Effect Of PH And High Hydrostatic Pressure Processing On Physicochemical Properties And Mechanism Of Rice/maize Starch-apple Polyphenol

Starch is not only the energy storage of plants,but also one of the main dietary components and energy sources of human beings.Starch affects the quality and structure of food,and plays an important role in postprandial glycemic response.Polyphenols have good antioxidant capacity,and have a considerable impact on starch.Previous studies have reported that polyphenols change the crystalline structure,gelatinization,rheological properties and digestibility of starch.However,food is a sophisticated system which includes interactions between components and has substantive changes under different pH conditions.Therefore,it is necessary to explore the effects of pH on the physicochemical properties of starch-polyphenol system.As a popular food processing technology,high hydrostatic pressure processing(HPP)has a very significant influence on the physicochemical properties and digestibility of starch.However,its influence on the physicochemical properties of starch-polyphenol system requires further study.Meanwhile,the study on the physicochemical properties and digestibility of starch-polyphenol system under different pH conditions by HPP treatment also needs to be conducted.In this study,normal rice starch(NRS),normal maize starch(NMS)and apple polyphenols(AP)were used as materials to establish NRS-AP and NMS-AP systems.The effects of AP on the physicochemical properties and digestibility of NRS and NMS,the effects of pH and HPP on physicochemical properties and digestibility of the two mentioned systems,and the effects of HPP on physicochemical properties and digestibility of the two systems under different pH were investigated.The following main conclusions was drawn from the work:The power model is considered suitable for describing the flow behavior of NRS-AP and NMS-AP with good correlation.Dynamic viscoelasticity and pasting results showed that AP concentration had different effects on NRS and NMS.FTIR results showed that AP interacted with NRS and NMS in noncovalent binding.After adding AP,the morphology of NRS and NMS changed significantly,the crosslinked network structure of NRS increased,while the structure of NMS was loose.Digestibility results showed that the addition of 5% AP(dry weight of starch)improved the resistant starch(RS)of NRS and NMS most,which was suitable for RS based food.NRS-AP and NMS-AP were established by adding 5% AP,and the effects of pH on the two systems were explored.With the increase of pH,the particle sizes of the two systems increased.Differential scanning calorimetry(DSC),X-ray diffraction(XRD)and FTIR results showed that the retrogradation of NRS-AP and NMS-AP was inhibited under low pH,and thermal stability was improved under high pH.Flow behavior and Dynamic viscoelasticity reports showed that NRS-AP and NMS-AP had relatively high viscosity,storage modulus(G'),and RS contents level under high pH,which indicated that NRS-AP and NMS-AP were suitable for RS based food under high pH.The effects of HPP treatment on physicochemical properties and digestibility of NRS-AP and NMS-AP were also investigated.Particle sizes and thermal stability of the two were decreased by HPP treatment.The decrease of ?H value and relative crystallinity indicated that HPP treatment could inhibit the retrogradation.XRD and FTIR results proved that no new substance was produced.HPP treatment at high value could improve the viscosity and G' of NRS-AP and NMS-AP.Digestibility results showed that RS contents level of NRS-AP and NMS-AP peaked at 600 MPa.The effects of HPP treatment on NRS-AP and NMS-AP under different pH conditions were investigated.The particle sizes of NRS-AP treated with HPP under pH 8 were the smallest.With pH increasing,the thermal stability of NRS-AP decreased,and the type of complex changed from type II to type I.The viscosity and G' of NRS-AP were the lowest under pH 3.The particle sizes of NMS-AP treated with HPP at pH 8 were the smallest.The thermal stability of NMS-AP treated with HPP under high pH was higher than that under low pH.The system had higher viscosity and G' under high pH.XRD and FTIR results further confirmed the structures of NRS-AP and NMS-AP with HPP treatment under different pH conditions.Digestibility results showed that HPP treatment further destroyed the RS of NRS-AP under pH 3 and pH 8.The RS contents level of NMS-AP treated with HPP were better than those without HPP treatment and peaked under pH 8,which was 64.47 ± 3.79%.Therefore,HPP treated NRSAP should avoid high and low pH in production,and NMS-AP was suitable for high pH RS based food treated with HPP.