Food Chemistry

1.2 Amino Acids 29

Fig. 1.8.Formation of heterocyclic amines by heating a model system of creatine, glucose and an amino acid
mixture corresponding to the concentrations in beef (according toArvidssonet al., 1997). For abbreviations, see
Table 1.7

1.2.5 Synthetic Amino Acids Utilized
for Increasing the Biological Value
of Food (Food Fortification)

The daily requirements of humans for es-
sential amino acids and their occurrence in
some important food proteins are presented in
Table 1.8. The biological value of a protein
(g protein formed in the body/100 g food
protein) is determined by the absolute con-
tent of essential amino acids, by the relative
proportions of essential amino acids, by their
ratios to nonessential amino acids and by fac-
tors such as digestibility and availability. The
most important (more or less expensive) in
vivoandin vitromethods for determining the
biological valence are based on the following
principles:

• Replacement of endogenous protein after pro-
  tein depletion.
  The test determines the amount of endoge-
  nous protein that can be replaced by 100 g of
  food protein. The test person is given a non-
  protein diet and thus reduced to the absolute
  N minimum. Subsequently, the protein to be
  examined is administered, and the N balance
  is measured. The biological valence (BV) fol-
  lows from

BV=

Urea-N(non-protein diet)+N balance

Nintake

× 100 , (1.59)

“Net protein utilization” (NPU) is based

on the same principle and is determined

in animal experiments. A group of rats