IJCBS, 23(3) (2023): 63-67 Azhar., 2023 63 Survival of Isolated Probiotic Yeast Strains from Kefir Towards Bile and Acidic Environments Azhar, M.A 1 & Munaim, M.S. 2 1,2 Faculty of Chemical and Process Engineering Technology, Universiti Malaysia Pahang As-Sultan Abdullah, Lebuh Persiaran Tun Khalil Yaakob, 26300 Kuantan, Pahang, Malaysia. Abstract Probiotic yeast is one of the most important probiotics in kefir drinks and has been shown to have positive effects on gut health. The abundance of probiotic yeast strains in kefir drinks provides an opportunity to identify potential probiotic yeast as dietary supplements or functional food. Currently, yeast products are not as widely available as bacterial strains, but this is expected to change in the near future. Probiotics must resist acid and bile and adhere to the intestinal surface to thrive and colonise the gastrointestinal tract. Therefore, this study aims to investigate the ability of locally isolated yeast strains to resist acid and bile stress. An in vitro experiment was conducted using sample strains isolated from kefir beverages such as Kodamaea ohmeri, Kazachstania unispora, Saccharomyces cerevisiae, and Saccharomyces boulardii. Acid tolerance was determined by varying the pH of YEPD broth from 2 to 7, and bile tolerance was determined using YEPD broth with bile salt concentrations of 0%, 0.3%, 0.5%, and 1%. The study findings show that most isolated yeast strains survive acidic and bile environments. They were able to survive pH 3 for 24 hours (about log 6 CFU/mL). Only Saccharomyces boulardii and Kodamea ohmeri could survive for 24 hours in 1% bile acid (log 6.41 to log 7.34 CFU/mL), whereas all strains survive in 0.3% bile salt (log 3.42 to 8.95 CFU/mL). This study shows that all isolated yeasts have remarkable potential probiotic properties. Keywords: Probiotics; yeast; acid tolerance; bile tolerance; Saccharomyces Full length article *Corresponding Author, e-mail: akmalazhar@ump.edu.my 1. Introduction Fermented foods have long been an important part of the human diet. Fermentation is one of the most common ways of food processing, as it prevents food spoilage and extends its shelf life [1]. Various fermented foods are traditionally produced worldwide, including wine, beer, yoghurt, kimchi, milk, cereals, soybeans, fruit, and fish [2]. The microorganisms and by-products produced during fermentation contribute to the unique taste and texture of fermented foods. The beneficial microorganisms are known as probiotics. FAO-WHO defines probiotics as "living microorganisms that provide health benefits to the host when administered in sufficient quantity" [3]. In fact, probiotics have functional capacities with anticancer, antigenotoxic, antioxidant, anti-inflammatory, osteoporotic, antihypertensive, and antidiabetic potentials [4]. In gastroenterological therapy, most probiotic products contain strains of lactic acid bacteria. However, it has been reported that only certain yeast strains can act as probiotics, such as Kluyveromyces marxianus, Saccharomyces boulardii, Pichia kudriavzevii, and Debaryomyces hansenii [5]. Yeast cells are 10 times larger than bacterial cells due to their larger size, giving them an advantage in colonising mucosal surfaces. They are resistant to antibiotics, which makes them suitable candidates for treatment in combination with antibiotics. There is also no evidence of antibiotic resistance gene transfer [6]. In addition, certain yeasts have beneficial probiotic properties such as resistance to gastric bile and acid as well as an antibacterial effect on intestinal infections. Currently, yeast products are not widely used as bacterial strains, but this trend will likely change soon. Probiotic yeast as one of the main probiotics in kefir has shown to have positive effect on gut health. Kefir is a fermented milk drink that originated from the Caucasus region. It is made by adding kefir grains to milk, which then ferments to produce a slightly acidic, fizzy drink. Kefir is rich in probiotics, which contain yeast and bacteria that are beneficial for gut health. The high proportion of a probiotic yeast strain in kefir drink provides an opportunity to identify probiotic yeast that can be used as dietary supplements or functional food. However, to develop an oral probiotic formulation, the probiotic microorganism should remain viable during the administration and transport to the recipient. At least 10 6 CFU/g or mL of viable probiotic organisms in the small intestine is recommended for them to be useful [7]. International Journal of Chemical and Biochemical Sciences (ISSN 2226-9614) Journal Home page: www.iscientific.org/Journal.html © International Scientific Organization