Physicochemical Variability and Biodiesel Potential of Seed Oils of Two Hibiscus sabdariffa L. Phenotypes

Abstract

Considerable interest is being focused on vegetable oils as fuel. Due to their characteristics being close to diesel and their renewable potential, studies recommend their use for agricultural applications. Hibiscus sabdariffa var. sabdariffa is widely studied for the nutritional properties of its calyces. Although the seeds of this species are known to be rich in fatty acids, their use is little known in Benin Republic. Similarly, a few studies have attempted to characterize the seeds of the green phenotype of this plant species. By following standard methods, the fatty acid profiles of oils extracted from the seeds of the two varieties (red phenotype, sabdariffa (HSS), and green phenotype, altissima (HSA)) of H. sabdariffa L. were established. A comparative study of their physicochemical properties was also performed to highlight their potential use as fuel. It follows that HSS seed oil is yellow while HSA seed oil is dark green. For the two varieties, values obtained for the kinematic viscosity (∼4 mm2/s), cetane number (∼55), and density (0.87 g/cm3) are in accordance with the U.S. and European standards. However, it is observed that HSA oil is significantly more acidic (23.10 ± 0.22 for HSS vs 18.20 ± 0.40 mg KOH/g oil for HSS) with a higher peroxide value (HSA: 0.280 ± 0.002 vs HSS: 0.140 ± 0.001). The major fatty acids are the following: palmitic (HSA: 27.09 vs HSS: 25.48%), oleic (HSA: 31.81 vs HSS: 35.21%), and linoleic (HSA: 31.43 vs HSS: 29.70%) acids. These fatty acid profiles give to the two oils calorific values (∼39.45 MJ/kg) lower than that of diesel but good oxidative stability and cold filter plugging. The two oils could be used as fuel oil, after their transesterification to improve their properties.