The addition of a cocktail of yeast species to Cantalet cheese changes bacterial survival and enhances aroma compound formation.

Indigenous yeasts can be detected at high populations in raw milk Cantal cheese, a French Protected Denomination of Origin (PDO) hard cheese. To investigate their use as adjunct cultures to promote flavour development in Cantalet (small Cantal) cheese, three strains isolated from raw milk Cantal cheese, Kluyveromyces lactis, Yarrowia lipolytica, and Pichia fermentans were added at 3 (E3) and 5 (E5) log(10) colony-forming units (cfu)/mL to microfiltered milk at a ratio of 80/10/10 viable cells, respectively. The global microbial, compositional and biochemical changes induced by the presence of yeasts in cheese were determined. Adjunct yeasts did not grow but stayed at viable populations of approximately 4 and 6 log(10) cfu/g in E3 and E5 cheeses, respectively, throughout the ripening period. They were mainly constituted of K. lactis, while P. fermentans and Y. lipolytica were not detectable after 3 and 45 days of ripening, respectively. Several species of indigenous yeasts were also detected in E3 cheeses at the beginning of ripening only, and in the control cheeses without yeasts added. Lactoccoci survived for longer periods in the presence of yeast adjuncts, while, conversely, the viability of Streptococcus thermophilus decreased more rapidly. The addition of yeasts did not influence cheese composition and total free amino acid content. In contrast, it slightly increased lipolysis in both E3 and E5 cheeses and markedly enhanced the formation of some volatile aroma compounds. The concentrations of ethanol, ethyl esters and some branched-chain alcohols were 6 to 10 fold higher in E5 cheeses than in the control cheeses, and only slightly higher in E3 cheeses. This study shows that K. lactis has a potential as cheese adjunct culture in Cantalet cheese and that, added at populations of 4-5 log(10) cfu/g cheese, it enhances the formation of flavour compounds.

[Milk and dairy products for human nutrition: contribution of technology]. / Laits et produits laitiers en alimentation humaine Apports des procédés technologiques.

The complex composition of milk has led to the development of innovative technological processes such as membrane separation. The dairy industry is now able to offer consumers safe classical products (liquid milk, raw-milk cheeses) with little or no heat treatment. Indeed, heat treatment undermines the organoleptic qualities and bioactivity of many molecules found in milk. New technologies, and especially membrane microfiltration, have allowed researchers to identify two groups of milk proteins in terms of their human absorption kinetics: slow micellar casein and fast whey proteins. The highly purified products thus obtained are used for infant foods and slimming aids, and as functional ingredients. The same technologies have been applied to colostrum, yielding a sterile "serocolostrum" containing biologically active immunoglobulins, growth factors, and polypeptides. Combined with other separation techniques, membrane technologies should soon allow the separation and purification of minor milk proteins described as having essential roles in bone calcium uptake and vitamin transport, for example. The use of enzymatic membrane reactors has led to the identification of several bioactive peptides, such as--kappa-caseinomacropeptide, which induces CCK (cholecystokinin) secretion and thus regulates food intake and lipid assimilation,--alpha(S1) CN (91-100), a compound with benzodiazepine activity,-- kappaCN (106-116), which has anti-thrombotic activity by inhibiting blood platelet binding to fibrinogen, and--alpha(S) and beta casein phosphopeptides, which are thought to increase iron and calcium absorption.

Influence of various phosphopeptides of caseins on iron absorption.

The influence of the origin and kind of caseinophosphopeptide (CPP) on iron absorption was assessed by comparing a commercially available CPP mixture (CPPs) and derived chromatographic fractions with the purified, chemically phosphopeptide of beta-casein [beta-CN(1-25)] using a perfused rat duodenal loop system; gluconate iron was used as control. Only iron complexed to beta-CN(1-25) displayed a better bioavailability than gluconate iron. The results obtained with various chromatographic fractions indicated that phosphopeptides of different origins (alpha(s)- versus beta-caseins) display specific effects. These findings contribute to the explanation of the discrepancy about the role of caseinophosphopeptides on mineral bioavailability in vivo.