Color developing card for detecting oxidation degree of carya illinoensis oil as well as preparation method and use method of color developing card

Abstract

The invention discloses a color developing card capable of detecting the oxidation degree of cold-pressed or hot-pressed carya illinoensis oil, and belongs to the technical field of biology, the color developing card utilizes the principle that aldehyde components volatilized by the carya illinoensis oil react with hydroxylamine sulfate to change the pH so as to change the color of Congo red, the color of the carya illinoensis oil can be detected according to the color of the color developing card, and the degree of oxidation of the carya illinoensis oil can be detected. Whether the peroxide value level exceeds the national standard or not is judged; the color developing card takes filter paper as a substrate material, so that the cost is low; the preparation method of the color developing card is simple and effective, and is convenient for large-scale production; the color developing card is portable and easy to operate, and is beneficial to quality control of carya illinoensis oil products in the storage and transportation process; common consumers without professional detection capability or non-technicians in the field can also judge the oxidation condition of the cold-pressed or hot-pressed carya illinoensis oil through the color developing card.

Description

Technical Field

[0001] The present invention relates to a technology for detecting the oxidation degree of vegetable oil, and particularly to a visualization technology for detecting the oxidation degree of pecan oil, belonging to the field of biotechnology. Background Art

[0002] The fatty acid composition in pecan oil is relatively balanced, mainly composed of oleic acid, linoleic acid and α-linolenic acid, and also contains various nutritional concomitants such as squalene and vitamin E, which is a high-quality edible vegetable oil. The high nutritional value of pecan oil makes it deeply loved by consumers. However, its unsaturated fatty acid content is as high as over 90%, and it is easily affected by factors such as light, air, moisture, microorganisms and its own fat structure during storage, resulting in oxidative rancidity, thus reducing the nutritional value and even making it unfit for consumption. GB 2716-2018 "National Food Safety Standard Vegetable Oil" stipulates that the peroxide value of vegetable oil should be ≤ 0.25 g / 100 g, and this index is usually used to measure the oxidation degree of vegetable oil. The inventor's research found that there are significant differences in the peroxide values of cold-pressed and hot-pressed pecan oils. Therefore, when detecting the oxidation degree of pecan oil, it is necessary to distinguish between cold-pressed and hot-pressed pecan oils to make the detection results more accurate.

[0003] Titration is a method for accurately determining the peroxide value, but this method has deficiencies such as high cost and complex operation, and it is difficult to meet the requirements of rapid and convenient detection. Colorimetry is a visualization technology, and the colorimetric sensor developed based on it can make up for the defects of titration method and has been widely used in the fields of food and medicine. The inventor previously developed a color card containing 12 gas-sensitive materials (see the invention patent CN118347997B), which can quickly, accurately and conveniently judge the degradation degree of the fishy smell of burdock. The invention patent CN113155824A discloses a sensing film, a preparation method and its application in food safety detection, which uses the color change of the acidic indicator congo red to detect the volatile aldehydes produced during the spoilage process of food to help consumers judge the freshness and safety of food. However, this sensing film was only tested with sunflower oil, and it is not clear about the detection effect on other edible oils; moreover, the cost of the used nano-chitin film is relatively high, which is not conducive to the popularization and application of the product.

[0004] At present, there is no colorimetric sensor at home and abroad that can detect the oxidation degree of cold-pressed or hot-pressed pecan oil. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a color card capable of detecting the oxidation degree of cold-pressed or hot-pressed pecan oil, and to provide its preparation method and usage method.

[0006] Technical solution: The color card for detecting the oxidation degree of pecan oil according to the present invention includes filter paper and Congo red and hydroxylamine sulfate fixed on the filter paper.

[0007] The inventor analyzed the flavor components of pecan oil during storage and found that aldehydes are the main volatile oxidation products. These aldehydes are the most important cleavage products of hydroperoxides in vegetable oils, and the change in their content can be used to indicate the oxidation state of food. Therefore, based on the principle that hydroxylamine sulfate can react with aldehydes to form Schiff base, releasing sulfuric acid and causing the pH to decrease, and then Congo red changes from red to blue, the present invention can detect the aldehydes volatilized from pecan oil and realize the detection of the oxidation degree of pecan oil by visually observing the color change of the color card.

