Determination of the anti-yeast activity of Lactobacillus spp. isolated from traditional Iranian cheeses in vitro and in yogurt drink (Doogh)

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 (10 6 and 10 8 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 (10 6 cfu/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 10 6 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. Fermented commodities present a crucial effect in human dietary all over the world owing to their beneficial effects on health. Fermentation is one of the ancient and most commercial approach applied for food preservation. The primary precedent exhibit that mankind was consuming 'acidified or fermented milk' dated to about 2000 years ago 1. 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 is a fermented dairy product that is obtained from the mixing of yogurt with water and some other additives such as salt and mint 2. Presently, 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. Acceptability of Doogh is not only related to the desirable sensory attributes but also to healthy fermented drink which make it accepted as national drink in Iran. Doogh has also gained high popularity in other countries according to the literature 3. Fungal spoilage of food and feed is a universal issue. It has been estimated that almost 5-10% of world food production is lost as a result of fungal spoilage with economic losses 4. Furthermore, the growth of particular f...

Microbial and Chemical Characteristics of Doogh (Iranian Fermented Milk Drink)

“…In current research, the amount of fungi in 15% of the tested samples was higher than the Iranian standard level (<10 2 CFU/mL). As far as Doogh and other fermented dairy products provides a selective condition for the growth of yeasts and molds due to their low pH, fungi are known as a major cause of spoilage of dairy products with side effects like CO 2 and acid production [10,12]. The most relevant fungi in Doogh are Kluyveromyces lactis, Saccharomyces cerevisiae, and Geotrichum sp.…”

“…The most relevant fungi in Doogh are Kluyveromyces lactis, Saccharomyces cerevisiae, and Geotrichum sp. [10]. Besides economic losses, shelf life, and sensory property reduction of the final product, mycotoxins as fungal by-products pose a crucial potential risks to consumer health [1,14].…”

“…High level of nutrients as well as low pH has made Doogh an ideal media for the proliferation of molds and yeasts [7]. Thus, microbial putrefaction referable to fungi describes as a serious complication for dairy industries, because of their capability to survive at low temperatures and acidic pH [10]. Different factors like the initial microbial quality of raw milk, inadequate thermal processing of milk, used starter cultures, and secondary microbial contaminations via equipment, air, ventilation, and packaging material have alter the quality and shelf life of the final product which in turn lead to the spoilage of Doogh by acid-resistant microorganisms, especially yeasts, molds, and bacteria during storage and safety reduction of this product [4,6,11,12].…”

“…Different factors like the initial microbial quality of raw milk, inadequate thermal processing of milk, used starter cultures, and secondary microbial contaminations via equipment, air, ventilation, and packaging material have alter the quality and shelf life of the final product which in turn lead to the spoilage of Doogh by acid-resistant microorganisms, especially yeasts, molds, and bacteria during storage and safety reduction of this product [4,6,11,12]. Fungal spoilage of Doogh is not only related to its consumers' acceptability and as a result of economic losses but also the growth of specific fungi can induce the production of mycotoxins, which are known to be severely harmful to humans [10].…”

Antifungal and antioxidant activity of two essential oils and Lactococcus lactis subsp. lactis extract on selected Iranian white cheese‐contaminating fungi

“…Yeasts such as Saccharomyces cerevisiae are also among the most important microorganisms responsible for dairy and beverage spoilage in the industry due to their ability to survive at low temperatures and acidic pH values, as well as the subsequent economic losses (Afzali et al . 2020).…”