Enzymatic modification is an important approach to changing the structure and expanding industrial application of natural starch. In the process of starch modification, thermostable enzymes are favored owing to their ...Enzymatic modification is an important approach to changing the structure and expanding industrial application of natural starch. In the process of starch modification, thermostable enzymes are favored owing to their compatibility with higher reaction temperatures and lower required dosage. In this study, thermostable glucoamylase from Thermothelomyces thermophilus(TtGA) was heterologously expressed in Pichia pastoris, and its effects on the structure and physicochemical properties of raw corn starch were determined. The purified TtGA had a molecular weight of approximately 66 kDa, and its optimum reaction temperature and pH were 50 ℃ and 5.0, respectively. TtGA retained > 60% of its activity following treatment at 60 ℃ for 2 h and remained stable within a pH range of 4.0–7.0 for 6 h. The enzymatic modification of raw corn starch with TtGA led to 3% hydrolysis at 50 ℃ for 24 h. In comparison with natural raw corn starch, TtGA-modified starch had a smaller particle size with an unchanged crystalline structure, increased relative crystallinity, and amylose content.Scanning electronic observation showed that larger pores were formed on the surface of starch particles, and Fourier-transform infrared spectroscopy indicated that TtGA increased the degree of order in the raw corn starch.TtGA modification caused enhanced viscosity of the raw corn starch and altered the rheological properties with decreases in storage and loss moduli, as well as shear viscosity. Moreover, TtGA treatment enhanced the thermal characteristics of the raw corn starch, and decreased gelatinization enthalpy. This study provides detailed evidence for TtGA modification of raw corn starch, which would be helpful for its practical utilization in starch modification.展开更多
Dumpling is one of the most important traditional wheat products in China. Dumpling quality is determined by the characteristics of both flour and filling, thus improvement of flour quality plays an important role in ...Dumpling is one of the most important traditional wheat products in China. Dumpling quality is determined by the characteristics of both flour and filling, thus improvement of flour quality plays an important role in improving dumpling quality. Thirty-nine Shandong winter wheat cultivars and advanced lines sown in Jinan, Shandong Province, China, in the 2008-2009 cropping season were used to determine genetic variation in Chinese raw dumpling quality and its relationship with flour characteristics. Large variations were observed for protein quality parameters in comparison with starch properties. Variation in color of the raw dumpling sheet was broader than that of sensory evaluation parameters of boiled dumpling among tested wheat cultivars, indicating the large influence of filling on dumpling color. Two cultivars, Jimai 20 and Zimai 12, were identified as possessing very good quality of raw dumpling, and 21 cultivars and advanced lines showed good quality. Protein and total starch content influenced the L＊ value of raw dumpling sheets. L＂ value at 0 and 2 h after sheeting were significantly influenced by protein content （r=-0.46 and -0.52, P〈0.01） and total starch content （r=0.55 and 0.57, P〈0.01）, respectively. Flour yellow pigment was significantly corrected with a＊ （r=-0.67 and -0.62, P〈0.01） and b＊ （r=0.87 and 0.84, P〈0.01） value of raw dumpling sheets at 0 and 2 h after sheeting, respectively. Gluten strength parameters such as farinograph mixing tolerance index （MTI, r=-0.55, P〈0.01） were positively associated with appearance. MTI and energy were also significantly and positively correlated with elasticity of raw dumpling, with r=-0.54 and 0.47 （P〈0.01）. The positive relationships between peak viscosity （r=0.51, P〈0.01）, breakdown （r=0.54, P〈0.01）, and smoothness of raw dumpling were also observed. Therefore, it is suggested that breeding programs should give more attention to gluten strength and starch pasting parameters for raw dumpling quality improvement.展开更多
基金supported by the National Key Research and Development Plan of China(grant number 2023YFC2604903)National Natural Science Foundation of China(grant number 22338013)+2 种基金Natural Science Foundation of Henan Province(grant number 242300421106)Henan Province Science and Technology Research and Development Plan Joint Fund Project(grant number 222103810063)Key Scientific and Technological Project of Education Department of Henan Province(grant number 23A210007).
文摘Enzymatic modification is an important approach to changing the structure and expanding industrial application of natural starch. In the process of starch modification, thermostable enzymes are favored owing to their compatibility with higher reaction temperatures and lower required dosage. In this study, thermostable glucoamylase from Thermothelomyces thermophilus(TtGA) was heterologously expressed in Pichia pastoris, and its effects on the structure and physicochemical properties of raw corn starch were determined. The purified TtGA had a molecular weight of approximately 66 kDa, and its optimum reaction temperature and pH were 50 ℃ and 5.0, respectively. TtGA retained > 60% of its activity following treatment at 60 ℃ for 2 h and remained stable within a pH range of 4.0–7.0 for 6 h. The enzymatic modification of raw corn starch with TtGA led to 3% hydrolysis at 50 ℃ for 24 h. In comparison with natural raw corn starch, TtGA-modified starch had a smaller particle size with an unchanged crystalline structure, increased relative crystallinity, and amylose content.Scanning electronic observation showed that larger pores were formed on the surface of starch particles, and Fourier-transform infrared spectroscopy indicated that TtGA increased the degree of order in the raw corn starch.TtGA modification caused enhanced viscosity of the raw corn starch and altered the rheological properties with decreases in storage and loss moduli, as well as shear viscosity. Moreover, TtGA treatment enhanced the thermal characteristics of the raw corn starch, and decreased gelatinization enthalpy. This study provides detailed evidence for TtGA modification of raw corn starch, which would be helpful for its practical utilization in starch modification.
基金supported by an international collaboration project on wheat improvement from the Ministry of Agriculture of China (2006GR)
文摘Dumpling is one of the most important traditional wheat products in China. Dumpling quality is determined by the characteristics of both flour and filling, thus improvement of flour quality plays an important role in improving dumpling quality. Thirty-nine Shandong winter wheat cultivars and advanced lines sown in Jinan, Shandong Province, China, in the 2008-2009 cropping season were used to determine genetic variation in Chinese raw dumpling quality and its relationship with flour characteristics. Large variations were observed for protein quality parameters in comparison with starch properties. Variation in color of the raw dumpling sheet was broader than that of sensory evaluation parameters of boiled dumpling among tested wheat cultivars, indicating the large influence of filling on dumpling color. Two cultivars, Jimai 20 and Zimai 12, were identified as possessing very good quality of raw dumpling, and 21 cultivars and advanced lines showed good quality. Protein and total starch content influenced the L＊ value of raw dumpling sheets. L＂ value at 0 and 2 h after sheeting were significantly influenced by protein content （r=-0.46 and -0.52, P〈0.01） and total starch content （r=0.55 and 0.57, P〈0.01）, respectively. Flour yellow pigment was significantly corrected with a＊ （r=-0.67 and -0.62, P〈0.01） and b＊ （r=0.87 and 0.84, P〈0.01） value of raw dumpling sheets at 0 and 2 h after sheeting, respectively. Gluten strength parameters such as farinograph mixing tolerance index （MTI, r=-0.55, P〈0.01） were positively associated with appearance. MTI and energy were also significantly and positively correlated with elasticity of raw dumpling, with r=-0.54 and 0.47 （P〈0.01）. The positive relationships between peak viscosity （r=0.51, P〈0.01）, breakdown （r=0.54, P〈0.01）, and smoothness of raw dumpling were also observed. Therefore, it is suggested that breeding programs should give more attention to gluten strength and starch pasting parameters for raw dumpling quality improvement.
