BLBS102-c05 BLBS102-Simpson March 21, 2012 12:2 Trim: 276mm X 219mm Printer Name: Yet to Come
5 Water Chemistry and Biochemistry 101soup and gravy, and starch is added to food for desirable tex-
ture and appearance. Water increases the molecular mobility of
starch, and starch slows the movement of water molecules. Food
processors are interested in a quantitative relationship between
water and starch and the viscosity of the suspension.
Glycogen, animal starch, is easily hydrolyzed to yield glu-
cose, which provides energy when required. In the hydrolysis of
polysaccharides, water molecules react at the glycosidic links.
Certain enzymes catalyze this reaction, releasing glucose units
one by one from the end of a chain or branch.
Polysaccharide chains in cellulose are very long, 7000–15,000
monosaccharides, and interchain hydrogen bonds bind them into
fibers, which further stack up through interfiber hydrogen bonds.
Many interchain hydrogen bonds make the penetration of water
molecules between chains a time-consuming process. Heating
speeds up the process.Water, Minerals, and VitaminsMost minerals are salts or electrolytes. These are usually in-
gested as aqueous solutions of electrolytes, discussed earlier.
Ions (Ca^2 +,Mg^2 +,Na+,K+,Fe^2 +,Zn^2 +,Cu^2 +,Mn^2 +,Cl−,I−,
S^2 −,Se^2 −,H 2 PO 4 −, etc.) present in natural water are leached
from the ground. Some of them are also present in food, be-
cause they are essential nutrients for plants and animals that
we use as food. A balance of electrolytes in body fluid must
be maintained. Otherwise, shock or fainting may develop. For
example, the drinking water used by sweating athletes contains
the proper amount of minerals. In food, mineral absorption by
the body may be affected by the presence of other molecules.
For example, vitamin D helps the absorption of calcium ions.
Small amounts of a group of organic compounds not syn-
thesized by humans, but essential to life, are called vitamins;
their biochemistry is very complicated and interesting; many
interact with enzymes, and others perform vital functions by
themselves. Regardless of their biological function and chem-
ical composition, vitamins are divided into water-soluble and
fat-soluble groups. This division, based on polarity, serves as a
guide for food processing. For example, food will lose water-
soluble vitamins when washed or boiled in water, particularly
after cutting (Hawthorne and Kubatova 2002).
The water-soluble vitamins consist of a complex group of
vitamin Bs, vitamin C, biotin, lipoic acid, and folic acid. These
molecules are either polar or have the ability to form hydrogen
bonds. Vitamins A (retinal), D2, D3, E, and K are fat soluble,
because major portions of their molecules are nonpolar organic
groups.
Vitamin C,l-ascorbic acid or 3-oxo-l-gulofuranolactone, has
the simplest chemical formula (C 6 H 8 O 6 ) among vitamins. This
diprotic acid is widely distributed in plants and animals, and
only a few vertebrates, including humans, lack the ability to
synthesize it.
Vitamin B complexis a group of compounds isolated together
in an aqueous solution. It includes thiamine (B1), riboflavin (B2),
niacin (or nicotinic acid, B3), pantothenic acid (B5), cyanocobal-
amin (B12), and vitamin B6 (any form of pyridoxal, pyridoxine,
or pyridoxamine). Biotin, lipoic acid, and folic acid are alsopart of the water-soluble vitamins. These vitamins are part of
enzymes or coenzymes that perform vital functions.FOOD CHEMISTRY OF WATER
Water ingestion depends on the individual, composition of the
diet, climate, humidity, and physical activity. A nonexercising
adult loses the equivalent of 4% of his or her body weight in
water per day (Brody 1999). Aside from ingested water, water
is produced during the utilization of food. It is probably fair to
suggest that food chemistry is the chemistry of water, since we
need a constant supply of water as long as we live.
Technical terms have special meanings among fellow food
scientists. Furthermore, food scientists deal with dynamic and
nonequilibrium systems, unlike most natural scientists who deal
with static and equilibrium systems. There are special concepts
and parameters useful only to food scientists. Yet, the funda-
mental properties of water discussed above lay a foundation for
the food chemistry of water. With respect to food, water is a
component, solvent, acid, base, and dispersing agent. It is also
a medium for biochemical reactions, for heat and mass transfer,
and for heat storage.
Food chemists are very concerned with water content and its
effects on food. They need reliable parameters for references,
criteria, and working objectives. They require various indicators
to correlate water with special properties such as perishability,
shelf life, mobility, smell, appearance, color, texture, and taste.Water as a Common Component of FoodWater is a food as well as the most common component of
food. Even dry foods contain some water, and the degree of
water content affects almost every aspect of food: stability, taste,
texture, and spoilage.
Most food molecules contain OH, C O, NH, and polar
groups. These sites strongly interact with water molecules by
hydrogen bonding and dipole-dipole interactions. Furthermore,
dipole-ion, hydrophilic, and hydrophobic interactions also occur
between water and food molecules. The properties of hydrogen-
bonded water molecules differ from those in bulk water, and
they affect the water molecules next to them. There is no clear
boundary for affected and unaffected water molecules. Yet it
is convenient to divide them intobound waterandfree water.
This is a vague division, and a consensus definition is hard to
reach. Fennema and Tannenbaum (1996) give a summary of var-
ious criteria for them, indicating a diverse opinion. However, the
concept is useful, because it helps us understand the changes that
occur in food when it is heated, dried, cooled, or refrigerated.
Moreover, when water is the major ingredient, interactions with
other ingredients modify the properties of the water molecules.
These aspects were discussed earlier in connection with aqueous
solutions.Water ActivityInteractions of water and food molecules mutually change their
properties. Water in food is not pure water. Water molecules in