The effectiveness of a novel steaming method in improving small scale syobean dehulling

Abstract

Locally grown Black (Ex Songea) and Bossier soybeans, Glycine max (L.) varieties
were used in a study to determine the effect of steaming on soybean dehulling properties. Prior to carrying out the experiment, soybeans were sorted and cleaned. This was followed by the determination of oil content, weight per grain, bulk density and moisture content before conditioning the seeds ready for dehulling. Proximate analysis showed that the Black (Ex Songea) soybeans had an average oil content, weight per grain, bulk density and moisture content of 18.36%, 1.45 g, 738 kg/m3 and 12.25% respectively. On the other hand, Bossier variety of soybeans were found to have an average oil content of 20.21%, weight per grain of 1.95g, bulk density of 789 kg/m3, and moisture content of 12.75%. Steaming was done using a double pot steamer and was conducted at 5, 10 and 15 minutes interval followed by solar drying for 24 hours using unsteamed soybeans as a control. The steaming procedure involved placing 500g of soybeans in the upper pot then tight fitting it on the lower pot that contained 4 litres of boiling water. Refilling of water was done every after 20 minutes of steaming to bring the water level to its original mark. After steaming, soybeans were dried in a cabinet solar drier capable of reaching temperatures in the range of 43- 46oC. The dehulling operation was carried out for 5 minutes using a Tangential Abrasive Dehulling Device (TADD) machine. The efficiency of steaming method was
determined based on the dehulling effectiveness index (η). Results showed that steaming followed by solar drying tends to significantly (p<0.05) improve the dehulling qualities of both Bossier and Black (Ex Songea) soybean varieties when compared to unsteamed beans, which performed poorly with consistently higher breakage levels. The cotyledon recovery percentage for unsteamed Black (Ex Songea) beans was 68.35% compared to 82.20% for soybeans steamed for 15 minutes. Similarly, unsteamed Bossier soybeans had 74.75% recovery of cotyledons compared to 85.40% for those steamed for 15 minutes. Results from this study showed that steaming led to better performance in the dehuller for the Bossier soybean variety than the Black (Ex Songea) variety. The tested steaming method is simple and can be applied in rural areas as a preconditioning stage to improve soybeans processing prior to dehulling especially at small scale level.

Keywords: soybean, steaming, abrasive, dehulling efficiency

AJFAND Vol. 8 (3) 2008: pp. 304-318