2.7. Zymoexpansiometer (ZEM)
A treatise by De Leyn and Vanneste (2003) appeared just in time to be considered in this chapter. It deals with an instrument designed for testing fermenting doughs. The authors have given the instrument a name that goes back to the old term for the complex of fermenting enzymes, namely zymase. It is also reminiscent of the mode of action of a similar device, the Zymatograph.

Cereal chemists have long been seeking a way to monitor rheological processes in fermenting doughs, which presents a considerable challenge. An overview of the instruments used for this in the past, such as the Chopin Rheofermentometer, the Brabender Maturograph and the Brabender Oven Rise Recorder, appeared a number of years ago (Brümmer, 1990). But these instruments mainly measure the development of volume, i.e. gas formation properties, and are less able to take changes in dough viscosity or gas retention into account. Nevertheless, the Rheofermentometer and the Maturograph have provided researchers with very important information in this field too. So it is not surprising that the basic principles of these earlier devices were included in the development of this new instrument.

The ZEM instrument measures changes in a dough over a certain period; the fermentation temperature, composition of the dough and pressure in the measuring chamber can be modified. In order to come closer to the dough processes usual in practice, these pressure alterations simulate the degassing that takes place in the punching of a dough. Ultimately, the aim of the measurements is to bring the measured volume of the dough as close as possible to the baked volume of products made from the same doughs.

As with the Brabender Oven Rise Recorder (ORR), the measurements are made with doughs enclosed in a basket and brought to the desired temperature by submerging in an oil bath. The ZEM curves are very similar to those of the ORR. The most important factor influencing measurements with the ORR is the time at which oil penetrates the dough specimen, thus greatly altering the properties of the dough. However, this point is not discussed in the treatise on the ZEM.

The ZEM can operate at normal pressure or at slight negative pressure and record the changes in dough volume that occur. The measurements are made in several stages, for example they may start by determining fermentation times at atmospheric pressure, followed by degassing of the dough at slight negative pressure in the measuring chamber and finally monitoring of one or several fermentation cycles.

Besides the volume of the dough, the resulting curves show its expansion and resistance. The fully automatic instrument has so far been used to test different wheat flour qualities, different dough yields, different types and doses of baker's yeast, different mixing and kneading processes and also different flour improvers. The fermentation time and a specific dough volume are selected as target values and compared with the fermentation times and/or baked volumes determined in baking trials. According to the authors, the correlations between the ZEM and baked volume are good (r = ± 0.9); the correlations between the ZEM volume and the protein content of wheat flour and the sedimentation value after Zeleny are also within the usual ranges of r = 0.5 to 0.7.

The ZEM instrument and the suggested testing method are intended to simulate fermentation of the dough, including degassing processes. From the results, De Leyn and Vanneste draw the conclusion that rheological tests on non-fermenting doughs are practically worthless for assessing the rheological properties of doughs leavened with baker's yeast. They therefore regard the results of the ZEM as particularly valuable, for example since they make it possible to monitor various flour qualities and the way they are treated, the quantity of yeast of a particular quality and various methods of mixing. Besides the rising power itself, the effect of these parameters on the properties of a dough is shown. But all these factors also influence doughs tested with the methods used in the past. The future will show whether the Zymoexpansiometer has real advantages. There can be no doubt that the current state of the art has advantages over the older measuring techniques.

This is surprising, since some of the studies by the author and also more recent findings (Hruskova and Kucerova, 2003) lead to different conclusions. In the past, the lack of correlation between the dough volume measured by instruments and actual baked volume has been explained by the fact that gas formation by micro-organisms, chiefly yeast, is only partly responsible for the leavening of baked products. A further important factor is leavening by water vapour, and this has not yet been measured adequately even by heating in an oil bath.

3. New Rheological Methods and Flour Treatment
Apart from the Perten Falling Number determination FFN (See Determining the Falling Number as a Measure of α-Amylase Activity), none of these new methods has so far yielded information on the effects of flour improvers – less still on possibilities of checking them. It is however conceivable that the functional effect of active substances in flour improvers can be monitored with these new methods. Of course it is still not known how far all or some of the effects of modern flour treatment, in particular correction of the oxidative or reductive or enzymatic potential, changes to the pH or the addition of minerals with a buffering effect can be detected and monitored. But the possibility that these methods will in future provide useful assistance and information in this field cannot be excluded. Indications that this is so are to be found in the principles on which they work, for example:


• their relevance to baking, which is already obvious;
• the amounts of extracted flours or meal used in relation to the water added (dough yield), which are certainly in line with normal bakery practice;
• their practical pH ranges, and
• their temperature gradients, which are similar to those either of dough or of the baking process.

At present this seems most likely in the case of the new analytical methods such as the Gluten Aggregation Test and the Rye Viscosity Test, since these directly investigate those complexes that have to do with modern flour improvement. In the GAT these are gluten formation capacity and the behaviour of wheat gluten, for example in the presence of additives with an oxidative/ reductive or enzymatic effect. In the RVT, too, it should be possible to detect all influences with a direct effect on the viscosity of the suspension. All in all, these new methods and developments open up additional possibilities, especially in the control of flour treatment.

<<<Previous Page

Modern Cereal Analysis by New Rheological Methods:

Post a Comment

Previous Post Next Post