Nutritional Improvement of Germinated Riceberry Rice (Oryza sativa) Cultivated with Pleurotus ostreatus Mycelium

Abstract

Riceberry rice is a whole grain rice variety, which is rich in vitamin E, anthocyanin, phenolic acids, flavonoids, phytosterol antioxidants and fiber. The nutritional of Riceberry rice could be further improved by germination process, with this process the g-aminobutyric acid (GABA) in rice samples is increased. Furthermore, solid stage fermentation (SSF) of rice and grains with fungi have been employed in the food industry such as rice fermented with Aspergillus oryzae for rice koji production, or soybean fermented with Rhizopus oryzae to produce Tempeh. This fermentation step is not only for the food preservation but also improve the nutritional in foods. In this study, the germination and fermentation with Pleurotus ostreatus mycelium can improve the nutritional content present in Riceberry rice. The amounts of GABA, anthocyanin, and bioactive substances contained in Riceberry rice (RR), germinated Riceberry rice (GR) and germinated Riceberry rice with P. ostreatus mycelium (MR) were compared. During germination, the g-aminobutyric acid (GABA) content of RR increased by 71 and 73 % when further fermented with P. ostreatus mycelium. The highest level of GABA was found in the MR (38.58±0.29 mg/100 g) treatment. Furthermore, an untargeted metabolomics approach using Liquid Chromatograph Quadrupole Time-of-Flight Mass Spectrometer; LC-QTOF, revealed an abundance of various amino acids such as valine, alanine, histidine, methionine, L-glutamic acid as well as essential fatty acids such as steric acid and linoleic acid in germinated Riceberry rice with P. ostreatus mycelium samples. The results from this study could lead to nutritional improvement of Riceberry rice through fermentation with P. ostreatus mycelium, which could be applied in further rice flour applications and the product could be recognized as functional food. HIGHLIGHTS The GABA content in Riceberry rice increased by 71 % during germination and 73 % when germinated Riceberry rice was further fermented with ostreatus mycelium Amino acids, fatty acids, and phenolic compounds differed significantly among Riceberry rice (RR), germinated Riceberry rice (GR) and germinated Riceberry rice with ostreatus mycelium (MR) Contents of different amino acids in Riceberry rice were significantly increased when the germinated Riceberry rice was fermented with ostreatus mycelium Essential fatty acids such as Stearic acid and Linoleic acid were the highest in the germinated Riceberry rice with ostreatus mycelium sample GRAPHICAL ABSTRACT