Cyperus esculentus oil-based frying oil as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of edible oil and particularly relates to cyperus esculentus oil-based frying oil as well as a preparation method and application thereof. According to the preparation method of the cyperus esculentus oil-based oil for frying, provided by the invention, the cyperus esculentus oil and the coconut oil are used as raw materials and are subjected to transesterification under the catalysis of the immobilized lipase so as to prepare novel oil suitable for frying. According to the cyperus esculentus oil-based frying oil prepared by the invention, the purity of triglyceride is up to 99% or above, the content of lipid with a medium-long carbon chain structure reaches 60% or above, and the cyperus esculentus oil-based frying oil has relatively high nutritional value and is beneficial to promoting digestion and reducing fat accumulation. After the frying oil is used for frying starch-based food, the frying stability of the frying oil can be effectively improved, meanwhile, the phenomena of acid value increase, color deepening and the like in the frying process are reduced, the viscosity of the oil can be reduced, the increase of total polar compounds can be slowed down, and particularly, the oil absorption rate of the food can be reduced; the method has extremely wide application potential in the field of preparation of high-quality frying oil.

Description

Technical Field

[0001] The invention belongs to the technical field of edible oils and fats, and in particular relates to cyperus oleifera oil-based frying oil and a preparation method and application thereof. Background Art

[0002] Fried foods have long been loved by consumers. As the core of this traditional cooking method, frying oil occupies an important position in the catering industry and home cooking. At present, the market demand for frying oil in my country continues to grow, accounting for more than half of special oils and fats, especially in the fast food industry, where it occupies an important market share. However, the frying oil used in the food industry is generally palm oil with a high content of saturated fatty acids, which has low nutritional value. Excessive consumption increases the risk of cardiovascular disease and easily causes obesity. In addition, some hydrogenated vegetable oils have been restricted as frying oils by many countries because they are prone to produce trans fatty acids. In addition, fried foods generally have problems such as high fat, high calories and nutrient loss. While bringing good flavor, they also bring health risks such as obesity and chronic diseases. Therefore, it is very urgent to reduce the oil absorption rate of fried products and develop frying oils that are both low-fat and nutritious.

[0003] In order to deal with these problems, scientific research institutions and food companies have increased their research efforts on frying oils in recent years. In addition to improving coating technology, using vacuum frying, spray frying, and optimizing frying process conditions, it is also particularly important to develop new functional oils suitable for frying.

[0004] In recent years, domestic and foreign scholars have conducted more and more extensive research on medium- and long-chain carbon structured lipids (MLCT), a new type of structural lipid. MLCT is a mixed triglyceride composed of medium-chain fatty acids (MCFA) and long-chain fatty acids (LCFA). Studies have shown that MLCT helps regulate body fat due to its unique structure and metabolic properties. Compared with bulk edible oils, MLCT improves the bioavailability of LCFA and fat-soluble bioactive substances in in vivo and in vitro experiments, while inhibiting the accumulation of body fat. Compared with a simple physical mixture of medium-chain triglycerides (MCT) and long-chain triglycerides (LCT), MLCT can provide a rapid and stable energy supply and reduce the metabolic burden on the liver. MLCT is now widely used in various food formulas, including infant formula, weight loss health foods, sports foods, and special medical purpose foods.

[0005] In view of the characteristics of MLCT, such as high nutritional value, good digestibility, and low obesity, applying it to traditional high-calorie foods can not only improve the nutritional structure of these foods, but also better meet the growing demand of modern consumers for healthy diets. At the same time, with the improvement of consumers' health awareness and the increase in demand for functional lipids, the low-cost, large-scale, and productized synthesis of MLCT is particularly important.

[0006] Therefore, MLCT has considerable application potential in the frying oil market. How to develop a functional frying oil with high nutritional value, low cost, good frying stability and low obesity can not only effectively respond to the changing market demand for healthy nutrition trends, but also help promote the entire food industry to move towards a more sustainable development direction. Summary of the invention

[0007] In order to overcome the deficiencies in the prior art, the first aspect of the present invention is to provide a method for preparing frying oil based on jatropha oil, the synthesis process of which is pollution-free, high-yield, high-efficiency, and suitable for factory production. The triglyceride content of the prepared frying oil is more than 99%, and the MLCT content is more than 60%. The oil is applied to fried foods, which can exert its high nutritional and frying-resistant properties while effectively reducing the oil absorption rate of the food, thereby having both fat-reducing and nutritional effects.

[0008] The second aspect of the present invention is to provide craper oil-based frying oil prepared by the above preparation method.

