- 42 - Scientific Journal of Frontier Chemical Development June 2013, Volume 3, Issue 2, PP.42-46 A Low-Field NMR Study on the Water Condition of Tripe Swelling in Sodium Carbonate-Solution Ying Han 1, Yingchun Zhu 1*, Lizhen Ma 2*, Caihong Liu 2, Yiqing Yang 2 1. College of Food Science, Shanxi Agriculture University, Taigu, 030801, China; 2. Department of Food Science, Tianjin Agricultural University, Tianjin, 300384, China; Email: 1 hanying_4135@126.com, 2 yingchun0417@163.com, 2 malizhen-6329@163.com. Abstract In this paper, a low-field NMR study was performed to obtain the information on the water condition of tripe swelling in sodium carbonate-solution (Na2CO3-solution). The study researched the water state during different soaking times, concluded that the crispy cooked tripe is closely related with transverse relaxation time (T2) rather than water content. In addition, the water mobility was also found to be affected by soaking time. The study demonstrated that NMR T2 relaxometry was a potential tool to explore the water state, mobility and the way the different water components shift. Keywords: NMR; T2 Relaxation; Water Content; Cutting Force 1 INTRODUCTION Ox-tripe is one of the most popular food in China, especially almost indispensable to hot pot. The original tripe was dried-product salted to prolong storage time. But after swelling in sodium carbonate-solution (Na 2 CO 3 -solution) and cooked in boiling water, the dried-product was crispy and delicious, with physical fitness, increasing the effectiveness of immunity. Soaking in Na 2 CO 3 -solution is the main processing method of swelling tripe. The structure of proteins can be damaged by lye [1]. Moreover, Na 2 CO 3 -solution can replace sodium hydroxide- solution (NaOH-solution), which was not allowed for foods. The process of tripe swelling in Na 2 CO 3 -solution is a procedure to absorb water gradually, ascribed to the damaged structure of proteins that promote the water channels and lead to water uptake [2]. However, the focus is the key factor of crispy after cooking. The study will research on the internal water during the swelling process and the corresponding cutting force. Nuclear magnetic resonance (NMR) transverse relaxation time (T2) has proven to be a very informative method to explore the water condition in process of tripe swelling [3]. Continuous relaxation time spectrum would give a full assessment on the properties of water in the meat [4]. Three components(bond, immobilized, and free-water) characterized with different transverse relaxation times, in the following referred to as T21 (0-10 ms), T22 (10-100 ms) and T23 (100-1000 ms), are generically detected in meats, the different forms of water bonding in meat, as these formations could easily be transformed into each other [3]. The objective of this study was to reveal the water condition in ox-tripe swelling in sodium carbonate-solution. 2 EXPERIMENTAL METHODS 2.1 Sample Preparation The fresh ox-tripe dried-product with salt stored in refrigerator was divided into five portions, each of which was approximately 2 g, and the salt was washed out by water. In addition, among these portions, four portions were randomly chosen and put into four beakers with 2% of Na 2 CO 3 -solution, respectively. The samples were soaked in the solution for 0 h, 2 h, 4 h, 6 h and 8 h at room temperature. 2.2 NMR T2 Measurements NMR relaxation measurements were performed on a NMR analyser (NIUMAG) with a magnetic field strength of 0.5
Tesla, operated at a resonance frequency for protons of 22 MHz. Each measurement included the registration of decaying transverse magnetization using Carr-purcel-Meibom-Gill (CPMG) sequence and free induction signal [6]. Approximately 0.5g of sample after soaking, rinsing Na 2 CO 3 -solution, was placed in a 15mm diameter cylindrical tube and inserted in the NMR probe [10] before draining the water and weighing. At last, the amplitude of all samples was normalized. 2.3 The Water Mobility Determination Water mobility has significant relations with NMR transverse relaxation time. The longer relaxation time is, the less closely it combined with the substrate is, and the water has more liquidity [9]. That was weighted mean T2 relaxation times increased reveals the increased water mobility that could be ascribed to the increased spacing of water channel [1]. 2.4 Cutting Force Determination T2 = i(t2i fi) / ifi The cutting forces of cooked ox-tripe after soaking that were instant-boiled in boiling water for 30 s were measured using a texture analyzer (Stable Micro System; TA: XT, England) with a knife blade. The test speed of knife blade was 1 mm/sec with the distance of 20 mm. The maximum force to cut transversally into of the sample that was cut for 2 cm width and 5 cm length was recorded as the cutting force, the lower, the more crispy and delicious. And a minimum of 3 tripes was analyzed [8]. 2.5 NMR Microimaging Measurements MRI microimaging was employed to test the water signal of the samples during the different soaking time. Approximately 0.5g of sample was placed in a diameter cylindrical tube and inserted in the NMR probe [10]. A multi-echo spin-echo sequence was used to acquire the images. 2.6 Statistical Analysis Data were analyzed using the General Linear Models procedure of Statistix 8.1 software package (Analytical Software, St. Paul, MN) for microcomputer. Analysis of variance (ANOVA) was done to determine the significance of the main effects. 3 RESULTS AND DISCUSSION 3.1 Changes of Water Condition 60 50 0 h 2 h 4 h 6 h 8 h 40 Amplitude 30 20 10 0 0.01 0.1 1 10 100 1000 T2(ms) FIG. 1 CHANGES IN CONTINUOUS T2 DISTRIBUTION SPECTRA OF DIFFERENT SOAKING TIMES The changes in continuous relaxation time distribution spectra were followed during shift of water from soaking tripe in different time. Fig. 1 showed the score plot for PCA (principal Component Analysis) analysis on the NMR T2 relaxation data obtained from different samples. The fig revealed the regulation of water shifting during the - 43 -
