Note: values were reported as mean \(\pm\) standard deviation.
Changes in the fatty components also affected the iodine value and the
saponification value of the original PFAD sample. Iodine value is
defined as the mass of iodine in grams absorbed by 100g of fat/oil. More
so, it is a measure for the average number of double bonds – the extent
of saturation – found in the fatty acids contained in the fat or oil
(Chang et al., 2016). Double bonds within the fatty acid structure have
halogen affinity, with any double bond consuming 1mol of halogen. The
average number of double bonds can then be concluded from the halogen
consumption (here: iodine). In Table 3.1, the mean iodine value (IV),
which was empirically determined was registered as 55.30\(\text{gI}_{2}/100g\). This IV was consistent with the mean values
reported by Chang et al. (2016). Saponification value SV describes the
amount of alkali (potassium hydroxide, KOH) required to saponify
(neutralise) a definite quantity of fatty acids resulting from the
complete hydrolysis of one gram of fat or oil as all fatty acids cleave
one molecule of KOH. Indirectly, the SV is a measure of the average
molecular weight of the triglycerides present in the fat or oil and
therefore a characteristic number. In this study, the mean SV recorded
in Table 3.1 was determined to be 219.05 mgKOH/g of oil and it is
slightly higher than the mean SV reported by Chang et al. (2016).
Elsewhere in the literature, the mean SV revealed from the studies made
by Bonnie and Mohtar (2009) was higher than the value recorded in Table
3.1. Observed variation in SV was as a result of method in which the
feedstock was processed, storage time of the feedstock and/or PFAD
sample, and storage conditions. In the later, elevated temperatures and
light contributed to the transformation of fatty acids to carbonyl
compounds which reduces the FFA content in the fat and hence lower the
SV. Both IV and SV were lower in NHPFAD when compared to PFAD due to the
removal of FFA by hydrolysis followed by neutralization.
PFAD contained a small amount of unsaponifiable matter. The
Unsaponifiable matter (USM) is defined as the oily (petroleum-ether
soluble) matter which cannot be converted into soap after saponification
(Abdulkadir and Jimoh, 2013). USM consist of some biological compounds
such as phytosterols, vitamin E (tocopherols and tocotrienols),
hydrocarbons like squalene etc. These group of compounds are available
in trace amounts contained in vegetable oils, the feedstock to FADs.
These substances are of pharmaceutical and nutritional importance and of
high commercial value. In Table 3.1, the USM of the PFAD sample was
recorded as 2.26%. The result was lower than those reported by Kifli
(1983). An increase in the content of USM from 2.26% (contained in
PFAD) to 10.35% after hydrolysis and neutralization was observed, and
this in turn increased the vitamin E concentration from 0.39% in the
original PFAD to 4.67%. Thus, these processes concentrated the vitamin
E content of the oil by 11.97 times the concentration of vitamin E in
the original PFAD.
Neutralization of PFAD increased mono- and diacylglycerol percentages
with diacylglycerols as with diacylglycerols as the main fatty
component. Percentage of triacylglycerol was almost undetected in HNPFAD
sample. The net change of lipase hydrolysis in PFAD sample was to
hydrolyse the di- and tri- acylglycerols into FFA and monoacylglycerol
as the main fatty component in HNPFAD sample. Levels of total fatty
component in HNPFAD sample was lower than that of PFAD because of the
transformations in fatty acids and acylglycerols.
Free fatty acids FFAs are straight-chain carboxylic acids (either
saturated or unsaturated) derived from the hydrolysis of fat or oil, or
synthesised in vivo and found as three main esters – triglycerides,
phospholipids, and cholesteryl esters. Its straight-chain falls under
the aliphatic class of hydrocarbons (Moss et al., 1987). The mean FFA
value empirically determined in this study was found to be 84.72%. This
value was higher than the mean FFA value reported in the study made by
Chang et al., (2016). Bonnie and Mohtah (2009), Moh et al., (1999) and
Kifli (1983) carried out similar study as well. In their study it was
observed that the mean value of FFA was also less than that also
reported in this work (Table 3.1). This indicated that samples are
subject to the following factors: processing techniques, such as
hydrogenation and lipid modification through traditional plant breeding
of parent stock, genetic transformation (Gunstone, 2002) aimed to
improve oxidative or functional properties, the geographical and
climatic conditions where the traditional plant (parent stock) was
grown.
Fatty acid composition of PFAD sample was determined using gas
chromatography equipment in conjunction with a mass spectroscopy
detector, after preparing sample methyl esters by a method known as
derivatisation. Based on the comparison of the retention times measured
by the analysis of the analytical standard and by that of the sample, it
was possible to identify the fatty acids contained in the PFAD sample.
Figure 3.1 shows the chromatogram of the derivatised fatty acid in
relation to peak value (abundance) and retention time (min).
Table 3.2 is an array of compounds the composition of FFA profile with
their respective value. From the PFAD sample, FFA profile included
lauric acid (C12:0), myristic acid (C14:0), palmitic acid (C16:0),
stearic acid (C18:0), two isomers of oleic acid (C18:1; n9 and C18:1;
n11), two isomers of linoleic acid (C18:2; n9 and C18:2; n12),
eicosenoic acid (C20:1; n11), arachidic (or eicosanoic) acid (C20:0) and
docosanoic acid (C22.0). These fatty acids were grouped into two
distinct classes, the saturated and the unsaturated fatty acids
respectively, and also the unsaturated class was further broken down to
give two subclasses – monounsaturated and polyunsaturated fatty acids
respectively as shown in Table 4.2.