PHYSICOCHEMICAL CHARACTERIZATION OF FRUIT AND VEGETABLE FIBER SUSPENSIONS. II: EFFECT OF VARIATIONS IN HEAT TREATMENT
The pectin content in the soluble and insoluble fractions of fiber suspensions from carrot, potato pulp and apple heat treated in four different ways was determined together with the particle size distribution, water-holding capacity (WHC), morphology and rheological properties of the fiber suspensions. In the carrot and apple suspensions, where beta-elimination was favored, the soluble pectin increased, whereas a significant but small decrease of the mean particle size of the insoluble material was obtained together with a significant decrease in WHC. For the potato pulp suspensions, however, only minor pectin solubilization was observed by heat treatment. Instead remaining starch in the cell matrix swelled on prolonged heating, leading to a different particle size distribution and a significant increase in WHC However, only minor effects on heating were seen on the elastic modulus for all fiber sources studied. But the source of fiber seems to be more important for the elastic modulus of the suspension, where the order of firmness in heated tissues (not the suspensions) seems to be the determining factor, being in the order of apple > potato > carrot. (Less)