BLBS102-c02 BLBS102-Simpson March 21, 2012 11:54 Trim: 276mm X 219mm Printer Name: Yet to Come
2 Analytical Techniques in Food Biochemistry 31nerve function), digestion (stomach acid production), and hor-
mone production (thyroxine), just to name a few. It has been
estimated that 98% of the calcium and 80% of the phosphorous
in the human body are bound-up within the skeleton (Hendriks
1998). Those that are directly involved in physiological func-
tion (such as in muscle contraction) include sodium, calcium,
potassium, and magnesium.
Most minerals (calcium, chloride, cobalt, copper, iodine,
iron, magnesium, manganese, molybdenum, nickel, phospho-
rous, potassium, selenium, sodium, sulfur, and zinc) are consid-
ered to be essential nutrients in the classical sense as they are
needed for physiological functions and must be obtained from
dietary sources. Additionally, there is a much smaller group of
minerals (arsenic, boron, chromium, and silicon) that have a
speculated role in human health, but their roles have not been
conclusively established, yet. Some minerals are referred to as
macro-minerals as they are required by humans in amounts
greater than 100 mg per day, including sodium, potassium, mag-
nesium, phosphorous, calcium, chlorine, and sulfur. A further
ten minerals are classified as micro or trace minerals as they
are required in milligram quantities per day, including silica,
selenium, fluoride, molybdenum, manganese, chromium, cop-
per, zinc, iodine, and iron (Hendriks 1998). In humans, both the
macro- and micro- minerals can contribute to disease develop-
ment in either excessive or deficient amounts.
Although many minerals are naturally found in most raw food
sources, some are added to foods during processing for different
purposes. An example of this is the addition of salt (sodium) dur-
ing processing to decrease water activity and to act as a preserva-
tive, for example, pickles and cheddar cheese (Hendriks 1998).
It should also be noted that food processing can also cause a de-
crease in the mineral content, for example, the milling of wheat
removes the mineral-rich bran layer. During the actual washing
and blanching of various foods, important minerals are often
lost in the water. It can therefore be concluded that accurate and
specific methods for mineral determination are in fact important
for nutritional purposes as well as in properly processing food
products for both human and animal consumption.
Many countries have laws specifying which minerals must
be added to specific foods in legally specified amounts and
forms. Iron is added to fortify white flour and various other
minerals, including calcium, iron, and zinc, are added to vari-
ous breakfast cereals. In North America, salt itself is fortified
with iodine to inhibit the development of goiter. Additionally,
minerals are affected by legal considerations. A food’s nutri-
tion label must declare the mineral content of the food in certain
cases, such as baked goods. In some countries such as the United
States, the link between a mineral in specified amounts and its
health effects is permitted, whereas in countries such as Canada,
legally predetermined statements may be put on the food product
packaging.
To determine the total mineral content in a food, the ashing
procedure is usually the method of choice. The word “ash” refers
to the inorganic residue that remains after either ignition or, in
some cases, complete oxidation of the organic material (Harbers
1998). Ashing can be divided into three main types—dry ashing
(most commonly used), wet ashing (oxidation) for samples witha high fat content such as meat products or for preparation for
elemental analysis, and plasma ashing (low temperature) when
volatile elemental analysis is conducted.
In dry ashing, food samples are incinerated in a muffle furnace
at temperatures of 500–600◦C. During this process, most miner-
als are converted to either oxides, phosphates, sulfates, chlorides,
or silicates. Unfortunately, some minerals such as mercury, iron,
selenium, and lead may be partially volatized using this high-
temperature procedure. Wet ashing involves the use of various
acids that oxidize the organic materials while the minerals are
subsequently solubilized without volatilization. Nitric or per-
chloric acids that are often used along with reagent blanks are
carried throughout the entire procedure and then subtracted from
sample results. In the low-temperature plasma ashing, the food
sample is treated in a similar manner as in dry ashing but under a
partial vacuum, with samples being oxidized by nascent oxygen
formed by an electromagnetic field.
Although the above three ashing methods have been proven
to be adequate for quantifying the total amount of minerals in
a sample, they do not possess the ability to differentiate nor to
quantify the actual mineral elements in a food sample. Atomic
absorption spectrometers became widely used in the 1960s and
1970s and paved the way for measuring the presence and trace
amounts of minerals in various biological samples (Miller 1998).
Essentially, atomic absorption spectroscopy is an analytical tech-
nique based on the absorption of UV or visible radiation by free
atoms in the gaseous state. However, the sample must first be
ashed and then diluted in weak acid. The solution is then at-
omized into a flame. According to Beer’s law, the absorption is
directly related to the concentration of a particular element in
the sample.
Atomic emission spectroscopy differs from atomic absorption
spectroscopy in that the source of the radiation is in fact the
excited atoms or ions in the sample rather than an external source
has in part taken over. Atomic emission spectroscopy does have
the advantages with regard to sensitivity, interference, and multi-
element analysis (Miller 1998).
Recently, the use of ion-selective electrodes has made online
testing of the mineral composition of samples a reality. In fact,
many different electrodes have been developed to directly mea-
sure various anions and cations, such as calcium, bromide, fluo-
ride, chloride, potassium, sulfide, and sodium (Hendriks 1998).
Typically, levels as low as 0.023 pm can be measured. When
working with ion-selective electrodes, it is common procedure
to establish a calibration curve.VITAMIN ANALYSIS
Vitamins are low-molecular weight organic compounds obtained
from external sources in the diet and are critical for normal
physiological and metabolic functions (Russell 2000). Vitamins
are divided into two groups based on liquid solubility, that is,
those that are water soluble (B vitamins and vitamin C) and
those that are fat soluble (vitamins A, D, E, and K). Since the
vast majority of vitamins cannot be synthesized by humans, they
must be obtained either from food sources or from manufactured
dietary supplements.