ABSTRACT

The aim of this study was to assess the growth and physiological properties of top and bottom fermenting yeasts from palm wine. 10 randomly selected palm wine samples were collected from different locations within Ikwuano local government area of Abia state. The samples were cultured by streaking and spread plate method, Yeasts were isolated from palm wine and subsequently characterized and identified. Results showed that (two top and two bottom fermenters) were isolated with varying prevalence in palm wine samples. The four isolates were Saccharomyces cerevisiae, Saccharomyces globosus (top fermenters), Saccharomyces carlsbengensis and Saccharomyces uvarum (bottom fermenters).  S. cerevisiae was found in all samples while S. globosus and S. carlsbengensis had 80% and 60% respectively with S. uvarum having the least occurrence (40%). The different yeasts have similarities in their growth physiological activities. The isolates show potentials to manage growth stress conditions. S. cerevisiae, had the best temperature tolerance (+ at 420C) while S. uvarum recorded the least growth (+) at 39oC.  Some of the isolates demonstrated flocculation ability and were positive in fermentative and assimilation test for glucose and other sugars. Three of the yeast isolates did not grow well at pH 2.0 but rather had just slight growth level (+). S. uvarum did not grow at pH 2.0. At pH 4.0, S. cerevisiae and S. globosus grew profusely (+++), S. carlsbengensis and S. uvarum had moderate growth (++). All the yeasts grew very well at pH 6.0. At ethanol concentration less than 10% (≤ 10% v/v), three of the isolates except  S. uvarum recorded slight growth at 16% ethanol concentration. None was able to grow at 19% ethanol concentration. CuSo4 tolerance test recorded moderate growth (++) for each yeast at 1.0g/l copper, slight growth (+) at 2.0g/l and no growth at 3.0g/l. All the yeasts were able to grow at 0.01% - 0.02% of sodium metabisulfite, the isolates recorded low response at 0.03% concentration. Only S. cerevisiae and S. globosus had slight growth at 0.04% but S. carlsbengensis and S. uvarum show no growth at 0.04% and none of the isolates was able to grow at 0.05% Comparatively, sucrose was the most suitable sugar from all the yeasts while S. cerevisiae had the highest CO2 production capacity among with 0.27ml/min. S. uvarum had the least CO2 production rate with 0.16ml/min. The result showed the ability of the yeasts to adapt to various parameters and the level of tolerance was dependent on intensity or concentration of the various parameters.