CN111413294B - Method for rapidly detecting wax in sunflower seed oil - Google Patents

Method for rapidly detecting wax in sunflower seed oil Download PDF

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CN111413294B
CN111413294B CN202010242352.3A CN202010242352A CN111413294B CN 111413294 B CN111413294 B CN 111413294B CN 202010242352 A CN202010242352 A CN 202010242352A CN 111413294 B CN111413294 B CN 111413294B
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smelting pipe
melting
smelting
wax
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CN111413294A (en
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于修烛
李泳霖
黄丹
陈佳
魏存成
刘恒
马世康
欧阳韶晖
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Changanhua Grain Oil Co ltd
Weinan Shiyang Changanhua Grain Oil Co ltd
Northwest A&F University
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Changanhua Grain Oil Co ltd
Weinan Shiyang Changanhua Grain Oil Co ltd
Northwest A&F University
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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Abstract

The invention discloses a method for rapidly detecting wax in sunflower seed oil, which comprises the following steps: step one, sample loading; step two, zone melting: solidifying a sample in a smelting pipe by using a refrigerant, melting a zone sample in the smelting pipe by using a heating coil to form a melting zone, moving the spraying position of the refrigerant on the smelting pipe and the heating position of the heating coil on the smelting pipe, moving the melting zone from one end of the smelting pipe to the other end of the smelting pipe at the speed of 0.5-1.1 mm/s, recording the movement from one end of the smelting pipe to the other end as one time, repeatedly carrying out 15-25 times, and taking out the sample at the starting point and placing the sample in a small test tube; step three, low-temperature crystallization; and step four, detecting crystallization. The detection method can quantitatively detect 10-200 mg/kg wax in the sunflower seed crude oil or refined oil, and has good accuracy. The detection method can greatly shorten the detection time to be within 2 hours.

Description

Method for rapidly detecting wax in sunflower seed oil
Technical Field
The invention belongs to the field of edible oil, relates to sunflower seed oil, and particularly relates to a rapid detection method for wax in the sunflower seed oil.
Background
The sunflower seed oil is an important edible oil product, has high linoleic acid content and good stability, and has various physiological functions, however, the seed coat of the sunflower seed contains about 2.5-3% of wax, the wax is mainly ester formed by free fatty acid and higher fatty alcohol, the carbon chain length of the fatty acid is mainly between 16-24, and the carbon chain length of the fatty alcohol is mainly between 23-37. At temperatures above 40 ℃, waxes are lipophilic, non-polar and soluble in oil; at temperatures below 30 ℃, waxes exhibit crystallinity and poor hydrophilicity. Wax enters oil along with the oil extraction process, when the oil is transported to a region with lower temperature for sale, if the wax content in the oil is too high due to the problems of raw materials or dewaxing process, the wax is gradually crystallized and separated out, so that the commodity sunflower seed oil is hazy or even turbid, and consumers mistakenly think that the oil is a adulterated product, thereby affecting the sale; in addition, the existence of the wax can also obviously reduce the digestibility of the vegetable oil, so that the nutritional quality of the vegetable oil is reduced. Therefore, the wax content detection has important significance for the product control of the sunflower seed oil.
