In general, the methods used to extract Prosopis seed from its fruit can be either mechanical or mechanical-chemical. However, regardless of the method of extraction employed, the ultimate goal is to obtain clean, high quality seed.
Seed extraction is often facilitated by allowing fruit to initially dry for several days at normal air temperatures. Once dry, the fruits can often be opened after immersion in boiling water and allowing it to cool as they soak for 24 hours. Also, the seed may be extracted by carefully rolling a heavy object over the dried pods. While the pods are easily broken at the constrictions, it can be extremely difficult to remove the seed from the enclosing endocarp. However, with effort, the seeds can be cleaned, commonly by hand or by dropping them through the air, i.e., mortar and wind separation. The pulp can be mechanically removed.
A motorized device, the details of which have been described by Flynt and Morton (1969) can eliminate the very laborious hand dissection of Prosopis seed from its fruit. In essence, this device, shown in Figure 2, is a modified cereal huller that operates as a thresher. The construction details and operation of the thresher are presented in Appendix 2.
Often, it is difficult to sufficiently dry Prosopis fruit at normal air temperatures to break them open and remove the seeds entirely. To some extent, this problem can be overcome by drying the fruit in a forced-draft oven for 18 hours at 32°C, as reported by Brown and Belcher (1979). Shortly after their removal from the oven, the fruit is placed in an electric scarifier for 10 to 15 seconds. The light debris is removed by air in a column blower, and the large material is scapled away with a size 11 or 12 screen1. This general technique has been successful in producing large quantities of clean, damage-free seed.
Figure 2. Modified cereal huller that operates as a thresher (See also Appendix 2.)
Source: Flynt and Morton 1969.
1 Sieve openings as follows: Size 11, 1.85 mm; Size 12, 1.70 mm.
It has been observed that sheep, goats, and other grazing animals often eat Prosopis fruit and then pass more or less clean seeds in their excreta. The general processes involved in this reaction are chewing, soaking in mild concentrations of HCl in the stomach, and passage under friction in the intestines. By simulating these processes in the laboratory, clean Prosopis seed has been extracted from its fruit. This simulation includes opening the fruit and removing the septed seed by mechanical methods, and then soaking these segments in 0.1 N solution of HCl for 24 hours. This dilute solution of HCl is harmless to handlers. Although only conducted on an experimental basis to date, it is anticipated that production costs would be substantially reduced if bulk treatments are undertaken.
Clean seed can also be obtained from Prosopis fruit by mechanically thrashing the pods, soaking the septed seed in concentrated sulfuric acid or a dilute solution of sodium hydroxide (NaOH) for a period of 30 minutes, and finally washing the seed with tap water and rubbing them between the two folds of a coarsely-textured cloth.
