Study On The Effect Of Starch Aging On The Drying Characteristics And Quality Of Sweet Potato Starch Noodles

As China’s traditional food,sweet potato starch noodles are popular among the masses.In its production process,aging,drying is an important link,from ripe noodles to dry noodles,starch gels inside the various levels of complex changes,we know little about this process,but it determines the qualities of noodles.The qualities of sweet potato starch noodles produced by natural air drying method are better than that by hot air drying method,but the qualities of sweet potato starch noodles produced by air drying in different weather are also different.The qualities of sweet potato starch noodles obtained by different aging methods are also different.There are a lot of scientific questions,and the reasons for the qualities improvements are not clear.Therefore,this paper mainly explores the differences between the qualities of dried sweet potato noodles under different relative humidity,and explores the influence of different ways of aging on the qualities of sweet potato noodles,and preliminaries to explore the reasons for the quality differences.Finally,natural drying method and dry sweet potato starch noodles soaking method were used to construct sweet potato starch noodles with specific moisture content and crystallinity to explore the influence of the structure characteristic of sweet potato starch noodles on their rehydration.The main conclusions are as follows:（1）The results showed that with the drying process,the ratio of 1047/1020 cm^-1increased,and the crystallinity increased.The crystallinity of dried sweet potato starch noodles at low,medium and high humidity were 14.72%,16.43%and 13.13%,respectively.SAXS results showed that the rotation radius of dried sweet potato starch noodles were the smallest,and the fractal dimension and lamellar peak area were the largest,which indicated that the internal arrangement of dried sweet potato starch noodles was the most compact and the order degree of starch molecules was the highest at this humidity.The sweet potato starch noodles dried under low humidity were the second,and the sweet potato starch noodles dried under high humidity had the largest radius of rotation,the smallest fractal dimension and peak area,which indicated that the order degree of starch molecules was the lowest,and the inner arrangement of the sweet potato starch noodles were the least compact.Microstructure analysis showed that sweet potato starch noodles had a typical gel mesh structure.Under low humidity,the shrinkage rate of gel pore is obviously faster than that of medium humidity and high humidity.The sweet potato starch noodles section obtained by drying are the most dense.The sweet potato starch noodles dried under high humidity are relatively loose inside,and the sweet potato starch noodles dried under low humidity have some holes.Combined with the results of water distribution,it is found that the crystallinity increases rapidly with the loss of water.（2）Under the three kinds of relative humidity,with the increase of drying time,the rehydration time and rehydration rate of vermicine increased,the swelling degree first decreased and then increased,the dry matter content first increased and then decreased,and the cooking loss was always decreased.Medium humidity（60%-72%RH）and low humidity（38%-40%RH）drying powder swelling degree is lower;At high humidity（75%-89%RH）,the dry sweet potato starch noodles have low rehydration rate,swelling degree and cooking loss.At the same time,with the increase of the drying time,sweet potato starch noodles hardness,chewiness,shear force and shear power,tensile strength,young’s modulus are increased,and when the sweet potato starch noodles in the humidity in the air,the maximum tensile,tensile strength,young’s modulus are maximum,showing resistance to chew,boiling,such as tensile characteristics of good quality.The results of correlation analysis showed that the structural properties of sweet potato starch noodles had a significant effect on the quality of sweet potato starch noodles,among which,the moisture content,short-range ordering,crystallinity,fractal dimension and lamellar peak area of sweet potato starch noodles had the most significant effect on the quality of sweet potato starch noodles（P<0.001）.（3）In order to study the effect of starch aging on the quality of sweet potato noodles,the effects of aging temperature（4℃,25℃）and water removal method（with or without plastic wrap）on the aging rate of starch gels were further discussed,and the differences of starch quality under different aging methods were compared.The results of infrared spectroscopy,crystallization characteristics and lamellar structure showed that the aging rate of sweet potato starch noodles at 4℃were faster than that at 25℃,and the loss of water would promote the aging of sweet potato starch noodles.Rehydration test results show that,compared with the rice noodles produced by industrial production（aging at 4℃for a certain time and drying in 70℃oven）,the rice noodles produced by traditional method（drying at 25℃for a certain time and then wrapping in plastic wrap for 12 h）had higher cooking loss,lower rehydrating rate and swelling degree,and higher dry matter content and cooking loss after cooking.For the sweet potato starch noodles aged at 4℃,the longer the aging time was,the swelling degree tended to decrease,and the dry matter content increased after cooking.However,the crystallization degree of the traditional method is higher than that of the industrial method,which further proves that the quality of the natural drying method is better than that of the hot air drying method.（4）The aging and water loss of sweet potato starch noodles during the drying process will result in the rehydration of sweet potato starch noodles.The final moisture state of the wet sweet potato starch noodles and the degree of starch crystallization will affect its water rehydration.Therefore,natural drying method and dry sweet potato starch noodles soaking method were used to build sweet potato starch noodles with specific water content and crystallinity,and the differences of rehydration quality were compared.The water gradually entered the semi-crystalline area inside sweet potato starch noodles and was closely connected with the starch gel framework,and most of the water was semi-bonded water.The results showed that the double helix structure inside the starch was destroyed and the order degree decreased with the increase of soaking time.For the sweet potato starch noodles in the natural drying group,the hardness,masticability,shear work,shear force,Young’s modulus and tensile strength of vermicelli increased with the increase of drying time.There was an opposite trend for the dry sweet potato starch noodles group.Correlation analysis results showed that the structure of sweet potato starch noodles（short-range ordered structure,lamellar structure,crystal structure）was closely related to the quality of sweet potato starch noodles（rehydration characteristics,texture characteristics,mechanical characteristics）,and the moisture content and short-range ordered structure had the most significant effects on the quality of sweet potato starch noodles（P<0.001）.