase (GGT) activity. To verify the identity of the GGT and further to characterize the generation of γ-glutamyl peptides, identification of GGT from bovine milk and quantification of kokumi peptides and free amino acids were performed. GGT was purified from skim milk and identified as the bovine protein (G3N2D8), and it reveals that it is composed of two subunits. Sequence alignment with human GGT and molecular mass determination showed that the bovine GGT was glycosylated and contained an N-terminal transmembrane part. Further activity characterization was performed in comparison with GGT from Bacillus amyloliquefaciens in terms of the ability to generate γ-glutamyl peptides from casein hydrolysates. During the transpeptidation reaction catalyzed by both GGT, γ-glutamyl peptides significantly (P < 0.05) increased after γ-glutamylation; addition of glutamine contributed to the generation of γ-glutamyl peptides, suggesting that glutamine could act as a γ-glutamyl donor. This study reveals that the GGT of skim milk membranes is a glycosylated membrane protein that can generate γ-glutamyl peptides.