A method for nondestructive detection of aroma components of fruits and vegetables based on carbon nano-PDMS

Abstract

The present invention discloses a method for nondestructive detection of aroma components of fruits and vegetables based on carbon nano-PDMS. First, polydimethylsiloxane (PDMS) base liquid and curing agent are prepared in a volume ratio of 10:1, and carbon nanofibers or carbon nanospheres are added. Carbon nano-PDMS materials of different thicknesses and shapes are obtained by selecting different molds; then, aroma substances in fruits and vegetables are adsorbed by the prepared carbon nano-PDMS material, methanol and ultrasound-assisted extraction of the adsorbed aroma substances are used, liquid sampling is used, and gas chromatography-mass spectrometry is used to separate the aroma substances and to qualitatively and quantitatively analyze them. The carbon nano-PDMS material of the present invention has a good effect of adsorbing target aroma substances, can be used repeatedly, and has a simple preparation process and low cost, which effectively improves the speed and work efficiency of aroma substance detection in a micro-domain environment, and can realize nondestructive online detection of volatile aroma substances.

Description

Technical Field

[0001] The invention belongs to the field of food detection and can be used for storage and preservation of fruits and vegetables. It specifically relates to a method for non-destructive detection of aroma components of fruits and vegetables based on the adsorption of volatile components by carbon nano-PDMS materials. Background Art

[0002] Aroma components are the main factors that constitute and affect the quality of fresh fruit and processing. With people's increasing requirements for fruit quality and the increasing demand for natural flavor substances in the food industry, fruit aroma has attracted much attention, and aroma has become one of the important research areas of fruit quality. At present, researchers at home and abroad have identified more than 300 aroma substances, mainly including esters, alcohols, aldehydes, ketones, terpenes, acids, etc. In recent years, with the development of analytical instruments and sample pretreatment technology, the analysis level of fruit volatile components has been greatly improved. Traditional fruit volatile component analysis usually requires pretreatment, such as liquid-liquid extraction, steam distillation extraction, supercritical fluid extraction, etc. These pretreatments guarantee the accuracy of sample analysis to a certain extent, but these methods have the disadvantages of large sample volume, long time consumption, high cost, and potential harm to the human body to varying degrees.

[0003] The main fruit storage methods include ordinary refrigeration and controlled atmosphere storage. The changes in the concentration of O2 and CO2 in the storage atmosphere will cause changes in the metabolism of the fruit, especially the loss or deterioration of volatile compounds as the storage time increases, producing other substances such as alcohols or acids. At present, the detection of aroma must be done through liquid nitrogen or juice extraction, and there is no convenient non-destructive detection method. In addition, the cold storage space is large and it is inconvenient to enter and take samples multiple times, which needs to be solved urgently.

[0004] In recent years, studies have found that the solid phase microextraction (SPME) sample aroma extraction method is more effective than traditional aroma separation and extraction methods (solvent extraction, steam distillation, nitrogen purge trapping, simultaneous distillation), and it analyzes a variety of aroma compounds with high content, making it the most widely used method. However, this method requires 50 / 30μm divinylbenzene / Carboxen / polydimethylsiloxane (DVB / CAR / PDMS), 100μm PDMS, 65μm PDMS / DVB, 75μm CAR / PDMS extraction heads to adsorb aroma substances. The price of this material is relatively high, with a price of about 1,000 yuan on the market, and a service life of about 100 times, so it is not easy to promote on a large scale. The use of this material is also often called headspace solid phase microextraction, and non-destructive testing of samples has not been achieved. Summary of the invention

[0005] The purpose of the present invention is to provide a method for non-destructive detection of aroma compounds of fruits and vegetables, which is based on the common extraction materials (DVB / CAR / PDMS), 100μm PDMS, 65μm PDMS / DVB, 75μm CAR / PDMS in the process of aroma compound determination, which are not portable, easy to break, difficult to desorb, inconvenient to transport, and require a large amount of sample destruction during sample pretreatment, resulting in a large amount of sample waste. In addition, the detection method can also be applied to other micro-environments, using a low-cost and reusable carbon nano-PDMS material to adsorb aroma compounds without destroying fruits and vegetables, and the aroma substances detected are mostly the main characteristic aromas.

