2 Analytical Techniques 29individual carbohydrates. Earlier methods, which
included paper chromatography, open column chro-
matography, and thin-layer chromatography, have
largely been replaced by HPLC and/or gas chro-
matography (Peris-Tortajada 2000). Gas chromatog-
raphy has been established as an important method
in carbohydrate determinations since the early
1960s (Sweeley et al. 1963, Peris-Tortajada 2000),
and several unique applications have since then been
reported (El Rassi 1995).
For carbohydrates to be analyzed by gas chro-
matography, they must first be converted into vol-
atile derivatives. Perhaps the most commonly used
derivatizing agent is trimethylsilyl (TMS). In this
procedure, the aldonic acid forms of carbohydrates
are converted into their TMS ethers. The reaction
mixtures are then injected directly into the chro-
matograph, and temperature programming is uti-
lized to optimize the separation and identification of
individual components. A flame ionization detector
is still the detector of choice for carbohydrates. Un-
like gas chromatography, HPLC analysis of carbo-
hydrates requires no prior derivatization of carbohy-
drates and gives both qualitative (identification of
peaks) and quantitative information for complex
mixtures of carbohydrates. HPLC has been shown to
be an excellent choice for the separation and analy-
sis of a wide variety of carbohydrates, ranging from
monosaccharides to oligosaccharides. For the analy-
sis of larger polysaccharides, a hydrolysis step is
required prior to chromatographic analysis. A vari-
ety of different columns can be used, with bonded
amino phases used to separate carbohydrates with
molecular weights up to about 2500, depending up-
on carbohydrate composition and, therefore, solubil-
ity properties (Peris-Tortajada 2000). The elution
order on amine-bonded stationary phases is usually
monosaccharide and sugar alcohols followed by dis-
accharides and oligosaccharides. Such columns have
been successfully used to analyze carbohydrates in
anything from fruits and vegetables all the way to
processed foods such as cakes, confectionaries, bev-
erages, and breakfast cereals (BeMiller and Low
1998). With larger polysaccharides, gel filtration be-
comes the preferred chromatographic technique, as
found in the literature. Gel filtration media such as
Sephadex® and Bio-Gel® have been successfully
used to characterize polysaccharides according to
molecular weight.
MINERAL ANALYSIS
Minerals are extremely important for the structural
and physiological functioning of the body. It has
been estimated that 98% of the calcium and 80%
of the phosphorous in the human body are bound
up within the skeleton (Hendricks 1998). Those
minerals that are directly involved in physiological
function (e.g., in muscle contraction) include sodi-
um, calcium, potassium, and magnesium. Certain
minerals (or macrominerals) are required in quanti-
ties of more than 100 mg per day; these include
sodium, potassium, magnesium, phosphorous, calci-
um, chlorine, and sulfur. Another 10 minerals (trace
minerals) are required in milligram quantities per
day; these include silica, selenium, fluoride, molyb-
denum, manganese, chromium, copper, zinc, iodine,
and iron (Hendricks 1998). Each of the macro- and
trace minerals has a specific biochemical role in
maintaining body function and is important to over-
all health and well-being.
Although minerals are naturally found in most
food materials, some are added to foods during pro-
cessing to accomplish certain objectives. An exam-
ple of this is salt, which is added during processing
to decrease water activity and to act as a preservative
(e.g., pickles and cheddar cheese; Hendricks 1998).
Iron is added to fortify white flour, and various other
minerals such as calcium, iron, and zinc are added to
various breakfast cereals. In fact, salt itself is forti-
fied with iodine in North America in order to control
goiter.
It should also be noted that food processing can
decrease the mineral content (e.g., the milling of
wheat removes the mineral-rich bran layer). During
the actual washing and blanching of various foods,
important minerals are often lost. It can therefore be
concluded that accurate and specific methods for
mineral determination are in fact important for nu-
tritional purposes as well as for properly processing
food products for both human and animal consump-
tion.
In order to determine the total mineral content of
a food material, the ashing procedure is usually per-
formed. Ash refers to the inorganic residue that re-
mains after ignition, or in some cases complete oxi-
dation, of organic material (Harbers 1998). Ashing
can be divided into three main types: (1) dry ashing
(most commonly used); (2) wet ashing (oxidation),