A method for preparing hempseed oil to inhibit the formation of trans fatty acids

Abstract

The application provides a preparation method of hempseed oil for inhibiting the generation of trans fatty acids, and belongs to the technical field of edible vegetable oil refining. The method is aimed at the problem that the low-oxygen state is destabilized again due to ultrasonic degassing after deoxygenation and residual oxygen input of high-flow nitrogen gas, and a continuous low-oxygen control mechanism of hidden oxygen release, re-removal and exogenous oxygen limitation is formed by setting the ultrasonic degassing between the first deoxygenation and the second polishing deoxygenation and controlling the cumulative input amount of residual oxygen of nitrogen gas in the refining process. Therefore, the oxidation and cis-trans isomerization tendency of unsaturated fatty acids can be reduced in the high-vacuum low-temperature spray deodorization process, the generation of trans fatty acids and oxidation byproducts is reduced, and the nutritional quality and deodorization effect of the hempseed oil are beneficially maintained.

Description

Technical Field

[0001] This invention belongs to the field of edible vegetable oil refining technology, and relates to a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. Background Technology

[0002] Hemp seed oil has a high content of unsaturated fatty acids such as linoleic acid and α-linolenic acid, which are easily oxidized and undergo cis-trans isomerization during deodorization due to the influence of temperature, oxygen content, and heating time. Existing processes typically reduce the formation of trans fatty acids and oxidation byproducts by using vacuum deoxygenation, high-purity nitrogen protection, and low-temperature short-time spray deodorization.

[0003] However, the low dissolved oxygen level at the deoxygenation unit outlet does not represent the actual oxygen exposure throughout the entire treatment process. Ultrasonic treatment after deoxygenation may cause the release of gases embedded in the microbubbles, trace amounts of aqueous phase, or oil phase micro-associations; simultaneously, high-purity nitrogen still contains a small amount of residual oxygen, which accumulates in the treatment system with the nitrogen usage during multi-stage, high-flow-rate applications. Especially after spray deodorization forms high specific surface area microdroplets, the aforementioned internal gas release and external oxygen supply may cause the low-oxygen state to become unstable again.

[0004] Therefore, existing technologies still need to address the problem of maintaining a stable low-oxygen state for hemp seed oil during ultrasonic treatment and nitrogen spray stripping, in order to reduce the tendency of unsaturated fatty acids to oxidize and undergo cis-trans isomerization during subsequent deodorization processes. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. This method solves the problem that during the ultrasonic treatment after deoxygenation in the existing hemp seed oil refining process, the embedded gas in the micro-bubbles, trace amounts of aqueous phase, and oil phase micro-association structure may be released again, and the residual oxygen in the low-oxygen drying nitrogen may accumulate and be introduced through multiple processes, making it difficult to maintain a stable low-oxygen state in the subsequent spray deodorization process of hemp seed oil.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids, comprising the following steps:

[0008] S1: The crude hemp seed oil is subjected to degumming, deacidification, decolorization and dehydration treatment in sequence to obtain decolorized hemp seed oil; food-grade nitrogen is subjected to deoxygenation and drying treatment to obtain low-oxygen dry nitrogen.

[0009] S2: The decolorized hemp seed oil is transported to a primary spray degassing device for spray deoxygenation, while the low-oxygen drying nitrogen gas is introduced to obtain primary deoxygenated hemp seed oil.

[0010] S3: The first-stage deoxygenated hemp seed oil is transported to a closed-loop ultrasonic treatment device under the protection of low-oxygen drying nitrogen to perform pulsed ultrasonic degassing, thereby obtaining ultrasonically degassed hemp seed oil, and the ultrasonically degassed hemp seed oil is then transported to a second-stage spray deoxygenation device.

[0011] S4: The ultrasonically degassing hemp seed oil is subjected to two-stage spray polishing and deoxygenation, while the low-oxygen drying nitrogen gas is introduced to obtain polished and deoxygenated hemp seed oil.

[0012] S5: The polished and deoxidized hemp seed oil is heated and then transported to a high-vacuum spray deodorization tower through a closed pipeline. The preheated low-oxygen dry nitrogen is used as both the atomizing medium and the stripping gas for spray deodorization to obtain deodorized hemp seed oil. Based on the actual oxygen volume fraction in the low-oxygen dry nitrogen, the nitrogen usage volume converted to standard conditions, and the corresponding hemp seed oil mass, the total cumulative input of residual nitrogen per unit mass of hemp seed oil in S2-S5 is controlled.

[0013] S6: Cool the deodorized hemp seed oil under vacuum conditions, filter it in a sealed container, and fill it to obtain hemp seed oil that inhibits the formation of trans fatty acids.

[0014] Preferably, in step S1, the moisture content of the decolorized hemp seed oil is not higher than 0.05 wt%.

[0015] Preferably, in step S1, the oxygen content of the low-oxygen dry nitrogen gas is not higher than 2 ppm, and the atmospheric pressure dew point is not higher than -50°C.

[0016] Preferably, in step S2, the temperature of the spray deoxygenation is 85-100℃, the absolute pressure is 20-50Pa, and the treatment time is 4-8min.

[0017] Preferably, in step S2, the volume of the low-oxygen drying nitrogen used is (0.5-2.7) L / kg to the mass ratio of the hemp seed oil decolorizing oil.

[0018] Preferably, in step S3, the primary deoxygenated hemp seed oil is adjusted to 50-70°C under the protection of low-oxygen drying nitrogen, and then transported to the closed-loop ultrasonic treatment device.