At present, the methods for detecting the wax at home and abroad mainly comprise a freezing test method, an insoluble substance measuring method, a turbidimetric method, a chromatography method and the like. The freezing test is to place the oil at 0 deg.C for a period of time, the national standard stipulates that the freezing time is about 5.5 hours, and the waxy content can be determined by observing the turbidity degree [5] . The freeze test method, although simple to operate, relies primarily on visual observation, is less accurate and takes longer (> 6 hours). Some vegetable oils contain about 80mg/kg wax, which passes the 24 hour freezing test, but become hazy after 48 hours. To simplify the detection process, an insoluble assay was established. The method comprises the steps of adding acetone or butanone into vegetable oil to separate out wax, filtering the vegetable oil by quantitative filter paper, and accurately weighing the vegetable oil to obtain the wax content, wherein an instrument for measuring insoluble substances is simple and convenient to operate, but when the wax content is lower than 500mg/kg, the error is large, and the consumption of samples and reagents is large; in order to solve the problem, researchers use a turbidimetric method to measure the content of the wax in the vegetable oil, the turbidimetric method is simple, convenient and time-saving, and is the most common method for rapidly detecting the wax in the oil at present, but the method consumes toxic and harmful chemical reagents, and the accuracy of a measurement result needs to be improved. In order to improve the detection accuracy, the chromatography is applied to the determination of the vegetable oil waxy content. Researchers use gas chromatography to measure the wax content in vegetable oil, and Chaojie and the like use gas chromatography to measure the wax content in sunflower seed oil, the lowest detection limit of the method is 0.095 mug/mL, the standard recovery rate is 86.12% -106.62%, and the relative standard deviation is 1.92% -4.28%. Although the method has accurate result and high sensitivity, a chromatographic instrument is expensive and time-consuming to operate, and the measurement result cannot effectively reflect the anti-crystallization capability of the vegetable oil, so that the application range of the method is limited.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method for rapidly detecting wax in sunflower seed oil, and solves the problem that a detection device in the prior art is difficult to consider detection accuracy and detection rapidity.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for rapidly detecting waxiness in sunflower seed oil comprises the following steps:
step one, sample loading:
taking sunflower seed oil as a sample, putting the sample into a smelting pipe, and sealing two ends of the smelting pipe;
step two, zone melting:
solidifying a sample in a smelting pipe by using a refrigerant, melting a zone sample in the smelting pipe by using a heating coil to form a melting zone, moving the spraying position of the refrigerant on the smelting pipe and the heating position of the heating coil on the smelting pipe, moving the melting zone from one end of the smelting pipe to the other end of the smelting pipe at the speed of 0.5-1.1 mm/s, recording the movement from one end of the smelting pipe to the other end as one time, repeatedly carrying out 15-25 times, and taking out the sample at the starting point and placing the sample in a small test tube;
step three, low-temperature crystallization:
crystallizing the small test tube at-6 to-8 ℃ for 30 to 40min, and taking out;
step four, crystal detection:
irradiating the bottom of a small test tube by adopting a laser light source with the wavelength of 635-650 nm and the power of 5-10 mW, detecting the scattering of light by a crystal by using a photosensor in the direction vertical to the irradiation direction to obtain a level value, measuring the level value by using a voltmeter, and substituting the level value into a formula y =0.0131x +1.255 to obtain the wax content, wherein:
x is wax content in mg-kg -1 (ii) a y is a level value in units of V.
The invention also has the following technical characteristics:
preferably, in the second step, the melting zone is moved from one end of the melting tube to the other end at a speed of 0.7 to 1.1mm/s, and the movement from one end of the melting tube to the other end is counted once, and after repeating 18 to 21 times, the sample at the starting point is taken out and placed in a cuvette.
Specifically, in the first step, the smelting pipe is a smelting pipe with the outer diameter multiplied by the thickness phi 4 multiplied by 0.2mm to phi 6 multiplied by 0.2mm and the length 95mm to 120 mm; the sample amount added into the smelting tube is 960-1000 mul.
Preferably, in the step one, the smelting pipe is a smelting pipe with an inner diameter multiplied by a thickness phi of 4 multiplied by 0.2mm and a length of 95-100 mm.
Specifically, in the second step, the refrigerant is 1, 2-tetrafluoroethane.
Specifically, in the second step, the axial length of the heating coil is 9mm, and the power is 6-8W; the sample at the starting point is taken out by 130-150 mu L and placed in a small test tube with phi of 5X 20 mm.
Preferably, in the second step, the axial length of the heating coil is 9mm, and the power is 6.22-6.84W; the sample at the starting point was taken 150. Mu.L and placed in a cuvette of 5X 20 mm.
Compared with the prior art, the invention has the following technical effects:
the detection method can quantitatively detect 10-200 mg/kg wax in the sunflower seed crude oil or refined oil, and has good accuracy.
