The Role of Enzyme Loading on Starch and Cellulose Hydrolysis of Food Waste

Abstract

Sugars production from secondary resources has been recognised as a strategic process unit within the valorisation routes of waste. In this context, food waste (FW) as an abundant waste stream with elevated concentrations of glucose and carbohydrates (cellulose, starch) could stand as a suitable feedstock for saccharification. To evaluate this new potential application of FW, FW enzymatic hydrolysis was investigated via non-commercial enzymes. FW was subjected to enzymatic hydrolysis by an amylolytic and a cellulolytic formulation under different enzyme loadings. At the optimum conditions, the time course of glucose production during enzymatic hydrolysis was also studied. In order to enlighten the viability of bioethanol production process from FW, the experimental results were evaluated in terms of cost of enzymes per liter of bioethanol produced. 81% starch hydrolysis was achieved after 1 h of hydrolysis by 45 μL amylolytic enzyme NS22109/g starch at 65 °C. With regard to the effect of cellulase loading, 175 μL NS22177/g cellulose achieved 50% saccharification yield. Further increase of enzyme dosage just slightly increased the yield. More specifically, by increasing the enzyme loading 540%, the resulting saccharification efficiency increased by just 16%. Last, the enzyme cost per ethanol yield was almost 3.5 times lower when just amylolytic enzymes were used for similar ethanol yields. Enzymatic hydrolysis of starch and cellulose present in FW proved to be technically efficient providing high yields. Nevertheless, the difference in the economic weight of the use of amylolytic and/or cellulolytic enzymes strongly influences the viability of FW valorization via bioethanol production.