128 Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking
AQUATICORGANISMS ANDDRINKINGWATER
Life originated in the water or oceans eons ago, and
vast populations of the earliest unicellular living or-
ganisms still live in water today. Photosynthesis by
algae in oceans consumes more CO 2 than the photo-
synthesis by all plants on land. Diversity of phyla
(divisions) in the kingdoms of Fungi, Plantae, and
Animalia live in water, ranging from single-cell
algae to mammals.
All life requires food or energy. Some living or-
ganisms receive their energy from the sun, whereas
others get their energy from chemical reactions. For
example, the bacteria Thiobacillus ferrooxidans
derive energy by catalyzing the oxidation of iron
sulfide, FeS 2 , using water as the oxidant (Barret et
al. 1939). Chemical reactions provide energy for
bacteria to sustain their lives and to reproduce.
Many organisms feed on other organisms, forming a
food chain. Factors affecting life in water include
minerals, solubility of the mineral, acidity (pH),
sunlight, dissolved oxygen level, presence of ions,
chemical equilibria, availability of food, and electro-
chemical potentials of the material, among others.
Water used directly in food processing or as food
is drinking water, and aquatic organisms invisible
to the naked eye can be beneficial or harmful. The
Handbook of Drinking Water Quality(De Zuane
1997) sets guidelines for water used in food services
and technologies. Wastewater from the food indus-
try needs treatment, and the technology is usually
dealt with in industrial chemistry (Lacy 1992).
When food is plentiful, beneficial and pathogenic
organisms thrive. Pathogenic organisms present in
drinking water cause intestinal infections, dysentery,
hepatitis, typhoid fever, cholera, and other diseases.
Pathogens are usually present in waters that contain
human and animal wastes that enter the water sys-
tem via discharge, runoffs, flood, and accidents at
sewage treatment facilities. Insects, rodents, and
animals can also bring bacteria to the water system
(Coler 1989, Percival et al. 2000). Testing for all
pathogenic organisms is impossible, but some or-
ganisms have common living conditions. These are
called indicator bacteria, because their absence
signifies safety.
WATER ANDSTAT E O FFOOD
When a substance and water are mixed, they mutu-
ally dissolve, forming a homogeneous solution, or
they partially dissolve in each other, forming solu-
tions and other phases. At ambient pressure, various
phases are in equilibrium with each other in isolated
and closed systems. The equilibria depend on tem-
perature. A plot of temperature versus composition
showing the equilibria among various phases is a
phase diagramfor a two-component system. Phase
diagrams for three-component systems are very com-
plicated, and foods consist of many substances,
including water. Thus, a strict phase diagram for
food is almost impossible. Furthermore, food and
biological systems are open, with a steady input and
output of energy and substances. Due to time limits
and slow kinetics, phases are not in equilibrium with
each other. However, the changes follow a definite
rate, and these are steady states. For these cases,
plots of temperature against the composition, show-
ing the existences of states (phases), are called state
diagrams.They indicate the existence of various
phases in multicomponent systems.
Sucrose (sugar, C 12 H 22 O 11 ) is a food additive and
a sweetener. Solutions in equilibrium with excess
solid sucrose are saturated, and their concentrations
vary with temperature. The saturated solutions con-
tain 64.4 and 65.4% at 0 and 10°C, respectively. The
plot of saturated concentrations against temperature
is the equilibrium solubility curve,ES, in Figure
5.17. The freezing curve, FE, shows the variation of
freezing point as a function of temperature. Aqueous
solution is in equilibrium with ice Ih along FE. At
the eutectic point,E, the intersection of the solubil-
ity and freezing curves, solids Ih and sucrose coexist
with a saturated solution. The eutectic point is the
lowest melting point of water-sugar solutions. How-
ever, viscous aqueous sugar solutions or syrups may
exist beyond the eutectic point. These conditions
may be present in freezing and tempering (thawing)
of food.
Dry sugar is stable, but it spoils easily if it con-
tains more than 5% water. The changes that occur as
a sugar solution is chilled exemplify the changes in
some food components when foods freeze. Ice Ih
forms when a 10% sugar solution is cooled below
the freezing point. As water forms Ih, leaving sugar
in the solution, the solution becomes more concen-
trated, decreasing the freezing point further along
the freezing curve (FE) towards the eutectic point
(E). However, when cooled, this solution may not
reach equilibrium and yield sugar crystals at the
eutectic point. Part of the reason for not having