CN114460121B - Method for detecting moisture and fat content of livestock meat by using low-field nuclear magnetic resonance technology - Google Patents
Method for detecting moisture and fat content of livestock meat by using low-field nuclear magnetic resonance technology Download PDFInfo
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- 238000005516 engineering process Methods 0.000 title claims abstract description 19
- 229910021380 Manganese Chloride Inorganic materials 0.000 claims abstract description 45
- GLFNIEUTAYBVOC-UHFFFAOYSA-L Manganese chloride Chemical compound Cl[Mn]Cl GLFNIEUTAYBVOC-UHFFFAOYSA-L 0.000 claims abstract description 45
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Abstract
The invention relates to a method for detecting the moisture and fat content of livestock meat by using a low-field nuclear magnetic resonance technology, which comprises the following steps of (1) sample treatment: pretreating livestock meat by using a manganese chloride solution; (2) detection of a sample; (3) establishing a calibration curve; and (4) calculation of moisture and fat content. The method applies the pretreatment process of the manganese chloride solution to the field of detecting livestock meat by using a low-field nuclear magnetic resonance technology, verifies the feasibility of the pretreatment process for the application in the field of foods, determines the specific use condition of the manganese chloride solution through condition optimization, and ensures the accurate detection of the moisture and fat content of the livestock meat.
Description
Technical Field
The invention belongs to the field of food detection, and particularly relates to a method for detecting moisture and fat content of livestock meat.
Background
With the development of science and technology and the improvement of living standard of people, consumers put higher demands on food quality safety, and the rapid detection technology of food safety is more widely developed. The rapid detection technology commonly used in the food field at present mainly comprises a chemical colorimetry, an enzyme-linked immunosorbent assay, a near infrared spectrum technology and the like. Compared with other detection technologies, the Low-field nuclear magnetic resonance (Low-field nuclear magnetic resonance, LF-NMR) technology has the advantages of economy, environmental protection, accurate data, rapidness, no damage and the like, and is widely applied to the food field.
Since 1945, the first discovery of nuclear magnetic resonance by the american physicists Bloch and Purcell has led to an increasingly widespread application of nuclear magnetic resonance techniques, which are mainly the nuclear transition of specific nuclei in a sample substance under certain actions and the generation of nuclear magnetic resonance signals to reflect some of the intrinsic properties of the sample substance. Nuclear magnetic resonance instruments can be generally classified into two types, high-field nuclear magnetic resonance and low-field nuclear magnetic resonance according to magnet field intensity. The low-field nuclear magnetic resonance, that is, nuclear magnetic resonance with a magnetic field strength of 0.5T or less, is mainly used for analysis of physical properties of a sample. The LF-NMR measurement index is mainly relaxation time, and relaxation refers to 1 The H-nuclei transition from a high energy state to a low energy state in a non-radiative manner. LF-NMR is mainly performed by determining the longitudinal relaxation time T 1 Transverse relaxation time T 2 And the diffusion coefficient D reflects the specific protons in the sample 1 H) Is a motion property of (c). To obtain information such as the physical and chemical environment in the system, the water flow distribution and the like to analyze the target components in the sample, the relaxation time T of the sample can be analyzed 1 And T 2 I.e. spin, interaction between the environment and the spin. The technology can observe the internal structure of the sample under the condition of no damage, and measure various indexes such as grease, moisture, protein and the like in the sample, and the technology is generally not influenced by the size and the shape of the sample, and has good detection effect and accuracy.
The current standard method for measuring the moisture and fat content is mainly a 105 ℃ drying constant weight method and the like, and the traditional dehydration modes belong to evaporation or sublimation of the moisture in the meat by physical means, so that the effect of removing the moisture can be achieved, but the traditional method needs longer pretreatment time for dehydration.
The prior art has applied low field nuclear magnetic resonance techniques to detect moisture and fat content in food products. For example, CN105606637a discloses a method for detecting the moisture and fat content in abalone by using low-field nuclear magnetic resonance technology, which can detect the moisture and fat content in abalone simultaneously, is not affected by the surface properties of abalone, and the measuring process has no damage to abalone itself. However, in the method, a method for establishing a prediction model is quantitatively used, water-oil signals are not obviously distinguished in pretreatment, and big data learning is performed by using a statistical means, so that if more accurate quantitative values are expected to be obtained, as many representative samples as possible need to be selected when the model is established.
At present, the prior art has no method for simultaneously and accurately detecting the moisture and fat content in livestock meat by a low-field nuclear magnetic resonance technology.
