The chemistry of croissants

Crosslinking in food

One of the characteristics that food manufacturers are interested in controlling is food texture – what it feels like to eat. This can be changed by altering the amount of crosslinking in the food. The crosslinks are made between the protein molecules in the food.

Crosslinking is a normal part of food processing, and affects the way the food holds together. Food that does not contain crosslinking will crumble and fall apart. Sausages, jelly beans and pastries all contain crosslinking.

Crosslinking used be done using a chemical called potassium bromate. However, this was linked with cancer, and is no longer allowed as a food ingredient. Ascorbic acid (vitamin C) can also be used, but the crosslinking reaction causes a shape change which means that it no longer acts as a vitamin in the finished loaf. Also, oxygen is required in order for ascorbic acid to act as an effective crosslinker, and this means that the product needs to made with a lot of vigorous mixing to allow for adequate aeration. That’s why bread dough has to be kneaded for such a long time.

It is also a challenge to get the amount of crosslinking ‘just right’. Too little, and you don’t get any of the advantages. Too much, and you end up with a product that is a bit like microwaved breadrolls – chewy and horrible.

Transglutamanase: An enzyme crosslinker?

Transglutamanase (TGA) is an enzyme known to cause crosslinks in proteins, although it works on slightly different parts of the protein molecules than chemical additives that are currently used. It also does not need oxygen to be effective. This means that the problem of aeration during food processing can be by-passed, resulting in a cheaper, more efficient manufacturing process. Also, the enzyme is inactivated during the baking process, meaning that the amount of the crosslinking reaction can be more carefully controlled.

Another advantage is that there is a perception among consumers that enzymes are more ‘natural’ than some of the chemical additives that are sometimes used. Because they are catalytic, you also don’t need so much of them in order to have the same effect.

Laboratory experiments

Laboratory experiments testing the effects of TGA on breads and croissants were very exciting. The photograph below shows the dramatic effects of TGA on croissant pastry. The puffiness was also maintained when the pastry was frozen. This is important for markets like Japan, which buy a huge number of New Zealand croissants.

TGA also improved the ‘crumb strength’ of pastry and breads. Crumb strength refers to the way bread and pastry holds itself together (bread that breaks when you spread butter on it has low crumb strength).

Another advantage is that the dough didn’t require as much mixing. This is measured using a bread mixer which can monitor the amount of energy that has been used to mix a dough to its optimal consistency. Commercial bakers get very excited by any new ingredient that can lower the amount of energy needed to mix a dough, as this saves them a lot of money on their power bill.

The experiments look good. Now what?

The next step would be for a food industry to consider ways in which the laboratory experiments can be up-scaled for commercial production. There are also a whole range of regulatory controls that need to be met. This is currently managed by Food Standards Australia New Zealand. Taste-testing and consumer testing would also require regulatory approval.

Before this story finishes, there are some important lessons to consider.

Lesson 1: Check for what you don’t expect to see

Experimental results looked very exciting. The TGA enzyme caused specific changes to the dough: crumb strength improved and pastry volume increased. It also appeared that TGA could be incorporated into an industrial process relatively easily, replacing some of the chemical crosslinking agents that are currently used.

However, understanding all the chemical reactions that take place in food is a big challenge. In this case, TGA does not only catalyse a crosslinking reaction between specific protein components. It may also change some of the amino acids in the proteins. Specifically, the amide side-group (CONH₂) of glutamines are changed into acidic groups (COOH). It was not clear what effect these other ‘side-reactions’ might have.

Lesson 2: Side reactions can be important

Coeliac disease is a chronic inflammation of the intestines. Medical reports suggest that TGA found naturally in the intestines may act as a ‘trigger’ for the disease in some people. Research has shown that the action of intestinal TGA changes wheat proteins that have been eaten. This change in a specific part of the wheat protein triggers an immune response in some people and causes inflammation.

It is possible that if TGA is used to modify bread products, it will cause the same protein changes in the wheat used to make the bread or pastry. This could mean that wheat products made with TGA may be extremely harmful for people who have coeliac disease. Although there is currently no experimental evidence suggesting that products baked in the presence of TGA exacerbate or trigger symptoms of coeliac disease, more tests are needed.

Since the coeliac response seems to be specific to certain cereal grains, there is no reason to suppose that TGA in other products (e.g. tofu, fish products) presents a risk to consumers.

Lesson 3: Regulation is important

In New Zealand, all new food ingredients need to be approved by Food Standards Australia New Zealand. This group is responsible for developing standards for food manufacturing, labelling, processing, and primary production; providing information to consumers to enable better consumer choice; coordinating national food surveillance, enforcement, and food recall; and undertaking risk assessments.

As a result of the questions raised about TGA, wheat products and coeliac disease, the baking industry has put on hold their investigation of the use of TGA to improve baked products and the Food Standards Authority has been notified of the potential risk of using this enzyme.

The final count-down

Some ingredients have potential to do some amazing things in foods, but if they are not safe then there is no point in pursuing their use. It is really important to do a complete safety check before taking a new ingredient to the marketplace.