Isolation of amylolytic bacteria from sourdough, determination of their technological properties, and investigation of their use in bread making

Bread is considered a staple food in Türkiye thanks to its high consumption rate and cultural significance. Recently, the growing interest in functional foods has also increased the demand for sourdough bread. Amylolytic bacteria present in sourdough convert starch into fermentable sugars, thereby supporting the fermentation process. As a result, the nutritional value, aroma profile, and shelf-life of sourdough bread are positively affected. The present study aimed to isolate amylolytic bacteria from sourdough samples obtained from different bakeries, determine their technological properties, conduct phenotypic and genotypic identification, and examine the effects of selected superior strains on bread quality. A total of 68 bacterial isolates were obtained from seven sourdough samples collected in Antalya and Isparta. Among these isolates, 13 were found to produce acid and gas from glucose, while 17 produced exopolysaccharides (EPS). Amylolytic activity was determined spectrophotometrically, and the highest activity was detected in the Pediococcus pentosaceus (P. pentosaceus) IF-53-2 strain at 0.134 U/mL fructose equivalent. For bread trials, P. pentosaceus NU-523, P. pentosaceus IF-53-2, Levilactobacillus brevis (L. brevis) ET-530-2, and Companilactobacillus mindensis (C. mindensis) FH-540-1 were selected. The four selected strains, together with commercial compressed yeast and laboratory-produced sourdough, were used to produce six different bread groups (M: commercial compressed yeast; EM: sourdough; AO: non-amylolytic lactic acid bacteria (LAB); AB: amylolytic LAB; A: both types of LAB; EME: a combination of commercial yeast and sourdough). Group A exhibited the highest weight (p<0.05). In contrast, Group EM showed the lowest volume (p<0.05). Regarding baking loss, the lowest value was recorded in Group AB (23.23 g, 11.36%), whereas the highest was in Group EME (36.16 g, 17.18%). The widths of the loaves ranged from 60 to 90 mm, their lengths from 65 to 73.3 mm, and their heights from 58.3 to 70 mm (p<0.05). Also, the groups were analyzed for total titratable acidity (8.20±0.74–10.6±2.33 mL), pH (4.97±0.009–6.12±0.07), and ash content (1.90–2.38%). The highest dry matter content was in Group M at 24 h (65.84%), while Group EM had the highest value on day 7 (68.45%).(p>0.05). In color analysis, the highest L* value of the crust was found in Group EM (p<0.05), and the highest crumb L* value was recorded in Group M (p<0.05). There were no statistically significant differences among groups for a* and b* values (p>0.05). Texture profile analysis showed that, after 24 h of storage, Group EM had the firmest crumb, while Group EME exhibited the softest texture (p<0.05). Firmness increased during storage, particularly in Groups AB and AO, while springiness generally decreased, with Group AB showing the lowest values (p<0.05). Cohesiveness was highest in Group EM but tended to decline over time in the other groups (p<0.05). Gumminess and resilience were higher in Groups AB and EM, whereas Group M displayed the lowest values (p<0.05). Due to the longer fermentation time, staling in Group EM was more pronounced, with greater firmness and textural deterioration. In contrast, the control groups M and EME demonstrated more stable textural properties throughout storage (p<0.05). Based on staling rates calculated from firmness, Group AO exhibited the fastest staling between days 3 and 7 (109.08%), while Group AB showed a moderate increase of 40.10% between days 1 and 7 (p<0.05). Sensory evaluation indicated that Group AB received the highest score, while Group EM had the lowest (p<0.05). In conclusion, improvements in quality parameters such as staling rate, baking loss, and loaf dimensions were achieved in Group AB, produced with P. pentosaceus IF-53-2 and C. mindensis FH-540-1. Furthermore, the fact that the Group AB received the highest overall acceptability score in sensory evaluation highlights the potential of these amylolytic bacteria to be used as starter cultures in bread production.