Behavior of Citrus Fruit under Special Respiratory Conditions as an Expedient Index of Vitality.

There is an ever recurring demand for some simple indicator of the vitality of citrus fruit in relation to its keeping quality in storage and transportation. A few such indicators have been tentatively suggested, as for example the KMnO4 method by KLOTZ.1 In April, 1935, the writers undertook to utilize toward this end the respiratory processes of citrus fruit under simple but specific conditions. The general method adopted consisted of filling with fruit a container capable of being made perfectly air-tight, and afterward recording the pressure changes as respiration of the fruit altered from approximately normal to the anaerobic type. One kind of container used was of 2.5-gallon capacity and desigrned to withstand pressures of at least 50 lb. per square inch. These containers were equipped with mercury manometers 175 cm. in length. The chief characteristics observed in this set-up were the rate of change and the final pressure attained. The results proved very interesting but such containers were unwieldy and the end point was reached only after two to three weeks. The range of final positive pressures observed in this manner was 40 to 165 cm. of mercury. The curves of such pressure increase made, after an initial delay, a straight line day after day until near the end point. For convenience, and to shorten the period of observation, the method was modified to allow a closer following of pressure changes previous to reaching a positive pressure of 10 to 20 cm. of mercury. This condition called for batteries of low pressure containers consisting simply of 2-quart AMason jars of the "wide mouth" type, and finally, of 1-gallon wide mouth glass jars commonly uised for mayonnaise (fig. 1). Both sizes of containers were equipped with mercury manometers 26 cm. long. The covers of the 1-gallon jars were made of steel disks 5 inches in diameter and 1 inch thick. To these were cemented pure gum gaskets 1 inch thick. Connections to the manometers were made by means of copper tubes passing through the center of the steel disks. The jars and lids were placed in strong oak frames so that the lids could be bolted down tightly while in use. The period of observation on fruit in these containers varied with the temperature. The majority of tests were made at 720 F., at which temperature the period was usually 24 to 72 hours. Many comparative tests, however, were carried out at 56°, 460, 420, and 380 F.