The Influence of Weathering and of Microorganisms on the Aqueous-Extract pH of Cotton Fiber

Abstract

Exposure of cotton in the field to wet weather following normal opening of the boll and fluffing of the fiber resulted in increases in the pH of aqueous extracts of the fiber, as determined by methods herein described, from a level in the general range of pH 6.3 to 7.3 for the un- weathered fiber to progressively higher values. The maximum pH attained was in the range of 9.5 to 10.0, and was sometimes reached within a period of 5 days. Cotton fiber subjected to wet weather during the process of boll opening, with the consequent unfluffed and darkened appearance characteristic of "fungus tight-lock" and "boll rot," had pH values ranging from 5.3 to 9.7. In the case of the common Diplodia tight-lock, serious fiber weakening and fiber disintegration were accompanied by pH values from 5.6 to 6.8. Pure-culture laboratory tests involving inoculation with fungi and humid-atmosphere incuba tion of fiber and unbleached cotton fabric, followed by pH determinations, indicated that several microorganisms, including certain types of common occurrence on field-weathered cotton, may bring about very rapid pH increases of the same general magnitude as those observed with fiber exposed to humid weather in the field. Both cellulose-decomposing and noncellulose-decom posing fungi brought about pH changes, which were upward in direction for 24 of the 27 isolates tested. Once high pH values were attained, no subsequent decrease in pH occurred dur ing incubation periods of 4 weeks' duration. On water-saturated cotton fiber mats, certain com mon bacteria and a common yeast produced pH increases. Data suggest that increases in the aqueous-extract pH of cotton fiber may be caused by the decomposition of malic or other organic acids in the fiber by microorganisms. Fiber which had attained a high aqueous-extract pH during weathering exhibited a decline in this value with time in storage. In tests here reported, the higher the original pH of the sample, the more rapid was the initial rate of decline in pH during storage. A decline in pH may occur also while the fiber is still on the plant in the field. The pH test appears to offer promise as a rapid method of fairly wide applicability for de tecting the growth of microorganisms on cotton fiber. The pH change measured is a response to growth on the noncellulosic constituents of the fiber and must be supplemented by further tests if one is to determine whether or not structural damage to the fiber has occurred.