Abstract: Pediococcus acidilactici L-19, a strain capable of phytase with high yield, was used as a starter culture for black bean sourdough bread production. The effects of the starter culture on the protein nutritional quality and baking properties of black bean sourdough bread were studied by measuring amino acid composition, nutritional properties, in vitro protein digestibility (IVPD), textural characteristics, ultrastructure and sensory properties. The phytase negative strain K-12 was used as a control. The results showed that after addition of black bean sourdough fermented by lactic acid bacteria, both the protein nutritional quality and baking properties of bread were significantly improved, with the most significant effect being observed in black bean bread prepared using (L-19SDB). Compared with control black bean bread (BB), phytic acid content of L-19SDB was decreased by 60.68% while IVPD was increased from 64.70% to 73.93%, and total amino acid content was increased by 73%. Moreover, as compared with the other three groups, L-19SDB had a better amino acid profile in terms of the ratio of essential amino acids to total amino acids (E/T), essential amino acid index (EAAI) and biological value (BV). Compared with BB, L-19SDB and K-12SDB showed an increase in specific volume of 31.45% and 23.59% and a decrease in hardness of 68.79% and 56.59%, respectively. ImageJ analysis results showed that the stomatal distribution of L-19SDB crumb was more uniform and this bread had the highest overall acceptability (7.72 points out of 9).

Key words: phytase; amino acid composition; in vitro protein digestibility; black bean sourdough; baking characteristics