Ultrasound-assisted extraction of anthocyanins from grape pomace using acidified water: Assessing total monomeric anthocyanin and specific anthocyanin contents.

This study aimed to optimize the ultrasound-assisted extraction (UAE) of anthocyanins from oven-dried and freeze-dried Vitis labrusca grape pomace, using acidified water as the solvent. The effects of power density (8.3-16.7 W/mL), pulse interval (0-2 s), and extraction time (1-5 min) on both total and specific anthocyanins were investigated. The findings suggested that acidified water can be a viable alternative to conventional solvents and that oven drying was an effective method for drying the pomace. Using response surface methodology, the study identified power density and extraction time as key factors influencing total anthocyanin content, with extracts reaching contents up to 2.56 mg/g. The analysis using LC-MS identified 14 anthocyanins, while NMR quantified 3 and malvidin diglucoside was generally the most abundant. However, higher power and longer extraction times were found to reduce its content while increasing malvidin monoglucoside content, suggesting ultrasound-induced anthocyanin hydrolysis. In conclusion, this study presents a sustainable method for extracting anthocyanins using acidified water, contributing to the valorization of Vitis labrusca grape pomace for industrial use.

Comparing the Chemistry of Malvidin-3-O-glucoside and Malvidin-3,5-O-diglucoside Networks: A Holistic Approach to the Acidic and Basic Paradigms with Implications in Biological Studies.

The kinetics, thermodynamics, and degradation of malvidin mono- and diglucosides were studied following a holistic approach by extending to the basic medium. In acidic conditions, the reversible kinetics of the flavylium cation toward the equilibrium is controlled by the hydration and cis-trans isomerization steps, while in the basic medium, the OH- nucleophilic addition to the anionic quinoidal bases is the slowest step. There is a pH range (transition pHs), between the acidic and basic paradigms, that includes physiological pH (7.4), where degradation reactions occur faster, preventing the system from reaching the equilibrium. The transition pH of the diglucoside is narrower, and in contrast with the monoglucoside, there is no evidence for the formation of colored oligomers among the degradation products. Noteworthy, OH- addition in position 4 to form B42-, a kinetic product that decreases the overall equilibration rate, was observed only for the diglucoside.