Álvaro García
Corn is a critical crop for many industries, particularly livestock feed, biofuel production, and food manufacturing. Two key components of corn kernels—starch and oil—play essential roles in these industries. Starch serves as the primary energy source, while oil provides energy density and other functional benefits. A common misconception is that corn with less oil will inherently have lower energy content, since oil provides more energy per gram than starch. However, starch is present in much greater quantities—approximately 7 to 8 times more than oil in a typical corn kernel. This means that even if oil content decreases, a higher starch concentration has a greater effect on the total energy in the grain. As a result, when starch content increases, the total energy in the grain should also increase, despite oil’s higher energy density per gram.
Correlation between starch and oil
We examined 13,396 samples collected by the U.S. Grains Council over a 12-year period, from 2011 to 2023. Each sample was analyzed for its starch and oil content, among other components, providing a thorough overview of the trends in corn nutrient composition over time. In a previous article, we discussed the strong negative correlation between protein and starch in corn. In this article, we focus on another, not as strong but still consistent, negative correlation between starch and oil. The analysis showed that as starch content increased, oil content tended to decrease, and vice versa. The correlation coefficient of approximately -0.47 suggests a moderate negative correlation.
This inverse relationship is not as strong as the one observed with protein, partly due to the distinct locations of starch and oil within the corn kernel.
- Starch is concentrated in the endosperm, the largest part of the kernel, which makes up approximately 80% of its weight. The endosperm’s primary role is to provide energy in the form of carbohydrates, primarily starch, to the developing plant embryo.
- Oil is found mostly in the germ, a much smaller portion of the kernel, accounting for only about 10-12% of its total weight. The germ is rich in lipids because it serves as the energy source for the seedling during germination.
Because these two components are in different parts of the kernel, there is less direct competition for resources. This physical separation likely reduces the intensity of competition during kernel development, which explains why the negative correlation between starch and oil is moderate rather than strong.
Additionally, from a market perspective, the demand for starch—especially in biofuel production, has led to corn hybrids that prioritize starch yield over oil. Ethanol production, which relies on starch, has driven much of the research and development in corn hybrids. However, despite the market’s focus on increasing starch content, the moderate negative correlation suggests that oil content has remained relatively stable, reflecting the biological constraints of the kernel’s structure.
Impact on Total Digestible Nutrients (TDN)
Despite the inverse relationship between starch and oil, Total Digestible Nutrients (TDN) —a measure of the total energy available to livestock from feed—has shown a slight upward trend over the years. This trend confirms the dominant role of starch in determining TDN because starch constitutes a much larger proportion of the kernel’s weight compared to oil. To determine TDN concentration we used the following equation developed previously when testing the correlation between protein and starch.
TDN % = 94.99 + (-0.11 × Protein (%) ) + (2,25 × Oil (%) ) + (-0.09 × Starch (%) ) + (0.03 × NDF + WSC (%) )
This study highlights the association between starch and oil in corn kernels. The moderate negative correlation between the two components reflects both biological limitations and market-driven goals, particularly the push for high-starch corn for ethanol production. However, because starch and oil are in different parts of the kernel, the inverse relationship is not as strong as it could be, allowing corn to remain an energy-dense crop, even when oil content fluctuates.
As plant breeding continues to advance, it may be possible to optimize both starch and oil content, minimizing the trade-offs between them. However, for now, the inverse relationship between starch and oil remains a key observation for producers, researchers, and industries that depend on corn as a major input.
The full list of references used in this article is available upon request.
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