Effects of Heat Treatment and Dehydration on Pineapple (Ananas comosus L. Merr) Cell Walls
The effects of thermal processing on the physico-chemical properties of cell walls from pineapple flesh tissues have been investigated. Commercially canned pineapple exhibited a similar cell wall composition to the fresh pineapple sample, although a marked increase in cell wall solubility, from 21 to 34%, was detected. Dehydration promoted important changes in cell wall components and related functional properties, in particular when relatively high air-drying temperatures were applied. Thus, samples dried at 60ºC and, in particular at 80ºC, exhibited a larger solubilisation/degradation of pectic polysaccharides, probably due to either ?-elimination processes or enzyme-catalyzed degradation. On a fresh weight basis, about 14% and up to 39% of cell wall pectins were not recovered for the dried pineapple at 60ºC and 80ºC, respectively. Pectins from the latter samples also exhibited a notable decrease in the degree of esterification. These physico-chemical changes were probably reflected on the decrease of functional properties such as swelling (Sw), water retention capacity (WRC) and fat adsorption capacity (FAC). Nevertheless, fresh, canned and dehydrated pineapple at 40ºC exhibited higher WRC and FAC values, about 30 g water/g AIR and 15 g oil/g AIR, respectively. A gradual decrease of Sw, WRC and FAC values was observed for the functional properties of pineapple samples dried at 60 and 80ºC. Moreover, high air-drying temperatures also promoted a significant decrease in cell wall solubility. Therefore, the influence that these effects might have on the nutritional properties of cell walls or dietary fibre of thermally processed fruits such as canned and/or dehydrated pineapple needs to be considered.