2009_Book_FoodChemistry

706 15 Cereals and Cereal Products
Table 15.33. Tocopherol content of parts of the wheat
kernel
Part of kernel Tocopherols in mg/kg
α-T β-T α-T-3 β-T-3
Germ 256 114 n.d. n.d.
Aleurone layer 0.5 n.d. 10 69
Endosperm 0.07 0.10 0.45 13.5
n.d., not detectable.
The composition of the tocopherols of wheat (Table
15.33) shows that the proportions of germ and
aleurone lipids in nonstarch lipids can be determinedbyusingβ-T
and β-T-3 as markers. Values
of ca. 25% have been found, but they can fluctuate
greatly depending on the milling process and
extraction grade.
Fig. 15.21. Absorption of ground wheat in the near IR
region. Sample dried (–·–·–) and with 9 w/w%water
(—–)
15.3 Cereals – Milling
15.3.1 Wheat and Rye
Quality control of the raw materials and milling
products usually includes the determination of
water, protein, and minerals. The absorption
bands of food in the near infrared region (0.8–
2.6 µm) are suitable for a quick basic analysis
(water, protein, fat, carbohydrates etc.).
The overtones of CH, OH, and NH valence vibrations
appear in the near IR region. Therefore,
foods give a large number of absorption bands
that can be assigned to definite components and
have intensities that correlate with the amounts of
the constituents. As an example, Fig. 15.21 shows
the absorption of wheat in the near IR region.
The sample containing water absorbs at 1.94 µm
in addition. Therefore, after subtraction of the
absorption of dried wheat and after calibration,
the water content can be determined. Other consituents
which can be determined in food by nearinfrared
(NIR) spectrophotometry are listed in Table
15.34.
In the development of methods for these materials,
the measurement of IR reflection was at first
given the most attention because it is technically
Table 15.34. Examples of quantitative analysis of foods
by near-infrared (NIR) spectrophotometry
Component
Water
Protein
Fat
Minerals
Starch
Pentosans
β-Glucans
Lysine
Food
Meat, cereals, control of fruit and
vegetable drying processes,
chocolate, coffee
Meat, cereals, milk and milk
products
Meat, cereals, milk and milk
products, oil seeds
Cereals, meat
Cereals
Wheat
Barley
Wheat, barley
easier to perform. Since reproducible results can
be obtained only if the surface and granulation of
the samples are constant, sources of error arise
here. In the meantime, however, technical improvements
allow food, e. g., cereal kernels, to be
irradiated in the range of 0.8–1.1 µm. Thus, the
water and protein content in unground samples
can also be determined by measuring the transmission.
In food technology, measurements in the
near IR region are widely used for the quick quality
control of raw materials (Table 15.34).