Abstract
Aqueous solutions of four natural organic acids, including lactic acid, acetic acid, citric acid and tartaric acid, were tested for their efficiency in recovering flavonoids from red grape pomace. The critical comparison was based on a Box-Behnken (central composite) factorial experimental design and response surface methodology, taking as independent variables the acid concentration (Cacid) and extraction time (t), and as responses the yield in total flavonoids (YTFn), total flavanols (YTF) and reducing power (PR) of the extracts obtained. The results showed that the evolution pattern during extractions for all responses considered, differed as a function of the acid used, Cacid and t. Furthermore, significant differences were observed amongst the acids, concerning the extraction efficiency. The highest YTFn (2310.3 ± 198.5 μg rutin equivalents per g dry pomace weight) was achieved using 0.5 % lactic acid after 298 min of extraction, while maximum YTF (102.5 ± 9.7 μg catechin per g dry pomace weight) was attained by using 4 % acetic acid after 320 min of extraction. However, the greater PR (80.2 ± 2.0 μM ascorbic acid equivalents) was expressed by the extract obtained with 0.8 % tartaric acid, following a 286 min extraction.
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