COMPARSION OF CHEMICALLY MEASURED AVAILABLE LYSINE WITH RELATIVE NUTRITIVE VALUE MEASURED BY A Tetrahymena BIOASSAY DURING EARLY STAGES OF NONENZYMATIC BROWNING

Tetrahymena pyriformis W (TPW) was used as a biological assay to study the loss of overall protein quality due to nonenzymatic browning. The Relative Nutritional Value (RNV) as determined by this organism decreases in a model food system as Maillard compounds are formed during storage at 35°C for 80 days and at three water activities (0.3, 0.5 and 0.7). These results were compared to the fluorodinitrobenzene (FDNB) chemical assay. The latter method shows a greater loss of available lysine than is seen by TPW growth at early stages of browning. Significant accumulation of brown pigment production does not occur until after RNV has diminished by 35–50% and FDNB has decreased by 60–70%. At advanced stages of browning, however, the TPW test showed equivalent or greater losses of nutritional value. Considerable variation in the TPW bioassay occurred due to the problems in the technique but analysis of all stored samples in a single test allowed comparison to a standard casein control for measurement of protein quality loss.