Vitamin C is a flour improver that increases dough strength, reduces stickiness, and improves the crumb structure and color. Ascorbic acid is typically added to bread dough in concentrations of 0.002 to 0.02 % (20-200 parts per million) in relation to the flour weight. A popular alternative to synthetic Vitamin C is acerola cherry powder.
In many countries around the world, the flour oxidizing agent bromate is banned due to concerns that it might be a carcinogenic substance. Ascorbic acid is less effective than bromate at increasing the loaf volume but it poses no health risk. Thus it has become the default flour improver in Germany and many other places around the world.
Take a look at the figure below. It is from a study of Serbian scientists. They performed baking experiments with different spelt cultivars. Adding just 0.02 % ascorbic acid to the dough had a huge impact on the loaf volume!
The following figure is from another paper that investigated the impact of ascorbic acid on the loaf crumb and volume. The loaves of bread with ascorbic acid on the left side have a larger volume and more height than the dense “flatbreads” on the right.
How does ascorbic acid improve the dough strength?
If you’re familiar with chemistry then you might insist that Vitamin C is no oxidizing agent. Vitamin C is a reducing agent that is prone to get oxidized into dehydroascorbic acid. And that is exactly what is happening in bread dough as soon as you hydrate the flour.
Wheat flour contains endogenous ascorbate oxidase enzymes that catalyze the oxidation of ascorbic acid into dehydroascorbic acid. This reaction happens rapidly in bread dough because we incorporate plenty of oxygen into our dough when we mix it. Just a few minutes into the mixing process, all the ascorbic acid in the dough is already oxidized.
Dehydroascorbic acid reacts in the dough with the antioxidant glutathione. This reaction is catalyzed by an enzyme called glutathione dehydrogenase. The end products of this reaction are oxidized glutathione and ascorbic acid.
If there would be no dehydroascorbic acid in the dough, then the reduced glutathione would depolymerize (shorten) the gluten network. The function of dehydroascorbic acid in bread dough is to oxidize the reduced glutathione because it would otherwise get oxidized by breaking disulfide bonds when binding to the gluten proteins. Dehydroascorbic acid keeps the bad boy glutathione away from breaking disulfide gluten bonds.
The oxidized glutathione also binds to the gluten proteins but it doesn’t break any existing bonds within the gluten network. It only binds to free sulfhydryl groups of the gluten proteins. In the picture below, you can see what I just told you in a visual form.
Now you might ask yourself: Why do we add ascorbic acid and not dehydroascorbic acid to the dough? Well, both these substances improve dough strength. However, ascorbic acid does it a little better than dehydroascorbic acid. That is because the oxidation of ascorbic acid to dehydroascorbic acid has some minor positive effects on the dough strength.
The oxidation of ascorbic acid to dehydroascorbic acid possibly leads to the formation of reactive intermediates (eg. superoxide anions) that can generate sulfhydryl radicals by cleaving wheat proteins. These sulfhydryl radicals reassociate and form new intramolecular disulfide bonds between the gluten proteins. Disulfide bonds are the strongest bonds through which the gluten network is connected and are crucial for good dough strength.
What are acerola cherries?
If you’re a health-oriented person with an interest in superfoods then you might’ve heard or even tried acerola cherry extract before. Acerola (Malpighia emarginata) is a fruit that is grown in warm and tropical climates, for example in Mexico, Southern Texas, South America, the Caribbean, and India. Acerola is one of the richest natural sources of Vitamin C. The Vitamin C content of an acerola cherry is roughly 50-100 times higher than that of oranges or lemons.
Besides its exorbitant Vitamin C content acerola is also rich in other antioxidants like anthocyanins and is used as a natural skin whitener and anti-aging agent. Nowadays, acerola cherries are grown on a large scale in Brazil because of increased consumer demand. If you go shopping at a bigger drug or grocery store, then take a look at the nutritional supplements section. I’m sure you will find acerola cherry powder there.
As you probably have already guessed, only the Vitamin C content of acerola cherries is of interest for bread bakers. But why do bakers use expensive acerola cherry powder if they could just use purified and cheap ascorbic acid? Well, the Vitamin C powder that you can buy at your local store is not extracted from lemons or acerola cherries. It is synthetic ascorbic acid that has been produced either by the traditional Reichstein process or, most likely, by a modern biotechnological process with the help of genetically modified microorganisms.
Some people try to avoid synthetic Vitamin C although I have to say that this is nonsense. There is no scientific evidence that would indicate that synthetic Vitamin C is harmful or inferior to food-derived Vitamin C. The reason I like to use acerola cherry powder is that it is easier to dose. The acerola cherry powder that I use contains about 17 % Vitamin C. So I can weigh five times the amount of acerola cherry powder compared to ascorbic acid. This makes a difference because we typically use less than 0.02 % Vitamin C in relation to the flour weight. That’s less than 200 milligrams of Vitamin C per kilogram of flour!
How to improve doughs with Vitamin C
- The addition of ascorbic acid is especially recommended for doughs made from old wheat species like spelt and emmer because their gluten quality is inferior to the one of bread wheat.
- Assuming you are working with untreated flour that has no ascorbic acid already added to it, 0.02 to 0.2 grams ascorbic acid per kilogram of flour can be added to improve dough strength. The ideal dosage is about 0.05 to 0.07 grams (50-70 parts per million) of Vitamin C per kilogram of flour. If you’d like to add acerola cherry powder instead, then 0.3 to 0.7 grams (300 to 700 parts per million) of acerola cherry powder per kilogram of flour is recommended. To measure these tiny quantities, you need an accurate laboratory scale.
- If you don’t own a laboratory scale, then you can dilute a larger amount of Vitamin C in water for accurate dosage. For example, if you’d like to add 0.1 grams of ascorbic acid to a dough made from 1 kilogram of flour, then you can dissolve 10 grams of Vitamin C powder in 100 grams of water (10 % solution). You then need to add 1 gram of this solution to your bread dough made from 1 kilogram of flour to achieve a Vitamin C concentration of 0.1 %.
- Ascorbic acid requires oxygen or another oxidizing agent like bromate to improve the dough strength because it needs to be oxidized to dehydroascorbic acid. Therefore, Vitamin C is most effective in doughs that are thoroughly kneaded. In no-knead bread, the positive effects of ascorbic acid are less pronounced because less atmospheric oxygen is incorporated into the dough.