Influence of addition of proteolytic strains of Lactobacillus delbrueckii subsp. bulgaricus to commercial ABT starter cultures on texture of yoghurt, exopolysaccharide production and survival of bacteria

Abstract

The effects of addition of proteolytic strains of Lactobacillus delbrueckii subsp. bulgaricus to commercial ABT starter cultures on the texture of yoghurt, exopolysaccharide production and survival of starter bacteria were studied. The firmness of set yoghurts was measured with a cone-penetrometer and the apparent viscosity with a Brookfield viscometer. Exopolysaccharides (EPS) was extracted by precipitation with ethanol. Supplementation of a proteolytic strain of L. delbrueckii subsp. bulgaricus 2501 or 2515 to ABT-1 or ABT-4 starter culture reduced the fermentation time in making yoghurt. Yoghurts made with ABT-1 and ABT-4 with added L. delbrueckii subsp. bulgaricus 2501 fermented in the shortest time of 5 h and 33 min and 5 h and 8 min, respectively. Quantities of EPS extracted from the different yoghurt batches did not show any significant differences (P < 0.222). In general, the firmness improved with the addition of the proteolytic strains of L. delbrueckii subsp. bulgaricus. Addition of L. delbrueckii subsp. bulgaricus to ABT-1 and ABT-4 did not produce significant (P < 0.001) improvement in firmness of yoghurt compared with the mix starter batches. Significant differences (P < 0.001) were observed in the viscosity of yoghurts supplemented with different combinations of starter cultures. However, the amounts of EPS isolated from yoghurt cultures did not correlate with the viscosities of the yoghurts. Viability of probiotic bacteria improved in the yoghurt product made with mix starter culture with the added L. delbrueckii subsp. bulgaricus proteolytic strains. © 2002 Elsevier Science Ltd. All rights reserved.