[0019] Preferably, the closed-loop ultrasonic treatment device uses low-oxygen dry nitrogen to replace the gas phase space before the primary deoxygenated hemp seed oil enters, and keeps it sealed after replacement. The low-oxygen dry nitrogen is not continuously introduced during the ultrasonic treatment process, and the volume of low-oxygen dry nitrogen used is (0.3-2.0) L / kg to the mass ratio of the primary deoxygenated hemp seed oil.

[0020] Preferably, in step S3, the pulsed ultrasonic gas release uses ultrasonic waves with a frequency of 20-35kHz and a power density of 25-60W / L, the ratio of ultrasonic start time to stop time is 1:(1-2), and the processing time is 2-5min.

[0021] Preferably, the ultrasonically released hemp oil is delivered to the secondary spray deoxygenation device within 0.5-2 minutes after the pulsed ultrasonic degassing ends.

[0022] Preferably, in step S4, the temperature of the secondary spray polishing deoxidation is 90-105℃ and the absolute pressure is 8-25Pa.

[0023] Preferably, in step S4, the volume of the low-oxygen drying nitrogen used is (0.8-4.0) L / kg to the mass ratio of the ultrasonically released hemp seed oil.

[0024] Preferably, in step S4, the dissolved oxygen content of the hemp seed oil after the secondary spray polishing and deoxidation treatment is not higher than 0.10 mg / kg.

[0025] Preferably, in step S5, the polishing and deoxidizing hemp oil is heated to 135-145°C and transported to the high vacuum spray deodorization tower through a closed pipeline.

[0026] Preferably, in step S5, the low-oxygen dry nitrogen gas is preheated to 125-140°C, so that the preheated low-oxygen dry nitrogen gas can be used as both an atomizing medium and a stripping gas.

[0027] Preferably, in step S5, the absolute pressure of the spray deodorization is 8-25 Pa, and the spray deodorization time is 3-7 min.

[0028] Preferably, in step S5, the volume ratio of the low-oxygen drying nitrogen gas used to the mass ratio of the polishing and deoxidizing hemp oil is (2.0-8.2) L / kg.

[0029] Preferably, based on the actual oxygen volume fraction in the low-oxygen drying nitrogen, the nitrogen usage volume converted to standard conditions, and the corresponding hemp seed oil mass, the total cumulative input of residual oxygen per unit mass of hemp seed oil in S2-S5 is controlled to be no higher than 0.05 mg / kg.

[0030] Preferably, in step S6, the deodorized hemp seed oil is cooled to 45-60°C under vacuum conditions for 5-15 minutes, a food-grade antioxidant is added under the protection of low-oxygen drying nitrogen, and the oil is obtained by sealed filtration and bottling.

[0031] Preferably, the food-grade antioxidant is a mixed tocopherol, and the amount of the mixed tocopherol added is 0.02-0.05 wt% of the hemp seed oil. After adding, the mixture is stirred for 5-10 minutes, and then filtered and filled in a sealed container.

[0032] Current hemp seed oil refining processes typically determine whether the oil is in a low-oxygen state based on the dissolved oxygen content at the deoxygenation unit outlet. However, this assessment does not consider the disturbance to the internal gas distribution of the oil phase caused by subsequent ultrasonic treatment. After primary spray deoxygenation, most of the free dissolved oxygen in hemp seed oil is removed, but small amounts of gas may still be trapped in the microbubbles, trace amounts of aqueous phase, and the microscopic association structure of the oil phase. If ultrasonic treatment is performed directly after final deoxygenation, the disruption of these microstructures by ultrasonic cavitation may cause the trapped gas to be released again, altering the established low-oxygen state.

[0033] This invention incorporates pulsed ultrasonic degassing between primary spray deoxygenation and secondary spray polishing deoxygenation. Primary spray deoxygenation first reduces the free dissolved oxygen in the oil phase; then, pulsed ultrasound actively releases the embedded gas that is difficult to remove directly using conventional spray deoxygenation; finally, secondary spray polishing deoxygenation removes the gas released after ultrasound. Therefore, secondary spray polishing deoxygenation is not a simple repetition of primary spray deoxygenation, but rather compensates for the hypoxic disturbance caused by ultrasonic degassing, ensuring that the hemp seed oil entering the spray deodorization process is once again in a controllable hypoxic state.

[0034] On the other hand, high-purity nitrogen may still contain a small amount of residual oxygen. When nitrogen is used continuously or in stages during primary spray deoxygenation, ultrasonic gas phase displacement, secondary spray polishing deoxygenation, and spray deodorization, residual oxygen will gradually accumulate with the volume of nitrogen used. Controlling nitrogen solely based on its nominal purity or the flow rate of nitrogen in a single process is insufficient to reflect the actual external oxygen load per unit mass of hemp seed oil throughout the entire refining process. This invention controls the total cumulative input of residual oxygen per unit mass of hemp seed oil in S2-S5 based on the actual oxygen volume fraction in low-oxygen drying nitrogen, the nitrogen usage volume converted to standard conditions, and the corresponding hemp seed oil mass. This establishes a linkage between nitrogen flow rate, actual oxygen content, and usage volume, reducing the accumulation of external oxygen caused by the use of nitrogen in multiple processes.

