2. 氮平衡（Nitrogen balance） (1) 必要的氮损失（obligatory nitrogen losses） (2) 氮平衡： B＝I－（U＋F＋S） Positive nitrogen balance N in > N out N in = N out Nitrogen equillibrium Negative nitrogen balance N in < N out
2. 氮平衡（Nitrogen balance） (1) 必要的氮损失（obligatory nitrogen losses） (2) 氮平衡： B＝I－（U＋F＋S） Positive nitrogen balance N in > N out N in = N out Nitrogen equillibrium Negative nitrogen balance N in < N out
四、食物蛋白质营养学评价 (1)真消化率（true -） (一) 蛋白质含量(content） (2)表观消化率（apparent -）: (二) 蛋白质消化率(digestibility) 100% Food N Food N (Fecal N Metabolic N ) TD − − = 100% Food N Food N Fecal N AD − =
四、食物蛋白质营养学评价 (1)真消化率（true -） (一) 蛋白质含量(content） (2)表观消化率（apparent -）: (二) 蛋白质消化率(digestibility) 100% Food N Food N (Fecal N Metabolic N ) TD − − = 100% Food N Food N Fecal N AD − =
(三) 蛋白质利用率（utilization） 1.Biological value, BV:生物价 Food N (Fecal N Metabolic N) Food N (Fecal N Metabolic N) (Urinary N endogenous N) BV − − − − − − = 100 absorbed N N retained = The amount of protein nitrogen that is retained for growth and maintenance, expressed as a percentage of the protein nitrogen that has been digested and absorbed. To determine the actual value of an absorbed protein as it is used by the body
(三) 蛋白质利用率（utilization） 1.Biological value, BV:生物价 Food N (Fecal N Metabolic N) Food N (Fecal N Metabolic N) (Urinary N endogenous N) BV − − − − − − = 100 absorbed N N retained = The amount of protein nitrogen that is retained for growth and maintenance, expressed as a percentage of the protein nitrogen that has been digested and absorbed. To determine the actual value of an absorbed protein as it is used by the body
2. Net Protein Utilization, NPU 蛋白质净利用率 The amount of protein nitrogen that is retained from a given amount of protein nitrogen eaten. To determine the amino acid composition and digestibility of a test protein. Food N Food N (Fecal N Metabolic N) (Urinary N Endogenous N) NPU − − − − = 100% food N N retain =BVTD =
2. Net Protein Utilization, NPU 蛋白质净利用率 The amount of protein nitrogen that is retained from a given amount of protein nitrogen eaten. To determine the amino acid composition and digestibility of a test protein. Food N Food N (Fecal N Metabolic N) (Urinary N Endogenous N) NPU − − − − = 100% food N N retain =BVTD =
3. Protein Efficiency Ratio, PER: 蛋白质功效比值 A measure of protein quality assessed by determining how well a given protein supports weight gain in growing rats. Used to establish the protein quality for infant formulas and baby foods. Protein Intake(g) Weight Gain(g) PER =
3. Protein Efficiency Ratio, PER: 蛋白质功效比值 A measure of protein quality assessed by determining how well a given protein supports weight gain in growing rats. Used to establish the protein quality for infant formulas and baby foods. Protein Intake(g) Weight Gain(g) PER =