[0006] To achieve the above object, the technical solution adopted by the present invention consists of the following steps:

[0007] Step 1: Stir and mix the polydimethylsiloxane (PDMS) base liquid, curing agent, carbon nanofibers or carbon nanospheres, pour them into a mold, heat at 60-70° C. for 10-12 hours, cool to room temperature and demold with ethanol to obtain a carbon nano-PDMS material;

[0008] Step 2: Place the carbon nano-PDMS material and fruits and vegetables in a fruit and vegetable fresh-keeping bag, seal the bag, and leave it for more than 48 hours to allow the carbon nano-PDMS material to fully absorb the volatile aroma substances of the fruits and vegetables;

[0009] Step 3: Use chromatographic grade methanol to extract the aroma substances adsorbed by the carbon nano-PDMS material, and use ultrasound-assisted extraction, and use gas chromatography-mass spectrometry to separate the aroma components in the obtained extract and conduct qualitative and quantitative detection thereof.

[0010] In the above step 1, preferably, the volume ratio of the polydimethylsiloxane base liquid to the curing agent is 10:1, and the density of the base liquid is 1.04 g / mL.

[0011] In the above step 1, the amount of the carbon nanospheres or carbon nanofibers added is preferably 1 to 1.5 mg / mL of polydimethylsiloxane base liquid. The specific surface area of ​​the carbon nanospheres is 160 to 1000 m 2 / g, a particle size of 2.5 to 8 nm; the specific surface area of ​​the carbon nanofiber is 275 to 1000 m 2 / g, and the particle size is 0.2~1nm. Both types of materials are microporous materials.

[0012] In the above step 2, the mass ratio of the carbon nano-PDMS material to the fruits and vegetables is preferably 1:0.1-10kg.

[0013] In the above step 3, the chromatographic column of the gas chromatography is a DB-WAX column, and the temperature program of the chromatographic column is: the initial temperature is 40°C and maintained for 3 minutes, then increased to 160°C at 5°C / min, maintained for 5 minutes, and then increased to 240°C at 10°C / min, maintained for 15 minutes; the injection volume is 1μL, the carrier gas is He gas with a purity of >99.999%, and the column flow rate is 1mL / min. The mass spectrometry conditions are: ionization mode EI; electron energy 70eV; mass scanning range 30-500amu; ion source temperature 230°C; interface temperature 250°C.

[0014] The beneficial effects of the present invention are as follows:

[0015] (1) The present invention uses carbon nanospheres or carbon nanofibers as adsorbents for solid phase microextraction materials. The materials have the advantages of large specific surface area and small particle size, and good dispersibility. They can be evenly mixed with the PDMS gel solution without any treatment to obtain carbon nano-PDMS materials with good reproducibility. At the same time, carbon nano-PDMS materials of different thicknesses and shapes can be obtained by selecting different molds. The preparation method is simple, the cost is low, and it is not easy to damage.

[0016] (2) The present invention collects aroma substances produced by fruits and vegetables through air bags, and at the same time, the aroma substances are adsorbed by the prepared carbon nano-PDMS material, and then the adsorbed aroma substances are desorbed by methanol, and then separated and qualitatively and quantitatively determined by GC-MS. The present invention is simple to operate and has accurate detection results, and overcomes the deficiency of the prior art that samples need to be destroyed when detecting aroma substances. In addition, the carbon nano-PDMS material used is relatively low in cost, the detectable peak area value of adsorbed aroma components is higher, and the types of aroma components that can be detected are also more, which is suitable for the detection of volatile aroma components of various fruits and vegetables. In addition, the material can also be applied to other micro-environments.

