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Impact of Proteins on Pasting and Cooking Properties of Nonparboiled and Parboiled Rice

¹Laboratory of Food Chemistry, Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium. ²Corresponding author. Phone: + 32-16-321634. Fax: + 32-16-321997. E-mail: veerle.derycke@biw.kuleuven.be ³Master Foods, Industrielaan 5, B-2250 Olen, Belgium. ⁴R&R Research Services Inc., 8831 Quail Lane, Manhattan, KS 66502, USA.

The role of proteins in the pasting and cooking properties of non-parboiled (npb) and parboiled (pb) rice was tested by means of a reducing agent dithiothreitol (DTT) and a protease (trypsin). DTT increased the swelling power and carbohydrate leaching of flour from npb rice flour but decreased its amylose leaching. Although DTT slightly increased the Rapid Visco Analyser (RVA) viscosity at the initial stages of the pasting process, it decreased RVA viscosity in the further phases of the experiment. Preincubation of flour with a trypsin decreased RVA viscosity along the whole temperature profile. Addition of DTT to the cooking water decreased water absorption and rice hardness and increased leaching of solids during cooking and stickiness of the cooked npb rice. Addition of DTT to the cooking water of flour from pb rice increased swelling power, carbohydrate leaching, and amylose leaching. Addition of DTT also increased RVA viscosity. Preincubation with trypsin had a similar effect but the changes were less pronounced. Addition of DTT increased stickiness of cooked pb rice and increased water absorption and leaching of solids during cooking. Taken together, the results provide evidence for the existence of a protein barrier affecting starch swelling, rheological, and cooking properties of both npb and pb rice.