[0035] Through the above setup, this invention establishes a continuous low-oxygen control process of "pre-removal of free dissolved oxygen - active release of encapsulated gas - further removal of released gas - cumulative restriction of exogenous residual oxygen." Specifically, the secondary spray polishing deoxygenation after ultrasonication eliminates the instability of the low-oxygen state caused by the re-release of endogenous hidden oxygen, while the cumulative nitrogen residual oxygen input control limits the continuous entry of exogenous oxygen. Together, these two processes ensure that hemp seed oil maintains a relatively stable low-oxygen environment even when forming high specific surface area spray droplets and undergoing deodorization treatment, reducing the reaction conditions for the oxidation and cis-trans isomerization of unsaturated fatty acids.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention incorporates a two-stage spray polishing deoxygenation process following pulsed ultrasonic gas release. This process removes the encapsulated gas released by the ultrasonic action before it enters the spray deodorization stage, transforming the low-oxygen state at the deodorization inlet from an indirect assessment after the first-stage deoxygenation to a direct control based on the endpoint of the ultrasonic polishing deoxygenation. This reduces the interference of ultrasonic treatment on the effectiveness of the preceding deoxygenation process.

[0038] This invention does not evaluate the protective effect of nitrogen solely based on nitrogen purity. Instead, it controls the cumulative total amount of residual oxygen input generated by nitrogen use in multiple processes, creating a constraint between the actual oxygen content of nitrogen, the volume used, and the corresponding hemp oil quality. While ensuring the amount of nitrogen required for spray deoxygenation, gas phase protection, atomization, and stripping, it can reduce the accumulation of residual oxygen caused by increasing nitrogen flow rate or extending usage time, avoiding a control disconnect between nitrogen-enhanced mass transfer and external oxygen input.

[0039] By synergistically controlling endogenous occult oxygen removal and exogenous residual oxygen limitation, the continuity of the hypoxic state in hemp seed oil from ultrasonic treatment to spray deodorization can be improved, reducing oxygen exposure fluctuations caused by changes in raw material condition, actual nitrogen oxygen content, and treatment gas volume. Under the condition of achieving the corresponding degree of deodorization treatment, it is beneficial to reduce the oxidation and cis-trans isomerization tendency of unsaturated fatty acids in hemp seed oil, reduce the formation of trans fatty acids and oxidation byproducts, and improve the consistency of product quality across different batches. Detailed Implementation

[0040] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that employ any obvious substitutions and modifications made to the embodiments described herein.

[0041] Example 1

[0042] This embodiment provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The preparation method specifically includes the following steps:

[0043] S1: The crude hemp seed oil is subjected to degumming, deacidification, decolorization and dehydration treatment in sequence to obtain decolorized hemp seed oil with a moisture content of 0.03wt%; food-grade nitrogen is subjected to deoxygenation and drying treatment to obtain low-oxygen dry nitrogen with an oxygen content of 1.0ppm and a normal pressure dew point of -60℃.

[0044] S2: The decolorized hemp seed oil is transported to the first-stage spray degassing device and deoxygenated under the conditions of 85℃ and 50Pa absolute pressure. At the same time, low-oxygen dry nitrogen is introduced. The volume ratio of low-oxygen dry nitrogen to the mass ratio of the decolorized hemp seed oil is 1.6L / kg. The processing time is 8min, and first-stage deoxygenated hemp seed oil is obtained.

[0045] S3: The primary deoxygenated hemp seed oil is adjusted to 60°C under low-oxygen dry nitrogen protection and then transported to a closed-loop ultrasonic treatment device. Before the primary deoxygenated hemp seed oil enters, the ultrasonic treatment device uses low-oxygen dry nitrogen to replace the gas phase space. The volume ratio of the low-oxygen dry nitrogen used to the mass of the primary deoxygenated hemp seed oil is 1 L / kg. After replacement, the device remains sealed, and low-oxygen dry nitrogen is not continuously introduced during ultrasonic treatment. Pulsed ultrasonic release is performed using ultrasound at a frequency of 35 kHz and a power density of 25 W / L, with an ultrasound start-up time to stop time ratio of 1:1.5 and a treatment time of 3.5 min, yielding ultrasonically released hemp seed oil. Within 0.5 min after the ultrasonic treatment ends, the ultrasonically released hemp seed oil is transported to a secondary spray deoxygenation device.

[0046] S4: The ultrasonically degassed hemp seed oil is subjected to two-stage spray polishing and deoxidation at a temperature of 105℃ and an absolute pressure of 15Pa, while low-oxygen dry nitrogen is introduced. The volume ratio of low-oxygen dry nitrogen to the mass of ultrasonically degassed hemp seed oil is 0.8L / kg. The dissolved oxygen content of the hemp seed oil at the outlet is 0.08mg / kg, thus obtaining polished and deoxidized hemp seed oil.

[0047] S5: The polished and deoxidized hemp seed oil is heated to 140℃ and transported to a high-vacuum spray deodorization tower through a closed pipeline; low-oxygen dry nitrogen gas preheated to 125℃ is used as both the atomizing medium and the stripping gas, and the oil is sprayed and deodorized for 5 minutes under an absolute pressure of 25Pa. The volume ratio of the low-oxygen dry nitrogen gas used to the mass ratio of the polished and deoxidized hemp seed oil is 5.0L / kg, and the deodorized hemp seed oil is obtained.

[0048] S6: The deodorized hemp seed oil is cooled to 45°C within 10 minutes under vacuum conditions. Food-grade antioxidant mixed tocopherols are added under low-oxygen, dry nitrogen protection. The amount of mixed tocopherols added is 0.04 wt% of the hemp seed oil mass. After addition, the mixture is stirred for 8 minutes, filtered and bottled in a sealed manner to obtain hemp seed oil that inhibits the formation of trans fatty acids.

