Screening of Antifungal Lactic Acid Bacteria as Bioprotective Cultures in Yogurt and a Whey Beverage

The demand for preservative-free food products is rising, and biopreservation is a potential alternative to replace or reduce the use of chemical preservatives. The objectives of this study were to assess the antifungal activity of lactic acid bacteria (LAB; n = 98) and the efficacy and applicability of the chosen bioprotective cultures against fungal spoilers in dairy products. First, 14 antifungal strains were preliminarily screened by in vitro tests against Pichia pastoris D3, Aspergillus niger D1, Geotrichum candidum N1, Kluyveromyces marxianus W1, and Penicillium chrysogenum B1 and validated by challenge tests in yogurt, indicating that the fungal-inhibiting activity of LAB was species specific and yogurt fermented with antifungal LAB cultures was more effective in extending shelf life. Second, the chosen 14 LAB strains were identified by the 16S rDNA sequence analysis and carbohydrate fermentation test. The results were as follows: nine strains were Lactobacillus plantarum, three were Lactobacillus paracasei, one was Enterococus faecium, and one was Lactobacillus rhamnosus. Among them, active L. plantarum N7 was the chosen and studied factor affecting antifungal activity by using the response surface methodology. Finally, in situ tests were conducted to validate the activity of L. plantarum N7 in actual dairy products (whey beverages). Physicochemical and microbial indices of whey beverages during storage indicated that antifungal L. plantarum N7 could slow yeast growth and be candidates of interest for industrial applications. HIGHLIGHTS Nine strains of 98 LABs showed fungal-inhibiting activity in vitro and in yogurt. Glucose, time, and temperature were the factors affecting antifungal activity. The effect of 3% of L. plantarum N7 inhibited yeast growth best in whey beverages.

Automated summary

The study found that certain strains of lactic acid bacteria (LAB) have species-specific antifungal activity, with fermented yogurt demonstrating an extended shelf life. Among the identified LAB strains, active L. plantarum N7 was found to be effective in inhibiting yeast growth in whey beverages, showing potential for industrial applications.