The release of peptides and glycopeptides by the action of heat on cow's milk

Abstract

SummaryThe release, as a result of heat treatment on cow's milk, of peptides and glycopeptides which are soluble in the 12% trichloroacetic acid (TCA) filtrate of the milk has been studied. The results showed that the amount of peptides released increased with temperature and duration of the heat treatment. There were differences between milks in their response to a given heat treatment. Glycopeptides were released at temperatures as low as 50 °C but not at 37 °C. A comparison was made of the glycopeptides released by heat treatment and of those released from κ-casein by the action of rennin on the milk. This showed that N-acetyl neuraminic acid, D-galactose and 2-acetamido-2-deoxy-D-galactose were invariably present in both groups of glycopeptides. D-Mannose was also present in the glycopeptides released by heat but was detected on the glycopeptides released by rennin in only one of 6 experiments. It is suggested that glycopeptides released by heat may be derived from κ-casein but that a definite conclusion cannot be reached at present because of lack of information on the carbohydrates attached to other milk proteins.

The Combined Effect of Fortification of Media with Peptone and Control of Acidity on the Growth of Lactic Acid Bacteria

“…When Lactobacillus casei grow at 34°C in sterilized skim milk in the absence of 1% peptone and of the controlled of culture acidity, and with fortification of the media with 1% peptone of the controlled culture acidity, the population density was several times higher in culture supplemented with peptone and control of culture acidity, reached a population density of 90x10 6 CFU/ml, compared with 11x10 6 CFU/ml by the same strain being grown as a control. This medium proved to be superior for lactic acid production Figures 5 and 6 these results agreed with those reported by Ismail (1991 b), Hindle and Wheelock(1970), and Thandon and Ganguli (1972).…”

Influence of pH on the heat-induced proteolysis of casein molecules

“…No low molar mass peptides from C-terminal fragment of β-casein, N-terminal of α s" -casein or C and N terminal of α s# -casein were detected. Moreover, no low molar mass glycosylated peptide from κ-casein, as reported by Hindle & Wheelock (1970), was detected. The release of phosphopeptides κ-CN f(149-169), β-CN f(1-16), β-CN f(1-17) and β-CN f(1-18) indicated that the phosphorus released during heating was not entirely inorganic.…”

“…During sterilization of milk or dairy products, increase in NPN fraction is a biochemical modification described and acknowledged by many authors (White & Davies, 1966 ;Hindle & Wheelock, 1970 ;Lorient & Alais, 1970 ;Saidi & Warthesen, 1993 ;Hustinx et al 1997 ;Morales & Jime! nez-Pe!…”

“…However, in these published studies, the exact nature and the origin of these released products in the NPN fraction was not determined in detail. Hindle & Wheelock (1970) suggested that, during heat treatment of milk, glycopeptides were released from κ-casein. Recently, Hustinx et al (1997) have identified, using a plasma desorption mass spectrometer, fifteen soluble peptides at pH 4n6 after a heat treatment of sodium caseinate at 140 mC and pH 7n0 for 120 min.…”

Milk Coagulation and Protein Denaturation

“…Glycopeptides have been found in milk at temperatures above 50°C (Hindle and Wheelock 1970), and peptides similar to macropeptides from chymosin (EC 3.4.23.4) hydrolysis are produced in milk heated to 120°C for 20 min (Alais et al 1967). Under severe ultra-high-temper-ature pasteurization conditions (up to 154.4 °C for 9 sec), casein is solubilized (Morgan and Mangino 1979).…”