A wheat kernel, also known as a wheat berry, is composed of three main anatomical parts that collectively determine its nutritional profile: the endosperm, bran, and germ. While the kernel is overwhelmingly comprised of carbohydrates, the other components, including protein, fiber, and micronutrients, play crucial roles in nutrition and processing. Understanding the specific makeup of each part helps explain the health benefits of whole grain wheat versus refined flour.
The Three Key Parts of a Wheat Kernel
Each part of the wheat kernel has a unique composition and function. Millers can separate these parts to produce different flours, with the removal of the bran and germ resulting in refined white flour.
- Endosperm: Making up around 83% of the kernel's weight, the endosperm is the primary source of white flour. It is predominantly composed of starch, along with significant amounts of protein. It also contains smaller quantities of B vitamins and iron.
- Bran: The bran is the hard, protective outer layer of the kernel and accounts for approximately 14.5% of its weight. It is exceptionally rich in dietary fiber, vitamins (especially B vitamins), minerals, and phytochemicals. In whole wheat flour, the bran remains intact.
- Germ: The germ is the embryo or sprouting section of the kernel, though it only comprises about 2.5% of the total weight. It is packed with nutrients, including unsaturated fats, B vitamins, antioxidants, and trace minerals. Due to its fat content, the germ is often removed during milling to prevent rancidity and extend shelf life.
A Closer Look at Wheat's Macronutrients
Carbohydrates: The Primary Building Block
As the most abundant component, carbohydrates form the main structural and energy-providing element of wheat.
- Starch: This is the most prevalent carbohydrate, making up over 90% of the total carb content in wheat. Starch provides the bulk of the calories and is concentrated primarily in the endosperm.
- Fiber: Found mostly in the bran and germ, dietary fiber is crucial for digestive health. Whole wheat contains significant insoluble fiber, which adds bulk to stool, and smaller amounts of soluble fiber.
Protein and the Role of Gluten
Wheat contains a moderate amount of protein, ranging from 7% to 22% of its dry weight depending on the variety.
- Gliadins and Glutenins: The majority of wheat protein (up to 80% of the total protein content) consists of gluten, which is a complex family of proteins primarily made of gliadins and glutenins. When mixed with water, gliadin provides extensibility and glutenin offers elasticity, creating the unique viscoelastic properties essential for bread-making.
Fats, Vitamins, and Minerals
Beyond its primary carbohydrates and protein, wheat contains a host of other nutrients.
- Fats: Present in small amounts, particularly concentrated in the germ.
- Vitamins: Whole wheat is a good source of B vitamins, including thiamine, niacin, and folate, which are largely found in the bran and germ and are lost during the refining process.
- Minerals: Important minerals like magnesium, phosphorus, zinc, iron, and selenium are more abundant in whole grains, as they are concentrated in the outer bran and germ layers.
Whole Wheat vs. Refined White Flour: A Compositional Comparison
The difference in composition between whole and refined wheat flour highlights why whole grains are generally considered more nutritious.
| Nutrient | Whole Wheat Flour | Refined White Flour |
|---|---|---|
| Parts of the Kernel | Endosperm, bran, and germ | Endosperm only |
| Dietary Fiber | Higher (e.g., 10.7g per 100g) | Lower (e.g., 3g per 100g) |
| Vitamins | Contains B vitamins (thiamin, niacin, folate) | Vitamins are stripped away, often added back synthetically |
| Minerals | Higher concentrations of iron, magnesium, zinc | Lower concentrations, with some added via enrichment |
| Fat | Higher due to the presence of the germ | Lower, as the germ is removed |
| Protein | Slightly higher, includes protein from the germ | Lower, containing only endosperm protein |
| Glycemic Index | Lower (e.g., 69) | Higher (e.g., 85) |
| Flavor | Nuttier, stronger flavor | Milder, softer flavor |
Conclusion
In conclusion, what is wheat mostly made of? Carbohydrates, specifically starch, which provides the bulk of its mass and calories. However, this simple answer overlooks the complexity and nutritional richness found in the rest of the kernel. The protein (gluten), fiber, fats, vitamins, and minerals concentrated in the bran and germ layers are essential for a complete nutritional profile. The processing of wheat into white flour removes these layers, stripping the grain of most of its non-carbohydrate nutritional value. For more comprehensive details on wheat's chemical composition and its nutritional significance, consult authoritative sources like this review from the National Institutes of Health.. Ultimately, the nutritional benefits of wheat depend on consuming the entire grain, not just the starchy endosperm.