[0049] Example 2

[0050] This embodiment provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The preparation method specifically includes the following steps:

[0051] S1: The crude hemp seed oil is subjected to degumming, deacidification, decolorization and dehydration treatment in sequence to obtain decolorized hemp seed oil with a moisture content of 0.02wt%; food-grade nitrogen is subjected to deoxygenation and drying treatment to obtain low-oxygen dry nitrogen with an oxygen content of 0.5ppm and a normal pressure dew point of -70℃.

[0052] S2: The decolorized hemp seed oil is transported to the first-stage spray degassing device and deoxygenated under the conditions of 100℃ and 20Pa absolute pressure. At the same time, low-oxygen dry nitrogen is introduced. The volume ratio of the low-oxygen dry nitrogen used to the mass ratio of the decolorized hemp seed oil is 0.5L / kg. The treatment time is 6min, and first-stage deoxygenated hemp seed oil is obtained.

[0053] S3: The primary deoxygenated hemp seed oil is adjusted to 50°C under low-oxygen dry nitrogen protection and then transported to a closed-loop ultrasonic treatment device. Before the primary deoxygenated hemp seed oil enters, the ultrasonic treatment device uses low-oxygen dry nitrogen to replace the gas phase space. The volume ratio of the low-oxygen dry nitrogen used to the mass ratio of the primary deoxygenated hemp seed oil is 0.3 L / kg. After replacement, the device remains sealed, and low-oxygen dry nitrogen is not continuously introduced during the ultrasonic treatment. Pulsed ultrasonic release is performed using ultrasound with a frequency of 28 kHz and a power density of 60 W / L. The ratio of ultrasonic start time to stop time is 1:2, and the treatment time is 2 minutes, resulting in ultrasonically released hemp seed oil. Within 1.5 minutes after the ultrasonic treatment ends, the ultrasonically released hemp seed oil is transported to the secondary spray deoxygenation device.

[0054] S4: The ultrasonically degassed hemp seed oil is subjected to two-stage spray polishing and deoxidation at a temperature of 98℃ and an absolute pressure of 8Pa, while low-oxygen dry nitrogen is introduced. The volume ratio of low-oxygen dry nitrogen to the mass of ultrasonically degassed hemp seed oil is 4.0L / kg. The dissolved oxygen content of the hemp seed oil at the outlet is 0.10mg / kg, thus obtaining polished and deoxidized hemp seed oil.

[0055] S5: The polished and deoxidized hemp seed oil is heated to 135℃ and transported to a high-vacuum spray deodorization tower through a closed pipeline; low-oxygen dry nitrogen gas preheated to 136℃ is used as both the atomizing medium and the stripping gas, and deodorization is carried out by spraying for 7 minutes under an absolute pressure of 15Pa. The volume ratio of low-oxygen dry nitrogen gas used to the mass ratio of polished and deoxidized hemp seed oil is 2.0L / kg, and deodorized hemp seed oil is obtained.

[0056] S6: The deodorized hemp seed oil is cooled to 55°C under vacuum for 12 minutes. Food-grade antioxidant mixed tocopherols are added under low-oxygen, dry nitrogen protection. The amount of mixed tocopherols added is 0.03 wt% of the hemp seed oil mass. After addition, the mixture is stirred for 5 minutes, filtered and bottled in a sealed manner to obtain hemp seed oil that inhibits the formation of trans fatty acids.

[0057] Example 3

[0058] This embodiment provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The preparation method specifically includes the following steps:

[0059] S1: The crude hemp seed oil is subjected to degumming, deacidification, decolorization and dehydration treatment in sequence to obtain decolorized hemp seed oil with a moisture content of 0.05wt%; food-grade nitrogen is subjected to deoxygenation and drying treatment to obtain low-oxygen dry nitrogen with an oxygen content of 2ppm and a normal pressure dew point of -50℃.

[0060] S2: The decolorized hemp seed oil is transported to the first-stage spray degassing device and deoxygenated under the conditions of 92℃ and 35Pa absolute pressure. At the same time, low-oxygen dry nitrogen is introduced. The volume ratio of low-oxygen dry nitrogen to the mass ratio of the decolorized hemp seed oil is 2.7L / kg. The processing time is 4min, and first-stage deoxygenated hemp seed oil is obtained.

[0061] S3: The primary deoxygenated hemp seed oil is adjusted to 70°C under low-oxygen dry nitrogen protection and then transported to a closed-loop ultrasonic treatment device. Before the primary deoxygenated hemp seed oil enters, the ultrasonic treatment device uses low-oxygen dry nitrogen to replace the gas phase space. The volume ratio of the low-oxygen dry nitrogen used to the mass ratio of the primary deoxygenated hemp seed oil is 2L / kg. After replacement, the device remains sealed. Low-oxygen dry nitrogen is not continuously introduced during the ultrasonic treatment. Pulsed ultrasonic release is performed using ultrasound with a frequency of 20kHz and a power density of 40W / L. The ratio of ultrasonic start time to stop time is 1:1, and the treatment time is 5 minutes, resulting in ultrasonically released hemp seed oil. Within 1 minute after the ultrasonic treatment ends, the ultrasonically released hemp seed oil is transported to the secondary spray deoxygenation device.

