Effect of soaking, germination and roasting on thiamine content in Pathum Thani 1 rice malt
Keywords:soaking, germination, roasting, malting, thiamine
Malting is the three step-process for achieving high quality and nutritious cooking rice with specific characteristics and flavor. Considerations for time and temperature are important in efficiently achieving the highest nutritional content. This process effectively increases the smaller peptide and oligosaccharide contents, especially amino acids and reducing sugars, which results in the development of color, taste, and aroma in malt. Experiments found that thiamine, a surrogate for overall vitamin content increased significantly by soaking in water peaking at 1.3 times unsoaked rice levels when soaked for 60 hours (0.237 and 0.185 mg/100 g, respectively). Moreover, it was found that period of germination greatly affects thiamine content. With extended germination periods, thiamine progressively increased from 0.237 mg/100 g to 0.758 mg/100 g (3.2 times) when paddy germinated for 72 hours. Malted rice was roasted at 160, 170, 180, 200, and 250°C for 20, 40, and 60 minutes in a drum rotary roasting machine. It was found that higher temperature and extended time led to significant reduction of thiamine content. However, for the industrial-scale production, the rice should be roasted at 170°C for 20 minutes in order to maintain both desired thiamine content and physical properties, such as color and flavor, corresponding with desired malt appearances. Consequently, these conditions could maintain sufficient thiamine content at 0.293 mg/100 g, which meets the level of 20% Thai RDI criterion.
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