Study On Extrusion Preparation And Digestibility Of Gluten-free Quinoa Noodles

Quinoa is an excellent gluten-free pseudo-grain,making it an ideal staple source for people with celiac disease.However,quinoa has weak protein cross-linking and low starch gel strength,which faces certain challenges in the deep processing of flour products.Therefore,in this paper,quinoa flour was used as raw material to prepare gluten-free noodles by twin-screw extrusion.The effects of extrusion parameters,exogenous protein addition levels and enzyme types on the cooking quality,texture properties and in vitro digestion properties of protein and starch of quinoa noodles were studied.This paper aims to provide a theoretical basis for the development of high-quality gluten-free quinoa noodles.Firstly,the effects of temperature and moisture content on the quality of gluten-free quinoa noodles using twin-screw extrusion were investigated.The results showed that when the extrusion parameters were 30℃-60℃-80℃-110℃-110℃-80℃-60℃,and the moisture content was 35%,the cooking loss of noodles(13.94%)was the lowest,and the texture properties were better.Compared with the untreated quinoa flour,the A-type crystal structure of starch in the extruded quinoa flour was destroyed,the gelatinization peak disappears,and the β-sheet content of the ordered structure in the quinoa protein increased.Besides,insoluble dietary fiber content was significantly decreased(p < 0.05).Further research on the effects of extrusion parameters on the in vitro digestibility of proteins in quinoa noodles found that with the increase of extrusion temperature,the quinoa protein was degraded with the large molecular weight subunits transformed into small molecular weight subunits and the contents of the main anti-nutritional factors decreased.It was found by in vitro simulated digestion that the digestibility of total protein was increased by 59.51%.Secondly,based on the optimized extrusion parameters,gluten-free soy protein isolate(SPI)and milk protein concentrate(MPC)with good gel properties were selected,which were extruded with quinoa flour to prepare noodles.The results showed that both exogenous proteins significantly improved the cooking quality and textural properties of quinoa noodles.Compared with the group without exogenous protein,the cooking loss of quinoa noodles with10% SPI was the lowest,which was reduced by 27.37%.In the SPI group,when the addition level was 7.5%,the noodles had the best hardness,springiness,chewiness and good tensile properties.In the MPC group,when the addition level was 5%,the noodles had the largest springiness and elasticity,indicating that the noodles showed good toughness.Simulated in vitro starch digestion of quinoa noodles found that adding SPI and MPC could significantly reduce the rapid digestible starch content and estimated glycemic index(e GI)in quinoa noodles(p < 0.05),and the starch digestibility was positively related to the cooking loss of noodles.Combined with scanning electron microscopy(SEM)observation and fourier transform infrared spectroscopy analysis,it was found that the noodles with exogenous protein showed a porous structure,which was beneficial to enhance the water holding capacity of noodles and improve the texture properties.The degree of short-range order of starch increased,the hydrogen bond interaction was enhanced,which was consistent with the decreasing trend of starch digestibility.The content of β-sheets in protein molecules increased,and the order was enhanced,which was conducive to its adsorption or encapsulation of starch granules,reducing the cooking loss of noodles and the accessibility of amylase.Finally,on the basis of 10% SPI addition level and 10% MPC addition level,glucose oxidase(GOD)and transglutaminase(TG)were introduced to strengthen protein cross-linking,and further improve the cooking quality and texture properties of gluten-free quinoa noodles.The results showed that adding GOD significantly improved the tensile properties of SPI-enhanced quinoa noodles,and adding TG significantly improved the hardness,springiness and chewiness of MPC-enhanced quinoa noodles(p < 0.05).Enzyme extrusion further reduced the cooking loss of exogenous protein-enhanced noodles,among which,SPI-enhanced quinoa noodles with GOD showed the lowest cooking loss of 8.37%,and the e GI value of the noodles decreased from a high level(> 70)to a moderate level(55 ～70).SEM and SDS gel electrophoresis analysis found that the addition of different enzyme formed a regular honeycomb continuous structure or thickened pore wall structure inside the noodles,indicating that GOD and TG promoted the cross-linking between quinoa protein and two exogenous proteins during extrusion process.In addition,starch swelling and free sulfhydryl content in quinoa noodles decreased after enzymatic extrusion,indicating that protein crosslinking hindered the water absorption and dissolution of starch,which were consistent with the reduction of cooking loss and starch digestibility.Compared with commercial quinoa noodles,the gluten-free quinoa noodles prepared by enzymatic extrusion exhibited similar cooking quality and sensory quality,and had higher protein content(22.03%)and in vitro protein digestibility(71.72%),and a lower e GI value(67.83).In conclusion,the gluten-free quinoa noodles produced by twin-screw extrusion process combined with exogenous protein and enzyme showed good cooking quality and texture,high in vitro protein digestibility and a moderate e GI level,providing a theoretical basis for the development of quinoa-based staple with high nutritional value.