Method for rapidly increasing yield of pineapple juice and improving aroma by using pulsed electric field

Abstract

The invention discloses a method for rapidly increasing the yield of pineapple juice and improving aroma by using a pulsed electric field, and belongs to the technical field of juice processing. The method comprises the following steps: selecting fresh pineapples, cleaning, peeling, crushing to obtain pineapple puree for later use, putting the pineapple puree into a pulsed electric field treatment chamber, and carrying out pulsed electric field treatment for 150-250 seconds; and pouring the pineapple puree treated by the pulsed electric field into a squeezer, and squeezing and filtering to obtain the pineapple juice. According to the method, the pineapple juice yield can be increased through short-time pulsed electric field extraction treatment, the content of nutrients and aroma components in the juice is increased, short processing time, high juice yield and strong pineapple flavor are taken into account, and the quality of the pineapple juice is remarkably improved.

Description

Technical Field

[0001] The invention relates to pineapple juice, in particular to a method for rapidly increasing the yield of pineapple juice and improving its aroma by utilizing a pulse electric field, and belongs to the technical field of juice processing. Background Art

[0002] Pineapple is a perennial plant of the Bromeliaceae family and is a major fruit variety in tropical and subtropical regions around the world. At the same time, the smell of pineapple is sweet and has a strong fruity aroma. The aroma of pineapple comes from its internal chemical composition, forming the well-known pineapple aroma. Pineapple is widely loved by consumers because its fruit is rich in fructose, glucose, polyphenols and other ingredients, and because of its strong pineapple aroma.

[0003] The main forms of pineapple consumption in the market are fresh fruit, canned pineapple and pineapple juice. Among them, pineapple juice has become the second largest juice in the juice sales market after orange juice due to its bright color, special aromatic flavor and rich nutrients. Pineapple is deeply loved by consumers and plays an important role in the market position of various countries. Because it has a special pineapple aroma, consumers will first smell the aroma of pineapple when they come into contact with pineapple and its deep-processed products. Aroma is very important for pineapple and its processed products. It is one of the important criteria for judging its quality. The richer and fuller the aroma, the more attractive it is. Therefore, for the processing of pineapple juice, it is particularly necessary to provide a processing technology that can effectively maintain the content of pineapple's characteristic aroma components.

[0004] The traditional pineapple juice processing technology is to directly squeeze out the juice through a juicer, but this process cannot fully disintegrate and destroy the pineapple pulp cells and subcellular structures, resulting in low juice yield, insufficient nutritional and aroma content, etc., ultimately affecting the quality of the finished juice.

[0005] At present, the pineapple juice extraction process is the technical bottleneck restricting the industrial production of pineapple juice. Therefore, how to effectively improve the processing juice yield of pineapple and quickly improve the quality of pineapple juice is crucial to promoting the deep processing and industrial production of high-quality pineapple juice.

[0006] In the preparation method of a pineapple concentrated clear juice disclosed in Chinese invention patent CN105249088B and the method of processing clarified pineapple juice disclosed in Chinese invention patent CN101147611B, a composite enzyme of pectinase and cellulase is used to pretreat pineapple pulp to improve the juice yield and juice quality. Under the action of the composite enzyme, the cell wall of the pineapple pulp cell is decomposed by the enzyme, so that the juice and nutrients are more easily dissolved from the pulp cell, which significantly improves the juice yield and nutritional value of the juice. However, this type of enzymatic hydrolysis method also has the following disadvantages: 1) high cost, the enzymatic hydrolysis method requires a large amount of expensive enzymes, which increases the production cost of the juice; 2) complex process, low efficiency, the pulp after enzymatic hydrolysis also needs to be deactivated and filtered, the production cycle is long, and the efficiency is low; 3) affecting the flavor of the juice, the juice produced by the enzymatic hydrolysis method needs to be subsequently treated with high temperature enzyme deactivation, the odor generated after the enzyme is deactivated and the subsequent high temperature treatment process will have an adverse effect on the flavor of the juice, and the pineapple flavor is seriously lost.

[0007] Therefore, in view of the problems existing in the existing methods for increasing the juice yield of pineapples and improving the quality of pineapple juice, there is an urgent need in the art for a processing method with simple steps, high efficiency, and the ability to effectively increase the juice yield of pineapples without affecting the pineapple aroma. Summary of the invention

[0008] In order to overcome the shortcomings and defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for quickly increasing the yield of pineapple juice and improving its aroma by using a pulsed electric field, which can increase the pineapple juice yield through a relatively short pulsed electric field extraction treatment, and increase the content of nutritional and aroma components in the juice, thereby achieving a short processing time, a high juice yield and a strong pineapple aroma, and significantly improving the quality of pineapple juice.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for rapidly increasing the yield of pineapple juice and improving its aroma by using a pulsed electric field comprises the following steps:

[0011] (1) preparing pineapple puree: selecting fresh pineapples, washing, peeling and crushing them to prepare pineapple puree;

[0012] (2) Pulsed electric field treatment: placing the pineapple puree in a pulsed electric field treatment chamber for pulsed electric field treatment;

[0013] (3) Juice extraction and filtration: Pour the pineapple puree pretreated by the pulse electric field into a squeezer, and filter the pineapple juice after squeezing.

