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Abstract
The objective of this study was to determine the anti-yeast effect of Lactobacillus spp. isolated from two popular Iranian cheeses known as Lighvan and Motal against food spoilage yeasts known as Rhodotorula mucilaginosa, Saccharomyces cerevisiae and Kluyveromyces lactis. Twenty strains of Lactobacillus were selected from Motal (16 isolates) and Lighvan cheeses (4 isolates). Anti-yeast activity was studied by Agar Spot and Well Diffusion Assay. Effect of pasteurization on inhibitory compounds was also investigated. Results showed that two strains of Lactobacillus brevis (M4 and M2) exhibited the highest anti- yeast activity in aforementioned methods, as well as tolerated pasteurization. M4 and M2 strains were inoculated into Doogh (a fermented yogurt drink) at two levels (106 and 108 cfu/ml). All samples were incubated in three storage temperatures (4, 25 and 37 °C) and were then examined for microbial parameters (Mold and yeast counts, Coliform, E. coli and Staphylococcus aureus) at specific intervals. Sample with M4 (106cfu/ml) showed superiority rather than control sample in microbial point of view. At temperatures of 25 and 37 °C, inoculated samples were not contaminated up to day- 21 and day-14, respectively. The propionic acid content for M4 and M2, was 14576.11 and 11697.3 ppm, respectively. Results indicate that incorporation of strain M4 (Lb. brevis) at a level of 106 cfu/ml can potentially postpone the yeast spoilage in Doogh and prolong the stability of this product. In conclusion, these strains had the highest activity against experimented yeasts.
Highlights
Fermented commodities present a crucial effect in human dietary all over the world owing to their beneficial effects on health
The aim of this study was to investigate the anti-yeast effect of Lactobacillus spp., isolated from Iranian raw milk Lighvan and Motal cheeses on Rhodotorula mucilaginosa, Saccharomyces cerevisiae and Kluyveromyces lactis as indicators for food spoilage yeasts in doogh both in vitro and in situ
In order to determine the in vitro anti-yeast activity of Lactobacillus strains in the culture medium, Agar Spot Assay with growing cells[16] and Well Diffusion Assay with the cell-free supernatant[17] were used
Summary
Fermented commodities present a crucial effect in human dietary all over the world owing to their beneficial effects on health. Yogurt drinks are known in the Middle East with various titles such as Lassi, Doogh, Yogurt and Ayran, and in Scandinavian countries, as acidophilus milk, Viili (a ropy, fermented milk that originated in Scandinavia, which is claimed to have various functional benefits and health-improving potential which is popular in Finland),[2]. Doogh has gained acceptable popularity and wide consumption in Iran and per capita consumption as well as industrial production has achieved noticeable growth in recent years. It has been estimated that almost 5–10% of world food production is lost as a result of fungal spoilage with economic losses[4]. The growth of particular fungi on food can lead to the production of mycotoxins, which are known to be toxic to humans and animals[5]. Sample code* M2 M3 M4 M5 M6 M7 M8 M9 M11 M12 M13 M15 M16 M17 M18 M19 M8(Lighvan milk) LF52 LF55 LF56
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