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Sodium Metabisulfite (SMBS)

Sodium metabisulfite (SMBS) has been used successfully for many years to modify the characteristics of the gluten and hence dough in order to produce quality hard sweet biscuits and in some kinds of snack (savoury) crackers. However, in the recent past, there has been a tendency to omit this effective reducing agent in many recipes and processes. The following text summarizes considerations for the use and replacement of SMBS and gives an example how to reduce or omit this chemical in a given formula.

Sodium metabisulfite helped to solve a problem

In the past before the establishment of SMBS, the dough for hard (semi) sweet products Marie and Petit Beurre type had to be mixed for a long time to weaken the gluten, and then laminated in order to obtain a smooth surface of the biscuits and control their shape.

Mixing times required were as long as 30 to 60 minutes or even more, depending on the formulation, type of mixer and flour quality. Pieces of dough were laminated and folded on hand brakes and rested to relieve the stress in the dough. The use of SMBS made it possible to reduce the long mixing times When the advantages of SMBS in the formulas became apparent, its use soon became widespread. Unfortunately, it is now often being used in excess to compensate for sub-optimal processing conditions.

However much SMBS simplifies the production and reduces costs, there are drawbacks

SMBS results in products with a distinct undesirable aftertaste, a lighter colour compared, and it causes the destruction of vitamin B1. Furthermore, some persons are sensitive to SMBS (it causes them, e.g., skin rushes and headaches), and it must be declared on the packaging. Since clean labelling has become an important issue, the elimination of sodium metabisulfite from the label should be considered. Enzymes are definitively a good solution to replace SMBS.

Factors affecting the action of enzymes

In particular, proteolytic enzymes are considered for replacement of SMBS, although other enzymes may have beneficial effects on processing and baked product quality. No matter what enzyme is being used, there are factors that should be taken into account, the most important being

  • availability of water (water activity),
  • enzyme concentration,
  • enzyme specificity,
  • substrate concentration,
  • temperature,
  • pH,
  • presence of inhibitors and activators,
  • agitation.

Variations in the conditions influence the speed of the reaction. During the process of the replacement of SMBS these inherent factors may have to be compensated with the appropriate choice and the quantity of enzymes in the formula.

SMBS and enzymes have different reaction patterns

The proteolytic enzymes act randomly on the polypeptide chain of the protein – gluten in this case – and break up the long molecule (Figure 3) into shorter peptides, whereas SMBS breaks up the disulfide bonds connecting different loops of the protein without reducing the length of the molecule.

Proteolytic enzymes acting on protein

In consequence, the doughs from each reaction have somewhat different characteristics. However, this difference should not be a deterrent for the changeover from SMBS to enzymes, and an experienced dough-maker will be able to determine the optimum conditions for the application of either agent. Furthermore, enzymes – particularly combinations – offer more freedom for optimization of the process and the baked products.

Importance of temperature

The enzymatic activity in the dough varies with differences in temperature. An increase of 10 ºC will double the enzymatic activity. Therefore, the temperature must be precisely controlled within a range of 0.5 °C, if possible.

Resting time requirements

Enzymes need time to act and to give the expected results, whereas the action of SMBS is a chemical reaction that runs much faster. Dough made with enzymes needs a resting time (unless uneconomically high dosages are applied); dough with SMBS can be processed almost directly. The time enzymes need varies from about 30 to 150 minutes (including mixing). The enzymes continue to work during the resting time.

The lay or resting time is often thought of as one of the main disadvantages: Because of the additional time required as compared with SMBS, more dough tanks and space for them is needed. Although this is often the case, positive effects will prevail: During the resting time, other (including endogenous) enzymes will also be able to function. Protease forms amino acids, and amylase reducing sugars; with these two components, the Maillard reaction will be more intensive and in consequence, the colouring (browning) and the flavour improve considerably. Pentosanase will help the return dough from the cutting-machine to stay soft and have a texture similar to fresh dough with which it re-joins in the hopper, because water released from the pentosans compensates for the loss of water during dough processing and transportation.


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