[0014] To further achieve the object of the present invention, preferably, in step (1), the fresh pineapple is a pineapple that is 70% to 80% mature, fresh and free of disease.

[0015] Preferably, in step (1), the crushing is to first wash and peel the fresh pineapple, cut it into pieces, and then put it in a blender to crush it.

[0016] Preferably, the size of the fruit pieces is less than 3cm×3cm×3cm.

[0017] Preferably, the mass of pineapples crushed by the blender at one time is 20-30 kg.

[0018] Preferably, in step (2), the pulse electric field treatment frequency is 20-40 Hz, and the electric field strength is 0.25-1.50 kV / cm.

[0019] Further preferably, the treatment frequency of the pulse electric field is 25-35 Hz, and the electric field strength is 0.75-1.25 kV / cm.

[0020] Preferably, in step (2), the pulse time of the pulse electric field is 175-225s, and the pulse width is 20-40μs.

[0021] More preferably, the pulse time is 150-250s.

[0022] Further preferably, the pulse width is 10-50 μs.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0024] 1) The method of the present invention for rapidly increasing the yield of pineapple juice and improving the aroma by using a pulsed electric field can effectively increase the juice yield of pineapples. It is found through testing that, by using the method of the present invention, the juice yield of pineapples is not only significantly higher than that of the traditional squeezing method, but also higher than that of the composite enzyme hydrolysis method of the prior art, and also higher than that of the ultrasonic method and microwave method used in fruit processing.

[0025] 2) Through the test of the examples, it was found that the method of the present invention can promote the dissolution of characteristic aroma components such as methyl caproate, methyl 2-methylbutyrate, methyl butyrate, isopentyl acetate, dimethyl malonate and methyl heptanoate in pineapple, and the characteristic aroma components such as methyl caproate, methyl 2-methylbutyrate, methyl butyrate, isopentyl acetate, dimethyl malonate and methyl heptanoate in the pineapple juice obtained by the method of the present invention are significantly higher than those in the pineapple juice obtained by the prior art and various strengthening measures.

[0026] 3) Through testing in the examples, it was found that the method of the present invention using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma can promote the dissolution of vitamin C and polyphenols in pineapple, and after treatment, it will not cause the temperature to rise and cause the degradation of these heat-sensitive components, and the nutrient retention rate is higher than that of the prior art.

[0027] 4) Compared with the prior art pineapple juice enzyme processing method for enhancing pineapple juice yield, the method of the present invention does not require the use of expensive complex enzymes and has a lower production cost.

[0028] 5) Compared with the prior art pineapple juice enzymatic processing method for enhancing pineapple juice yield, which requires several hours of enzymatic hydrolysis treatment time, the pulse time of the electric field pulse treatment of the present invention is 175-225s, the processing time is short, and the processing advantage is obvious. DETAILED DESCRIPTION

[0029] The following embodiments are only a part of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The existing technology for extracting pineapple juice mainly focuses on promoting the improvement of extraction rate, and the current research is mainly focused on the application of enzymatic hydrolysis; however, since the special pineapple aroma of pineapple is the embodiment of the quality of pineapple juice and the basis for consumer certification, the existing technology cannot take into account the pineapple aroma, and there is no solution specifically for this problem. In addition, vitamin C and polyphenols in pineapple are important nutrients, and their content is an important indicator of the grade of pineapple juice. Traditional squeezing technology and pineapple juice enzyme processing methods that enhance pineapple juice yield cannot take into account both the juice yield and pineapple aroma; let alone taking into account the increase in the content of vitamin C and polyphenols.

[0031] The present invention finds that the use of pulse batteries combined with squeezing technology not only improves the juice yield of pineapple juice, but also takes into account the pineapple aroma. The vitamin C and polyphenols in the pineapple are also significantly improved, which qualitatively improves the quality of the pineapple juice.

