TIMAR PETROS MENBERE2026-05-262026-05-262025-10http://41.89.96.81:4000/handle/123456789/3771This study tested the possibility of using the fruit and vegetable residues, namely banana peels, mango peels, and carrot pomace, which were sourced in Nakuru city, to produce xylanase using solid-state fermentation with Aspergillus brasiliensis. The substrates were dried (70°C, 24 h), milled (0.5mm particle size), and subsequently inoculated with Aspergillus brasiliensis spores (1 × 10⁶ spores/mL). The Box Behnken design was used to systematically optimize fermentation conditions by varying pH (4.0, 5.0, 6.0), temperature (25, 30, 35°C), and duration (96, 120, 144 h). The production of xylanase was suspected by the development of clear zones on xylan agar medium. ANOVA with Tukey’s post-hoc test (p less than 0.05) in Minitab and SAS 9.4 revealed that pH and cultivation time had significant effects, and not temperature, on enzyme activity. The optimal enzymatic performance was obtained at pH 4.2, 100.9 h of fermentation, and 25o C, indicating the presence of a strong interaction between pH and time. The crude enzyme extract was added to cookie formulations in concentration levels of 0 to 1500 IU, and enzymatic treatment significantly improved the texture of cookies, as shown by decreased hardness and increased fracturability, diameter, and thickness. Even when the dose of the enzyme increased, the parameters redness (a*) and yellowness (b*) were nearly remained constant, while lightness (L*) decreased. No significant modulation of farinograph characteristics was found, but pasting behaviour was modified; the values of viscosity varied significantly at most of the gelatinisation stages. Consumer acceptability tests showed a uniform high total liking score throughout the whole range of enzyme concentrations and a hedonic scale of scores that ranged between 6.00 and 6.40. Taken together, these results show that the valorization of fruit and vegetable waste to the production xylanase enzyme is successful and that xylanase can be used effectively to enhance the quality of cookies and, thus, provides a sustainable approach to waste management and food processingenThesis