Hazelnut Origin and Roasting Conditions Affect the Shelf Life of Chocolate With Whole Nuts

Chocolate bars with whole nuts are a popular type of chocolate. However, their shelf life is limited by the roasted hazelnuts, which can become rancid or cause fat bloom, a whitish layer on the chocolate surface. Both are thought to be related to the nut oil that rises to the surface. Surface oil is prone to rancidity due to contact with oxygen. In addition, when the nuts are used in chocolate, the surface oil can be washed off by the chocolate during mixing or can migrate into and through the chocolate to become visible as fat bloom. Although fat bloom tends to occur on only a few nuts in a bar, the presence of fat bloom on just one nut is enough to reduce enjoyment because consumers associate it with mold. In this study, the influence of origin and roasting conditions on both quality changes was investigated. Hazelnuts of caliber 11–13 mm harvested from two different regions of Turkey, namely, Akçakoca and Ordu, were subjected to four different roasting conditions. The roasting process was performed either at low temperature for a long time (at 142°C for 30 or 50 min) or at high temperature for a short time (at 200°C for 7 or 9.5 min) in an industrial scale roaster (capacity of 50 kg per batch). Assessment of oxygen consumption and hexanal headspace measurement, both indicative of rancidity, showed increased oxidative stability for nuts roasted at the lower temperature. Roasted nuts from all roasting trials were used to produce various nut chocolate bars for storage tests. During these storage tests, the development of fat bloom was quantified using the DigiEye colorimetric measurement system, which is a box with defined lighting conditions and a fixed and calibrated digital camera. Images taken with this system were used to evaluate the whiteness index, an indicator of fat bloom. The migration of oil from the roasted hazelnuts into liquid cocoa butter was studied in a model system. Higher oxygen consumption and hexanal formation could be clearly related to the higher roasting temperature of 200°C. Oil migration in the model system as well as in the chocolate bars was independent from the roasting conditions, but hazelnuts from Ordu showed a higher oil release than those from Akçakoca. Fat bloom formation was clearly related to the storage temperature of the chocolate bars but independent of the origin of the hazelnuts and the roasting conditions. However, in individual bars with the same production processes, hazelnuts of the same origin and roasting conditions showed fat bloom only on some nuts and not on all, indicating that there are additional factors affecting fat bloom formation.