Efeito da temperatura de secagem no rendimento da extração de compostos antioxidantes da torta de chia (Salvia hispanica)

Abstract

A considerable amount of residue is generated along the productive chain of chia processing industries whose oil is rich in bioactive compounds. However, the byproducts of these seeds, which in most cases are thrown away, have great nutritional potential. The objective of the present work is to investigate the effect of drying temperature on the yield of extraction of antioxidant compounds from chia cake (Salvia hispanica). For this, the raw material was dried at temperatures of 40, 50, 60, 70 and 80 ± 0.1°C until reaching the equilibrium moisture. Empirical models (Verna, Page, Newton, Two Terms, Henderson and Pabis and Page Modified) from the literature were adjusted in kinetics curves, which were plotted using the experimental data, with the aid of software Statistica 7.0 [marca registrada]. After the drying process, ultrasonic assisted extraction were applied to obtain extracts from chia cake in natura and previously dried samples by adopting the independent variables: time (15, 45 and 60 minutes) and solvent (Water, Methanol and Hexane). All extracts were submitted to analysis of antioxidant activity (DPPH and Total Phenolic) and the data were statistically analyzed (ANOVA). The dried and in natura samples were characterized by Scanning Electron Microscopy (SEM). In the drying results, it was observed that the air temperature had direct influence on the process. The empirical model that best fit the experimental data, based on statistical parameters (𝑅 2,% 𝑆𝐸𝑃, 𝐷𝑅 and 𝑅𝑀𝑆𝐸) and the Akaike Information Criterion (AIC) was the Newton. All the independent variables were statistically significant. In the extraction, methanol solvent showed higher yield of phenolic compounds, followed by water and hexane, presenting better yields in the 60°C/60min, 50°C/45min and 50°C/45min conditions, respectively. The results showed that the polarity of the solvent was a determining factor. The hexane (non-polar) presented a much lower antioxidants compounds extraction yield than methanol (polar) and water (polar). For short extraction periods (15min), the result showed that it is economic and environmentally friendly to use water as solvent extractor. For longer extraction times (45 min and 60 min), the yield for methanol is significantly higher and therefore more economically viable. The micrographs confirm the analysis of antioxidant activity. Fresh and dry samples under 40°C presented a smooth and expanded surface that may have reduced the extraction efficiency. The dry samples at 50°C and 60°C presented a porous matrix presenting higher yields for the aqueous and methanolic extractions. However, dry samples under 70°C and 80°C showed granular character, crystalline regions and worn surfaces allowed the oxidation and the structural transformation of the antioxidant compounds, reducing yield of the extraction. It was concluded that the studied variables had an influence on the extraction yield of antioxidant compounds from chia cake.