[0008] The present invention also provides a preparation method of the color card, including the following steps: Step 1, dissolve Congo red and hydroxylamine sulfate in a mixed solvent at a mass ratio of 1:20. The mixed solvent is methanol, water and glycerol (10:9:1, v / v) to obtain an aldehyde sensing solution; the concentration of Congo red in the aldehyde sensing solution is 0.25 g / L; Step 2, immerse the filter paper in the aldehyde sensing solution for 30 - 240 min; Step 3, dry the soaked filter paper to obtain the color card.

[0009] Preferably, in Step 2, soak for 120 - 180 min; Preferably, in Step 3, dry naturally at room temperature.

[0010] Preferably, in Step 3, place the soaked filter paper in a dryer for drying.

[0011] The present invention also provides the application of the color card in detecting the oxidation degree of pecan oil.

[0012] Preferably, the pecan oil is cold-pressed or hot-pressed pecan oil.

[0013] Preferably, place the pecan oil in a sealed container, fix the color card at the inner top of the container, and there is no contact between the pecan oil and the color card; place it at 35 - 37 °C for 20 - 24 h; after placement, judge the oxidation degree of the pecan oil according to the color change of the color card.

[0014] The color change of the color card can be judged by the naked eye.

[0015] Preferably, for cold-pressed pecan oil, when the color card shows blue-violet, it means that its peroxide value reaches 0.25 g / 100 g.

[0016] Preferably, for hot-pressed pecan oil, when the color display card shows brownish red, it indicates that its peroxide value reaches 0.25 g / 100 g.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: 1. The color display card provided by the present invention can detect the oxidation degree of cold-pressed or hot-pressed pecan oil, and judge whether its peroxide value exceeds the national standard according to the color of the color display card; 2. The color display card uses filter paper as the base material, with low cost; 3. The preparation method of the color display card is simple and effective, facilitating large-scale production; 4. The color display card has portability and easy operation, which is beneficial to the quality control during the storage and transportation of pecan oil products; ordinary consumers or non-professionals without professional detection ability can also judge the oxidation situation of cold-pressed or hot-pressed pecan oil through the color display card. Description of the Drawings

[0018] Figure 1 is the color display card for detecting the oxidation degree of pecan oil provided by the present invention; Figure 2 is the content of flavor components in pecan oil (CPO: fresh cold-pressed pecan oil; HPO: fresh hot-pressed pecan oil; ECPO: expired cold-pressed pecan oil; EHPO: expired hot-pressed pecan oil); Figure 3 is the relationship between the peroxide value of pecan oil and the color of the color display card. Detailed Embodiments

[0019] The technical solutions of the present invention will be further described below with reference to the drawings.

[0020] The filter paper used in the examples is double-circle qualitative filter paper (CAT No: 99-102-090), purchased from Cytiva Biotechnology (Hangzhou) Co., Ltd. Unless otherwise specified, other raw materials and reagents are from the market.

[0021] Example 1: Optimize the soaking time of the filter paper in the aldehyde sensing solution in the preparation method of the color display card for detecting the oxidation degree of pecan oil Test method: Dissolve 5 mg of congo red and 100 mg of hydroxylamine sulfate in 20 mL of a mixed solvent of methanol, water, and glycerol (10:9:1, v / v) to prepare an aldehyde sensing solution. Cut the filter paper into several 1 cm × 1 cm squares and immerse them in the aldehyde sensing solution for 30, 60, 90, 120, 150, 180, 210, and 240 min respectively; after soaking, store the color cards in a desiccator and allow them to dry naturally at room temperature. After drying, observe the color of the color cards with the naked eye and measure the color parameters (L* (brightness), a* (red / green), b* (yellow / blue)) of the color cards using a DR-10 color difference meter (Konica Minolta, Japan).

[0022] Test results: As shown in Figure 1 (b), color cards showing red can be obtained after soaking for 30 - 240 min, and the color cards show bright red after soaking for 150 min and longer. As shown in Table 1, as the soaking time increases, the L* value decreases and the color becomes darker; within 180 min, the a* value first increases and then decreases, and the color is most reddish at 120 min. Although the a* value increases again after 180 min, 150 min is the most suitable choice to save time.

