Eect of Amaranthus and buckwheat proteins on the rheological properties of maize starch Feliciano P. Bejosano, Harold Corke* Cereal Science Laboratory, Department of Botany, University of Hong Kong, Pokfulam Road, Hong Kong Received 12 December 1997; accepted 28 September 1998 Abstract The relationship between pasting properties (determined with a Rapid Visco-Analyser) of maize starch and the texture of the resulting gel was examined after addition of Amaranthus and buckwheat proteins. An increase in the peak viscosity due to the addition of protein concentrates was observed, and a lesser increase from the addition of protein hydrolysates. The increase in starch pasting viscosity was related to protein solubility, and could be attributed to the starch granule stabilizing action of proteins. The interactions between starch and proteins were further investigated using oscillation and creep/recovery rheological tests. Gen- erally, the proteins weakened starch gel structure, shown by the lower elastic modulus (G 0 ) and higher phase degree () compared to gels without any proteins added. The same results were obtained from creep/recovery experiments. It seemed that, since native proteins interact more with the granules, they act as a barrier to the release of amylose molecules; hence the resulting gels became weak. If desired, such eects could be lessened by partially hydrolyzing the proteins. # 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction The two most abundant and nutritionally important components of cereal flours are starch and protein. The properties of these components determine the function- ality of flours, particularly that of wheat flour. Wheat protein, specifically gluten, is unique among other cereal proteins in its extreme influence on the physical properties of wheat dough as well as on the final product. Other cereal proteins do not have the same properties, although their interactions with starch and other ingre- dients can also aect the physico-chemical state of the food system. Ring (1985) described a starch gel as a composite material in which swollen gelatinized starch granules reinforce an interpenetrating amylose gel matrix. A gelatinized starch suspension is therefore biphasic in nature, with a continuous phase made up of solubilized amylose and a dispersed phase made up of swollen granules containing the amylopectin molecules. Hansen, Hoseney, and Faubion (1991) reviewed studies claiming that the physical characteristics of starch pastes and gels depend on the concentration of the granules, the amount of amylose and amylopectin leached from the granules during heating, the shape and swelling power of the granules, the degree of entanglement between amylose and amylopectin, and granule–granule, amy- lose–granule, and amylopectin–granule interactions. Considering the numerous factors that could influence starch gelatinization and retrogradation, further studies are still being made to elucidate this complex system. Lindahl and Eliasson (1986) studied the interactions between wheat proteins and dierent starches based on oscillatory rheological measurements of starch gels. They found an increase in G 0 of wheat and rye starch gels when gluten was added. However, a decrease in the G 0 was observed for maize starch while no eect was found on triticale, potato and barley starches. De Gen- nes (1971) believed that, as starch gelatinizes and pro- teins denature, it is possible that entanglements develop a network structure which results in a synergistic increase in viscosity. Hamaker, Grin, and Molden- hauer (1991) also demonstrated the significant influence of starch-granule-associated protein on cooked rice tex- ture. However, Friedman (1995) in a review on starch– protein interactions indicated that the two polymers are probably not miscible. Food Chemistry 65 (1999) 493–501 0308-8146/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(98)00227-1 * Corresponding author. Tel.: +852-2857-8522; fax: +852-2857- 8521; e-mail: harold@hku.hk