[0032] In terms of technical measures, the present invention provides a method for rapidly increasing the yield of pineapple juice and improving the aroma by using a pulsed electric field, comprising the following steps:

[0033] (1) preparing pineapple puree: selecting fresh pineapples, washing, peeling and crushing them to prepare pineapple puree;

[0034] (2) Pulsed electric field treatment: placing the pineapple puree in a pulsed electric field treatment chamber for pulsed electric field treatment;

[0035] (3) Juice extraction and filtration: Pour the pineapple puree pretreated by the pulse electric field into a squeezer, and filter the pineapple juice after squeezing.

[0036] The technical measures of the present invention are mainly the combination of pulse electric field treatment and squeezing, which makes the quality of pineapple juice obtained by the method of the present invention qualitatively improved; the preparation of pineapple puree in the above steps is also involved in the traditional squeezing process, and the selection of fresh pineapples, cutting into pieces, crushing in a blender, the definition of the size of the pieces, and the quality of the pineapples crushed in a blender can all be inspired by traditional processing methods, or obtained through experiments in combination with the purpose of the present invention. The specific process selection and preferred process conditions for the pulse electric field can be obtained through experiments based on the purpose of the present invention and in combination with the conventional practice of the pulse electric field.

[0037] The pulse electric field method of the present invention improves the production efficiency of pineapple puree compared with the traditional squeezing method and the complicated composite enzyme hydrolysis method, and the comprehensive quality of the obtained pineapple juice is improved in all directions. This may be due to the fact that the pineapple pulp cells generate transmembrane potentials at both ends of the cell membrane wall under the polarization of the pulse electric field. With the continuous treatment of the electric field, the transmembrane potential gradually increases, causing the potential difference at both ends of the cell membrane wall to increase and eventually produce electroporation, promote the outflow of intracellular juice and the dissolution and mass transfer of active and flavor substances, and effectively improve the juice yield and the nutritional flavor quality of the juice. At the same time, due to the short pulse electric field treatment time and low temperature rise, it will not cause the loss of heat-sensitive nutrients and flavor components in the juice, and can further protect the quality of the juice.

[0038] Through the embodiments and comparative examples of the present invention, it is found that even though the ultrasonic technology and microwave technology involved in the prior art may theoretically be applied to pineapple juice extraction, these physical field processing technologies, although not reported to be applied to pineapple juice extraction, also have the potential to increase the yield of pineapple juice and improve its quality. For example, ultrasonic treatment has been shown to increase the juice yield of strawberries and raspberries and improve the content of bioactive substances in juice (Piecko J., Mieszczakowska-Frac M., Celejewska K., Szwejda-Grzybowska J. Impact of ultrasound pretreatment on juice yield and bioactive content in juice produced from selected berries fruit. Foods, 2024, 13(8): 1231); compared with traditional pressing, microwave treatment has also been shown to significantly increase juice yield (Quek M C., Chin N L., Yusof Y A. Optimisation and comparative study one extraction methods of soursop. Journal of Food Agriculture & Environment, 2012, 10(3-4): 245-251). However, through comparative test of the present invention, it is found that such strengthening technology mainly has a certain effect on the juice yield of pineapple juice, and there is still a larger gap with the present invention in terms of pineapple flavor components, vitamin C and polyphenol content in pineapple. Only the present invention will truly achieve the combination of pulsed electric field treatment and pressing to achieve the balance of juice yield, pineapple flavor components, vitamin C and polyphenol content in pineapple.

[0039] The pulse electric field equipment used in the embodiment is preferably the PEF-EX-1900-3 pulse electric field equipment of Guangzhou Paihu Technology Co., Ltd.; the ultrasonic extraction equipment is the EX-TE ultrasonic extraction equipment of Shanghai Shunyi Technology Co., Ltd.; and the microwave extraction equipment is the industrial microwave equipment of Guangzhou Diwei Company.

[0040] Example 1

[0041] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 20kg of the prepared pineapple puree and put it into the pulse electric field treatment room, and then put it into the pulse electric field equipment for treatment. The treatment conditions of the pulse electric field are a treatment frequency of 25Hz, an electric field strength of 0.75kV / cm, a pulse time of 175s, and a pulse width of 20μs. After the treatment, pour the pineapple puree into a squeezer, squeeze it, and filter it to obtain pineapple juice.

[0042] Comparative Example 1

[0043] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and place them in a blender and stir them for 1 minute to obtain pineapple puree for later use; take 20kg of the prepared pineapple puree and squeeze and filter it to obtain pineapple juice.

[0044] Comparative Example 2

[0045] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them and prepare pineapple puree for later use; take 20kg of the prepared pineapple puree and heat it at 53°C for gelatinization for 20 minutes, then add 0.05% pectinase and 0.075% cellulase according to the weight of the puree, and perform composite enzymolysis treatment at 50°C for 2 hours. After the treatment, the puree is treated to inactivate enzymes at 83°C for 25 minutes, and after cooling to room temperature, it is squeezed and filtered to obtain pineapple juice.

