Rice (Oryza sativa L.), belonging to the grass family Gramineae (Poaceae), is one of the main staple crops consumed by more than half of the world’s population. The large scale of cultivation and production makes rice a readily available raw material for various applications. Recent studies have shown that young rice leaves at the growth stage contain valuable nutrients and bioactive compounds. Leaves of black rice varieties have been reported to contain polyphenols and flavonoids with antioxidant, anti-inflammatory, and anticancer properties.

Some studies have indicated that biotic and abiotic stress factors can alter the content and composition of bioactive compounds in plants. One of the most common adverse abiotic factors is shading or light intensity. Changes in light intensity significantly affect plant development, morphological, physiological, biochemical traits, and photosynthetic capacity, ultimately influencing crop yield. Research results show that higher shading rates reduce peanut yield. Therefore, determining optimal cultivation conditions helps obtain the highest plant product yield.

Currently, fungal infections rank fourth among causes of bloodstream infections, and Candida species are the most common fungi involved. Among all species, Candida albicans is the most common cause of mucosal and systemic infections and accounts for about 70% of fungal infections worldwide. Plant-derived products containing bioactive compounds such as chlorophyll and polyphenols have been reported to exhibit effective antifungal activity. Antifungal activity against C. albicans from rice grains has been documented. However, no studies have yet reported the antifungal potential of rice leaves. Therefore, this study aims to evaluate the effects of rice leaf harvest time and shading level on chlorophyll and polyphenol contents and the antifungal activity against C. albicans of rice leaf extracts.

The study used six commonly grown rice varieties in the Mekong Delta region: IR50404, Nang Thom, Tai Nguyen, Huong Lai, Nep Tim, and Huyet Rong. Rice leaves were harvested at six time points (1, 2, 3, 4, 5, and 6 weeks after sowing) and subjected to three shading treatments (no shade, single-layer shade net, and double-layer shade net). Leaves were extracted with 80% ethanol. Analyzed parameters included chlorophyll content, polyphenol content, and antifungal activity against Candida albicans.

Results showed that chlorophyll content in leaf extracts of Huong Lai, Huyet Rong, Nep Tim, and Nang Thom varieties gradually increased from week 1, reaching the highest level (1286–1469 μg/g leaf) at week 4. However, with longer growth time, chlorophyll content decreased. Specifically, at week 5, chlorophyll content in leaf extracts ranged from 1206 to 1313 μg/g leaf across varieties. Comparing the effect of shading levels on chlorophyll content, results showed that chlorophyll content in leaf extracts under no shading and single-layer shading conditions was higher than under double-layer shading.

Similar to chlorophyll, polyphenol content in leaf extracts of Tai Nguyen, IR50404, and Nang Thom varieties also changed with growth time, increasing from week 1 and reaching the highest at week 5. However, at week 6, polyphenol content decreased. Additionally, polyphenol content in leaf extracts of tested varieties was highest under no shading conditions, ranging from 5.2 to 6.3 mg/g leaf, while under single- and double-layer shading, the values were only about 2 to 2.6 mg/g leaf.

Antifungal activity analysis against C. albicans showed variations in inhibition percentages depending on rice variety, shading condition, and harvest time. Leaf extracts of variety IR50404 showed the highest antifungal activity, reaching nearly 50% inhibition. Regarding shading, leaf extracts from Huyet Rong variety showed about 50% inhibition under no shading, whereas shading conditions reduced inhibition to 25–35%. Furthermore, antifungal activity of IR50404 leaf extracts was less affected by shading conditions.

The study results indicate that shading conditions and growth duration significantly affect chlorophyll and polyphenol contents as well as antifungal properties of rice leaves. It demonstrated that changes in these compound levels due to shading and growth time altered the antifungal characteristics of rice leaf extracts. Moreover, polyphenol and chlorophyll contents and antifungal properties depend on the rice variety. Results also show a correlation between chlorophyll, polyphenol content, and antifungal activity. These values peaked when rice grew under no shading conditions during the 3–5 week growth stage.

This research lays the foundation for selecting rice varieties with high Candida resistance suitable for producing extracts applied in skincare cosmetics.