Increasing the Oxidation Stability and Shelf-Life Quality of Hazelnuts Using a New Peeling Technique.

Hazelnuts without skin are preferred by consumers. Traditionally, the skin is peeled off by the roasting technique (RT). However, RT causes undesirable reactions such as lipid oxidation. Therefore, pressurized water technique (PWT) was developed as an alternative hazelnut peeling method. In this study, the effect of PWT on quality parameters including chemical composition, ultrastructure, peroxide value (PV), free fatty acidity (FFA), total antioxidant capacity (TAC), total phenolic content (TPC), total aflatoxin content (AFC), and volatile compounds of hazelnut samples during long-term storage (12 months) was evaluated and compared with RT. Generally, FFA, TAC, AFC, and fatty acid contents in hazelnuts were not affected by peeling methods. Before storage, hazelnuts peeled by PWT exhibited slightly higher TPC and slightly lower protein and oil contents than hazelnuts peeled by RT. Additionally, no peroxide formation was detected in hazelnuts peeled by PWT before storage. Nevertheless, after storage, hazelnuts peeled by RT showed 8.2 times higher PV compared to hazelnuts peeled by PWT. Unlike hazelnuts peeled by PWT before storage, a total of 17 different volatile compounds, mostly lipid oxidation products, were detected in hazelnuts peeled by RT. Hexanal, an indicator for secondary oxidation, in hazelnuts peeled by RT before storage was determined to be 1.9 times higher than hazelnuts peeled by PWT. More burst oleosomes in microstructure of hazelnuts peeled by RT were observed by SEM. These results indicate that PWT demonstrated more oxidation stability and shelf-life quality in hazelnuts compared to RT. Therefore, among these peeling methods, PWT can be recommended for safe food production. PRACTICAL APPLICATION: While the roasting process is used to peel the hazelnut skin, lipid oxidation formation is inevitable during this process. Lipid oxidation products not only deteriorate the product quality but also pose a health risk. The newly developed, pressurized water peeling technique increases the lipid oxidation stability in hazelnuts. Increasing oxidation stability by the pressurized water peeling technique ensures that the quality of the hazelnut is preserved, and its shelf life is increased.