[0046] Comparative Example 3

[0047] Select pineapple fruits that are 70% to 80% ripe, fresh and free of disease as raw materials, wash and peel them, cut them into fruit pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 20kg of the prepared pineapple puree and treat it in an ultrasonic extraction device under the conditions of 20KHz frequency and 750W power for 25min, and squeeze and filter to obtain pineapple juice after the treatment is completed.

[0048] Comparative Example 4

[0049] Select pineapple fruits that are 70% to 80% ripe, fresh and free of disease as raw materials, wash and peel them, cut them into fruit pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 20kg of the prepared pineapple puree and treat it in a microwave extraction equipment, the microwave treatment condition is 850W, the treatment is for 2min, and after the treatment is completed, squeeze and filter to obtain pineapple juice.

[0050] The total phenol content in the samples of Example 1 and Comparative Examples 1-4 was determined with reference to T / AHFIA005-2018.

[0051] The vitamin C content in the samples of Example 1 and Comparative Examples 1-4 was determined by spectrophotometry. 400 μL of juice was mixed with NaCl solution (0.50 mol / L), centrifuged at 5000 r / min for 10 min, and then mixed with 100 μL of sodium acetate buffer (0.02 mol / L), and the absorbance value was measured at 265 nm using a spectrophotometer. After the above test solution was reacted with 50 μL of copper sulfate solution (2.4 M), the absorbance blank was measured at 265 nm. The ascorbic acid standard was used to prepare a standard solution (0-15 μg / mL), and the vitamin C content in the juice was calculated using a standard curve.

[0052] The aroma components in the samples of Example 1 and Comparative Examples 1-4 were determined by gas chromatography-mass spectrometry. Sample pretreatment: 8g of juice was poured into an SPME sample bottle, and 1.5g of NaCl was weighed and added to the bottle, followed by dripping 6μL of 2-octanol internal standard solution (concentration of 100mg / L). The SPME extraction needle used for detection was DVB / CAR / PDMS, 50 / 30μm (Supelco, USA), and the chromatographic column model was HP-WAX (60m×0.25mm×0.25μm, Agilent, USA). The total cycle time for gas chromatography-mass spectrometry was 64min, and the detection procedure was: the initial temperature was 40°C, maintained for 6min, raised to 100°C at a rate of 3°C / min, and then heated to 230°C at a rate of 10°C / min and maintained for 20min. Helium was used as the carrier gas with a flow rate of 1.0 mL / min, and mass spectrometry fragmentation was performed in electron impact (EI) mode (ionization energy, 70 eV; source temperature, 230 °C). Compounds were identified by retention index and NIST 20 database, where the retention indices (RIs) of substances were calculated by the elution time of n-alkanes (C7-C40).

[0053] Table 1. Changes in temperature, juice yield, total phenol content and vitamin C content before and after treatment in Example 1 and Comparative Examples 1-4

[0054]

[0055] The juice yield, total phenol, vitamin C content and temperature changes before and after treatment of Example 1 (pulsed electric field) and Comparative Examples 1-4 are shown in Table 1. As shown in Table 1, the sample of Example 1 has the highest juice yield (66.41%), total phenol content (495.66 μg / mL) and vitamin C content (132.47 μg / mL), indicating that compared with traditional squeezing, enzymatic hydrolysis, ultrasonic method and microwave method, the electroporation of the pulsed electric field can more effectively destroy the pineapple pulp cell structure and promote the dissolution of juice and bioactive components. In the enzymatic hydrolysis method, although enzymatic hydrolysis can effectively destroy the pulp cell wall and promote the dissolution of juice, the subsequent long-term high-temperature enzyme inactivation treatment will cause the degradation of heat-sensitive components such as polyphenols and vitamin C, resulting in the total content and vitamin C content in the reorganized sample being even lower than that of the traditional squeezing method sample. It can be seen from Table 1 that, compared with the method of the comparative example, the pulse electric field treatment combined with pressing method of the present invention can well protect phenolic substances and vitamin C from degradation while ensuring a good juice yield, so that the juice has better nutritional quality.