[0023] Table 1 Color difference values of color cards prepared with different soaking times L* a* b* 30 <![CDATA[65.91±0.66 a > <![CDATA[40.24±0.55 e > <![CDATA[8.31±0.51 g > 60 <![CDATA[61.69±0.33 b > <![CDATA[43.81±0.12 d > <![CDATA[11.69±0.21 f > 90 <![CDATA[61.58±0.06 b > <![CDATA[44.18±0.28 c > <![CDATA[12.89±0.12 e > 120 <![CDATA[57.88±0.41 c > <![CDATA[44.72±0.26 c > <![CDATA[13.11±0.30 e > 150 <![CDATA[57.40±0.24 c > <![CDATA[45.59±0.20 b > <![CDATA[14.64±0.07 c > 180 <![CDATA[54.46±0.58 d > <![CDATA[44.58±0.18 c > <![CDATA[13.83±0.28 d > 210 <![CDATA[54.19±0.05 d > <![CDATA[46.63±0.57 a > <![CDATA[16.61±0.49 a > 240 <![CDATA[52.08±0.23 e > <![CDATA[45.25±0.29 b > <![CDATA[15.73±0.09 b > The superscripts a - g indicate that there are significant differences (P < 0.05) in the means with different superscripts among the treatment groups in the same column.

[0024] Example 2: A color card for detecting the oxidation degree of pecan oil and its preparation method The color card in this example is prepared through the following steps: Dissolve 5 mg of congo red and 100 mg of hydroxylamine sulfate in 20 mL of a mixed solvent of methanol, water, and glycerol (10:9:1, v / v) to prepare an aldehyde sensing solution. Cut the filter paper into several 1 cm × 1 cm squares and immerse them in the aldehyde sensing solution for 150 min; after soaking, store the color cards in a desiccator and allow them to dry naturally at room temperature. The color cards are obtained after drying is completed.

[0025] Example 3: Application of the color card for detecting the oxidation degree of pecan oil Based on the color card prepared in Example 2, this example detects the oxidation degree of fresh and expired cold-pressed and hot-pressed pecan oil respectively.

[0026] Test method: Take 5 ml of pecan oil and put it into a 20 ml vial. Stick the color card on the inner side of the vial cap, and react the vial at 35 °C for 24 h. Set 3 replicates for each group. After the reaction, observe the color of the color card with the naked eye.

[0027] Test results: As Figure 1 (a) shown. 1 - 4 correspond to fresh cold-pressed pecan oil, fresh hot-pressed pecan oil, expired cold-pressed pecan oil, and expired hot-pressed pecan oil respectively. The color card remains red in fresh cold-pressed and hot-pressed pecan oil, and turns blue-violet and brown-red in expired oxidized cold-pressed and hot-pressed pecan oil. The oxidation states of cold-pressed and hot-pressed pecan oil samples are sensitively and accurately identified by the color card.

[0028] The color change of the color card is corroborated with the detection results of volatile organic components in pecan oil. Figure 2 It is the result of HS-SPME-GC-MS analysis of volatile flavor components in fresh or expired cold-pressed or hot-pressed pecan oil. 30 volatile components are isolated and identified from the samples, including alcohols, aldehydes, ketones, acids, and heterocycles. There is no obvious difference in the content of the main volatile components between cold-pressed pecan oil and hot-pressed pecan oil. Aldehydes are the main volatile oxidation products among them. These aldehyde substances are the most important cleavage products of hydroperoxides in vegetable oils, and their content changes can be used to indicate the oxidation state of food. Among them, hexanal has the highest content, and its concentration change is the most obvious in cold-pressed, hot-pressed, and expired cold-pressed pecan oil. The content of hexanal in expired cold-pressed / hot-pressed pecan oil is three times that of fresh cold-pressed / hot-pressed pecan oil. Thus, based on the principle that sulfur hydroxylamine reacts with aldehyde to produce acid and makes congo red change color, the color card prepared in Example 2 can distinguish whether cold-pressed and hot-pressed pecan oil is expired.

[0029] Example 4: Explore the relationship between the peroxide value of pecan oil and the color of the color card Based on the color card prepared in Example 2 and the detection method provided in Example 3, this example explores the corresponding relationship between the peroxide value and the color of the color card of cold-pressed and hot-pressed pecan oil with different oxidation degrees.

