Evaluation of the acidogenic fermentation potential of food industry by-products

Food industry annually generates huge amounts of waste and by-products, which represent untapped renewable resources to produce platform chemicals (e.g., organic acids) through biological processes, such as acidogenic fermentation (AF). Here, the AF potential of nine food industry by-products has been evaluated in anaerobic batch experiments, with main attention to the spectrum of attained products and related conversion yields. Farinaceous by-products, especially Bread Crust (BC) and Reground Pasta (RP), exhibited the highest conversion yield of the initial Chemical Oxygen Demand (COD) into AF products, up to values of 55 ± 2% and 75 ± 9% (for BC and RP, respectively). Substantially lower values, ranging between 6 ± 1% (for Spinach, SP) and 22 ± 1% (for Grape pomace Lees, GL) were achieved with by-products from the vegetable and winery industry. Further experiments with GL, SP, and WP (White exhausted grape Pomace) in the presence of glucose as reference substrate, revealed the coexistence of both recalcitrant and inhibitory compounds in GL and WP, whereas no inhibition on microbial activity was displayed by SP. A sonication pre-treatment experiment (at a low frequency of 20 kHz for 15 minutes and at room temperature) allowed increasing the conversion yield of GL by approximately 45%.