Accumulation of Steroidal Sapogenins and Fixed Oil in Developing Fruits of Balanites aegyptiaca Del.

The fruits of Balanites aegyptiaca, a wild savannah tree, constitute a promising source of steroidal sapogenins, chemicals in demand by the pharmaceutical industry, in addition to an untapped source of an edible fixed oil. Large guantity of the fruit (ca. 400 000 tons per annum) are traditionally collected and marketed in Sudan due to their edible mesocarp. This study is concerned with accumulation of the fixed oil as well as of steroidal sapogenins in 11 fruit developmental stages, from the young immature to the fully ripe, dry stages. The fruits were separated into "kernels" and combined "epicarp+ mesocarp" tissues. An infra-red spectrophotometric method was used for sapogenin quantification. Total sapogenin contents expressed per tissue was 0.5 mg in kernels and 2.5 mg in "epicarp=mesocarp" in the first stage (S1). Thereafter, these values rose sharply in later fruit developmental stages so that by stage S7 (a mature but still green stage), they contained maximum values of 22.0 and 60.0 mg/tissue, respectively. Similarly, balanites kernel oil (BKO) dramatically increased in amount with fruit development; from < 5.0% in the first two very young stages to over 45.0% of kernel dry weight by stages 7 and 8. Thus, harvesting fruits at the still green 7th stage would minimize losses of the dry, sapogenin-rich epicarp encountered during traditional harvesting and handling of dry fruits. "Epiarp+mesocarp" tissue contained both 25a and 25b sapogenins, the proportion of 25b increased with fruit maturation. On the other hand, kernel tissue contained only 25a (diosgenin type) sapogenin till the very late fruit stage, when plastid degradation occurred. Linoleic acid was the major fatty acid of balanites kernel oil in all fruit developmental stages. Linolenic and palmitoleic acids were present in the kernel oil of very young fruits but disappeared with the degradation of plastid-membrane lipids on further fruit maturation and desication. [ABSTRACT FROM AUTHOR]