Enzymatic pre-treatments in the valorisation of agri-food residues

Grapes and other fruits processed into wine and juices generate huge amounts of solid residues (pomace) which are still rich in bioactive compounds including fibre and phenolics with potential healthy properties. However, the fibre fraction is mainly insoluble which is not the best from either a nutritional, or a technological point of view. Furthermore, some of the phenolics are present in a form bound to the cell walls with consequent low bioavailability. The overall objective of the Italian project ReMarcForFood (Fondazione Cariplo, 2016-0740 grant) is the development of new concepts of use for winemaking by-products based on their biotechnological conversion into innovative value-added ingredients through application of enzymatic treatments and their use as substrate for the growth of high protein mushrooms. Part of the project is aimed to develop a low-cost and environmentally friendly enzymatic hydrolysis treatment to obtain a fibre powder with improved phenolic compounds release and technological properties for food use. Different commercial enzyme preparations and different operational variables (hydrolysis of dried or fresh red grape skins, enzyme concentrations, hydrolysis and time temperature) have been investigated in terms of effect on free phenolics, dietary soluble and insoluble content, and water and oil holding capacity of the hydrolysed residue. Other industrial fruit residues (apple and blackcurrant) were similarly treated for comparison purposes (FODIAC project, Marie Sklodowska-Curie grant No 778388). Very different results were obtained depending on the fruit pomace and the enzyme preparation. Apple pomace was the only one for which enzyme pre-treatment could greatly increase the free phenolics fraction. Blackcurrant and grape pomace were not significantly affected by the pre-treatment in terms of free extractable phenolics, even though there was a reduction in the dietary fibre content.