The Role of Water in the Retrogradation of Wheat Starch Gels and Bread Crumb

Cereal Chem. 63(5):407-411 The moisture content of a starch gel determines the extent to which that granular form, we concluded that the remnant of the granule structure did starch will retrograde. Maximum crystallinity occurs in gels of 50-60% not affect retrogradation. Retrogradation in bread was also studied by starch. In this study, the effects on recrystallization of adjusting the water differential scanning calorimetry. Bread baked with several antistaling level during gelatinization and aging were examined. The degree of agents was aged at various moisture levels to determine if these agents act recrystallization was measured by differential scanning calorimetry, by altering moisture availability to the starch and, thereby, the extent of Retrogradation in wheat starch gels was controlled by the amount of water starch retrogradation in the bread. The effect of moisture on present during aging, regardless of the amount present during recrystallization was not significantly different between the bread samples gelatinization. It was also found that solubilized amylopectin did and the starch gels. It appears, therefore, that the action of these antistaling retrograde, and as with starch, the extent of retrogradation was controlled agents in bread is brought about by another mechanism. by the amount of water present. Because the amylopectin used was not in The involvement of starch retrogradation in bread staling has MATERIALS AND METHODS been a major focus of research since Katz (1928) showed by X-ray diffraction that starch in bread returns to the semicrystalline state The effect of moisture on the retrogradation in bread crumb, during staling. There is extensive work on the physical and starch gels, and isolated amylopectin was examined by DSC. The chemical changes that occur in starch during baking and staling instrument used was a Perkin-Elmer DSC-2 with FTS Systems (Willhoft 1973, Maga 1975, Knightly 1977, Kulp and Ponte 1981). Flexi-cooler and temperature controller. It was calibrated with The semiquantitative method of X-ray diffraction was widely used indium, and enthalpy (,A H) was determined by measuring the area as the most direct means of estimating the degree of of the endotherm, as described by Lund (1983), using a polar recrystallization in starch (Zobel and Senti 1959, Dragsdorf and planimeter. In the calorimeter the temperature sensors are not in Varriano-Marston 1982), but the more quantitative thermal direct contact with the sample; therefore, the recorded temperature analysis techniques are now the preferred means of studying is that of the sample holders rather than the sample. The effect of crystallinity. Differential scanning calorimetry (DSC) in particular this temperature lag can be corrected for, using the procedure has proved to be a valuable tool to quantify crystallinity, both in described by Richardson (1972). native starch and the retrograded starch of bread crumb and aged All samples were encapsulated in aluminum pans and gels (Longton and LeGrys 1981, Fearn and Russell 1982). It hermetically sealed to prevent moisture loss. They were heated at enables us to directly measure the influence of various factors on 10' C/min, using a sensitivity of 0.5 mcal/sec. The temperature the thermal properties of starch during gelatinization and range of the scan was typically 7-127' C, but the upper limit was recrystallization. Thermal analysis shows that storage time, adjusted according to the temperature necessary to allow storage temperature, and reheating after storage, which are known gelatinization to be completed. All materials (starch, crumb, and to influence the firming rate of bread, also affect the rate of starch water) were weighed directly into the calorimeter sample pan using retrogradation (Axford and Colwell 1967, Colwell et al 1969, a Cahn 21 automatic electrobalance. Enthalpy, the energy required Russell 1983, Ghiasi et al 1984). Longton and LeGrys (1981) to melt the crystalline material, was used as the index of reported that recrystallization in starch gels is profoundly crystallinity in the samples. It is reported as A H in calories per influenced by gel moisture. Using DSC enthalpy values as the gram. All samples were run in duplicate or more. The standard index of crystallinity in aged gels, they noted that crystallinity deviation of A H values was 0.06 cal/ g. reached maximum development in 50% gels and disappeared altogether in very dilute (10%) or concentrated (80%) gels. This Preparation of Bread Crumb DSC data supports the X-ray diffraction studies of Hellman et al The effect of sample moisture content on enthalpy values during (1954), who found that 50% gels produce the most intense X-ray DSC heating was studied on aged bread crumb. Bread without pattern but that pattern intensity decreases at higher or lower shortening was baked according to the standard pup loaf concentrations. These studies indicate that water plays an integral procedure (Finney 1984). It was aged for five days in plastic bags at role in controlling retrogradation, and its involvement in the 250°C, the crust was removed, and the crumb was frozen and process bears closer scrutiny. lyophilized. The dried crumb was weighed into the calorimeter The goal of this study was to investigate how and when moisture sample pan, and distilled water was added with a microsyringe to content becomes influential in retrogradation. Does the amount of obtain 56, 39, 30, and 25% starch (determined by weighing pan plus water present during granule swelling and gelatinization influence sample) in the final mixture. The samples were equilibrated for 1-2 subsequent recrystallization? Or does water exert its effect only by hr before heating in the calorimeter. Enthalpy calculations were mediating the formation and growth of crystallites during based on the weight of starch (in milligrams) in the crumb sample. retrogradation? A starch model system was chosen for the main Crumb was estimated to contain approximately 65% starch. portion of this study, but the influence of water on retrogradation DSC was also performed on bread to study the combined effect of starch in bread was also examined. DSC was used because it of moisture and various antistaling agents on starch provides a reproducible means to quantify crystallinity in both retrogradation. Bread was baked with each of the following: 3% starch gels and bread. shortening (Crisco or Durkee D-10) and 0.5% monoglyceride (Dur-Em, Durkee). The control loaf contained none of these. Once cooled, the crumb was promptly frozen and lyophilized. A small 'C o tr but on 86- 03 ,