CN106841265B - A kind of pork kills postcooling Moisture Movement detection method - Google Patents

Abstract

The invention discloses a method for detecting moisture migration in the post-mortem cooling process of pork. The method includes (1) sample preparation; (2) low-field nuclear magnetic imaging analysis: the meat sample is put into a sample tube, and a low-field nuclear magnetic resonance instrument is used for imaging analysis, thereby obtaining an image of the sample, and according to the depth of the color in the image, Determine the moisture distribution. (3) Low-field NMR relaxation time _T2 analysis: put the meat sample into a sample tube, and use a low-field NMR instrument to measure the low-field NMR relaxation time _T2 to detect the water distribution in the meat. The key of the present invention is to provide a detection method for water migration in the pork cooling process combining low-field nuclear magnetic imaging and T2 relaxation method, which provides a standardized method for studying the loss mechanism in the pork cooling process and developing cooling loss control technology.

Description

A method for detecting moisture migration during post-mortem cooling of pork

technical field

The invention relates to the technical field of meat food processing and production, and relates to a method for detecting moisture migration in the post-mortem cooling process of pork, in particular to a method for detecting moisture distribution in the post-mortem cooling process of pork based on large-aperture low-field nuclear magnetic imaging and T2 relaxation technology method.

Background technique

Pre-cooling is an important part of cooling pork processing, and the water loss of pig carcass in the cooling process is 1.85% to 3.5%, which has caused serious economic losses to the enterprise. Therefore, meat companies try various techniques to reduce carcass cooling loss. Atomized spraying technology is a technology that can not only accelerate the cooling rate of carcass, but also reduce the loss of water in the cooling process, and can effectively reduce the economic loss caused by cooling dry consumption.

At present, most domestic research on cooling dry consumption and atomization spray technology is limited to the optimization of dry consumption and specific technical parameters, and the detection method is mainly to detect the change of overall moisture content by weighing method. It cannot well explain the migration and change of moisture in pork during the cooling process, and the principle of reducing the cooling dry consumption by the atomization spray cooling method. In recent years, low-field NMR technology has been widely used in meat moisture detection. However, the application of traditional low-field NMR technology in meat moisture detection has certain defects, mainly in the fact that the meat sample is too small (2×1×1cm), and the degree of damage to the sample is relatively large during the sample preparation process, which may cause Affect the accuracy and representativeness of the measurement results. Therefore, establishing a meat moisture detection method based on large-sample low-field NMR technology will help to better analyze meat processing, such as changes in moisture migration during post-mortem cooling and its impact on cooling dry consumption, Provide theoretical support for further research and development of cooling dry consumption control technology.

Contents of the invention

The purpose of the present invention is to address the above-mentioned deficiencies in the prior art, and provide a method for detecting moisture distribution in the post-mortem cooling process of pork based on large-aperture low-field nuclear magnetic imaging and T2 relaxation technology.

The purpose of the present invention can be achieved through the following technical solutions:

A method for detecting moisture migration in the post-mortem cooling process of pork based on large-aperture low-field nuclear magnetic imaging and T2 relaxation technology is carried out according to the following steps:

(1) Sample preparation: select the whole longissimus dorsi muscle within 2 hours after slaughter, take meat pieces with a size of 14×10×6 cm along the direction perpendicular to the muscle, and cool for at least 16 hours;

(2) Low-field nuclear magnetic imaging (MRI) analysis: put the meat sample into the sample tube, and perform imaging analysis with a low-field nuclear magnetic resonance instrument, and obtain an image of the sample based on this, and determine the water distribution according to the color depth in the image.

(3) Low-field NMR relaxation time _T2 analysis: put the meat sample into a sample tube, use a low-field NMR instrument to measure the low-field NMR relaxation time _T2 , and detect the water distribution in the meat;

The diameter of the sample tube described in the method of the invention is preferably 120 mm.

The described low-field nuclear magnetic imaging (MRI) analysis method preferably adopts SE imaging sequence, uses MRI imaging software and MSE multi-layer spin echo sequence, collects the proton density image of sample cross-section, MRI imaging parameters: GSliceZ=1, GPhaseY= 1. GReadX＝1, TR＝800ms, TE＝11ms, FOV Read＝80mm, FOV Phase＝80mm, accumulative 8 times, K space size 256×192; meat sample layer thickness 3.0cm.

