Drying is one of the ways to reduce postharvest waste and processing in agricultural products. Drying with hot air is one of the most popular drying methods in the food industry. The purpose of this study is to investigate the effect of ultrasound and temperature on the quality and thermodynamic properties in the process of drying nectarine slices in a hot air dryer. The drying process was performed at four levels of ultrasonic pre-treatment of 0 min (control sample), 10, 20, and 40 min and three temperature levels of 50, 60, and 75°C. Experiments were performed on 5 mm thick How to cite this article: Jahanbakhshi A, Yeganeh R, Momeny M. Influence of ultrasound pre-treatment and temperature on the quality and thermodynamic properties in the drying process of nectarine slices in a hot air dryer.

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Peach, which is one of the most critical garden products in Iran has a lot of postharvest lesions. In this sense, processing the product would result in reducing the postharvest lesions. Recently, ultrasound waves have been widely applied as a new pretreatment method in drying food. Herein, we aim at investigating the effect of high power ultrasound pretreatment on the drying kinetics of peach slices. The effective moisture penetration coefficient, color changes and elastic modulus were investigated. The drying process was modeled using mathematical equations. The results showed that the ultrasound use as a pretreatment before drying reduces the drying time by up to 40%. The ultrasound treatment effect and the duration of their application on the color changes of the samples are not significant, and the reason for the color change is due to maillard reactions. The results of the effect of ultrasound pretreatment on the elastic modulus due to loading in the compression test showed that the application of pretreatment on the deformation of the samples is significant and reduced the modulus of elasticity by about 46%. The midilli model in different pretreatments, as compared to other models, had the best fitting with the experimental data. Moreover, the amount of effective diffusivity coefficient in the dried samples of peach slices, in different pretreatments, varies from 1.345 × 10−9 to 5.370 × 10−10 m2 s−1. In addition, it is worth mentioning that ultrasound pretreatment can be regarded as a promising approach. As far as food and agricultural products have typical structure and composition, ultrasound pretreatment application requires more through research. Practical Applications As compared to the untreated peach slices, a significant enhancement was witnessed in the ultrasound (US)‐treated slices. Herein, a new method is proposed, which results in producing slices with an improved quality. Generally, peach‐slice processing has been applied to get high‐quality products.

Hot air roasting is the classical way for processing pistachio. In this study, the classical operation was compared with a frying operation that was assumed to be as efficient as classical roasting and permit flavour intensification. The final moisture content at 180 °C was 5.6% at 5 min for fried samples and at 160 °C was 6% at 11 min for roasted samples. The breaking force of pistachio kernels was found to decrease from 2,008 N for raw pistachio to 780, 860, 975 and 1,030 N and then increased from there to 930, 1,460, 1,930 and 2,130 N at 140, 160, 170 and 180 °C, respectively, during frying. The results are similar for roasting. Oil content values ranged between 47 and 48% for the raw pistachio kernels and 53, 54, 55 and 56% after 5 min of frying at 140, 160, 170 and 180 °C, respectively. The results suggest that frying is an efficient intensive and innovative processing technique.

In this research, ' Ahmad Aghaei' pistachio cultivar harvested from Iran in 2011 was supplied by the Pistachio Research Institute. The effect of roasting times (5, 10, 15, 20, 25 and 30 min) and temperatures (120, 130, 140, 150 and 160 °C) on the colour of pistachio nuts was investigated. Initially, the L value (lightness) decreased for all temperatures and then increased for 120 and 130 °C with increases in roasting temperature and time. Values of a (redness) and ΔE (colour difference) for pistachio samples showed an increase while b decreased. Changes in L, a and b (yellowness) values of pistachio were used to develop and to validate a numerical dynamic model. The developed prediction models satisfactorily described the colour development as a function of roasting temperature and time for L, a, b and ΔE of ground-state measurements. As a result of variance analysis, the effects of the roasting process on colour values of pistachios were found to be statistically significant. In addition, changes in colour values gave high R² and the obtained nonlinear equations may be utilised to determine the optimum roasting degree based on time and temperature. A reverse approach for modelling is used in order to establish that it is possible to obtain the optimal condition directly from the experimental data modelling step.