[0030] Test method: Store fresh cold-pressed and hot-pressed pecan oil at 60 °C, take samples at 10, 20, 30, 40, and 50 days respectively, and detect the peroxide value and oxidation degree. The determination of the peroxide value refers to the first method of GB 5009.227-2023 "National Food Safety Standard - Determination of Peroxide Value in Foods". The oxidation degree is determined by the color card, record the color of the color card observed with the naked eye, and measure the color parameters of the color card with a DR-10 color difference meter and calculate the color difference value (ΔE). The color difference value calculation formula is where ΔL* = L* - L 0 , Δa* = a* - a 0 , Δb* = b* - b 0 , L 0 , a 0 , b 0 are the color values of the color card before use, and L*, a*, b* are the color values of the color card after the analyte is exposed for 24 h.

[0031] Test results: as Figure 3 shown. (a) and (b) respectively correspond to the relationship between the peroxide value of cold-pressed and hot-pressed pecan oil and the color of the color card. The 5 circles in (a) correspond to the colors of the color cards for detecting the oxidation degree of cold-pressed pecan oil stored for 10, 20, 30, 40, and 50 days from left to right; the 5 circles in (b) are the same. According to the provisions of GB 2716-2018 "National Food Safety Standard Vegetable Oil", the peroxide value of vegetable oil should be ≤ 0.25 g / 100 g, and the corresponding relationship between the peroxide value of pecan oil and the color of the color card is obtained: For cold-pressed pecan oil, when its peroxide value is lower than the national standard, the color card shows and maintains different degrees of red; when the color card shows blue-violet, that is Figure 3 the color of the 3rd color card in (a), it means that its peroxide value reaches the national standard; for hot-pressed pecan oil, when its peroxide value is lower than the national standard, the color card shows and maintains different degrees of red; when the color card shows brownish-red, that is Figure 3 the color of the 5th color card in (b), it means that its peroxide value reaches the national standard.

[0032] In summary, the color card provided by the present invention can accurately display the oxidation states of cold-pressed and hot-pressed pecan oil and provide a clear indication according to the color change. The color card provides great convenience for people to consume pecan oil in daily life.

Claims

1. A color developing card for detecting the oxidation degree of thin-shell pecan oil, characterized in that: The color developing card comprises filter paper and Congo red and hydroxylamine sulfate fixed on the filter paper.

2. A method for preparing a color developing card as claimed in claim 1, characterized in that: The following steps are involved: Step 1, dissolving Congo red and hydroxylamine sulfate in a mixed solvent at a mass ratio of 1:20, wherein the mixed solvent is methanol, water and glycerol (10:9:1, v / v), to obtain an aldehyde sensing solution; the concentration of Congo red in the aldehyde sensing solution is 0.25 g / L; Step 2, immersing the filter paper in the aldehyde sensing solution for 30 to 240 minutes; Step three, drying the soaked filter paper to obtain the color developing card.

3. The preparation method according to claim 2, characterized in that: In step 2, soak for 120-180 min.

4. The preparation method according to claim 2, characterized in that: In step 3, dry naturally at room temperature.

5. The preparation method according to claim 2, characterized in that: In step three, the soaked filter paper is placed in a dryer for drying.

6. Use of the color developing card as claimed in claim 1 in detecting the oxidation degree of walnut oil.

7. The use according to claim 6, characterized in that: The pecan oil is cold-pressed or hot-pressed pecan oil.

8. The use according to claim 6, characterized in that: Place the thin-shell pecan oil in a sealed container and fix the color card on the top of the inner side of the container, without contact between the thin-shell pecan oil and the color card; place it at 35-37℃ for 20-24 hours; after the placement is completed, judge the oxidation degree of the thin-shell pecan oil according to the color change of the color card.

9. The use according to claim 8, characterized in that: For cold-pressed thin-shell pecan oil, when the color card shows blue-purple, it means that its peroxide value reaches 0.25 g / 100 g.

10. The use according to claim 8, characterized in that: For hot-pressed thin-shell pecan oil, when the color card shows brown-red, it means that its peroxide value reaches 0.25 g / 100 g.

Images