From food industry wastes to second generation bioethanol: a review

One-third of food produced for human consumption is lost as waste along the food supply chain. The food industry wastes contain carbohydrates, proteins, lipids, and lignocellulosic substances such as cellulose, hemicellulose, and lignin. These wastes are produced in large quantities worldwide and cause serious environmental problems. Due to the high concentration in organic and nutrient substances, food industry wastes are used for bioethanol production by microorganisms through various fermentation systems. The conversion of a lignocellulosic substance into bioethanol includes three steps: pretreatment, enzymatic hydrolysis, and fermentation. The problems concerning bioethanol production from food industry wastes are related to handling of biomass and application of pretreatment methods in order to improve the conversion of lignocellulosic materials into fermentable sugars. This review provides detailed overview and current knowledge on the pretreatment methods of lignocellulosic substances such as chemical (acid or alkaline, organic solvent), physical (milling, pyrolysis, microwave oven irradiation), physicochemical (steam explosion, hydrothermal processes, ammonia fiber explosion, CO2 explosion), and biological (fungi, bacteria). Pretreatment is followed by enzymatic hydrolysis with a mixture of suitable enzymes (mainly cellulase, β-glucosidase, pectinase) at 50 °C for 48 or 72 h. The production of bioethanol from food industry wastes is enhanced by enzymatic hydrolysis of the total polysaccharides into metabolizable sugars. The conversion of wastes from the food industry to the second generation ethanol is discussed in details.Graphical abstract