Valorisation of food industry by-products: extraction, encapsulation, characterization and microstructural analysis

Abstract

Each year, 16 million t of food are lost and wasted in Argentina (FAO). About 90% is lost duringproduction, while 10% is wasted by consumers. It is reported that vegetables and legumesby-products represent a good source of bioactive compounds with antioxidant properties. Inthis context, green and low-cost water-based extractions were proposed to recover phenoliccompounds from agricultural leftovers of beet (Beta vulgaris), cowpea (Vigna unguiculata),and artichoke (Cynara scolymus L.). Each part of the leftovers (bracts, stems, leaves or pods)was analysed to determine the most suitable material for the extraction of phenoliccompounds in terms of composition and efficiency. To improve their stability andbioavailability, extracts were encapsulated by ionotropic gelation in Ca(II)-alginate beads.Loading efficiency of total phenolic compounds (L.E.TP) and remaining antioxidant activity(R.A.A.ABTS+) of each system were measured by Folin-Ciocalteu and ABTS+ scavengingmethods. Macro and microstructural parameters were studied by image analysis and SAXS.Extracts with high concentration of bioactive compounds were successfully encapsulated,obtaining L.E.TP between 22-48% and R.A.A.ABTS+ between 11-43%. Acceptable values ofroundness for food industry were obtained (0.84-0.95). SAXS fractal analysis allows for theobservation of changes in the microstructure of beads related to the incorporation of theextracts. Significant changes were detected at the supramolecular level (100 nm) whereextracts from cowpea and beet greatly increased the interconnectivity of the alginatenetwork while artichoke extracts had a slight opposite effect. At the molecular level (1-10 nm)all the extracts improved the compactness of the structure and reduced the size of thenanometric alginate basic unit. However, for its density, contrasting results were foundbetween beet and artichoke and cowpea. Thus, the differences in the phenolic compositionand concentration of cations in the extracts, had a profound impact on the microstructure ofthe gels. We hereby demonstrated that the green extraction of bioactive compounds fromthese by-products and their subsequent encapsulation in Ca(II)-alginate beads is a feasibleand transferable method to the food industry for applications in added-value products.