FREEZE-DRYING CHARACTERISTICS OF STRAWBERRIES

ABSTRACT Drying kinetic, as well as color and volume variation, of whole and sliced strawberries were investigated after freeze-drying under various temperatures (30, 40, 50, 60 and 70°C). Dehydration time increased proportionally to the thickness of the product and heating plate temperature markedly reduced it. Freeze-drying caused a pronunciation in red color of strawberries. A decrease in hue angle by 22.5% (skin) and by 42.4% (pulp) was noted, with no significant effect of freeze-drying temperature up to 70°C. The strawberries had a volume reduction of 8% (whole) and 2% (sliced) due to freeze-drying although the level of shrinkage was also independent of freeze-drying temperature. However, the percentage of collapsed strawberries increased with process temperature. At heating temperatures higher than 50°C, the strawberry dry layer temperature was higher than the estimated glass transition temperature of dried fruit, increasing the risk of collapse.

[1]  Y. Roos.  Effect of Moisture on the Thermal Behavior of Strawberries Studied using Differential Scanning Calorimetry , 1987 .

[2]  Z. Maroulis,et al.  EFFECT OF DRYING METHOD ON SHRINKAGE AND POROSITY , 1997 .

[3]  R. Wrolstad,et al.  COLOR QUALITY OF FROZEN STRAWBERRIES: EFFECT OF ANTHOCYANIN, pH, TOTAL ACIDITY AND ASCORBIC ACID VARIABILITY , 1970 .

[4]  C. S. Yang,et al.  Effect of Four Drying Methods on the Quality of Intermediate Moisture Lowbush Blueberries , 1985 .

[5]  Yasuyuki Sagara,et al.  MEASUREMENT OF TRANSPORT PROPERTIES FOR THE DRIED LAYER OF COFFEE SOLUTION UNDERGOING FREEZE DRYING , 1994 .

[6]  R. Brouillard,et al.  Recent developments in the stabilization of anthocyanins in food products , 1987 .

[7]  P. Bridle,et al.  Strawberry juice colour : the effect of some processing variables on the stability of anthocyanins , 1992 .

[8]  S. Michałowski,et al.  Freeze-Drying of the Black Currant Juice , 1995 .

[9]  F. René,et al.  Determination of freeze-drying process variables for strawberries , 1997 .

[10]  S. Khalloufi,et al.  Mathematical Model for Prediction of Glass Transition Temperature of Fruit Powders , 2000 .

[11]  M. Karel,et al.  Volumetric shrinkage (collapse) in freeze-dried carbohydrates above their glass transition temperature , 1995 .

[12]  N. K. Sharma,et al.  Influence of product thickness, chamber pressure and heating conditions on production rate of freeze-dried yoghurt , 1995 .

[13]  Yrjö H. Roos,et al.  Plasticizing Effect of Water on Thermal Behavior and Crystallization of Amorphous Food Models , 1991 .

[14]  J. Flink.  Nonenzymatic Browning of Freeze‐Dried Sucrose , 1983 .

[16]  Jorge Chirife,et al.  Structural Collapse and Volatile Retention During Heating and Rehumidification of Freeze‐Dried Tomato Juice , 1981 .

[17]  K. Pääkkönen,et al.  Processing, Packaging, and Storage Effects on Quality of Freeze‐Dried Strawberries , 1991 .

[18]  R. Wrolstad,et al.  CAUSATIVE FACTORS OF COLOR DETERIORATION IN STRAWBERRY PRESERVES DURING PROCESSING AND STORAGE , 1979 .

[19]  Vaios T. Karathanos,et al.  Effect of freeze-drying conditions on shrinkage and porosity of dehydrated agricultural products , 1998 .

[20]  L. Gerschenson,et al.  Air Dehydration of Strawberries: Effects of Blanching and Osmotic Pretreatments on the Kinetics of Moisture Transport , 1995 .

[21]  M. Rosa,et al.  Freeze-dried strawberries rehydrated in sugar solutions : mass transfers and characteristics of final products , 1997 .

[22]  T. Labuza,et al.  Compositional Influence on the pH of Reduced‐Moisture Solutions , 1992 .

[23]  G. Saravacos.  Effect of the Drying Method on the Water Sorption of Dehydrated Apple and Potato , 1967 .

[24]  R. P. Konstance,et al.  Dehydrated Blueberries by the Continuous Explosion-Puffing Process , 1982 .

[25]  T. Schenz.  Glass transitions and product stability—an overview , 1995 .