104 Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking
Science has developed many scientific concepts
as powerful tools for the study of water. Although
the study of water reveals a wealth of scientific con-
cepts, only a selection of topics about water will be
covered in the limited space here.
Biochemistry studies the chemistry of life at the
atomic and molecular levels. Living organisms con-
sist of many molecules. Even simple bacteria consist
of many kinds of molecules. The interactions of the
assembled molecules manifest life phenomena such
as the capacity to extract energy or food, respond to
stimuli, grow, and reproduce. The interactions fol-
low chemical principles, and water chemistry is a
key for the beginning of primitive life forms billions
of years ago. The properties of water molecules give
us clues regarding their interactions with other
atoms, ions, and molecules. Furthermore, water va-
por in the atmosphere increases the average temper-
ature of the atmosphere by 30 K (Wayne 2000),
making the earth habitable. Water remains important
for human existence, for food production, preserva-
tion, processing, and digestion.
Water is usually treated before it is used by food
industries. After usage, wastewaters must be treated
before they are discharged into the ecological sys-
tem. After we ingest foods, water helps us to digest,
dissolve, carry, absorb, and transport nutrients to
their proper sites. It further helps hydrolyze, oxidize,
and utilize the nutrients to provide energy for vari-
ous cells, and eventually, it carries the biological
waste and heat out of our bodies. Oxidations of var-
ious foods also produce water. How and why water
performs these functions depends very much on its
molecular properties.
THE COMPOUND WATER
A compoundis a substance that is made up of two
or more basic components called chemical ele-
ments(e.g., hydrogen, carbon, nitrogen, oxygen,
iron) commonly found in food. Wateris one of the
tens of millions of compounds in and on earth.
The chemical equation and thermal dynamic data
for the formation of water from hydrogen and oxy-
gen gas is
2H 2 (g) O 2 (g) 2H 2 O(l), H^0 571.78 kJ
The equation indicates that 2 mol of gaseous hydro-
gen, H 2 (g), react with 1 mol of gaseous oxygen,
O 2 (g), to form 2 mol of liquid water. If all reactants
and products are at their standard statesof 298.15
K and 101.325 kPa (1.0 atm), formation of 2 mol of
water releases 571.78 kJ of energy, as indicated by
the negative sign for H^0. Put in another way, the
heat of formationof water, Hf^0 , is 285.89 (
571.78/2) kJ/mol. Due to the large amount of en-
ergy released, the water vapor formed in the reaction
is usually at a very high temperature compared with
its standard state, liquid at 298.15 K. The heat of
formation includes the heat that has to be removed
when the vapor is condensed to liquid and then
cooled to 298.15 K.
The reverse reaction, that is, the decomposition of
water, is endothermic, and energy, a minimum of
285.89 kJ per mole of water, must be supplied. More
energy is required by electrolysis to decompose
water because some energy will be wasted as heat.
A hydrogen-containing compound, when fully
oxidized, also produces water and energy. For exam-
ple, the oxidation of solid (s) sucrose, C 12 H 22 O 11 ,
can be written asC 12 H 22 O 11 (s) 12O 2 (g) 12CO 2 (g) 11H 2 O(l),
H^0 5640 kJThe amount of energy released, 5640 kJ, is called
the standard enthalpy of combustionof sucrose.
The chemical energy derived this way can also be
used to produce high-energy biomolecules. When ox-
idation is carried out in human or animal bodies, the
oxidation takes place at almost constant and low tem-
peratures. Of course, the oxidation of sucrose takes
place in many steps to convert each carbon to CO 2.THE POLAR WATER MOLECULES
During the 20th century, the study of live organisms
evolved from physiology and anatomy to biochem-
istry and then down to the molecular level of in-
termolecular relations and functions. Atoms and
molecules are the natural building blocks of matter,
including that of living organisms. Molecular
shapes, structures, and properties are valuable in ge-
netics, biochemistry, food science, and molecular
biology, all involving water. Thus, we have a strong
desire to know the shape, size, construction, dimen-
sion, symmetry, and properties of water molecules,
because they are the basis for the science of food
and life.
The structure of water molecules has been indi-
rectly studied using X-ray diffraction, spectroscopy,