VALORIZATION OF AGRO-INDUSTRIAL RESIDUES IN BIOCOMPOSITES

Introduction and study objectives The increasingly pressing demand of civil society to move towards the circular economy models drives the scientific community to explore new routes to fully valorise wastes in order to achieve the zero-waste objective. From this perspective, even the residues of agro-industrial processing must not be considered as a waste, the disposal of which involves an economic cost, but as a potential source of valuable products. In particular, in Europe the food processing of legumes, fungi and coffee resulted to produce a very large amount of residues: for example, the European production of chickpeas, green peas, and green beans almost achieves two million tons per year which correspond to 200.000 tons of reusable residues per year. Moreover, a total of 3.9 million tons of green coffee beans are imported and processed further in Europe (FAOSTAT, 2017), producing 156.000 tons per year of coffee silver skin and about the same amount in non-compliant green coffee beans, that are separated during quality control. Therefore, this large amount of wastes requires sustainable exploitation, which can consist in extractions of residual compounds. Indeed, this kind of leftover biomasses and food production by-products are particularly rich in proteins, carotenoids, polyphenols, caffeine, and fibres, which could find application in various sectors as food, nutraceuticals, cosmetics and packaging. Within the PROLIFIC project, a range of green and innovative processing technologies to recover significant amounts of the above-mentioned value-added compounds from industrial processing residues of legumes (seeds of peas, beans and chickpeas), fungi (cuttings and mycelia of different species) and coffee (silver skin residue and not compliant roasted seeds) has been tested and developed. The protein extraction has been performed by using environmentally friendly aqueous extraction (EFAE), enzyme-assisted extraction (EAE) and ultrasound-assisted (UAE) and microwave-assisted (MAE) extractions. The resultant residues have been further exploited by using supercritical CO2 extraction (SFE-CO2), subcritical water extraction (SWE) and alkali extraction to recover polyphenols, caffeine and fibres. The described biocascading approach (Figure 1) allows actually collecting interesting compounds but also produces an ultimate fibrous waste, which, with the purpose to keep it into the circular economy loop, can be differently valorised. In fact, it is well known the use of natural fibre residues as filler in polymeric matrices to prepare bio-composites, characterized by decreased costs but retained mechanical properties. Therefore, the results described in this work aims to demonstrate how also the final fibres and agro-residues can be used, allowing the complete valorisation of the studied food streams. Extracted Legume Green Beans (LGB), Peas (P), Chickpeas (CP), Coffe Green Beans (CGB), and Coffee Silver Skin (CSS) by-products have been used as residues. Biodegradable and bio-sourced polymers have been chosen as polymeric matrices. The composites have been prepared by melt mixing polymeric matrices and residues in different ratios. The quality of the prepared composites has been evaluated by considering thermal and mechanical properties, determined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests. Results and conclusions Composites based on biodegradable polymers and tested residues have been successfully prepared. All the materials are characterized by high thermal stability and in any case, the temperature of thermal degradation resulted far higher than the polymer processing temperatures. The addition of residues has not affected the crystallization and melting processes of the polymeric matrices. The tensile tests have shown an increment in the Young modulus and a decrement in both the strength and the elongation at break consistent with filler loadings. However, for a reduced amount of filler, the overall properties of the matrix have been retained. Then, the results demonstrate that also the ultimate agro-residues, after the extraction of high value molecules, can be successfully exploited. Finally, it is notable that the obtained material costs can be remarkably reduced and applications in different packaging sectors, such as cosmetic area and food industry, can be taken into consideration.