Machine learning helps identify cause of old phenomenon in meat tenderness

When you bite into a juicy steak, you don’t want it tough. From tough to gentle, there’s a lot of science behind it.

Chaoyu Zhai, assistant professor of animal sciences in the Department of Agriculture, Health and Natural Resources at University University, recently published a paper. Agricultural and Food Chemistry Journal We use machine learning algorithms to explain how the activity of the enzyme responsible for meat tenderness changes at the molecular level.

This is the first time such research has been conducted in the field of meat science.

An enzyme called calpain, specifically calpain-1, is known as a “meat tenderizing enzyme.” Calpain-1 cleaves other proteins in meat, making these protein fragments more water soluble. The more protein molecules in meat are fragmented, the more tender the meat will be.

Scientists have known about the role of calpain-1 in meat tenderness since the 1990s, but less about how calpain-1 can alter it.

“Modifying proteins is like wearing different clothes every day,” says Zai. “Even though we are the same ‘person’, depending on how we dress, we may be ready to tackle different tasks.”

Scientists found that packaging meat with high oxygen levels to preserve its color made it tougher, but they didn’t know why.

Zhai and his colleagues explain this mystery by discovering that the presence of compounds known as lipid peroxidation products can alter the activity of calpain-1.

“We have provided new explanations for things we see often,” says Zai. “Studying this will help other researchers understand similar events.”

Lipid peroxidation occurs when lipids such as cell membranes and fatty acids are exposed to oxygen. Free radicals “steal” electrons from lipids in cell membranes and damage cells. For example, as fresh food ages, lipid peroxidation occurs, causing it to deteriorate and produce odors.

In this paper, Zhai focused on three previously identified lipid peroxidation products in meat: malondialdehyde (MDA), hexenal, and 4-hydroxynonenal (HNE).

These compounds have 3, 6 and 9 carbons respectively. The more carbon molecules a compound contains, the more hydrophobic or water-repellent it tends to be. This means that these compounds may inhibit calpain activity at varying levels.

“As the number of carbon chains increases, those compounds tend to become more hydrophobic,” says Zai. “They can cause further functional changes in the protein.”

Zai worked with Calpine experts Stephen M. Lonergan and Elizabeth J. Huff Lonergan at Iowa State University. The research team used artificial intelligence algorithms to understand the structural changes that correspond to changes in protein function.

Usually, to determine the 3D structure of a protein, scientists freeze it and quickly take X-ray images. Machine learning algorithms allow researchers to simply input a protein sequence and determine its structure, making the process faster and less expensive.

“By using these algorithms, we can understand the results more effectively and interpret them better,” says Zhai.

This approach can be used for any field of interest in protein activity, a long and diverse list.

Zhai found that HNE, the most hydrophobic compound his group tested, significantly reduced calpain-1 activity, but unexpectedly did not completely eliminate it. Another compound called hexenal had a similar effect, but the decrease in activity was less dramatic. Some compounds, like MDA, surprisingly increased calpain-1 activity at the lowest concentrations the researchers tested.

“It’s definitely amazing,” says Zai. “We usually just assume that when it affects activity we see a decrease rather than an increase.”

The researchers also found that in freshly cut muscle that had not been exposed to air, calpain-1 had already begun to be modified.

“People never looked for it,” says Zai. “They think it happens when the meat is exposed to oxygen because this kind of processing involves oxygen. .”

In another area, researchers have found that lipid peroxidation is associated with natural aging, and high calpain-1 activity is associated with many human diseases such as heart failure and Alzheimer’s disease.

The body’s metabolism is imperfect and produces by-products such as lipid peroxidation products. These byproducts bind to and modify proteins. As they accumulate over a lifetime, the effects of aging become increasingly visible.

“This direction of research is definitely worth pursuing because it’s more common than we thought,” says Zai. “This is very interesting because these are high quality commercial pigs that are bred to be healthy and strong and can also withstand many protein denaturations caused by lipid oxidation products. ”

The next step in this research is to study which other enzymes are modified by compounds such as MDA and HNE in meat production.

“More results mean more research questions,” says Zai. “If you don’t look for it, you won’t find it.”

reference: Zhai C, Lonergan SM, Huff-Lonergan EJ, et al. Lipid peroxidation products covalently affect calpain-1 function in vitro. J Agro-Food Chemistry. 2023;71(20):7836-7846. Doi: 10.1021/acs.jafc.3c01225

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