(II) the detection method can greatly shorten the detection time to within 2 hours;
(III) the assay method of the invention consumes less assay sample to 1mL.
(IV) the detection method does not use toxic and harmful chemical reagents, does not generate harmful wastes, and is environment-friendly.
Drawings
FIG. 1 is a schematic view of zone melting.
FIG. 2 is a schematic diagram of crystal detection.
FIG. 3 is a standard curve of level value versus wax content for sunflower oil.
FIG. 4 mid-IR spectra before and after zone melting containing 100.00mg/kg waxy sunflower oil.
FIG. 5 is a photomicrograph (640 times magnification) of a melt in the 100.00mg/kg waxy sunflower oil field.
FIG. 6 is a photomicrograph (640 times magnification) of 100.00mg/kg waxy sunflower oil after low temperature crystallization.
The meaning of the individual reference symbols in the figures is: 1-smelting tube, 2-heating coil, 3-small test tube, 4-laser light source, 5-optical sensor and 6-black inner surface.
The present invention will be explained in further detail with reference to examples.
Detailed Description
Zone melting is widely used in the fields of metallurgy and inorganic chemistry as a separation and purification technology. The principle is that under the condition of a certain temperature, the purposes of separation and purification of trace impurities are realized through different distribution concentrations of the trace impurities between a solid phase and a liquid phase (namely, segregation phenomenon of the impurities). The magnitude of the segregation of impurities is often described by the segregation coefficient:
at a certain temperature, the concentration of the impurity in the liquid phase is c l In the solid phase at a concentration of c s Defining the segregation coefficient K s ：
Figure SMS_1
In vegetable oils, the melting temperature range of the waxes is much higher than the melting point of the vegetable oil, so the K of the waxes is s More than 1, i.e. when the solid-liquid two-phase is formed, the wax concentration in the solid phase is constantly higher than that in the liquid phase. Therefore, based on the zone melting technology, wax-containing oil is subjected to zone melting treatment by using a heating coil and a refrigerant (non-toxic and harmless 1, 2-tetrafluoroethane is selected as the refrigerant), wax can be enriched and crystallized, and finally, quantitative analysis of wax content is realized by detecting the crystallization amount.
The wax content is obtained by carrying out zone melting treatment on the wax-containing oil, detecting the amount of crystallization by adopting a laser and a light sensor after the crystallization at low temperature, and substituting the amount of crystallization into a standard curve. Compared with the traditional method, the method only has a difference of about 3mg/kg from the true value, the standard deviation is less than 4mg/kg, the method has higher accuracy, is simple and convenient to operate, greatly shortens the detection time (within 2 hours), overcomes the defects of time consumption, labor consumption and the like in the traditional process, effectively reduces the sample consumption (less than 1 mL) in the vegetable oil detection process, saves the cost, and provides an accurate and environment-friendly method for quickly detecting the wax content of the edible oil.
To illustrate the changes in the oil sample during zone melting and crystallization, applicants examined the waxes in sunflower seed oil, scanned their infrared spectra, and photographed a photomicrograph of the crystals, with specific tests including:
raw materials: sunflower seed oil (first grade), shanxi grain agriculture oil group Co., ltd; crude oil (obtained by frying and squeezing); the sunflower seed wax is prepared by extracting and purifying factory filter cakes provided by Shanghai Jinlongyu grain oil food GmbH.
Instruments and equipment: a Vertex 70 fourier transform infrared spectrometer, bruker, germany; DMBA400 digital microscope, xiamen miaody industries ltd.
And (3) detection flow: as shown in fig. 1 and fig. 2, the method for rapidly detecting wax in sunflower seed oil of the present application is used.
Standard curve: a standard curve is prepared by referring to the detection process, the linear regression equation is y =0.0131x +1.255, R 2 =0.998, y level value in volts (V), x wax content in mg kg -1 The standard curve is shown in FIG. 3, in which the corresponding level values of the refined oils are subtracted.
Infrared spectrum: to illustrate the changes that occur to the sample during zone melting, mid-infrared spectra of 100.00mg/kg of accurately formulated sunflower seed oil before and after zone melting were scanned and the results are shown in FIG. 4.
