Results and discussion
Electronic nose analysis
The odor of oils is one of the crucial factors influencing quality.
Aroma profiles of these vegetable oils were obtained using electronic
nose. The responses of ten electronic nose MOS sensors to the oils were
shown in Table 1 , and the radar charts of the vegetable oils in
the odor amplitude were shown in Fig. 1 . As was shown byFig. 1 and Table 1 , all of the oils had more intensive
responses to the electronic nose MOS2, MOS7 and MOS9, which meant that
the oils contained the same major fragrance compounds. However,
different oils held variations in the amounts of the compounds.
Furthermore, MRSO and EVOO with lower odor amplitudes on ten electronic
nose MOS sensors than others illustrated that MRSO and EVOO were
different from the other oils in the odor profiles. To distinct the
differences, principal component analysis was carried out.
Principal component analysis of odor compounds
The data of electronic nose matrix with 10 rows (responses from ten
sensors) and 60 columns (ten samples of one kind of oils) was analyzed
by means of principal component analysis (PCA) to reduce the number of
variables down to important factors only [24]. Principal component
analysis (PCA) and the correlation analysis of MRSO and other vegetable
oils in odor character were shown in Fig. 2 and Table
2 , respectively. The first principal component (PC 1) and the second
principal component (PC 2) described 96.99% of the total variance,
which were sufficient to build a good model. Among the percentage, PC 1
and PC 2 explained 54.90% and 42.09%, respectively. Examining the
score plot in the area defined by PC 1 and PC 2, the oils were separated
into four groups. Specifically, MRSO, EVOO and CNSO formed three groups
separately, and the others formed another group. TGSO, CNSO and HUSO had
high positive scores along PC 1, while MRSO and EVOO had high positive
scores along PC 2. As was shown in Table 2 , MRSO possessed
highest correlation with EVOO in odor characters than the others. Some
literatures reported that the sensory properties of EVOO mostly depended
on the odor descriptors of C6 and C5compounds grouped in 9 different odorant series: grass, leaf, wood,
bitter-like, sweet-like, pungent-like, olive fruit, apple and banana
[25-27]. Therefore, the odor descriptors of these compounds may
contribute to the odor properties of MRSO.
Chemical analysis of basic properties
The AVs, PVs, IVs and SVs of MRSO and other vegetables oils determined
in our study were given in Table 3 . And they were in good
quality before off-flavors were encountered. The AV of MRSO (0.42) was
significantly lower (p<0.05 = than others except EVOO (0.34) and
CNSO (0.71), followed by CNSO (0.71), TGSO (0.95), HUSO (2.57) and CSO
(4.19), which indicted the content of free fatty acid in MRSO is
significantly lower (p<0.05 = compared with others. PV of MRSO
(1.43) was close to that of EVOO (1.21) and significantly lower
(p<0.05 = than those of TGSO (7.46), HUSO (3.78), CSO (3.21) and
CNSO (2.36). This may be due to the presence of natural antioxidants
such as β-carotene, and α-tocopherol which had been found in olive oil
[28] and grape seed oil [21]. In addition, fatty acid profiles
of MRSO may influence its PV, which may have antioxidant activity just
like grape seed oil [21, 29]. MRSO had the highest IV of 107.43,
followed by CNSO (105.68). MRSO and CNSO were better sources of
polyunsaturated fatty acids which possess health benefits, such as
regulating blood cholesterol levels and lowing elevated blood pressure,
since unsaturated fatty acids were richer in MRSO and CNSO than others.
Among these vegetable oils, SVs were in order of EVOO> MRSO > CNSO >
TGSO > HUSO > CSO. Therefore, the molecular of fatty acids in MRSO was
smaller than those of others except EVOO, and was more easily absorbed
by human body.
Fatty acid composition
Fatty acid composition of the vegetable oils studied in this research
was shown in Table 4 . The content of unsaturated fatty acids in
these vegetable oils was over to 80%, and that of MRSO was 84.92% only
behind EVOO (84.96%). Even α-Linolenic acid (C18:3)
(0.62%) was not found in MRSO but in EVOO, HUSO, CSO and CNSO, the
content of docosadienoic acid (C22:2) was up to 2.48%
in MRSO rather than the other. TGSO contained a larger amount of
long-chain unsaturated fatty acids (12.53%) than the other. Squalene
(C30:6) was found and up to 2.39% of fatty acids in
HUSO, which was unusual in vegetable oils. Besides, MRSO, TGSO and HUSO
were rich in long chain polyunsaturated fatty acids in comparison with
other vegetable oils studied in the paper. Monounsaturated fatty acids
like oleic acid had been revealed in decreasing low-density lipoprotein
(LDL) levels in blood [30-32], while some polyunsaturated fatty
acids played important roles in reducing the risks of cancer, heart
disease, cardiovascular disease, autoimmune and inflammatory disorders
and disrupted neurological functions [33, 34]. Therefore, these
vegetable oils especially MRSO may be beneficial to human health.
Oxidative stability of MRSO
Oxidative stability of MRSO was presented in Fig. 3 . The effect
of storage temperature on oxidative stability of MRSO at 25, 40, 50, 60
℃ was determined, PV was measured as a function of time (1-10 days) and
the results for PV were shown in Fig. 3 (A) . Briefly, when the
temperature was less than 60 ℃, the PV of MRSO changed slowly. However,
it increased sharply when the temperature exceeded 60 ℃. Therefore,
Temperature is one of important factors of oil oxidation, because the
high temperature not only promotes the OTM middle resulting from the
base, but also the decomposition and polymerization of hydrogen
peroxide, speeding up the oxidation process of the unsaturated fatty
acid. As was shown in Fig. 3 (B) , in the dark condition, the PV
of MRSO increased more slowly six days later than other illumination
conditions, especially sunshine. Although PVs of MRSO were lower in
lightshine and ultraviolet sunlight than those in dark and sunshine
before five days, then they rose quickly and were higher than those in
dark and sunshine. Based on the research by Zhao et al., 27 PAH-diones
generate a dose-related lipid peroxidation, which is mediated by ROS
[10]. Fig. 3 (C) provided information about the effect of
added antioxidants on the PV of MRSO. The PVs of antioxidants-added
groups were higher than that of control group, suggesting that
antioxidants had certain delayed effect on the oxidation of MRSO and
improved the stability of the oil. The effects of antioxidants on the
seed oil were in order of PG > TBHQ > BHT
> BHA. As was shown in Fig. 3 (D) ,
Fe2+ and Cu2+ can accelerate the
oxidation of MRSO. Therefore, MRSO should be stored avoiding those metal
ions.
Antiproliferation properties on human colon cancer cells
DMSO solution of the seed oil at final dose levels of 1, 3, 5 and 7 mg
of oil equivalents/ml in the cell culture media, were tested against
HepG-2 and HT-29 colon cancer cells for its antiproliferative effects.
The results indicated a dose- and timed-dependent effect of MRSO on
human colon cancer cells as presented in Fig. 4 . MRSO at final
concentration of 7 mg/mL of media suppressed cell proliferation during
the treatment on HepG-2 and HT-29 especially the latter, whereas the low
concentration of MRSO had no significant antiproliferative effect on the
cancer cells. The seed oil showed the greatest effects on inhibiting the
growth of HepG-2 and HT-29 by as much as 46% and 57% at 96 h,
respectively and had more significant antiproliferative effect on HT-29
than HepG-2.