Metals in meat: Bioavailability assessed by spectroscopy

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  • Published: Oct 15, 2017
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Metals in meat: Bioavailability assessed by spectroscopy

Thermal meat treatment

Various techniques including graphite furnace atomic absorption spectrometry have been used to assess the bioavailability of metals ions present in beef, pork, and chicken after thermal treatment. The study shows that high temperatures make nutrient metal ions of calcium, copper, iron, magnesium and zinc less readily available. (Photo by David Bradley)

Various techniques including graphite furnace atomic absorption spectrometry have been used to assess the bioavailability of metals ions present in beef, pork, and chicken after thermal treatment. The study shows that high temperatures make nutrient metal ions of calcium, copper, iron, magnesium and zinc less readily available.

Eveline Menezes of the Universidade da Integração Internacional da Lusofonia Afro-Brasileira, in Acarape, and colleagues in Brazil, explain that it is important from a nutritional perspective to know how much mineral content from different kinds of meat is available for absorption by the human body given different ways of preparing those meats. They have now submitted three different kinds of meat to five different heat treatments and used simulated stomach acid and digestive enzymes to look at bioaccessibility of crude protein and metal ions. The team applied inductively coupled plasma optical spectrometry was used to quantify the dialyzable fraction and the total mineral content after microwave-assisted digestion. In parallel they used graphite furnace atomic absorption spectrometry quantified Cu in chicken dialyzable fraction.

Nutritious meat

Meat contains many valuable nutrients for human health, the team says, protein and fat perhaps being the most important nutrients. However, beef and other meats are also an important source of mineral ions including the aforementioned trace metals as well as selenium. Beef is widely consumed in North America, but pork, particularly in the form of ham, sausages and other processed meat products, is the most widely consumed meat. Chicken is often considered a healthier option because of its lower fat content and higher proportion of polyunsaturated fatty acids compared to beef, for instance.

While some meat products are eaten uncooked, albeit smoked, salted or otherwise cold processed, the majority of meat is cooked prior to ingesting. As is well known to cooks and meat eaters around the world, there are many ways to cook meat and each has different effects on the chemical and sensory properties of the meat, leading to loss of mass, changes in how much water is in the meat, textural changes due to protein and fat denaturation, colour changes, and development of aroma compounds. Cooking, however, can also lead to leeching and loss of mineral ions, unless juices released during cooking are used to make an accompanying sauce or gravy or otherwise served with the meat. Boiling, roasting, frying, and microwave cooking each have different effects on mineral release as well as the taste and texture of the final cooked product.

The team points out that lots of research has taken a general view of mineral release as meat is cooked. However, there has not been sufficient focus on the bioavailability of mineral ions in meat. After all, it is possible that denature protein and Maillard reaction products might incorporate metal ions in a form that makes the morsel less digestible and the mineral ions trapped within this meat matrix. "There is little information on the effects of thermal treatment on bioaccessibility of nutrients to our knowledge. Depending on factors such as meat type and processing, the constituents can be more or less bioaccessible," the team reports.

Bioaccessibility

The team has carried out spectrometric assessment of raw and thermally processed, cooked, meat and also used Fourier transform infrared (FTIR) spectroscopy to analyse how protein is transformed during cooking.

The team found that the concentrations of each metal element fell when meat was cooked in water, which they suggest is explained by leaching. The biggest loss was of calcium from boiled beef. For chicken and pork, roasting led to a big loss of calcium, although grilling pork was worse in terms of calcium loss. The team suggests that this might be explained by calcium ions bonding to degraded protein, which isn't broken down in the stomach for absorption. Copper levels did not change significantly with the exception of a small decrease for boiled chicken and boiled pork. Ultimately, the simulated digestion of cooked meats in a gastric acid solution with pepsin as digestive enzyme showed that only a minor fraction of the total mineral content of any cooked meat is bioaccessible.

Related Links

Food Chem 2018, 240, 75-83: "Bioaccessibility of Ca, Cu, Fe, Mg, Zn, and crude protein in beef, pork and chicken after thermal processing"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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