Effect of co-pressing of niger (Guizotia abyssinica Cass.) and black cumin (Nigella sativa) seeds on yield, oxidative stability and sensory properties of cold pressed oil

Abstract

Oxidation is an important problem in edible oil industry. This is relevant when the edible oil is composed of poly unsaturated fatty acids that are prone to oxidation. This study was performed to investigate the effectiveness of black cumin seed co-pressing on improving oxidative stability (OS) of niger seed oil (NSO) without adversely affecting its sensory quality. Four black cumin seed (BCS) with levels (0, 5, 10 & 15%) were co-pressed with niger seed (NS) at two screw speeds (SS) (28.9 and 46.6 rpm). Oil yield, Rancimat induction period (IP), and sensory attributes were measured. No significant interaction of SS and BCS level was observed to influence oil yield (p>0.05). However, SS has imparted a significant influence on oil yield (p<0.05). The oil yield obtained by 28.9 rpm SS was found to be higher at all levels of BCS. IP was significantly affected by the interaction of SS and BCS level (α<0.05). Progressive increase of BCS level was more effective in improving IP at the 28.9 rpm SS than at 46.6 rpm. Most sensory attributes of BCS co-pressed NSO samples significantly deteriorated as BCS level was increased beyond 5% (α<0.05). Application of BCS co-pressed NSO in Shiro Wot preparation (cooked sample) however was best accepted by panelists at 10% BCS level in all sensory attributes. The present study suggested that BCS co-pressing at 5 and 10% levels improves the stability and sensory property of NSO for raw and cooked edible food application respectively.

Keywords: Black Cumin Seed, Co-pressing, Screw Speed, Oxidative Stability, Niger Seed Oil