The significance of the research is that the use of new technology in the production of high-quality young rice flour by spray drying or freeze-drying technology contributes to lower production costs. In line with the project on restructuring the agricultural sector in the direction of increasing added value. Moreover, young rice flour is completely extracted from young leaves of the rice plant, grown in a fresh climate, a clean environment, no insects, especially ensuring no preservatives and no additives. Young rice flour is an ultra-fine powder that contains many healthful chemical compounds such as polyphenols and chlorophyll. These are substances that have the effect of increasing resistance, keeping the body healthy, reducing stress, creating a spirit of euphoria, refreshment, anti-aging, preventing atherosclerosis, high blood fat, and blockage of blood vessels. blood and cardiovascular diseases.
This study aims to compare two methods of spray drying and freeze-drying of young rice materials to evaluate the quality of young rice flour (antioxidant activity) obtained by analyzing chlorophyll content, total polyphenol content, DPPH free radical scavenging (antioxidant capacity of young rice). Experiment to select high yielding rice variety IR504 to continue the previous research and development process of young rice flour production.
Experimental layout
Conduct experiments:
- Seed treatment process: Seed treatment: Seeds are treated with warm water (45-50oC). Soak seeds for 24 hours and incubate for the next 36 hours before sowing seeds. Seeds are sown on plastic trays with soil substrate. The seeding trays are left in natural outdoor conditions. Seeds are sown on plastic trays when the rice plants reach 2 weeks old, harvest and grind.
*Process: Young rice leaves after harvesting are then ground with a blender, then filtered through a fine mesh filter. Wet milling with the ratio of rice leaves: water is 1: 2. The young rice juice obtained after grinding is dried through a spray dryer with a pump flow rate of 7-8ml/min corresponding to 5 different temperatures and freeze-dried. dry with a moisture content of 5%.
Pictures of sample grinding, sample filtration, and young rice juice collection
Flowchart of the implementation process
Monitoring indicators: chlorophyll content by spectrophotometric method, total polyphenol content by Folin-Ciocalteu method, antioxidant capacity through DPPH free radical scavenging activity.
Weight of young rice flour obtained
The obtained results show that the volume of young rice flour after freeze-drying is highest (8.58 g) which is 2.37 times higher when spray drying at 1500C (3.62 g) and 2.25 times higher when spray drying at high temperature. degree 1200C (2.47 g).
Effect of drying temperature on chlorophyll content in young rice flour
Note: Mean values at the top of the column followed by one or more similar letters are not significantly different in the LSD test at 5% significance level.
From the results of the chart above, it shows that the higher the temperature, the lower the amount of chlorophyll obtained. The highest chlorophyll content was obtained when treated by freeze-drying with a content of 1560.08 µg/l, which was statistically significant different from the rest of the treatments.
In the spray-drying method, the appropriate temperature to obtain the powder with the highest chlorophyll content was 1267.17 µg/l at 120oC, the difference was statistically significant with the remaining temperatures. The chlorophyll content decreased gradually with increasing temperature, this may be because chlorophyll is a color pigment that is easily changed under heat effect during the long-term drying process. When living cells chlorophyll is in the form of complexes with proteins, when dead cells denature proteins, chlorophyll separates and easily participates in chemical reactions.
From the chart results, it shows that the higher the temperature of spray drying of young rice, the lower the amount of total polyphenols obtained. The highest total polyphenol content was 2.6 mg GAE/g in the spray drying method at 120oC, the difference was not statistically significant with the freeze-drying and spray drying methods at 130oC and the difference was significant in terms of statistics compared with the rest of the treatments. This shows that the total amount of polyphenols depends on the drying temperature and drying method. When spray drying at higher temperatures, the amount of polyphenols decreases. Within a certain limit, increasing drying temperature reduces the loss of total polyphenol content, but too low drying temperature results in a longer drying time, leading to faster oxidation of polyphenol compounds by air, thus loss of energy. polyphenols increased. Besides, when the drying temperature is too high, the total polyphenol content also decreases, possibly due to the change of polyphenol compounds under heat effect.
Effect of drying temperature on DPPH . free radical scavenging ability
Note: Mean values at the top of the column followed by one or more similar letters are not significantly different in the LSD test at 5% significance level.
From the results of the graph as shown in the figure, the free radical scavenging ability reached the highest value of 8.5mM Trolox/g when spray drying at 130oC, the difference was not statistically significant with the spray drying method at temperature. 120oC and freeze-drying method. The difference is statistically significant compared with the rest of the treatments. When increasing the drying temperature to 140oC, 150oC and 160oC, the DPPH free radical scavenging ability (antioxidant capacity) of young rice gradually decreased.
In the current context, the rice growing area in the Mekong Delta is very large, but the situation of rice prices is often unstable, causing difficulties in output for farmers. Therefore, finding a new product such as young rice flour is very necessary to increase the added value from rice, contributing to raising income for farmers.
Nguyen Thi Van
Đăng ngày: 25/09/2020