Some recipes require ascorbic acid to keep fruit from browning. It is also useful as a dough improver or dough conditioner in that it strengthens the gluten in bread dough. If you are working with apples or other fruits that are subject to enzymatic browning or want to make bread with a finer crumb, you may need to find some ascorbic acid. If you prefer to use something else to achieve similar effects, consider one of the ascorbic acid substitutes below.
Your best bet: Citric acid or potassium bromate
If you are looking for an ascorbic acid substitute that will act as a preservative and prevent the browning of fruits, citric acid is your best option. It is also called sour salt and you may be able to find it in your grocery store’s kosher food section. Citric acid is not vitamin C, so it will not give you many of the benefits that you would get via ascorbic acid (vitamin C); however, it is an antioxidant. Citric acid can also make minerals like iron and magnesium more bioavailable. Another difference has to do with the flavor—ascorbic acid has a bitter flavor but citric acid is tart.
If you need an ascorbic acid substitute for improving your bread dough, you will need something other than citric acid. Your best bet for this purpose will be potassium bromate. Like ascorbic acid, it strengthens the gluten in bread dough. Stronger gluten results in greater volume. A bromated flour is one that has been blended with potassium bromate.
Citric acid can also stand in for ascorbic acid as an additive to smoked meats where it can be helpful for maintaining the red color and preventing nitrosamine formation.
A decent second choice: Lemon/lime juice or Azodicarbonamide
Lemon and lime juice both contain ascorbic acid, which means that they can provide the desired effects in certain applications. They will lower the fruit’s pH and can reverse oxidation. That said, there are some recipes in which lemon and lime juice will not be effective ascorbic acid substitutes. If you need an ascorbic acid alternatives for improving bread dough, consider Azodicarbonamide. Azodicarbonamide is another additive used to strengthen dough. It is also an effective whitening agent. Note that overusing it can make your dough dry and difficult to work in addition to causing the surface of bread to crack.
Azodicarbonamide is used mainly in commercial baking, which means that it may be difficult for home bakers to source.
In a pinch: Vinegar
Vinegar is diluted acetic acid. While it has different properties from those of ascorbic acid, it can serve some of the same functions. For example, it is an effective preservative. While ascorbic acid preserves food by way of its antioxidant properties, vinegar is effective because it kills the microbes that cause food to spoil. Vinegar is also beneficial for making bread. It helps with the bread’s flavor as well as gluten development. By helping with gluten development, it can increase dough volume. Note that too much of it can stop the fermentation of yeast and hinder the bread’s ability to brown.
A simple way to keep cut fruit like apples and pears from browning is to submerge the fruit pieces in water. This keeps oxygen from getting to the fruit, which prevents browning.
Still more options include natural sources of ascorbic acid like rosehips and cranberries. Acerola cherries are also a good natural ascorbic acid source. Much of the ascorbic acid used in baking is extracted from them.