Disclosure of Invention
To solve the above technical problems, a first aspect of the present invention provides a method for detecting moisture and fat content of livestock meat by using low-field nuclear magnetic resonance technology, comprising the following steps:
(1) Sample preparation: stirring fowl and livestock meat into meat emulsion, uniformly dividing into two parts, and firstly weighing one part with mass of M f To be added with MnCl 2 ·4H 2 O solution, vortex mixing, standing, preserving heat,obtaining a first sample to be tested; weighing another sample with mass of M, and adding no MnCl 2 ·4H 2 O solution, directly preserving heat to obtain a second sample to be detected;
(2) Determination of the samples: acquiring signals of a sample to be detected by using a low-field nuclear magnetic resonance analyzer to obtain two main relaxation peaks, wherein the second relaxation peak is a fat peak, and the peak area is recorded as A f The method comprises the steps of carrying out a first treatment on the surface of the Acquiring signals of a sample to be detected to obtain T 2 The spectrogram is subjected to inversion calculation to obtain a total peak area which is recorded as A;
(3) Establishment of a calibration curve: selecting MnCl with different qualities 2 ·4H 2 The O solution and the livestock oil are respectively used as standard samples for quantifying moisture and fat, and nuclear magnetic signals are acquired by using the same parameters as those of sample detection to obtain T 2 A spectrogram; linear fitting is carried out by taking the abscissa as the water mass or the livestock oil mass and the ordinate as the peak area, and the obtained fat mass linear equation is recorded as Y=a f X+b f The moisture mass linear equation is noted as y=a w X+b w ；
(4) Calculation of moisture and fat content: the fat content was calculated according to the following formula: f= (a f -b f )/(a f ·M f ) X 100%, wherein F is fat content, A f For the fat peak area, M, of the livestock meat sample to be detected f The mass of the sample is pretreated by manganese chloride solution; the moisture content was calculated according to the following formula: w= [ (A/M) - (A) f /M f )-b w ]/a w X 100%, wherein W is the moisture content, a is the total peak area of fresh meat, and M is the mass of fresh meat sample.
Preferably, the livestock meat in the method step (1) is pork.
Preferably, mnCl is added in the method step (1) 2 ·4H 2 The mass concentration of the O solution is 5-50%, more preferably MnCl is added 2 ·4H 2 The mass concentration of the O solution is 10-30%, and more preferably MnCl is added 2 ·4H 2 The mass concentration of the O solution is 20-30%, most preferably MnCl is added 2 ·4H 2 The mass concentration of the O solution was 20%.
Preferably, mnCl is added in the method step (1) 2 ·4H 2 The volume of the O solution is 1-3ml, more preferably MnCl is added 2 ·4H 2 The volume of the O solution was 1.5ml.
Preferably, in the step (1) of the method, the vortex mixing time is 5-20min, more preferably, the vortex mixing time is 10min.
Preferably, in the step (1) of the method, the mixture is stirred and mixed uniformly and then is kept stand for more than 30 minutes, more preferably, the mixture is stirred and mixed uniformly and then is kept stand for more than 60 minutes.
Preferably, the incubation temperature of the first sample to be tested and the second sample to be tested in the step (1) of the method is 50-70 ℃, more preferably, the incubation temperature is 50 ℃.
Preferably, the detection parameters in the method step (2) are set as follows: the resampling wait time TW is 2000ms, the echo time TE is 0.3ms, and the resampling number NS is 32.
Preferably, the detection parameters in the method step (2) are set as follows: the receiver bandwidth SW is 200, the analog gain RG1 is 20, the digital gain DRG1 is 3, the pre-amplification gain PRG is 2, and the parameter control RFD for the start sampling time is 0.08ms.
Preferably, the livestock oil in the step (3) of the method is lard.
Preferably, in step (3) of the method, mnCl 2 ·4H 2 The mass concentration of the O solution was 0.85%.
Preferably, in step (3) of the method, mnCl of different masses 2 ·4H 2 The O solutions were 0.4958g,0.9916g,1.4884g,1.9808g,2.4823g and 2.9867g, respectively, and the poultry meat of different masses were 0.0248g,0.0398g,0.0809g,0.1637g,0.2492g,0.3282g,0.4868g and 0.6413g, respectively.
Preferably, the fat mass linear equation obtained in the method step (3) is y=34319x+82.457, and the moisture mass linear equation y=344638x+98.647.
The second aspect of the present invention provides MnCl 2 ·4H 2 The O solution is applied to a method for detecting the moisture and fat content of livestock meat by using a low-field nuclear magnetic resonance technology.