[0017] (3) Compared with traditional materials, the carbon nano-PDMS material prepared by the present invention has a better effect of adsorbing aroma substances, and can adsorb the main aroma substances of various fruits. The ester substances detected mainly include ethyl 2-methylbutyrate, 2-methyl-1-butyl acetate, propyl 2-methylbutyrate, butyl butyrate, butyl 2-methylbutyrate, 2-methylbutyl butyrate, hexyl acetate, butyl caproate, hexyl 2-methylbutyrate, hexyl caproate, etc., and alcohol substances include 2-methyl-1-butanol, 1-butanol, 1-hexanol, 1-pentanol, etc. Other types are mainly farnesene, which are mostly complete fruit aroma substances, realizing non-destructive detection of fruit aroma substances. In addition, the material is easy to desorb and has a wide range of applications.

[0018] (4) The method of the present invention can also be used to monitor the morbidity of fruits in cold storage or to guide the time for fruits to be removed from cold storage. When certain aroma components appear or disappear, or when the content of some characteristic indicative aroma changes, it means that measures should be taken to remove the batch of apples. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a graph showing the specific surface area of ​​carbon nanofibers in Example 1.

[0020] Figure 2 This is a graph showing the particle size measurement of carbon nanofibers in Example 1.

[0021] Figure 3 This is a graph showing the specific surface area of ​​carbon nanospheres in Example 2.

[0022] Figure 4 This is a graph showing the particle size of carbon nanospheres in Example 2.

[0023] Figure 5 This is a chromatogram of the carbon nanofiber / PDMS microextraction material of Example 1 that adsorbs aroma compounds in apples.

[0024] Figure 6 These are photos of the PDMS solid phase microextraction material in Comparative Example 1 (left), the carbon nanofiber / PDMS microextraction material in Example 1 (middle), and the carbon nanosphere / PDMS solid phase microextraction material in Example 2 (right).

[0025] Figure 7 These are full scanning microscope images of the PDMS solid phase microextraction material in Comparative Example 1 (top), the carbon nanofiber / PDMS microextraction material in Example 1 (middle), and the carbon nanosphere / PDMS solid phase microextraction material in Example 2 (bottom). DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0027] In the following examples, the specific surface area of ​​the carbon nanofibers used is 275.8 m 2 / g, the particle size is 0.2nm, and the preparation method thereof refers to the preparation method of JIe et al. (DANG J, ZHU R, ZHANG S, et al. Bean Pod-Like SbSn / N-Doped Carbon Fibers toward a Binder Free, Free-Standing, and High-Performance Anode for Sodium-Ion Batteries[J]. Small, 2022, 18(21).), the carbon nanospheres are dispersed in N,N-dimethylformamide, and then the carbon nanofibers are obtained by electrospinning. The characterization results are shown in Figure 1 and Figure 2 .

[0028] The specific surface area of ​​the carbon nanospheres used is 161.24 m 2 / g, and a particle size of 2.5nm. The preparation method thereof refers to the preparation method of Jie et al. (DANG J, ZHU R, ZHANG S, et al. Bean Pod-Like SbSn / N-Doped Carbon Fibers toward a Binder Free, Free-Standing, and High-Performance Anode for Sodium-Ion Batteries[J]. Small, 2022, 18(21).), tetraethyl orthosilicate (TEOS) is added to a mixture of ethanol and deionized water, and hydrolyzed at room temperature, and then resorcinol and formaldehyde solution are added for in-situ polymerization. The obtained SiO2@SiO2 / RF is carbonized to SiO2@SiO2 / C under an argon atmosphere at 650°C, and then SiO2 is removed in a 2 mol / L sodium hydroxide aqueous solution to obtain carbon nanospheres. The characterization results are shown in FIG. Figure 3 and Figure 4 .

[0029] The PDMS base liquid (density of 1.04 g / mL) and PDMS curing agent used were provided by Xi'an Jingbo Biotechnology Co., Ltd.

[0030] Example 1

[0031] Step 1: Stir and mix 4 mL of PDMS base liquid (density 1.04 g / mL), 0.4 mL of PDMS curing agent, and 5 mg of carbon nanofibers, pour them into a cylindrical mold, heat at 70 °C for 12 h, cool to room temperature and demold with ethanol to obtain carbon nano-PDMS material (referred to as carbon nanofiber / PDMS microextraction material).

