Under room temperature conditions, brown rice kernels with a moisture content of 14.8% were soaked in deionized water for various durations: 0, 15, 30, 45, 60, 75, 90, and 105 minutes. After soaking, the grains were centrifuged, and any surface moisture was carefully removed using filter paper. The moisture content of each sample was then measured. Two parallel samples were prepared for each treatment, and the arithmetic mean was taken as the final result.
In addition, brown rice seeds (also with 14.8% moisture) were treated under an ultrasonic field (25W, 30kHz) for the same time intervals. After soaking, the grains were centrifuged, and surface moisture was wiped off with filter paper. Moisture and organic phosphorus levels were measured for each sample. Again, two parallel samples were used, and the average value was recorded.
To further analyze phosphorus content, 5g of brown rice was placed into a 100ml Erlenmeyer flask. Then, 50ml of deionized water and 4ml of 0.4U/ml phytase working solution were added. The mixture was soaked for 0, 15, 30, 45, 60, 75, and 90 minutes before being centrifuged. Surface moisture was removed with filter paper, and phosphorus levels were determined. This process was repeated for two parallel samples, and the average was calculated.
Similarly, another set of samples was treated with ultrasound (25W, 30kHz) at the same time intervals. After treatment, the samples were centrifuged, and surface moisture was removed. Phosphorus content was then measured. As before, two parallel samples were tested, and the mean was taken as the result.
Since more than 90% of the organic phosphorus in brown rice exists as phytate phosphorus, the organic phosphorus content was calculated by subtracting the inorganic phosphorus content from the total phosphorus content.
For the determination of inorganic phosphorus, no digestion was performed. However, total phosphorus was determined after digestion. This distinction is crucial for accurately identifying the different forms of phosphorus present.
The effect of ultrasound on water absorption was also studied. Phytase hydrolyzes phytic acid, a reaction that requires water molecules. The availability of water in the system plays a key role in this enzymatic process. Water not only acts as a transport medium but also helps activate enzymes and substrates through hydration.
After 30 minutes of ultrasonic treatment, the moisture content of the brown rice increased to 17.9%, representing a 20.9% increase compared to the untreated sample, which showed only a 2.1% increase. This significant rise suggests that the endosperm starch began to absorb water and swell rapidly. This indicates that ultrasound enhances mass transfer, increasing the penetration rate of external substances.
According to the data, after 30 minutes of ultrasonic exposure, the foreign matter had reached the aleurone layer, allowing exogenous phytase to directly act on the substrate—phytic acid. This facilitates enzymatic hydrolysis and reduces anti-nutritional factors. The main product of phytic acid degradation by phytase is inositol diphosphate.
Phosphorus in brown rice includes inorganic phosphorus, phytate phosphorus, and phospholipids. Therefore, some phosphorus remains even after hydrolysis.
In conclusion, ultrasound enhances mass transfer processes, accelerating the penetration of external materials and reducing reaction times. Appropriate ultrasonic power can also enhance enzyme activity and promote enzymatic reactions. Studies have shown that the optimal conditions for phytase hydrolyzing phytic acid in brown rice are an ultrasonic power of 25W and a treatment time of 30 minutes.
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