3.4.4. Oryzanol contents
Rice
bran is one of the most abundant sources of oryzanol. RBO contains about
0.9-2.9% oryzanol which can vary greatly according to the origin of the
rice bran (Arab, Alemzadeh & Maghsoudi, 2011).
Oryzanol
is a mixture of esters of ferulic acid with sterols and triterpene
alcohols, and has similar antioxidant activity as vitamin E (Lloyd,
Siebenmorgen & Beers, 2007). In
Table
3, the content of oryzanol in AEEO was significantly higher (p
< 0.05) than in SEO, which can be attributed to the
degradation
of oryzanol caused by the increase of temperature and the prolongation
of SE treatment time.
3.5 Thermal behavior of
AEEO and SEO
DSC
is to determine the thermal behavior of oils during heating or cooling
and it provides another method for studying the chemical composition of
oils. The crystallization and melting curves of the AEEO and SEO were
shown in Fig. 2 and their corresponding transition temperatures were
also given.
In Fig. 2a, the crystallization curves of RBO extracted by Alcalase 2.4L
and n-hexane were represented. The cooling curve of AEEO and SEO
exhibited three exothermic peaks,
with a major peak (a2, b2) and two small
shoulder peaks (a1, b1) and
(a3,
b3).
It could be clearly seen that the points of crystallization peaks of the
two extraction methods were obviously different. The initial
crystallization peaks of AEEO and SEO were 30.93 ℃ and 33.70 ℃,
respectively. Compared with the SEO, the crystallization point of AEEO
was lower.
The
various of crystallization peaks might
be due to the different extraction
methods, which could influence the degree of saturation in RBO (Tan,
Chong, Hamzah & Ghazali, 2018).
Generally,
each kind of oil has unique characteristic of fatty acids and
triacylglycerol
(TAG) profiles and the thermal transition of lipids is affected by the
compositional changes of the degree of saturation and fatty acid chain
length.
The
crystallization peaks of oils with high levels of saturated fatty acids
and tri-saturated TAGs would be at a relatively high temperature
(Mohammadpour, Sadrameli, Eslami & Asoodeh, 2019).
The
melting curves of RBO extracted by
Alcalase 2.4L and n-hexane were represented in Fig. 2b. It was found
that SEO displayed one peak (b1) at low-melting region
(< 0 ℃) and the other peak (b2) at
high-melting region (> 0 ℃). However, this phenomenon was
not observed in the melting curves of AEEO and all the melting peaks of
AEEO were located in the low-melting
region.
Results showed that the melting behavior of RBO was significantly
related to the extraction method. As discussed, the possible reason of
these differences might be the variations in the proportional
distributions of the identified fatty acid and TAG components.
It
might be due to the saturated compounds of SEO were slightly higher than
AEEO. Therefore, higher temperatures were needed to melt SEO completely.