The low-field NMR relaxation time _T2 analysis is preferably at 32°C and 22.4MHz resonance frequency, using CPMG pulse sequence, repeated scanning 8 times with an interval of 3s, to obtain 2000 echoes, and calculate the following indicators according to the _T2 curve : ①t _2b , A _2b , P _2b represent the highest peak time of bound water in pork, the peak area and the percentage of bound water in the total water in pork; ②t ₂₁ , A ₂₁ , P ₂₁ represent the The highest peak time, peak area and ratio of non-flowing water to the total water in pork; ③t ₂₂ , A ₂₂ , and P ₂₂ respectively represent the highest peak time, peak area and free water to total water in pork Moisture ratio. The CPMG pulse sequence preferably has a time τ=200 μs between the 90° pulse and the 180° pulse.

The beneficial effects of the present invention are:

(1) The size of the meat sample can reach 14×10×6cm. Its advantage is that the degree of damage to the meat sample is relatively small, which can more truly reflect the distribution of moisture in the meat in actual production. ;

(2) Compared with the traditional method, the resonant frequency is higher (the resonant frequency of the traditional method is 100KHz), which better meets the determination needs of large samples.

(3) Compared with the traditional method, the size of the K-space is larger (the size of the K-space of the traditional method is 16×128), which better meets the measurement needs of large samples and obtains more accurate sample information.

Description of drawings

Figure 1. Pork moisture imaging by low-field NMR during air drying

Fig.2 Effects of different cooling methods and time on bound water t _2b , A _2b , P _2b in pork with or without skin

The three small pictures on the left are air cooling; the three small pictures on the right are spray cooling (different letters represent significant differences, P<0.05)

Fig.3 Effects of different cooling methods and time on the non-flowing water t _2b , A _2b , P _2b in pork with or without skin

The three small pictures on the left are air cooling; the three small pictures on the right are spray cooling, and different letters represent significant differences (P<0.05)

Fig.4 Effects of different cooling methods and time on the non-flowing water t _2b , A _2b , P _2b in pork with or without skin

The three small pictures on the left are air cooling; the three small pictures on the right are spray cooling, and different letters represent significant differences (P<0.05)

Detailed ways

The present invention will be further illustrated below in conjunction with specific examples. This specific embodiment is implemented on the premise of the technical solution of the present invention. It should be understood that these modes are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

Example 1

(1) Raw material selection: select the whole longissimus dorsi (tong ridge) within 2 hours after slaughter, take meat pieces with a size of 14×10×6 cm along the direction perpendicular to the muscle, and divide them into 2 groups (one group removes pigs The fascia tissue on the surface of the skin and pork is used as the red strip group; one group retains the fascia tissue on the surface of the pig skin and pork, and the fascia tissue with a dense structure and a certain thickness is simulated as a fat layer, which is used as the white strip group). Blowing cooling and atomizing spray cooling were carried out in the cold storage environment, and the meat samples were subjected to low-field nuclear magnetic resonance transverse relaxation time at 6:30, 8:00, 9:30, 11:00, 13:30 and 15:00, respectively. (T2) and low-field MRI measurements.

(2) Low-field nuclear magnetic imaging: The SE imaging sequence test was used to change the proton density and the influence of T2 on the image by changing the sequence parameters TE and TR. Using MRI imaging software and MSE multi-layer spin echo sequence to collect the proton density image of the sample cross section, MRI imaging parameters: GSliceZ=1, GPhaseY=1, GReadX=1, TR=800ms, TE=11ms, FOVRead=80mm, FOV Phase=80mm, accumulated 8 times, K-space size 256×192; thickness of selected layer of meat sample is 3.0cm.

(3) Low-field NMR relaxation time: Put the meat sample into a specific sample tube for T2 measurement by a low-field NMR instrument. Each meat sample was measured twice in parallel, and the average value was taken. At 32°C and 22.4MH resonance frequency, use CPMG (carr-purcell-meiboom-gill) pulse sequence (time between 90° pulse and 180° pulse τ = 200μs), repeat the scan 8 times with an interval of 3s, and obtain 2 000 echoes. t _2b , A _2b , P _2b represent the highest peak time of bound water in pork, the peak area and the percentage of bound water in the total water in pork; t ₂₁ , A ₂₁ , P ₂₁ represent the non-flowing water t ₂₂ , A ₂₂ , and P ₂₂ respectively represent the highest peak time, peak area, and the ratio of free water to total moisture in pork .

