Abstract: The introduction of unconventional processing treatments for red grape seed extract-based functional food requires information about their impact on polyphenols. To this end, the work investigates the influence of microwaves, ultrasound, UVA and X-rays on total polyphenols (TPC), free polyphenols (FPC), total flavonoids (TFC) and cyanidin-3-O-glucoside (C3G) in red grape seed extract powder (GSEP) and GSEP encapsulated in an alginate-whey protein matrix (GSEB). In response to 2 min of microwave treatment, the amount of TPC, FPC, TFC and C3G was reduced by >90 % in both GSEP and GSEB. Encapsulation was found to have the most effective protection on polyphenols exposed to X-ray for up to 72 h. Thus, TPC was not significantly reduced in GSEB, while FPC, TFC and C3G were reduced by 6.95 %, 15.56 % and 17.48 %. For GSEP, declines of 10.15 % for TPC, 17.02 % for FPC, 24.50 % for TFC and 28.51 % for C3G were observed. One-hour ultrasound treatment reduced TPC in GSEP and GSEB by 21.99 % and 18.44 %, respectively, with no significant difference. Compared to the original amount, there was no impact on FPC in GSEB, whereas TFC and C3G were reduced by 28.04 % and 28.42 %, respectively. The levels of FPC, FTC and C3G decreased by 47.10 %, 31.19 % and 34.75 %. Regarding 1-h UVA exposure, the alginate-whey protein matrix moderately protected C3G with a reduction of 21.92 % in GSEB compared to a value of 27.37 % in GSEP, and there were no significant differences between the TPC, FPC and TFC values GSEP and GSEB. The deconvolution of the reflectance spectra revealed the expression of hypochromic and bathochromic effects of the groups of optically active compounds in GSEP and GSEB.
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