Water Binding of Wheat Flour Doughs and Breads as Studied by Deuteron Relaxation

Abstract

Water mobility in wheat flour doughs and breads was investigated by deuteron relaxation using pulsed NMR. Water was replaced by deuterlum oxide in dough and bread at different concentrations. Mixograms indicated that wheat flour associated more strongly with D20 than it did with H20. Varying the D2O:HzO ratio of flour doughs had no effect on the longitudinal (Tt) or transverse (Tz) relaxation times of deuteron. Hard wheat and soft wheat flour doughs showed similar increases in Tt and T2 with increasing moisture content. Staling of bread crumb was accompanied by decreased Tt and T2, indicating an overall decrease in water mobility and increase in water binding. The decrease in water mobility of bread crumb with storage time was shown to be independent of reduction in moisture content.

Effect of Brea Gum on the characteristics of wheat bread at different storage times

“…However, after 24 hours, there was no difference in the hardness of the crumbs in the presence or absence of BG although breads containing BG had significantly lower values of crumb hardness at 48 and 72 hours of storage resulting in a softer crumb than the control. The lower crumb hardness obtained in the samples containing BG could be related to the high moisture content of these crumbs at 48 and 72 hours of storage since the inverse relationship between hardness and moisture content has been widely reported (HUG-ITEN; ESCHER; CONDE-PETIT, 2003; SHARADANANT; KHAN, 2003;FIK;SUROWKA, 2002;LEUNG;MAGNUSON;BRUINSMA, 1983;RIBOTTA;AÑÓN, 2003). Similar results have been found by other authors who have studied other gums such as HPMC, alginate, and k-carrageenaner.…”

Nuclear Magnetic Resonance Studies of Water Mobility in Bread during Storage

“…These T 2 s represent three states of water present in the dough. The single T 2 reported by Leung et al (11) for bread crumb with a moisture content of 0.57 g/g solid was 8.0 ms. Generally, pure water has a T 2 of about 1-2 s. The T 2 of the so-called bound water (i.e. reduced mobility) in the food matrix is believed to be in the range of a few to tens of µs, which is far smaller than those reported by the above authors, suggesting that their techniques failed to detect the very short T 2 that may be associated with structural water.…”

“…The increase in the less mobile water portion may be attributed to one or more of the following reasons: (i) some water molecules initially at more mobile states, e.g. at T 23 state, were locally incorporated into the starch matrix upon staling (11,12) and became less mobile, which may just fall into the T 21 and/or T 22 categories; or (ii) there possibly exists a partially crystalline structure of retrograding starch, since retrogradation is a slow process (20), and relatively immobile water molecules, e.g. those in the T 22 state, which are initially associated with the amorphous regions of starch, may be trapped inside the partially crystalline structure (compartments or 'pockets') of retrograding starch, resulting in a decrease in mobility of these water molecules, part of which may just fall into the T 21 category; (iii) water migration between starch and gluten molecules and hence reassociation of water with these molecules may result in a change in the mobility of water molecules.…”

“…u.-Technol., 30, 178-183 (1997) 0023-6438/97/020178 + 06$25.00/0/fs960163 ©1997 Academic Press Limited that the decrease in water mobility is due to the incorporation of the water molecules into the starch crystalline structure that develops upon staling (11,12). However, no solid evidence to support this hypothesis was presented.…”

Physical investigations of surface membrane–water relationship of intact and gelatinized wheat–starch systems

“…The first layer, referred to as the BET monolayer, defines the most strongly sorbed and least mobile or bound water, and provides maximum stability of a dry product. 6 The second and third layers represent the continued adsorption of additional layers, referred to as free or mobile water. These water components have been studied using nuclear magnetic resonance (NMR); although the information obtained is still debatable.…”