Germinating Conditions of Brown Rice to Increase Gamma-Aminobutyric Acid (GABA) Content: A Systematic

Abstract

Rice is the most important crop that provides calories for more than half of the world’s population. As a source of carbohydrate, rice fulfills up to 700 calories/day/person. With the rising concern on the food and health-related issues, the functional foods are receiving increased interest globally. Brown rice (BR) is a rice product that has superior nutritional characteristics and functional compounds over the white rice (WR). However, due to its poor texture, unpleasant bran odor, low digestibility, and hard texture, BR is less considered as a suitable rice-table. Germination is a strategy to increase the acceptability of rice and also to improve its functionalities. Germinated brown rice (GBR) was reported to increase the rice phytochemicals content, especially -aminobutyric acid (GABA). Therefore, this systematic review aimed to structurize current processing methods for producing GBR with enhanced GABA content. This study followed the Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines. The literature search was conducted on three databases: Wiley Online Library, ResearchGate, and Google Scholar. Up until 27 May 2020 with no time restrictions, 624 publications were obtained and organized using Mendeley Dekstop, Elsevier. Out of the 624 articles initially collected, there were only 48 articles met the inclusion criteria and used for the qualitative synthesis. Current GBR production methods could be grouped as: (i) fully soaking method, (ii) soaking in combination with humidification, (iii) spraying in combination with humidification, and (iv) humidificationmethod. The most suitable method for producing GABA-enriched GBR was soaking in combination with humidificationmethod. Temperature, time, pH, RH, and the ratio of kernel to water were the most studied factors in producing GABA-enriched GBR. The optimum time were 12-24 hours of soaking and 24-96 hours of humidification, while the optimum temperature was at 25-40 oC. Low pH imbibiton solutions could also stimulate the GAD activity which causes the increase of GABA content accumulation. Other than that, germinating BR in combination with other treatments like mild pressure, plasma, ultrasound and/or under conditions like darkness, hypoxic systems could also produce GBR with enhanced GABA content.