Rice 3-5% unsaponifiable (sterols, tocotrienols, triterpene alcohols) (Oliveira

Rice bran is a by-product of rice milling process, obtained through
polishing of brown rice (Sengar, Kaushal, Sharma, &
Kaur, 2014),
representing 8-11% by weight of the rice grain and contains about 16-22% of oil
(Pestana-Bauer, Zambiazi, Mendonca,
Beneito-Cambra, & Ramis-Ramos, 2012). Rice bran oil (BRO) is mainly produced through solvent extraction
or hydraulic pressing of rice bran (Kordsmeier, Howard, Brownmiller,
Proctor, & Hauer-Jensen, 2015).  Crude RBO contains between
90 – 96% saponifiable lipid components (Mono-, di-, and triglycerols, free
fatty acids and waxes) and 3-5% unsaponifiable (sterols, tocotrienols,
triterpene alcohols) (Oliveira et al., 2011). Refined RBO oil is a very good source of several micronutrients
and natural antioxidants and such as ?-oryzanol, tocopherols and tocotrienols (Jaiswal, Pradhan, Patel, Naik,
& Naik, 2015; Kordsmeier et al., 2015); phospholipids or lecithin (Chem, Sci, & Chem, 1986; Patel
& Naik, 2004; Jala & Prasad, 2015); phytosterols, squalene, and ferulic acid (Dunford & King, 2000; Sakunpak,
Suksaeree, Pathompak, & Sermkaew, 2014). RBO has been widely used for food, pharmaceuticals and cosmetics
applications because of its health benefit of its abundant micronutrients (Sugano & Tsuji, 1996; McCaskill
& Zhang, 1999;  Kaur, Jassal, Thind,
& Aggarwal, 2012; Pali, 2013; Sengar, Kaushal, Sharma, & Kaur, 2014;
Sohail, Rakha, Butt, Iqbal, & Rashid, 2017). 

Micronutrients are need in small
quantity to help normal body functioning and development (Lohry, 2007). The micronutrient also considered bioactive components of the RBO
are mostly concentrated at the unsaponifiable fraction of the oil. This
fraction consist of 43% phytosterols, 10% steryl esters and 1% tocopherol (Dunford & King, 2000). Most of these micronutrients are often lost or reduced to a large
to degree during oil refining processes, and often get concentrated in number
of by-products or residues such as gum and soap stock from chemical refining
steps, deodoriser distillate and wax from both physical and chemical refining (Sawadikiat & Hongsprabhas,
2014; Sengar et al., 2014).  For example 90% of
tocopherols and tocotrienols are lost during deodorization process (Kordsmeier et al., 2015), 80 – 89% gamma oryzanol lost in chemical refining (Nagendra Prasad MN, Kr, &
Khatokar M, 2011).
However, several methods such as solvent extraction and crystallization, supercritical
fluid extraction, saponification, esterification and molecular distillation are
used to recover these bioactive compounds (Sawadikiat & Hongsprabhas,
2014; Sengar et al., 2014). In this chapter, the most important of these micronutrients such
oryzanol, tocopherols, tocotrienols, phytosterols, and phospholipids as well as
their benefits will be discussed.

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Oryzanol

Gamma-oryzanol (?-oryzanol) in RBO was
first extracted from soap stock by-product of the oil refining, and was
considered a single component until later found to be a mixture of steryl
ferulate (Orthoefer, 2005; Xu & Godber,
1999). The
unsaponifiable fraction (4.2%)  of RBO contains
1.6% ?-oryzanol (Al-Okbi et al., 2014) and refined  RBO contains
high content of ?-oryzanol 248 – 887 mg/100 g of oil (Sawadikiat & Hongsprabhas,
2014). The
?-oryzanol is consist of a mixture of ferulic acid ester of sterol and
triterpene alcohols such as 24-methyelene cycloartenol (494 mg%) and
cycloartenol (106 mg%) (Al-Okbi et al., 2014; Patel &
Naik, 2004). The
four major components in ?-oryzanol (as shown in Figure 1)  are cycloartenylferulate,
24-methylenecycloartanyl ferulate, campesterylferulate, and
?-sitosterylferulate (Patel & Naik, 2004; Sakunpak et
al., 2014). The
complete oryzanol is unique to RBO, however, its exact composition may defers
depending on the rice cultivar (Al-Okbi et al., 2014), with long and medium grain rice containing  6.4 mg/g and 5.17 mg/g respectively (Orthoefer, 2005).