As can be seen from FIG. 4, 913.5cm, representing a carbon-carbon double bond, was used after zone melting -1 、968.6cm -1 、1417.8 cm -1 、1654.1cm -1 And 3008.5cm -1 The absorbance at the position is reduced in different degrees, which shows that the concentration of double bonds is reduced, and the concentration of the carbon-carbon double bonds in the sample is relatively reduced because the wax does not contain the carbon-carbon double bonds, which shows that the wax content at the starting point is increased by zone melting, namely the wax is effectively enriched, thereby being beneficial to the subsequent crystallization process.
Photomicrographs: to illustrate the change of the sample during the zone melting and crystallization, 100.00mg/kg sunflower seed oil was subjected to zone melting and crystallization, and the crystal thereof was observed under a microscope, and the results are shown in FIGS. 5 and 6.
As can be seen from FIGS. 5 and 6, after zone melting, small crystals were observed, most of which were between 1 and 7 μm in size and a few of which were over 10 μm in size, whereas after low temperature crystallization, the number of crystals decreased and the size increased, and most of which were over 15 μm in size, and the scattering of the laser light was detected by the photosensor.
The following embodiments are given as examples of the present invention, and it should be noted that the present invention is not limited to the following embodiments, and all equivalent changes based on the technical solutions of the present invention are included in the protection scope of the present invention.
Example 1:
this example provides a method for rapidly detecting wax in sunflower seed oil, which includes the following steps:
step one, sample loading:
taking sunflower seed oil as a sample, putting the sample into a smelting pipe, and sealing two ends of the smelting pipe;
the smelting pipe is a smelting pipe with the outer diameter multiplied by the thickness phi 4 multiplied by 0.2mm and the length 95 mm.
The amount of the sample added to the melting tube was 960. Mu.L.
Specifically, the samples are divided into three types, wherein the first type is a sample with known concentration prepared from dewaxed refined oil, namely a No. 1-10 sample; the second is a randomly diluted sample of 1.009% mother liquor prepared from dewaxed refined oil, i.e. sample No. 11-17; the third type is a sample obtained by freezing crude oil at 0 ℃ for 8 hours, 12 hours and 24 hours and then filtering, namely a sample No. 18-20.
Step two, zone melting:
solidifying a sample in a smelting pipe by using a refrigerant, melting a zone sample in the smelting pipe by using a heating coil to form a melting zone, moving the spraying position of the refrigerant on the smelting pipe and the heating position of the heating coil on the smelting pipe, moving the melting zone from one end to the other end of the smelting pipe at the speed of 1.1mm/s, recording the movement from one end to the other end of the smelting pipe as one time, repeatedly carrying out the steps for 20 times, and taking out the sample at the starting point and placing the sample in a small test tube;
the refrigerant is 1, 2-tetrafluoroethane.
The axial length of the heating coil was 9mm and the power was 6.22W.
The sample at the start point was taken 150. Mu.L and placed in a small tube of 5X 20 mm.
Step three, low-temperature crystallization:
crystallizing the small test tube at-7 deg.C for 30min, and taking out;
step four, crystal detection:
irradiating the bottom of a small test tube by adopting a laser light source with the wavelength of 640nm and the power of 7.5mW, detecting the scattering of light by a crystal by using a light sensor in the direction vertical to the irradiation direction to obtain a level value, measuring the level value by using a voltmeter, and substituting the level value into a formula y =0.0131x +1.255 to obtain the wax content, wherein:
x is wax content in mg-kg -1 (ii) a y is a level value in units of V.
The samples in the embodiment were tested, and the test results are shown in table 1, and it can be seen from table 1 that the standard deviation of the test results of the method is less than 4mg/kg, the difference between the actual value and the test result of the nephelometry is about 5mg/kg at low wax content, the difference between the test result of the method and the actual value is about 3mg/kg, the accuracy is slightly higher than that of the nephelometry, and the test results of the method and the nephelometry are very close to the actual value with the increase of wax content.
