Effect Of Tea Polyphenols On Digestibility Of Modified Waxy Maize Starch

Slowly digestible starches prepared by chemical, physical and enzymatic methods havedrawn more and more attention recently since its ability to produce a relatively stable andlong-lasting glycemic response. As natural bioactive compounds, tea polyphenols (TP) havebeen confirmed to inhibit digestive enzymes and to reduce glycemic level. This research isbased on the combination of the slowly digestible property of octenyl succinic anhydridemodified starch (OSA starch) and TP, and investigated the effect of TP on starch digestibilityand the possible mechanism of their interactions. The results may provide a theoretical basisfor making use of starch resources and TP. The main contents are as follows:OSA starch with a DS of0.0194was prepared in aqueous media and was confirmed tobe esterified successfully by FT-IR. OSA starch was found to contain significantly moreslowly digestible starch (SDS) content (27.6%) than its native part which only contained9.3%.OSA starch was followingly treated by heat-drying and heat-moisture under differentconditions, and it was found that after these two treatments, namely130℃-4h and120℃-15%water content-4h, SDS increased to36.8%and38.2%respectively. So OSA starchtreated with heat-moisture was chosen for following studies.The content of free TP was measured by a UV-VIS spectrophotometer afterco-gelatinized with both OSA starch and waxy maize starch before and after storage at4℃for24hours. And it was found that the content of free TP in OSA starch-TP system decreasedby13%, while there was no significant difference of waxy maize starch-TP system. The resultindicates that there might be interactions between TP and OSA starch. The RVA andrheological property results also support this view.The effect of TP on in vitro enzymatic hydrolysis of starch was investigated, and it wasfound that the effect differed with the change of TP content, retrogradation time and starchtypes. In the early retrogradation stage (0day&1day), the digestibility of both starches wereinhibited. Compared with control group, the inhibitory ratios were8.72%(0day) and7.44%(1day) for waxy maize starch and10.15%(0day) and7.1%(1day) for OSA starch whenadding15%TP. However, in the later retrogradation stage (3day&7day), the inhibitoryratios were6.8%(3day) and-8.03%(7day) for waxy maize starch and1.81%(3day) and-8.75%(7day) for OSA starch. These results indicate that the effect of TP on starchdigestibility was not simply inhibition but promotion to some extent. And it differs betweenthese two kinds of starch especially on the3rdand7thday of retrogradation, viz. a: TPfacilitated OSA starch enzymatic hydrolysis with10%content on the3rdday while inhibitedwaxy maize starch, b: the promotive effect of TP (with every content)on OSA starchdigestibility is more evident than on waxy maize starch on the7thday. The DSC resultsconfirmed that TP can inhibit retrogradation of both starches, and the inhibitory effect on OSAstarch is more apparent than on waxy maize starch. Consistently, the XRD analysis showed adecrease of recrystallinity.In the in vivo experiment, male Wistar rats were fed with waxy maize starch and OSAstarch (with different TP content), and it was found that glycemic level of OSA starch-TP groups were significantly reduced compared with waxy maize starch group, while there wasno significant difference between OSA starch-TP groups and OSA starch group. So in vivostudy indicates that TP and OSA starch can affect postpradial glycemic response but the effectisn’t significantly.