Figure 1. Structure of four major
components of ?-oryzanol

Source: Patel & Naik, (2004)

Most of the ?-oryzanol is lost
during the oil refining process, leading to several by-product or residues with
high contents of phytochemicals. Among the by-product of RBO refining such as
degumming, soap precipitation, bleaching earth filtering, dewaxing and
deodorisation distillation, soap precipitation was found to be the best source
of ?-oryzanol with 43.1 mg/g representing 11.5% of total ?-oryzanol in crude
RBO (Pestana-Bauer et al., 2012). Depending on the refining process, the oryzanol content of
physically refined RBO remained 1.1–1.74% as original, but reduces to 0.19 –
0.20 % for chemically refined RBO (Nagendra Prasad MN et al., 2011). Various methods are reported to be used for extraction of
?-oryzanol from these by-products including direct solvent extraction, liquid –
liquid phase extraction, solid phase extraction, and supercritical fluid
extraction (Xu & Godber, 2000). High performance liquid chromatography (HPLC) and ultraviolet
spectrophotometry (UV) are the most common techniques for the determination of
?-oryzanol content. The HPLC method has a greater accuracy and efficiency,
however, the high cost involve is a disadvantage when compared to the later
method, which is simple, inexpensive and practical but the results are not
always accurate due to absorbance reading that may be influence by the matrix
or sample components  (Heidtmann-bemvenuti, Nora, &
Badiale-furlong, 2012).

Oryzanol has many application in nutraceuticals, pharmaceutical and
cosmeceutical preparations (Nagendra Prasad MN et al., 2011;
Patel & Naik, 2004; Sohail et al., 2017), due to its diverse health benefits such as hypolipidemic effect,
promotion of growth, stimulation of hypothalamus, and increase bile excretion  (Dunford & King, 2000; Ahmad
Nayik, Majid, Gull, & Muzaffar, 2015). It has the ability to lower blood cholesterol (Xu & Godber, 1999), and antioxidant activity four times higher than tocopherols and
can prevent cancer causing free radicals (Ahmad Nayik et al., 2015; Nagendra
Prasad MN et al., 2011). The ferulic acid ester of triterpene alcohols in RBO has been
shown to exhibit strong stabilization effect during frying (T. Wang, K.B. Hicks, 2002). The oryzanol was reported to 
remain stable even when RBO was heated at 180oC for 8 hours (Sanghi & Tiwle, 2015). Additionally, oryzanol is known to possess anti-dandruff, anti-itching
and anti-aging properties, and effective in treating many gastrointestinal
disorder such as stress-induce gastric and duodenal ulcers (Al-Okbi et al., 2014).

Tocopherols

About 1% of unsaponifiable fraction
of RBO is vitamin E (Dunford & King, 2000; Ko et
al., 2003). It
was first known as tocopherol in 1924 and synthesised 1938 (Aggarwal, Sundaram, Prasad, &
Kannappan, 2010). Tocopherols
and tocotrienols are subgroup that collectively known as vitamin E family (Fiume & Heldreth; Al-Okbi et al., 2014) also referred to as tocols (Kordsmeier et al., 2015). There are four naturally occurring structural analogues of
tocopherol (? alpha-, ? beta-,
? gamma-, and ?delta-analogues). They differ from tocotrienol in the presence
of additional methyl groups around the aromatic ring of the chromanol core. Tocopherol
is an analogue to tocotrienol (Figure 2) and shares some similar structure with
common chromanol head and side-chain at C-2 position (Ko et al., 2003). A crude RBO contain about 2-4% tocopherol with
nutritional and antacid effects (Sanghi & Tiwle, 2015). A 100 g
tocopherol consist of 19-46 mg ? alpha-tocopherol, 1-3 mg ? beta-tocopherol,
1-10 mg ? gamma-tocopherol and 0.4-0.9 mg ? delta-tocopherol (Orthoefer, 2005), while refined
RBO was reported to contain 48 -70 mg% tocopherols (Krishna, Hemakumar, & Khatoon, 2006).   

`                       Figure
2 A chemical structure of Tocopherols

Source: Colombo (2010).

Tocopherols are one of the most
abundant natural antioxidants with an excellent biological antioxidants which
protect cellular membranes and increase stability in fat and oil  (Bruscatto et al., 2017). The ?-tocopherol was historically considered the homolog of
vitamin-E with greatest value because of its important level of physiological
activity until recently (Chen & Bergman, 2005). Tocopherols have gain more recognition in cosmetics industry for
their strong antioxidants, exhibiting soothing, moisturing, improving skin
elasticity, and anti-aging properties (Aggarwal et al., 2010). They were also found to suppress tumor-cell proliferation,
inhibit cholesterol synthesis, and lower serum cholesterol levels in many
animal models (Chen & Bergman, 2005).

