Hydrothermal extraction of antioxidants from Camellia sinensis fruit husks: Experimental design in the development of enriched gels

Abstract

The phenolic and saccharidic fractions from Camellia sinensis seed husks were extracted under selected conditions of hydrothermal treatment and further concentrated with membranes and nonionic polymeric resins. The fraction extracted heating up to 160 °C contained 30 % oligomers, being concentrated by ultrafiltration up to 1.4 times. The waste solids were further processed up to 220 °C to extract an additional phenolic fraction. Both the permeate from ultrafiltration membranes and the extract obtained in the second hydrothermal stage were concentrated by nanofiltration and by resin adsorption (SP-700). The refined extracts after elution in ethanol contained 75 % and 50 % phenolics, respectively and exhibited antiradical properties comparable to synthetic antioxidants. The xylooligosaccharide (XOS) and the phenolic (Ph) containing fractions were used to formulate starch-based hydrogels and a Box-Behnken experimental design was used to optimize the relative content of each fraction and the gelling temperature to maximize the rheological and color parameters of the hydrogels. Evaluating the multiple response of the effect of the formulation conditions on the viscoelastic behavior through tan δ and the luminosity of the gels through L*, the maximum values were observed for gels prepared in the absence of XOS and 29.8% of E160 at 63.5 °C.