swelling process. 2 h latter, the samples started soaking in water from the solution. Fig. 1 showed the more free water had appeared, compared with none soaked. The position of the major component clearly shifted towards higher relaxation times, which can explain the protein structure that had been damaged by lye, providing the channel for water moving into tripe. Subsequently, 4 hours later, the water from solution continued moving into them. Further more, the transverse relaxation time (T2) 0-1 ms water (the most closely combined with substrate) appeared. While after the 6th hour, this component disappeared. Besides, the immobilized water was gradually into the more free water [5]. And on the 8th hour, the content of all the three components water increased again. Accordingly, the tripe swelling procedure is a dynamic process. The water state changed with the extent of the protein denaturing. 3.2 The Water Mobility Fig. 2 presents the changes in the weigh mean T2 relaxation times of the three components water cluster. The longer the relaxation time is, the higher the water mobility is. Along with the extended of soaking time, the mobility of the bond water (T21) cluster had a rising tendency even though fluctuated, which can explain the lye making the tripe collagen structure in relaxation [2], the same as T22. In contrast T23, this phenomenon that is not obvious, can explain this component water combined loosely with the macromolecules, and showing that it s high degree of freedom. 5.0 4.5 T21 T22 T23 44 42 40 320 300 280 4.0 38 260 T21(ms) 3.5 3.0 36 34 32 T22(ms) 240 220 200 T23(ms) 2.5 30 180 2.0 28 26 160 140 1.5 24 120 0h 2h 4h 6h 8h Soaking time FIG. 2 CHANGES IN NORMALIZED T2I IN DIFFERENT SOAKING TIMES 3.3 Changes in Cutting Force 8000 7000 6000 Cuting force 5000 4000 3000 2000 0h 2h 4h 6h 8h Soaking time FIG. 3 CHANGES IN CUTTING FORCE IN DIFFERENT SOAKING TIMES Fig. 3 displays the changes in cutting force at the different soaking times, which decreased significantly in 0 h 2 h, and continued to decrease slightly two hours later, the forth hour to a minimum and ascribed to the water tightly - 44 -
combined with macromolecules at that time, so it was hardly flowing out although were placed in boiling water. Subsequently, cutting force was increased slightly between 6 h and 8 h. 3.4 Visualization of Water Migration in Tripe Using NMR Microimaging Fig. 4 showed representative T2 images acquired at 0 h 2 h 4 h 6 h 8 h showing areas of intensity with higher values (white), which was the signal of water [7]. During the measuring period, the intensity became increasingly evident. The signal intensity increased after 0 h, which reflected more and more water moving into the samples, and there was the most water content in samples at the 8th hour. It should be emphasized that although the water in tripe increased gradually over time, the most tightly water appeared at the point of 4 h with the minimum cutting force. 0 h 2 h 4 h 4 CONCLUSIONS 6 h 8 h FIG. 4 THE MRI IMAGE OF THE TRIPE The purpose of tripe swelling is to make water move to the internal. Sodium carbonate can destroy the protein structure and make it become loose, providing the water channel for swelling. This procedure is a dynamic process of three components water mutually transformed each other. Moreover, the crispy of cooked tripe and the bond water were closely related, instead of water content, because it was affected slightly by boiling water while the free water flowing out easily, and the shorter the relaxation time is, the more tightly it combined with macromolecules. Beside, the NMR T2 relaxometry was a potential tool to explore the water state, mobility and the way different water components shift. REFERENCES [1] Bin Li, Jin Li. Study on the Effect of Lye on the Rehydration of Beef Tripe. Journal of Food Research and Relationship Development, 2011 [2] Bertram, H. C., Purslow, P. P., Andersen, H. J. Relationship between meat structure, water mobility, and distribution: A low-field nuclear magnetic resonance study. Journal of Agricultural and Food Chemistry, 50, 824-829, 2002b [3] Bertram, H. C., D Strup, S., Karlsson, A. H., Andersen, H. J., Continuous distribution analysis of T2 relaxation in meat-an approach in the determination of water holding capacity. Meat Science, 60, 279-285, 2002a [4] Bertram, H. C., Karlsson, A. H., Andersen, H. J. The significance of cooling rate on water dynamics in porcine muscle from heterozygote carriers and non-carriers of the halothane gene - a low-field NMR relaxation study. Meat Science, 65, 1281-1291, 2003b [5] Bertram, H. C., Engelsen, S. B., Busk, H., Karlsson, A. H., Andersen, H. J. Water properties during cooking of pork studied by - 45 -
low-field NMR relaxation: Effects of curing and the RNgene. Meat Science, 66, 437 446, 2004b [6] Lda Krestine S, Marianne r, Jorgen A H, et al. Aging-induced changes in microstructure and water distribution in fresh and cooked pork in relation to water-holding capacity and cooking loss: a combined confocal laser scanning microscopy(clsm) and low-field nuclear magnetic resonance relaxation study[j]. Meat Science, 75: 687-695, 2007 [7] Laurent, W., Bonny, J. M., Renou, J.P. Muscle Characterisation by NMR imaging and spectroscopic techniques. Food Chemistry, 69, 419 426, 2000 [8] M. B. Hale, and M. E. Waters, Marine Fish Review, 42, 18, 1981 [9] Ran Li, Zhenchuan Li. Study of Water Absorption of Mung Beans Based on Low-field Nuclear Magnetic Resonance Technology. Journal of the Science of Food, 15, 2009 [10] Soriand G H, Larsen P M, Lundby F. Determination of total fat and moisture content in meat using low field NMR [J]. Meat Science, 66: 543-550, 2004-46 -