The effect of different drying methods and pretreatments on drying and some quality parameters in the production of melon and watermelon chips

In this study, the effect of different drying methods and pretreatments on the drying characteristics, color changes, rehydration ability, shrinkage ratio and chemical properties of melon and watermelon were investigated. The drying rates of the samples dried with hot air, vacuum, microwave, and microwave assisted-hot air methods increased with the increment in temperature and microwave power. Besides, more color degradation and burning on the surface were observed in the samples dried with microwave and microwave assisted-hot air methods. Increment of temperature and microwave applying enhanced the rehydration ability and reduced shrinkage ratio. The pretreatments increased the drying rate, had negative effect on color properties and reduced shrinkage ratio. No remarkable effect of different drying methods on organic acid content of samples were observed, however, glucose and fructose content decreased. Whereas increment in temperature and microwave power increased loss of ascorbic acid, β-carotene and lycopene retained well with the temperature increasing. No significant effect of microwave power on β-carotene content of watermelon was observed, whereas the increment of microwave power led to loss of β-carotene content of melon. Microwave and microwave assisted-hot air methods caused less loss in total phenolic content. It has been determined that the increase of temperature and/or microwave power reduced the loss of antioxidant activity and increased HMF formation. Pretreatments caused the reduction in organic acid content, whereas immersing citric acid solution increased the citric acid content. Besides, ascorbic acid, glucose and fructose content were reduced by preatreatments. The highest β-carotene and lycopene resulted from the immersing ethanol solution. Moreover, immersing ethanol solution and ultrasound pretreatments caused the highest loss of total phenolic content and antioxidant activity. Reduction in HMF content were provided by pretreatments. Hot air drying at 70 °C after immersing hot water at 70 °C and hot air drying at 80 °C were determined as the best drying options.