Glutamate Decarboxylase (GAD) Extracted from Germinated Rice: Enzymatic Properties and Its Application in Soymilk

Abstract

Glutamate decarboxylase (GAD) is an important enzyme in biological metabolisms acting on catalyzing the irreversible a-decarboxylation of L-glutamic acid to g-aminobutyric acid (GABA) and CO2, which was focused in this study. Three rice varieties different in color were germinated at different times and used for crude GAD extraction. Crude GADs with an optimal germination time from germinated black (GBR), red (GRR), and white (GWR) rice were evaluated for enzymatic properties, including the effect of pHs, temperatures, and concentrations of both L-glutamic acid and pyridoxal 5′-phosphate (PLP). Crude GAD with optimum enzymatic properties was selected to be partially purified using ammonium sulfate (AMS) precipitation. The obtained GAD was supplemented to soymilk and determined for GABA content. All crude GADs from germinated rice at 10 germination days presented the highest enzyme activity. For enzymatic properties, crude GADs showed the highest activity at pH in a range of 5.6-6.0 at 60˚C. The Km values of crude GADs were in the range of 7.68-8.06 mm for L-glutamic acid and 0.15-0.20 mm for PLP and were the lowest in crude GAD from GBR. GAD from GBR presented the highest enzyme activity in the fraction with 50% saturation (v/v) after AMS precipitation and it was purified for 14.61 folds. The addition of this GAD (1.0%, v/v) resulted in the increasing of GABA content in soymilk to 53.79 mg/100 mL, accounted for 1.23 times compared with control.

Reformulating Bread Using Sprouted Pseudo-cereal Grains to Enhance Its Nutritional Value and Sensorial Attributes

“…On the other side, germination of pseudo-cereal grains is known to increase the digestibility of protein, starch, vitamins, minerals, bioactive compounds (GABA and phenolic compounds) and AA of sprouts [ 9 , 10 , 12 ]. Particularly, increased GABA amounts in sprouts are attributed to the activation of glutamate-decarboxylase (GAD) during germination, which is involved in the conversion of glutamate to GABA [ 30 ]. Similarly, evidence from earlier studies demonstrates that germination of cañihua and kiwicha increase significantly TSPC by the activation of cell wall-degrading enzymes and esterases and up-regulation of biosynthesis routes such as the phenylpropanoid pathway [ 7 ].…”

Anatomical and Image Analysis of Grain Coloration in Rye

“…In cereals the close correlation between the color parameters of grains or flour and pigments content was also established. Anthocyanins (cyanidin-3-O-glucoside, peonidin-3-O-glucoside) in black rice flour were negatively correlated with L*, b*, C*and h* values, proanthocyanidin in red rice flour was positively correlated with a* [22]. Grain color analysis of uncolored, red and black rice, shows that white rice varieties have the highest values of L*, b*, h* and the lowest a*, red rice varieties have the maximum value of a* and C*, and black rice is characterized by the minimum values of L*, b* and C*.…”

“…Twenty six accessions were divided into five groups in accordance with the color of their grains and genes of anthocyanin pigmentation. These groups were named according to the previous publication [5] as anthocyinin-less (#1-7), yellow-grained (#8-11), brown-grained (#12-15), green-grained (# [16][17][18][19][20][21][22], and violet-grained (# [23][24][25][26]. The results were analyzed by comparing the means in five groups of lines using ANOVA and Turkey's test at P≤ 0.05.…”

“…In these lines, the yellow color of the grains is attributable to homozygosity for recessive alleles of the genes Vs and C [3]. In accordance to rye genetics the dominant allele C leads to green grain (# [16][17][18][19][20][21][22], and Vs -to violet one (# [23][24][25][26]. Brown grain is due to the combination of the allele Vs with the homozygosity for recessive mutations vi1 (# [12][13][14] or vi2 (#15).…”

Recent innovations in processing technologies for improvement of nutritional quality of soymilk

“…GAD is an enzyme that converts L-glutamic acid to γ-aminobutyric acid (GABA), which functions as an inhibitory neurotransmitter in the nervous system and has a potent anti-hypertensive effect (Diana et al, 2014). Soymilk with added GAD (1.0%, v/v) had 1.23 times higher GABA content relative to the control soymilk (Pramai et al, 2019). Additionally, soymilk containing green coffee extracts indicated significantly high total phenolic content and antioxidative capacity with increasing concentration of phenolic contents in coffee extracts (0.25-1 mg/mL) (p < .05).…”