Test example 1

(1) Low-field nuclear magnetic imaging of pork moisture during air drying

Low-field nuclear magnetic imaging (from top to bottom) of pork with skin in different time periods during air cooling was selected from all the images. The red part in the image indicates high moisture weight and high moisture content; the green part indicates low moisture weight and low moisture content. The imaging area gradually decreases from top to bottom, indicating that the dry consumption of water during the blowing cooling process leads to a decrease in the volume of the meat. At the beginning of the experiment, it can be clearly found from the figure that the imaging moisture weighting at the first two test points is very low, which does not mean that the moisture content in the pork is low, but because the temperature difference of the test object leads to a difference in signal intensity. The higher the signal strength is, the weaker it is, and the lower the temperature, the higher the signal strength. This phenomenon can visually confirm the temperature change of pork during the cooling process. On the whole, the moisture signal of the outer pork is higher than that of the inner moisture; from a single picture, the signal around the meat is significantly higher than the middle signal, which shows that the cooling process of the meat is to cool the outside first, and then gradually cool to the inside . After cooling for 4.5 hours, the pork moisture signal is uniform, indicating that the entire cooling process is completed. From the last four time periods of the signal, it was found that the red part of the picture was significantly reduced, and the green part was significantly increased, indicating that the migration loss of water occurred in the later stage of the experiment. Although the internal moisture content is significantly higher, its moisture content also decreases significantly in the later stage, indicating that moisture migrates outside the meat. Therefore, through imaging, it is found that the migration of water is from the outside to the air, and at the same time, the inside of the meat piece migrates to the outside.

(2) Effects of cooling method and skin on the water relaxation time of pork during cooling

As shown in Figure 2, different cooling methods and skinned or not had no significant effect on the peak area and peak area ratio of bound water in pork during cooling (P>0.05), but the difference in peak time of bound water was significant (P< 0.05). Because the proportion of bound water in pork is very small and closely combined with protein, different cooling methods and skinned or not have no effect on bound water in pork during cooling.

As shown in Figure 3, whether skinned or not has no significant effect on the peak time of the non-flowing water of pork (P>0.05). The cooling method has a significant effect on the peak time of non-flowing water in the pork cooling process. Among them, air cooling significantly reduces the peak time of non-flowing water (P<0.05), while atomization spray cooling does not affect the peak time of non-flowing water. The highest water peak time. Both atomizing spray cooling and blowing cooling significantly increased the proportion of non-flowing water in the total water in pork during cooling (P<0.05). The peak area of non-flowing water tends to increase under different cooling methods.

As shown in Figure 4, the peak area of free water and the proportion of free water in the total moisture decreased significantly (P<0.05) during the cooling process of pork with skin and without skin, but the difference between pork with skin and pork without skin There was no significant difference between them (P>0.05).

Claims (2)

1. A method for detecting moisture migration in the pork post-mortem cooling process based on large-aperture low-field nuclear magnetic imaging and T2 relaxation technology, characterized in that it is carried out according to the following steps: (1) Sample preparation: select the whole longissimus dorsi muscle within 2 hours after slaughter, take meat pieces with a size of 14×10×6 cm along the direction perpendicular to the muscle, and cool for at least 16 hours; (2) Low-field nuclear magnetic imaging analysis: put the meat sample into the sample tube, and perform imaging analysis with a low-field nuclear magnetic resonance instrument, based on which the image of the sample is obtained, and the water distribution is determined according to the color depth in the image; among them, the sample tube The diameter of the sample is 120mm; adopt SE imaging sequence, use MRI imaging software and MSE multi-layer spin echo sequence to collect the proton density image of the cross section of the sample, MRI imaging parameters: GSliceZ =1, GPhaseY =1, GReadX=1, TR= 800 ms, TE=11 ms, FOV Read=80 mm, FOV Phase=80 mm, accumulated 8 times, K space size 256×192; meat sample layer thickness 3.0cm; (3) Low-field NMR relaxation time _T2 analysis: put the meat sample into the sample tube, and use a low-field NMR instrument to measure the low-field NMR relaxation time _T2 to detect the water distribution in the meat; Time T ₂ analysis At 32°C and 22.4 MHz resonance frequency, use CPMG pulse sequence to repeat the scan 8 times with an interval of 3 s to obtain 2 000 echoes. Calculate the following indicators according to the T ₂ curve: ① t _2b , A _2b , P _2b , _respectively represent the peak time of bound water in pork, the peak _{area and} the percentage of bound water in the total water in pork; Peak time, peak area and the ratio of non-flowing water to total water in pork; ③ t ₂₂ , A ₂₂ , P ₂₂ represent the highest peak time of free water, peak area and the ratio of free water to total water in pork, respectively. 2. the method for detecting moisture migration in the post-mortem cooling process of pork according to claim 1 is characterized in that the time τ=200 μs between the 90 ° pulse and the 180 ° pulse of the CPMG pulse sequence.