[0032] Step 2: Place 1g of carbon nano-PDMS material and 1kg of late-ripening Fuji apples in a fruit and vegetable preservation bag, seal the bag tightly, and let it stand for 48 hours to allow the carbon nano-PDMS material to fully absorb the volatile aroma substances of the apple.

[0033] Step three: Use chromatographic grade methanol to extract the aroma substances adsorbed by the carbon nano-PDMS material, and after ultrasonic-assisted extraction for 5 minutes, use gas chromatography-mass spectrometry to separate the aroma components in the obtained extract and perform qualitative and quantitative detection. Repeat the experiment three times. The chromatographic column of the gas chromatography is a DB-WAX column, and the temperature program of the chromatographic column is: the initial temperature is 40°C for 3 minutes, then increased to 160°C at 5°C / min, maintained for 5 minutes, and then increased to 240°C at 10°C / min, maintained for 15 minutes; the injection volume is 1μL, the carrier gas is He gas with a purity of >99.999%, and the column flow rate is 1mL / min. The mass spectrometry conditions are: ionization mode EI; electron energy 70eV; mass scanning range 30-500amu; ion source temperature 230°C; interface temperature 250°C. Each aroma substance is qualitatively identified through the NIST retrieval library and its peak area value is recorded. The chromatogram of the aroma compound detected under this condition is as follows Figure 5 shown.

[0034] Comparative Example 1

[0035] In step 1 of Example 1, 4 mL of PDMS base liquid (density 1.04 g / mL) and 0.4 mL of PDMS curing agent were stirred and mixed uniformly, poured into a cylindrical mold, heated at 70° C. for 12 h, cooled to room temperature and demolded with ethanol to obtain a solid phase microextraction material (referred to as PDMS microextraction material). Steps 2 and 3 are the same as in Example 1.

[0036] Example 2

[0037] In step 1 of this embodiment, 4 mL of PDMS base liquid (density 1.04 g / mL), 0.4 mL of PDMS curing agent, and 5 mg of carbon nanospheres were stirred and mixed uniformly, poured into a cylindrical mold, heated at 70° C. for 12 hours, cooled to room temperature, and demolded with ethanol to obtain a carbon nano-PDMS material (referred to as carbon nanosphere / PDMS microextraction material). Steps 2 and 3 are the same as in Example 1.

[0038] The test results of Examples 1 and 2 and Comparative Example 1 are shown in Table 1.

[0039] Table 1 Comparison of adsorption effects of different carbon nano-PDMS materials on aroma components of Fuji apple

[0040]

[0041] Note: - in the table means not detected.

[0042] It can be seen from Table 1 that: the carbon nano-PDMS material prepared by carbon nanofibers in Example 1 detected 17 aroma components, the carbon nano-PDMS material prepared by carbon nanospheres in Example 2 detected 14 aroma components, and the solid phase microextraction material of Comparative Example 1 detected 15 aroma components. However, the peak area response values ​​of most aroma substances detected in carbon nanospheres and carbon nanofibers were higher than those of Comparative Example 1, indicating that the carbon nano-PDMS material prepared by the present invention has a better effect of adsorbing aroma substances. The main ester substances detected include ethyl 2-methylbutyrate, 2-methyl-1-butyl acetate, propyl 2-methylbutyrate, butyl butyrate, butyl 2-methylbutyrate, 2-methylbutyl butyrate, hexyl acetate, butyl hexanoate, 2-methylbutyrate hexyl, 2-methylbutyl hexanoate, hexyl hexanoate and other esters; the alcohol substances include 2-methyl-1-butanol, 1-butanol, 1-hexanol, and 1-pentanol; the others are mainly farnesene, most of which are complete apple aroma substances.

