Maria J. Sousa

Advances in the study of proteolysis during cheese ripening

Cheese ripening involves a complex series of biochemical, and probably some chemical events, that leads to the characteristic taste, aroma and texture of each cheese variety. The most complex of these biochemical events, proteolysis, is caused by agents from a number of sources: residual coagulant (usually chymosin), indigenous milk enzymes, starter, adventitious non-starter microflora and, in many varieties, enzymes from secondary flora (e.g., from Penicillium sp. in mould-ripened cheeses or Propionibacterium sp. in Swiss cheese). Proteolysis in cheese has been the subject of active research in the last decade; there have been developments in the analytical techniques used to monitor proteolysis and patterns of proteolysis in many cheese varieties have now been investigated. This review focuses on certain aspects of proteolysis, including proteolytic agents in cheese and specificity of some ripening enzymes, comparison of proteolysis and contribution of proteolysis to cheese flavour.

Preliminary observations on proteolysis in Manchego cheese made with a defined-strain starter culture and adjunct starter (Lactobacillus plantarum) or a commercial starter

Different authors have demonstrated the potential of adding lactobacilli as adjunct cultures to pasteurized milk used in cheese manufacture. The aim of this work was to observe the effect of the use of a defined-strain starter culture and the addition of an adjunct culture (Lactobacillus plantarum) to cheesemilk in order to determine their effect on the ripening of Manchego cheese. Manchego cheeses were manufactured using one of the following starter culture systems: a defined starter consisting of Lactococcus lactis ssp. lactis and Leuconostoc mesenteroides ssp. dextranicum; a defined starter, as described above, and Lb. plantarum, which were isolated from a good quality Manchego cheese made from raw milk, or a commercial starter comprised of two strains of Lc. lactis. The cheeses were sampled at 15, 45, 90 and 150 d of ripening. Principal component analysis of peak heights of reversed-phase HPLC chromatograms of 70% (v/v) ethanol-insoluble and -soluble fractions distributed the samples according to the starter used in their manufacture. Quantitative differences in several peptides were evident between the three cheeses. Cheeses made with the defined-strain starters received higher scores for the flavour quality and intensity and for overall impression than the cheeses made with the commercial starter.

Ripening of ovine milk cheeses: effects of plant rennet, pasteurization, and addition of starter on lipolysis

Abstract The influences of type of rennet (from animal sources or from flowers of Cynara cardunculus ), pasteurization (or not) of the milk, and addition (or not) of starter cultures prior to cheesemaking, on the release of major fatty acid residues of ovine milk cheese were evaluated throughout the ripening period. The long-chain saturated (C 16:0 and C 18:0 ) and unsaturated (C 18:1 , C 18:2 and C 18:3 ) free fatty acids (FFA) were the most abundant types at all stages of ripening. The overall concentrations of FFA released by 68 days of ripening were 6517 and 7802 mg kg −1 cheese for ovine milk cheeses manufactured from the same batch of raw milk and ripened under the same conditions without deliberate addition of a starter culture, using plant or animal rennet, respectively; therefore, such plant rennet appears to be a good substitute for animal rennet from a lipolytic point of view. The overall concentrations of FFA in fresh cheese were 3538, 3002 and 3283 mg kg −1 cheese for raw milk without addition of a starter culture, pasteurized milk without addition of a starter culture, and pasteurized milk with addition of a starter culture, respectively; these values increased to 6517, 8115 and 4847 mg kg −1 cheese by 68 days, of which 1791, 3887 and 1649 mg kg −1 cheese were accounted for by short-chain FFA.

Acceleration of proteolysis during ripening of Cheddar-type cheese using of a streptokinase-producing strain of Lactococcus

Bovine milk contains a number of indigenous proteolytic enzymes, of which plasmin is the most important (Grufferty & Fox, 1988; Bastian & Brown, 1996; Kelly & McSweeney, 2003). Plasmin (EC 3.4.21.7) is a serine proteinase with pH and temperature optima of 7·5 and 37 °C, respectively. In milk, most of the plasmin is present as its inactive precursor, plasminogen, which is converted to active plasmin by plasminogen activators (PA) present in milk, e.g., urokinase-type (u-PA) and tissue-type PA (t-PA) (Bastian & Brown, 1996). Since plasmin, plasminogen and PA are associated with casein micelles, they are incorporated into cheese curd, while plasmin inhibitors and inhibitors of PA are lost with the whey. Plasmin incorporated in cheese curd acts on its substrate, the caseins, contributing significantly to primary proteolysis during ripening (Upadhyay et al. 2004b).