Performance of mechanical co-extraction of Jatropha curcas L. kernels with rapeseed, maize or soybean with regard to oil recovery, press capacity and product quality

Abstract

Jatropha curcas L. shelled seeds (kernels) have been gaining attention as protein source due to their high protein content. However, due to the soft texture, screw pressing the kernels resulted in a low performance, which was indicated by high residual oil content in the press cake. In order to overcome the low oil recovery from the extraction process, J. curcas kernels blended with rapeseed, maize or soybean as additives were studied. The blending effects on the performance of mechanical oil extraction, along with the quality of oil and press cake were evaluated. To achieve the maximum oil recovery, blending ratio, nozzle diameter and screw speed were optimised using response surface methodology. Higher blending ratio showed significantly higher oil recovery (p<0.05). Soybean blend exhibited highest oil recovery of 91.0%. Specific energy requirement and oil recovery were negatively correlated with throughput. Oil from maize blend generated the highest acid value and free fatty acid of 8.39mg KOH/g and 4.19%, respectively. Carbon residue of the sedimented oil from all material blends fulfilled the standard threshold of German Institute for Standardization (DIN 51605). The highest press head temperature of 104.6°C was observed from soybean blend. The ash content of the press cake from pure J. curcas kernels was lower than the other material blends. Press cake from soybean blend revealed low pepsin insoluble nitrogen and high crude protein content, pepsin plus trypsin digestibility and available lysine. Regarding the antinutritional factors, press cake from rapeseed blend showed highest phytate and trypsin inhibitors of 4.1% and 22.7mg trypsin inhibited/100mg sample, respectively. In terms of oil recovery and press cake quality, soybean appears to be the most suitable additive compared with rapeseed and maize.