[0062] S4: The ultrasonically degassed hemp seed oil is subjected to two-stage spray polishing and deoxidation at a temperature of 90℃ and an absolute pressure of 25Pa, while low-oxygen dry nitrogen is introduced. The volume ratio of low-oxygen dry nitrogen to the mass ratio of ultrasonically degassed hemp seed oil is 2.4L / kg. The dissolved oxygen content of the hemp seed oil at the outlet is 0.05mg / kg, thus obtaining polished and deoxidized hemp seed oil.

[0063] S5: The polished and deoxidized hemp seed oil is heated to 145℃ and transported to a high-vacuum spray deodorization tower through a closed pipeline; low-oxygen dry nitrogen gas preheated to 132℃ is used as both the atomizing medium and the stripping gas, and deodorization is carried out by spraying for 3 minutes under an absolute pressure of 8Pa. The volume ratio of low-oxygen dry nitrogen gas used to the mass ratio of polished and deoxidized hemp seed oil is 8.2L / kg, and deodorized hemp seed oil is obtained.

[0064] S6: The deodorized hemp seed oil is cooled to 60°C within 5 minutes under vacuum conditions. Food-grade antioxidant mixed tocopherols are added under low-oxygen, dry nitrogen protection. The amount of mixed tocopherols added is 0.02 wt% of the hemp seed oil mass. After addition, the mixture is stirred for 10 minutes, filtered and bottled in a sealed manner to obtain hemp seed oil that inhibits the formation of trans fatty acids.

[0065] Example 4

[0066] This embodiment provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The preparation method specifically includes the following steps:

[0067] S1: The crude hemp seed oil is subjected to degumming, deacidification, decolorization and dehydration treatment in sequence to obtain decolorized hemp seed oil with a moisture content of 0.04wt%; food-grade nitrogen is subjected to deoxygenation and drying treatment to obtain low-oxygen dry nitrogen with an oxygen content of 1.5ppm and a normal pressure dew point of -55℃.

[0068] S2: The decolorized hemp seed oil is transported to the first-stage spray degassing device and deoxygenated under the conditions of 95℃ and 25Pa absolute pressure. At the same time, low-oxygen dry nitrogen is introduced. The volume ratio of low-oxygen dry nitrogen to the mass ratio of the decolorized hemp seed oil is 2.2L / kg. The processing time is 7min, and first-stage deoxygenated hemp seed oil is obtained.

[0069] S3: The primary deoxygenated hemp seed oil is adjusted to 55°C under low-oxygen dry nitrogen protection and then transported to a closed-loop ultrasonic treatment device. Before the primary deoxygenated hemp seed oil enters, the ultrasonic treatment device uses low-oxygen dry nitrogen to replace the gas phase space. The volume ratio of the low-oxygen dry nitrogen used to the mass of the primary deoxygenated hemp seed oil is 1.5 L / kg. After replacement, the device remains sealed, and low-oxygen dry nitrogen is not continuously introduced during ultrasonic treatment. Pulsed ultrasonic release is performed using ultrasound at a frequency of 32 kHz and a power density of 50 W / L, with an ultrasound start-up time to stop time ratio of 1:1.2 and a treatment time of 4 minutes, yielding ultrasonically released hemp seed oil. Within 2 minutes after the ultrasonic treatment ends, the ultrasonically released hemp seed oil is transported to a secondary spray deoxygenation device.

[0070] S4: The ultrasonically degassed hemp seed oil is subjected to two-stage spray polishing and deoxidation at a temperature of 100℃ and an absolute pressure of 20Pa, while low-oxygen dry nitrogen is introduced. The volume ratio of low-oxygen dry nitrogen to the mass ratio of ultrasonically degassed hemp seed oil is 3.2L / kg. The dissolved oxygen content of the hemp seed oil at the outlet is 0.06mg / kg, thus obtaining polished and deoxidized hemp seed oil.

[0071] S5: The polished and deoxidized hemp seed oil is heated to 138℃ and transported to a high-vacuum spray deodorization tower through a closed pipeline; low-oxygen dry nitrogen gas preheated to 140℃ is used as both the atomizing medium and the stripping gas, and deodorization is carried out by spraying under an absolute pressure of 20Pa for 6 minutes. The volume ratio of low-oxygen dry nitrogen gas used to the mass ratio of polished and deoxidized hemp seed oil is 6.5L / kg, and deodorized hemp seed oil is obtained.

[0072] S6: The deodorized hemp seed oil is cooled to 52°C under vacuum for 15 minutes. Food-grade antioxidant mixed tocopherols are added under low-oxygen, dry nitrogen protection. The amount of mixed tocopherols added is 0.05 wt% of the hemp seed oil mass. After addition, the mixture is stirred for 7 minutes. After sealed filtration and bottling, hemp seed oil that inhibits the formation of trans fatty acids is obtained.

[0073] Comparative Example 1

[0074] This comparative example provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The difference from Example 1 is that after obtaining the primary deoxygenated hemp seed oil in step S2, a secondary spray deoxygenation is performed according to the process parameters of step S4 in Example 1. Then, the hemp seed oil after secondary spray deoxygenation is subjected to pulsed ultrasonic treatment according to the process parameters of step S3 in Example 1. After ultrasonic treatment, a secondary spray polishing deoxygenation is not performed. Instead, the temperature is directly raised and spray deodorization is performed. Other operation steps and process parameters are exactly the same as in Example 1.