The invention has the beneficial effects that: the method for detecting the moisture and fat content in the food by the low-field nuclear magnetic resonance technology reported in the prior art lacks a pretreatment process, and can not effectively distinguish the moisture and fat detection signals obviously, so that the detection result is inaccurate.
Drawings
FIG. 1 shows the effect of a manganese chloride solution on a multi-component relaxation spectrum of lard oil;
FIG. 2 shows the effect of manganese chloride solution on a multi-component relaxation spectrum of pork;
FIG. 3 shows the effect of resampling latency on signal stability;
FIG. 4 shows the effect of echo time on a relaxation spectrum;
FIG. 5 shows the effect of echo time on the degree of signal attenuation;
FIG. 6 shows the effect of the number of repeated scans on the signal to noise ratio;
FIG. 7 shows the effect of repeat scan times on a relaxation spectrum;
FIG. 8 shows the number of repeated scans with A 22 Is a correlation of (2);
FIG. 9 shows the effect of mass concentration of manganese chloride solution on relaxation spectra;
FIG. 10 shows solution volume versus T 2 Spectrogram influence;
FIG. 11 shows blending time versus T 2 Spectrogram influence;
FIG. 12 shows the effect of rest time on T2 spectra;
FIG. 13 shows a spectrum of lard T2 of different mass;
FIG. 14 shows standard curves for different quality lard;
FIG. 15 shows calibration curves for different mass concentration manganese chloride solutions;
FIG. 16 shows the T2 spectra of different mass manganese chloride solutions (mass concentration of 0.85%);
FIG. 17 shows standard curves for different mass manganese chloride solutions (mass concentration of 0.85%);
fig. 18 shows a low field nuclear magnetic method compared to soxhlet extraction fat content.
Detailed Description
Test example 1 detection of moisture and fat content of livestock meat Using Low field Nuclear magnetic resonance technology
1. Test method
1.1 determination of moisture and fat content
According to the measurement of fat in GB 5009.6-2016 food and the measurement of moisture in GB 5009.3-2016 food.
1.2, low field Nuclear magnetic resonance Signal acquisition
1.2.1 sample treatment methods
A uniformly stirred minced pork was weighed 2.0g (M f ) Adding MnCl with certain mass concentration and certain volume into a nuclear magnetic sample bottle 2 ·4H 2 O solution is evenly mixed and kept at constant temperature for signal acquisition after standing, the same sample cannot be continuously acquired, and the sample is put back into a dry type thermostat to be kept at constant temperature after the signal is acquired once, and then the next signal acquisition is carried out.
Weighing 2.0g (M) of uniformly stirred minced pork in a nuclear magnetic sample bottle, and adding no MnCl 2 ·4H 2 And (3) directly keeping the temperature of the O solution and then collecting signals.
1.2.2 Signal acquisition method
The instrument was first calibrated using a free induction decay (Free induction decay, FID) sequence according to the instrument operating instructions. Setting certain detection parameters under CPMG sequence, and collecting transverse (T 2 ) Relaxation signals. Three replicates were taken per sample and each sample was scanned in duplicate, and relaxation data was expressed as mean ± standard deviation.
1.3 determination of instrument parameters
The parameters detected by the instrument mainly consist of two parts, namely a system parameter and a sampling parameter. Wherein the system parameters are determined by the instrument characteristics, the environment and the corresponding pulse sequence, the instrument automatically adjusts the parameters under the FID sequence. Including center frequency, 90 pulse and 180 pulse. The sampling parameters are determined by the instrument characteristics and the research purpose, and mainly comprise: number of repeated scans (number ofrepeated scans, NS), repetition Time (TR), echo Time (TE) and echo count (NECH). Where TR has no significant effect, but NECH needs to ensure complete attenuation of the sample signal. Therefore, the test mainly examines NS and TE.
1.3.1 waiting Time (TW)
The repeated sampling waiting time is the time from the end of the previous sampling to the start of the next sampling. If TW is set too short, the amplitude of the signal will decrease in the next sampling, and in general, TW is set to be more than 5 times of T1, so that the signal of the sample is ensured to be recovered by at least 98%. The test sets the latency to 1000ms, 1500ms, 2000ms, 2500ms, 3000ms, 3500ms and 4000ms, compares the signal mode maximum and makes it relatively stable as an optimal condition.
