Regulation Of Processing And Quality Characteristics Of Whole Tartary Buckwheat Dried Noodles Based On Component Modification

Tartary buckwheat is often used as one of the ingredients for noodle staples because of its richness in protein,various vitamins,minerals,trace elements,dietary fiber,and flavonoids(rutin).Tartary buckwheat noodles are popular in Asian countries,but the lack of gluten network structure leads to challenging preparation of whole Tartary buckwheat dried noodles(WTBDN).Currently,WTBDN could be prepared directly by extruded buckwheat flour mixed with raw buckwheat flour from,but there are problems such as high cooking losses and poor tensile properties of the noodles.In addition,the mechanism of the starch fraction in extruded Tartary buckwheat flour on the processing characteristics of WTBDN need to further explore.To solve these problems,in this study,the extruded buckwheat starch was first obtained by changing the extrusion temperature and investigated the effect of extruded starch on the processing characteristics of whole buckwheat noodles and the formation mechanism of extruded starch gel network in noodles.Furthermore,egg white and protein cross-linking agent were introduced to investigate the quality enhancement mechanism of egg white and the effect of protein crosslinking agent on the protein cross-linking network and quality of whole Tartary buckwheat noodles,respectively.Firstly,to obtain extruded buckwheat starch,the effect of extrusion temperature on the structure and physicochemical properties of buckwheat starch was investigated.It was found that the starch granules lost their original morphological characteristics and aggregated in blocks after extrusion.With the increase in extrusion temperature(85-105 °C),the relative crystallinity of starch gradually reduced(p<0.05),the amylose content gradually increased(p<0.05),and starch molecular weight gradually reduced(p<0.05).When the temperature exceeded 105 °C,a higher extrusion temperature(110-140 °C)no longer promoted the reduction of Mw and Mn of starch molecules(p>0.05),which could promote the generation of more linear molecules in the starch molecular chain.In addition,the water absorption and solubility of starch were significantly enhanced(p<0.05),the cold viscosity was significantly increased(p<0.05),and the pasting viscosity was significantly decreased(p<0.05)after extrusion.Besides,E125 starch(starch obtained by extrusion temperature of 125 °C)possessed a higher consistency coefficient K* and gel strength.The correlation analysis showed that the size of gel strength of extruded starch showed a highly significant positive correlation(p<0.01)with extrusion temperature and amylose content,and a highly significant negative correlation(p<0.01)with starch molecular weight,total starch content and relative crystallinity of starch.Secondly,30% of extruded modified starch and 70% of buckwheat flour were mixed to prepare WTBDN.The effect of extruded modified starch on the processing characteristics of WTBDN was investigated,and the mechanism of starch gel network formation in the WTBDN during processing was also explored.The addition of extruded starch(ES)significantly reduced the dough formation time and stabilization time(p<0.05)and significantly increased the water absorption of the dough(p<0.05).The addition of E110,E125,and E140(representing extruded starch obtained at extrusion temperatures of 110°C,125°C,and 140°C,respectively)reduced the weakness of the whole Tartary buckwheat noodle dough from 54.53% to 21.58%,22.42%,and 22.17%.With the decrease in roller gap from 2.0 mm to 0.8 mm,the elasticity of the whole buckwheat raw noodles prepared by E110,E125 and E140 increased by 16.10%,34.80%,and25.11%,respectively.Noodle microstructure showed that an extruded starch gel entrapped the raw starch structure in the WTBDN dough sheet was formed after sheeting.The comprehensive analysis showed that the formation of the gel entrapped network in the WTBDN benefited from ES gel,and mechanical forces during gaps decreased.In addition,the higher gel strength of E125 extruded starch in the noodle processing had better processing adaptability.Further,the effect of starch structure evolution and gel network changes during cooking on the quality of WTBDN was investigated.It was found that E30%-F and E40%-F(WTBDN prepared with ES contents of 30% and 40%)had higher hardness and chewiness and adhesiveness before cooking for 4.5 min.However,at the optimal cooking time(OCT),the hardness of both E30%-F(OCT was 6 min)and E40%-F(OCT was 7.5 