2009_Book_FoodChemistry

716 15 Cereals and Cereal Products
15.4.1.3 Storage
Rye flour acquires optimal baking properties after
1–2 weeks of storage after milling. Wheat flour
requires 3–4 weeks. This storage period is the
flour “maturation time”. In wheat the time is needed
for oxidative processes to occur and thus provide
a stronger (shorter) gluten. In this time, the
concentrations of endogenous glutathione (GSH,
GSSG), which reduces the stability of gluten in
dough making (cf. 15.2.3), and PSSG decrease,
the rate depending on the wheat cultivar.
Flour with a moisture content of <12% may be
stored at 20 ◦ C and a relative humidity of <70%
for more than 6 months without significant
change in baking quality.
Flour fumigation with Cl 2 ,ClO 2 ,NOCl,N 2 O 4
or NO, or treatment with dibenzoyl or acetone
peroxide results in carotenoid destruction. The
flour becomes bleached. Other reactions, not yet
elucidated, are involved with Cl 2 ,NOCl,ClO 2
and acetone peroxide treatment since they
provide simultaneous improvement in baking
quality of flours which have weak gluten.
15.4.1.4 Influence of Additives/Minor
Ingredients on Baking Properties
of Wheat Flour
The baking properties of wheat flours differ
widely (cf. Table 15.41). In small traditional
plants, a baker can use his experience to compensate
for changes in the quality of raw materials:
flexibility in formulations, dough handling and
baking – all these parameters can be adjusted in
order to obtain the desired end-product.
In a large-scale automated bakery, economic production
demands uniform raw materials with uniform
properties. Additives are used when necessary
to adjust the flour characteristics to match
the baking process (for instance, shortened dough
handling time with low energy input). Additives
are also used to ensure that the end-product meets
existing standards. Incorporation of ascorbic acid,
alkali bromates or enzyme-active soy flour improves
the quality of weak gluten flour – e. g., in
bread or bun baking. In these cases the dough becomes
drier and there are increases in dough resistance
to extension, mixing tolerance and fermentation
stability. In addition, baking volume
will increase and the crumb structure will improve.
Ascorbic acid and lipoxygenase require
oxygen for their actions; hence their beneficial
role is very dependent on the intensity of dough
mixing, which traps oxygen from the air.
In contrast, opposite effects may be observed by
adding cysteine or proteinases, the result being
gluten softening. Biscuits are made from such
mellowed, softened doughs, which are made with
little energy input. Additives which affect the
rheological quality of the dough and/or the
quality of baked products include emulsifiers,
shortenings, salt, milk, soy flour, α-amylase and
proteinase preparations and starch syrups.
15.4.1.4.1 Ascorbic Acid
The improver effect of ascorbic acid (Asc)
was recognized by Jorgensen as early as 1935.
He found that small amounts (2–10 g Asc per
100 kg flour) caused an improvement in flour.
The dough becomes stronger (Fig. 15.31)
and drier and the bread volume increases in
most cases. The oxidation product of Asc,
dehydroascorbic acid (DHAsc) is also effective
(Table 15.42), but its use would be uneconomical.
In the example in Fig. 15.31, the addition of
40 mg/kg of Asc has a greater strengthening
effect on dough than 20 mg/kg. A further increase
in Asc to 80 or even 160 mg/kg no longer
increases the effect. But in comparison with
Fig. 15.31. Rheological properties of wheat dough as
a function of different concentrations of added L-threoascorbic
acid (Asc) (according to Kieffer, unpublished).
Tensile tests with dough made of 10 g of flour of the
variety Flair. Addition of Asc (mg/kg): 20 ◦–◦), 40 (•–
•), 80 and 120 (–), 160 (Δ–Δ). Control without additive:
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