# Effects of Different Pretreatments on the GABA Content of
## 1 Introduction  
Brown rice is regarded as a healthier choice than polished white rice because it retains more germ and bran layers during processing, maintaining dietary fiber, vitamins, plant sterols, and bioactive components such as GABA [1]. However, brown rice is rarely consumed as a staple food because of its dark appearance and hard texture. The germination of brown rice can be used to improve its taste and further enhance its nutritional value and health functions [2]. In addition, brown rice germination can improve water absorption, cooking gelatinization quality, and hence, brown rice texture. [PERSON] et al. [3] reported that the water absorption stage of brown rice took 8 h, and moisture content increased from 15.9% to 36.8% after 48 h of germination. The sprouting ratio increased to 97% at 32 h.  
Brown rice germination can enhance the nutritional value and bioactive components, including total polyphenols, and flavonoids, to increase antioxidant activity [4; 5]. Both \(\gamma\)-oryzanol and \(\gamma\)-aminobutyric acid (GABA) can be improved by germination and fermentation [6; 7]. GABA is widely present in both animals and plants, where it serves critical functions. In plants, GABA not only regulates the internal environment to cope with biotic/abiotic stimuli, but it also serves as a signaling molecule. When plants are stimulated externally, GABA can perform a variety of tasks, including regulating the carbon/nitrogen (C/N) ratio [8], plant defense [9], and phenolic compound accumulation [10]. In animals, GABA serves a variety of physiological functions, including reducing blood stress [11], improving sleep [12], and relieving stress [13]. Consequently, functional foods rich in GABA, such as tea, beverages, and dairy products, have gained popularity in many countries [14]. GABA metabolism occurs in the cytoplasm and is primarily divided into two pathways: GABA shunt and polyamine degradation. The GABA shunt is the primary synthetic pathway, producing 70% of GABA under anaerobic conditions [15]. The GABA shunt involves the irreversible decarboxylation of cytoplasmic L-glutamic acid at the \(\alpha\) position by glutamate decarboxylase (GAD, EC 4.1.1.15), resulting in GABA. Inside plant cells, Ca2+ can bind to its receptor protein, calmodulin (CaM), initiating the response. As the Ca2+ concentration increases, active enzymes known as Ca2+/CaM complex promote production. [PERSON] et al. [16] postulated that GAD, which is involved in GABA production, is a binding protein (CaM) that can be activated by Ca2+ and CaM, hence increasing GAD activity and thus metabolizing more GABA content. High-pressure processing (HPPP), also known as high hydrostatic pressure processing or ultra-high-pressure processing, is an emerging non-thermal food preservation technique. The primary purposes ofHPP are microbial inactivation, effectively eliminating hazardous pathogens or spoilage microorganisms present in food, and altering the characteristics of food. HPP can change the texture, appearance, and flavor of food. Moreover, HPP can cause cold gelatinizing effects, imparting unique properties to food and improving food quality [17]. [PERSON] et al. [18] investigated the effect of HPP on GABA in germinated brown rice and found that treating germinated brown rice at 300 MPa for 10 min increased the GABA content by 45.16%. The HPP conducted at 100 MPa increased the GABA content in germinated brown rice, which can be attributed to the stimulation of glutamate metabolism, as glutamate is a precursor of GABA [19; 20; 21]. Therefore, combining germination and HPP treatment can accelerate GABA and glutamate metabolism pathways, resulting in increased GABA content. Ultrasonication, an emerging processing technique, is used in the food industry and biotechnology processes such as filtering, extracting, and degassing [22].