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Title: MODELING GROWTH OF SACCHAROMYCES ROSEI IN CUCUMBER FERMENTATION

Author
item PASSOS, FREDERICO - U. FED. DE VICOSA, BRAZIL
item Fleming, Henry
item FELDER, RICHARD - NCSU
item OLLIS, DAVID - NCSU

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cucumbers are fermented in brine primarily by naturally occurring lactic acid bacteria that are present on the fruit. These bacteria produce lactic acid from natural sugars of the cucumber, which, in combination with salt in the brine, results in preservation of the cucumbers. Unfortunately, the concentration of lactic acid produced is too high for a desirable flavor and must be reduced after fermentation by washing part of it from the fermented cucumbers. This results in removal of flavorful compounds and nutrients that are desirable and creates a waste disposal problem. This paper describes how selected cultures of yeasts might be used in combination with lactic acid bacteria to reduce the concentration of lactic acid in fermented cucumbers. The information in this paper is based on the mathematical prediction of the growth of the bacteria and yeasts in cucumber juice. If the prediction model can be applied to whole cucumbers, it may be possible to improve the flavor, as well as reduce processing wastes in the preservation of cucumbers by fermentation.

Technical Abstract: Objectives of this study were to assess the effects of key variables involved in cucumber fermentation on growth of the yeast, Saccharomyces rosei, and to develop a mathematical description of those effects. The growth medium for the studies was cucumber juice. Effects of concentrations of lactic, acetic, and hydrochloric acids and sodium chloride on growth at 30 deg C were determined in batch culture. Effect of substrate concentration on the specific growth rate was also defined. The specific growth rate decreased from 0.355 h-1 at pH 6.0 to 0.189 h-1 at pH 3.2. The undissociated form of lactic acid was more inhibitory than that of acetic acid. A predictive equation for specific growth rate was developed for predicting growth of S. rosei in batch culture. The molar yield of ethanol was 1.75 (+/-0.07) mM ethanol per mM hexose. Malate was not utilized, and glycerol was produced. The apparent biomass yield under anaerobic condition was 12.2 (+/-1.3) g cells/mol hexose. Aerobically, the biomass yield was 30.7 g cell/mol hexose. Similar specific growth rates were observed anaerobically (0.358 h-1) and aerobically (0.352 h-1). The predictive model for growth of S. rosei in cucumber juice should prove useful in modeling the mixed culture (yeast and lactic acid bacteria) fermentation of brined, whole cucumbers.