[0056] Methyl caproate, 2-methylbutyric acid, methyl butyrate, isoamyl acetate, dimethyl malonate and methyl heptanoate are characteristic aroma components of pineapple. The volatile flavor component contents of Example 1 (pulsed electric field) and Comparative Examples 1-4 are shown in Table 2. As shown in Table 2, it can be seen from Table 2 that the content of key flavor compounds in the sample of Example 1 (pulsed electric field) is relatively high, and methyl caproate, methyl 2-methylbutyrate and methyl butyrate are significantly higher than those of other comparative examples. Compared with Comparative Examples 1-4, the content of methyl caproate is increased by 12.50%, 30.42%, 15.62% and 26.31% respectively; the content of methyl 2-methylbutyrate is increased by 10.31%, 4.28%, 14.62% and 44.46% respectively; the content of methyl butyrate is increased by 3.20%, 8.70%, 0.10% and 31.47% respectively. Existing sensory description studies on these aroma substances have shown that methyl caproate has fruity and pineapple aromas, methyl 2-methylbutyrate has apple, floral and fresh aromas, and methyl butyrate has pineapple, apple and banana aromas. These aroma substances are compounds with higher content in pineapple juice and are also one of the most abundant components of pineapple. They are characteristic aroma substances of pineapple (George, J., Nguyen, T., Williams, D., Hardner, C., Sanewski, G., & Smyth, H., E. Review of the Aroma Chemistry of Pineapple (Ananas comosus). Journal of Agricultural and Food Chemistry, 2023, 71: 4069-4082). The increase in the abundance of characteristic aroma substances in juice after electric field treatment may be due to the fact that the polarization perforation effect of the pulsed electric field effectively destroys the pulp cell structure and promotes the dissolution of characteristic aroma components in the pulp cells. Moreover, the subsequent enzyme inactivation by enzymatic hydrolysis, the cavitation effect of ultrasound and the molecular vibration caused by microwaves cause the juice to heat up, causing the characteristic aroma components of the pineapple juice to partially degrade or volatilize. Compared with the treatment technology of the comparative example, the electric field treatment combined with the squeezing treatment of the present invention can well avoid the degradation and loss of the dissolved characteristic aroma components of the pineapple, further improve the flavor of the pineapple juice, and can play a significant effect of enhancing the flavor during the juice processing process, so that the juice product can still retain the original characteristic aroma and sensory evaluation of the fruit to the greatest extent after processing.

[0057] Table 2. Results of key flavor compounds in pineapple juice prepared by different methods

[0058]

[0059]

[0060] Example 2

[0061] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 25kg of the prepared pineapple puree and put it into the pulse electric field treatment room, and then put it into the pulse electric field equipment for treatment. The treatment conditions of the pulse electric field are a treatment frequency of 30Hz, an electric field strength of 1.00kV / cm, a pulse time of 200s, and a pulse width of 30μs. After the treatment, pour the pineapple puree into a squeezer, squeeze it, and filter it to obtain pineapple juice.

[0062] Comparative Example 5

[0063] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into fruit pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 25kg of the prepared pineapple puree and squeeze and filter it to obtain pineapple juice.

[0064] Comparative Example 6

[0065] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 25kg of the prepared pineapple puree and heat it at 53°C for gelatinization for 20 minutes, then add 0.05% pectinase and 0.075% cellulase according to the weight of the puree, and perform composite enzymolysis treatment at 50°C for 2 hours. After the treatment, the puree is treated to inactivate enzymes at 83°C for 25 minutes, and after cooling to room temperature, it is squeezed and filtered to obtain pineapple juice.

[0066] Comparative Example 7

[0067] Select pineapple fruits that are 70% to 80% ripe, fresh and free of disease as raw materials, wash and peel them, cut them into fruit pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 25kg of the prepared pineapple puree and treat it in an ultrasonic extraction device under the conditions of 20KHz frequency and 750W power for 25min, and squeeze and filter to obtain pineapple juice after the treatment is completed.

[0068] Comparative Example 8

[0069] Select pineapple fruits that are 70% to 80% ripe, fresh and free of disease as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 25kg of the prepared pineapple puree and treat it in a microwave extraction equipment, the microwave treatment condition is 850W, the treatment is for 2min, and after the treatment is completed, squeeze and filter to obtain pineapple juice.

[0070] The total phenol content in the samples of Example 2 and Comparative Examples 5-8 was determined with reference to T / AHFIA005-2018.

[0071] The vitamin C content in the samples of Example 2 and Comparative Examples 5-8 was determined by spectrophotometry. 400 μL of juice was mixed with NaCl solution (0.50 mol / L), centrifuged at 5000 r / min for 10 min, and then mixed with 100 μL of sodium acetate buffer (0.02 mol / L), and the absorbance value was measured at 265 nm using a spectrophotometer. After the above test solution was reacted with 50 μL of copper sulfate solution (2.4 M), the absorbance blank was measured at 265 nm. The ascorbic acid standard was used to prepare a standard solution (0-15 μg / mL), and the vitamin C content in the juice was calculated using a standard curve.

