Preliminary tests for the valorisation of food by-products - Brewer's Spent Grains (BSG) and Apple Pomace (AP) - through biotechnological approaches

Over the years, the world population has significantly grown, and it has been estimated to exceed 9 billion by 2050. This will be linked to a significant increase in the food demand and it will entail the intensification of production processes with higher consumption flows of required feedstock to transform raw materials into finished products. Further exacerbating this scenario are the drastic effects of climate changes and declining agricultural productivity due to increasingly arid soils and poor fertiliser availability. Therefore, there is an urgent need to develop valorisation strategies for the by-products of the food industry alternative to waste-to-energy. This thesis aims to carry out experimental tests for the recovery of two key by-products in food supply chains, Brewer's spent grains (BSG) and Apple pomace (AP). The chosen biotechnological approach aims at characterizing the matrices and at preliminarily evaluating the compatibility between these matrices and certain microorganisms (i.e., Rhizopous oligosporus, Chlorella vulgaris and Lentinula edodes) which are widely used in the food industry on similarly-composed matrices. The thesis work includes also the establishment of the cell lines of each microorganism and performs exploratory fermentation tests (in submerged and in solid state conditions, using single and co-cultures). The first preliminary respirometric tests of R. oligosoporus on chickpeas (as free or entrapped matrix) in microcosms yielded 1.01 ± 0.07 mg/gTS with little difference for co-cultured systems with C. vulgaris. In flasks submerged culture tests (slurries at 10% wTS/w), R. oligosporus and L. edodes tended to acidify the matrices (ΔpH = 2.06 and ΔpH = 2.03 respectively in the presence of BSG, ΔpH= 2.11 and ΔpH = 2.13 respectively in presence of AP) and to exhibit proteolytic activity with at least two times higher titers in the final homogenates compared with the starting matrices; differences were observed in co-cultivation systems with C. vulgaris. For the state-solid tests, the pH increases in the systems (from 2.18 ± 0.08 to 4.84 ± 0.2 for the systems placed under dark conditions, from 2.18 ± 0.08 to 4.94 ± 0.39 for the systems under light conditions), accompanied by a decrease of titratable acidity (the volumes of NaOH used to titrate the tempeh samples are 60.32% lower than the volume used to titrate the starting matrix sample) and protein content (from 100.76 ± 0.05 (g/L) to 21.70 ± 0.18 (g/L) for systems under dark conditions, from 100.76 ± 0.05 (g/L) to 21.16 ± 0.15 (g/L) for systems under light conditions) in final homogenized samples, which could indicate a higher preference for biomass growth in this configuration. In general, the results suggest that BSG and AP matrices are compatible to cultivate the examined fungal species (serving as complex media) and that in the submerged configurations, there is a preference for more fermentative activity (with the production of organic acids) and that complex proteins from these matrices can be hydrolyzed to generate greater availability in the liquid phase. For solid-state cultures, a greater preference was observed towards biomass growth, with the consumption of organic acids and the use of the starting proteins in the matrices. Lastly, more tests are necessary to evaluate the safety of the elaborated products here, and to analyse their properties in more detail, to later move on to more advanced development phases in the valorisation strategy.