Optimization of roasting temperature and time during oil extraction from orange (Citrus sinensis) seeds: A response surface methodology approach

Abstract

Nutritionally, oils obtained from oilseeds provide the calories, vitamins and essential fatty acids in the human diet in an easily digested form. The rate of vegetable oil consumption is increasing compared with animal fat due to its low sterol. In addition to being nutritious, edible vegetable oils also have industrial uses. Separation of oil from oil seeds is an important processing operation because it affects the quality and quantity of oil obtained from the oil seeds. Literature on oil extraction from some cultivars of citrus seeds showed good potential, therefore, focus on optimization of oil extraction could enhance economic status of the seed. In this study, response surface modeling approach was employed to optimize oil extraction from orange (Citrus sinensis) seed. Each sample was roasted for 10, 20, 30, 40 and 50 minutes at temperatures of 110, 120, 130, 150, and 170 oC. The parameters analysed included oil yield, free fatty acid, color, refractive index, specific gravity and pH. The treatments resulted in oil yield ranging from 32.0 ± 2.7 to 56.0 ± 6.5 %, free fatty acid (0.3 ± 0.0 to 3.01± 1.7%), colour (3.45 ± 1.9 to 20.5 ± 1.8 abs), refractive index (1.4 ± 0.1 to 1.46 ± 0.1), specific gravity (0.87 ± 0.1 to 0.94 ± 0.0) and pH (4.05 ± 1.0 to 5.66 ± 1.1). Maximum oil yield of 56.0 ± 6.5 % was obtained after roasting citrus seed at 170 oC for 30 min. Roasting temperature and duration showed significant (p < 0.05) effect on oil yield, free fatty acid, colour and specific gravity of the oil. However, nonsignificant (p > 0.05) effect was recorded on refractive index and pH of the extracted oil. The computer software package (Design-Expert) used for optimization gave four possible optimum conditions with desirability ranging from 0.50 to 0.68. The best desirability (0.68) was achieved at roasting temperature and duration of 150o C and 20 min., respectively. At these conditions oil yield was 52.6 ± 0.1%; free fatty acid, 1.4 ± 0.0%; colour, 4.7 ± 0.0 abs; specific gravity, 0.92 ± 0.0, and pH, 5.4 ± 0.1. The quantity, free fatty acid, colour and specific gravity of extracted oil from orange seed significantly depend on temperature at which the seed is roasted and duration of roasting.