The effects of some essential oils applied before storage on the storage quality of natural hazelnut kernels

In this study, natural hazelnut kernels of cultivar 'Çakıldak' grown in Ordu province that belong to the 2022 harvest season were used. Essential oils of thyme, peppermint and Anatolian sage were applied to the hazelnut kernels. In the application, the hazelnuts did not come into direct contact with the essential oils. Cotton soaked with essential oils was placed in perforated containers and then placed in covered plastic containers containing the hazelnuts, where they were kept for 15 days. At the end of the period, the hazelnuts were vacuum-packed and stored in a room where temperature and humidity values were recorded for 12 months. Moisture (%), water activity (a_w), free fatty acid (%), peroxide (meqO_2/kg), total viable count, total oil content, total mold-yeast count, and color measurements (L*, a*, b*, chroma, hue angle) were conducted every 4 months. Each analysis was performed three times repetitively using approximately 350 g of natural hazelnut kernels each time. At the end of the study, the effects of essential oil applications on moisture, total mold-yeast count, L*, and a* values were found to be statistically significant (p<0.05). The effect of storage duration on a_w , free fatty acid, peroxide value, total oil content, total viable count, b*, chroma, and hue values was significant (p<0.05). The most effective essential oil in reducing total mold-yeast count was the thyme essential oil application. In this application, the L* value decreased, while the a* value increased significantly. Free fatty acid, peroxide, and total viable counts were generally lower in groups that were applied with essential oils, but these changes were not statistically significant. Additionally, with the consideration of the correlation results, there were relationships between different parameters in the application groups. These results suggest that different essential oils might have variable effects on the fruit tissue. Considering the essential oils used in this study, it can be said that thyme essential oil shows significant potential for both its antimicrobial effect and its ability to preserve fruit characteristics in the storage of kernels. However, the effect of thyme essential oil should not be attributed only to its high carvacrol content; but also the interactions between its components should also be considered as well. Additionally, when using these essential oils in foods, their allergenic properties should be taken into account, and shouldn't be forgotten to place labels that inform consumers should be provided.