The production of Cheddar-type cheese, unlike many other cheese varieties, does not require the use of secondary cultures. However, adjunct cultures offer the means of improving and accelerating flavor development in a controlled manner (24,25). Adjuncts evaluated in Cheddar cheese production include both viable and attenuated preparations of Lactococcus spp. and Lactobacillus spp. (26).
Attenuated preparations, produced by physical, chemical, or enzymic treatments, are unable to grow in the curd but enhance enzymic activities during ripening (27). Evaluation of Cheddar cheese made with attenuated adjunct strains of Lb. helveticus and Lb. casei indicated improved sensory and textural characteristics (28-31). Thermophilic Lactobacillus spp. (Lb. helveticus, Lb. delbruckii) similarly do not proliferate significantly during maturation but their inclusion can improve flavor acceptability (32,33). However, mesophilic Lactobacillus adjuncts do grow in Cheddar curd during ripening and several studies on their use have been published (26). In the earliest studies (34,35) a reference flora that was composed of groups of nonstarter bacteria isolated from cheese and raw milk was added and shown to accelerate and intensify flavor development. Subsequent studies (36-46) specifically investigated the effects of individual strains of Lactobacillus spp. as adjunct cultures and recently the effects of combinations of adjuncts have been assessed (47). Adjunct cultures studied have, in general, been restricted to strains of Lb. casei, Lb. paracasei subsp.
paracasei, Lb. curvatus, Lb. rhamnosus, and Lb. brevis. These species also tend to dominate the cheese nonstarter flora, but the inclusion of adjunct strains is a specific strategy in flavor control. The selection thus cannot be random but must be based on the metabolic attributes exhibited by the strains. Typically, the inclusion of adjunct strains of lactobacilli has been shown to result in improved flavor intensity, increased aroma, and accelerated ripening, and although primary proteolysis was not affected by the adjunct cultures, the levels of small peptides and free amino acids were higher than in the control cheese. The same volatiles were present in both the control and adjunct-containing cheeses but their relative concentrations differed significantly. The inclusion of inappropriate adjunct strains, can, however, result in the occurrence of textural defects and development of undesirable off-flavors (36,38,42). An alternative strategy to accelerate cheese ripening is the use of bacteriocin-producing lactococcal adjunct cultures (48). The bacteriocins released by this strain increased the rate of starter cell lysis during ripening and in consequence the adjunct-containing cheese had elevated free amino acid concentrations and higher sensory grading scores. The potential for the inclusion of adjunct cultures with probiotic properties has also been evaluated because Cheddar cheese appears to offer some advantages over yogurt-type products in the delivery of viable probiotics to the human gastrointestinal tract (49). The dairy industry is continually examining opportunities for expanding the diversity of its product range, and it is inevitable that the range of adjunct cultures employed in the production of fermented dairy products will continue to expand as organisms with beneficial characteristics are identified (50).
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