Abstract: 【Objective】The conditions of alkali extraction method of Se-enriched rice bran protein (RBP) was optimized. Nutritive compound of mixed proteins was studied and evaluated according to the principle of protein complementarity. 【Method】RBP was extracted using alkali method, and the conditions of extraction were optimized by orthogonal experiment L9 (34). RBP was mixed with soybean protein (SP) in different proportions (60%, 70%, 80%, 90%, and 100%) after extraction. Kjeldahl method, hydride generation-atomic fluorescence spectrometry (HG-FAS) and portable color meter were used to determine the protein contents, selenium contents and color values of RBP, soy protein (SP) and the compound of mixed proteins, respectively. Amino acids contents of different protein products were measured by high-speed amino acid analyzer. Nutritive evaluation for the compound of mixed proteins was assessed by WHO/ FAO and amino acid ratio coefficient method. 【Result】By investigating extraction rate, Se-content and color values of RBP in orthogonal experiment, the optimal conditions were a volume-weight ratio of 20:1, 0.08 mol•L-1 NaOH, an extraction time of 3 h and a temperature of 30℃. A protein product of (80.2±1.1)% protein content, (0.269±0.132)mg•kg-1 Se and 69.7±1.2 color value was obtained. Selenium and protein contents of regular rice bran, Se-enriched rice bran and their protein products using optimum extraction conditions were compared. No significant difference was showed between the protein contents of Se-enriched rice bran and regular rice bran, a similar result was also found in their protein products (P<0.01). However, both selenium content of Se-enriched rice bran (0.401±0.021 mg•kg-1) and RBP (0.269±0.132 mg•kg-1) were significantly higher than that of regular rice bran ((0.023±0.010)mg•kg-1) and its protein ((0.052±0.011)mg•kg-1), respectively (P<0.01). Protein contents and selenium contents of RBP mixed with SP in different proportions were also compared in this study. Results showed that selenium contents of all the compound of mixed proteins were significantly higher than that of SP [(0.013±0.005)mg•kg-1]. With the increase of RBP proportion in different compounds, selenium contents were increased from (0.141±0.014)mg•kg-1 to (0.269±0.032)mg•kg-1. Nutritional value of RBP and the compounds were assessed by WHO/FAO and amino acid ratio coefficient method. According to the score of ratio coefficient (SRC), the nutritional value of each protein products were arranged in descending order as follow: 60% RBP > 70% RBP > 50% RBP > 80% RBP > 90% RBP > RBP. SRC values of all compounds were higher than that of RBP (SRC = 64.1). This result indicated that the nutritional values of the compounds of mixed proteins were all higher than that of RBP, and 60% RBP possess the highest nutritional value, of which selenium content and protein content were (0.167±0.024)mg•kg-1 and (84.1±0.8)%, respectively. 【Conclusion】Nutritional value could be enhanced and a high quality protein rich in trace element selenium could be obtained by mixing SP with RBP.

Key words: selenium , rice bran protein , soybean protein , extraction , WHO/ FAO , nutritive compound