[0075] Comparative Example 2

[0076] This comparative example provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The difference from Example 1 is that the low-oxygen dry nitrogen with an oxygen content of 1.0 ppm and an atmospheric dew point of -60°C is replaced with dry nitrogen with an oxygen content of 6 ppm and an atmospheric dew point of -60°C. The amount of nitrogen used in each step is the same as in Example 1. The total cumulative input of residual oxygen in nitrogen per unit mass of hemp seed oil in steps S2-S5 is 0.0720 mg / kg. Other operating steps and process parameters are exactly the same as in Example 1.

[0077] Comparative Example 3

[0078] This comparative example provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The difference from Example 1 is that after obtaining the first-stage deoxygenated hemp seed oil in step S2, a second-stage spray deoxygenation is performed according to the process parameters of step S4 in Example 1, followed by pulsed ultrasonic treatment according to the process parameters of step S3 in Example 1. After ultrasonic treatment, a second-stage spray polishing deoxygenation is not performed. At the same time, the low-oxygen dry nitrogen with an oxygen content of 1.0 ppm and an atmospheric dew point of -60°C is replaced with dry nitrogen with an oxygen content of 6 ppm and an atmospheric dew point of -60°C. The amount of nitrogen used in each process is the same as in Example 1. The total cumulative input of residual oxygen in nitrogen per unit mass of hemp seed oil in steps S2-S5 is 0.0720 mg / kg. Other operating steps and process parameters are exactly the same as in Example 1.

[0079] Comparative Example 4

[0080] This comparative example provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The difference from Example 1 is that the pulsed ultrasonic degassing treatment in step S3 is omitted, and the primary deoxygenated hemp seed oil obtained in step S2 is directly transported to the secondary spray deoxygenation device, and secondary spray polishing deoxygenation is performed according to the process parameters of step S4 in Example 1. Other operating steps and process parameters are exactly the same as in Example 1.

[0081] Comparative Example 5

[0082] This comparative example provides a method for preparing hemp seed oil that inhibits the formation of trans fatty acids. The difference from Example 1 is that the secondary spray polishing and deoxygenation treatment in step S4 is omitted, and the ultrasonically degassing hemp seed oil obtained in step S3 is directly heated and transported to a high-vacuum spray deodorization tower for spray deodorization. Other operating steps and process parameters are exactly the same as in Example 1.

[0083] The performance of the hemp seed oil obtained in Examples 1-4 and Comparative Examples 1-5 was tested, and the specific process is as follows:

[0084] Dissolved oxygen testing: Sealed bypass sampling ports were set up at the inlet of the ultrasonic treatment device after primary spray deoxygenation, before pulsed ultrasonic gas release, after pulsed ultrasonic gas release, after secondary spray polishing deoxygenation, and after spray deodorization. After sampling, the samples were cooled to 25±1℃ without contact with air, and the dissolved oxygen content was measured using a fluorescence dissolved oxygen analyzer calibrated with hemp seed oil matrix. For samples treated with pulsed ultrasonic gas release, the difference between the dissolved oxygen content after pulsed ultrasonic gas release and the dissolved oxygen content immediately before pulsed ultrasonic gas release was taken as the change in dissolved oxygen caused by ultrasonic gas release. The terminal secondary spray polishing deoxygenation refers to the secondary spray polishing deoxygenation set after pulsed ultrasonic gas release to restore the low-oxygen state before entering the spray deodorization stage; for samples without pulsed ultrasonic gas release treatment, the secondary spray deoxygenation set after primary spray deoxygenation was taken as the terminal secondary spray polishing deoxygenation. For Examples 1-4 and Comparative Example 2, the difference between the dissolved oxygen content after pulsed ultrasonic gas release and the dissolved oxygen content after secondary spray polishing deoxygenation was used as the amount of dissolved oxygen reduction after the final secondary spray polishing deoxygenation. For Comparative Example 4, the difference between the dissolved oxygen content after primary spray deoxygenation and the dissolved oxygen content after secondary spray polishing deoxygenation was used as the amount of dissolved oxygen reduction after the final secondary spray polishing deoxygenation. In Comparative Examples 1 and 3, the secondary spray deoxygenation was set before pulsed ultrasonic gas release, and no secondary spray polishing deoxygenation was set after ultrasonic treatment, so the amount of dissolved oxygen reduction after the final secondary spray polishing deoxygenation was not calculated. In Comparative Example 5, no secondary spray polishing deoxygenation was set, so the corresponding amount of dissolved oxygen reduction was not calculated.

[0085] Test for increase in trans fatty acids: The decolorized hemp seed oil from the same batch and the finished hemp seed oil obtained from each example and comparative example were taken respectively. The total trans fatty acid content was determined by gas chromatography according to GB 5009.257-2016 "National Food Safety Standard - Determination of Trans Fatty Acids in Food". The difference between the total trans fatty acid content of the finished hemp seed oil and the total trans fatty acid content of the corresponding decolorized hemp seed oil was taken as the increase in trans fatty acids.

[0086] Peroxide value test: The finished hemp seed oil obtained from each example and comparative example was taken and the peroxide value was determined according to Method I of GB 5009.227-2023. The test results are expressed in g / 100g. The same batch of decolorized hemp seed oil was used in each group, and the test was carried out within the same time period after spray deodorization, cooling and filling.

[0087] Deodorization effect test: The total peak area of ​​volatile aldehydes, ketones and alcohols in decolorized hemp seed oil and finished hemp seed oil was determined by headspace solid phase microextraction-gas chromatography-mass spectrometry. The odor component removal rate was calculated according to the formula: "Odor component removal rate = (total peak area of ​​odor components in decolorized hemp seed oil - total peak area of ​​odor components in finished hemp seed oil) / total peak area of ​​odor components in decolorized hemp seed oil × 100%".

