Long‐Term Storage Effect in Frozen Dough by Spectroscopy and Microscopy

Abstract

Storage of dough at low temperatures (‐20°C) has a considerable effect on the final quality of baked bread; this is most obviously reflected in lowered specific volumes. In this study, a suite of structural characterization techniques is applied to examine the underlying mechanism of storage damage at the molecular, microstructural, and macroscopic level. By using infrared spectroscopy, the dehydration of the gluten component could be established at the molecular level, and its kinetics could be monitored in time. Time‐domain nuclear magnetic resonance (NMR) showed increased water mobility, which could be attributed to a release of water from the gluten matrix. At the microstructural level, the growth of ice crystals could be monitored by means of cryogenic scanning electron microscopy (cryo‐SEM). These ice crystals are preferably formed in gas cells with kinetics that are slower than those during infrared spectroscopy but similar to those in time‐domain NMR. At the macroscopic level, ice crystals are not evenly distributed over the molded dough, nor are the gas cells homogeneously distributed over the dough. This has implications for the macroscopic water distribution during frozen storage, which could be substantiated by magnetic resonance imaging (MRI) measurements.

The effects of soy on freezable bread dough: A magnetic resonance study

“…During frozen storage, water phase-separates from the gluten and starch matrix to form ice crystals. Although water redistributes upon thawing, it is not expected that the water will reoccupy congruent configurations because of permanent damage to the matrix (Berglund et al, 1991;Esselink et al, 2003). Esselink et al (2003) and Yi, Kerr, and Johnson (2009) have also described an increase in T 2 values with frozen storage time.…”

“…Although water redistributes upon thawing, it is not expected that the water will reoccupy congruent configurations because of permanent damage to the matrix (Berglund et al, 1991;Esselink et al, 2003). Esselink et al (2003) and Yi, Kerr, and Johnson (2009) have also described an increase in T 2 values with frozen storage time. Our results agree with those of Yi et al (2009) who described dough samples with two major populations of water; a major population (85-88%) with a lower T 2 relaxation time than the minor population.…”

“…Differences in formulation (higher water content, inclusion of yeast, frozen storage temperature, etc.) may have contributed to differences in these observations (Esselink et al, 2003). Moreover, sample preparation (preparing samples while still frozen vs. after thawing) could also drastically affect the properties of water.…”

“…This relationship also suggests that increased T 1 and T 2 times correlate with higher proton mobility. In a frozen dough system, relaxation times were shown to increase with increased frozen storage (Esselink, van Aalst, Maliepaard, & van Duynhoven, 2003), likely due to the formation of ice crystals during storage, and it is hypothesised that the rate and/or extent of change during frozen storage can be modulated by the hygroscopic properties of soy protein.…”

Calorimetric and Microstructural Investigation of Frozen Hydrated Gluten

“…60,61 In gluten, a monomolecular water layer interacts with gluten, mostly by hydrogen bonding, and remains unfreezable. 62 Therefore, in both cases, a thin layer of water is always in equilibrium with the ice, and ice cannot interact directly with other hydrophilic groups (-OH, -NH) of gluten. This layer has thickness δ and is important for very small pores, as will be discussed below.…”