NMR spectroscopy and its components and nuclei in meat sciences

 NMR:

It is a nuclear magnetic resonance and used for chemical, physical and biological properties of matter. They have low- and high-resolution NMR. In low resolution, peaks are not properly clear and overlapped with each other that create issues in determine complex structure. In high resolution NMR, peaks are clear. There are two types of NMR nuclei.

1.     NMR Active Nuclei

·       They spin and they are in odd numbers such as 31P, 1H, 13C etc.

2.     NMR Inactive Nuclei

·       They do not spin and they are in even numbers such as 12C

Principle:

The nuclei that have positively charged when magnetic field with wavelength of radio waves is applied then they absorb energy and spin and move from ground state to excited state and then return to ground state with same wavelength and emit the energy and these waves tells about the results.

Components:

·       Magnet (Produce magnetic field)

·       Detector (Detect the signals)

·       Radio Frequency Transmitter

·       Receiver (Show the results)

NMR in Meat Sciences:

31P NMR Nuclei:

Phosphorus 31 nucleus is widely used in NMR spectroscopy because it is naturally available and can be applied in meat sciences for detecting various factors. I.e., species, genotypes, slaughtering and further dietary supplements for determining different meat parameters. Firstly, qualitative studies for comparing post mortem metabolism rates in different muscles. Proved that high rates in porcine muscle as compared to ovine and bovine muscles.

Research compares the post mortem metabolism in 3 different compositions of rabbit muscles. Results shows that the metabolic rates were highest in oxidative muscles and lowest in glycolytic ones. Different parameters were observed i.e., pH (decrease was more significant in glycolytic than oxidative muscles). Temperature Effect was more significant in oxidative than the glycolytic. Thus, conclude that rates increase by raising temperatures. Others factors like genetics, feeding and slaughter procedures were also observed to determine meat quality and post mortem processes. Now a day this technique is an essential tool to determine these factors.

Generally, meat is classified into 3 types Normal, PSE and DFD meats depending upon water holding capacity and pH. PSE results due to short term stress and increases post mortem rates of temperature and glycolysis on the other hand DFD due to long term stress and decreasing glycogen rates. NMR technique will help in easy differentiation between these meats within no time. i.e., 30 min of post mortem thus this will help in predicting the final quality of meat.

31P NMR will measure intracellular pH on the basis of Hesselbach equation other hand NMR spectroscopy will determine both intracellular and extracellular pH. However, limitations lie in determining the pH of post mortem muscles by NMR Spectrometry, as it shows dependency of pk values on two factors ionic strength and temperature.  As these factors are difficult to calculate in post mortem quality of muscles because ionic strengths at different points in post mortem is not clearly known. However, pH determination by 31 phosphorus is more advantageous and non-destructive method as it will take measurements on same tissue location as well.

1H NMR Nuclei:

1H NMR Spectroscopy has high sensitivity but shows difficulty in separating single resonance because of interaction of water in large amount i.e., Biological Systems. However, this technique is beneficial in intact carcasses.

Now a day’s consumers consider meat color its quality and freshness indicator. Meat color is available in 3 myoglobin states. (Deoxymyglobin, Oxymyoglobin and Metmyoglobin). 1 H NMR Spectroscopy is used to determine the auto oxidation of myoglobin in 2 different bovine muscles samples. i.e., Methyl group peak is taken as oxidation indicator. Furthermore, both samples show different rates of auto oxidation.

13C NMR Nuclei:

13C technique is less sensitive as compared to 1H and 31P NMR spectroscopy. 13C NMR has few applications in meat technology but main focus is on muscle glycogen which is considered an important factor in post mortem anaerobic analysis.