با همکاری انجمن علمی منظر ایران
نوع مقاله : مقالات پژوهشی
نویسندگان
1 گروه علوم و مهندسی باغبانی، دانشکده کشاورزی، دانشگاه علومکشاورزی و منابعطبیعی خوزستان، ملاثانی، ایران
2 دانشگاه علوم کشاورزی و منابع طبیعی خوزستان
کلیدواژهها
عنوان مقاله English
نویسندگان English
Introduction
Hibiscus sabdariffa, commonly known as roselle, is a rich source of valuable compounds such as natural pigments and bioactive substances, whose extraction is of great interest in the food and pharmaceutical industries. Typically, roselle calyces are harvested with high moisture content (about 85%); therefore, drying is a crucial post-harvest process that helps reduce moisture and increase the shelf life of the product. Drying settings and conditions can affect the aroma, flavor, and visual properties, such as the color of roselle. Since temperature influences the biochemical properties of medicinal plants during the drying process, and visual attributes like color impact the marketability and quality of the product, this study aimed to investigate the effect of drying temperature on the biochemical properties and color indices of roselle to determine the optimal drying temperature.
Materials and Methods
In this study, the effects of different temperatures (30, 50, 70, and 85°C) over 48 hours on the color indices, anthocyanin content, total phenolic content, total flavonoid content, and antioxidant activity of roselle calyces were examined in a completely randomized design with three replications. The study was conducted in the Horticultural Science Department of Khuzestan University of Agricultural Sciences and Natural Resources in 2023. All plant samples used were collected from a farm located in Bavi County, at a specific time and under completely identical conditions. After preparing methanolic extracts from the dried samples, total phenolic content was measured using the Folin-Ciocalteu reagent, total flavonoid content using the aluminum chloride colorimetric method, total anthocyanin content using the pH differential method, and antioxidant activity based on the DPPH radical scavenging assay. Color indices were also evaluated, including color intensity, hue, yellow, red, and blue percentages, and the browning index. Additionally, correlations between the data were analyzed using Pearson’s correlation method, and the sensitivity analysis was also evaluated on variables. Principal Component Analysis (PCA) was applied to better understand the relationships between the variables.
Results and discussion
The findings indicated that temperature significantly affected the phenolic content, flavonoid content, anthocyanin content, antioxidant activity, and color indices of roselle calyces. The results showed that 70°C was the optimal temperature for preserving essential biochemical compounds and enhancing color properties. At this temperature, the highest levels of phenolic compounds (1560.3 mg GA.100g-1 DW), flavonoids (415.96 mg Q.100g-1 DW), and anthocyanins (48.48 mg CG.g-1DW) were recorded. Additionally, the percentage of red color and overall color intensity peaked at 70°C, with a significant increase in red color compared to other temperatures. In contrast, raising the temperature to 85°C resulted in significant degradation of anthocyanins and flavonoids, with anthocyanin content dropping dramatically to 1.69 mg, and an increase in the browning index, clearly indicating the degradation of these compounds. The browning index, a primary indicator of quality loss, rose from 10.17 at 70°C to 18.25 at 85°C, highlighting the negative impact of high temperatures on product quality. Moreover, antioxidant activity, measured using IC50, increased significantly at 85°C, reflecting reduced antioxidant efficiency. Correlation analysis revealed a positive and significant correlation between antioxidant activity and both anthocyanin and total flavonoid content, while a negative correlation was found between the browning index and anthocyanin content. This suggests that higher temperatures lead to anthocyanin degradation and a reduction in red color. The analysis of the sensitivity and stability of biochemical compounds and color indices showed that among color indices, color intensity and the percentage of red color were more sensitive to temperature changes, while blue color exhibited higher stability. Biochemically, flavonoids and anthocyanins were highly sensitive to temperatures above 70°C, with anthocyanins showing the least stability between 70°C and 85°C, followed by a decrease in antioxidant activity at higher temperatures. According to PCA’s results, the first two principal components (PC1 and PC2) explained 85.1% of the total variance. PC1, accounting for 59.2% of the variance, was primarily associated with red color, color intensity, phenol, flavonoid, and anthocyanin content. These are the key factors responsible for the roselle calyces’ visual and biochemical quality. PC2, explaining 25.9% of the variance, was mainly linked to the browning index, IC50, and blue color. This suggests that higher temperatures lead to a reduction in red color and antioxidant activity, alongside an increase in browning and blue.
Conclusion
The study concluded that 70°C was the optimal drying temperature, as it maximized the retention of bioactive compounds and antioxidant activity while enhancing color indices such as overall color intensity and red color percentage. On the other hand, increasing the temperature to 85°C led to a significant reduction in these compounds and an increase in browning, yellow, and blue color indices, which was attributed to anthocyanin degradation at this temperature. Additionally, the positive correlation between antioxidant activity and anthocyanin and flavonoid content, along with the negative correlation between the browning index and anthocyanin content, and the sensitivity of various compounds, especially anthocyanins and flavonoids, to high temperatures (85°C), emphasizes the importance of preserving these compounds for improving the final product quality. Therefore, 70°C is recommended as the optimal drying temperature for roselle calyces to prevent the degradation of bioactive compounds and preserve the color and quality of the product. Temperatures above 70°C may reduce product quality and marketability and should be avoided.
Acknowledgments
The present article is derived from a research project registered under the code 04/1402. Therefore, the authors of this article would like to sincerely express their gratitude to the Vice Presidency for Research and Technology of Khuzestan University of Agricultural Sciences and Natural Resources for their financial and moral support of this project.
کلیدواژهها English
