It’s time to re-understand wheat bran (Part 2)

Fruits, vegetables, whole grains, etc. are indispensable foods in our diet. In addition to providing nutrition, their beneficial properties are largely attributed to phytochemicals . Many of these phytochemicals are secondary metabolites produced by plants during their growth, mainly used to help plants better adapt to the environment.

It is estimated that whole grains contain approximately 5,000-25,000 phytochemicals[1]. Among them, phenolic compounds have received widespread attention due to their strong antioxidant properties and outstanding advantages in preventing chronic diseases such as chronic inflammation and cardiovascular disease.

0 1Underestimated Phenols in Cereals

As a secondary metabolite in plants, phenols not only act as defenders against pathogens, parasites and predators, but also give plants their colorful colors.

As a food ingredient in the diet, it can exhibit antioxidant activity in the human body, reduce the risk of chronic diseases, and is beneficial to health.

The color of black rice and red rice comes from phenols such as anthocyanins

Phenolic acids and flavonoids are the most common phenolic compounds

Vegetables and fruits can be said to be the best antioxidant foods. Especially after many years of research and popular science, some members with outstanding antioxidant capabilities have become deeply rooted in people's minds, such as cruciferous vegetables such as broccoli and purple cabbage, and berry fruits such as blueberries and grapes.

In comparison, whole grains are less well known. In fact, they are not only a good source of dietary fiber, but also have certain antioxidant properties.

Let’s first compare the antioxidant levels of several common foods and the phenols they contain.

Total antioxidant activity (top) and total phenolic content (bottom) of common fruits, vegetables, and whole grains. It can be seen that the phenols in whole grains are mainly in a bound state, which is very different from fruits and vegetables. [2]

Whole grains, especially corn, wheat, and oats, have strong antioxidant activity. The total antioxidant activity of each gram of corn is equivalent to 181.4 μmol of vitamin C, which is comparable to cranberries, while each gram of wheat is equivalent to 76.7 μmol of vitamin C, which is close to red grapes and strawberries, and stronger than many vegetables.

An important basis for the antioxidant activity of whole grains is phenols . Unlike fruits and vegetables, phenols in grains are often present in a bound form, with bound phenols accounting for 85%, 76%, 75%, and 62% in corn, wheat, oats, and rice, respectively.

These bound phenols are bound to dietary fiber and protein through ether bonds, ester bonds, etc. and are firmly bound in the cell walls. In scientific research using traditional extraction methods, only free phenols can be extracted, while the bound phenols, which account for the majority, are difficult to extract. Therefore, people once greatly underestimated the phenolic content in grains and its antioxidant capacity.

Phenols (E) are often linked to macromolecules such as dietary fiber and structural proteins. [1]

0 2Main phenols in wheat bran——Ferulic acid

Ferulic acid is one of the polyphenolic compounds with the highest content and strongest antioxidant activity in wheat bran.

Nutritional information of wheat bran | [4]

It cross-links with carbohydrates such as dietary fiber in wheat bran, acting as a physical and chemical barrier. On the one hand, its antioxidant activity can fight against destructive oxygen free radicals, and on the other hand, its astringency can prevent insects and other animals from eating it. In our body, it can enhance the body's own anti-inflammatory and antioxidant capabilities, improve endothelial and lipid metabolism levels, and benefit the health of patients with atherosclerosis. The FDA has listed ferulic acid as an antioxidant.

Due to the health benefits of ferulic acid, its derivatives have also been developed into drugs, and many of them are included in the Chinese Pharmacopoeia [5]. For example, sodium ferulate is a cardiovascular drug used as an adjuvant treatment for cardiovascular and cerebrovascular diseases such as atherosclerosis, coronary heart disease, and cerebrovascular disease. Ferulic acid esters , also known as oryzanol, are a mixture of ferulic acid esters with triterpene alcohols as the main component, which can be used for sedation and sleep.

In addition, ferulic acid is also used in the field of skin care. First, because of its strong antioxidant effect, it can inhibit the activity of tyrosinase (tyrosinase is an oxidase that participates in the production of melanin), thereby inhibiting skin aging and achieving the effect of whitening the skin; second, it has good absorption in the ultraviolet region around 290-330nm, while the ultraviolet region that is more likely to induce skin spots is 305-310nm. In Japan, companies have long developed a series of ferulic acid skin care products and sunscreens [6].

