Microwave-Osmotic Dehydration of Cranberries under Continuous Flow Medium Spray Conditions

Abstract

Microwave-osmotic dehydration of cranberries was evaluated under continuous �ow medium spray (MWODS) conditions aer some pretreatments. A central composite rotatable design was used with three input variables at �ve levels (temperature, 33 ∘ C-67 ∘ C; sucrose concentration, 33 ∘ B-67 ∘ B; and contact time, 5-55 min). Responses were moisture loss (ML), solids gain (SG), and weight reduction (WR) as well as color and texture parameters. e responses were related to process variables using response surface methodology and statistical analysis: each model was tested for lack of �t to assure nonsigni�cance (and each process variable was tested for signi�cance ( or . Temperature was found to have the most prominent effect as it was signi�cant with all drying (ML, SG, and WR) and quality (hardness and chewiness) parameters, while contact time was found to be signi�cant with ML and WR. Concentration wasn�t found to be signi�cant for any response. Increasing skin pretreatment severity generally promoted SG but had little effect on ML. e exception was chemical peeling, which favored ML but had no effect on SG. Overall, MWODS enables food dehydration in a much faster period of time than conventional osmotic dehydration (COD), while speci�cally promoting moisture loss over solids gain.

Development of a Microwave–Vacuum-Based Dehydration Technique for Fresh and Microwave–Osmotic (MWODS) Pretreated Whole Cranberries (Vaccinium macrocarpon)

“…[22] Therefore, IQF whole cranberries (Atoka Cranberries Inc., Manseau, QC, Canada) were kept frozen (À21 to À27 C) until use, at which point the berries were thawed by floating %200 g batches of berries in approximately 2 L of room temperature tap water for 1 h as previously described. [22] During this time, the berries were sorted, where only whole, undamaged, and ripe cranberries of medium size (approximately 10-15 mm diameter) were selected and underripe (white), broken, crushed, or otherwise damaged berries were discarded. Samples were then blotted to remove surface moisture before being weighed and transferred either directly to the MWV setup or first to the MWODS pretreatment.…”

“…[21,22] The only variation to the setup was the use of a new spray head (model RPB-173C, Waterpik Technology Inc., Markham, ON, Canada) instead of the now-discontinued model that was used previously. The RPB-173C was chosen because its diameter matches that of the sample container (12.5 cm) and due to its even spray distribution over the entire area of the sample stage.…”

“…The MWODS process used in this study employed a sucrose-based osmotic solution and parameters (50 C, 50% (w=w), and 30 min) that 2 WRAY AND RAMASWAMY represented the midpoint of the previously established central composite rotatable design for this process. [22] In this process, the sample is held inside the microwave cavity under a spray head that continually showers the product with osmotic solution that is circulated and maintained at a fixed input temperature (50 C in this case). This setup allows for the product to be coated in a thin layer of osmotic solution, which allows for temperature maintenance and moisture removal while still allowing the majority of the microwave energy to be absorbed by the product itself.…”

“…[21] This technique has also been applied to whole cranberries where it was found that the process was able to overcome the moisture barrier property of cranberry skin with no skin pretreatment. [22] This is despite previous work on osmotic dehydration of cranberries that suggested that it is necessary to disrupt the skin prior to osmotic treatment where chemical, thermal, mechanical, or combined techniques have been tested. [23] The objective of this study was to develop a bench-top MWV drying setup and determine suitable treatments for MWV finish drying of cranberries by subjecting the berries to a wide range of treatments by monitoring the berries visually for quality degradation and taking into consideration energy consumption and drying kinetics as well as to determine the applicability of combining MWODS with MWV finish drying.…”

Novel Concepts in Microwave Drying of Foods

“…[18,59] Moreover it was found that MWV dried samples showed softer texture and were less tough that convective dried berries, where additional benefits were noted in terms of energy efficiency. [1] As opposed to solely as a finish drying method, microwaves have more recently been applied during osmotic dehydration, in either immersion [136] or spray [89,[137][138][139][140][141][142] based configurations. Initially [136] it was found that apple cylinders that were exposed to microwave energy while submerged in a continuous flow of osmotic syrup had improved moisture transfer rates when compared to conventional osmotic dehydration (COD), while solids gainwas reduced compared to prior studies using both traditional static batch [143] and continuous flow [144] conditions in the same experimental setup.…”