The effect of lipolytic Gram-negative psychrotrophs in stored milk on the development of rancidity in Cheddar cheese

Abstract

SummaryThe highest incidence of lipolytic activity among the psychrotrophic Gram-negative flora of commercial raw milks was found in strains ofPseudomonas fluorescensandPs. fragi.The lipases of all of the lipolytic strains remained wholly or partly active after heat treatment at 63°C for 30 min. Two of the strains tested further had lipases which retained 20–25% of their activity even when heated at 100 °C for 10 min. Cheeses made from milks in which strains or a single strain of lipolytic Gram-negative rods (GNR) had been allowed to multiply to > 107colony forming units/ml became rancid after 4 months even though the GNR had been killed by pasteurization. The rancidity was characterized by a soapy off-flavour in cheeses containing free fatty acid concentrations from 3 to 10 times higher than those in control cheeses made from stored milks with low counts of GNR. Strong rancidity could be reproduced by adding the culture supernatant of a pre-grown lipolytic strain, but not the washed cells, to milk and pasteurizing it immediately before cheese-making, demonstrating the extracellular nature of the rancidity-inducing lipases.

Caractérisation de l'emmental français "grand-cru". II. Analyses sensorielles

“…L'emmental français «grand-cru», dont l'odeur rance est la plus faible, est aussi le moins lipolysé. Le stockage des laits, dans le fromage de Cheddar, expliquerait, d'après Law et al (1976), l'apparition de flaveurs rances et de goûts de savon. L'origine de ces modifications étant dans ce cas due aux lipases de la flore psychrotrophe.…”

Bitter flavour in dairy products. I. A review of the factors likely to influence its development, mainly in cheese manufacture

“…Similarly, Greek Teleme cheeses made with raw milk stored for 5 days were unacceptable for body and texture and were rejected because of rancidity, unclean flavour and bitterness due to the presence of psychrotrophic bacteria (Kalogridou-Vassiliadou and Alichanidis, 1984). Other workers (Chapman et al, 1976;Law et al, 1976;Hicks et al, 1986) have found similar off-flavours in Cheddar cheese made from cold-stored milk.…”

Microbiological Spoilage of Dairy Products

“…Low pH limits the rate of lipase activity, but in some cheeses, e.g., Brie and Camembert, the pH rises to near neutrality as ripening progresses, making them especially susceptible to lipolysis (Dumont, Delespaul, Miquot, & Adda, 1977). For Cheddar cheese, however, a high concentration of lipase is needed to create the desired flavor (Law, Sharpe, & Chapman, 1976). Products such as whole milk powder may be affected by residual heat-resistant bacterial lipases.…”