Flour Treatment : Emulsifiers

Fig. 128: Properties of emulsifiers in bread baking

Due to their polar character, emulsifiers have interactions with most ingredients of wheat flour. Fig. 128 summarizes the effects of emulsifiers in 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
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.

2. Mono- and Diglycerides
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.

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.


Popular posts from this blog

Dough and Gluten Strength Tests

Product Tests (A Guide to Understanding Wheat and Flour Quality)

Wheat Milling Part 3 (Dampening and Tempering, The Second Cleaning Section)