Study On The Effect Of Particle Size On The Quality Of Maize Flour And Extruded Maize Noodles

Maize extruded noodles is a kind of maize gel food,which is made from maize flour under low moisture,high pressure and high shear force,after partial gelatinization of starch and aging.At present,high cooking loss is common in the market of maize extruded noodles.Studies have shown that the cooking loss is mainly related to the particle size of the raw maize flour.However,most of the existing studies use the sieve analysis method to study the effect of particle size effect(mainly referring to the component difference caused by different particle size)on the quality of maize flour and noodles.The influence of particle size effect(mainly referring to the difference of particle size and its distribution)caused by different degrees of mechanical force in the grinding process is ignored.Based on this,starting from the two aspects of particle size effect(particle size and its distribution difference and component difference caused by particle size),this paper compared and studied the quality difference of maize flour caused by particle size effect under the two conditions,and on this basis,studied the correlation between particle size effect and maize flour gel quality.The edible quality and digestion characteristics of maize extruded noodles under two kinds of grain size effects were analyzed,in order to clarify the correlation between grain size effect and cooking loss of maize extruded noodles,and to provide theoretical reference and technical support for the development of high quality maize extruded noodles.Firstly,a hammer cyclone mill was used to prepare corn flour with the same composition but different particle size characteristics(denoted as MF)by controlling the number of grinding passes.Based on the particle characteristics of corn flour with bimodal distribution,two kinds of materials corresponding to bimodal distribution(different components and different particle size characteristics)were prepared by screening method based on the bimodal cut-off point(45 μm).The material on the screen was denoted as LF(>45 μm),the sieve is denoted as SF(< 45μm).The results showed that the D50 and D90 of the three kinds of corn flour decreased gradually with the increase of the number of grinding channels,the specific surface area increased,and the particle size distribution range decreased.With the increase of the number of grinding channels,the particle size of LF particles decreased after screening,and the volume proportion of smaller particles increased.Moreover,further grinding did not significantly reduce the particle size of SF.With the decrease of grain size,the damaged starch content of MF,LF and SF gradually increased from 3.70%,undetectable and 25.40% to 26.80%,22.10% and 29.95%,respectively.At the same grinding degree,the total starch content in LF is lower,and the amylose and protein content are higher.The proportion of protein transferred from LF to SF was higher than that of starch as the number of grinding channels increased.At the same time,amylose accounted for a relatively high proportion in the transferred starch.Scanning electron microscope(SEM)showed that the corn endosperm crushing followed the volume crushing model,and the LF crushing might follow the volume-surface area crushing model.In vitro digestion rate and final digestion degree increased by 85.00% and 89.49% respectively with the decrease of particle size.The final digestion degree of LF is higher and the digestion rate is lower.Secondly,the effects of particle size on the gel properties and digestibility of corn flour were investigated.Texture(TPA)results showed that with the decrease of particle size,the strength and hardness of MF prepared gel first increased and then decreased,the viscosity first decreased and then increased,and the chewiness showed a decreasing trend.At the same time,the viscosity of the gel prepared by LF increases and the hardness decreases with the decrease of particle size.The hardness,stickiness and chewability of the gel prepared by SF were lower.SEM plots showed that reducing the grain size of corn flour resulted in a looser structure of the corn flour gel network and an increase in the mesh size.Meanwhile,LF gel showed lamellar and loose microstructure,while SF gel showed dense network structure.The results of low field NMR showed that with the decrease of particle size,the T23 value of MF gel and LF gel decreased by 11.51% and 11.37% respectively,and the proportion of weakly bound water showed a trend of first increasing and then decreasing.The gel network of small grain corn flour has a strong ability to bind water and a low degree of water freedom.In vitro digestibility results showed that with the decrease of particle size,the digestibility of MF,LF and SF gel increased by 31.08%,56.49% and 67.63%,respectively.The final digestion degree increased by 46.13%,15.51% and 14.55% respectively.At the same time,compared with LF,the digestion rate of the gel prepared by SF was lower,and the final digestion degree was higher.Finally,different grain size corn flour was used as raw material to prepare corn extruded noodles,and the effects of two aspects of grain size effect on edible quality,macro and micro structure and in vitro digestibility of corn extruded noodles were explored.The SEM plots showed that the network structure density of the corn flour extruded noodles prepared by the three samples increased after cooking as the grain size of the corn flour decreased.Under the condition of different components,the network structure of corn extruded noodles prepared by SF was more dense after cooking.The cooking characteristics showed that with the same composition,the breakage rate and cooking loss rate decreased by 7.50% and 7.01%respectively with the decrease of corn flour particle size.The starch loss rate and the proportion of starch in cooking loss decreased by 11.42% and 15.29% respectively.The protein loss rate and the proportion of protein in cooking loss decreased first and then increased.Under the condition of different components,the breaking rate of extruded noodles prepared by LF was lower,which were 10.98%,9.76% and 8.54%,respectively.The extrusion noodles prepared by SF had a lower cooking loss rate and a higher water absorption rate.With the decrease of corn flour particle size,the starch loss rate and proportion of the sample showed a decreasing trend,and the protein proportion showed a decreasing trend first and then an increasing trend.The protein loss rate of extruded noodles prepared by LF showed an increasing trend.On the contrary,the protein loss rate in the extruded noodles prepared by SF showed a decreasing trend.In vitro digestion results showed that reducing the grain size of corn flour could increase the digestion rate and starch digestion degree of corn extruded noodles to a certain extent.With different components,the digestion rate and final digestion degree of corn extruded noodles prepared by SF were higher.In conclusion,reducing the grain size of corn flour within a certain range can improve the quality of corn extruded noodles.The extruded noodles prepared with large grain corn flour have better texture characteristics,while the extruded noodles prepared with small grain corn flour have lower cooking loss rate.