Yeasts microbial interactions

Microbial interactions that occur in wine may be beneficial or detrimental to wine quality depending on the species involved. Examples of detrimental interactions are the inhibition of S. cerevisiae by Lactobacillus species and the inhibition of O. oeni by S. cerevisiae when MLF is desired. However, the inhibition of O. oeni may also be beneficial to wine quality if MLF is undesirable. Additional beneficial interactions include the stimulation of LAB growth due to yeast lysis and the inhibition of Pediococcus species by O. oeni. A better understanding of the complex interactions between LAB and S. cerevisiae will lead to the selection of compatible yeast and bacterial strains for the induction of alcoholic and malolactic fermentations. 

Microbial interactions (LAB x yeast as well as LAB x LAB) are also known to impact the success of MLF. 

Conversion of the Microbially Produced Preadhesive to an Adhesive Protein. The polyphenolic protein purified from yeast adheres to a wide variety of surfaces including glass and plastic. The adherence probably results from the presence of many polar residues capable of hydrogen bonding and lysine residues that can form ionic interactions. However, this protein does not generate water-resistant bonds to surfaces nor does it have cohesive strength. For those purposes, it is necessary to convert at least a portion of the tyrosine residues to dopa and permit crosslink formation to occur after surface adhesion is achieved. That is, it is necessary to mimic the natural mussel process in which the dopa form of the polyphenolic protein is applied and then rapidly... 

Organic matter (OM) ruminal digestibility tended to be lower for L than for S, but OM total tract digestibility did not differ between diets (Table 1). No difference among diets was observed for microbial, nonmicrobial and total N duodenal flows, but efficiency of microbial N synthesis tended to be higher for lupin diets. Lupin diets resulted in more faecal N and less urinary N than soybean meal diets. Yeast and the interaction between yeast and protein source were not significant for any parameter. 

It must be pointed out that yeast-mediated biotransformations may be complicated by side reactions that interfere or even dominate the desired conversion workup may be somewhat time consuming and messy due to the separation of the product from the huge amount of biomass. The ideal interactions between the yeast and the substrate are scarcely found in praxi. Ideal interactions between substrate yeast and product include that both substrate and product are able to pass the cell membrane, should be soluble in the fermentation medium, and must not inactivate the catalytic activity of the involved microbial enzymes. Finally, high turnover rates and high regio- and stereospecificity are also of high practical relevance. Some advice on how to deal with these basic problems often encountered in such biotransformations is provided in Fig. 1 [9,11,13,19,20]. 

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