Adriana Paucean

Carbohydrate metabolic conversions to lactic acid and volatile derivatives, as influenced by Lactobacillus plantarum ATCC 8014 and Lactobacillus casei ATCC 393 efficiency during in vitro and sourdough fermentation

The use of sourdough returned to be popular due to its beneficial nutritional, sensorial properties and physical features. In this study, two types of experiments aimed to evaluate comparatively the efficiency of two Lactobacillus (Lb.) strains, Lactobacillus plantarum ATCC 8014 and Lactobaciluscasei ATCC 393, to metabolize different carbohydrates (glucose, fructose, maltose and sucrose) in vitro and to compare their efficiency, combined with/without Saccharomyces cerevisiae on sourdough fermentation. Their efficiency was monitored by cellular growth dynamics, pH values and metabolite production (lactic and acetic acid, volatile derivatives) determined by HPLC and GC–MS analysis. Lb. plantarum ATCC 8014 was, generally, more efficient than Lb.casei for carbohydrate consumption in vitro and release of lactic acid. Unexpected, Lb.casei was able to produce trehalose in vitro, especially when glucose and sucrose were added in media. During sourdough fermentation, Lb. plantarum had a superior growth dynamic and a dominant nonaerobic fermentation, opposite to Lb.casei. By the addition of yeast to lactobacilli after a short-time lactic fermentation, a combined nonaerobic and aerobic fermentation was noticed, reflected by a more complex mixture of volatile derivatives. In vitro, both Lb. strains produced seven volatile compounds (carbonyl derivatives), but during sourdough fermentation, especially after yeast addition, a complex mixture of alcohols, carbonyl derivatives and acetate esters were determined. Lb. strains (especially Lb. plantarum) determined a moderate volatiles production dominated by alcohols, while addition of yeast to Lb. intensified the volatiles’ production and increase the alcohols proportion against carbonyl derivatives.