INFLUENCE OF HEAT TREATMENT ON THE QUALITY OF VEGETABLES: CHANGES IN VISUAL GREEN COLOR

Abstract

ABSTRACT Frozen asparagus, green beans, and green peas were properly defrosted and packed in 211 × 011 cans together with city water. The prepared samples were then heat processed at 175–300°F for 0.5–20 min. The tristimulus values of puree prepared from heat processed vegetables were determined by using a color difference meter. The ratio ‐a/b was used to determine the values of reaction kinetic parameters, D and z, for the discoloration of the vegetables since this ratio was closely related to the visual color of green vegetables. A D value was estimated from the slope of a linear portion of a curve. This curve was obtained by plotting the common logs of ‐a/b against isothermal heating times. A z value was determined from the slope of a thermal death time curve, which was obtained by plotting log 1 0 D against temperature. The z values for the discoloration of asparagus, green beans and green peas were found to be equal to 75 (°F), 70 and 71, respectively. Apparent activated energies for changes in visual green color, which was represented with ‐a/b, were estimated by assuming first order reaction kinetics. These energies for asparagus, green beans, and green peas were respectively equal to 18,080 (cal/mole), 19,800 and 15,200.