Development and Characterization of Biscuits Prepared from Fermented Sweet Potato (Ipomoea batatas L.), Spirulina (Spirulina platensis L.), and Wheat (Triticum aestivum L.) Flours

Abstract

Owing to its high energy value and rich nutritional composition, Ipomoea batatas L. is a promising ingredient for food formulations. However, its relatively low protein content and the presence of flatulence-inducing sugars limit its wider use. Due to its high nutritional value, spirulina represents a suitable complementary ingredient for overcoming these limitations. This study evaluated the potential of fermented sweet potato and spirulina powders as partial substitutes for wheat flour in the production of protein-enriched biscuits. Sweet potatoes were fermented at room temperature for 96 h, then dried and milled into powder. Design-Expert 13 software was used to optimize formulations containing wheat flour (WF, 40–90%), spirulina powder (SP, 0–10%), and fermented sweet potato powder (FSPP, 10–50%). The resulting formulations were used to prepare biscuits, which were subsequently evaluated for their physicochemical, functional, and sensory properties. During sweet potato fermentation, lactic acid bacteria exhibited the highest microbial counts, reaching 7.9 ± 0.36 log CFU/g after 48 h, suggesting potential health benefits associated with the use of FSPP. The biscuit formulation containing 33% FSPP, 57% WF, and 10% SP exhibited the highest protein content (12.41 ± 0.05 g/100 g DM). However, the formulation containing 27% FSPP, 68% WF, and 5% SP showed the highest sensory acceptability. This formulation had a hardness of 3.70 N and real and apparent water absorption capacities of 102.94% and 115.39%, respectively. These findings demonstrate that fermented sweet potato and spirulina flours can successfully replace part of the wheat flour used in biscuit production, resulting in nutritionally enhanced, energy-rich products with acceptable technological and sensory properties.