Page 276 - Advances in Eco-Fuels for a Sustainable Environment

Ecofuel conversion technology of inedible lipid feedstocks to renewable fuel 239

consume a large amount of energy and increase the global cost of biodiesel production,
so that proper selection/elimination of the process step need to be considered. Other
components in microalgae—particularly proteins, pigments, and carbohydrates—
should be converted into valuable coproducts that can be applied in the cosmetic, food,
or pharmaceutical industries [27]. The utilization of the above-mentioned components
based on the biorefinery concept can maximize the profit of the end product [27].
Separation and purification of minor components in the microalgae cell are the keys
to obtain valuable products.
The spent mixture of Arabica and Robusta coffee grounds obtained from the coffee
roaster industry were found to be rich in polysaccharides, lignin, and protein [28].
Moreover, findings on the prospective residual phenolic compounds in spent coffee
grounds have led more studies to transform this waste into fuels and various valuable
products instead of treating it as a cheap source of cattle feed and fertilizer, or even
discarding it into landfills [29].

9.2 Inedible biodiesel feedstocks

9.2.1 Rice bran and rice bran oil (RBO)
Besides lipids, rice bran also contains compounds such as proteins, starch, fiber, min-
erals, vitamin B, phytin, phosphatides, and waxes. Compared to other cereal brans,
rice bran is a rich source of oil, phosphatides (lecithin), and good-quality wax. Unfor-
tunately, much of the bran is used only as livestock feed or boiler fuel because of its
inherent instability. This instability is due to the presence of lipase and lipoxygenase
enzymes that are activated through the milling process and rapidly act on the RBO
present. This enzymatic rancidity makes rice bran unpalatable, even to livestock.
The rate of FFA formation in brown rice depends on the degree of surface disrup-
tion, moisture content, microbial levels, temperature, and storage time of the rice bran
[6, 9]. Juliano observed that the rate of FFA formation in rice bran is very high, up to
5%–10% in 1 day and about 70% in 1 month under high humidity and temperature [9].
The lipids were hydrolyzed or oxidized to fatty acids or peroxide during aging. High
temperature accelerates lipid oxidation. Fatty acids are in turn oxidized to an array of
secondary metabolic compounds. This causes an increase in acidity and a deteriora-
tion of taste and the production of rancid odors.
Several stabilization methods have been employed in inactivating the lipase of rice
bran such as chemical stabilization, refrigeration, hydrothermal treatment, steaming,
extrusion, microwave heating, ohmic heating, and infrared radiation [30]. Chemicals
and fumigants were ineffective in inactivating the lipase of rice bran; only heat treat-
ment was shown as a suitable safe method [9, 30].
RBO is one of the most nutritious oils because of its favorable fatty acid compo-
sition and a unique combination of naturally occurring biologically active and antiox-
idant compounds. Since the 1930s, the use of RBO as an edible oil has increased. FFA
content is the major determinant of RBO quality and can range from 4% to 76% of the
total oil [6]. Gum (phosphatides) and wax content fall between 1% and 3% and