[0088] The test results are shown in Table 1.

[0089] Table 1: Performance test results of Examples 1-4 and Comparative Examples 1-5

[0090]

[0091] As shown in Table 1, the test results of Example 1 and Comparative Example 1 indicate that setting the secondary spray deoxygenation before pulsed ultrasonic release, the change in dissolved oxygen caused by ultrasonic release, calculated based on the dissolved oxygen content immediately before and after ultrasonic treatment, is still close to that of Example 1. This suggests that even after the pre-secondary spray deoxygenation, ultrasonic treatment still promotes the release of residual or embedded gases in the oil phase, causing a change in the measurable dissolved oxygen content. However, since no final secondary spray polishing deoxygenation is performed after ultrasonic treatment, there is no process for reducing dissolved oxygen for the gases released after ultrasonication. The released gases enter the spray deodorization stage with the hemp seed oil. Consequently, the actual oxygen exposure of hemp seed oil increases under high specific surface area spray and heating conditions, and the increase in trans fatty acids and peroxide value are higher than in Example 1. The removal rate of odor components is close to but slightly lower than that of Example 1, indicating that changing the deoxygenation sequence does not completely disable the deodorization function, but it is difficult to simultaneously control the formation of trans fatty acids and primary oxidation.

[0092] As can be seen from the test results of Example 1 and Comparative Example 2 in Table 1, the first-stage spray deoxygenation, pulsed ultrasonic gas release, and the second-stage spray polishing deoxygenation after ultrasonication were retained. Therefore, the amount of dissolved oxygen change caused by ultrasonic gas release and the amount of dissolved oxygen reduction in the terminal second-stage spray polishing deoxygenation were close to those of Example 1, indicating that the endogenous buried gas can still be released and removed again before deodorization. However, Comparative Example 2 used dry nitrogen with a high residual oxygen content, and exogenous oxygen continued to enter the treatment system along with the amount of nitrogen used in the subsequent atomization and stripping processes. Although the dissolved oxygen at the deodorization inlet has been reduced to a low level, the increase in trans fatty acids and the peroxide value of the finished product in Comparative Example 2 are higher than those in Example 1, indicating that under the process conditions described in this application, the higher cumulative input of nitrogen residual oxygen corresponds to the increase in the above indicators. Given that the peroxide value of the finished product is also affected by the initial oxidation state of the raw materials, the generation and decomposition of hydrogen peroxide during heating, and the storage conditions after filling, it is not entirely quantitatively attributed to the input of nitrogen residual oxygen. The removal rate of odor components is slightly lower than that in Example 1, indicating that increasing the nitrogen residual oxygen load cannot further improve the deodorization effect, but instead weakens the stability of the low oxygen state throughout the process.

[0093] As shown in Table 1, the test results of Example 1 and Comparative Example 3 indicate that by setting the secondary spray deoxygenation before pulsed ultrasonic gas release and canceling the total cumulative input control of residual nitrogen oxygen, the change in dissolved oxygen caused by ultrasonic gas release, calculated based on the dissolved oxygen content immediately before and after ultrasonic treatment, is close to that in Example 1. This indicates that even after the pre-treatment secondary spray deoxygenation, ultrasonic treatment still promotes the release of residual or embedded gases in the oil phase, causing a change in the measurable dissolved oxygen content. However, since no end-stage secondary spray polishing deoxygenation was set after ultrasonic treatment, there was no corresponding dissolved oxygen reduction process, and the endogenous released gases were not removed before deodorization. At the same time, the residual oxygen in the nitrogen formed an exogenous cumulative input during the subsequent spray deodorization process. The simultaneous existence of the endogenous gases not being removed by end-stage polishing deoxygenation and the increase in residual nitrogen oxygen input resulted in a higher increase in trans fatty acids and a higher peroxide value in the finished product compared to Example 1. This indicates that the combination of these two unfavorable conditions is not conducive to maintaining the low-oxygen state throughout the process. The removal rate of odor components remained at a relatively high level but was lower than that in Example 1, indicating that simply maintaining the spray stripping intensity cannot compensate for the instability of the low-oxygen state.

[0094] From the test results of Example 1 and Comparative Example 4 in Table 1, it can be seen that without pulsed ultrasonic gas release, there is no change in dissolved oxygen caused by ultrasonic gas release. The gas embedded in the microbubbles, trace amounts of aqueous phase, and the microscopic association structure of the oil phase in hemp seed oil was not actively released. The subsequent two-stage spray polishing deoxygenation constitutes the final two-stage spray polishing deoxygenation before entering the spray deodorization stage, which can still reduce some free dissolved oxygen. Therefore, there is a certain amount of dissolved oxygen reduction, but this reduction is lower than that in Example 1. The embedded gas that was not released in advance may continue to escape during the subsequent heating and spraying process, resulting in an increase in trans fatty acids and peroxide value higher than in Example 1. The removal rate of odor components is slightly lower than that in Example 1, indicating that basic deodorization can still be completed after canceling ultrasonic gas release. However, relying solely on two-stage spray deoxygenation is insufficient to fully treat the hidden oxygen in the oil phase, making it difficult to obtain the same low oxygen control effect as in Example 1.

