Lactose-negative mutants of Lactococcus lactis subsp. lactis and Lacto-coccus lactis subsp. cremoris with good autolytic properties were used at two different levels in addition to the normal starter in Gouda-type cheesemaking experiments. Increased numbers of bacteria were observed in fresh cheese, and the pH changes during ripening were as normal. A more rapid development of soluble N compounds was observed in cheeses with mutant addition, especially with Lc. lactis subsp. lactis IMN-L2–3 and Lc. lactis subsp. cremoris IMN-C12–1, compared with the control cheese. Cheese with added Lc. lactis subsp. lactis IMN-L2–3 and Lc. lactis subsp. cremoris IMN-C12–1 showed the most extensive ripening and the highest product quality of the mutants tested. The experimental cheeses were graded higher than the control cheese. The ripening time was significantly reduced, and the quality was retained at an acceptable level during storage.

The isolation and identification of low molecular mass peptides formed during the ripening of Parmigiano-Reggiano cheese is described. A strategy was used based on the fractionation of nitrogenous material using chemical methods followed by HPLC to isolate peptides and fast atom bombardment-mass spectrometry to identify them. It was found that the majority of cheese oligopeptides arose from the proteolysis of β-casein. Several phosphopeptides and oligopeptides known in vivo to be biologically active have also been identified during the ripening of cheese.

The relationships between the composition, texture and microstructure of chhana (an Indian-style soft cottage cheese analogue) and rasogolla (a sweetened dairy product made from chhana) were analysed. Chhana contained a significantly higher proportion of fat, protein, lactose and minerals than did rasogolla. Cooking of chhana in 60% sucrose solution introduced sucrose and changed the texture and structure to that typical of rasogolla. As chhana was transformed to rasogolla, the Instron textural properties, hardness, gumminess and chewiness, fell significantly, whereas springiness increased dramatically. Market rasogolla had a slightly different composition from the laboratory-made samples, but both had similar Instron textural and sensory textural attributes. Scanning electron microscopy showed that chhana had a structure like cottage cheese or cream cheese, a compact, coalesced casein matrix with fat globules embedded in it. Rasogolla had a conglomerated, ragged and porous casein matrix with uneven surface and numerous large void spaces. The collapsed and ruptured fat globules were found embedded in the agglomerated protein particles of rasogolla. The textural attributes of both chhana and rasogolla could be explained by the microstructure.

α-Lactalbumin (α-La) is a protein found in the milk of all mammalian species and is involved in lactose biosynthesis in association with galactosyltransferase (Brodbeck et al. 1967). The primary structure of α-La from several species such as bovine (Brew et al. 1970), human (Findlay & Brew, 1972), and goat (McGillivray et al. 1979) has been determined. Hall et al. (1982) have established the nucleotide sequence and the organization of the human α-La gene (Hall et al. 1987).

The keeping quality of properly refrigerated pasteurized milk and cream is primarily determined by post-pasteurization contamination by Gram-negative psychrotrophic bacteria (Phillips et al. 1981; Schröder et al. 1982). Reliable and rapid methods of assessing the levels of contamination by these organisms are therefore of commercial interest.