Hydrolysis of fat and protein in small cheeses made under aseptic conditions

Abstract

SummaryAseptically drawn milk was made into small cheeses (100 g) under aseptic conditions. The influence of the cow's feeding régime on the composition of the cheese fat, and the hydrolysis of the cheese fat and protein by bacterial and native milk enzymes, was studied.In the absence of a strongly lipolytic bacterial cheese flora, the free fatty acid (FFA) content of cheese appeared to depend on several variables:1. The initial FFA content of the milk varied according to the mode of milking (the lowest was obtained by cannulation of the udder) and the feeding régime of the cow. When one of a pair of monozygotic twin cows was maintained on pasture and the other on winter feed (hay and concentrates), the cheese made from the milk of the latter contained less FFA than did that from the former.2. The major changes in the composition of the milk fat of the cows on winter regime were an increase of myristic and palmitic acids from 8 to 11% and 21 to 28%, respectively, and a decrease in stearic and oleic acid from 11 to 7·5% and 38 to 28%; minor changes in the other fatty acids were also observed.3. The milk lipase in raw milk cheese liberated substantially more FFA than did the weakly lipolytic lactic acid streptococci. Milk lipase was active at the low pH value of cheese, but was inactivated when the milk was pasteurized at 63°C for 30 min.4. Although rennet did not produce any amino acids in the mature cheeses it hydrolysed some of the cheese protein to nitrogen soluble in water (WS), trichloroacetic acid (TCA-S) or phosphotungstic acid (PTA-S). Some of the WS-N appeared to be utilized by the lactic acid streptococci. The native milk protease resisted the heat treatment used and liberated amino acids at the low pH value of cheese, but its contribution to the proteolysis was relatively less important than the contribution of the milk lipase to the fat breakdown in cheese.5. The free amino acids of the milk, which appeared in the whey, were not recovered in the cheese. The cheese made from unheated milk with δ-gluconic acid lactone contained low amounts of free amino acids apparently due to the action of milk protease. The proteolytic activity of the lactic acid bacteria increased the amino acid content appreciably.

Chemical methods for the characterization of proteolysis in cheese during ripening

“…Rennet is responsible for the production of sorne of the 12% TCA-soluble N, but starter proteinases and peptidases make a substantial contribution (Reiter et al, 1969;0' Keeffe et al, 1976) to the formation of 12% TCA-soluble N. Venema et al (1987) reported that the level of 12% TCA-soluble N is a better index of maturity than WSN. The development of 12% TCA-soluble N in an Irish artisanal blue cheese is shown in figure 1.…”

“…acid (2-hydroxy-5-sulphobenzoic acid; SSA), a discriminating protein precipitant, has been used at 3% to prepare extracts of cheese for ami no acid analysis (Reiter et al, 1969;Ramos et al, 1987), or as an index of amino acid N (Cliffe and Law, 1991). However, Kuchroo and Fox (1982a) found that 2.5% SSA precipitated only 10% of the WSN.…”

“…It is generally necessary to deproteinize sampIes prior to amino acid analysis to reduce interference from peptides; reagents used have incIuded sulphosalicylic acid (Reiter et al, 1969;Omar, 1984), ethanol (Visser, 1977Polychroniadou and Vlachos, 1979), picric acid (Weaver et al, 1978;Shindo et al, 1980), TCA (Zarmpoutis et al, 1996) or Ba(OH)z/ZnS04 (Hickey et al, 1983). An internaI standard (eg, norleucine) is normally added to facilitate quantitation of amino acids.…”

Assessment of proteolysis and lipolysis in Serra cheese: effects of axial cheese location, ripening time and lactation season

“…The samples of curd exhibited low levels for WSP and FA; this observation was expected, however, because it is weil established that freshly secreted milk contains small amounts of peptides and amino acids, on the one hand, and free fatty acids, on the other, which are not necessarily the result of proteolysis (Reiter et al, 1969) and Iipolysis (Needs and Anderson, 1984), respectively. Differences in FA in the curd thraughout the lactation season were also expected because the fat composition of ewe's milk varies within fairly wide limits, and these limits are a direct function of the composition of the feed (Ramos and Juarez, 1981) which in turn depends on such seasonal factors as the weather (the Iivestock is predominantly fed with silage during winter and with fresh grass during spring).…”

The lipolytic properties of Candida mycoderma and Debaryomyces kloeckeri isolated from limburger cheese and some properties of the lipases produced by these yeasts

“…Although considerable literatures3, 7,11,13,17) have been published on the lipases produced by moulds and bacteria isolated from various cheeses, little is known of the lipolytic properties of yeasts subsisting in cheeses16,18).…”