(P03-021-23) Starch Digestibility in Phenolic-Rich Flours Is Modified by Treatments That Foster Interactions With Ferulic Acid

Objectives: Formation of starch-ferulic acid complexes by acidic steeping with purified phenolics in model systems increases resistant starch (RS) content and reduces glycemic responses in animal models. Here we examined the potential to generate similar starch-phenolic complexes in phenolic-rich flours (black rice, BR; purple maize, PM) and assessed impacts to starch digestibility and phenolic bioaccessibility in vitro.

Methods: Starch-phenolic complexation was performed using an acidic steeping method previously reported in pure starch-phenolic models [Li et al., Food Hydrocoll, 2018]. Potato starch (PS) and BR and PM flours (~4 g) were mixed with 0, 200, or 500 mg ferulic acid (FA) dispersed in HCl-acidified water (pH 2). After oscillation overnight, precipitates were washed three times with water and dried. Characterization of phenolic content in starting materials and post-treatment was carried out by UPLC-MS. In vitro starch digestibility was determined using starch hydrolysis curves from gelatinized samples and estimated glycemic index (eGI) and rapidly digestible (RDS), slowly digestible (SDS), and RS content were calculated. Bioaccessibility of phenolics was determined from gelatinized samples using a three-stage in vitro digestion model.

Results: Processing flours with acidified water resulted in decreased phenolic content (74-92%; p< 0.0001) and increased starch digestibility. Steeping resulted in increased RDS and eGI and decreased RS. Potential PM-FA complexes had reduced eGI compared to acid treatment (p < 0.0001), consistent with formation of starch-FA complexes. FA loading capacity on PS (60-77%) was greater than for PM and BR flours (11-28%). In PS and flours, increasing the amount of FA decreased FA bioaccessibility. The lowest FA bioaccessibility was found in PS samples with 500 mg FA (1-2%), while the lowest in the flours was for PM (14%).

Conclusions: Acidified steeping with FA modifies starch digestibility, however this effect was greater in purified starch (e.g., PS) compared to phenolic-rich ingredients (e.g., PM or BR). Use of FA to modify starch macrostructure and/or digestibility in flour ingredients may be limited by FA loading capacity and processing loss of native phenolics.

Funding Sources: PepsiCo. The views expressed in this abstract are those of the authors and do not necessarily reflect the position or policy of PepsiCo, Inc.