Investigation of changes in total phenol, flavonoid, antioxidant activity, fatty acids, polyphenol and mineral profiles of hazelnut kernels dried in air, oven and microwave

Background: Hazelnut is one of the most consumed nuts in the world. Appropriate drying methods should be chosen to prevent microbiological and oil oxidation, which will affect the quality of hazelnuts after harvest. Results: Total phenolic and flavonoid contents of fresh and dried hazelnuts were detected between 40.83 (fresh (control)) and 82.98 mg GAE/100 g (conventional oven) to 105.95 (control) and 234.05 mg/100 g (conventional oven), respectively. Also, antioxidant activities of fresh and dried hazelnuts changed between 4.08 mmol/kg (control) and 7.46 mmol/kg (conventional oven). Gallic acid, 3,4-dihydroxybenzoic acid, catechin, caffeic acid, syringic acid and rutin were the abundant phenolic compounds of fresh and dried hazelnuts. Catechin amounts of hazelnut samples varied between 12.53 (control) and 37.78 mg/100 g (conventional oven). Also, while oleic acid amounts of hazelnut oils are determined between 73.21 (microwave) and 73.80% (air), linolenic acid amount of the ash of fresh and dried hazelnuts were identified between 17.57 (control) and 18.33% (conventional oven). P, K, Ca, Mg, S were the key macroelements of fresh and dried hazelnuts, while Fe, Cu and Zn are determined as the abundant microelements of hazelnuts. Results showed charges depending on drying types compared to the control. Conclusion: As a result, the differences in the nutritional properties and phytochemicals of hazelnuts were revealed during the drying of hazelnuts with different drying types, which is important due to their nutritional and physiological importance. Drying types and times were effective on the elemental contents of hazelnuts. Generally, considering the oil content, bioactive properties, phenolic components and fatty acids of hazelnut, it is thought that the conventional oven drying system can be chosen because it can achieve better results for consumers.