Extraction of free and insoluble-bound phenolic compounds from pigmented rice by commonly used procedures: a comparative study

Abstract

The benefits of food phenolic compounds on human health are well documented, and reliable data about phenolic content in foods are more and more necessary for dietary recommendations. However, no standard methods have been developed for the determination of phenolic compounds in foods. Moreover, a thorough literature search shows that several aqueous-organic mixtures have been used so far to isolate free phenolic compounds (FPC) and different hydrolytic procedures have been used in the determination of insoluble-bound phenolic compounds (BPC) from plant foods and cereals, making results hardly comparable and/or the comparison misleading. The aim of this study was to compare different extraction procedures reported in current literature for the isolation of FPC and BPC from pigmented rice. In detail, five different procedures for the extraction of FPC and four procedures for the hydrolysis of BPC were tested and compared. Results showed that a two-step extraction with acidified methanol and aqueous acetone promoted the isolation of FPC from rice matrix, while as concerns BPC the highest content was obtained by using sodium hydroxide 2M under ultrasound treatment. Recovery tests of gallic acid were also performed and results were good (>95%).