Rheology, Microstructure, and Baking Characteristics of Frozen Dough Containing Rhizopus chinensis Lipase and Transglutaminase

Cereal Chem. 88(6):596–601 The beneficial effects of a new recombinant lipase (Rhizopus chinensis lipase [RCL]) and transglutaminase (TG) were investigated on frozen dough systems and their breadmaking quality. Rheological properties and microstructure of doughs were measured using a dynamic rheometer, rheofermentometer F3, and scanning electron microscopy (SEM). Measurements of viscoelastic properties showed that both G′ and G′′ of dough containing RCL and TG were greater than those of the control after 35 days of frozen storage. The SEM micrographs showed that dough containing RCL and TG had the most starch granules embedded in or attached to the gluten network, and the gluten seemed more powerful and resilient than for the control dough after 35 days of frozen storage. Results of the gas production and dough development tests indicated that RCL and TG improved the rheofermentative characteristics of frozen dough. RCL and TG could improve water-holding capacity and significantly increase the glycerol content of the control dough. Image analyses showed that bread crumbs containing RCL and TG had a more open network and uniform crumb structure, which resulted in higher specific volume. This combination also yielded a product with higher sensory scores for test breads. The frozen dough market has grown in recent years because of consumer demand for convenient, high-quality baked products. Frozen dough is thawed, proofed, and baked to serve to customers as oven-fresh bread and offers a number of advantages compared with the conventional method. Customers enjoy a freshly baked loaf of bread, and the food service industry saves on labor and equipment costs while facilitating transportation (Wang et al 2006; Kim et al 2008). However, a major shortcoming of frozen dough is that its breadmaking quality deteriorates substantially as time in frozen storage increases (Wolt and D’Appolonia 1984a, 1984b; Inoue and Bushuk 1991; Huang et al 2008; Asghar et al 2011). Two factors have been identified as possible reasons for the observed deterioration: 1) decreased gassing power resulting from a decline in yeast activity (Ribotta et al 2003) and 2) gradual loss of dough strength (Inoue and Bushuk 1991). Additives are used in bakeries to facilitate processing, to compensate for variations in raw materials, to guarantee constant quality, and to preserve freshness and food properties. A variety of additives and ingredients have been used to modify dough behavior during freezing (Ribotta et al 2004; Huang et al 2008; Kim et al 2008; Huang et al 2011). Transglutaminase (TG) (EC 2.3.2.13) catalyzes protein cross-linking through the formation of interor intramolecular ε (γ-glutamyl) lysine isopeptidic bonds. These bonds cause the homologous and heterologous polymerization of proteins (Motoki and Seguro 1998). The formation of cross-linked polypeptide chains by the action of TG may lead to the secondary formation of disulphide bonds, thereby decreasing the free thiol group content (Gujral and Rosell 2004). Therefore, TG may improve dough elasticity and crumb strength. TG is often used in weak gluten systems, such as damaged flour, rice flour bread, and gluten-free bread because TG may transform weak gluten into strong gluten through its effects on rheological behavior (Gujral and Rosell 2004; Caballero et al 2005; Moore et al 2006). There is some evidence that TG in frozen dough polymerizes proteins, enhances the properties of dough, and stabilizes the dough structure, all of which may help reduce problems in the production of frozen-dough bread that result, at least in part, from the weakening of dough strength (Hozova et al 2002; Huang et al 2008). Lipase is a carboxylesterase that catalyzes the hydrolysis of acylglycerol, liberating free glycerol. One of the properties that glycerol could confer is increased freeze tolerance of yeast cells (Myers and Attfield 1999; Huang et al 2011). Some surfactantlike lipids, such as phospholipids and galactolipids, have also been shown to be products of lipase that can form lipid-protein complexes through the interaction of lipophilic portions with hydrophobic regions of proteins (Martín et al 2006) and improve water-holding capacity (Lilbaek et al 2006), which might influence the rheological properties of bread dough (Jascanu and Stefoane 2005). Lipase made via conventional methods has been associated with very high production costs that made it impractical to implement into the mainstream baking industry. A new recombinant lipase (Rhizopus chinensis lipase [RCL]) from R. chinensis CCTCC M201021 (He et al 2008; Yu et al 2009) could reduce production costs significantly and make the use of lipase a possibility for the baking industry (Zhang et al 2010). The combined effects of RCL and TG at different concentrations on frozen dough bread were studied in our preliminary experiments through response surface methodology (data not shown), and the optimum amount was obtained for each enzyme. The objectives of this study were to investigate the reasons for the abilities of RCL and TG at the optimum amounts to improve frozen dough systems utilizing a dynamic rheometer, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and rheofermentometer F3. Further related properties of thiol groups and the glycerol content were chemically analyzed. The quality of the final product made from frozen dough was evaluated by making bread and by analysis of crumb structure parameters with ImageJ software (http://rsb.info.nih.gov/ij/). Finally, a test panel evaluated the bread samples. MATERIALS AND METHODS Materials Commercial bread flour (brand name Jiafeng) was obtained from East Ocean Oils and Grains Industries (ADM joint venture, Zhangjiagang, China). The bread-flour moisture, ash, and protein content were 12.8, 0.58, and 13.5% (14% mb), respectively, as 1 Graduate research assistant, professor, and visiting professor, respectively, The State Key Laboratory of Food Science and Technology, School of Food Science and Technology, International Exchange and Cooperation Program, Jiangnan University, Wuxi, Jiangsu 214122, China. 2 Corresponding author. Tel.: +86 (510) 8591 9139. Fax: +86 (510) 8591 9139. E-mail: [email protected] 3 Research scientist, Zhejiang Newland Foods Co., Hangzhou, Zhejiang 311107, China. 4 Research chemist, U.S. Department of Agriculture (USDA), Center for Grain and Animal Health Research, Manhattan, KS. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. USDA is an equal opportunity provider and employer. http://dx.doi.org/10.1094 / CCHEM-07-11-0082 © 2011 AACC International, Inc.