Effects of germination conditions on enzyme activities and starch hydrolysis of long‐grain brown rice in relation to flour properties and bread qualities

Abstract

Gluten-free products from rice are gaining popularity because of its hypoallergenic characteristic. The absence of gluten results in inferior bread qualities such as hard texture, reduced volume, and shorter shelf-life. Hydrolytic enzymes are activated during germination to stimulate plant growth, and germinated brown rice (GBR) has been shown to improve gluten-free bread properties. However, the changes in hydrolytic enzyme activities under different germination conditions and their relationship with the properties of germinated rice flour and bread have not been reported. Therefore, the objectives of this work were to investigate the activities of amylases and protease in GBR under aerobic and anaerobic germination for 2 and 4 days and their impacts on starch hydrolysis, flour properties, and bread qualities. Greater enzyme activities were observed in GBR germinated under aerobic condition and a longer time, and correlated with increased sugar content and foaming capacity. Breads were prepared from GBR along with brown rice (control). GBR breads showed a greater specific volume (4% to 10%), a reduced hardness (34% to 90%), and a lower starch retrogradation (66% to 90%) compared with the control. Bread prepared from 4-day aerobic GBR had the largest reduction in starch molecular size and displayed the lowest hardness and starch retrogradation. After stored for 5 days, GBR breads exhibited no change in specific volume and less hardness and retrogradation than the control bread. In conclusion, greater activities of protease and amylases in GBR significantly increased foaming capacity and reduced starch molecule size, respectively, which were responsible for the improved GBR bread qualities.Practical Application: Rice flour is widely used as the main ingredient in gluten-free breads, which however tend to have poor texture and reduced shelf-life due to the absence of gluten. The qualities of gluten-free breads are usually improved by the addition of many ingredients such as tapioca and potato starches. Germination process naturally produces bioactive compounds and activates enzymes. Germination conditions that produce greater activities of amylases and protease can be used to produce gluten-free breads with better qualities and longer shelf-life without the addition of starch.

Increased γ-Aminobutyric Acid Content of Germinated Brown Rice Produced in Membrane Reactor

“…Moreover, Wunthunyarat et al . ( 5 ) also confirmed that during germination, by the actions of α-amylase, increased concentrations of saccharides with lower degrees of polymerization were observed.…”

“…Amongst various approaches introduced to increase brown rice acceptance, germination has been considered as the most suitable method to especially ameliorate brown rice sensory attributes, nutrient contents and functional compounds ( 5 , 6 ). Significant biochemical changes during germination lead to the increase in free amino acids, reducing sugars (due to the action of amylolytic enzymes), γ-aminobutyric acid (GABA) and soluble fibre content in germinated brown rice ( 7 ).…”

Sprouts Use as Functional Foods. Optimization of Germination of Wheat (Triticum aestivum L.), Alfalfa (Medicago sativa L.), and Radish (Raphanus sativus L.) Seeds Based on Their Nutritional Content Evolution

“…Numerous authors worked on different varieties of wheat [12][13][14][15][16], whereas fewer studied mung beans, buckwheat, broccoli, radish, alfalfa, chickpeas, brown rice, etc. [1,[17][18][19][20][21][22][23].…”

Effects of sourdough on improving the textural characteristics of microwave‐steamed cake: A perspective from dielectric properties and water distribution

“…A speed of 1.7 mm/s was utilized for the MSSC strain to 40% of the initial state. Three slices (20 ± 2 mm thickness) obtained from the middle of MSSC were made for each measurement (Wunthunyarat, Seo, & Wang, 2020).…”