The survival of yeasts and probiotics as adjunct starters in cheese
Kotze, Annie Dorethea
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A literature review dealing with various aspects of cheesemaking and ripening is given in Chapter 1. With respect to starter cultures, the criteria for strain selection as well as the taxonomy of different starter strains were discussed. Cheese ripening is a complex system that involves numerous chemical, physical and bacteriological changes and can be accelerated by various techniques. Special reference was made to yeasts associated with dairy products, their characteristics as well as their contribution in the dairy industry. Yeasts play a very important role in the ripening and manufacturing of a wide variety of cheeses and can cause spoilage or have beneficial effects on cheese ripening. Furthermore, the properties of probiotic bacteria were discussed including their therapeutic value, their survival in bio-products and the possible expansion of the probiotic product range. Cheese offers certain advantages as a delivery system for live probiotic bacteria to the human gastro-intestinal tract. Debaryomyces hansenii and Yarrowia lipolytica are typical foodborne yeast species frequently associated with dairy products and capable of predominating the yeast composition in such systems. The two species fulfil a number of criteria to be regarded as co-starters for cheese making. They are known for their proteolytic and lipolytic activity as well as their compatibility and stimulating action with the lactic acid starter cultures when co-inoculated. Recent studies indicated that yeasts could be included as part of starter cultures for the manufacturing of cheese, enhancing flavour development during the maturation. The potential of D. hansenii and Y. lipolytica as agents for accelerated ripening of matured Cheddar cheese has been evaluated during four cheese treatments. The interaction between the two yeast species and the lactic acid bacteria was surveyed incorporating (i) D. hansenii, (ii) Y. lipolytica and (iii) both species as adjuncts to the starter culture and (iv) a control cheese without any additions for the production of matured Cheddar cheese. The physical and chemical properties of the cheeses were monitored in order to evaluate the contribution of the yeasts to cheese maturation. The yeasts grew in association with the lactic acid bacteria without any inhibition. An enhanced viability of the lactic acid starter bacteria was observed. The yeasts species when individually added contributed to the development of bitter and fruity flavours despite accelerated development of strong Cheddar flavours. When both species were incorporated as part of the starter culture, the cheese, however, had a good strong flavour after a reduced ripening period. The cheese retained the good flavour and aroma for nine months after production. Furthermore, the significant differences in the fatty acid contents of the model and control cheeses designated enhanced enzymatic activities in the model cheese, attributed to the presence of the two yeast species in the model cheese. The simultaneous application of D. hansenii and Y. lipolytica as part of the starter culture for the production of matured Cheddar cheese is proposed. The health benefits of probiotic-containing products are becoming a key factor affecting consumer choice, and therefore the existing limited range of such products needs to be expanded. Cheese may offer certain advantages as a carrier system for live probiotic organisms to the human gastro-intestinal tract. The possibility of introducing strains of Bifidobacterium bifidum and Lactobacillus acidophilus into South African commercial Cheddar and Gouda cheese were explored. The organisms viability during long-term ripening and storage, their effect on cheese flavour and texture as well as the chemical properties of the cheese were determined. L. acidophilus remained highly viable for at least 120 days of ripening, while the numbers of B. bifidum remained above the therapeutic minimum for 70 days in both cheeses, satisfying the criteria for probiotic foods in Gouda cheese with its shorter shelf life. The viability profile of the lactic acid starter bacteria was not affected and a normal good cheese texture and appearance were retained. Both Cheddar and Gouda cheese offer potential to be effective vehicles for the delivery of probiotic strains to the consumer despite the development of sour and bitter tastes. Additional strains need to be selected and evaluated to prevent these constraints.