0 3 Phenolic lipids unique to wheat: ARs

ARs (alkyl resorcinol) is a wheat-specific phenolic lipid first discovered in wheat and rye in 1964. It not only has antioxidant properties, but also plays an important role in intestinal health and inhibiting the growth of cancer cells. It is an important active substance in whole grains.

Since ARs are almost only found in the bran of whole grains such as wheat and rye, and their content in refined flour or refined products obtained from fine milling is extremely low, they are usually used as biomarkers for human intake of whole grain products such as wheat and rye. In 2015, the State Food and Grain Administration included it as one of the important criteria for evaluating the quality of whole wheat flour in the grain industry standards.

Quality indicators of whole wheat flour[7]

0 4 Phenols in grains have two major characteristics

1. Focus on the outer layer

The phenols in whole grains tend to be concentrated in the outer structure. For example, in whole wheat flour, wheat bran contributes 83% of phenols, 79% of flavonoids, 78% of zeaxanthin, 51% of lutein, and 42% of β-cryptoxanthin.

Percentage distribution of phytochemicals in whole wheat flour | [2]

2. Released in the colon

The bound phenols in grains are tightly bound in dietary fiber, which is difficult to digest in the upper digestive tract. Therefore, these active ingredients go straight to the colon. Under the action of intestinal microorganisms, dietary fiber is broken down and utilized, and various substances attached to dietary fiber are released and activated, thereby showing health benefits. This may also be a key factor in the ability of whole grains to exert a healthy effect in the colorectum and reduce the risk of colorectal cancer.

The total content of bound phenolic substances released by simulated wheat bran dietary fiber in the digestive system in vitro, soluble fiber on the left and insoluble fiber on the right. The fermentation of colonic microbiota released more bound phenolic substances. As the colonic fermentation time prolonged, the content of released bound polyphenols increased. The decrease in the content at 12 and 24 hours was speculated to be due to the gradual degradation of the released phenolic acids or their slow absorption and utilization by the body. [3]

In real life, whole grains must be washed, steamed, and cooked before they can be eaten. This process may cause the loss of some phenols. Especially during cooking, some soluble free phenols will dissolve into the water and be lost. Relatively speaking, steaming may be better than cooking in retaining the antioxidant activity of whole grains[8].

In addition, wheat bran fermented by microorganisms may maintain good antioxidant properties or even enhance them. Lactic acid bacteria and yeast are both relatively effective strains. In daily life, wheat bran can be added to raw milk for fermentation to obtain high-fiber and high-protein yogurt. It can also be used in the production of fermented staple foods such as steamed bread and bread. It not only improves nutrition and facilitates digestion and absorption, but also has a certain improvement effect on flavor and taste [9].

Combining the results of epidemiological and dietary surveys in recent years in my country, looking at the health status of friends and relatives around us, and then comparing them with our own physical examination results, we might as well take a little time to re-examine our diet and see whether we have truly fulfilled our responsibility as the person who puts our health first. If not, then start from now!

References:

[1]Acosta-Estrada et al. Bound phenolics in foods, a review[J]. Food Chemistry, 2014, 152: 46-55.

[2]Liu R H. Whole grain phytochemicals and health[J]. Journal of Cereal Science, 2007, 46(3):732-737.
[3] Zhang Ling. Study on the release of bound polyphenols in wheat bran dietary fiber[D]. Tianjin University of Science and Technology, 2022.
[4] United States Department of Agriculture National Nutrient Database for Standard Reference.
[5] Pharmacopoeia of the People’s Republic of China 2020 edition.

[6]Xu Renpu et al. Application and development of ferulic acid[J]. Grain and Oils, 2000(06):7-9.
[7] LS/T 3244-2015 Whole wheat flour.

[8] Yang Lingxiao. Study on the effect of processing methods on the in vitro antioxidant activity of whole grain extracts[D]. Jiangnan University, 2015.

[9] Wang Yuqing, Xin Jiaying, Xu Yang, et al. Research progress on the application of wheat bran in food and microbial fermentation modification[J]. Food Research and Development, 2022, 43(17): 194-202.