Study On The Prepararion And Quality Assessment Of Whole Buckwheat Frozen Extruded Noodles

The nutritional value of buckwheat is comprehensive.Buckwheat noodles make up for the nutritional deficiency and imbalance of traditional wheat noodles greatly.However,buckwheat is short of gluten and cannot form protein network structure.Extrusion could make the buckwheat starch gelatinize under the action of high temperature and shearing force.After molding,through the following aging regulation,starch network formed to replace the protein network and noodles with good quality are obtained.However,the structure of buckwheat noodles made by this technology is compact,resulting in longer reheating time and loss.The noodles are not convenient to eat.Whole buckwheat frozen noodles were developed by this study.The effects of cooling water treatment,frozen temperature and freeze-thaw cycle treatment on the quality of whole buckwheat frozen noodles,and the quality change of noodles during frozen storage were investigated.The results exhibited that the reheating time and loss of extruded noodles decreased significantly,and after the frozen treatment,the noodles retained the quality similar to that of fresh noodles which is convenient to eat.The results are as follows:1.The effect of cooling water treatment on the quality of whole buckwheat frozen noodles was investigated.The results showed that the reheating time and loss declined and the broken rate was zero,indicating the frozen extruded noodles had good quality.The reheating loss decreased from 6.15% in control samples to 4.07% after cooling water treatment for 30 s.After further cooling water treatment,the reheating loss increased.The hardness,springiness,gumminess and chewiness exhibited the increased trend firstly and then decreased tend and reached the highest value after cooling water treatment for 30 s.The adhesiveness value showed a contrary trend.Relative crystallinity increased after cooling water treatment,which resulted from the short-time retrogradation of amylose.After 30 s cooling water treatment,the hole structure at the surfaces of noodles and the lowest freedom of water were observed.The above results demonstrated that 4? cooling water treatment was useful to make the starch gel age quickly after extrusion,improving the quality of frozen noodles.However,a longer cooling time may lead to the increase of ice,and the ice may lead to the damage of starch network.2.The effect of frozen temperature on the quality of whole buckwheat noodles was investigated.The results showed that after-40 o? frozen treatment,noodles exhibited the lowest reheating loss(5.09%)and water absorption(126.51%)as well as the highest hardness(2567.83 g)and springiness(0.98).Moreover,smaller ice and more integrated inner structure were observed by SEM after-40? treatment.Correspondingly,these samples had the lowest freezable water content(35.30%)tested by DSC and the highest bound water and lowest free water obtained by LFNMR,which resulted in less ice formed inside noodles and less damage of starch gel structure.Therefore,the noodles showed the lowest reheating loss and the best texture properties.The above results demonstrated that a suitable frozen temperature(-40?)is helpful to reduce the damage of inner structure of noodles by ice and maintain the quality of noodles.3.The effect of freeze-thaw cycle treatment on the quality of whole buckwheat noodles was investigated.The results showed that the water content decreased while the reheating time and water absorption increased significantly.The reheating loss reached the lowest value(3.53%)after once freeze-thaw treatment.However,the reheating loss increased with the further freeze-thaw cycle treatment.After seventh freeze-thaw cycle treatment,the reheating loss was 6.53% which was far lower than 10%and the broken rate was still zero,indicating that whole buckwheat frozen noodles can resist the damage of inner structure caused by temperature fluctuation and maintain a good quality.For texture properties,hardness increased while springiness decreased.The starch network was more integrated in noodles with no or once freeze-thaw cycle treatment,while cracks appeared on the section of noodles and obvious damage on the surface of the samples treated for more than one time were observed after reheating tested by SEM.It was observed that the relative crystallinity increased from 12.58% to27.92%.The results of DSC and LFNMR showed that freezable water content and mobility declined.The above results demonstrated that amylose and amylopectin interacted with each other and the degree of aging increased.However,with the further freeze-thaw cycle treatment,the enlarged volume of ices brought about the damage to the inner structure of noodles,resulting in the declination of the synesis and quality of noodles.4.The quality changes of frozen whole buckwheat noodles during 180 d frozen storage were investigated.The results showed that the water content decreased while reheating time,water absorption and dry consumption rate increased.Reheating loss increased from 3.20% to 4.31%.Hardness increased and then decreased while springiness decreased slightly.Starch gel structure was damaged after long time storage and the porous structure became uneven and cracks appeared observed by SEM.The result of XRD exhibited that the relative crystallinity increased gradually during frozen storage.The freezable water content decreased observed by DSC.The above results demonstrated that the qualities of noodles were affected by two factors including the retrogradation of starch and recrystallization of ice.In general,the qualities of whole buckwheat frozen noodles were relatively stable during 180 d frozen storage at-18?.