A STUDY ON ULTRASOUND ASSISTED AQUEOUS EXTRACTION OF RICE BRAN OIL
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Date
2018
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Acharya N.G. Ranga Agricultural University
Abstract
Rice (Oryza sativa) is a major cereal crop cultivated globally. Rice bran is
cuticle between paddy husk and the rice grain. Rice bran is a by-product of rice milling
industry. It contains 12-22% oil, 11-17% protein, 6-14% fibre, 10-15% moisture and 8-
17% ash. Rice bran offers various health benefits due to its content of antioxidants,
vitamin E, B complex vitamins and essential fatty acids. It also serves as a natural
source of phytosterols which provide blood sugar control and cholesterol metabolism.
Commercial rice bran oil is extracted using organic solvents such as hexane. n-hexane
has been used as the solvent for rice bran oil extraction due to the high oil extractability
and easy availability. This process, however, has some problems with respect to the oil
quality. To improve the oil quality, aqueous enzymatic extraction was used and to
improve the yield, combination of ultrasound and aqueous enzymatic extraction of rice
bran oil was investigated. Mechanism of ultrasound extraction is attributed to
mechanical and cavitation efficacies which can result in disruption of cell wall and
enhanced mass transfer across cell membrane.
Firstly, moisture content of rice bran was determined. Rice bran was stabilized at
110 °C for 20 min in hot air oven. Rice bran oil was extracted for 6 h using soxhlet
apparatus. The oil yield from conventional (hexane) extraction was set as 100% oil
recovery for comparison. For aqueous enzymatic extraction, enzymes such as cellulase
of 90 U, 144 U, 270 U, 360 U; amylase of 72 U, 180 U, 216 U, 135 U and protease of
45 U, 90 U, 135 U, 180 U individually were added to 50 g of rice bran and mixture was
incubated at 37 °C. Incubated rice bran was mixed with water at the ratio of 1:6 (w/v)
and pH of the slurry was adjusted to 7.0 with 0.1 N NaOH. Sample was centrifuged at
8000 rpm for 20 min to separate supernatant. Supernatant was evaporated for getting oil
and the oil obtained was dried in hot air oven at 100 °C for 30 min to eliminate the
traces of water. Experiment was performed in triplicates. Then, extraction with
combination of enzymes for incubation periods of 1 h, 2 h, 3 h and 4 h was performed.
The optimized combination was used for ultrasound treatment. Ultrasound treatment
time of 15, 30, 45 and 60 min with on and off timings of 60 s on 5 s off, 60 s on 10 s
off, 60 s on 15 s off and 60 s on 20 s off were conducted. Oil recovery with ultrasound
assisted aqueous enzymatic extraction was observed and quality parameters like free
fatty acid, peroxide value, color and viscosity of rice bran oil were examined.
Moisture content of the fresh rice bran was found to be 11.80% (w.b.).
Conventional method of extraction gave 8.0 g of oil per 50 g of rice bran. Among the
four concentrations of three enzymes, 270 U of cellulase gave highest oil recovery
(35.22%). From the combination of enzymes cellulase, amylase and protease (270
U+216 U+135 U) gave highest recovery of 62.68%, because of appropriate combination
of enzymes and then this combination used for different incubation times. For 4 h of
incubation, the highest oil recovery (76.48%) was obtained with (270 U+216 U+135 U)
combination of enzymes. This combination was used for ultrasound treatment.
Ultrasound treatment period of 30 min with 60 s on and 5 s off timings gave highest
recovery of 88.15%. Ultrasound assisted aqueous enzymatic extraction of oil has a
substantially lower content of free fatty acid (1.496 mg KOH/g) than that of
conventionally (hexane) extracted oil (2.692 mg KOH/g). The peroxide value of the oil
obtained from ultrasound assisted aqueous enzymatic extraction of rice bran oil was
little higher (1.567 meq/ kg of oil) than the peroxide value of conventionally (hexane)
extracted oil (1.220 meq/kg of oil). Ultrasound-assisted aqueous-extracted oil had a
lower content of colouring substances (15Y+2R) than hexane extracted oil (20Y+2.8R)
and viscosity of ultrasound assisted aqueous enzymatic extraction of rice bran oil (39.03
cP) was almost similar to that of conventional (hexane) extraction of oil (39.20 cP).
Keywords: Rice bran oil; Oil extraction; Aqueous extraction of oil; Ultrasound assisted
extraction; Ultrasound assisted aqueous enzymatic extraction
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