Study On The Preparation And Formation Mechanism Of Resistant Starch Regulated By Extrusion Technology

Resistant starch(RS)plays a fairly important role in maintaining blood sugar stability,promoting intestinal health and controlling body weight.The increasing threat of diabetes to global health makes the development of RS crucial for patients with diabetes and obesity.Resistant starch of typeⅢ(RS3,recrystallized starch)and resistant starch of typeⅤ(RS5,starch-lipid complexes)have high thermal stability and are green and safe.However,the industrialization level of RS3 and RS5 is low and there are few commercial forms.Amylose content is the key factor affecting the formation of RS3 and RS5.In addition,amylose content is also the key factor affecting the formation of starch-protein covalent complexes,the covalent interaction between starch and protein is expected to effectively slow down the digestibility of starch.Based on this,this paper used the production technology of food industrialization—extrusion technology,explored the formation and formation mechanism of RS3,RS5 and starch-protein complexes regulated by amylose in extrusion,clarified the influence of the structural and properties of RS3,RS5 and starch-protein complexes on their digestibility,and revealed their enzyme-resistant mechanisms.It is expected to provide new ideas for the industrial production of safe and effective RS,and promote the development of RS.Corn starch(CS)and potato starch(PS)were extruded and recrystallized,and the effects of amylose content,extrusion moisture content and recrystallization time on the structure and properties of RS3 were investigated.Compared with native starch,both extruded CS(ECS)and extruded PS(EPS)exhibited a significant decrease in their measured molecular weight,the chain length distribution did not change significantly,but the amylose content increased remarkably.In comparison with the recrystallization time,the influence of extrusion moisture content on the crystalline pattern,thermal properties and digestibility of recrystallized ECS(RECS)and recrystallized EPS(REPS)was greater.Both RECS and REPS with 60%moisture content presented a typical B-type crystalline pattern,and RECS also exhibited V-type characteristic peaks.The melting temperature of recrystallized amylopectin ranged from 46℃to 64℃,and the melting temperature of recrystallized amylose ranged from 136℃to 158℃.RECS had lower in vitro digestibility than REPS,the SDS and RS contents of RECS-60%-7d were 25.62%and 12.47%,respectively.The effects of the amylose content and lauric acid(LA)content on the structure and properties of extruded starch-lipid complexes were explored.Potato starch(PS),corn starch(CS),and pea starch(PES)with different amylose contents all formed ordered extruded starch-lauric acid(ES-LA)form II complexes with a range of LA content(1%,2%and 4%,w/w).The V-type crystal structure of the complexes became more obvious as the LA content increased from 1%to 4%,the relative crystallinity increased with the increase of amylose and LA content.The dissociation temperature of complexes ranged from 110℃to 140℃,and the enthalpy change increased with increasing LA content.Moreover,the complexes rapidly reformed after dissociation and cooling.The solubility and swelling power of the complexes decreased with increasing LA content.The peak viscosity of the complexes was significantly reduced compared with extruded starch,which is consistent with the results of swelling power.The RS content of the complexes was closely related to both the amylose and the LA contents,the RS content of the extruded pea starch-lauric acid(EPES-LA)complexes with 4%LA content was 16.7%.The“extrusion–debranching”strategy was put forward to realize the enzymatic debranching of starch in extrusion and obtain the short amylose,and improve the yield of RS3.Corn starch was fully gelatinized and partially degraded via first extrusion to obtain ECS,then ECS and different amounts of pullulanase(20,40,60,80,and 100 U/g,w/w)were mixed and subjected to a second extrusion,which resulted in the debranching of amylopectin at high starch substrate concentrations and a short time,and enzymatically debranched ECS(EECS)was obtained.Increasing the pullulanase amount to 100 U/g(EECS-100U)also increased the amylose content to 90.21%and decreased the weight-average molecular weight(Mw)to6.66×10~3g/mol,with a starch concentration of 66.6%(w/v).EECS presented a B+V-type crystalline pattern and showed excellent thermal stability,the melting temperature of the recrystallized short amylose and starch-lipid complexes was ranged from 90℃to 135℃,and the melting temperature of the recrystallized long amylose was ranged from 140℃to 167℃.The short amylose exhibited rapid recrystallization.RS content increased with increasing amounts of pullulanase,the RS content of EECS-80U was 40.39%.The results suggest that the extrusion–debranching strategy for improving amylose content is both feasible and effective,the findings will provide new idea for the continuous industrialized production of amylose and RS3.The“extrusion–debranching–complexing”strategy was proposed to prepare RS5.The gelatinized and degraded CS obtained by the first extrusion was mixed with pullulanase(60U/g)and LA with different contents(4%,6%and 8%,w/w)for the second extrusion.An increase in amylose content and the formation of amylose-lipid form II complexes(EECS-LA)were achieved in the second extrusion.The short-range molecular order of EECS-LA complexes was significantly improved,the dissociation temperature was ranged from 105℃to 145℃,and Tp was approximately 125℃.The enthalpy change values increased with the increase of LA contents,the enthalpy change value of EECS-8%LA complexes was 9.42 J/g,and the complexes could be reformed after dissociation.The EECS-LA complexes exhibited an irregular lamellar structure with small size as observed by scanning electron microscopy(SEM).The RS contents of EECS-LA complexes increased significantly,and the RS content of EECS-8%LA complexes was 38.34%.The results suggest that the extrusion–debranching–complexing strategy for preparing RS5 is both feasible and effective,the findings will provide new idea for the continuous industrialized production of RS5.The“extrusion–debranching–complexing”strategy was also used to prepare amylose-protein complexes.The gelatinized and degraded CS obtained by the first extrusion was mixed with pullulanase(60 U/g)and different amounts of pea protein(PP)or pea protein peptide(PPP,10%,20%and 30%,w/w)for the second extrusion,in order to obtain amylose-pea protein(EECS-PP)and amylose-pea protein peptide(EECS-PPP)complexes.The arginine and lysine contents of complexes decreased,indicating that the occurrence of covalent interaction between the free amino group in PP or PPP and the terminal aldehyde group of amylose,and the XRD pattern exhibited a new peak at 32°,suggesting the formation of new structure in complexes.Raman spectra showed that EECS-PPP complexes had higher short-range molecular order.Both EECS-PP and EECS-PPP complexes exhibited a small-sized block structure as observed by SEM.The digestibility of starch in the complexes was regulated by covalent interaction and hydrogen bonds between starch and protein.The EECS-PPP complexes showed a lower starch digestibility in comparison with EECS-PP complexes,and the RDS,SDS and RS contents of EECS-30%PPP complexes were 55.92%,22.09%and 22.49%,respectively.The results indicated that the extrusion–debranching–complexing strategy is an effective method for preparing amylose-protein complexes with low digestibility.