Table 1 example 1 sunflower seed oil samples test results
Figure SMS_2
Figure SMS_3
Note: mean value. + -. Standard deviation of
Example 2:
this example provides a method for rapidly detecting wax in sunflower seed oil, which includes the following steps:
step one, sample loading:
taking sunflower seed oil as a sample, putting the sample into a smelting tube, and sealing two ends of the smelting tube;
the smelting pipe is a smelting pipe with the outer diameter multiplied by the thickness phi 4 multiplied by 0.2mm and the length 97 mm.
The amount of the sample added to the melting tube was 980. Mu.L.
Specifically, the samples are divided into three types, wherein the first type is a sample with known concentration prepared by dewaxed refined oil, namely a No. 1-10 sample; the second is a randomly diluted sample of 1.009% mother liquor prepared from dewaxed refined oil, i.e. sample No. 11-17; the third type is a sample obtained by freezing crude oil at 0 ℃ for 8 hours, 12 hours and 24 hours and then filtering, namely a sample No. 18-20.
Step two, zone melting:
solidifying a sample in a smelting pipe by using a refrigerant, melting a zone sample in the smelting pipe by using a heating coil to form a melting zone, moving the spraying position of the refrigerant on the smelting pipe and the heating position of the heating coil on the smelting pipe, moving the melting zone from one end to the other end of the smelting pipe at the speed of 0.9mm/s, recording the movement from one end to the other end of the smelting pipe as one time, repeatedly carrying out 18 times, and taking out the sample at the starting point and placing the sample in a small test tube;
the refrigerant is 1, 2-tetrafluoroethane.
The axial length of the heating coil was 9mm and the power was 6.52W.
The sample at the start point was taken 150. Mu.L and placed in a small tube of 5X 20 mm.
Step three, low-temperature crystallization:
crystallizing the small test tube at-6 deg.C for 35min, and taking out;
step four, crystal detection:
irradiating the bottom of a small test tube by adopting a laser light source with the wavelength of 635nm and the power of 5mW, detecting the scattering of light by a crystal by using a photosensor in the direction vertical to the irradiation direction to obtain a level value, measuring the level value by using a voltmeter, and substituting the level value into a formula y =0.0131x +1.255 to obtain the wax content, wherein:
x is wax content in mg-kg -1 (ii) a y is a level value in units of V.
The samples of the present embodiment were tested, and the test results are shown in table 2, as can be seen from table 2, the standard deviation of the measured value of the method is less than 4mg/kg, the difference between the result of the nephelometry and the actual value is about 5mg/kg at low wax content, the difference between the result of the method and the actual value is about 3mg/kg, the accuracy is slightly higher than that of the nephelometry, and the measured value of the method gradually approaches the true value as the wax content increases.
Table 2 example 2 detection results of sunflower seed oil samples
Figure SMS_4
Note: mean value. + -. Standard deviation of
Example 3:
this example provides a method for rapidly detecting wax in sunflower seed oil, which includes the following steps:
step one, sample loading:
taking sunflower seed oil as a sample, putting the sample into a smelting pipe, and sealing two ends of the smelting pipe;
the smelting pipe is a smelting pipe with the outer diameter multiplied by the thickness phi 4 multiplied by 0.2mm and the length of 100 mm.
The amount of the sample added to the melting tube was 1000. Mu.L.
Specifically, the samples are divided into three types, wherein the first type is a sample with known concentration prepared by dewaxed refined oil, namely a No. 1-10 sample; the second is a randomly diluted sample of 1.009% mother liquor prepared from dewaxed refined oil, i.e. sample No. 11-17; the third type is a sample obtained by freezing crude oil at 0 ℃ for 8 hours, 12 hours and 24 hours and then filtering, namely a sample No. 18-20. .
Step two, zone melting:
solidifying the sample in the smelting tube by using a refrigerant, melting the area sample in the smelting tube by using a heating coil to form a melting area, moving the spraying position of the refrigerant on the smelting tube and the heating position of the heating coil on the smelting tube, moving the melting area from one end to the other end of the smelting tube at the speed of 0.7mm/s, recording as one time when the melting area moves from one end to the other end of the smelting tube, repeatedly carrying out 21 times, and taking out the sample at the starting point and placing the sample in a small test tube;
the refrigerant is 1, 2-tetrafluoroethane.
