Ultrasound assisted osmotic dehydration of organic cranberries (Vaccinium oxycoccus): Study on quality parameters evolution during storage

Cranberries are appreciated for their high amount of antioxidants such as flavonoids, anthocyanins, phenolic acids, carotenoids and vitamins. However, due to their sour and tart taste they request to be processed into sweeter dried fruits in order to be acceptable for the consumers. The aim of this work was to analyse the effect of ultrasound assisted osmotic dehydration on mass transfer parameters and on quality characteristics during storage of cranberries. Ultrasound treatment was performed at the frequency of 21 kHz for 30 min in three osmotic solutions - 61.5% sucrose, 30% sucrose with an addition of 0.1% of steviol glycosides and 40% trehalose on cut in half cranberries. Afterwards, the cranberry samples were subjected to osmotic dehydration process at 40 °C for 72 h. The osmodehydrated samples both with or without ultrasound pre-treatment were collected and stored at 10 °C in climatic chamber in microperforated plastic bags (PLA) for 8 weeks. The weight reduction, dry matter, water activity, colour, and microbiological analysis were performed after 1, 2, 4 and 8 weeks of storage. The obtained results indicated that ultrasound application significantly affected the mass transfer parameters during osmotic treatment, as well as it did the type of osmotic solution used. Thermal analysis showed variations in sugar melting temperature and enthalpy as a result of osmotic treatment and storage. During the storage, lower weight loss and higher lightness were observed in US pre-treated samples. The sample that preserved the best chemico-physical and microbiological characteristics during storage was the one treated with 61.5% sucrose solution, due to its lowest water activity.