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Journal of Food and Drug Analysis, Vol. 12, No. 3, 2004, Pages 221-227
Water Status of Two Gelatin Gels during Storage as Determined by Magnetic Resonance Imaging
YI-LIN CHUNG AND HSI-MEI LAI*
Department of Agricultural Chemistry, National Taiwan University, 1, Sec. 4, Roosevelt Rd., Taipei 106, Taiwan, R.O.C.
(Received: October 20, 2003; Accepted: May 12, 2004)
ABSTRACT
A two-gelatin-gel model system was used to investigate the water status of two gels with different Aw, 0.968 (H-gel) and 0.828 (L-gel), using magnetic resonance imaging (MRI) techniques. A multi slice-multi echo pulse sequence was applied and the transverse relaxation time (T2) of water protons was calculated. During storage the average T2 values of H-gel decreased, while those of L-gel increased. However, at the end of storage (15 days) when the Aw of two gels were the same, the average T2 values of L-gel were larger than those of H-gel, and heterogeneous T2 values were observed in both gels. This was due to water migration between the two gels and redistribution of water in each gel during storage. The two-gelatin-gel model system and nondestructive MRI technique established in this study offer a good method to monitor moisture redistribution between gels with different Aw and to investigate the water status and structural changes in food systems during storage.
Key words: water status, gelatin gel, magnetic resonance imaging (MRI), transverse relaxation time (T2), water activity (Aw)
INTRODUCTION
Water is the most important component in foods that affects their quality, stability, textural properties, and processing. Water status describes the chemo-physical state of water molecules and is associated with the interaction between water and other molecules. However, various foods with the same water content differ in stability and it has been recognized that water content alone is not an adequate indicator of food stability(1,2). Scott introduced the concept of water activity (Aw) as an indicator of water status(3). Although Aw has been widely used as a measurement for quality control of lipid oxidation(4), nonenzymic browning(5), nutritional quality(6), texture(7), and microbial growth(8), several studies also indicated some of the theoretical and practical limitations of Aw(2,9,10,11). Pham and
others found that water activity failed to predict mold germination with changing solid composition(11). They also claimed NMR was a better indicator of water...