Preserving Food with Natural Ingredients

The various stages of processing rye, from berries to alkylresorcinols (top left to bottom right): rye berries, rye chops (coarsely ground rye berries), rye bran, and alkylresorcinols (extracted and purified from rye bran).

The food industry is seeing a big push for natural alternatives to replace synthetic ingredients, a rising movement driven by consumers who are confused about the chemical-sounding ingredients on food labels and not deeming them healthy.

While there’s been some effort to meet this growing demand of natural alternatives, there has been little work done to identify new, natural antioxidants resulting in a depleted list of available, effective, and safe antioxidants for use.

That led Andrew Elder, a PhD candidate, department of food science at Penn State University, to lead a study that examined the practicality of using grain bran to help preserve food longer.

“In our work we are looking to use antioxidants to preserve oil rich foods because as oils oxidize and degrade, they lose their health promoting benefits and develop off aromas/flavors in food products,” Elder says. “Concurrent research in our lab focused on a class of compounds called Alkylresorcinols (ARs) which are found in the bran layer of cereal grains (e.g. rye, wheat, barley).”

ARs are thought to be defense compounds protecting the grain kernels from the growth of fungi. Additionally, ARs are used as a biomarker for whole grain consumption as they are located in the bran layer (outer, seed husk), which is removed during flour refining and therefore wouldn’t appear in the urine of individuals who consume highly refined flours.

The researchers noticed similarities in the chemical structure of ARs to commonly used antioxidants (i.e. a phenolic ring) and hypothesized that ARs might exhibit antioxidant activity.

According to Elder, determining ARs ability to function as antioxidants has two major advantages: 1) ARs from bran would be a natural alternative to synthetic antioxidants that is also pantry friendly as consumers know what rye and bran are; and 2) ARs can be extracted from a common waste stream, bran, which is usually used for animal feed which in turn creates a value-added product.

“Based on this, we set out to determine the antioxidant activity of rye bran extract rich in ARs as compared to alpha-tocopherol (Vitamin E, a commonly used natural antioxidant) and butylated hydroxytoluene (BHT, a commonly used synthetic antioxidant) in model food emulsions,” he says. “Emulsions were investigated because consumers often consume oils as emulsions (e.g. mayonnaise, salad dressings, etc.) rather than as bulk oils. By determining ARs ability to preserve oils we hoped to understand the viability of ARs as a new source of natural antioxidants.”

What It All Means

The major finding of the study was that a rye bran extract rich in ARs was able to preserve a model food emulsion by slowing the rate of oxidation, preserving the quality of the emulsion longer than emulsions which did not contain antioxidants. This indicates ARs have the ability to function as antioxidants.

While these findings indicate ARs have the potential to be used as an effective, natural antioxidant in foods replacing synthetic antioxidants which aligns with consumer demands, there is still a lot of work that needs to be done before they might begin to be used within the food industry.

“Next steps include purifying ARs to verify that they are the active compound responsible for the observed antioxidant activity of the rye bran extract,” Elder says. “Additionally, ARs exist as a homologous series which vary slightly in structure, which might impact antioxidant activity.”

Future work includes determining if this carbon tail impacts antioxidant activity and if it does, will this allow different AR homologues to be used in different food applications such as oil rich emulsions or bulk oils.

Longer Lasting?

Based on the data, the researchers can’t calculate how much longer ARs can preserve foods as they would have to extrapolate a small amount of data to a variety of food products with very different properties. However, the rye bran extract rich in ARs tripled the time before the on-set of oxidation (i.e. lag time) in the experiment compared to the control treatment that did not contain any antioxidants—12 days compared to 4 days.

“In a different food system, this improvement in shelf life could be more or less pronounced depending on the food and storage conditions,” Elder says. “There are a variety of factors which would impact the ability of ARs to preserve foods as these factors might promote oxidation or might exhibit a synergistic or antagonistic interaction with ARs.”

Intrinsic factors include the composition of the food (e.g. water, carbohydrate, fat/oil, protein, vitamin/mineral content), while extrinsic factors include the storage conditions of the food (e.g. modified atmosphere packaging, light transmission through the packaging, storage temperature of the food).

“Current research indicates that ARs are likely responsible for the observed increase in shelf life of whole grain breads over refined flour (i.e. white) breads, where AR content is negligible, due to their antioxidant activity,” Elder says. “Our work focused on a very simple model food emulsion system in which we attempted to mimic the conditions of oil-in-water emulsions such as salad dressings and mayonnaise. It is possible that this work could be relevant to other food based emulsions such as creams, dips, soups, sauces, and certain beverages.”

Additionally, he believes, ARs could be effective antioxidants in bakery goods that contain incorporated oils and fats as these components can oxidize giving off flavors and previous work has established that ARs are likely responsible for the increased shelf life of whole grain baked goods.

“Finally, ARs might be applicable to the meat industry where processed meats (e.g. sausages), which are high in fat content, still use synthetic antioxidants such as butylated hydroxytoluene to preserve product quality and ARs might be an effective, natural alternative,” Elder says. “However, further work needs to be done on ARs to understand their mode of antioxidant action, effective concentrations, etc.”