Palou do

Assessment of pretreatment methods and osmotic dehydration for cranberries
P.S. Sunjka and G.S.V. Raghavan Department of Bioresource Engineering, McGill University, Ste. Anne de Bellevue, Quebec, Canada H9X 3V9

Sunjka, P.S. and Raghavan, G.S.V. 2004. Assessment of pretreatment methods and osmotic dehydration for cranberries. Canadian Biosystems Engineering/Le génie des biosystèmes au Canada46: 3.35-3.40. In this research, different drying pretreatment methods were tested on cranberry fruit (Vaccinium macrocarpon). Mechanical and chemical pretreatments were examined, as well as osmotic dehydration. Two types of assessed mechanical pretreatments were cutting the berries in halves and into quarters and chemical pretreatment consisted of testing different temperatures of chemical agentand dipping times for cranberries. Osmotic dehydration involved evaluation of different osmotic agents, their concentrations, and different times of osmotic dehydration. There were three observed parameters: mass gain, solids gain, and moisture loss. The mechanical pretreatment that showed the best results for observed parameters was cutting the berries into quarters, but chemical pretreatmentshowed no significant difference. Time and concentration of osmotic agent significantly promoted the moisture removal and sugar uptake. Keywords: cranberry, drying pretreatment, moisture loss, osmotic dehydration. Dans cette étude, différentes méthodes de prétraitement pour le séchage de la canneberge (Vaccinium macrocarpon) ont été évaluées. À savoir, la méthode mécanique, la méthode chimique et laméthode de déshydratation osmotique. En ce qui concerne la méthode mécanique, deux types de prétraitements ont été utilisés : le découpage en deux ou en quatre des canneberges. La méthode chimique consistait à optimiser température des agents chimiques et la durée d’immersion des canneberges. La méthode de déshydratation osmotique impliquait l’évaluation des différents agents osmotiques, desconcentrations, ainsi que des durées du prétraitement. Les paramètres utilisés pour comparer les méthodes étaient: le gain de masse du fruit, le gain des solides solubles, et la perte d’eau. Les meilleurs résultats ont été obtenus avec le prétraitement mécanique avec découpage des baies en quatre quartiers. Le prétraitement chimique n’a montré aucune avantage sur les baies non traitées. Le temps et laconcentration de l’agent osmotique avaient accentué l’élimination d’eau et d’accumulation de sucre dans les baies.

dipping of a product into a chemical solution (normally alkaline or acid solution of oleate esters) of a specific concentration for a specific amount of time. Mechanical pretreatment consists of skin abrasion, puncturing, or cutting the product into smaller pieces. One of the mostuseful pretreatments for drying of fruit is osmotic dehydration (Beaudry 2001). Osmotic dehydration is the incomplete removal of water from a food product by means of an osmotic agent (usually either sugar or salt solution). The main advantage of this process is its influence on the principal drying method, shortening of the drying process, resulting in lower energy requirements. Considering thatheat is not applied in this stage, osmotic dehydration offers higher retention of initial food characteristics, such as colour, aroma, nutritional constituents, and flavour compounds (Beaudry 2001). Skin pretreatment Chemical pretreatment involves immersion of the product in alkaline or acid solutions of oleate esters prior to drying. Alkaline dipping facilitates drying by forming fine cracks onfruit surface (Salunkhe et al. 1991), and dipping in oleate esters causes wax platelets on the fruit skin to dissociate, helping the removal of moisture (Venkatachalapathy 1998). It was determined by Ponting and McBean (1970) that, for fruits with a waxy surface layer, the most effective treatment is with ethyl esters of fatty acids, especially oleic acid. Saravacos et al. (1988) and Tulasidas et...