Introduction
Rice
bran, as a raw material for rice bran oil (RBO) extraction, is a
by-product of rice processing, in which oil content can reach 12-22%
(Amarasinghe, Kumarasiri & Gangodavilage, 2009; Pandey & Shrivastava,
2018).
RBO
is a new type of edible oil with high nutritional value. Its fatty acid
composition is reasonable and contains more than 80% oleic acid,
linoleic acid and linolenic acid.
In
addition, RBO contains significant amounts of γ-oryzanol, tocopherols,
squalene, phytosterol and other important bioactive substances, so it is
known as ”nutritional health oil” by nutritionists (Khoei & Chekin,
2016; Trevisani Juchen, Nolasco Araujo, Hamerski, Corazza & Pedersen
Voll, 2019).
Current
extraction methods of RBO used in oil industry mainly include cold
pressing method, solvent extraction (SE) method
and
pre-pressed
followed by SE. Cold pressing method can maintain the unique flavor of
oils (Liu et al., 2011). However, this method has many problems, such as
high residual oil rate, high cost, high labor intensity and power
consumption, and easy to cause protein denaturation (Dun et al., 2019).
SE method is often used in commercial RBO production, which is
relatively efficient in oil production, and the residue of oil is low
(Amarasinghe & Gangodavilage, 2004), but there are also some
shortcomings such as its toxicity, no renewability and easy to cause
environmental
pollution
(Hanmoungjai, Pyle & Niranjan,
2001).
Pre-pressed treatment followed by SE method can obtain high oil
extration yield.
This
process, however, has some problems in the protein structure leading to
protein
denaturation.
Furthermore, n-hexane has been
identified as an air pollutant that is emitted during extraction and
recovery.
Compared with the other two methods, aqueous enzymatic extraction (AEE)
process has the advantages of good oil quality, no chemical pollution,
low energy consumption and good retention of protein, polysaccharide and
other components.
However,
AEE has certain limitations.
Due
to the low solubility of oil in water, the efficiency of AEE is lower
than that of
SE.
This
disadvantage may be overcomed by using selected enzymes and optimizing
process parameters (Mat Yusoff, Gordon, Ezeh & Niranjan, 2016). AEE has
become a new oil extraction technology for simultaneous extraction of
oil and protein, polysaccharide and other components with broad
application prospects.
It
was reported that Sengupta & Bhattacharyya (1996) used pectinase and
cellulase for the first time to extract RBO by AEE combined with organic
solvent.
Hernandez, Rodriguez-Alegría, Gonzalez & Lopez-Munguia (2000) obtained
glucose, protein hydrolysate, RBO in three steps by adding glucoamylase
and protease before extracting RBO with solvent. After
that,
Hanmoungjai, Pyle & Niranjan (2002) focused on the extraction yield of
RBO, protein and the level of reducing sugar in the enzymatic hydrolysis
process, and finally indicated that Alcalase 2.4L could significantly
improve the yield of oil and protein, while the use of carbohydrase
could improve the level of reducing sugar in the enzymatic hydrolysate.
Although
these papers have published on the extraction of RBO by AEE, no
systematic studies have been conducted on the analysis of quality,
thermal behavior and extraction mechanism of the extracted oil.
The
objective of this study was to investigate the extraction of oil from
rice bran using the AEE with different enzymes (Celluclast 1.5L,
Hemicellulase, Pectinex Ultra SP-L, Viscozyme L and Alcalase 2.4L) and
selected appropriate enzymes for AEE. The physicochemical properties,
fatty acid compositions, bioactive compounds and thermal behavior of
AEE-extracted oil (AEEO) were evaluated and compared with those of
Soxhlet-extracted oil (SEO). In addition, the microstructure of rice
bran before and after different extraction processes were observed, and
the mechanism of rice bran oil by enzyme extraction was clarified.