基于低场核磁和差示量热扫描的面条面团水分状态研究

为了解低水分面条面团中水分的存在状态，明确真空度及和面时间对水分状态的影响，该研究以3个小麦品种（济麦20、宁春4号、济麦22）磨制的面粉为材料，采用真空和面制作低水分面条面团（含水率35%），采用低场核磁共振技术（LF-NMR，low-field nuclear magnetic resonance）和差示量热扫描（DSC，differential scanning calorimetry）2种技术，测定不同真空度（0、0.06、0.09 MPa）和搅拌时间（4、8、12 min）下面团中水分的形态和分布，并进一步分析2种技术测定水分形态结果的相关性。结果表明，在低水分面条面团中，水分主要以弱结合水形态存在。不同品种的小麦粉面团的水分形态及分布存在差异，强筋小麦粉（济麦20）制作面团的水分自由度较低。真空和面（0.06 MPa）可以促进水分与面筋蛋白的相互作用，降低面团中水分子流动性，促进水分结构化；而非真空或过高真空度均会导致面团中水分自由度增加。济麦20、济麦22小麦粉和面时间为8 min时，面团水分流动性较低；而宁春4号小麦粉面团在4 min时，水分自由度较低；继续搅拌，深层结合水减少、弱结合水增多。LF-NMR和DSC测得面团水分状态的结果具有一致性。LF-NMR测得的弱结合水峰面积百分比与DSC测得的可冻结水百分比具有相同的变化趋势（r=0.695），且深层结合水峰面积百分比与非冻结水百分比具有相同的变化趋势（r=0.564）。研究结果为认识制面过程中水分的作用，优化和面工艺和调整产品特性提供参考。

Water state and distribution in noodle dough using low-field nuclear magnetic resonance and differential scanning calorimetric

Abstract: Dough mixing is the key step in noodle production, which has a great influence on noodle quality and performance in subsequent processing. During the noodle dough mixing, there is a limited development of gluten due to low water addition (only 30%-37% moisture content), resulting in crumbly dough pieces. Studying the state and distribution of water in noodle dough has important implications for better understanding physical and chemical changes during dough mixing, illuminating the effect of water on noodle processing and providing the guidance for mixing technology optimization. In this study, 3 kinds of wheat flour with different qualities were used as test materials, and the noodle doughs (with the moisture content of 35%) were made by vacuum mixing at different vacuum degrees and mixing time. The state and distribution of water in sheeted noodle dough were determined by low-field nuclear magnetic resonance (LF-NMR) and differential scanning calorimetric (DSC). The correlation between the results of water state detected by the 2 techniques was also analyzed. The results showed that 3 spin-spin relaxation time constants, namely T21, T22 and T23, were identified by the LF-NMR experiments using the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. The second category of water (T22, 0.49-21.54 ms) represented the less tightly bound water, and made up almost 80% of the total moisture in noodle dough. The gluten content and quality of wheat flour had influence on the state and distribution of water in noodle dough, and the mobility of water in dough from strong gluten wheat (Jimai 20) was lower than that from other 2 weak gluten wheats. According to the effects of vacuum degree on T2 and its corresponding peak area, the vacuum mixing at 0.06 MPa may promote the interaction of water and gluten protein, and result in a decrease in the molecular mobility of water in noodle dough. And non-vacuum condition or excessive vacuum (0.09 MPa) could also increase the molecular mobility of water in dough. For Jimai 20 and Jimai 22, the mobility of water was low in noodle dough after being mixed for 8 min, and the mixing time of deficiency (4 min) or excess (12 min) could lead to significantly higher water mobility as evidenced by LF-NMR and DSC. While for the flour of Ningchun 4 with low protein and gluten content, the water mobility was low in dough after mixed for 4 min; with mixing time prolonging, the fraction of less mobile water decreased and the more mobile fraction increased. The results of water state in noodle dough measured by LF-NMR and DSC were consistent. The change tendency for the less tightly bound water (T22) detected by LF-NMR was the same to that for freezable water detected by DSC, and the change tendency for the tightly bound water (T21) was the same to that for non-freezable water. LF-NMR technique is accurate, sensitive, convenient and non-destructive, which is the preferred technique to analyze the state and distribution of moisture in food.