Tocotrienols

Tocotrienols are one of the categories of tocols family consisting
of four isomers (Figure 4) of different saturated analogues (?,
?, ?, and ?).
They differs from tocopherols in the number and location of methyl groups on
the chromanol rings (Aggarwal et al., 2010). However, according to the definition
by cosmetic ingredient review, tocotrienols does not include the ?-analogues (Fiume & Heldreth, 2014; Zielinska
& Nowak, 2014). Tocotrienols
differs from tocopherol for having farnesyl rather than saturated isoprenoid
C16 side chain (Colombo, 2010).

Figure 3 A chemical structure of
Tocotrienols

Source: Colombo (2010).

Tocotrienol consist of  14-33
mg ?-tocotrienol and 9-69 mg ?-tocotrienol per 100 g (Orthoefer, 2005). Among the tocols family, ? and ?-analogues of
tocotrienol are the most effective and strongest natural preventive agents
against cancer and harmful effects of exposure to radiation (Kordsmeier et al., 2015). In an in vitro study, ?-tocotrienol was reported to have
more than three times free radical scavenging activity of ?-tocopherol (Chen & Bergman, 2005). Tocotrienols are used in sun screen and body lotion to protect harmful UV radiations, and help in
skin softening and repair (Ahmad Nayik et al., 2015). Ko et al. (2003) has also reported that tocotrienol is
substantially different to tocopherol in capacity to suppress proliferation of
a tumor cell. When tocotrienols are applied to the skin, it rapidly penetrates
and get absorbed, and thereby act as first line of defence because of their
antioxidant properties. They stabilised free radicals generated in the skin
during exposure to oxidative rays, and help to repair skin by protecting
against UV radiation induced skin damage and ageing (Nagendra Prasad MN, Kr, &
Khatokar M, 2011; Zieliska & Nowak, 2014).

Phytosterol

Phytosterols are defined as plant sterols
found mainly in plant cell wall and membranes. The major component of
phytosterols (Figure 4) in lipid extract are sitosterol, stigmasterols and
campesterol.  Phytosterols are classified
as either sterols or stanols, depending on the presence of double bond within
the ?5 position and are found in a free or esterified form  (Özdestan, Özgül, Tu?çe Erol, 2014). The plant sterols are synthesis from squalene one of the first
intermediate products is cycloartenol (a 4,4′-dimethylsterol) (Al-Okbi et al., 2014). Additionally, RBO contains a mixture ferulic acid esters of
4-desmethylsterol like campesterol and ?-sitesterol an end product of plant
sterol synthesis from squalene (Vissers, Zock, Meijer, & Katan,
2000).

Figure 3
Chemical structures of some phytosterols

Source: Özdestan, Özgül, Tu?çe Erol (2014)

An unsponifiable fraction of RBO
contains about 43% phytosterols (Dunford & King, 2000). The crude and commercially refined RBO contains 1362-1376 mg/100
g and 858- 1034 mg/100 g of phytosterols respectively (Sawadikiat & Hongsprabhas,
2014). A
total sterol in an Egyptian RBO extracted by n-hexane and supercritical CO2
subscript were reported to be 12.0 % and 7.6% (Al-Okbi et al., 2014).

Phytosterols are important in foods and pharmaceuticals industries (Özdestan, Özgül, Tu?çe Erol, 2014) due to their important bioactive activities for human health. They
can reduce low density lipoprotein (LDL) and total cholesterol level in the
blood by preventing the cholesterol absorption, and have antibacterial,
antifungal and antiulcer effect. The cycloartenol and
2.4-methylenecycloartanol, which formed more than 40% of the total phytosterols
are present in high very concentration in RBO (Özdestan, Özgül, Tu?çe Erol, 2014). Phytosterols have a strong antioxidant activity. The avenasterol
of RBO act as antioxidants at elevated frying temperature because of its
ethylidene group on the side chain of the molecules (T. Wang, K.B. Hicks, 2002). Research has shown that administration of 2.1 g of sterol from
RBO by humans lowered serum total cholesterol by 5% and LDL cholesterol by 9%,
this has been related to its inhibition of cholesterol absorption properties (Vissers et al., 2000). However, the effect of RBO sterol is probably due to the
4-desmethysterol ?-sitosterol not due to 4, 4?-dimethysterols example
cycloartenol and 24-methylene cycloartenol. This is because RBO contains mainly
4,4?-dimethylsterols and less 4-desmethylsterol (Vissers et al., 2000).

