Abstract
In this study, oil extraction from Niger seeds was evaluated with different microwave irradiation times (0–200 s) and pulsed electric fields (PEF) intensities (0–5 kV/cm) as pretreatments. Then, oil extraction was completed with a screw press at different rotation speeds (11–57 rpm). Quality parameters including extraction efficiency, acidity and peroxide values (PVs), chlorophyll, and phenolic contents along with fatty acid profiles and tocopherol levels of the extracted oils were determined as responses. With enhancements in microwave time, PEF intensity and press rotation, the chlorophyll contents, acidity/PVs, and total phenolics of oils increased similar to oil extraction efficiency although it was reduced later. The optimized conditions selected by response surface methodology were determined as 156.23 s, 1.18 kV/cm, and 20 rpm for microwave time, PEF intensity and press speed, respectively. Fatty acid analysis revealed that linoleic acid was the most predominant fatty acid in the extracted oil. Application of the mentioned pretreatments may lead to a reduction in unsaturated fatty acids and escalation of saturated ones (p < .05). High‐performance liquid chromatography results indicated that α‐tocopherols are the most common tocopherols in Niger seed oil and microwave‐PEF pretreatments may lead to 2.79% increase in tocopherols content.
Highlights
Oil seeds are important sources of edible, industrial, and medicinal oils which could have bioactive compounds with functional properties for further consideration (Melaku, 2015)
We proposed this study for the first time to optimize the oil extraction from Niger seeds, with the use of microwave-pulsed electric fields (PEF) approach as pretreatments and applying response surface methodology (RSM) as the optimization technique
It was found that screw press rotational speed and quadratic effect of microwave irradiation time had the highest effects on oil extraction efficiency
Summary
Oil seeds are important sources of edible, industrial, and medicinal oils which could have bioactive compounds with functional properties for further consideration (Melaku, 2015). Niger seeds with the scientific name of Guizotia abyssinica Cass and English name of Niger from Asteraceae family contain high-quality oils with potential applications in nutraceutical and pharmaceutical fields. It has flowers in yellow color and rarely in light green, fruits in dark color to yellow, hard shell and a white germ (Getinet & Teklewold, 1995). This plant species is cultivated in high scale in Ethiopia and India and in low scale in several countries in Africa, Asia as well as in America.
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