3.2 Fatty acid profile
A total of 17 and 15 fatty acids in Futura 75 and inCarmagnola , respectively, were identified and quantified by fast GC-FID analysis, within a run time less than 7 minutes. As showed in Table 2, the predominant fatty acid in all samples was linoleic acid (C18:2, ω -6), ranging from about 49 to 54%. Oleic acid (C18:1cis9 ) was the second major fatty acid detected (~15-16%), followed by α-linolenic acid (C18:3,ω -3, ~ 12-15%), palmitic acid (C16:0, ~ 7-9 %), stearic acid (C18:0, ~ 2-3%) and γ-linolenic acid (C18:3, ω -6, ~2-3%).
In Futura 75 , the saturated fatty acids (SFA) were present in significantly (p < 0.05) greater amount at the first harvesting time (16.7%), whereas mono-unsaturated fatty acids (MUFA) did not showed significant differences among the three different harvest stages (18.7%, 18.3% and 18.1% for F1, F2 and F3, respectively). Polyunsaturated fatty acids (PUFA), on the other hand, increased significantly (p < 0.05) their concentration with hemp maturation, accounting for 64.6%, 69.6% and 69.6% for F1, F2 and F3, respectively. These trends reflect those of the main fatty acid: in fact, PUFA was the most abundant class because of linoleic acid concentration. In Carmagnola , SFA had a significantly higher (p < 0.05) concentration at first harvest stage (12.2%), than the other two (11.8% and 11.6% in C2 and C3, respectively); while MUFA did not show significant differences between first and third harvest stages (18.2% and 18.0%, respectively), with a slightly decrease in the middle stage (16.7%). PUFA, on the contrary, showed a significant increase (p < 0.05) at the second harvest stage (71.6%), between first and third harvestings (69.7% and 70.5%). Comparing our results with literature, SFA content is generally higher than data already reported for hemp native from Italy (7%, Da Porto et al., 2012) and from other countries like Croatia (9-11%, Petrović et al., 2015), Spain (11%, Montserrat-de la Paz et al., 2014) and Turkey (9-10%, Kiralan, Gül & Metin Kara, 2010); this because of palmitic and stearic acid content that is higher than reported literature. Only in a study conducted by Devi & Khanam (2019) is reported a similar concentration of palmitic acid compared to our results, 10% referred to hemp cultivated in India. MUFA content was higher in our study than literature; 12-16% (Kiralan et al., 2010), 11% (Da Porto et al., 2012), 13% (Montserrat-de la Paz et al., 2014) and 10-14% (Petrović et al., 2015). This because of oleic acid, that represent almost the entire MUFA content. On the contrary, PUFA determined in this study was lower than the already cited literature; in fact, Kiralan et al. (2010) showed a 73-78%; Da Porto et al. (2012) a 80-81%, Montserrat-de la Paz et al. (2014) a 75% and Petrović et al. (2015) a 74-80%. For this reason, the ratio between unsaturated and saturated fatty acids reported in our study, 3-5 in Futura 75 and 5-6 in Carmagnola is slightly lower than that reported in literature (6,7 showed by Montserrat-de la Paz et al., 2014). In general, this characteristic high ratio between unsaturated and saturated fatty acids can reduce serum cholesterol and atherosclerosis; and prevent heart diseases (Reena & Lokesh, 2007). On the other hand, because of its high unsaturation level and susceptibility to oxidation, hemp seeds oil has a short shelf life (Kiralan et al., 2010) and it is not suitable for hot uses (Da Porto et al., 2012).
As regard to the ratio between the two essential polyunsaturated fatty acids, linoleic and α-linolenic acid, both varieties, Futura 75and Carmagnola , showed the highest value at the first harvest, 4.05 and 3.90, respectively (Table 2). This even though linoleic and α-linolenic acids did not have the same trend in the two different varieties. In Futura 75 linoleic acid showed a significant (p < 0.05) increase from the beginning to the end of maturation (49.2%, 52.3% and 52.5% for F1, F2 and F3); inCarmagnola , instead, its concentration increased significantly (p < 0.05) from first (53.7%) to second harvest (54.7%) and then decreased again at the third harvest stage (53.9%). α-linolenic acid, instead, in Futura 75 increased significantly (p < 0.05) between first (12.1%) and second harvest (14.3%), before decreased again at third harvest stage (13.9%); inCarmagnola its concentration increased significantly during all the maturation; 13.8%, 14.6% and 14.9% for C1, C2 and C3, respectively. The high quantity of α-linolenic acid improves hemp oil quality for its positive nutritional implications and beneficial effects against coronary disease and cancer (Arshad, Al-Leswas, Stephenson, Metcalfe & Dennison, 2011; Fretts et al., 2013). In general, our results about these two fatty acids are slightly lower than results in literature. In fact linoleic acid content is reported in a range between 48 and 59% and α-linolenic acid in a range between 16 and 26% (Montserrat-de la Paz et al., 2014; Orsanova, Misurcova, Ambrozova, Vicha & Mlcek, 2015; Petrović et al., 2015; Mikulcová, Kašpárková, Humpolíček & Buňková, 2017; Devi & Khanam, 2019; Siudem et al., 2019).