Vol. 83, No. 4, 2006 411 Effect of Hydrophilic Gums on the Quality of Frozen Dough: Electron Microscopy, Protein Solubility, and Electrophoresis Studies 1 R. Sharadanant 2 and K. Khan 2,3 ABSTRACT Cereal Chem. 83(4):411–417 Hydrophilic gums have been shown to improve the shelf-life stability of frozen doughs during long periods of frozen storage. The objective of this research was to determine the effect of gums on starch and protein characteristics of frozen doughs using electron microscopy and elec- trophoresis studies. Frozen doughs, supplemented with three levels of gum arabic, carboxy methyl cellulose (CMC), kappa (κ) carrageenan, and locust bean gum, were studied after day 1 and after 4, 8, 12, and 16 weeks of frozen storage. Changes in the ultra structure of the frozen doughs were investigated, as well as the solubilities and composition of dough proteins by SDS-PAGE. Scanning electron micrographs of doughs evaluated on day 0 (unfrozen) showed starch granules securely embedded in the gluten matrix. However, after 8 and 16 weeks of frozen storage, the frozen control dough without the gum additives clearly showed damage to the gluten network, and the starch granules appeared to be separated from the gluten. Doughs with locust bean gum and gum arabic showed better retention of the gluten network compared with the frozen control evaluated after different periods of storage. The SDS-soluble protein content increased while residue protein content decreased as the frozen storage time increased. After each frozen storage period, the control dough without the gum additive had the highest amount of SDS-soluble proteins and the lowest amount of residue proteins when compared with the doughs treated with gums. κ-Carrageenan and locust bean gum had the lowest amount of SDS-soluble proteins compared with doughs with CMC and gum arabic. The frozen control had the lowest amount of residue proteins at any particular time of frozen storage. κ-Carrageenan treated doughs had the highest amount of residue proteins, followed by doughs with locust bean gum. Doughs with gum arabic and CMC had the lowest amount of residue proteins but still higher than the control doughs. The loss of stability of frozen dough subjected to extended frozen storage and freeze-thaw cycles is still a problem that needs to be solved. Frozen dough is characterized by increase in proofing periods during preparation of bread and finally a lower loaf vol- ume. This is attributed to the changes in rheological properties of frozen doughs due to the physical damage on the gluten network caused by ice recrystallization (Berglund et al 1991) subjected to long periods of frozen storage and freeze-thaw cycles. Many effects have been attributed to the loss of stability of frozen dough. According to Mazur (1961), water available for freezing forms ice crystals that injure the yeast cells. Varriano-Marston et al (1980) and Wolt and D’Appolonia (1984b) found changes in the rheological properties of the dough. Wolt (1982) suggested that ice crystallization and recrystallization causes physical damage to the gluten network, leading to changes in the rheological prop- erties of the frozen dough. Kline and Sugihara (1968) postulated that dead yeast cells release reducing substances during frozen storage that lead to the weakening of the frozen dough. Varriano-Marston et al (1980) found that the number of dis- rupted yeast cells increased in frozen dough and suggested the possibility of reducing substances from the yeast cells accounting for dough weakening. In contrast, Wolt and D’Appolonia (1984a) found that thiol compounds were not weakening the dough structure because the changes in the rheological properties were not similar to those expected. Autio and Sinda (1992) demonstrated that the rheological properties of the dough were not affected by the addition of dead yeast cells to the dough. Berglund (1988) used low temperature scanning electron micro- scopy (SEM) to determine changes in the water distribution and dough ultrastructure of frozen doughs during frozen storage and freeze-thaw cycles. The gluten matrix appeared less continuous, more ruptured, and separated from the starch granules after 24 weeks of frozen storage (Berglund et al 1991). Poor gas retention was considered to be due to thinner gluten matrix. Some internal damage of starch granules was also observed along with separation of water from the gluten matrix and starch, and formation of large ice masses due to recrystallization. Weakening of gluten leading to the loss of frozen dough strength and changes in the rheological properties of the dough result from frozen storage. These changes seem to be due to the water migra- tion from gluten and starch, increase in the freezable water, ice crystallization and recrystallization during frozen storage, and freeze-thaw cycles (Wolt 1982). Recently, Sharadanant and Khan (2003a,b) investigated various gums in frozen dough formulas and found that bread quality was improved compared with control frozen doughs without gums. By incorporating gums in frozen dough, freeze-thaw damage may be reduced because gums trap free water and control moisture migration (Ward and Andon 1993; Kobbs 1997). Gums are HMW molecules with either hydrophobic or hydrophilic properties. Hy- drophilic gums, or the vegetable gums, are naturally occurring, water-soluble, HMW polysaccharides with traces of protein (Ward and Andon 1993). They form highly viscous suspensions or solu- tions with colloidal properties at low dry substance content in an appropriate solvent such as water (Whistler and BeMiller 1993). Gums hold water and minimize the freeze-thaw damage by controlling the moisture migration while thawing frozen products (Kobbs 1997). Locust bean gum, guar gum, and xanthan gum have been recommended in frozen systems. However, the level of gum and its suitability to frozen dough is yet to be studied. Depending on their molecular size, orientation, molecular asso- ciation, water-binding capacity, and concentration, gums are able to bind as much as 100 times their weight in water (Ward and Andon 1993). Apling et al (1978) reported that the moisture con- tent of guar-wheat bread was increased to 45–48% versus that of bread without gum addition, which was 35%. The loss of mois- ture in bread and increased staling have been highly correlated. According to Zeleznak and Hoseney (1986), the amount of water present during aging, regardless of the amount of water present during gelatinization, regulates the retrogradation in wheat starch gels. Bread with a higher moisture content was significantly fresher than bread with lower moisture (Bechtel and Meisner 1954). The objective of this study was to add gums (hydrocolloids) such as carboxy methyl cellulose, carrageenan, gum arabic, and locust bean gum to a frozen dough formulation and evaluate the effects on frozen dough quality through electron microscopy, pro- tein solubility, and gel electrophoresis studies. 1 Published with the approval of the Director, Agricultural Experimental Station, North Dakota State University, Fargo, ND 58105. 2 Dept. Cereal and Food Sciences, North Dakota State University, Fargo, ND 58105. 3 Corresponding author. E-mail: Khalil.Khan@ndsu.edu DOI: 10.1094 / CC-83-0411 © 2006 AACC International, Inc.