Retrogradation Characteristics And Mechanism Of Potato Starch Gel Under Subfreezing Temperature

Temperature is an important factor in regulating starch aging.Aging at different temperatures affects the nucleation types of starch molecules in the process of aging and regeneration,and then affects the aging rate of starch molecules.The optimal subfreezing temperature of potato starch gels at different concentrations and different gelatinization degrees was found out in this paper.Then the storage and retrogradation tests of potato starch gels with a concentration of 8% in the completely gelatinized state were carried out,and the gel retrogradation characteristics under subfreezing temperature and other control temperatures were compared and analyzed.The aim of this paper is to improve the quality characteristics of starch products without additive by using the moderate retrogradation of starch gel regulated by temperature and to provide theoretical basis for starch deep processing industry.The results are as follows:(1)Aging process of non-additive potato vermicelli and the quality changes during storageThe process optimization of potato vermicelli without addition was carried out by single factor and orthogonal test and combining the hardness,elasticity,break rate and paste rate of potato vermicelli.It was found that the processing parameters without potato vermicelli were as follows: setting time of 60 s,aging time of 90 min at room temperature,and aging temperature of-2 ℃ at low temperature.The sensory score was the highest,and the quality of vermicelli was the best.It was found that the quality of potato vermicelli began to decline after six days of storage through the low-temperature storage test of the optimal processing vermicelli.(2)Study on subfreezing temperature of potato starch gels with different concentrationsThe potato starch concentration has obvious changes on the undercooling effect,the initial freezing point,the glass transition temperature and the melting temperature.In the process of quick freezing,when the temperature was lower than-3 °C,the content of liquid water in the gel decreased greatly,and the density of hydrogen protons also decreased rapidly.The lowest initial freezing point of potato starch gel at the four concentrations was-1.4 °C,the lowest glass transition temperature was-3.69 °C,and the highest melting temperature was 10.02 °C.Because the retrogradation temperature range of starch gel is between the glass transition temperature(-3.69 °C)and the melting temperature(10.02 °C).At the same time,the subfreezing temperature range is between the glass transition temperature(-3.69 °C)and the freezing temperature(-1.4 °C).Moreover,when the temperature is closer to the glass transition temperature,the internal molecular state of the gel is more stable.Therefore,-3 °C was selected as the subfreezing temperature of potato starch gel at different concentrations in the range of 3 °C～-18 °C.(3)Study on subfreezing temperature of potato starch gel under complete and incomplete gelatinization conditionsIn incomplete gelatinization,the free moisture content of potato starch gel was higher,and it was more likely to change into ice phase.In incomplete gelatinization,the glass transition temperature of the gel was-4.87 °C and the initial freezing temperature was-0.7 °C.Because the retrogradation temperature range of starch gel is between the glass transition temperature(-4.87 °C)and melting temperature(6.54 °C),it is more accurate to choose-3 °C as the subfreezing temperature between the freezing point temperature(-0.7 °C)and the glass transition temperature(-4.87 °C)in the incomplete gelatinization state.(4)The effect of subfreezing temperature treatment on the macroscopic properties of potato starch gelThe gel strength and growth rate of gel were the highest under the subfreezing temperature.The rheological dynamic viscoelastic measurement of gel showed that the gel regenerated faster at subfreezing temperature,its elasticity gradually increased,and its stability was enhanced.The water holding capacity of the gel was higher than that of other temperatures.The gel whiteness at subfreezing temperature showed no significant difference compared with the other two control temperatures(3 ℃ and 0 ℃),but was higher than that at control temperatures(25 ℃ and-18 ℃).The freezable water content of gel increased with gel retrogradation,but the freezable water content of gel at subfreezing temperature was lower than that at control temperature,and the non-freezable water content was about 10% higher than that at other control temperatures.(5)The effect of subfreezing temperature treatment on the microcosmic properties of potato starch gelAccording to the water relaxation time and the light and dark change of hydrogen proton density image,it could be seen that potato starch gel regenerated fastest under the subfreezing temperature treatment compared with other regenerating temperature treatments.At the same time,compared with other temperatures,the relative crystallinity and the increased rate of crystallinity at subfreezing temperature was the highest.Microscopic scanning electron microscope analysis showed that the gel reticulum wall was relatively intact at subfreezing temperature without large area damage phenomenon,indicating that the ice crystal nucleus played a positive role in the gel at the early stage of regeneration.Infrared spectrum analysis showed that the short-range order of the gel was more obvious and the helical structure was more at subfreezing temperature.However,there was no significant difference in gel thermodynamic properties.In this paper,potato starch gel was treated by subfreezing without adding potato vermicelli,and better results were obtained.The results indicated that subfreezing temperature storage had a positive effect on the treatment of starch gel.This study provides some theoretical value for the retrogradation of starch and the processing and research of non-added starch products.