The axial length of the heating coil is 9mm, and the power is 6.84W.
The sample at the beginning was taken 150. Mu.L and placed in a small tube of phi 5X 20 mm.
Step three, low-temperature crystallization:
crystallizing the small test tube at-8 deg.C for 40min, and taking out;
step four, crystal detection:
irradiating the bottom of a small test tube by adopting a laser light source with the wavelength of 650nm and the power of 10mW, detecting the scattering of light by a crystal by using a light sensor in the direction vertical to the irradiation direction to obtain a level value, measuring the level value by using a voltmeter, and substituting the level value into a formula y =0.0131x +1.255 to obtain the wax content, wherein:
x is wax content in mg-kg -1 (ii) a y is a level value in units of V.
The samples in this example were tested, and the test results are shown in table 3, and it can be seen from table 3 that the standard deviation of the test results of the method is less than 4mg/kg, the difference between the results of the nephelometry and the actual value is about 5mg/kg at low wax content, and the difference between the results of the method and the actual value is about 3mg/kg, the accuracy is slightly higher than that of the nephelometry, and the higher the wax content is, the closer the test results are to the actual value.
Table 3 example 3 sunflower oil samples test results
Figure SMS_5
Note: mean ± standard deviation.

Claims (1)

1. A method for rapidly detecting wax in sunflower seed oil is characterized by comprising the following steps:
step one, sample loading:
taking sunflower seed oil as a sample, putting the sample into a smelting tube, and sealing two ends of the smelting tube;
in the first step, the smelting pipe is a smelting pipe with the outer diameter multiplied by the thickness phi 4 multiplied by 0.2mm and the length 95-100 mm; the amount of the sample added into the smelting pipe is 960-1000 mu L;
step two, zone melting:
solidifying a sample in a smelting pipe by using a refrigerant, melting a regional sample in the smelting pipe by using a heating coil to form a melting region, moving the spraying position of the refrigerant on the smelting pipe and the heating position of the heating coil on the smelting pipe, moving the melting region from one end of the smelting pipe to the other end of the smelting pipe at the speed of 0.5-1.1 mm/s, recording the movement from one end of the smelting pipe to the other end as one time, repeatedly carrying out 15-25 times, and taking out the sample at the starting point and placing the sample in a small test tube;
in the second step, the refrigerant is 1, 2-tetrafluoroethane;
in the second step, the axial length of the heating coil is 9mm, and the power is 6-8W; taking out 130-150 mu L of the sample at the starting point, and placing the sample in a small test tube with phi of 5 multiplied by 20 mm;
in the second step, the melting area is moved from one end of the melting tube to the other end at the speed of 0.7-1.1 mm/s, the movement from one end of the melting tube to the other end is recorded as one time, and after 18-21 times of repeated operation, the sample at the starting point is taken out and placed in a small test tube;
in the second step, the axial length of the heating coil is 9mm, and the power is 6.22-6.84W; taking out 150 mu L of the sample at the starting point, and placing the sample in a small test tube with phi of 5 multiplied by 20 mm;
step three, low-temperature crystallization:
crystallizing the small test tube at-6 to-8 ℃ for 30 to 40min, and taking out;
step four, crystal detection:
irradiating the bottom of a small test tube by adopting a laser light source with the wavelength of 635-650 nm and the power of 5-10 mW, detecting the scattering of light by a crystal by using a photosensor in the direction vertical to the irradiation direction to obtain a level value, measuring the level value by using a voltmeter, and substituting the level value into a formula y =0.0131x +1.255 to obtain the wax content, wherein:
x is wax content in mg-kg -1 (ii) a y is a level value in units of V;
the detection method can quantitatively detect 10-200 mg/kg wax in the sunflower seed crude oil or refined oil, and has good accuracy;
the detection method can greatly shorten the detection time to within 2 hours.
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