Factors Affecting Rye Sour Dough Fermentation with Mixed-culture Pre-ferment of Lactic and Propionic Acid Bacteria

Abstract

The effect of factors such as dough yield, temperature and pre-ferment quantity on rye dough fermentation using mixed-culture pre-ferments of Lactobacillus brevis together with Propionibacterium acidi-propionici or P. jensenii was examined according to a statistical experimental design and empirical modelling. The dough yield and temperature were the most dominating factors affecting the second-degree polynomial models to described pH, titratable acidity, lactic acid concentration, acetic acid concentration, molar ratio of lactic to acetic acid and propionic acid concentration during rye dough acidification. Further, under the experimental rye sour dough fermentation conditions, a pH less than 4 and a typical titratable acidity of about 16 (ml 0·1 M NaOH/5 g flour) of fermented sour were obtained usually in 17 to 24 h with both bacteria combinations used in the pre-ferment. A dough yield of 320%, temperature of 35°C and amount of pre-ferment of 32% (rye flour weight basis) gave the highest propionic acid concentration of 0·55 g/100 g sour dough with the pre-ferment of L. brevis together with P. acidi-propionici. Titratable acidity values of about 27 to 35 ml 0·1 M NaOH/5 g flour, indicative of medium to strong sour rye dough, were obtained, and the lactic to acetic acid molar ratio of 1·9 to 4·0 were within the optimal range. Consequently, the mixed-culture pre-ferment of lactic and propionic acid bacteria appeared to be a potential alternative along with conventional starters in rye sour dough fermentation, providing for an improved mould-free shelf-life of bread.