[0072] The aroma components in the samples of Example 2 and Comparative Examples 5-8 were determined by gas chromatography-mass spectrometry. Sample pretreatment: 8g of juice was poured into an SPME sample bottle, and 1.5g of NaCl was weighed and added to the bottle, followed by dripping 6μL of 2-octanol internal standard solution (concentration of 100mg / L). The SPME extraction needle used for detection was DVB / CAR / PDMS, 50 / 30μm (Supelco, USA), and the chromatographic column model was HP-WAX (60m×0.25mm×0.25μm, Agilent, USA). The total cycle time for gas chromatography-mass spectrometry was 64min, and the detection procedure was: the initial temperature was 40°C, maintained for 6min, raised to 100°C at a rate of 3°C / min, and then heated to 230°C at a rate of 10°C / min and maintained for 20min. Helium was used as the carrier gas with a flow rate of 1.0 mL / min, and mass spectrometry fragmentation was performed in electron impact (EI) mode (ionization energy, 70 eV; source temperature, 230 °C). Compounds were identified by retention index and NIST 20 database, where the retention indices (RIs) of substances were calculated by the elution time of n-alkanes (C7-C40).

[0073] The juice yield, total phenol, vitamin C content and temperature changes before and after treatment of Example 2 (pulsed electric field) and Comparative Examples 5-8 are shown in Table 3. As shown in Table 3, the sample of Example 2 has the highest juice yield (79.44%), total phenol content (538.60 μg / mL) and vitamin C content (143.56 μg / mL), indicating that compared with traditional squeezing, enzymatic hydrolysis, ultrasonic method and microwave method, the electroporation of the pulsed electric field can more effectively destroy the pineapple pulp cell structure and promote the dissolution of juice and bioactive components. In the enzymatic hydrolysis method, although enzymatic hydrolysis can effectively destroy the pulp cell wall and promote the dissolution of juice, the subsequent long-term high-temperature enzyme inactivation treatment will cause the degradation of heat-sensitive components such as polyphenols and vitamin C, resulting in the total content and vitamin C content in the reorganized sample being even lower than that of the traditional squeezing method sample. As shown in Table 3, the method of the present invention can well protect phenolic substances and vitamin C from degradation, so that the juice has better nutritional quality.

[0074] Table 3. Changes in temperature, juice yield, total phenol content and vitamin C content before and after treatment in Example 2 and Comparative Examples 5-8

[0075]

[0076] Methyl caproate, 2-methylbutyric acid, methyl butyrate, isoamyl acetate, dimethyl malonate and methyl heptanoate are characteristic aroma components of pineapple. The volatile flavor component contents of Example 2 (pulsed electric field) and Comparative Examples 5-8 are shown in Table 4. As shown in Table 4, it can be seen from Table 4 that the content of key flavor compounds in the sample of Example 2 (pulsed electric field) is relatively high, and methyl caproate, methyl 2-methylbutyrate and methyl butyrate are significantly higher than those of other comparative examples. Compared with Comparative Examples 5-8, the methyl caproate content is increased by 53.46%, 66.36%, 36.04% and 50.51% respectively; the methyl 2-methylbutyrate content is increased by 35.19%, 87.28%, 43.63% and 84.24% respectively; the methyl butyrate content is increased by 15.19%, 39.32%, 6.03% and 37.58% respectively. Existing sensory description studies on these aroma substances have shown that methyl caproate has fruity and pineapple aromas, methyl 2-methylbutyrate has apple, floral and fresh aromas, and methyl butyrate has pineapple, apple and banana aromas. These aroma substances are compounds with high content in pineapple juice and are also one of the most abundant components of pineapple. They are characteristic aroma substances of pineapple (George, J., Nguyen, T., Williams, D., Hardner, C., Sanewski, G., & Smyth, H., E. Review of the Aroma Chemistry of Pineapple (Ananas comosus). Journal of Agricultural and Food Chemistry, 2023, 71: 4069-4082). The increase in the abundance of characteristic aroma substances in juice after electric field treatment may be due to the fact that the polarization perforation effect of the pulsed electric field effectively destroys the pulp cell structure and promotes the dissolution of characteristic aroma components in the pulp cells. The electric field combined with the squeezing treatment process of the present invention can well avoid the degradation loss of dissolved pineapple characteristic aroma components, further improve the flavor of pineapple juice, and can play a significant effect of enhancing the flavor during the juice processing process, so that the juice product can still retain the original characteristic aroma and sensory evaluation of the fruit to the greatest extent after processing.

