Reactions between Amino-Acids, Organic Acids and Sugars in Freeze-dried Apricots

Abstract

Haas and Stadtman¹ separated an apricot concentrate (30 per cent solids) into cationic, anionic and neutral fractions and showed that browning occurred when any two fractions were combined and stored at 57° C. The reactions of individual cations, anions and neutral compounds in freeze-dried apricot puriée stored at 25° C. and 70 per cent relative humidity (79 per cent solids) have now been studied. After sixteen months/this material was a mid-brown colour. It contained 1-deoxy-1-(N-amino-acid)-fructoses² and traces of 2-deoxy-2-(N-amino-acid)-glucoses³, together with sucrose, glucose and (traces of) fructose half-esters of malic and citric acids. These compounds replaced almost quantitatively the apparent losses of free amino-acids and malic and citric acids. After allowing for these reactions, there was a loss of 11 m.moles of glucose and 8 m.moles of fructose per 100 gm. fruit solids. It appears that, at this relatively early stage of browning, the coloured compounds were formed from sugars without the incorporation of any significant amount of amino-acid or organic acid residues. If the 1-deoxy-1-(N-amino-acid)-fructoses were intermediates in browning, subsequent reactions must have included the release of the amino-acid⁴. The behaviour of glucose-6-phosphate⁵ suggests that the malic and citric acid esters may also be important intermediates in browning.