Impact of fermentation time on the in vitro enzymatic digestibility of traditionally extracted pearl millet (Pennisetum glaucum) starch

Abstract

In this study, we used a traditional Sudanese fermentation methods to extract starch from pearl millet ( Pennisetum glaucum L.) varieties and investigated the impact of fermentation time (1 and 7 days) on in vitro starch digestibility. From fermented grains two distinct layers of starch were obtained i.e. the upper layer ( Jir Khadim), and the lower layer ( Jir Hur ). The in vitro digestibility analysis of all the starch samples showed that both starch layers exhibited rapid hydrolysis rates within the first 60 min of enzymatic digestion, although the 7-day fermented starches exhibited significantly higher hydrolysis rates after 120 min than 1-day fermented samples. Scanning electron microscopy have shown that the longer fermentation time impacted starch granule morphology with surface perforations, indentations, and granule degradation that might have contributed to higher starch digestibility. Pearl millet varieties with higher amylose content i.e. Ashana and Bioda, showed slower hydrolysis rates, higher resistant starch (RS) levels, and reduced readily digestible starch (RDS). These findings demonstrate that fermentation time significantly affects starch digestibility and fraction distribution, with amylose content and fermentation-induced structural modifications playing key roles. This study underlines the potential for standardizing indigenous food-processing methods for developing modern food products with tailored digestibility profiles. • Two distinct starch layers were extracted from millet grains • Isolation methods impacted starch properties and in-vitro digestibility • Longer fermentation time impacted starch granule morphology • Hydrolysis rate increase with fermentation time and decreasing amylose content • High-amylose cultivars showed lower rapidly digestible starch and higher resistant starch

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