| As a characteristic economic forest fruit,Chinese chestnut is favored by consumers as one of the most important snack foods and food supplements.The planting area and output of Chinese chestnut ranks among the top of world.However,the content of starch in chestnut is relatively high.After processing,the content of fast-digested starch was significantly increased,which could easily lead to blood glucose disorder and can increase the risk of chronic metabolic diseases such as type 2 diabetes and obesity.At present,many processing methods have been used to improve the anti-digestive properties and nutritional functions of starch.Yet,enhanced starch retrogradation phenomenon often happened at the same time,which would affect food quality and shorten the shelf life of starch-based foods.Therefore,coordinated regulation of digestion and retrogradation is one of the bottlenecks that restricts the development of starch and starch-based foods.Motivated by this,this paper proposed that the introduction of polyphenol compounds was to induce the multi-scale structural evolution of chestnut starch through the non-covalent interaction between them and chestnut starch molecules in the environment of heat-moisture treatment(HMT).Therefore,the synergy regulation of improving the anti-digestibility properties of chestnut starch and inhibiting its retrogradation behavior can be achieved.Then modern analysis techniques combined with density functional theory was adopted to clarify the relevant molecular mechanisms.The relevant research results and conclusions are as follows:The influence of HMT processing parameters such as water content of system,treatment temperature and treatment time on the digestion and retrogradation properties of chestnut starch was systematically discussed.The results showed that the HMT caused the breakage of long amylopectin chains of chestnut starch,thus forming more short amylopectin and amylose molecules.This chain structure change would promote the orientation and aggregation of the starch molecular chains to form an ordered structure,thereby improving the slow digestible starch(SDS)and anti-digestible starch(RS)content.But it also promoted the short-term and long-term retrogradation of chestnut starch.Response surface design was used to obtain the optimized process for regulating the digestion properties of chestnut starch by HMT.The optimized process parameters were as follows: the treatment temperature was 105°C,the water content of system was 20%,and the treatment time was 2h.The ACE(SDS+RS)content of the HMT treated chestnut starch was 18.24%.Compared with chestnut starch,the ACE content of HMT treated chestnut starch was increased by 88.04%,but its retrogradation degree(RD)value was also increased by 16.03%.The synergistic regulation effects of polyphenols with different structures(epicatechin EC/epicatechin gallate ECG/procyanidin OPC)and their added amount on the digestion and retrogradation properties of chestnut starch during the heat-moisture treatment process were explored.The results showed that with the increase of polyphenols,the SDS and RS contents of the chestnut starch-polyphenol complexes continued to increase,and the short-term and longterm retrogradation rates continued to decrease.At the same dosage,the order of ACE content and anti-retroversion rate(AR)value was EC complex > ECG complex > OPC complex.It shows that the introduction of polyphenols could not only effectively improve the antidigestibility of chestnut starch,but also could significantly inhibit its retrogradation behavior.The structure and amount of polyphenols significantly affected this synergistic regulation effect.Modern analytical techniques were used to investigate the effects of HMT and polyphenol combined action on the multi-scale structures and rheological properties of chestnut starch.The results showed that the intermolecular non-covalent interaction between chestnut starch and polyphenols could increase the compactness of chestnut starch by increasing single helix structure,double helix structure and nano-aggregate structure,and would promote the formation of V-typed crystal structure.With the increased amount of added polyphenols,the degree of these ordered structures continued to increase,and the amount of amorphous structure continued to decrease.The smaller molecular volume and better flexibility of EC had the most obvious effect on these ordered structures of chestnut starch.And despite of large molecular volume of OPC,more hydroxyl groups of OPC could form intermolecular hydrogen bonds with starch to promote the formation of double helix structure.In addition,the hydrogen bonding between polyphenols and chestnut starch molecules and the steric hindrance formed could effectively hinder the aggregation and entanglement of starch molecular chains,resulting in decreased G' and G'' values of the starch gel system after HMT,and thus reduced gel strength of starch-polyphenols gel system.Further density functional theory methods were used to clarify the interaction modes and differences between chestnut starch and different polyphenol molecules.ESP quantitative analysis and density functional theory calculation results showed that the phenolic oxygen in the polyphenol molecule was the main action site of the hydrogen bond acceptor,and the phenolic hydrogen was the main action site of the hydrogen bond donor.The C atom of polyphenol benzene ring could also form a weak hydrogen bond with the glucose dimer as a hydrogen bond acceptor.The RDG scatter plot showed that hydrogen bonds of the glucose dimer-polyphenol complex system were mainly distributed in the polyphenol phenol group and the hydroxyl groups of glucose dimer.Van der Waals interactions were mainly distributed in the space area where the polyphenol molecule and the glucose dimer interacted with each other.While the strong steric hindrance was concentrated in the space area in the polyphenol benzene ring and the glucose ring.Furthermore,AIM theory analysis results showed the hydrogen bond interaction strength of between polyphenols and glucose dimers was determined by the spatial structure of the polyphenol molecules.There are two types of hydrogen bonds: a mediumstrength hydrogen bond dominated by electrostatic attraction,and a weak hydrogen bond dominated by electrostatic attraction and dispersion.The hydrogen bond interaction strength of different structure polyphenols and glucose dimers was as follows: EC > OPC > ECG.Based on the above research results,a physical model of the coordinately regulation effect of polyphenol combined interaction on the multi-scale structures,thus digestion and retrogradation properties of chestnut starch in the HMT environment was established.And its molecular regulation mechanism was proposed as follows: polyphenols could promote the formation of local ordered domains of chestnut starch in different scales through hydrophobic and hydrogen bond interactions.Theses ordered structural changes hindered the degradation of amylase and realizing the regulation of the anti-digestibility of chestnut starch.During retrogradation of chestnut starch,the starch molecular chain aggregation was hindered by hydrogen bonding between chestnut starch molecules and polyphenols,which made it difficult to form a long-range ordered crystalline structure.Besides,the formation of V-typed crystalline complex would prevent amylose to provide amylose crystal nuclei for amylopectin to be crystallized,thus reducing the efficiency of recrystallization and the retrogradation of chestnut starch.Different structures of polyphenol molecules resulted in different spatial structure arrangement and steric hindrance effects,thus different interaction way and degree with chestnut starch,and eventually different multi-scale structures of chestnut starch-polyphenol complexes.These regulation effect of polyphenol structures on multi-scale structures of chestnut starch-polyphenol complexes determined the regulation of digestive properties and retrogradation properties of chestnut starch.The proposed ideas of using polyphenol combined interaction to coordinately regulate the digestive and retrogradation properties of chestnut starch,and obtained methods and molecular mechanisms in this paper had important academic value and practical significance,and it can provide theoretical basis and technical support for the creation of high-quality,nutritious and healthy starch foods. |
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