Development of an enzyme-assisted fermentation for high-protein rice snacks: design, implementation, evaluation

Thesis Abstract

The growing demand for healthier, protein-rich snack options with enhanced digestibility and functional properties drives the need for novel processing approaches in cereal-based foods. This study addresses the challenge of delivering high-protein rice snacks with improved sensory acceptance and nutritional quality through enzyme-assisted fermentation, integrating bioprocessing with product design to span formulation, processing, and evaluation. The aim is to develop, implement, and evaluate an enzyme-assisted fermentation protocol that augments protein availability, reduces antinutritional factors, and enhances textural and shelf-stability attributes of rice-based snacks. Specific objectives are (1) to optimize a co-fermentation system employing selected proteolytic and amylolytic enzymes in combination with Lactobacillus plantarum and Saccharomyces cerevisiae inocula to produce high-protein rice snack prototypes; (2) to quantify protein digestibility, amino acid profiles, in vitro starch hydrolysis, and antinutritional factor reduction (phytates and tannins); (3) to characterize physicochemical properties including water activity, texture (Logflexural rigidity and fracture force), and colorimetric parameters; (4) to evaluate sensory acceptability and consumer suitability through a structured hedonic test and willingness-to-pay assessment; (5) to model process optimization and quality evolution during storage using response surface methodology and shelf-life modeling. The research adopts a mixed-methods design combining experimental bioprocessing and consumer-centered evaluation, underpinned by the theories of enzyme kinetics and the Food Expectancy Model to link biochemical changes with sensory perception. The population comprises commercial-grade parboiled rice, heat-stable proteases and amylases, and starter cultures with documented proteolytic activity; a 3×3 factorial design explores enzyme concentrations (0.5%, 1.0%, 1.5% w/w) and fermentation durations (12 h, 24 h, 36 h). A pilot-scale fermentation system (5 kg batches) generates prototype snacks for laboratory analysis. Data collection instruments include high-performance liquid chromatography (HPLC) for amino acid profiling, proximal analysis and Kjeldahl nitrogen for total protein, HPLC/GC for aroma-active compounds, spectrophotometric methods for phytate and tannin content, texture analyzers for mechanical properties, a colorimeter for surface color, and a nine-point hedonic scale questionnaire for consumer testing with 120 untrained panelists stratified by age and gender. Validity and reliability are ensured through calibration of analytical instruments, standard reference materials, and test-retest procedures for sensory data. Data analysis employs ANOVA to detect factorial effects on digestibility, antioxidant potential, and textural attributes; Tukey’s HSD for post hoc comparisons; multiple regression to relate enzymatic parameters to product quality indicators; and principal component analysis (PCA) to synthesize sensory and instrumental results. Regression models will assess the relationship between fermentation time, enzyme loading, and protein digestibility. The study anticipates that enzyme-assisted fermentation will significantly improve in vitro protein digestibility (target >85%), raise essential amino acid availability (notably lysine and leucine), and reduce phytic acid by 25–40%, while maintaining acceptable textural properties ( hardness within 3.5–5.0 N) and desirable color indices. Market-relevant outcomes include enhanced sensory scores for crispness and roasted aroma, and a positive consumer willingness-to-pay differential compared with conventional rice snacks. The contribution to knowledge lies in demonstrating a scalable bioprocess that couples enzymatic modification with microbial fermentation to elevate protein quality and reduce antinutritional factors in cereal snacks, providing a framework for designing functionally enhanced, protein-rich snacks with extended shelf life. The study concludes that carefully optimized enzyme combinations and fermentation duration can produce high-protein rice snacks with superior nutritional profiles and consumer acceptance, offering a viable route for food industry adoption. Recommendations include scaling to industrial fermenters with inline monitoring of proteolysis and amylolysis, integrating real-time texture analysis during processing, and exploring additional starter cultures to tailor flavor and antioxidant profiles for diverse markets.