[0043] The microextraction materials obtained in Examples 1 and 2 and Comparative Example 1 were characterized by their structures. Figure 6 and Figure 7 , Figure 7 yes Figure 6 Scanning electron microscope image of Figure 7 It can be seen that without adding carbon nanospheres or carbon nanofibers, the surface of the obtained PDMS microextraction material is relatively smooth. After adding carbon nanofibers and carbon nanospheres, carbon nanofibers and carbon nanospheres can be clearly seen on the surfaces of the obtained carbon nanofiber / PDMS microextraction material and carbon nanosphere / PDMS microextraction material, indicating that the two form a composite material.

[0044] According to relevant literature records, the main characteristic aromas in Fuji apples include ethyl 2-methylbutyrate, 2-methyl-1-butyl acetate, 1-butanol, hexyl acetate, 1-hexanol, α-farnesene, etc., which are also considered to be key aroma compounds. The non-destructive detection method of Example 1 and the existing destructive detection method (GIANNETTI V, MARIANI MB, MANNINOP, et al. Volatile fraction analysis by HS-SPME / GC-MS and chemometric modeling for traceability of apples cultivated in the northeast italy [J]. Food Control, 2017, 78: 215-221.) can simultaneously detect these aroma substances (see Table 2). In addition, it is speculated that they can also be detected in other micro-domain environments.

[0045] Table 2 Comparison of apple aroma substance detection results by different detection methods

[0046]

[0047]

Claims

1. A method for nondestructive detection of aroma components of fruits and vegetables based on carbon nano-PDMS, characterized in that: The following steps are involved: Step 1: Stir and mix the polydimethylsiloxane base liquid, curing agent, carbon nanofibers or carbon nanospheres evenly, pour them into a mold, heat them at 60-70 °C for 10-12 h, cool them to room temperature and demold them with ethanol to obtain a carbon nano-PDMS material; the amount of the carbon nanospheres or carbon nanofibers added is 1-1.5 mg / mL polydimethylsiloxane base liquid; the specific surface area of ​​the carbon nanospheres is 160-1000 m 2 / g, a particle size of 2.5 to 8 nm; the specific surface area of ​​the carbon nanofibers is 275 to 1000 m 2 / g, and the particle size is 0.2-1 nm. Both types of materials are microporous materials; Step 2: Place the carbon nano-PDMS material and fruits and vegetables in a fruit and vegetable preservation bag, seal the bag, and leave it for more than 48 hours to allow the carbon nano-PDMS material to fully absorb the volatile aroma substances of the intact fruits and vegetables; Step 3: Use chromatographic grade methanol to extract the aroma substances adsorbed by the carbon nano-PDMS material, and use ultrasound-assisted extraction, and use gas chromatography-mass spectrometry to separate the aroma components in the obtained extract and conduct qualitative and quantitative detection thereof.

2. The method for nondestructive detection of aroma components of fruits and vegetables based on carbon nano-PDMS according to claim 1, characterized in that: In step 1, the volume ratio of the polydimethylsiloxane base liquid to the curing agent is 10:1, and the density of the base liquid is 1.04 g / mL.

3. The method for nondestructive detection of fruit and vegetable aroma components based on carbon nano-PDMS according to claim 1, characterized in that: In step 2, the mass ratio of the carbon nano-PDMS material to the fruits and vegetables is 1:0.1-10 kg.

4. The method for nondestructive detection of fruit and vegetable aroma components based on carbon nano-PDMS according to claim 1, characterized in that: In step three, the chromatographic column of the gas chromatography is a DB-WAX column, and the temperature program of the chromatographic column is as follows: the initial temperature is 40°C for 3 min, then increased to 160°C at 5°C / min, maintained for 5 min, and then increased to 240°C at 10°C / min, maintained for 15 min; the injection volume is 1 μL, the carrier gas is He gas with a purity of >99.999%, and the column flow rate is 1 mL / min.

5. The method for nondestructive detection of fruit and vegetable aroma components based on carbon nano-PDMS according to claim 1, characterized in that: In step 3, the mass spectrometry conditions are: ionization mode EI; electron energy 70 eV; mass scanning range 30-500 amu; ion source temperature 230°C; interface temperature 250°C.

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