ABSTRACT
BACKGROUND: Food spoilage caused by molds is a severe problem. In food and feed, e.g. dairy products, sourdough bread and silage, lactic acid bacteria are used as starter cultures. Besides lactic and acetic acid, some strains produce other low molecular weight compounds with antifungal activities. One of these metabolites is phenyllactic acid (PLA), well known for its antifungal effect. The inhibitory effect of PLA has only partially been investigated, and the objective of this study was to elucidate in detail the antifungal properties of PLA. RESULTS: We investigated the outgrowth of individual conidia from Aspergillus niger, Cladosporium cladosporioides and Penicillium roqueforti, and observed the morphologies of resulting colonies on solid media using different acid concentrations. We found that PLA inhibits molds similar to weak acid preservatives. Furthermore, it has an additional activity: at sub-inhibitory concentrations, fungal colonies displayed slower radial growth and inhibited sporulation. The L isoform of PLA is a more potent inhibitor than the D form. Increased expression of phiA was observed during PLA treatment. This gene was initially identified as being induced by Streptomyces-produced macrolide antibiotics, and is shown to be a structural protein in developed cells. This suggests that PhiA may act as a general stress protectant in fungi. CONCLUSION: From a food protection perspective, the results of this study support the usage of lactic acid bacteria strains synthesizing PLA as starter cultures in food and feed. Such starter cultures could inhibit spore synthesis, which would be beneficial as many food borne fungi are spread by airborne spores.
Subject(s)
Antifungal Agents/pharmacology , Aspergillus niger/drug effects , Cladosporium/drug effects , Lactates/pharmacology , Penicillium/drug effects , Spores, Fungal/drug effects , Antifungal Agents/metabolism , Aspergillus niger/growth & development , Aspergillus niger/ultrastructure , Cladosporium/growth & development , Cladosporium/ultrastructure , Food Preservation , Fungal Proteins/genetics , Fungal Proteins/metabolism , Gene Expression Regulation, Fungal/drug effects , Lactates/metabolism , Lactobacillus/physiology , Penicillium/growth & development , Penicillium/ultrastructure , Spores, Fungal/growth & development , Spores, Fungal/ultrastructure , Stress, Physiological/geneticsABSTRACT
The crossing of Saccharomyces strains by spore conjugation is one of the ways to obtain new starter cultures for the fermentation industry. One of the major difficulties of this practice is the identification of the newly formed hybrids. In this work we describe an effective molecular method for the validation of Saccharomyces intraspecific crosses. The method described is based in the hypothesis that hybrids constructed by spore conjugation contain the sum of the genomes of both parental strains. As a consequence, the conjugation of spores of two yeasts showing different genomic fingerprinting profiles will result in a hybrid culture that will show the sum of both profiles. We demonstrated that the detection of polymorphism in two genes containing minisatellite-like sequences, either SED1 or AGA1, is suitable for this purpose. Using this strategy we were able to validate 15 crosses out of 162 hybridization attempts.
Subject(s)
Industrial Microbiology/methods , Minisatellite Repeats/genetics , Saccharomyces cerevisiae/physiology , Cell Adhesion Molecules/genetics , Membrane Glycoproteins/genetics , Polymorphism, Genetic , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/geneticsABSTRACT
We propose an efficient and time-saving strategy for starter culture selection. Our approach is based on the accomplishment of 3 phases: (i) the selection of yeast strains dominating spontaneous fermentations, (ii) the selection among the dominant strains of those showing the best technological characteristics, and (iii) the final selection among good technological strains of those showing the desired qualitative traits. We applied this approach to wine fermentations, even though the same strategy has the potential to be employed for the selection of any type of starter culture. We isolated and identified yeast strains at the mid- and final stages of 6 spontaneous fermentations carried out in 3 different Spanish wineries. We identified all strains as Saccharomyces cerevisiae by restriction fragment length polymorphism of the ribosomal DNA internal transcribed spacer region, and subsequently distinguished each strain by analyzing the polymorphism of the inter-delta regions. Strains that were detected both at the mid- and final stages of the fermentation were considered dominant. Four dominant strains were finally selected and tested in pilot-scale fermentation, and their performance was compared with that of a commercial wine strain. All dominant strains showed good fitness and resulted suitable to be employed as starter cultures. One of the dominant strains isolated in this study is currently commercialized.
