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.
For an efficient production of spray‐dried fine powders having controllable properties (size, size distribution, and morphology), finding suitable operating conditions and an appropriate initial composition of the fluid material is important. For this purpose, a suspension device is employed to investigate the drying kinetics of a single droplet of hydroxypropylated pea starch (HPS). In the current work, the effect of the drying air temperature (80–160°C) and of the initial solid content of the agent (15–30%w/w) on the drying kinetics, shrinkage, and locking point of a single droplet was systematically investigated to acquire the optimal conditions required for producing HPS powder using a pilot‐scale spray dryer. In addition to the previously mentioned parameters, the atomization pressure effect (2–3 bars) on the spray‐drying process yield, thermal efficiency, and final powder properties were also considered. A laboratory‐scale X‐ray microtomograph and a camsizer‐XT were employed for the acquisition of three‐dimensional images and surface morphology of single dried particles and spray‐dried powder, respectively. Hollow particles were obtained in all single droplet experiments. The drying kinetic study results were supported by those obtained by the spray drying of HPS. An increased temperature of the drying air and the initial solid content of the solution results in higher powder recovery, lower residual moisture content, and larger particle size. Otherwise, the final particles are larger at a decreased atomization pressure. The optimized parameters for the high spray‐drying process yield (24.54%; 3 bars, 140°C, 25 wt%) and better powder homogeneity (span = 2.31; 3 bars, 140°C, 20 wt%) were defined. A mixture of particle morphologies was observed among the different final powders. A broken shell corresponding to rigid particles was obtained at a drying temperature of 140°C and an initial solid content of 25 wt%. A nonbroken particle refers to a pliable particle that corresponds to inflated and collapsed particles dried at high and low drying temperatures.
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