Under room temperature conditions, brown rice kernels with a moisture content of 14.8% were soaked in deionized water for varying durations: 0, 15, 30, 45, 60, 75, 90, and 105 minutes. After soaking, the samples were centrifuged, and the surface moisture was carefully wiped off 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 used as the final result.
In addition, the same brown rice samples were subjected to ultrasonic treatment at 25W and 30kHz for 0, 15, 30, 45, 60, 75, and 90 minutes. After the treatment, the samples were centrifuged, and the surface moisture was removed with filter paper. Both moisture and organic phosphorus content were analyzed. Again, two parallel samples were taken for each condition, and the average value was recorded.
To further investigate the effects of phytase on phosphorus release, 5g of brown rice was placed into a 100ml Erlenmeyer flask, followed by the addition of 50ml deionized water and 4ml of a 0.4U/ml phytase working solution. The mixture was incubated for 0, 15, 30, 45, 60, 75, and 90 minutes before being centrifuged. Surface moisture was removed with filter paper, and phosphorus content was measured. This process was repeated with two parallel samples for each time point, and the average was calculated.
Similarly, another set of experiments involved ultrasound-assisted phytase treatment. Brown rice samples were treated under the same conditions (25W, 30kHz) for 0, 15, 30, 45, 60, 75, and 90 minutes. After treatment, the samples were centrifuged, and the surface moisture was removed. Phosphorus levels were determined, with two parallel samples per treatment.
Since over 90% of the organic phosphorus in brown rice exists as phytate, the organic phosphorus content was calculated by subtracting the inorganic phosphorus from the total phosphorus. Inorganic phosphorus was determined without digestion, while total phosphorus required digestion prior to analysis.
The presence of water is crucial for phytase activity, as it facilitates the hydrolysis of phytic acid. Water not only acts as a medium for the reaction but also enhances enzyme and substrate hydration, promoting more efficient catalysis. Ultrasonic treatment significantly enhanced water absorption in brown rice. After 30 minutes of sonication, the moisture content increased to 17.9%, representing a 20.9% increase compared to the control, which only showed a 2.1% increase. This suggests that ultrasound accelerates water penetration, possibly due to the swelling of endosperm starch.
According to the results shown in Figure 2, after 30 minutes of ultrasonic exposure, the foreign matter had reached the aleurone layer, allowing exogenous phytase to directly interact with phytic acid. This leads to effective enzymatic hydrolysis and the reduction of anti-nutritional factors. The enhancement of mass transfer by ultrasound is primarily attributed to cavitation effects.
When phytase breaks down phytic acid, the main product formed is inositol diphosphate. Brown rice contains various forms of phosphorus, including inorganic phosphorus, phytate phosphorus, and phospholipids. Therefore, some phosphorus remains even after treatment.
In conclusion, ultrasound can enhance the mass transfer process, accelerate the penetration of external materials into brown rice, and reduce reaction times. Appropriate ultrasonic power can also activate enzymes and promote hydrolysis. Studies have shown that the optimal conditions for phytase hydrolysis of phytic acid in brown rice are an ultrasonic power of 25W and a treatment time of 30 minutes.
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