Biochemical Production of Oxalic Acid from Carbohydrates

Abstract

THIS paper reports the production of oxalic acid from starch through the intermediary of salivary enzymes. Oxalic acid has long been of interest to nutritionists and the dental profession because in the presence of available calcium it forms calcium oxalates. Kohman, in considering oxalic acid in foods, reported on a study in animals involving subcutaneous injection of oxalic acid.' He concluded that the calcium that combines with oxalic acid introduced into the blood is rather promptly replaced by calcium being mobilized from other tissues of the body *and the toxic symptoms are thus relieved. Ershoff stated that there seems to be no doubt that oxalates do interfere with efficient calcium utilization. The relatively insolubility of calcium oxalate has long been of concern to the medical profession because of the precipitation of calcium oxalate in the renal tubules, ureters, and urinary bladder.3 As early as the writings of Lavoisier4 starch was known as a source of oxalic acid. Madame Gruzewska5 in 1912 listed oxalic acid as among the in vitro products of the oxidation of starch by H202. Loeper6 discussed oxalic acid as an intermediate in carbohydrate breakdown. More recently, Caldwell CHO and Hixon7 have shown glyoxal (one oxidative step from oxalic acid) CHO to be an end product of acid hydrolysis of periodate starch. Girard, as reported by Loeper,6 found that the oxidation of sugar is in three stages, namely-glycolic aldehyde, glyoxal, and oxalic acid. It has long been common manufacturing knowledge that cellulose is a source for the production of oxalic acid.8 In spite of these observations, physiologically and biochemically, starch has had scant attention as a precursor of oxalic acid. In this paper we report the production and measurement of oxalic acid from starch through the action of human salivary enzymes and through the action of alpha amylase (Wallenstein). Earlier findings9 indicated that the saliva of individuals with extensive dental caries incubated with starch produces several times as much acid (as measured with .01 N NaOH) as the saliva of caries-free individuals. This finding stimulated the attempt to determine whether oxalic acid is among the acids produced from starch. The analytical procedure was as follows: The saliva of twelve individuals with extensive active caries (8 to 10 cavities in the previous six months) was pooled. Fifty milliliters of this saliva was added to 50 ml. of 1 per cent corn starch. To this, 1 Gm. of calcium acetate powder was added.'0