Food Chemistry

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 .5n.d. 10 69
Endosperm 0 .07 0.10 0.45 13. 5

n.d., not detectable.

The composition of the tocopherols of wheat (Ta-
ble 15.33) shows that the proportions of germ and
aleurone lipids in nonstarch lipids can be deter-
minedbyusingβ-T andβ-T-3 as markers. Values
of ca. 25% have been found, but they can fluctu-
ate greatly depending on the milling process and
extraction grade.

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 vi-
brations 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 con-
situents which can be determined in food by near-
infrared (NIR) spectrophotometry are listed in Ta-
ble 15.34.
In the development of methods for these materi-
als, the measurement of IR reflection was at first
given the most attention because it is technically

Fig. 15.21.Absorption of ground wheat in the near IR

region. Sample dried (–·–·–) and with 9 w/w%water

(—–)

Table 15.34.Examples of quantitative analysis of foods

by near-infrared (NIR) spectrophotometry

Component Food

Water Meat, cereals, control of fruit and

vegetable drying processes,

chocolate, coffee

Protein Meat, cereals, milk and milk

products

Fat Meat, cereals, milk and milk

products, oil seeds

Minerals Cereals, meat

Starch Cereals

Pentosans Wheat

β-Glucans Barley

Lysine 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 im-

provements 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 trans-

mission. In food technology, measurements in the

near IR region are widely used for the quick qual-

ity control of raw materials (Table 15.34).