Xylanase Production from Fruit and Vegetable Waste Using <i>Aspergillus brasiliensis</i> and Its Application in Cookie Production

This study assessed the potential of using fruit and vegetable waste, including banana and mango peels and carrot pomace, to produce xylanase enzymes via solid-state fermentation with Aspergillus brasiliensis. Fruit and vegetable waste was collected from Nakuru city, dried for 24 hours at 70˚C, then ground into 0.5 mm powder. Box-Behnken Design (BBD) was employed to optimize fermentation parameters, where pH levels were adjusted to 4.0, 5.0, and 6.0. The substrates were inoculated with 1 × 106 spores/mL of Aspergillus brasiliensis and then incubated at 25˚C, 30˚C, and 35˚C for a duration of 96, 120, and 144 hours in triplicate. Aspergillus brasiliensis produced xylanase, which is indicated by a clear zone around a sample hole in a medium containing xylan. Data analysis using Minitab and SAS 9.4, with significance levels set at p < 0.05, revealed that pH and cultivation time significantly influenced enzyme activity, whereas temperature did not. Optimal conditions for maximal enzyme activity were pH 4.2, a cultivation time of 100.9 hours, and a temperature of 25˚C. Interaction effects between pH and time impacted enzyme activity. Further evaluation included the effects of enzyme concentrations (ranging from 0 to 1500 IU) on various properties of cookies. Xylanase treatments significantly affected cookie texture, with reductions in hardness and increased fracturability, diameter, and thickness with increasing enzyme concentration. Changes in color and viscosity were noted, although Farinograph properties remained relatively unaffected. Changes in time and temperature, depending on enzyme concentration, had notable effects on the onset of gelatinization, maximum viscosity, and end of the cooling period. Consumer acceptability scores indicated high ratings for cookies treated with xylanase, reflecting positive perceptions of the product. This study highlights the potential of utilizing fruit and vegetable waste for xylanase production, with promising implications for waste utilization and food processing.