Polyphenols from plant sources are increasingly recognized as functional ingredients with multiple health benefits. Finger millet (Eleusine coracana), a major millet grown in Asia and Africa is a significant source of polyphenols. The extraction of polyphenols from millets which are under-utilized has received less research attention compared to other plant matrices. Therefore, the present study was carried out to identify an effective method of extracting the polyphenols from finger millet (v. GPU 28) seed coat (FMSC). Two eco friendly methods namely ultrasonication (UA) and enzyme treatment followed by ultrasonication (EUA) were compared with the conventional heat reflux method (HR). The polyphenolic profile and content along with the antioxidant potential of the extract were evaluated. Phenolic yield increased 2.3 fold using EUA with xylanase (XUA) compared to heat reflux extraction (HR). However, yield with UA was equivalent to the conventional method. Total flavonoids increased 1.4 fold in UA and 1.3 fold in XUA, similarly, tannins also showed a significant increase (1.1 fold in UA and 1.2 fold in XUA). FTIR spectra revealed the presence of all phenolic functional groups and ESI-MS showed 80% similarity in the individual polyphenols in the extracts. Catechins, luteolin and cyanidin were identified in the UA and XUA treated samples, whereas, shikimic acid derivatives-caffeoyl and di caffeoyl were present only in XUA extracts. This is the first report on enhanced extraction of polyphenols from FMSC using a combination of enzyme treatment and ultrasonication, providing a green technology for utilization of polyphenols in nutraceuticals and functional foods. Keywords Polyphenols Á Finger millet seed coat Á Ultrasonication Á Xylanase pretreatment Á Total polyphenol content Á Cyandins Abbreviations ATR-FTIR Attenuated total reflectance-Fourier transform infrared spectroscopy CCD Central composite design CE Catechin equivalents CUA Cellulase ultrasonic assisted DPPH 1,1-Diphenyl-2-picrylhydrazyl EC Enzyme cellulase ESI MS Electrospray ionization mass spectrum EX Enzyme xylanase EUA Enzyme treatment and ultrasonication FMSC Finger millet seed coat GAE Gallic acid equivalent HPLC High performance liquid chromatography HR Heat reflux RSM Response surface methodology TPC Total polyphenol content UA Ultrasonic assisted XUA Xylanase ultrasonic assisted Electronic supplementary material The online version of this article (
The effect of polyphenols from finger millet seed coat (FMSC) on the oxidative stability of refined peanut oil (RPO) and unrefined peanut oil (UPO), at different concentrations and storage conditions was compared with butylated hydroxytoluene (BHT). A significant dose‐dependent reduction of oxidation in RPO compared with UPO was observed. FMSC polyphenols at 800 ppm inhibited oxidation equivalent to BHT (200 ppm), while at 1000 ppm, FMSC effectively reduced the peroxide value (5.1 ± 0.3 and 9.5 ± 0.5 meq/kg oil), acid value (0.97 ± 0.3 and 1.16 ± 0.4 KOH/g), and Thiobarbituric acid reactive species (TBARS) (18.08 ± 0.39 and 20.32 ± 0.56 mg MDA/kg) in RPO and UPO, respectively, during regular storage (RS; 28 ± 5°C, 7 weeks). Oxidative deterioration was higher in terms of all parameters in the oils during accelerated conditions (AS; 65 ± 5°C, 6 days). The Rancimat induction time confirmed the stability of both RPO and UPO in the presence of polyphenols. Regular storage up to 7 weeks and accelerated storage (AS) up to 3rd day (equivalent to 3 months) were achieved with FMSC polyphenols (1,000 ppm), confirming its potential as a natural antioxidant in vegetable oils. Practical applications Peanut oil contains high levels of PUFA that are susceptible to lipid oxidation leading to rancidity and off flavors. The food industry relies largely on synthetic antioxidants such as butylated hydroxytoluene (BHT), butylated hydroquinone (BHQ) and tert‐butyl hydro quinine (TBHQ) to inhibit deterioration caused by fats; however synthetic compounds have shown toxic effects. The study demonstrates the ability of finger millet polyphenols in delaying oxidation in both refined and unrefined peanut oils. Millet polyphenols as potential antioxidants in lipid food systems have the added advantage of providing food safety while maintain quality.
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