Ultrasound‐assisted Osmotic Dehydration of Cranberries: Effect of Finish Drying Methods and Ultrasonic Frequency on Textural Properties

In this study, the effect of osmotic pretreatments (with or without ultrasound) in combination with hot‐air or microwave‐assisted hot‐air drying methods on the texture, microstructure, color and water activity of dried cranberries were investigated. Osmotic pretreatments were done in a ternary solution (sucrose–NaCl–water) under three different temperatures: 30, 40 and 50C. The concentrations of osmotic solutions were 40, 50 and 60% of sucrose and 0, 4 and 8% of NaCl. Also, the influence of the two levels of frequency of ultrasound (35 and 130 kHz) on the quality properties was investigated. Our results showed lower hardness and water activity (aw) when higher temperature, sucrose and salt were used. Applying ultrasound reduced the hardness and aw of samples. With increasing the frequency of ultrasound, hardness (N) and aw were decreased. Microwave energy reduced drying time and can modify the structure, texture strength and color of the final product. PRACTICAL APPLICATIONS Cranberry contains high levels of phytochemicals, which have health‐promoting properties. Some of these phytochemicals, such as anthocyanins, act as an antioxidant, reducing the oxidative damage to cells, which can lead to cancer, heart disease and other degenerative diseases. Recently, cranberry products have been used with the hope of preventing or treating urinary tract infections or Helicobacter pylori infections, which can lead to stomach ulcers, or to prevent dental plaque. Osmotic dehydration is a suitable way to produce shelf‐stable products or partially dehydrated foods without enduring heat damage. The osmotically dehydrated cranberries can be consumed as healthy snacks or can be suited to a wide range of food formulations, including jams or sweets.