Oil Quality Values (O/L and IV)
The ratio of oleic acid to linoleic acid (O/L ratio) and iodine value (IV) determine the nutritional quality, storability and shelf-life of peanut oil and its products. A high oleic to linoleic (O/L) acid ratio (>10:1) in peanut results an increased self life (up to 10 times) and improved flavor when compared to a normal O/L ratio (1.5/1). In addition, the iodine value was used to determine the degree of unsaturated fatty acid and the stability of peanut oil. High O/L ratio and low IV value generally indicate good stability and long shelf-life (; Chaiyadee et al., 2013; Chamberlin et al., 2014).
As it can be seen in Table 3, the differences between the peanut varieties for the O/L values were statistically significant in main crop growing season. According to a three-year average, O/L values of the peanut varieties varied between 0.97 and 1.91. The O/L value was 0.97 in Florispan, 1.23 in G.Red, 1.50 in G.Green and 1.91 in Halisbey peanut varieties in a three-year average. The highest O/L ratio was obtained from Virginia market type peanut variety due to higher oleic acid and lower linoleic acid percentage compared to other market types of peanut varieties. On the other hand, the lowest O/L ratio was obtained from Spanish market type peanut variety due to lower oleic acid and higher linoleic acid percentage. Bakal and Arioglu (2019) indicated that O/L value in peanut oil was increased when the harvesting delayed. They also indicated that the reason of O/L increases because the oleic acid percentage was increased and the linoleic acid was decreased when the harvesting times were delayed. Bovi (1982), Raheja et al. (1987) and Onemli (2012) reported that there was a negative correlation between oleic acid and linoleic acid. Gulluoglu et al. (2016) reported that the O/L ratio of the peanut oil varied between 1.92 and 2.23 at different harvesting times in main crop growing season. The O/L ratio was increase when the harvesting delayed. Oleic and Linoleic acids percentage of peanut varieties were found different. For these reasons, O/L ratio of the peanut varieties was found different. Hassan et al. (2005) reported that significant differences for unsaturated fatty acids and O/L ratio among peanut cultivars are attributable to the genotype.
Iodine values (IV) of the peanut oils were calculated using the (% oleic acid x 0.8601) + (% linoleic acid x 1.7321) equation given by Chowdhury et al. (2015). IV is important quality factor in peanut oil. Chaiyadee et al. (2013) and Brown et al. (1975) reported that the ratio of oleic acid to linoleic acid (O/L ratio) and iodine value determine the quality, storability and shelf-life of peanut oil and its products. In addition, the iodine value (IV) was used to determine the degree of unsaturated fatty acid and the stability of peanut oil. High-oleic peanut has longer self-life than low-oleic peanut and it has better flavor quality or stability than low-oleic peanut. Worthington et al. (1972) and Young et al. (1972) indicated that Iodine value indicates of the stability and self life of peanut oil. Low iodine value generally indicates good stability and long shelf-life.
The differences between the peanut varieties for the iodine value were found statistically significant in a three-year average. According to a three-year average, the iodine values of the peanut varieties varied between 91.80 and 99.23 in main crop growing season (Table 3). Iodine value was the highest in Florispan (99.23) and the lowest in Halisbey (91.80) varieties. Iodine value was the highest in Spanish market type peanut varieties due to higher linoleic acid percentage compared to other market types of peanut varieties. High linoleic acid percentage increases the iodine value (% Linoleic acid x 1.7321). Linoleic and oleic acids percentage was the important factors for indicating the iodine value. Andersen and Gorbet (2002) concluded that biochemical relationships between variables of fatty acids were more greatly affected by genetic effects than by environmental conditions. The reason for the differences between the varieties for the iodine value was them having different oleic and linoleic acids content. These results are in agreement with the findings of Andersen and Gorbet (2002), Chaiyadee et al. (2013), Chamberline et al. (2014), Chowdhury et al. (2015), Gulluoglu et al. (2016) and Arioglu et al. (2018) were indicated similar results.