Use of red onion skin (Allium cepa L.) in the production of bioactive extract and application in water-absorbing cryogels based on corn starch

Abstract

Onion skin is biomass commonly discarded in the environment, rich in bioactive compounds with antioxidant and antimicrobial potential; thus, we propose valorizing this residue using cryogels as carriers. This study aimed to produce bioactive cryogels based on corn starch and red onion skin extract (ROSE). Cryogels were prepared by starch gelatinization, with five freeze/thaw cycles, adding 5, 10, and 15% (w/w) of ROSE. The ROSE presented total phenols, flavonoids, and volatile organic compounds (VOCs), with esters being the majority. These compounds are responsible for the biological activity of ROSE. The cryogels displayed homogeneous morphology and randomly oriented pores. The water absorption capacity of the cryogels reached 658.3%. The cryogels showed low density reaching 0.153 g/cm3; high porosity of up to 83.76%; thickness of up to 0.83 cm; and low moisture of up to 3.4%. The texture profile showed that the incorporation of ROSE increased hardness. The ROSE incorporated in the cryogel had higher thermal stability when compared to its free form, increasing degradation temperature of about 155.28 °C. The cryogels with ROSE presented high antioxidant activity against ABTS and DPPH radicals ranging from 45.4 to 90.5%. In addition, they showed antibacterial action, with total inhibition of the proliferation of pathogenic bacteria Salmonella Typhimurium and Listeria monocytogenes. The cryogel, without ROSE presented greater in vitro degradability due to the breaking of the glycosidic bonds. The cryogels are efficient matrices with the potential for application as water absorbents in fresh food products that release exudates and carriers of antioxidant and antimicrobial compounds.