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.
The germination process activates amylolytic enzymes that can produce rice syrup through mashing, however the factors affecting enzyme activities and soluble saccharides have not been investigated. This study characterized amylolytic enzymes activities, including α‐amylase, β‐amylase, and α‐glucosidase, and soluble saccharides from germinated rice cultivars of four rice cultivars, including waxy, short grain, medium grain, and long grain, under aerobic and anaerobic germination conditions over 4 days and then mashed at 55, 65, 75, and 85 °C. The results showed that the long‐grain rice had higher activities of all three enzymes, whereas the waxy rice exhibited lower activities. Glucose and maltose were the predominant saccharides at low mashing temperatures of 55 °C and 65 °C; saccharides of degree of polymerization 3 to 7 became significant at mashing temperatures of 75 °C and 85 °C. The amount and composition of saccharides were strongly influenced by rice cultivar, and germination and mashing conditions. The findings highlight the importance of rice components and starch structure on the amount and composition of soluble saccharides from germinated brown rice. Practical Application Rice syrup is commercially produced by the addition of external bacterial enzymes to brown or milled rice. Germinated brown rice is naturally rich in nutrients and amylases, both are produced during the germination process. Because of the presence of naturally activated amylases, germinated brown rice could be used to produce rice syrup without the addition of external enzymes while preserving the nutrients from germination of brown rice.
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