[0077] Table 4. Results of key flavor compound content test of pineapple juice prepared by different methods

[0078]

[0079]

[0080] Example 3

[0081] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 30kg of the prepared pineapple puree and put it into the pulse electric field treatment room, and then put it into the pulse electric field equipment for treatment. The treatment conditions of the pulse electric field are a treatment frequency of 30Hz, an electric field strength of 1.25kV / cm, a pulse time of 225s, and a pulse width of 40μs. After the treatment, pour the pineapple puree into a squeezer, squeeze it, and filter it to obtain pineapple juice.

[0082] Comparative Example 9

[0083] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into fruit pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 30kg of the prepared pineapple puree and squeeze and filter it to obtain pineapple juice.

[0084] Comparative Example 10

[0085] Select pineapple fruits that are 70% to 80% ripe, fresh and disease-free as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 30kg of the prepared pineapple puree and heat it at 53°C for gelatinization for 20 minutes, then add 0.05% pectinase and 0.075% cellulase according to the weight of the puree, and perform composite enzymolysis treatment at 50°C for 2 hours. After the treatment, the puree is treated to inactivate enzymes at 83°C for 25 minutes, and after cooling to room temperature, it is squeezed and filtered to obtain pineapple juice.

[0086] Comparative Example 11

[0087] Select pineapple fruits that are 70% to 80% ripe, fresh and free of disease as raw materials, wash and peel them, cut them into fruit pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 30kg of the prepared pineapple puree and treat it in an ultrasonic extraction device under the treatment conditions of 20KHz frequency and 750W power for 25min, and squeeze and filter to obtain pineapple juice after the treatment is completed.

[0088] Comparative Example 12

[0089] Select pineapple fruits that are 70% to 80% ripe, fresh and free of disease as raw materials, wash and peel them, cut them into pieces smaller than 3cm×3cm×3cm, and put them in a blender to crush them to obtain pineapple puree for later use; take 30kg of the prepared pineapple puree and treat it in a microwave extraction equipment, the microwave treatment condition is 850W, the treatment is for 2min, and after the treatment is completed, squeeze and filter to obtain pineapple juice.

[0090] The total phenol content in the samples of Example 3 and Comparative Examples 9-12 was determined with reference to T / AHFIA005-2018.

[0091] The vitamin C content in the samples of Example 3 and Comparative Examples 9-12 was determined by spectrophotometry. 400 μL of juice was mixed with NaCl solution (0.50 mol / L), centrifuged at 5000 r / min for 10 min, and then mixed with 100 μL of sodium acetate buffer (0.02 mol / L), and the absorbance value was measured at 265 nm using a spectrophotometer. After the above test solution was reacted with 50 μL of copper sulfate solution (2.4 M), the absorbance blank was measured at 265 nm. The ascorbic acid standard was used to prepare a standard solution (0-15 μg / mL), and the vitamin C content in the juice was calculated using a standard curve.

[0092] The aroma components in the samples of Example 3 and Comparative Examples 9-12 were determined by gas chromatography-mass spectrometry. Sample pretreatment: 8g of juice was poured into an SPME sample bottle, and 1.5g of NaCl was weighed and added to the bottle, followed by dripping 6μL of 2-octanol internal standard solution (concentration of 100mg / L). The SPME extraction needle used for detection was DVB / CAR / PDMS, 50 / 30μm (Supelco, USA), and the chromatographic column model was HP-WAX (60m×0.25mm×0.25μm, Agilent, USA). The total cycle time for gas chromatography-mass spectrometry was 64min, and the detection procedure was: the initial temperature was 40°C, maintained for 6min, raised to 100°C at a rate of 3°C / min, and then heated to 230°C at a rate of 10°C / min and maintained for 20min. Helium was used as the carrier gas with a flow rate of 1.0 mL / min, and mass spectrometry fragmentation was performed in electron impact (EI) mode (ionization energy, 70 eV; source temperature, 230 °C). Compounds were identified by retention index and NIST 20 database, where the retention indices (RIs) of substances were calculated by the elution time of n-alkanes (C7-C40).

[0093] The juice yield, total phenol, vitamin C content and temperature changes before and after treatment of the samples of Example 3 and Comparative Examples 9-12 are shown in Table 5. As shown in Table 5, the sample of Example 2 has the highest juice yield (72.51%), total phenol content (478.61 μg / mL) and vitamin C content (101.17 μg / mL), indicating that compared with traditional squeezing, enzymatic hydrolysis, ultrasonic method and microwave method, the electroporation of the pulsed electric field can more effectively destroy the pineapple pulp cell structure and promote the dissolution of juice and bioactive components. In the enzymatic hydrolysis method, although enzymatic hydrolysis can effectively destroy the pulp cell wall and promote the dissolution of juice, the subsequent long-term high-temperature enzyme inactivation treatment will cause the degradation of heat-sensitive components such as polyphenols and vitamin C, resulting in the total content and vitamin C content in the reorganized sample being even lower than that of the traditional squeezing method sample. As shown in Table 5, the method of the present invention can well protect phenolic substances and vitamin C from degradation, so that the juice has better nutritional quality.

