1.The inactivation temperature of the oxidase of fruits is of interest in
connection with the processing of fruits and fruit products by heat, as inactivation
of the oxidase is essential to retention of the original fruit color.
OVERHOLSER and CRUESS (4) in 1923 reported that the organic peroxide
of fresh apple juice was temporarily inactivated by 20 minutes heating at
73.5° C. and the peroxidase by 20 minutes at 900 C. While the inactivation
of fruit catalase by heat was not investigated by us except incidentally, it
is of interest to mention the results reported by MORGULIS, BEBER and
RABKIN (3) who found that the pH value of the medium exerted a marked
effect on the temperature required for inactivation of catalase from beef
GALLAGHER (2) has reported on the behavior of the peroxidase of the
mangold after heating at 1000 C. but gives no data on the effect of hydrogenion
concentration. CRUESS and FONG (1) have reported preliminary observations
on the effect of pH value on the inactivation temperature of oxidase
in certain fruit juices.
The temperature required for the inactivation of the peroxidase of apricots,
pears, peaches, prunes, figs, lemon peel, tomato, banana and dates was
found to vary with the hydrogen-ion concentration. Resistance to heat was
greatest in the range of pH 5 to 7. Resistance decreased with decrease in
pH value between pH 5 and 2, and decreased with increase in pH value
between pH 8 and 12. At pH 12 and pH 2-2.2 the peroxidase was inactivated
at room temperature in 24 hours or less.
The organic peroxide behaved similarly to the peroxidase between pH 2
and 7. At pH values above pH 8 the organic peroxide failed to give positive
tests. There was considerable evidence that the inactivating effect of
temperature at any given pH is progressive rather than abrupt.
FRUIT PRODUCTS LABORATORY,
UNIVERSITY OF CALIFORNIA.