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. Antinutrient
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.