发芽处理对粳米和糯米理化特性与结构特征的影响及调控机制

Effects and Regulatory Mechanism of Germination Treatment on Physicochemical Properties and Structural Characteristics of Japonica Rice and Glutinous Rice

摘要:

为探究发芽处理对糙米(2种粳米和2种糯米)理化特性和结构特征的影响,采用红外光谱、X射线衍射、拉曼光谱、差示量热扫描和快速黏度分析等方法,分析未发芽、发芽24h、发芽48h的粳米和糯米中直链淀粉含量、支链淀粉含量、还原糖含量和α-淀粉酶活性等指标,并借助实时荧光定量 PCR 技术从分子层面解析发芽过程中淀粉代谢相关基因的表达模式。同时,对淀粉晶体特征、糊化特性的变化规律进行了探究。结果表明,糯米的灰分含量在发芽24h时达到最高值(松粘一号1.60%和中宝佳糯1.80%),而粳米的灰分含量随发芽时间的延长呈降低趋势。在相同发芽时间处理条件下,与粳米相比,糯米中支链淀粉含量、还原糖含量、α-淀粉酶活性更高。PCR结果显示,OsAMY1基因可能通过调控α-淀粉酶活性,进而促进了糙米中淀粉的水解。发芽后糯米中宝佳糯中OsAMY1基因的相对表达水平显著高于粳米,这一上调表达使α-淀粉酶活性升高,最终表现为中宝佳糯中还原糖含量高于粳米。发芽处理后4种糙米淀粉的短程分子有序性降低,其中糯米中宝佳糯变化更明显,其峰强度比值R1047/1022降低27.30%,半高宽FWHH值增加17.44%。发芽处理后4种糙米淀粉的相对结晶度下降,糯米的降低幅度更大(松粘一号50.49%和中宝佳糯28.85%)。随着发芽时间的延长,粳米的糊化焓逐渐下降,而糯米的糊化焓逐渐上升。此外,4种糙米的糊化黏度均呈现下降趋势,糯米表现出更优的抗回生性和热稳定性。主成分分析发现,上调的OsAMY1基因激活了α-淀粉酶活性,进而加速了淀粉分子向无序结构转化,增强了粳米和糯米的抗回生性和热稳定性。研究旨在为粳米和糯米加工适用性的优化以及产品开发提供数据支撑。

Abstract:

In order to explore the effects of germination treatment on the physicochemical properties and structural characteristics of brown rice (2 Japonica rice and 2 glutinous rice), several advanced analytical techniques, including infrared spectroscopy, X-ray diffraction, Raman spectroscopy, differential scanning calorimetry, and rapid visco-analysis, were utilized to analyze the changes in amylose content, amylopectin content, reducing sugar content, and α-amylase activity of Japonica rice and glutinous rice germinated for 0h, 24h, and 48h. Meanwhile, quantitative real-time PCR technology was used to analyze the expression patterns of starch metabolism-related genes during germination at the molecular level. The changes in starch crystal structure and gelatinization properties were also investigated. The results showed that the ash content of glutinous rice reached its peak value at 24h of germination, with Songnianyihao at 1.60% and Zhongbaojianuo at 1.80%, while that of Japonica rice exhibited a decreasing trend with the extension of germination time. Under the same germination time treatment, glutinous rice had higher contents of amylopectin and reducing sugars, as well as higher α-amylase activity compared with Japonica rice. Quantitative real-time PCR results indicated that the gene OsAMY1 might dominate the regulation of α-amylase activity in brown rice, thereby promoting the starch hydrolysis of brown rice. Germination led to a significantly higher relative expression level of the OsAMY1 gene in Zhongbaojianuo compared with Japonica rice. This up-regulated expression resulted in increased α-amylase activity, which ultimately contributed to a higher reducing sugar content in Zhongbaojianuo compared with Japonica rice. Germination treatment reduced the short-range molecular order of starch in the four brown rice varieties, with the most significant change observed in glutinous rice variety Zhongbaojianuo, where R1047/1022 decreased by 27.30% and the full width at half height value FWHH increased by 17.44%. The relative crystallinity of starch in 4 brown rice varieties decreased after germination, with the most notable decline of 50.49% (Songnianyihao) and 28.85% (Zhongbaojianuo) observed in glutinous rice. And germination treatment also had an impact on gelatinization properties. As germination progressed, the gelatinization enthalpy of Japonica rice decreased, while that of glutinous rice increased. The gelatinization viscosity of all four brown rice varieties showed a downward trend, and glutinous rice exhibited better retrogradation resistance and stronger thermal stability. Principal component analysis revealed that the up-regulated OsAMY1 gene activated α-amylase activity, thereby accelerating the transformation of starch molecules into amorphous structures and enhancing the retrogradation resistance and thermal stability of Japonica and glutinous rice. This study provided an evidence-based foundation for optimizing the processing adaptability and guiding the product development of both Japonica and glutinous rice.