Impact of altitudinal gradients on biochemical traits and fatty acid profiles of Iranian hazelnuts

This study investigates the influence of altitudinal gradients on the fatty acid composition, antioxidant capacity, flavonoid and phenolic content of eight hazelnut cultivars. Samples were collected from orchards at low (0-500 m), mid (500-1000 m), and high (> 1000 m) altitudes in Gilan province of Iran. Duncan's test (p ≤ 0.01) revealed that altitudinal gradients were significantly alternated the antioxidant capacity, phenolic, and flavonoid contents of hazelnut cultivars. With increasing altitude, a decreasing trend in the antioxidant capacity (ranged from 74.33 to 27.33%) and phenolic content (ranged from 380.22 to 104.68 mg GAE/ 100 g dw) was observed. In contrast, a fluctuating trend in flavonoid content was ranged from 60.33 to 170.99 (mg QE/g dw) across altitudinal gradients; subsequently Round cultivar showed the highest flavonoid at mid altitude. In terms of fatty acids, an increase in the biosynthesis of unsaturated acids, including oleic (46.93-82.37%) and linoleic acid (0.1-6.52%) occurred at high altitude. While an increase in the concentration of saturated acids such as palmitic acid (3.61-37.86%), behenic acid (0.11-0.55%), stearic acid (3.12-7.5%), arachidic acid (0.41-6.05%), 11-Eicosenoic acid (0.33-6.19%), and myristic acid (0.11-0.69%) happened at low altitude. It was found that the ratio of unsaturated/saturated acids increased along with rising altitude, and vice versa. Conversely, the production of palmitoleic, as unsaturated acids, and tetracosanoic and pentadecanoic acids, as saturated acids, induced at low and high altitudes, respectively. In contrast, under all three altitudes condition, the biosynthesis of the oxirane octanoic was enhanced remarkably. These results highlight that the alterations in biochemical and fatty acid profile of hazelnut were cultivar type-, altitude-, and altitude-cultivar type interaction dependents. This aspect validated by PCA and heatmap analysis, which segregated cultivars into distinct groups. This highlights the importance of environmental and genetic factors in shaping hazelnut quality. These findings underscore the significance of considering altitude and cultivar selection in hazelnut cultivation to optimize nutritional quality, which can be valuable to producers, breeders, and the food industry.