Inactivation of Nutrients by Heating With Glucose

Abstract

Aliquots of a soln. containing known amts. of l-tryptophan and d-glucose were heated under conditions to cause browning resembling that which occurred during autoclaving of media. The extent of browning was measured by the decrease in transmission at 610 m[mu] in a Coleman spectrophotometer. Hydroxymethylfurfural content, used as an indicator of the concn. of browning reaction products, was estimated from the absorption increase at 284 m[mu] in a Beckmann spectrophotometer. The loss of /-tryptophan in the browning reaction was detd. by microbiologic assay using sucrose medium to prevent further browning. Aliquots at pH 10 gave samples in which browning was only partially due to interaction with tryptophan. These mixtures gave more browning in less time. Growth of Streptococcus faecalis R was measured turbidimetically after 16 hrs. by decrease in transmission at 610 m[mu]. Better growth was obtained from the tryptophan-glucose sample heated at pH 10 although more browning occurred and hydroxymethylfurfural was formed. The soln. containing only glucose and tryptophan showed less browning and less hydroxymethylfurfural formation and permitted poorer growth. Decrease in growth was apparently due to actual destruction of part of the tryptophan. Both /-lysine and dl-methionine upon heating in the presence of glucose underwent similar destruction. Curves are presented indicating that nutrients in both the vitamin and amino acid class suffered damage during autoclaving with glucose. Inactivation of nutrients was minimized by substituting sucrose for glucose.