Combination of Formaldehyde with Casein

Abstract

Graphs are presented to show the effects of concentration of formaldehyde, pH, time, and temperature on the amount of recoverable formaldehyde remaining in combination with casein after exhaustive washing of the reaction product with distilled water. The results are compared with related data of other investigators and are discussed in terms of possible reactions of various structural units in the protein. The analytical procedures employed for distillation and titration of recoverable formaldehyde were extensively studied and improved. Experiments are also described that show appreciable conversion of formaldehyde to the nonrecoverable form in the presence of casein at 100' C. and above.HE prevailing use of formaldehyde as a hardening agent in T the manufacture of plastics and textile fiber from casein makes it important to know the extent to which formaldehyde is bound by this protein under various conditions. Immersion of casein or other protein in a solution of formaldehyde leads to combination of the latter with varying degrees of stability, which are not easy or possible to distinguish quantitatively. Nevertheless, the formaldehyde taken up by the protein can be classified as to (a) whether it is in sufficiently loose form to be dissipated by washing with cold water or by exposure to air, or (a) whether it is held firmly enough to resist prolonged washing. Measurements of the total amounts of formaldehyde taken up by proteins or allied materials while in equilibrium with the formaldehyde bath obviously include formaldehyde bound in both manners. Such studies have provided valuable information concerning amino acids as well as proteins. Carpenter %nd Lovelace (9) have reported data for casein which represent the difference between the original and final formaldehyde concentrations of the treating bath. On the other hand, the formaldehyde responsible for improved properties in plastics and fibers must be the fraction retained under ordinary conditions of use-that is, the more firmly bound. The formaldehyde content of collagen, washed or pressed free of the loosely held material, has been extensively studied (15) by Highberger and co-workers and by 'Theis and associates, who employed distillation with acid to 'liberate the aldehyde.The work reported in this paper was undertaken to determine the effects of the four major factors-concentration, pH, time, and temperature-on the amounts of formaldehyde firmly bound by casein, and, if possible, to correlate the results with amino acid composition. Nitschmann and Hadorn (17) have reported data on the effects of time and concentration but no series of results showing the effects of pH or temperature.tein selected was a high quality acid casein obtained commercially and ground to pass a 60-mesh screen. Preliminary experiments showed that particle size had a negligible effect over the range studied (40 to 150 mesh).. Air-dried casein equivalent to 2.00 grams on the dry, ash-free basis was added t o 100 ml. of the buffered aqueous solution of formaldehyde in a large tes...

Formaldehyde Curing of Zein Fibers

“…Swain et al [ 15 ] also found a rapid increase in the binding of formaldehyde by casein as the temperature was increased to 60°C. At this temperature, under the conditions employed, the binding capacity of casein appears to be saturated because no further increase in binding was obtained by raising the temperature to 85 ° C.…”

“…We have used the technique developed and described by Swain et al [15] in carrying out the distillation and bisulfite titration of formaldehyde. This method does not determine irreversibly bound formaldehyde and we have made no studies toward evaluating this factor.…”

“…Although the reaction is complicated and leaves much to be desired, no other reaction seems to accomplish the same purpose. Various authors [6,9,11,15] have reviewed the recent literature, and show that every reactive group in proteins, with the possible exception of the carboxyl group, may bind formaldehyde. Zein has only recently gained industrial importance and the technical literature covering its utilization is largely limited to patents.…”

“…However, even in the presence of ammonium salts and at pH valuesTABLE III. EFFECT OF VERY HIGH ACIDITIES ON FORMALDEHYDE CURING OF ZEIN FIBERS AS MEASURED BY CONTROL OF SHRINKAGE * Curing bath was 10% formaldehyde at 60°C for15 …”

Influence of Various Formaldehyde Treatments on the Nutritional Value of Casein for wool Growth

“…The assessment of the amount of formaldehyde bound to the protein is a major problem. It is difficult to recover all of the bound formaldehyde by conventional methods such as distillation from hot concentrated phosphoric acid solution (Swain et al 1948;Middlebrook 1949; Reddie and Nicholls 1971). [14C]Formaldehyde was used in most of the present experiments to provide a simple and convenient way of assessing the total amount of formaldehyde carbon which remained in the products after subjecting them to a standard washing procedure. The amount of 14C in these products was taken as an index of "bound formaldehyde".…”