Mechanical Oil Expression from Groundnut (Arachid hypogaeaL) Kernels using a Spring-Controlled Hydraulic Press

Abstract

Micro and medium scale groundnut (Arachid hypogaea L) oil processors are earnestly struggling to increase their production capacity to meet market demands in terms of quantity and quality. The existing traditional method of extraction involves roasting of the kernels using firewood as a fuel;
pounding and crushing of the roasted kernels by mortar and pestle or between two stones; mixing the crushed mass with water; cooking of the mixed paste in order to obtain the oil by floating and skimming and drying of the oil by further heating. This traditional method (known as wet
extraction process) is tedious, time consuming, energy sapping, drudgery prone, inefficient and low in yield and quality. Research has revealed that mechanical expression process could substantially improve the yield and quality of groundnut oil and a mechanical press designed and built in this regard has demonstrated promising results. Building on past research, this present study was conducted to investigate the effects of some processing factors on the yield and quality of groundnut oil using a spring-controlled hydraulic press. In this research, a 2 x 4 factorial experiment under Completely Randomized Design (CRD) was used to study the effects of 2 levels of nature of groundnut kernel (dehulled and undehulled) and 4 levels of heating temperature (70, 80, 90 and 100 0C) on the yield , extraction efficiency, extraction time and quality characteristics of oil
during groundnut oil extraction. Results showed that average oil yield and extraction efficiency of 24.43% and 55.55% respectively were obtained from the dehulled sample at 90 0C while the values for undehulled samples were 21.08% and 47.95% respectively. Samples of oil obtained at the extraction temperature of 90 0C had specific gravity, saponification value and free fatty acid value of 0.9937, 198.5 and 6.452% respectively from undehulled sample; 0.9973, 190.8 and 6.312% respectively from dehulled sample and 0.9957, 192.2 and 6.171% respectively from mixture. The result of this study presents a remarkable improvement over the traditional method of extraction and could be used for developing a process for industrial extraction of groundnut oil.

Keywords: Groundnut (Arachid hypogaea L), Heating temperature, Hydraulic press, Oil expression