Pretreatment of fruits prior to drying has shown success in reducing drying time and costs. In this work, ultrasound-assisted osmotic dehydration has been implemented as a method to increase water diffusivity and reduce drying time in strawberries. Strawberry halves were immersed in distilled water and in two different concentrations of sucrose solutions while pretreatment time and ultrasonic frequency levels were varied to determine their effect on drying time, water loss, and soluble solids gain. A microscopic analysis was carried out to evaluate the formation of microchannels and other changes to the fruit tissue structure. Greater sucrose concentration used in ultrasound-assisted osmotic dehydration resulted in greater water loss with greatest loss observed for the strawberry halves pretreated for 45 min in a 50% w/w sucrose solution. The pretreatment carried out for 30 min employing an osmotic solution of 50% w/w of sucrose resulted in the highest drying rate among the pretreatments. Osmotic dehydration used alone during pretreatment increased total processing time, whereas osmotic dehydration combined with ultrasonic energy during pretreatment reduced total processing time and increased effective water diffusivity. Cell distortion and breakdown were observed not only in pretreatments employing ultrasound-assisted osmotic dehydration but in conventional osmotic dehydration. Formation of microchannels through ultrasonic application and effects of osmotic pressure differential were considered to be largely responsible for reducing drying time for strawberry halves.

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The aim of this study was to evaluate the use of sonicated pineapple juice as substrate for producing a probiotic beverage by Lactobacillus casei NRRL B442. Maximal microbial viability was found by cultivating L. casei at 31°C and pH 5.8 (optimised conditions). After fermentation, samples of sweetened and non-sweetened juice were stored. After 42 days of storage under refrigeration (4°C), the microbial viability was 6.03 Log CFU/mL in the non-sweetened sample and 4.77 Log CFU/mL in the sweetened sample. The pH of both samples decreased during storage due to lactic acid production (post acidification). The characteristic colour of the juice was maintained throughout the shelf life and no browning was observed. Sonicated pineapple juice was shown to be a suitable substrate for L. casei cultivation and for the development of an alternative non-dairy probiotic beverage.