Revalorización de subproductos vegetales. Efecto del procesado sobre la extracción, estabilidad y bioaccesibilidad de compuestos antioxidantes

Abstract

The agri-food industry must face the growing legislative and social pressure about the mitigation of the environmental impact of its activities and, in this regard, it is addressing major challenges aimed to contribute to environmental sustainability. The purpose of this work is to evaluate the potential of plant residues and by-products as a source of antioxidant compounds, to propose the use of an emerging and sustainable methodology such as power ultrasound for their extraction, and to study the effect of processing on the bioaccessibility of these compounds. The use of orange by-products as a source of antioxidant compounds has been validated, furthermore, the extraction process has been improved by applying power ultrasound. The kinetics of acoustic extraction and the temperature effect on them were studied and compared to those of conventional extraction by mechanical agitation. The use of power ultrasound allowed the use of water as solvent, obtaining extraction yields (40-80 %) similar to those proposed in the literature for the extraction with organic solvents. The extraction yields of total polyphenols, total flavonoids contents, and antioxidant activity (ABTS method), after 10 min at 25 ° C and acoustic density of 790 W/L, were higher (28, 44 and 157 % higher, respectively) that the yields obtained at the same temperature by mechanical agitation assisted extraction. The extraction curves of total polyphenols and total flavonoids contents, and antioxidant activity (ABTS method) from orange by-products were adequately simulated by using the modified Weibull model, obtaining mean relative error (ERM) figures lower than 5 %, both in mechanical and acoustic assisted extraction processes, within the temperature range of 5-25 ºC. Next, the effects of the application of different processing techniques (freezing, lyophilization and convective drying) on the bioaccessibility of the antioxidant compounds during in vitro digestion were evaluated. These effects were different depending on the structure of the food matrix. The microstructure and the initial composition of both apple and beetroot samples changed after freezing and drying processes. These structural modifications resulted in changes in the behavior of these samples during the in vitro digestion process. It was observed that, in general, processing contributed to the improvement of the bioaccessibility of compounds with antioxidant properties present in both apple and beetroot (bioaccessibilities ~ 50% and ~ 60% higher, respectively, than in untreated samples). The Weibull model allowed the description of both mass transfers that took place during the in vitro digestion process, the loss of bioactive compounds from the solid matrix (with an ERM <5.3 % in apple digestion and ERM <7.1 % in beetroot digestion), and the gain of antioxidant compounds, in the case of beetroot digestion with gastric juice with ERM <8.7 %. The application of image analysis allowed a quantitative analysis of the effects of both drying and in vitro digestion. Drying process promoted increases in the number of cells per area unit. In conclusion, this work contributes to the validation of the use of orange residues and by-products as a source of antioxidant compounds, improving the aqueous extraction process through the application of power ultrasound; and to demonstrate the effect of processing by freezing and drying, on the bioaccessibility of the antioxidant compounds present in different food matrix such as apple and beetroot.