Variation of Some Biologically Active Compounds in Rice Influenced by Different Environmental and Genetic Factors

Abstract

Some biologically active compounds in rice influenced by different environmental and genetic factors were investigated. The impact rice aroma compound, 2-acetyl-1-pyrroline (2AP), and the strongest antioxidant compounds known as vitamin E and γ-oryzanols were determined in mutant rice samples, which obtained from gamma irradiation of Khao Dowk Mali 105 (KDML 105) and Rice Department 15 (RD 15) varieties. Additionally, the effect of rice cultivation factors on 2AP content and grain yield of Thai fragrant rice samples were studied. Due to many mutant rice samples, analytical methods employing gas chromatography (GC) and high-performance liquid chromatography (HPLC) have been developed and validated for rapid and effective analysis of 2AP, vitamin E and γ-oryzanols in these rice samples. Static headspace-gas chromatographic technique (SHS-GC) with more selective nitrogen phosphorus detection (NPD) for quantitative analysis of 2AP in the rice leaf and grain samples was successfully developed with total analysis time of only 10 min. For determination of all vitamin E analogues, α, β, γ, δ-tocopherol and α, γ, δ-tocotrienol, the developed normal phase-HPLC (NP-HPLC) method was achieved using a mobile phase consisting of hexane/isopropanol/ethyl acetate/acetic acid (97:1:1:1, v/v/v/v). The total analysis time of all vitamin E analogues was less than 10 min. In addition, the developed method for determination of major components of γ-oryzanols, cycloartenyl ferulate, 24-methylene cycloartanyl ferulate, campesteryl ferulate and β-sitosteryl ferrulate, in bran of rice mutants using reverse phase-HPLC (RP-HPLC) gave effective separation of all γ-oryzanol components in 20 min. Isocratic elution of methanol/acetonitrile/dichloromethane/ acetic acid (35:50:14:1, v/v/v/v) was employed. All these developed methods are validated in terms of precision, (LOD and LOQ), repeatability (intraday) and reproducibility (interday). The contents of 2AP, vitamin E and γ-oryzanols were varied depending on different genetic conditions of mutant rice samples. Eighty-six mutants of KDML 105 and 133 mutants of RD 15 contained these phytochemicals in the range of 0.19-5.07 µg/g grain, 108.45-336.21µg/g bran and 1725.09-3028.29 µg/g bran, respectively. The rice group classification showed that the mutants obtained from KDML 105 gave high content of 2AP (averagely 3.50 µg/g grain) and total γ-oryzanols (averagely 2305.88 µg/g bran), but the total vitamin E content was low, averagely 164.76 µg/g bran. In contrast, the higher total vitamin E content, averagely 207.38 µg/g bran, was found in mutants of RD 15. Another aim of this study was to identify the cultivation factors and their degrees of influence on the aroma quality and yield of two Thai fragrant rice varieties, KDML 105 and Pathum Thani 1 (PTT 1), using an interaction model with full factorial design. Under the influences of co-interaction of cultivation factors, 2AP contents in rice leaves and grains were measured throughout all growth stages of both rice varieties. The results showed that low grain 2AP content and grain yield occurred under high temperature conditions for both rice varieties but with different extents. Due to different soil type of rice cultivation, the 2AP content in rice leaves following growth stages was varied for both rice varieties. Increasing of 2AP contents in both leaves and grains were found under water stress treatment, however, grain yield decreased under this stress. Results on the co-interaction effects of the cultivation factors showed that rice variety × temperature had strong interaction with all other factors regarding 2AP content. However, rice variety × soil type affected rice grain yield. These findings can aid in cultivation management practices for fragrant rice to achieve high aroma quality and high yield.