1.3.2 echo Time (TE)
After the rf pulse, the time interval from the initial generation of the transverse magnetization to the reception of the signal is called the echo time, which is typically greater than 6 times the 90 pulse width set point. In the test, TE is set to be 0.1, 0.15, 0.2, 0.25, 0.3 and 0.35ms respectively, the attenuation degree and the relaxation information of the curves are compared, and the final attenuation signal amplitude is the average value of ten signal amplitudes at the end.
1.3.3 times of repeated scans (NS)
The number of repeated scans is the number of repeated samplings performed by the instrument. The number of NS is set to 16, 32, 64 and 128 times according to the actual signal strength of the sample, and the sample is compared and analyzed to obtain T 2 Relaxation characteristics of the spectrogram and signal-to-noise ratio, wherein the signal-to-noise ratio is the average value of 10 signals of the first point signal/the tail point.
1.4 determination of sample pretreatment conditions
The test mainly examines the mass concentration, the adding volume and the mixing time of the manganese chloride solutionThe rest time and the sample temperature were measured on the fat peak area (A 22 ) Is a function of (a) and (b).
1.4.1 mass concentration of manganese chloride solution
1ml of manganese chloride solutions with different mass concentrations (5%, 10%, 15%, 20%, 30%, 40%, 50% and 60%) are respectively added into the sample, the sample is kept stand at 50 ℃ and then signals are collected in a nuclear magnetic sample tube, and the change of the signals of different samples is examined.
1.4.2 volumes of manganese chloride solution
After adding different volumes (0.5 ml, 1.0ml, 1.5ml, 2.0ml and 3.0 ml) of manganese chloride solution with mass concentration of 20%, the change of the signal of different samples was examined after collecting the signal.
1.4.3 mixing time
1ml of manganese chloride solution with the mass concentration of 20% is added into 2g of meat emulsion, vortex mixing is carried out for different times (3 min, 5min, 10min, 15min and 20 min), then standing is carried out for 30min at 50 ℃, and the change of signals of different samples is inspected after the signals are collected.
1.4.4 standing time
After weighing 2g of meat emulsion, adding 1ml of manganese chloride solution with mass concentration of 20%, mixing by vortex for 10min, standing at 50 ℃ for different times (10 min, 30min, 60min, 120min, 180min and 240 min), collecting signals, and inspecting the change of signals of different samples.
1.4.5 sample temperature
The sample was added with 1ml of 20% manganese chloride solution, allowed to stand at different temperatures (32 ℃, 40 ℃, 50 ℃, 60 ℃ and 70 ℃) for 30 minutes, and the signal was collected and then the signal change of the different samples was examined.
1.5 determination of the concentration of the moisture quantitative Standard sample
1g of manganese chloride solutions with different concentrations (0.5%, 1.0%, 3.0%, 5.0%, 8.0% and 10.0%) were weighed respectively, and a calibration curve of the water peak area and the solution concentration was established to obtain equation E1. And carrying out E1 calculation according to the change degree of the peak area when the sample reduces 1g of water, so as to obtain the solution concentration with consistent hydrogen proton density.
1.6 drawing of Standard Curve
Drawing a fat quantification standard curve: weighing lard of different mass, taking mass as abscissa, fat peak area (A 22 ) A linear equation is established for the ordinate by least squares regression, specifically as follows:
Y＝a f X+b f (1)。
drawing a moisture quantitative standard curve: weighing manganese chloride solutions with different mass of 0.85%, taking the mass of water in the solution as the horizontal and vertical coordinates, and the area of the water peak (A 21 ) A linear equation is established for the ordinate by least squares regression, specifically as follows:
Y＝a w X+b w (2)
1.7 calculation of fat and moisture content
The fat content was calculated according to the following formula: f= (a f -b f )/(a f ·M f )×100％
Wherein F is fat content, A f For the fat peak area of the pork sample to be detected, M f Is the mass of the sample pretreated by the manganese chloride solution.
The moisture content was calculated according to the following formula: w= [ (A/M) - (A) f /M f )-b w ]/a w ×100％
Wherein W is the moisture content, A is the total peak area of fresh meat, and M is the mass of fresh meat sample.
1.8, data analysis
The relaxation data results under different processing conditions were analyzed for significance by variance using SPSS software, origin software mapping. Multi-component inversion is carried out by self-contained analysis software of low-field nuclear magnetic resonance spectrometer to obtain T 2 Spectrograms, data are all expressed as mean ± standard deviation.
2. Test results
2.1 Effect of manganese chloride solution pretreatment on Multi-component relaxation spectra of lard and pork
The invention firstly utilizes a low-field nuclear magnetic resonance apparatus to examine the influence possibly generated by the pretreatment of livestock meat by using the manganese chloride solution.
