Optimization of γ-Aminobutyric Acid Production in Brown Rice via Prolonged Seed Priming

Abstract

Germinated whole seeds possess elevated levels of bioactive nutrients; however, their application is hindered by several constraints. The germination process is typically time-consuming, and germinated seeds present challenges in terms of storage and transportation compared to dry seeds. This study introduces a novel processing method for rice, termed prolonged priming (PLP), aiming to combine the benefits of germinated and dry seeds. PLP involves soaking the seeds until the embryo exposure stage, followed by redrying. At 10 h (hour) germination post PLP, the γ-aminobutyric acid (GABA) levels in Hanyou73 (HY73) and IRAT exceeded 20 mg/100 g. Additionally, there was an induction of various nutrient components, including an increase in protein content, a reduction in amylose levels, and an elevation in fatty acid content, among others. Malondialdehyde levels, indicating oxidative damage, remained stable, and PLP preserved better seed integrity compared to routine priming in the desiccation-tolerant HY73. Collectively, the PLP treatment demonstrates an optimization of the nutritional value and storage in germinated brown rice (GBR). This novel process holds potential for enhancing the nutritional profile of GBR and may be applicable to other crop species.

Keywords: desiccation tolerance; germinated brown rice; prolonged priming; routine priming; seed integrity; γ-aminobutyric acid.

Figure 1

Comparative analysis of seed germination among different treatments. (A) Comparative analysis of ZXM under different treatments: (a) PLP; (b) hydro-primed seeds; (c) control. (B) Comparative analysis of HY73 under different treatments: (a) PLP; (b) hydro-primed seeds; (c) control. (C) Comparative analysis of germination percentage among different varieties under different treatments. Different letters in (C) indicate significant difference (p < 0.05). Bars indicate standard errors. Each sample contained 8 to 10 replicates (10 seeds per replicate).

Figure 2

The comparison of GABA contents in IRAT109, ZXM, MH63, and HY73 during different germination processes show that the highest levels of GABA were found in PLP at 10 h. The soaking conditions were 10 h soaking, and soaking temperature at 35 °C. GABA contents were determined at 0, 5 and 10 h of soaking. Data are mean ± SD (n = 3). The *, ** indicate significant (p < 0.05, p < 0.01, respectively) increase of GABA compared with the control. #, ## indicate significant (p < 0.05, p < 0.01, respectively) increase of GABA at 5 h or 10 h of soaking compared with other treatments. n., non-pretreated, non-soaked seeds. CK: Control treatment. HP: hydro-primed, a technique in which the plant seeds are presoaked in water at an optimal temperature for a specified duration, followed by a natural drying process that returns them to their initial seed weight. PLP-ageing: HY73 PLP seeds stored at 4 °C for 4 months.

Figure 3

Comparative analysis of rice husk yield, percentage of whole brown rice and hardness among different treatments. (A) Husked rice yield. HP notably decreased husked rice yield. (B) Seed intactness comparison. Hydropriming resulted in significantly lower husked rice yield than other treatments. (C) Seed hardness comparison. Bars indicate standard errors. Each sample contained two or three replicates. Data are mean ± SD (n = 3). The * indicates significance (p < 0.05). Different letters indicate significant difference (p < 0.05).

Figure 4

Impact of soaking time on nutrient levels. (A) The level of HY73 control seeds (three replicates) was significantly different from PLP (four replicates) seeds. (B) MDA level with different soaking durations within the same variety and the same pre-treatment. Each sample contained three replicates. Different letters and * indicate significant difference (p < 0.05).

Figure 5

Graphic summary of tillage with extended priming and drought-resistant seed and experiments on seed peeling. (A) Graphical summary of extended priming and brief germination using drought-resistant seeds. (B) Experimental dehulling of seeds. (a) Measuring the water volume as a preparation for germination, seeds were then subjected to imbibition and collected once embryo exposure was detected, from 24 to 55 h of germination; (b) blast air-drier for seeds in gauze; (c) a JLGL45 husk machine (JLGJ45-B, Guangzhou Hu Ruiming Instrument Co., Ltd. Guangdong, China), which peels the seeds and separates the brown rice seeds; both intact and broken seeds were collected and then weighed; (d) brown rice seeds were then incubated in 2 mL centrifugal tubes.

Figure 6

Standards for detecting seed embryo exposure. (A) Front view of embryo exposure in ZXM. (B) Flank view of embryo exposure in ZXM. (C) Front view of dehiscence in HY73. (D) Flank view of dehiscence in HY73. The arrows indicate the tiny dehiscence with exposed white embryo. (E) The left three seeds represent the accepted very tiny protrusion (also for DT test), and the right three ones were unaccepted for seed preparation for physio-chemical studies. The accepted criteria for the DT test is the protrusion of the plumule to a length of 0.5–1 mm. (F) The process of collecting seeds with embryo exposed.