Water mobility for Chinese dried noodles with varied gluten and moisture content during drying
Y. WEI (1), Y. Zhang (1), X. Yu (1), Z. Wang (1) (1) Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences, , China; (2) Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences, Beijing, China.
The objective of this study was to investigate the water mobility in Chinese dried noodles with different gluten and moisture content during drying process. Reconstituted noodles were produced using gluten and wheat starch with gluten content of 10, 12.5, 15, 17.5, 20, 22.5 and 25% and noodle moisture content were set as 30, 32 and 34%. The fresh noodles were produced as square with the length of cross section of 2 mm after dough resting for 30 min, and then were dried at 40°C and relative humidity of 75% for 4 hours in a humidity chamber. Water status and distribution within noodles during drying were measured using NMR spectroscopy and MR imaging, and the microstructure of the dried noodles were examined by SEM. The results revealed that 80% of the moisture in dough and fresh noodles was strongly and less bound water with spin-spin relaxation time T22 of 4-8 ms. T22 increased with gluten and moisture content, but it was less affected by dough resting time. During drying, T22 decreased from 5-6 ms to 1-1.7 ms with increased drying time, indicating the moisture is more strongly bounded with the noodles. T23 peak was also found in the drying process, indicating that the moisture may be transferred as vapor during drying. The moisture transfer in noodles was slowed down with increased gluten content, which decreased the drying rate of the noodle for all different initial moisture contents. This was also confirmed by the denser noodle microstructure from SEM image. The drying rate was larger for noodles with lower gluten content and higher initial moisture content, but the final noodle moisture contents were approximately 15% and not significantly affected by the gluten and moisture content. Moreover, the drying front was found in cross sections of noodles during drying, and the high moisture gradient in this area may lead to noodle warping.
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