COMPARISON OF FOUR TECHNIQUES FOR MEASURIFG GROWTH OF Tetrahymena pyriformis W WITH RAT PER BIO ASSAYS IN ASSESSING PROTEIN QUALITY

Abstract

ABSTRACTFour techniques for measuring growth of Tetrahymena pyriformis W (TpW), namely, direct microscopic count (DMC), tetrazolium dye‐reduction (TPTZ), oxygen uptake (O2 ‐UT), and ATP bioluminescence (ATP‐biol.), were compared with rat protein efficiency ratio (PER) assays for assessing protein quality. Relative nutritive value (RNV) of the test material was compared to a casein standard by slope ratio assay and by use of one concentration of nitrogen in the growth medium of TpW. Samples consisted of breads, made with wheat flour, soybean meal and nonfat milk solids, which contained different concentrations of glucose and of nutritionally complete diet mixtures containing either ANRC casein, peanut meal, or wheat gluten as a source of protein. Correlations between RNV determined by TpW growth and by rat PER were high. It was concluded that TPTZ, O2 ‐UT, or ATP‐biol. could be used to replace the tedious and time‐consuming DMC in measuring growth of TpW for protein quality assay. There were no apparent differences in results obtained by the slope ratio method and those derived from use of only 0.3 mg N/ml of growth medium, and the latter technique is faster.