Investigation of roasting temperature, time and relative humidity on quality of hazelnuts

The present study was conducted on investigation of roasting temperature, time and relative humidity on quality of hazelnuts. Response surface methodology was used to study effects of temperature, time and relative humidity during roasting process on the color, moisture, texture, peroxide and sensory evaluations of hazelnuts. In the preliminary study, total 20 treatments were applied to hazelnut with different combinations of time, temperature and humidity. After applying 20 roasting treatments, each samples were vacuum packaged and stored at 4oC. In the preliminary study, roasting temperature, time and humidity were in the ranges of 115-155oC, 10-50 min and 1.9-9.5% RH respectively. According to the color results, the ranges of L-value, a-value and b-value were 33.34-62.98, 6.63-10.75 and 11.47-28.65, respectively. The color results were found a little bit lower in terms of L-value, whereas higher in terms of a-value and b-value. There was a high variation between the moisture values with a lack of fit. In addition to this, the texture values were also found with high variation so resulted in a lack of fit. As a result, the data did not fit the model. The effect of roasting relative humidity except at ambient humidity (1.9% RH) and maximum humidity (9.5% RH) was not found as significant on quality parameters of hazelnuts during roasting. Also, the hazelnuts roasted at maximum time and temperature were found burnt as not expected. So, it was decided to revize analysis methods and narrow temperature and time range to understand and optimize the roasting variables on quality parameters of hazelnuts for the main experiments. In the main experiments, a narrow ranges of temperature, 105-135oC, and time, 10-30 min, were investigated under dry (1.9% RH) and humidified (9.5% RH) conditions in two separate experimental designs each with 14 treatments. After applying 28 roasting treatments, each samples were vacuum packaged and stored at 4oC. In addition to the color, moisture and texture analysis, sensory evaluation was applied to analyze the effects of time, temperature and relative humidity on the roasting process of hazelnuts. According to the color and moisture evaluation of hazelnuts, as temperature and time increased, L value and moisture decreased significantly and varied between 52-77 and 0.67-2.55, respectively. By increasing roasting time and temperature, a-value, b-value and peroxide value increased significantly and their values were in the ranges of 1.29-12, 26.95-40.03, and 1.22-1.68 respectively. As the temperature and time increased during roasting, the first fracture point (F1) (ranged from 41.30 to 78.36 N) and the second fracture point (F2) (ranged from 63.33 to 152.49 N) decreased significantly. According to the sensory analysis results, it can be said that roasting time and temperature variance had a significant effect on sensory color, rancidity, crispiness, crunchiness, hardness, roasted hazelnut odour and flavor changes of hazelnuts whereas the sensory fat aroma was not significantly affected. Also, there was a high correlation found between instrumental texture, color, peroxide value and sensory texture, color and rancidity values. When roasting relative humidity effects were analyzed during roasting on quality parameters of hazelnuts, the moisture, sensory roasted hazelnut odour, sensory hazelnut flavor, sensory crispiness and rancidity of hazelnuts were significantly affected by the roasting relative humidity. The hazelnuts roasted under 9.5% roasting RH were found having 17% higher moisture, 12% higher crispiness and 15% higher roasted hazelnut flavor whereas having 23% less rancid taste and 12% less oil aroma than hazelnuts roasted at 1.9% roasting RH. In conclusion, the variation of time, temperature and roasting relative humidity affected the color, moisture, peroxide, texture and sensory of hazelnuts. For the optimization of roasting hazelnuts, the conditions that maximized roasted hazelnut odour and flavor, crispiness and crunchiness; minimized F1-value, F2 value and hardness; having L-value with 70 target value were evaluated by using response optimizer. Overall, roasting at 129oC for 26 min under humidified (9.5% RH) environment resulted in best quality criteria on hazelnuts based on texture, sensory and color evaluations.