No abstract

The aim of this study was to analyze the impact of traditional and combined pretreatment on dehydration kinetics and quality of dried swamp cranberries. Fruits were blanched, cut, or treated by combined technique consisting of blanching and application of pulsed electric field. Afterwards, fruits were subjected for osmotic dehydration (OD; 72 hr) in 61.5% sucrose solution or in ternary solution consisting of 30% sucrose with 0.1% addition of steviol glycosides to ensure similar sweetness of both mixtures. In the case of samples treated by combined method, OD was enhanced during first 30 min by sonication. Partially dehydrated cranberries were air dried at 70 °C. The quality of dehydrated fruits was assessed by the means of phenolics content, anthocyanin content, flavonoid content, vitamin C content, water activity, and color. Blanching decreased drying time by 48% to 50% in comparison to cutting. Utilization of combined method reduced drying time of cranberries up to 55% in comparison to cut samples. Water activity of all samples was below 0.6. Blanched samples or blanched and then treated with pulsed electric field and ultrasound contained more anthocyanins and flavonoids and less sucrose than cut samples. Practical Application According to current trends in food and beverage industry, consumers seek for products which does not contain excessive amounts of sugars, salt, or fats. Dried cranberry fruits are rich in bioactive compounds and need to be osmotically dehydrated in sugar solutions to make the taste of the final product acceptable. Osmotic dehydration is also carried out to decrease time of drying, which is one of the most energy intensive processes. Therefore, there is a need to develop a technology with potential to maintain the bioactive compounds, reduce sugar content in comparison to traditionally process fruits, and enhance the kinetics of drying.

The aim of this study was to investigate the effect of a pretreatment, performed by a combined method based on blanching, ultrasound, and vacuum application, on the kinetics of osmotic dehydration and selected quality properties such as water activity, color, and bioactive compound (polyphenols, flavonoids, and anthocyanins) content. The pretreatment was carried out using blanching, reduced pressure, and ultrasound (20 min, 21 kHz) in various combinations: Blanching at reduced pressure treatment conducted three times for 10 min in osmotic solution; blanching with reduced pressure for 10 min and sonicated for 20 min in osmotic solution; and blanching with 20 min of sonication and 10 min of reduced pressure. The osmotic dehydration was performed in different solutions (61.5% sucrose and 30% sucrose with the addition of 0.1% of steviol glycosides) to ensure the acceptable taste of the final product. The changes caused by the pretreatment affected the osmotic dehydration process by improving the efficiency of the process. The use of combined pretreatment led to an increase of dry matter from 9.3% to 28.4%, and soluble solids content from 21.2% to 41.5%, lightness around 17.3% to 56.9%, as well as to the reduction of bioactive compounds concentration until even 39.2% in comparison to the blanched sample not subjected to combined treatment. The osmotic dehydration caused further changes in all investigated properties.