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| Fig. 128 : Properties of emulsifiers in bread baking |
It has been shown that the flour's own polar lipids – mainly
phospholipids (lecithin) and galactolipids already have a positive effect on
the volume yield (MacRitchie and Gras, 1973).
 |
| Fig. 129 : Effect of wheat lipids on volume yield of defatted wheat flour (modif. from MacRitchie and Gras, 1973) |
Flour from which all lipids had been extracted only showed an
improvement in volume yield when the polar lipids (or all lipids) were readded,
but not with non-polar lipids (i.e. oil) alone (Fig. 129).
 |
| Fig. 130 : Formation of lipoprotein complexes by emulsifiers |
It is probable that all emulsifiers build complexes with gluten, as
shown in Fig. 130 for lecithin. On the one hand they increase the binding
forces between the protein chains, but on the other hand they act as a kind of
lubricant, improving the gliding of the protein layers over each other.
Some emulsifiers with long non-polar, linear chains, such as
monoglycerides, form complexes with starch, preventing the
recrystallization of the gelatinized starch upon storage and thus prolonging
shelf-life.
1. Lecithin as a emulsifier
Bakers, especially, have been familiar with lecithin longer than with
any other emulsifier.
At first it was mainly the effect of lecithin from egg
yolk that was used to distribute large amounts of fat evenly in the product and
achieve a finer crumb and higher baked volume, but now concentrated lecithin
from soybeans is available for this purpose.
In its deoiled form it is also
well suited for use in mills. The most obvious benefit of lecithin is probably
the noticeably reduced stickiness of the dough; bound up with this is better
machinability, that is also a result of greater smoothness.
The interaction of
lecithin with the starch and its ability to bind water also prolong the
shelf-life of the crumb. Lecithin also has a positive effect on volume yield,
but in this respect it tends to fall behind synthetic emulsifiers such as
diacetyl tartaric esters of mono- and di-glycerides (DATEM).
A consumer trend
towards slightly lower volume yields observed in some parts of Europe is likely
to increase the use of lecithin again, if the problem with raw material from
genetically modified (GM) organisms is finally solved.
There are already
effective IP 29 systems for sourcing non-GM soybean lecithin.
Moreover, lecithin fractions are available that offer the advantage of being
natural emulsifiers with properties specially adjusted to specific
applications.
There is a fraction with a very low HLB30 value
(hydrophobic) and one with a very high HLB (hydrophilic); this makes one more
suitable for emulsification of water in oil and the other for emulsification of
oil in water.
The dosage of lecithin for flour treatment is in the range of 30 - 150
g to 100 kg of flour. Such low doses mainly have the effect of improving the
processing characteristics of the dough, whereas a considerably larger dose
increases the stability of the dough, crumb structure, fermentation tolerance,
and shelf-life.
Note :
29 IP = Identity Preservation. IP is an active process in which actions are taken to preserve the identity of a higher value product as it moves through the chain to a specific end market. Keeping apart or segregating raw materials is one of the consequences of applying an IP system. Consumer demand for non-GM or GM free food provides an economic incentive for farmers, processors and distributors to supply such products, which require IP to be accepted by the consumer (modif. from Codex Alimentarius Commission, 2001).
30 HLB = hydrophilic-lipophilic balance; the theoretical values of HLB range from 1 to approximately 50. The more hydrophilic emulsifiers have HLB values greater than 10, while the more lipophilic emulsifiers have HLB values from 1 to 10. As a general rule, emulsifiers with HLB values in the range of 4 to 6 promote water-in-oil emulsions; values between 8 to 18 promote oil-in-water emulsions.
2. Mono- and Diglycerides as a emulsifier
Mono- and diglycerides are produced by splitting off a single or two
fatty acids from edible fats and oils. By selecting the fatty acids remaining
on the glycerol backbone it is possible to produce emulsifiers with greatly
differing properties.
For flour treatment there is mainly a demand for the
mono- and diglycerides with good anti-staling properties. These are attributed to linear,
saturated fatty acids that interact well with starch and thus slow down the
staling process.
The best monoglyceride for this purpose is glycerol
monostearate (GMS). Although GMS and other mono- or diglycerides show their
best functionality when hydrated, i.e. as paste, and can therefore only be used
in the bakery, they are also suitable for use in milling when in a fine powder
form.
The large surface: volume ratio results in fast hydration, and thus
almost the same efficacy.
In other respects, too, these emulsifiers have similar effects to
lecithin, namely a finer crumb and a greater volume yield. With fatrich
products, especially, the dose required may be up to 1% of the flour.
In many cases it is possible to enhance the properties of an emulsifier by combining it with another emulsifier. An example of this is the mono- and diglycerides, that achieve their optimum suitability for use in flour treatment through combination with lecithin.
The lecithin improves their solubility and dispersion, and clearly their interaction with constituents of the flour as well.
Well-known and widely used organic flour improvers fall into this category. The combination makes it possible to reduce the dose necessary for optimum effect to 100 - 300 g with 50% emulsifier in the complex.
Diacetyl tartaric esters of mono- and diglycerides are also receptive to enhancement with lecithin: the addition of as little as 10% lecithin improves their emulsifying effect and also reduces the vinegar smell.
The above combinations are only effective if the emulsifiers are mixed before being converted into their powdered form. Interestingly, it is not sufficient just to mix the individual powdered components.
4. Diacetyl Tartaric Acid Esters of Mono- and Diglycerides (DATEM) as a emulsifier
One very effective group of emulsifiers in respect of volume yield is mono- and diglycerides of edible fats esterified with mono- and diacetyl tartaric acid. DATEM is a heterogeneous mixture of molecules derived from esterification of acetic acid, tartaric acid and fatty acids (bound to glycerol).
Some of the resulting emulsifier molecules are more active than others. The structures shown in Fig. 131 were the most efficient in bread baking trials (Köhler, 1999). Both molecules were derived from glycerol monostearate.
But most probably the other molecules do have a co-emulsifying effect, which means that the mix is more effective than a single, purified emulsifier.
DATEM is one of the main constituents of most baking improvers, especially when the aim is to produce voluminous baked goods with a crisp crust. DATEM is not often used in flour treatment; its main application is in bread improvers utilized in bakeries.
The optimum dose is about 300 - 400 g to 100 kg, but for reasons of cost the dosage is often reduced to as little as 150 g.
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| Fig. 131 : Hypothetical structure of the most baking-active components of DATEM |
5. Sodium and Calcium Stearoyllactylate (SSL and CSL) as a emulsifier
These emulsifiers are made from the fatty acid stearic acid esterified with a double ester of lactic acid. The remarks concerning DATEM also apply to these, but with the difference that SSL and CSL are especially suitable for baked goods with a soft crust.
Furthermore, they have a better effect on the retention of crumb softness.
6. Other Emulsifiers
Tab. 92 summarizes the emulsifiers suggested for baking. Sucrose esters seem to be interesting since they are produced in a wide range of HLB (hydrophilic or lipophilic).
The high-HLB variants, especially, have a good effect on volume yield and crumb structure at quite low dosages, but the price is still much higher than that of conventional baking emulsifiers.
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