Integrated multi-stream valorization of kitchen food waste through enzymatic hydrolysis and selective fermentation

Abstract

Food waste (FW) management has emerged as a global priority due to its environmental burden and loss of valuable resources. Kitchen FW, rich in carbohydrates, proteins, and fats, has a great potential for the bioconversion of value-added products. Conventional valorization strategies have largely focused on single-product pathways. This study explored a component-specific conversion strategy to recover fats, hydrolyze starch, ferment glucose to ethanol and 3-hydroxypropionic acid (3-HP), and obtain proteins from kitchen FW. Results showed that 62.64% of fats were first separated from kitchen FW, and they were rich in oleic acid (C18 : 1, 34.14%), linoleic acid (C18 : 2, 24.64%), palmitic acid (C16 : 0, 20.14%), and stearic acid (18 : 0, 6.81%). The hydrolysis time, enzyme dosage, and temperature were optimized using a one-step enzymatic hydrolysis (OSEH) of starch, employing response surface methodology. This optimization resulted in a starch hydrolysis efficiency of 82% and a glucose concentration of 60 g L⁻¹. Using the resulting glucose hydrolysate, 21 g L⁻¹ of ethanol (0.35 g g⁻¹ glucose) and 12 g L⁻¹ of 3-HP (0.20 g g⁻¹ glucose) were produced with Saccharomyces cerevisiae and Issatchenkia orientalis, respectively. The protein-rich (>68%) residue after OSEH contained about 50% of glutamic acid, aspartic acid, leucine, valine, and alanine. This work provides new insights into multi-product biorefineries for precision FW valorization, enabling waste reduction and advancing a circular bioeconomy.