FIG. 1 shows the steps before and after adding 1ml of 40% strength by mass manganese chloride solution to lard of different massesT 2 Changes in the spectrogram. From the figure, two completely separated relaxation peaks, T, can be observed 21 And T 22 The distribution ranges of (a) are 0.01-0.977ms,16.832-622.257ms respectively. T in the sample added with manganese chloride solution 21 The peaks show hydrogen protons in solution, whereas in pure oil samples T 21 Peaks are likely to be "false positives" due to systematic errors in the instrument caused by too small a volume. T (T) 22 The peak is a relaxation peak generated by the fat in the sample, so that only the fat bulk peak T is compared thereafter 22 The variation of the (A) shows that the distribution curves of the lard with different qualities are almost completely consistent before and after the manganese chloride solution is added into the lard 22 There was no significant difference in (peak area), indicating that the manganese chloride solution did not affect the relaxation properties of the lard. Manganese ions are paramagnetic ions and are soluble in water but insoluble in oil, so that only hydrogen ions in water are affected, and signals of hydrogen ions in fat or oil are not affected.
As can be seen from FIG. 2, pork T 2 The spectrum is also composed of two peaks, in which the relaxation time is shorter T 21 The peak represents bound water, T 22 Peaks are produced by the combination of moisture and fat in the meat, and it is difficult to distinguish between the two from the curve. Therefore, manganese ions are added into pork and permeate into water of a sample through ion migration, and after the manganese chloride solution is added, the T is obviously observed 22 The peak area is greatly reduced, T 21 The peak becomes larger, on the one hand because the water in the sample is affected by the manganese ions and the relaxation time shifts to the left, on the other hand the hydrogen signal due to the added manganese chloride solution. Treated pork sample and lard T 22 There was no significant difference, at which point T was considered 22 The peaks are only generated by hydrogen protons in fat, and many studies have also shown that the relaxation time of lipids is typically around 100ms, because hydrogen in lipids has a more complex structure than moisture and thus flowability is limited.
2.2, optimizing the test results of the instrument detection parameters
2.2.1 waiting time
As shown in FIG. 3, the mode maximum value of the sample at each waiting time is preservedThe sample is stable, and the variation range of the maximum value of the front and back modes is less than 1%, which indicates that the sample can be restored to the equilibrium state in the selected waiting time. The time for waiting for the different samples is different, which is related to the speed at which they release energy, taking into account the difference in fat content of the different samples, T 2 Also different (see table 1), so that the TW is set to 2000ms to meet the detection requirements of all livestock and poultry meat samples.
TABLE 1 Effect of fat content on relaxation time
| Fat content (%) | Relaxation time T 2 |
| 0.818±0.007 | 7.42±2.22 |
| 1.365±0.066 | 46.36±8.9 |
| 3.428±0.1102 | 94.17±0.96 |
| 5.936±0.245 | 128.33±1.9 |
| 6.450±0.121 | 126.25±2.93 |
| 23.052±0.334 | 171.3±3.33 |
2.2.2 echo time
FIG. 4 shows T at different echo times 2 The spectrogram can be obviously observed that the echo time leads to T 21 The peak moves to the right and the peak area decreases significantly. This is because the self-diffusion of moisture is stronger than that of oil, and the change in the echo time affects the molecular self-diffusion and the relaxation properties of the molecular exchange, the longer the echo time, the stronger the molecular self-diffusion, resulting in a transverse relaxation time T 2 Is a prolonged period of time. Within 0.35ms, the echo time changes do not have a significant effect on fat peak area and relaxation time. At the same time, the echo time can have an influence on the attenuation degree of the CPMG curve and the distribution interval of the relaxation time.
FIG. 5 shows the attenuation of different echo times, when the echo time is 0.1ms, the signal amplitude of the sample is attenuated to 257.42, T is increased with TE 2 The relaxation interval is gradually increased, the final signal amplitude of the attenuation curve is also gradually reduced to 57.31, the final signal attenuation amplitude does not change significantly after the echo time is 0.3ms, the signal is considered to be completely attenuated at the moment, the stability of the peak area is also good, and the RSD is less than 5%, so that the echo time is selected to be 0.3ms.
