Techno-functional and Rheological Transformation of Unripe Banana Flour: Kinetic Profiling of Five Lactic Acid Bacteria Strains

Abstract

Unripe banana flour (UBF) is a starch-rich ingredient with promising nutritional value but limited functional flexibility due to its high viscosity, strong gelation, and rapid retrogradation. This study systematically investigated the impact of lactic acid bacteria (LAB) fermentation on the properties of unripe banana flour (UBF) using five different strains, namely Lactiplantibacillus plantarum, Lactobacillus acidophilus, Lacticaseibacillus casei, Limosilactobacillus fermentum, and Levilactobacillus brevis. Time series fermentations were conducted over 20 h, with samples analyzed for proximate composition, starch characteristics, functional properties, and rheological behavior. Fermentation followed a time-progressive acidification and predigestion continuum captured by the first principal component (PC1), which explained 47.5% of the total variance. As pH declined during fermentation, the UBF matrix underwent structural degradation. Within this kinetic landscape, L. fermentum displayed the most vigorous behavior, reaching pH 4.0 at 15.10 h and producing the greatest structural breakdown. The degradation precipitated rheological collapse, reflected in marked reductions in peak viscosity and gel hardness, with L. plantarum showing the largest decrease in hardness (12.2%). Native structural constituents also declined significantly (p < 0.05), including resistant starch, total starch, and dietary fiber. This was confirmed by the strong negative Spearman correlation between resistant starch and titratable acidity (r = -0.937, p < 0.05). Conversely, depolymerization was associated with functional improvements including, water solubility index (r = 0.934 with titratable acidity, p < 0.05), oil absorption capacity, and emulsification capacity, while reducing the least gelation concentration. Principal component analysis further revealed a secondary protein/interfacial functionality axis (PC2), highlighting strain specific differences in the generation of surface-active components. L. brevis showed a unique transient positive excursion (PC2 = 1.649 at 16 h) indicative of superior early interfacial modification. The collective evidence demonstrates that LAB fermentation can convert UBF into a lower viscosity, high functionality ingredient with improved emulsifying and hydration behavior. These changes, largely driven by microbial metabolism, enable distinct formulation opportunities in gluten free doughs, extruded snacks, and emulsified systems, while also implying a nutritional trade-off due to irreversible losses in native resistant starch.