Squalene

Squalene was first discovered by
Mitsumaru Tsujimoto, a japanese researchr and expert in fats and oil at Tokyo Industrial
Testing Station in 1906, and Dr. Keijiro Kogami studied its health beneficial
effect in 1930 (Gunes, 2013; Popa, B?beanu, Popa,
Ni??, & Dinu-Pârvu, 2015). Squalene (Figure 4) is a triterpene (Huang, Lin, & Fang, 2009; Al-Okbi et al., 2014) that is known primarily for it is
role as an intermediate metabolite during synthesis cholesterol (Kelly, 1999). The name ‘squalene’ was derived
from a shark fish (Squalus spp.) liver oil which is the richest source
of squalene in large quantity (Kelly, 1999). It is widely found in RBO and
other sources such as olive oil, wheat-germ oil,  palm oil, and amaranth oil (Huang et al., 2009).

Figure 4.
Chemical Structure of squalene

Source: Huang, Lin, & Fang (2009).

Squalene
has been reported to possess an inhibitory effect for cancer and anti-tumor
activity (Gunes, 2013). Squalene just like tocotrienols
are used in sun screen to help protect harmful UV radiation, improve skin
softening and repair (Ahmad Nayik et al., 2015). Some cheap and rich source of this
compound include deodorizer distillate, a by-product of deodorization step of
RBO refining. Different methods can be used to quantify squalene such gas
chromatography (GC), GC-coupled with mass spectroscopy (GC-MS), high
performance liquid chromatography (HPLC) or HPLC- coupled with mass
spectroscopy (Popa et al., 2015).

Phospholipids

Phospholipids (PLs) are one of the
major class of lipid in RBO (Liu, Waters, Rose, Bao, & King,
2013)
constituting up to 10% of the total rice grain lipid content (Sumit, 2017). They contain glycerol, fatty acids, phosphate and polyhydroxy
groups and the phosphate is always linked to sn-3 position of glycerol
molecule. Phospholipids also have two fatty-acyl groups and one polar head
group (Jangle, Magar, & Thorat, 2013). RBO contains about 1.2-1.9 % phospholipids (Adhikari & Adhikari, 1986;
Nayik & Muzaffar, 2015). Water degumming is the simplest method of removing the hydratable
phospholipids from the crude oil. The non-hydratable are often remove by pre-treating
the oil with phosphoric acid or citric acid (Tyagi et al., 2012). Phospholipids consist predominantly of hydratable
phosphatidylcholine (PC) (Figure 5), phosphatidylinositol (PI),
phosphatidylethanolamine (PE), and phosphatidic acids (PA) of calcium and
magnesium salt (Sengar et al., 2014).

 

Table 1 Composition of RBO Phospholipids

 Phospholipids

Components

Crude PLs

De-oiled PLs

PC

20.4

46.2±0.256

PA

12.2±0.104

PE

17.8

23.5±0.188

PI

5.8

9.8±0.023

PS

0.9

Other

9.4

7.4

Source: Adhikari & Adhikari, 1986;
Sumit, (2017)

The term lecithin is used
synonymously as pure phosphatidylcholine, a main component of phospholipids (Machado, Assis, Inês, &
Machado, 2014).
The phospholipids in RBO contains different components (Figure 5) such as fatty
acid ester, glycerol, phosphate, and choline, ethanolamine, inositol or serine (Liu et al., 2013). 

Figure 5.
Structures of the major phospholipids

Source:

The dietary PLs have a number of health benefits for a range of
human diseases such as cancer, coronary heart diseases, and inflammation (Liu et al., 2013; Sumit, 2017). The pure form of phospholipids are used as value added nutritional,
pharmaceutical and cosmetics compounds, they also have good surface-active
properties for improving emulsion stability and shelf life (Jangle et al., 2013). PLs are also used as emulsifying agents in foods, agrochemicals,
cosmetics and pharmaceuticals (Sumit, 2017). PLs are fundamental components of cell membrane and therefore
vital for growth, maturing and good function of cells (Jangle et al., 2013).  

Conclusion

RBO is a co-product of rice milling process that is getting global popularity
and wide application mainly due to its health benefits associated with the
various micronutrients such as oryzanol, tocols, phytosterols, squalene, phospholipids,
etc. Many researchs have confirmed their health benefits.  These micronutrients are mostly concentrated
in different by-product of the oil refining steps such as deodorisation,
degumming and deacidification, and dewaxing. Thus, there potentials are most of
the time not properly tapped especially when these by-products are considered
as waste or animal products. Therefore, extraction of these micronutrients from
the by-product will generate more income and add value to the RBO sectors.

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