2.2.3 times of repeated scanning
The number of repeated scans has a direct effect on the signal-to-noise ratio of the sample, with higher signal-to-noise ratios requiring more repeated scans. In fig. 6, as the number of repeated scans increases, the signal-to-noise ratio increases from the original 184.82 to 290.44, and of course, the time taken to acquire the signal increases exponentially, there is no significant difference in signal-to-noise ratio between 32 scans and 64 scans, and it takes longer to scan 128 scans to significantly increase the signal-to-noise ratio, thereby decreasing the efficiency of detection. As can be seen from FIG. 7, T is detected for different scan times 2 Spectrograms, each exhibiting two peaks, can be found from FIG. 8 for NS and A 22 There is a good linear relationship (y= 64.41X-5.0905), R 2 Reaching 0.9999. There are studies showing that an increase in the number of repeated scans may cause the magnet to heat up, resulting in a slight change in the temperature of the sample, from T 22 The right shift of the peak can be manifested. Thus, considering the combination of the above, it is considered that the repeated scans are performed 32 times, and the relaxation characteristics of the sample show good stability (RSD less than 5%).
2.3 optimization test of pretreatment conditions of manganese chloride solution
2.3.1 mass concentration of manganese chloride solution
FIG. 9 is a graph of T after adding different mass concentrations of manganese chloride solution to pork 2 Spectrogram, T caused by moisture in sample with increasing concentration 21 The peak moves leftwards, when the concentration reaches about 10%, the relaxation time is basically stable, only the peak area gradually decreases, and when the manganese ion content increases, the peak area of the moisture is reduced, because the manganese ion accelerates the relaxation of hydrogen in water, and therefore, most of the hydrogen proton signals are lost. This is probably because when the concentration of manganese ions is too low, there are no manganese ions that can be dissolved in the moisture in the meat. At the same time T 22 The peak also shifts significantly to the left until the mass concentration is 20%, T 22 Peak shape is similar to lard, A 22 No significant change occurs, RSD gradually increases with increasing solution concentration, RSD is already up to 14.52% at 50% concentration, and RSD is only 2.38% at 20% concentration (see table 2), which can be satisfactory. In combination with the above analysis, the concentration of the manganese chloride solution was set to 20% most suitably.
TABLE 2 mass concentration of manganese chloride solution versus fat peak area (A 22 ) Influence of (2)
| Mass concentration | A 22 | RSD |
| 1％ | 292.84 c ±78.52 | 26.81％ |
| 5％ | 437.03 b ±11.32 | 2.59％ |
| 10％ | 433.51 b ±3.83 | 0.88％ |
| 20％ | 472.38 a ±11.24 | 2.38％ |
| 30％ | 488.24 a ±14.67 | 3.01％ |
| 40％ | 480.95 a ±30.67 | 6.38％ |
| 50％ | 465.41 ab ±67.59 | 14.52％ |
Note that: a is that 22 The same letter (a, b, c) in the upper right hand corner of the data indicates that the peak area difference is not significant (p>0.05 The peak area varies significantly from letter to letter (p<0.05 The upper right hand letter meaning of the data in tables 3-6 below is the same as in table 2.
2.3.2 adding volume of manganese chloride solution
Table 3 shows the relaxation behavior of the fat in the sample when different volumes of manganese chloride solution were added, whenThe area of the fat peak at the inlet volume of 1.5-3.0ml is significantly higher than that of the treatment group added with 0.5-1.0ml, and the relative standard deviation of the sample gradually decreases with the increase of the volume of the solution, and the sample stability is the worst when 0.5ml is added, and the RSD is 5.05%. From T 2 The spectrum 10 also shows that the distribution of relaxation peaks is substantially stable when the added volume is greater than 1.5ml, and T is greater when the added volume is greater 21 The smaller the peak, the more volume of solution added indicates that more manganese ions are added to the sample and thus have an effect on more moisture hydrogen protons, whereas an excessively small volume of solution may be due to T 21 The peak is relatively large, resulting in a peak to peak ratio T 22 The result of the peak inversion was more biased and therefore the addition volume was chosen to be 1.5ml.
