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.