Introduction

Rice (Oryza sativa) is one of the major staple crops. Rice grains are widely used in the food, pharmaceutical, and cosmetic industries. In recent years, products derived from the stems and young leaves of rice plants have also attracted increasing research interest. Studies have shown that young leaves or seedlings contain higher levels of bioactive phytochemicals compared to mature grains. Investigations of the seed, seedling, and sprout stages of wheat, corn, and barley revealed that total phenolic content and antioxidant capacity are higher in seedlings and sprouts than in seeds.

The content of bioactive compounds, particularly chlorophyll and polyphenols, plays an important role in determining the antioxidant potential of plant-derived products. Antioxidant properties are crucial in defining the applicability of plant products. Several factors influence the composition, concentration, and antioxidant activity of bioactive compounds in plants, including plant species, plant part used, cultivation method, harvest time, extraction solvent, and processing conditions.

In black rice varieties, total chlorophyll content peaks between 10–25 days after sowing, while in white rice varieties, total polyphenol content is highest at 5–7 days. Colored rice varieties tend to exhibit higher antioxidant capacities than white rice. Thepthanee et al. (2021) reported that ethanol was the most effective solvent for extracting polyphenols and enhancing antioxidant activity from black rice leaves. During the processing of plant-based products, the inactivation of the enzyme polyphenol oxidase (PPO) is essential to minimize the oxidation of bioactive compounds. Additionally, applying spray-drying at appropriate temperatures helps retain beneficial compounds in the final product.

Young rice leaves have shown potential for development into powder, tablet, or extract forms for use in functional foods, pharmaceuticals, and cosmetics. IR50404 is a rice variety widely cultivated in the Mekong Delta region of Vietnam due to its short growth cycle, high yield, ease of cultivation, and high nutritional content—especially in protein and amylase. Therefore, this study aimed to evaluate the effects of processing factors—such as extraction solvent, PPO inactivation method, and spray-drying temperature—on the total chlorophyll content, total polyphenol content, and antioxidant activity of IR50404 young rice leaf powder.

Materials and Methods

The study utilized the IR50404 rice variety harvested at five weeks old to produce young rice leaf powder. The effects of different factors—PPO inactivation method, extraction method, and spray-drying temperature—on total chlorophyll content, total polyphenol content, and DPPH (1,1-Diphenyl-2-picrylhydrazyl) free radical scavenging capacity were investigated.

Young rice leaves were treated either by blanching or microwave heating to inactivate PPO, with treatment durations ranging from 1 to 5 minutes. Fresh leaves were ground and extracted using ethanol at varying concentrations (20%, 40%, 60%, and 80%). Spray drying was carried out at temperatures of 120°C, 130°C, 140°C, 150°C, and 160°C with a consistent feed flow rate of 280 mL/h and an exhaust air velocity of approximately 1.4 m/s.

Results

The results indicated that blanching for 4 minutes inhibited 84% of PPO activity. The highest levels of total chlorophyll and total polyphenols were obtained using 60% ethanol as the extraction solvent with a solvent-to-leaf ratio of 10:1. Spray drying at 120°C preserved the highest levels of total chlorophyll (1,338.82 µg/g dry weight), total polyphenols (4.25 mg/g dry weight), and antioxidant activity (1.71 µmol TE/g dry weight) in the young rice leaf powder.

Conclusion

The present study demonstrated that processing steps such as blanching, extraction, and spray drying significantly influence the levels of bioactive compounds in young rice leaves. The results highlight the potential for developing young rice leaf powder as a functional food, pharmaceutical, or cosmetic product. However, further research is needed to optimize processing parameters and evaluate storage stability to establish a more complete production protocol.