TABLE 3 Effect of manganese chloride solution volume on fat peak area
| Volume of solution | A 22 | RSD |
| 0.5ml | 404.3 a ±20.41 | 5.05％ |
| 1ml | 413.15 a ±14.68 | 3.55％ |
| 1.5ml | 442.93 b ±13.27 | 3.00％ |
| 2ml | 439.93 b ±10.09 | 2.29％ |
| 3ml | 440.26 b ±9.58 | 2.18％ |
2.3.3 mixing time
To ensure that the added manganese chloride solution can fully contact the sample, different mixing times are compared, and the result is shown in Table 4, sample A is mixed for 3min 22 The mixing time is obviously lower than other mixing time, after the manganese chloride is added, the manganese chloride needs to be fully combined with moisture in meat, so that the purpose of water-oil signal separation is achieved, and when the mixing time is too short, the manganese chloride solution can not be fully mixed with meat emulsion, so that the magnetic field of hydrogen ions in lipid is influenced. When the mixing time is more than 5min, no obvious change occurs, and meanwhile, T is observed 2 The spectrum (FIG. 11) also shows T at different mixing times 22 No significant differences and T between treatment groups 22 The peak distribution remained almost uniform, and T 22 The peak areas RSD were all less than 5%, but to ensure that the samples were thoroughly mixed, the optimal mixing time was considered to be 10min.
TABLE 4 Effect of blend time on fat peak area
| Mixing time | A 22 | RSD |
| 3min | 415.77 a ±10.54 | 2.54％ |
| 5min | 425.83 b ±12.83 | 3.01％ |
| 10min | 427.78 b ±12.13 | 2.84％ |
| 15min | 432.08 b ±15.56 | 3.60％ |
| 20min | 435.97 b ±8.40 | 1.93％ |
2.3.4 standing time
The sample needs to be kept stand for a period of time to ensure that manganese ions completely permeate, and to keep the sample at a constant temperature to observe T 2 The spectrum (FIG. 12) shows little T against different rest times 22 The peak shape and the relaxation time are influenced, the fat peak area is not changed obviously along with the change of the standing time, and the RSD is less than 5% at different times, so that in order to ensure that the samples are constant in temperature and consistent in temperature, it is recommended to ensure that the standing time is at least 30min so that the samples are constant in temperature.
TABLE 5 influence of the rest time on the fat peak area
| Standing time | A 22 | RSD |
| 10min | 462.29 a ±14.89 | 3.22％ |
| 30min | 468.51 a ±10.51 | 2.24％ |
| 60min | 469.47 a ±7.5 | 1.60％ |
| 120min | 473.24 a ±18.06 | 3.82％ |
| 180min | 474.72 a ±14.62 | 3.08％ |
| 240min | 473.98 a ±6.98 | 1.47％ |
2.3.5 sample temperature
Analysis of relaxation times (T) under different temperature conditions 22 ) Sum peak area (A) 22 ) Is a difference in (a) between the two. As can be seen from Table 6, the relaxation time increases with increasing temperature due to hydrogenThe binding force of protons is weakened, so that the fluidity of grease molecules is increased. Peak area peaks at a temperature of 40 ℃ and is significantly higher than other sample temperatures, but peak area ratio (P 22 ) Exhibiting a certain downward trend. When the temperature is higher than 50 ℃, the peak area is not changed significantly any more, and the melting point of animal fat is 23-48 ℃ and the temperature is lower than 50 ℃, the existence state of the lipid can have both solid lipid crystals and liquid components, so that the temperature of the sample is determined to be 50 ℃ in order to ensure that all the sample is liquid fat, and the relative standard deviation of the peak area of the sample fat is 3.52%, which indicates that the stability of the sample is better under the condition.
TABLE 6 influence of sample temperature on relaxation behavior
| Sample temperature | T 22 | A 22 | P 22 |
| 32℃ | 69.13±12.1 | 474.46 a ±18.16 | 9.95±0.95 |
| 40℃ | 88.49±13.39 | 534.33 b ±31.73 | 9.59±0.61 |
| 50℃ | 106.12±14.58 | 483.39 a ±17.03 | 8.54±1.15 |
| 60℃ | 137.45±12.49 | 485.23 a ±25.83 | 6.8±0.55 |
| 70℃ | 142.33±40.64 | 489.72 a ±37.09 | 5.69±0.33 |
2.4 drawing of Standard Curve
FIG. 13 shows the results of signal acquisition on standard samples prepared from lard of different qualities, where T 22 The peak is fat peak, and T is increased with the increase of lard quality 22 The peak also becomes larger. As can be seen from FIG. 14, A is in the range of 0.0248-0.6413g of lard mass 22 The regression equation obtained by fitting is Y=3499X+82.457, and the correlation coefficient R is linear with the increase of the mass 2 1.000, indicating a very significant correlation between the two. And according to the peak area reading, the corresponding fat mass in the sample can be calculated, so that the fat content can be calculated.
