Study On Multi-scale Structure Of Cold Plasma Treated Starch And The Effect On Tartary Buckwheat Starch-quercetin Interaction

Starch is one of the most abundant biopolymers in nature,the inherent defects of natural starch limit its application.Based on the theory of polymer science,new food processing technology was introduced to regulate the structure and properties of starch and broaden the application fields of starch.Currently,it has become the mainstream direction in the starch field.Plasma technology is a dry physical modification technology with potential industrial application in starch,which is more efficient,convenient,and environmentally friendly.However,the research about plasma modified starch is mainly used in long-term treatment mode and there lacks the systematic research on the relationship between plasma treatment and multi-scale structural properties of starch.Moreover,there is no report on the combination of plasma treatment and quercetin complexation to modulate the physicochemical and functional properties of starch.Therefore,in this study,the effects of plasma treatment intensity on starch structure and in vitro digestibility were evaluated treated by a new type of high-voltage and short-time（HV-ST）cold plasma equipment using the multi-scale structure of starch as the starting point.The effects of HV-ST cold plasma on the multi-scale structures and in vitro digestibility properties of representative starches with different crystalline types（type A,type B,and type C）,and maize starches with different amylose contents were also investigated.The relationship between changes in multi-scale structure and in vitro digestibility was explored by using the NLLS model to fit the in vitro hydrolysis curve.Furthermore,a novel dual modification method by combining the HV-ST cold plasma treatment and quercetin complexation to alter in vitro digestibility properties of starch was firstly evaluated.The main research contents and results are as follows:（1）The physicochemical and in vitro digestibility properties of Tartary buckwheat（TBS）,sorghum（SS）,wheat（WS）and quinoa（QS）starches treated by HV-ST cold plasma for 30 s were investigated.Plasma treatment reduced amylose contents,molecular weight（Mw）and viscosities of starch.However,there was a dramatically increase in solubility,paste clarify and particle size distribution for different modified samples.The Mw fell drastically from 44.5×10⁶g/mol to 0.3×10⁴ g/mol for QS which had the biggest decline.More fissures and holes were observed on the surface of TBS and SS,whereas aggregation predominated for WS and QS.The relative crystallinity and pasting temperature of starch were increased by HV-ST cold plasma,while the crystalline type remained unchanged.Both hydrolysis kinetic parameters（C∞and K）of two phases increased after plasma treatment.（2）The effects of HV-ST cold plasma on the multi-scale structures and in vitro digestibility properties of representative starches with different crystalline types,TBS for type A,potato starch（PTS）for type B,and pea starch（PS）for type C,were investigated with multiple analysis techniques.The results showed that the Mw of PTS fell drastically from 2.45×10⁷ g/mol to 1.74×10⁷ g/mol,which showed the largest decrease.HV-ST cold plasma treatment resulted in pores extending from the hilum to the surface of starch,which gradually transformed the surface fractal structure to mass fractal structure.Moreover,HV-ST cold plasma treatment caused the decrease in the thickness of amorphous lamellae,single helix content and proportion of amorphous phase while increase in the thickness of crystalline lamellae and double helix content.The in vitro digestibility of starches increased significantly treated by HV-ST cold plasma,in which TBS had the biggest increase for its“inside-out”and“side by side”enzymatic digestion manners.（3）The effects of HV-ST cold plasma treatment on the multi-scale structure,thermal and in vitro digestibility properties of maize starches with different amylose contents were evaluated.The Mw of waxy maize starch decreased from 2.39×10⁷g/mol to 0.96×10⁷g/mol,whose Mw decreased the most.The thickness of crystalline lamellae and the order of starch molecular of waxy maize starch and normal maize starch increased after HV-ST cold plasma treatment,which belonged to a more compact mass fractal structure with higher gelatinization temperature and gelatinization enthalpy.The thickness of crystalline lamellae and amorphous lamellae of high-amylose maize starch decreased after HV-ST cold plasma treatment,thus the gelatinization temperature and gelatinization enthalpy decreased accordingly.More holes,channels and deposits were observed on the surface of starch granules,the increased specific surface area of starch facilitated the binding of starch and enzyme,thus the in vitro digestibility and hydrolysis rate were significantly improved.（4）To systematically explore the effects of plasma treatment on TBS,TBS was exposed to HV-ST cold plasma at 15 and 20 k V for 20 and 40 s.The FT-IR result showed that the full width at half height（FWHH）at 1720 cm^-1 was more intense while much weaker at 1149and 929 cm^-1,indicating that oxidation occurred on the surface molecules of TBS.The results were consistent with the data of p H values,which was significantly decreased from6.99 to 3.22 after HV-ST cold plasma treatment.Besides,it resulted in chains depolymerization of TBS,which induced the increment in short molecular chains（DP～6-24）and reduction in medium and long molecular chains（DP≥25）and the plasma treatment shifted the chains to shorter ones.The depolymerization caused dramatically decreased viscosity,weak starch gel as well as increased digestibility and hydrolysis rate.The order of long-range and short-range structures as well as the thermal stable property in plasma-treated TBS increased.All these changes were positively correlated with treatment voltage and time length.（5）The effects of a combined modification method by both plasma treatment and quercetin complexation on the multi-scale structure properties and in vitro digestibility of TBS were investigated based on the characters of increased the specific surface area of starch and more short and small molecular chains after HV-ST cold plasma treatment.Non-inclusive complex was formed between starch and quercetin as‘bridges’via non-covalent interactions,which not only formed a more compact structure but also improved the thermal stability of starch.Flow behaviors of the complex showed an increased consistency coefficient and decreased flow behavioral index of starch after the quercetin addition,which limited the accessibility of starch to hydrolytic enzymes.The RS content of plasma treated TBS-quercetin complexation was 44.21%（pre-TBS-P-Q-80）which was higher than native TBS（20.66%,pre-TBS）.The results showed that the HV-ST cold plasma technology was an effective method to change the starch granular structure,crystal structure,lamellar structure,fractal structure and chain structure.In addition,the new combined modification method（plasma treatment and quercetin complexation）could produce higher RS content.This study can provide a theoretical basis for realizing plasma technology to regulate the starch properties at the molecular level,provide a new way for starch modification with green technology and provide new materials for the development of nutritious and healthy starch foods.