min)noodles was significantly lower than that of E20%-F(WTBDN prepared with 20% ES content,OCT was5.25 min)(p<0.05).The results of water molecular migration and cooking loss measurements of WTBDN indicated that the higher ES content could hinder water migration in the noodles.However,the disruption of the internal structure of the noodles after optimal cooking could facilitate the proton exchange between free water and soluble material.The gelatinization degree and starch structure characterization of WTBDN revealed that the higher ES content had an inhibitory effect on the starch gelatinization and starch structure disruption of WTBDN before the noodles were cooked thoroughly.Combined with the microstructure of WTBDN and Angio Tool vascular network fitting analysis,it was found that the increase of internal voids and the precipitation of soluble substances in the cooked noodles were likely to be the main cause of the hardness deterioration of E40%-F noodles.In addition,the cooking quality of WTBDN was enhanced by adding egg white(EW)to enhance the protein network in WTBDN and the mechanism was investigated in depth.It was found that the increase in egg white content helped to enhance the viscoelastic properties of whole buckwheat noodle dough sheets.The addition of 15% egg white significantly reduced the cooking loss of WTBDN(p<0.05)and significantly increased the tensile distance and elasticity of the noodles(p<0.05).In addition,the addition of egg white promoted the covalent cross-linking polymerization of proteins in WTBDN,and further analysis of protein crosslinking polymerization in WTBDN showed that the elution peak areas of salt-soluble and watersoluble proteins and alcohol-soluble proteins in WTBDN decreased significantly(p<0.05)with the increase of EW addition.These results suggest that egg white might be crosslinked with salt-soluble and water-soluble protein,gliadin in Tartary buckwheat protein.The analysis of protein subunits and protein interactions showed that the addition of EW promoted the interaction between egg white protein(EWP)and Tartary buckwheat protein(TBP),and this interaction was mainly based on increased hydrogen bonding,decreased hydrophobic interaction,and increased disulfide bonding.The presence of cross-linking reactions between EW and TBP was further verified by the EW-TBP model.In addition,the EW-ES gel model found that with the addition of EW,extruded modified starch as a substrate gel network system was transformed into an EWP-ES network interpenetration of the binary network system(at egg white content greater than 15%).In summary,EW through the EW-EW cross-linking and EW-TBP cross-linking enhanced the protein network in the WTBDN during cooking.The EW could fill the starch gel gap and thus enhance the cooking quality of WTBDN.Finally,the effect of transglutaminase(TGase)and glucose oxidase(GOD)on the quality of WTBDN was investigated.It was found that the addition of 0.2% TGase significantly reduced the cooking loss of noodles(p<0.05)and significantly increased the water absorption and hardness(p<0.05).However,the cooking quality of WTBDN deteriorated with the increase of TGase addition(>0.2%).In addition,the addition of the GOD enzyme(0.01-0.04%)also had a degrading effect on the quality of WTBDN.The enhancement mechanism of WTBDN quality by low addition of TGase was further investigated in terms of protein cross-linking.It was found that the SDS extractability of protein in WTBDN decreased from 44.22% to 35.16% with the increase of TGase(0-0.04%).The protein fractions and protein-interaction forces and protein secondary structure of WTBDN were determined,and it was found that the salt-soluble-watersoluble protein(Pyw)content of proteins in WTBDN was significantly reduced(p<0.05),the disulfide-bonded cross-linked protein(Ps-s)content was significantly increased(p<0.05),the hydrophobic interactions between proteins were weakened and the disulfide-bonding was enhanced by 0.2% TGase addition,and promote the α-helix and β-folding of proteins.Through cross-linking agent-induced protein subunits,WTBDN quality correlation analysis and protein network fitting analysis showed that 0.2% TGase by promoting protein cross-linking(ε-(γ-glutamyl)-lysine isopeptide bonds and disulfide bonds)to enhance the quality of WTBDN.The high addition of TGase led to excessive protein aggregation,which increased the hydrophobic interactions between proteins in the noodles and inhibited the cross-linking of disulfide bonds between proteins,ultimately leading to the deterioration of WTBDN quality.