FIG. 15 is a calibration curve of manganese chloride solutions of different mass concentrations, in which a negative correlation between the solution concentration and the peak area, a power-of-power correlation between the two, and a correlation coefficient R 2 0.9505, the fitted curve is y= 43.496x -0.82 . The degree of change in peak area per 1g of water reduced in the sample was obtained from the previous experiment, and the peak area was found to be uniform when the mass concentration of the solution was 0.85%. Thus taking manganese chloride solutions with different masses as x-axis, A 21 A standard curve is established for the y-axis,as in fig. 15. FIG. 16 is a T of different mass manganese chloride solutions 2 Spectrogram, obviously found that as the quality of the solution increases, T 21 The peak increases with it and is similar to fat, the water mass in solution is equal to A 21 Has extremely high correlation, and the regression equation obtained by fitting is Y=34468X+98.647, R 2 1.000 (FIG. 17). The moisture content in the sample can be calculated according to the standard curve.
2.5 quantitative detection test of moisture and fat in pork
The method of the present invention was compared with the national standard moisture and fat determination methods (determination of fat in food GB 5009.6-2016 and determination of moisture in food GB 5009.3-2016), wherein FIG. 18 shows a linear relationship between fat content determined by the different methods. The correlation coefficient of the two methods is 0.99, which indicates that the fat content can be quantified by using lard as a standard sample to establish a calibration curve. Table 7 shows that the relative error between the two can reach below 5% compared with the water content measured by the traditional drying method and the low-field nuclear magnetic method, and the method can achieve the effect of simultaneously measuring water and oil.
Table 7 comparison of moisture content in low field nuclear magnetic method and direct drying method
Claims (7)
1. A method for detecting the moisture and fat content of livestock meat by using a low-field nuclear magnetic resonance technology, which is characterized by comprising the following steps:
(1) Sample preparation: stirring fowl and livestock meat into meat emulsion, uniformly dividing into two parts, and firstly weighing one part with mass of M f To be added with MnCl 2 ·4H 2 Mixing the O solution uniformly by vortex, standing, and preserving heat to obtain a first sample to be tested; weighing another sample with mass of M, and adding no MnCl 2 ·4H 2 O solution, directly preserving heat to obtain a second sample to be detected;
(2) Determination of the samples: acquiring signals of a sample to be detected by using a low-field nuclear magnetic resonance analyzer to obtain two main relaxation peaks, wherein the second relaxation peak is a fat peak, and the peak area is recorded as A f The method comprises the steps of carrying out a first treatment on the surface of the Acquiring signals of a sample to be detected to obtain T 2 The spectrogram is subjected to inversion calculation to obtain a total peak area which is recorded as A;
(3) Establishment of a calibration curve: selecting MnCl with different qualities 2 ·4H 2 The O solution and the livestock oil are respectively used as standard samples for quantifying moisture and fat, and nuclear magnetic signals are acquired by using the same parameters as those of sample detection to obtain T 2 A spectrogram; linear fitting is carried out by taking the abscissa as the water mass or the livestock oil mass and the ordinate as the peak area, and the obtained fat linear equation is recorded as Y=a f X+b f The moisture linear equation is noted as y=a w X+b w ；
(4) Calculation of moisture and fat content: the fat content was calculated according to the following formula: f= (a f -b f )/(a f ·M f ) X 100%, wherein F is fat content, A f For the fat peak area, M, of the livestock meat sample to be detected f The mass of the sample is pretreated by manganese chloride solution; the moisture content was calculated according to the following formula: w= [ (A/M) - (A) f /M f )-b w ]/a w X 100%, wherein W is the moisture content, A is the total peak area of fresh meat, and M is the mass of fresh meat sample;
the MnCl is added in the step (1) 2 ·4H 2 The mass concentration of the O solution is 10-30%;
the detection parameters in the step (2) are set as follows: the resampling wait time TW is 2000ms, the echo time TE is 0.3ms, and the resampling number NS is 32.
2. The method of claim 1 wherein the livestock meat in step (1) is pork.
3. The method of claim 1, wherein the step of determining the position of the substrate comprises,MnCl is added in the step (1) 2 ·4H 2 The mass concentration of the O solution is 20-30%.
4. The method according to claim 1, wherein MnCl is added in step (1) 2 ·4H 2 The volume of the O solution is 1-3ml.
5. The method of claim 1, wherein the vortex mixing time in step (1) is from 5 to 20 minutes.
6. The method of claim 1, wherein the step (1) is performed by vortexing and then standing for 30 minutes or more.
7. The method according to claim 1, wherein the incubation temperature of the first sample to be measured and the second sample to be measured in the step (1) is 50 to 70 ℃.
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