Study On The Quality Of Sweet Potato Starchnoodles And Its New Drying Technology

Sweet potatoes are rich in nutrients,especially rich in starch,and have a variety of healthcare function,so they are the excellent raw materials for food processing.Due to its high viscosity properties,sweet potato starch noodles have the better elasticity,chewiness,and they are resistant to boiling.Therefore,it is an ideal material for starch noodles.Although starch noodles have been in our country for a long time,the research on their sensory science is relatively backward,which obstructs the rapid development of this kind of products.Drying is the key link that its operating parameters heavily affected the quality of the final product.The traditional natural air-drying has the long cycle and many uncontrollable factors,and hot air drying has the short cycle and is easy to control.However,some research has found that the product quality of hot air drying is inferior to that from natural air-drying.Nevertheless,the underlying quality inferiority mechanism of hot air drying to natural air-drying in drying starch noodles was not been adequately explored and remained unknown.The purpose of this study is to study the difference of quality between natural air-drying and hot air drying and discuss the mechanism of the difference of quality.Meanwhile we try to improve the quality of hot air dried starch noodles by controlling the drying parameters?temperature and relative humidity?in the drying process.The final aim is to find a new drying technology for sweet potato starch noodles with high quality and high efficiency.At the same time,it provides a theoretical basis for the mechanism of its improvement of quality.The results are as follows:?1?Based on the relationship between the texture,cooking quality index of objective analysis index and the consumer acceptance of sensory evaluation,a new prediction model for the consumer acceptability of starch noodles was established.The model extracted three principal components from eight physicochemical characteristics indexes of forty commercial starch noodles?thirty-two in calibration set and eight in validation set?by principal component analysis.Moreover,their cumulative variance contribution rate of the model was up to 74.9%,which could represent the majority of the original eight quality indexes?74.92%?.The consumer acceptance standard value?A_z?prediction model?A_z=0.509Y₁+0.291Y₂+0.200Y₃?was also established.The internal verification and the external verification showed that the correlation coefficients between the predicted value and the measured value were very high,and the correlation coefficient was very close to 0.900.?2?Based on the comparison of quality of sweet potato starch noodles with two conventional drying methods,which was natural air-drying and hot air drying.The results showed that the surface of natural air-dried sweet potato starch noodles was shiny and smooth,but hot air dried starch noodles became rougher,shrunk and cracked with the increase of drying temperature.The cooking loss,swelling index and broken rate of natural air-dried starch noodles were significantly lower than those from hot air drying.Hardness and chewiness of natural air-dried starch noodles were significantly higher than those from hot air drying.All that showed the natural air-dried starch noodles was resistant to boiling,chewy and elastic.However,with the increase of drying temperature,swelling index of hot air dried starch noodles increased significantly,but hardness,elasticity and chewiness decreased significantly.Thus,the quality of natural air-dried starch noodles was superior to that from hot air drying.Through the determination of crystallinity,gelatinization enthalpy and microstructure,it could be largely ascribed to the higher crystallinity and gelati;nization enthalpy of the natural dried starch noodles,the structure was more compact,less porosity,less shape deformation as well as smoother surface.?3?By controlling the relative humidity during the hot air drying process,it showed that with the increase of relative humidity,the total drying time increased significantly.However,the surface of starch noodles became smoother,swelling index decreased significantly but cooking loss increased significantly.Both hardness and chewiness increased significantly.Through the determination of crystallinity,gelatinization enthalpy and microstructure,this could be largely ascribed to the crystallinity and gelatinization enthalpy of the starch noodles increased significantly,and the structure was more compact,less porosity,less shape deformation as well as smoother surface upon the elevating relative humidity in hot air.The quality of 60%relative humidity hot air dried starch noodles were similar to those from natural air dried starch noodles and the total drying time was relatively shorter.?4?In order to improve the drying efficiency and shorten the total drying time,the drying technology with temperature 70 ^oC and relative humidity 60%was further studied.The drying process divided into two stages.The effects of drying time of the first stage and drying temperature of the second stage on drying characteristics,cooking characteristics,rehydration rate and crystallinity was studied,respectively.The results showed that the total drying time was prolonged significantly with the increase of drying time of the first stage.After 45 min,with the increase of drying time of first stage,it had no significant effect on the cooking loss,swelling index and rehydration rate of starch noodles,which may be attributed to the maximum crystallinity after 45 min.Under the constant condition that temperature was 70 ^oC,the relative humidity was 60%drying 45min,then with the increase of drying temperature of second stage,the total drying time reduce significantly,cooking loss decreased significantly,swelling index and rehydration rate have no significant change as well as crystallinity.Thus,the best drying technology of sweet potato starch noodles was 70 ^oC,relative humidity 60%drying 45min,then 100^oC drying 26 min,total drying time was 71 min,and the quality of sweet potato starch noodles was close to that from natural air drying.