[0095] From the test results of Example 1 and Comparative Example 5 in Table 1, it can be seen that retaining pulsed ultrasonic gas release results in a similar change in dissolved oxygen as in Example 1, indicating that the embedded gas in the oil phase has been released. However, after removing the ultrasonic secondary spray polishing deoxygenation, there is no process to reduce dissolved oxygen for the released gas; the gas released by ultrasonication directly enters the high-vacuum spray deodorization stage with the hemp seed oil. Under the conditions of increased specific surface area of ​​spray droplets and increased temperature, the unremoved gas increases the opportunity for unsaturated fatty acids to contact oxygen, resulting in a higher increase in trans fatty acids and peroxide value than in Example 1. The removal rate of odor components is similar to but slightly lower than that in Example 1, indicating that removing the secondary spray polishing deoxygenation mainly weakens the recovery and maintenance of the low-oxygen state after ultrasonication, rather than causing the spray stripping itself to completely lose its deodorization ability.

[0096] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing hemp seed oil that inhibits the formation of trans fatty acids, characterized in that, Includes the following steps: S1: Hemp seed oil crude oil is subjected to degumming, deacidification, decolorization and dehydration treatment in sequence to obtain decolorized hemp seed oil; food grade nitrogen is subjected to deoxygenation and drying treatment to obtain low oxygen dry nitrogen; S2: The decolorized hemp seed oil is transported to a primary spray degassing device for spray deoxygenation, while the low-oxygen drying nitrogen gas is introduced to obtain primary deoxygenated hemp seed oil. S3: The first-stage deoxygenated hemp seed oil is transported to a closed-loop ultrasonic treatment device under the protection of low-oxygen drying nitrogen to perform pulsed ultrasonic degassing, thereby obtaining ultrasonically degassed hemp seed oil, and the ultrasonically degassed hemp seed oil is then transported to a second-stage spray deoxygenation device. S4: The ultrasonically degassing hemp seed oil is subjected to two-stage spray polishing and deoxygenation, while the low-oxygen drying nitrogen gas is introduced to obtain polished and deoxygenated hemp seed oil. S5: The polished and deoxidized hemp oil is heated and then transported to a high-vacuum spray deodorization tower through a closed pipeline. The preheated low-oxygen dry nitrogen gas is used as both the atomizing medium and the stripping gas for spray deodorization to obtain deodorized hemp oil. S6: The deodorized hemp seed oil is cooled under vacuum, filtered and bottled in a sealed manner to obtain the hemp seed oil.

2. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 1, characterized in that, In step S1, the moisture content of the decolorized hemp seed oil is not higher than 0.05 wt%; the oxygen content of the low-oxygen drying nitrogen is not higher than 2 ppm, and the dew point at normal pressure is not higher than -50℃.

3. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 1, characterized in that, In step S2, the temperature of the spray deoxygenation is 85-100℃, the absolute pressure is 20-50Pa, and the treatment time is 4-8min; the volume of the low-oxygen drying nitrogen used is (0.5-2.7)L / kg to the mass ratio of the hemp seed oil decolorization oil.

4. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 1, characterized in that, In step S3, the primary deoxygenated hemp seed oil is adjusted to 50-70°C under the protection of low-oxygen dry nitrogen and then transported to the closed-loop ultrasonic treatment device. Before the primary deoxygenated hemp seed oil enters, the closed-loop ultrasonic treatment device uses the low-oxygen dry nitrogen to replace the gas phase space. The ratio of the volume of low-oxygen dry nitrogen used for replacement to the mass of the primary deoxygenated hemp seed oil is (0.3-2.0) L / kg. After the replacement is completed, the device is kept sealed, and the low-oxygen dry nitrogen is not continuously introduced during the pulsed ultrasonic gas release process.

5. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 4, characterized in that, In step S3, the pulsed ultrasonic gas release uses ultrasonic waves with a frequency of 20-35kHz and a power density of 25-60W / L. The ratio of ultrasonic start time to stop time is 1:(1-2), and the processing time is 2-5min. Within 0.5-2min after the pulsed ultrasonic gas release ends, the ultrasonically released hemp seed oil is delivered to the secondary spray deoxygenation device.

6. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 1, characterized in that, In step S4, the temperature of the secondary spray polishing deoxidation is 90-105℃, and the absolute pressure is 8-25Pa; the volume of the low-oxygen drying nitrogen used is (0.8-4.0) L / kg to the mass ratio of the ultrasonically released hemp seed oil.

7. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 6, characterized in that, In step S4, the dissolved oxygen content of the hemp seed oil after the secondary spray polishing and deoxidation treatment is no higher than 0.10 mg / kg.

8. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 1, characterized in that, In step S5, the polishing and deoxidizing hemp seed oil is heated to 135-145℃; the low-oxygen drying nitrogen is preheated to 125-140℃; the absolute pressure of the spray deodorization is 8-25Pa, and the spray deodorization time is 3-7min; the volume ratio of the low-oxygen drying nitrogen used to the mass ratio of the polishing and deoxidizing hemp seed oil is (2.0-8.2)L / kg.

9. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 8, characterized in that, Based on the actual oxygen volume fraction in the low-oxygen drying nitrogen, the nitrogen usage volume converted to standard conditions, and the corresponding hemp seed oil mass, the total cumulative input of residual oxygen in nitrogen per unit mass of hemp seed oil in steps S2-S5 is controlled to be no higher than 0.05 mg / kg.

10. The method for preparing hemp seed oil that inhibits the formation of trans fatty acids according to claim 1, characterized in that, In step S6, the deodorized hemp seed oil is cooled to 45-60°C under vacuum conditions for 5-15 minutes, and then food-grade antioxidants are added under low-oxygen drying nitrogen protection before the sealed filtration and filling are performed.

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