Rēwena sourdough fermentation with Propionibacterium freudenreichii: Impacts on structure and texture

Abstract

Rēwena sourdough is a unique form of bread that has cultural significance in Māori cuisine. It is unique due to its use of mashed potatoes as a carbohydrate source in its starter culture (Sun et al. 2022). Propionibacterium freudenreichii is a gram-positive probiotic that improves human intestinal health. P. freudenreichii also acts as a Vitamin B12 producer when added to bread (Zhang et al. 2023). P. freudenreichii conducts CO2 production during fermentation meaning it can directly affect the structure and texture of fermented food products. The aim of this work was to characterise the impacts P. freudenreichii addition has on the structure and physical characteristics of Rēwena sourdough. This work was conducted in two stages, firstly the sourdough recipe was optimised. Variables considered included Potato variety, proofing time, and proofing temperature. The second stage investigated the effects of P. freudenreichii addition to either the sourdough starter or directly to the sourdough dough (before proofing). Sourdough structure was measured using image analysis tools and instrumental texture analysis was conducted. Optimal sourdough was prepared using the Van Rose potato variety proofed at room temperature for 2 h. The addition of P. freudenreichii to the starter culture significantly decreased (P<0.05) the Number and significantly increased (P<0.05) the Total Area (%) of gas bubbles in the sourdough crumb (compared to the Control). There were no significant differences (P > 0.50) in the sourdough structure due to the direct addition of P. freudenreichii to the sourdough dough (compared to the Control). It was also found that the method of P. freudenreichii addition did not significantly (P > 0.50) affect the Hardness, Springiness, or Gumminess of the sourdough. P. freudenreichii has been shown to be a potential tool as a bio-fortification tool in foods however, its method of addition may affect food structures.