Investigation of Volatile Reducing Substances as an Indicator of Decomposition for Raw and Processed Foods
Abstract Volatile reducing substances (VRS) in foods were determined by an empirical procedure in which volatiles are stripped by aeration from an aqueous extract of a sample, passed through alkaline potassium permanganate, and measured by the extent of permanganate reduction. Experimental parameters were investigated as a step toward developing a standardized procedure. Dilute methanol was investigated as a reference solution, the equipment described in published procedures was simplified, and some operating conditions were controlled. The amount of permanganate reduction increased with length of aeration, but variations in aeration rate from 1360 to 1790 ml/min were not critical. The method was applied to ground beef, shrimp, and peaches. The raw food materials were stored at ice or refrigeration temperatures until they reached a decomposed state. Samples withdrawn at intervals during storage were processed and preserved by freezing or by freeze-drying. The content of VRS in raw samples increased as the foods decomposed. The VRS were partly lost during cooking and completely lost during freeze-drying. Therefore, the VRS content appears to have promise as an index of decomposition for a variety of raw foods and possibly for some cooked foods, but not for foods that have been freeze-dried.