Effects of Processing on Proximate Composition of Hibiscus rosa-sinensis Leaf

Leaves of Hibiscus rosa-sinensis are processed using different methods depending on the intended application. Using three different processing methods, we investigated the effects of processing on the proximate constitution of the leaf. Result demonstrated that the fresh raw leaf had moisture content of 82.30 ± 0.42%, which were significantly (p<0.05) reduced by drying but not extraction and blanching. The protein content of the raw leaf was low (1.80 ± 0.10%). Extraction and blanching reduced the protein content, whereas drying increased the protein content significantly (p < 0.05) for raw dried leaf powder and blanched leaf products. The raw leaf contained vitamins A, B2, C and E, which were significantly reduced by extraction and blanching, but were concentrated by drying. Anti-nutrient contents of the raw leaf were low and were reduced to negligible levels by the processing techniques employed. Comparing the nutrient and chemical constituents with recommended dietary allowance (RDA) values, we found that the leaves contain an appreciable amount of nutrients, minerals, vitamins, proteins and phytochemicals and low degree of toxicants. These findings suggested that the treatment method employed in processing this leaf affected the proximate composition, and this should be considered in utilization of this leaf (and other leaves) product in various food and pharmaceutical formulations. Various heat processing techniques applied during the preparation of the processed products from Hibiscus rosa-sinensis leaves, caused adverse effects on the chemical composition of the processed leaf products. This was evident especially for the vitamins and minerals constitution of the processed products. More so, blanching and drying caused a significant reduction in the nutrients and anti-nutrient composition of the formulated samples. While the best processed samples were the dried powdered products, especially the RDLP, whereas the worst processed samples were the extracts, notably B2LE. It is recommended that other processing techniques such as freezing, solar and spray drying and ethanol extraction can also be applied in order to determine their effects on nutrient retention and anti-nutrient reduction on the plant leaves and compare it with the results of this study.

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