Food processing waste: Problems, current management and prospects for utilisation of the lignocellulose component through enzyme synergistic degradation

Waste from the food processing industry (e.g. juice production) is produced in large quantities worldwide and contains high levels of lignocellulose. To some extent, value-added products are extracted from this waste, but the majority of the waste is currently unutilised and discarded. Energy generation from this waste has been investigated in the form of production of biogas, hydrogen and bioethanol. Efficient bioethanol production requires the enzymatic hydrolysis of the total polysaccharides within this waste into monomer sugars for further fermentation into ethanol. Factors limiting this process are the complexity of the lignocellulose, its recalcitrance and insolubility and the number of enzymes required to degrade it. Obtaining complete enzymatic hydrolysis of these substrates requires an understanding of the composition of the polysaccharides and their associations within the overall substrate. This will allow appropriate selection of enzymes. It has also been established from work on other lignocellulose substrates that the associations between polysaccharides pose an obstacle to their hydrolysis and cooperative enzyme interaction is required to overcome these obstacles. With respect to the enzymatic hydrolysis of food waste, the knowledge gaps have been identified as: (1) accurate knowledge of the polysaccharide composition and structures; (2) knowledge about the associations that exist between different polysaccharides; (3) and the enzymes required for hydrolysis of the overall polysaccharide component and the synergistic interactions between these enzymes. This review investigates these aspects in literature, exposing the gaps in knowledge, while making proposals for future work that could assist in the utilisation of food waste, through enzyme synergistic degradation, as a potential feedstock for biofuel production.