Subcritical water extraction of bioactive compounds from by-products of hazelnut and blueberry processing

Hazelnut pericarp and blueberry peel as food supply wastes of easy accessibility and available in very large amounts represent an interesting renewable resource for the extraction of polyphenols and other antioxidant components. The SWEs of polyphenols from hazelnut pericarp and blueberry peel have been investigated on both laboratory- and pilot-plant scales. The hazelnut pericarp extraction using SWE shows an optimum extraction temperature at 125°C with an extraction yield of 249.31 mg/g, a TPC value of 732.74 GAE mg/g extract, and an EC50 toward DPPH of 2.2 ug/mL. Analogously blueberry extraction using SWE shows an optimum extraction temperature at 125°C using acid water solution (HCl) at pH3 resulting in an extraction yield of 117.45 mg/g, a TPC value of 103.42 GAE mg/g extract, and an EC50 toward DPPH of 0.012 mg/mL. The total anthocyanin content in blueberry decreases above 100°C and showed a higher content in the extract obtained by using citric acid, suggesting a protective effect of citric acid toward anthocyanins. Both optimized SWE extracts performed showed higher extraction yields and antioxidant activity than the conventional method. Blueberry also showed a higher TPC value than conventional protocol. The defatting protocol applied on the hazelnut dry extracts demonstrated that using SWE is possible to partially maintain lipophilic components of the matrix using water as a solvent and the extraction lipophilic yields are directly correlated to the rise of temperature. The HPLC analysis showed the presence of proanthocyanidins and procyanidins in the hazelnut extracts and several anthocyanins in the blueberry extracts. The GC-MS analysis of the lipophilic extraction of hazelnut dry extracts showed the presence of 6-octadecynoic acid and vitamin E (tocopherols). These results corroborate the validity of SWE as a green method for polyphenol extraction from hazelnut and blueberry. The extraction yield from preliminary pilot-scale SWE was lower than the lab-scale SWE for both hazelnut pericarp and blueberry peel but showed similar value in TPC and antioxidant activity. These results indicate that SWE is an efficient and rapid method for the extraction of polyphenols and potentially a suitable and profitable technique for large-scale applications. Further studies are needed to improve the extraction yields on the pilot plan and complete the design trials. The collaboration with Alpiflor s.r.l. enabled a formulation design of a food supplement starting from extracts obtained on the pilot-scale. A big impact of the morphology and the rheology of the final dry extract is related to the downstream process. Three different methods were tested: vacuum evaporation, lyophilization, and spray drying. The latter was selected for the preparation of the pilot-scale dry extract. Work is still in progress for the optimal formulation of the food supplement containing our selected extracts. In conclusion, SWE provides a highly potential green route for the valorization of hazelnut pericarp and blueberry peels and contributes to a source of biobased products and a sustainable production protocol for food systems development in the 21st century.