Abstract
The study aims to isolate the yeast strains that could be used effectively as baker's yeast and compare them with the commercial baker's yeast available in the market of Nepal. A total of 10 samples including locally available sources like fruits, Murcha, and a local tree “Dar” were collected from different localities of Bhaktapur, Kavre, and Syangja districts of Nepal, respectively. Following enrichment and fermentation of the samples, 26 yeast strains were isolated using selective medium Wallerstein Laboratory Nutrient Agar. From the differential tests which included morphological and microscopic observation and physiological and biochemical characterization such as nitrate reduction and lactose utilization tests, 8 strains were selected as possible Saccharomyces strain. The selected strains were further assessed for their efficient leavening ability by tests such as ethanol tolerance, osmotolerance, invertase test, and stress exclusion test. The three most potent strains ENG, MUR3B, and SUG1 isolated from grape, Murcha, and sugarcane, respectively, were used in the fermentation and baking of dough. These strains also carried a possibility of being used as industrial baker's yeast.
Highlights
Saccharomyces cerevisiae, the microorganism used in baking industry as a leavening agent [1], with the advancements in bread industry, has been continuously improvised for decades [2]
The fermentation products like vitamins and amino acids are responsible for the health and nutritional benefits that are obtained from bread [7]
The selected colonies were subsequently subcultured on Yeast Malt (YM) Agar medium supplemented with chloramphenicol (0.01%) to obtain pure isolates
Summary
Saccharomyces cerevisiae, the microorganism used in baking industry as a leavening agent [1], with the advancements in bread industry, has been continuously improvised for decades [2]. The main yeast strain is commonly reported to be responsible for alcoholic fermentation [3]. This yeast utilizes the hexose sugars especially maltose to produce CO2, ethanol, and variety of secondary metabolites such as esters, aldehydes, and amino acids that contribute to the development of flavor and aroma of the fermented food [4, 5]. The fermentation products like vitamins and amino acids are responsible for the health and nutritional benefits that are obtained from bread [7]. Yeast exists in natural environment like plant tissues, fruits, grains, leaves, dung, soil, and other fermented products [8]. Yeast strains present on fruit surfaces are able to ferment variety of sugars to alcohol and can withstand high alcohol concentration
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