Florida AgricWultral E'peri'ment Station 133

 An interesting point in this connection is that all attempts to grow
upon sterilized orange juice the blue-molds (Pc)nicillinti italicmii and I'.
olict'ceetlit), common upon citrus fruits, resulted instead in the growth of
this WTillia with two or more accompanying bacteria. There seems to be a
general impression that the preservation of orange juice is largely a ques-
tion of preventing the growth of these blue-molds in the juice. As a
matter of fact it seems probable that these molds will not ordinarily grow
readily upon orange juice, perhaps on account of the acidity of the medium,
but that the molds which are occasionally found upon orange juice are
really species of Wehmner's oenus Citrno cc~s. or some of the PcIictilli
more resistant to acid.
 But the theory that darkening was caused by micro-organ-
isms was soon abandoned because it was found that the juice
was usually sterile after heating to only 60 C.; moreover those
samples which were pasteurized at higher temperature appeared
to deteriorate and darken even more than those which had re-
ceived less heat.
 In view of these facts it seemed most likely that the darken-
ing was caused by some spontaneous chemical change takin,
place in the juice, probably an oxidation.
 Enzymes of the oxidase and peroxie ae cl ass l i'rteqiu ny the can
of such changes in fruit i)poducts. Tests for thee bodies Ihowed that
peroxidaIi e was 'present in the peel and seeds of the orange, but not iln ith-
juice. In fact, it was found to be totally unable to withl:tand an acid
reaction and that as little as 1 cc. of orange juice added to 10 cc. of acti e
peroxidase solution was sufficient to destroy its activity completely. The
peel also contained a catalase and a very active invertase, but they could.
not be detected in the juice.
 Since no oxidizing enzymes were found in the juice. it was
thought that the darkening must be due to a simple process tot
autoxidation which could be prevented by preserving the pas-
teurized juice out of contact with oxygen (air). One of the
simplest methods for accomplishing this would be to replace all
of the air dissolved in the juice, as well as that above it, by
some inert non-oxidizing gas such as carbon dioxide, hydrogen,
or nitrogen. Accordingly, a series of tests was carried out to
investigate this possibility. The preliminary tests carried out
with small amounts of juice in test tubes, showed that darken-
ing could be entirely prevented by saturating the juice with
carbon dioxide and replacing the air above the juice with that
gas; that hydrogen could be used in place of carbon dioxide,
altho it was much more difficult to handle; and that the nitrogen
used (which contained 7 percent of oxygen as an impurity)
could not be substituted for the pure carbon dioxide, altho it
decreased the amount of darkening somewhat. Incidentally, it