[0094] Table 5. Changes in temperature, juice yield, total phenol content and vitamin C content before and after treatment in Example 3 and Comparative Examples 9-12

[0095]

[0096] Methyl caproate, 2-methylbutyric acid, methyl butyrate, isoamyl acetate, dimethyl malonate and methyl heptanoate are characteristic aroma components of pineapple. The volatile flavor component contents of Example 3 (pulsed electric field) and Comparative Examples 9-12 are shown in Table 6. As shown in Table 6, it can be seen from Table 6 that the content of key flavor compounds in the sample of Example 3 (pulsed electric field) is relatively high, and methyl caproate, methyl 2-methylbutyrate and methyl butyrate are significantly higher than other comparative examples. Compared with Comparative Examples 9-12, the methyl caproate content is increased by 6.72%, 24.24%, 9.88% and 21.95% respectively; the methyl 2-methylbutyrate content is increased by 26.10%, 68.39%, 38.08% and 99.35% respectively; the methyl butyrate content is increased by 12.26%, 45.21%, 20.20% and 38.74% respectively. Existing sensory description studies on these aroma substances have shown that methyl caproate has fruity and pineapple aromas, methyl 2-methylbutyrate has apple, floral and fresh aromas, and methyl butyrate has pineapple, apple and banana aromas. These aroma substances are compounds with high content in pineapple juice and are also one of the most abundant components of pineapple. They are the characteristic aroma substances of pineapple (George, J., Nguyen, T., Williams, D., Hardner, C., Sanewski, G., & Smyth, H., E. Review of the Aroma Chemistry of Pineapple (Ananas comosus). Journal of Agricultural and Food Chemistry, 2023, 71: 4069-4082). The increase in the abundance of characteristic aroma substances in the juice after electric field treatment The increase in the abundance of characteristic aroma substances in the juice after electric field treatment may be due to the polarization perforation effect of the pulsed electric field, which effectively destroys the pulp cell structure and promotes the dissolution of characteristic aroma components in the pulp cells. The subsequent enzyme inactivation by enzymatic hydrolysis, the cavitation effect of ultrasound and the molecular vibration caused by microwaves will also cause the juice to heat up, causing partial degradation or volatilization loss of the characteristic aroma components of pineapple juice. The method of the present invention can well avoid the degradation loss of the dissolved characteristic aroma components of pineapple, further improve the flavor of pineapple juice, and can play a significant effect of enhancing the flavor during the juice processing process, so that the juice product can still retain the original characteristic aroma and sensory evaluation of the fruit to the greatest extent after processing.

[0097] Table 6. Results of key flavor compounds in pineapple juice prepared by different methods

[0098]

[0099] The implementation methods of the present invention are not limited to the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A method for rapidly increasing the yield of pineapple juice and improving its aroma by using a pulsed electric field, characterized in that The following steps are involved: (1) preparing pineapple puree: selecting fresh pineapples, washing, peeling and crushing them to prepare pineapple puree; (2) Pulsed electric field treatment: placing the pineapple puree in a pulsed electric field treatment chamber for pulsed electric field treatment; (3) Juice extraction and filtration: Pour the pineapple puree pretreated by the pulse electric field into a squeezer, and filter the pineapple juice after squeezing.

2. The method of claim 1, wherein the pulsed electric field is used to rapidly increase the yield of pineapple juice and improve its aroma. In step (1), the fresh pineapple is a pineapple that is 70% to 80% mature, fresh and free of disease.

3. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 1, characterized in that: In step (1), the crushing is to first wash and peel the fresh pineapple, cut it into pieces, and then put it in a blender to crush it.

4. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 3, characterized in that: The size of the fruit block is less than 3cm×3cm×3cm.

5. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 3, characterized in that: The mass of pineapples crushed by the mixer at one time is 20-30kg.

6. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 1, characterized in that: In step (2), the pulse electric field treatment frequency is 20-40 Hz, and the electric field strength is 0.25-1.50 kV / cm.

7. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 6, characterized in that: The treatment frequency of the pulse electric field is 25-35 Hz, and the electric field strength is 0.75-1.25 kV / cm.

8. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 1, characterized in that: In step (2), the pulse time of the electric field pulse treatment is 175-225s, and the pulse width is 20-40μs.

9. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 8, characterized in that: The pulse time is 150-250s.

10. The method of using a pulsed electric field to quickly increase the yield of pineapple juice and improve the aroma according to claim 8, characterized in that: The pulse width is 10-50 μs.

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