Estimation of α-keto acids in plant tissue: a critical study of various methods of extraction as applied to strawberry leaves, washed potato slices and peas

Abstract

Various methods of inactivating the enzymes in strawberry leaves, in washed potato slices and in peas have been critically compared as a preliminary to estimation of [alpha]-keto acids by the chromatographic method of Isherwood and Cruickshank (1954). Use of hot acid or strongly alkaline media, or boiling methanol, led to both formation and destruction of [alpha]-keto acids by chemical reactions occurring in the tissue extract during disintegration. Any method of heat inactivation was open to the suspicion that enzymes were not inactivated sufficiently rapidly to avoid a brief period of heat stimulation, thus causing a significant change in [alpha]-keto acids in the tissue. In the recommended method, the tissue was frozen in a mixture of methanol and solid carbon dioxide and then disintegrated in 0.6 [image] metaphosphoric acid at -2[degree]. The principle of this procedure, that it is best to arrest activity of enzymes by cooling to a low temperature and inactivative them by chemical treatment while they are still in this arrested state, is important in estimation of other labile intermediates such as phosphoric esters.