Honge oil is derived from the seeds of the Millettia pinnata tree, which is native to tropical and temperate Asia. Millettia pinnata, also known as Pongamia glabra, is common throughout Asia and thus has many different names in different languages, many of which have come to be used in English to describe the seed oil derived from M. pinnata; Honge is the Kannada word for this tree. Other names for this oil include Karanja oil (from Hindi), Pungai oil (from Tamil) and Pongamia oil (from the genus as described by Étienne Pierre Ventenat).
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Honge oil is yellowish-orange to brown in color. It is toxic and will induce nausea and vomiting if eaten but it is used in many traditional remedies. Honge oil is antiseptic and resistant to pests. It has a high content of triglycerides, and its disagreeable taste and odor are due to bitter flavonoid constituents including karanjin and karanjachromene.[1]
Honge oil is composed of the following fatty acids:[2]
| Fatty acid | Nomenclature | Percentage |
|---|---|---|
| Palmitic | C16:0 | 11.6% |
| Stearic | C18:0 | 7.5% |
| Oleic | C18:1 | 51.5% |
| Linoleic | C18:2 | 16.0% |
| Linolenic | C18:3 | 2.6% |
| Arachidic | C20:0 | 1.7% |
| Eicosenoic | C20:1 | 1.1% |
| Behenic | C22:0 | 4.3% |
| Lignoceric | C24:0 | 1.0% |
It has been used as lamp oil, in leather tanning, in soap making, and as a lubricant for thousands of years. Its toxicity, as well as its color, bitter taste, and disagreeable odor, keep it from being used in cooking but it does have uses in traditional medicine for treating skin disease and liver disease.[3]
Recent studies have shown some potential for biocidal activity against V. cholerae and E. coli, as well an anti-inflammatory, antinociceptive (reduction in sensitivity to painful stimuli) and antipyretic (reduction in fever) properties. There is also research indicating that the oil can be used as a natural insecticide.[4]
Many studies have been done to convert Honge oil into biodiesel.[2][5][6]
One recent comparison of the methyl esters of Honge oil to the ASTM D6751 standard for biodiesel fuels shows that processed Honge oil is within the standards. Against the European EN 14214 standards, Honge oil does not meet the storage stability standard; Oxidation stability needs to be a minimum of 6 hours at 110°C, but the stability of processed Honge oil is only 2.24 hours. This can be improved by adding antioxidants.[2]
The methyl esters of Honge oil have a cloud point of 19°C and a pour point of 15°C which would be problematic in lower temperature climates.[2]