Uso do ultrassom seguido de secagem para o aproveitamento do bagaço do pedúnculo do caju (Anacardium occidentale L.): efeitos sobre o potencial antioxidante e bioacessibilidade de nutrientes

Abstract

This thesis describes some effects of high power ultrasound to the reuse of cashew apple bagasse. Thus, the objectives of this study were: 1) Develop a optimized process for sonication of cashew apple bagasse, evaluating the effect of ultrasound on enzymatic and non-enzymatic antioxidant compounds and 2) study the effects of ultrasound in drying process evaluating the effects on bioactive compounds and bioaccessibility after processing. To define the best conditions for sonication, a 23 factorial central composite design was used with independent variables: bagasse:water ratio, ultrasonic power intensity (W/cm2) and processing time (min). Nonenzymatic antioxidants such as vitamin C, β-carotene and total phenolic compounds were determined. The total antioxidant capacity (ABTS and DPPH) and the activity of antioxidant enzymes such superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.1) and peroxidase enzymes (EC 1.11.1.7) and polyphenol oxidase were also evaluated. Sonication changed the bagasse aspect from a fibrous residue to a pleasant yellow puree. The maximal concentration of vitamin C, phenolics and β-carotene was obtained when the bagasse:water ratio was 1:4, the ultrasound power intensity 226 W/cm2 and 6 minutes of processing. The high total phenolic content (2186 mg of gallic acid/100 g DW), vitamin C (148 mg/100 g DW) and β-carotene (12 mg/100g) obtained proved the sonication efficiency. Furthermore, the antioxidant activity determined by the DPPH and ABTS assays confirmed the suitability of ultrasound for the preparation of antioxidant-rich cashew apple bagasse puree. The stimulus from sonication has a direct effect on the production of reactive oxygen species such hydrogen peroxide, and consequently, on the activities of superoxide dismutase, catalase and ascorbate peroxidase. Sonication resulted in perceptible color changes in cashew apple bagasse. Despite this result, there were no evidences of browning since h° of sonicated samples was close to the characteristic color of cashew apple pulp. The effect of ultrasound in delaying browning could be correlated to the enhanced antioxidant enzyme activity and decrease in guaiacol peroxidase activity. In a second stage, the effect of ultrasound on drying of cashew bagasse was evaluated. The parameters effective diffusivity of water, water activity and the sorption isotherms were evaluated. During drying, the concentration of vitamin C, phenolics, total antioxidant activity and the enzyme activities of peroxidase and polyphenol oxidase were determined. The in vitro bioaccessibility of vitamin C and phenolic compounds was evaluated. Sonication induced disruption of cashew bagasse parenchyma, which resulted in lower resistance to water diffusion, less hysteresis effect and increased rehydration rate. Sonication did not affect the lignocellulosic fibers, or eschlerenquima cells. For sonicated samples, in the first 2 hours of drying, water activity reached values below 0.4, considered appropriated in order to prevent bacterial and fungi growth. The increase of the mass transfer due to ultrasound processing can be attributed to the reduction on the boundary layer thickness produced by pressure variations, oscillating velocities and microstreaming. The sorption isotherms of cashew apple bagasse had sigmoid-shape for all samples and followed the type II of BET classification. Sonicated cashew apple bagasse presents high antioxidant activity, and high total phenolic compounds (TPC) and vitamin C values. The increase in phenolic compounds and the high final amount of vitamin C may lead to enhance the antioxidant activity. The ultrasound processing caused some reduction of bioaccessibility of vitamin C but increase on TPC bioaccessibility, compared to control. Moreover, sonication reduces the severity of conventional drying treatments, improving the quality of the dried product