[0009] The third aspect of the present invention is to provide the use of the above-mentioned cyperus oleifera oil-based frying oil.

[0010] To achieve the above object, in the first aspect of the present invention, the technical solution adopted is:

[0011] A method for preparing cyperus oleifera oil-based frying oil comprises the following steps:

[0012] Under the catalysis of immobilized lipase, cyperus oleiferus oil and coconut oil are subjected to transesterification reaction, the immobilized lipase is separated after the reaction, and then molecular distillation is used for purification to obtain cyperus oleiferus oil-based frying oil;

[0013] The molar ratio of cyperus oleifera oil to coconut oil is (1-2):(1-2); the fatty acid composition of the cyperus oleifera oil contains oleic acid ≥65%; the fatty acid composition of the coconut oil contains medium-chain fatty acids ≥50%; and the immobilized lipase is one of Lipozyme RM C, Lipozyme TL IM and Novozym 435.

[0014] As a preferred solution, the molar ratio of jatropha oil to coconut oil is 1:1, and the immobilized lipase is Lipozyme RM C. The present invention adopts the above molar ratio and immobilized lipase to obtain the best transesterification effect, and the yield of MLCT in the product is the highest.

[0015] As a preferred solution, in the fatty acid composition of the jatropha oil, the content of oleic acid is 65% to 80%, the content of palmitic acid is 10% to 15%, and the content of linoleic acid is 6% to 14%.

[0016] Medium-chain fatty acids are defined in biochemistry and nutrition as fatty acids with 8 to 12 carbon chains (including caprylic acid, capric acid, and lauric acid). As a preferred embodiment, the fatty acid composition of the coconut oil comprises 5% to 10% caprylic acid, 4% to 8% capric acid, and 45% to 55% lauric acid.

[0017] In the transesterification reaction of the present invention, in order to meet the needs of factory production, cyperus oleifera oil and coconut oil can be magnified by any mass multiple of the total substrate within the above molar ratio range, and the obtained product components have no significant difference.

[0018] As a preferred solution, the addition amount of the immobilized lipase is 6wt% to 10wt% of the sum of the mass of cyperus oleifera oil and coconut oil, and more preferably 8wt%.

[0019] As a preferred solution, in the present invention, the immobilized lipase obtained by separation can be rinsed with n-hexane, dried at low temperature and reused; the number of times of reuse is 10 to 20 times.

[0020] As a preferred solution, the temperature of the transesterification reaction is 55 to 85° C., more preferably 65° C. As a further preferred solution, the time of the transesterification reaction is 4 to 8 hours, more preferably 4 hours.

[0021] In order to promote the transesterification reaction, as a preferred solution, the transesterification reaction is carried out under stirring conditions; the stirring speed is 200 to 400 rpm.

[0022] The product after the transesterification reaction of the present invention can realize the rapid preparation and factory application of structured fats through molecular distillation. After molecular distillation, non-oil components such as fatty acids can be removed, and finally frying oil rich in MLCT is obtained. In the present invention, in order to improve the purification efficiency, molecular distillation can adopt a continuous feeding and discharging device, so as to obtain a frying oil product by large-scale production. As a further preferred scheme, the process of molecular distillation is: the evaporation temperature is 180°C to 220°C, the feed rate is 1 to 5mL / min, the vacuum pressure is 20 to 200Pa, and the film scraping speed is 100 to 300rpm.

[0023] The second aspect of the present invention adopts the following technical solution:

[0024] The cyperus oleifera oil-based frying oil prepared by the preparation method has a triglyceride content of ≥99% and a medium- and long-carbon-chain structural fat content of ≥60%.

[0025] The third aspect of the present invention adopts the following technical solution:

[0026] The application of the above-mentioned cyperus oleifera oil-based frying oil is the application of frying oil in frying starch-based foods. The present invention does not specifically limit the starch-based foods to be fried, and technicians can select common starch-based foods. For example, the starch-based foods can be potato chips, sweet potato chips, banana chips, etc.

[0027] As a preferred solution, the frying temperature is 160-200° C. More preferably, the frying time is 20-40 hours.

[0028] The technical solution of the present invention has the following advantages and beneficial effects:

[0029] (1) The method for preparing frying oil based on cyperus oleifera oil provided by the present invention is to use cyperus oleifera oil and coconut oil as raw materials, and to carry out transesterification reaction under the catalysis of immobilized lipase, so as to prepare a novel oil suitable for frying. The whole process of the present invention does not generate wastewater, is green and efficient, and has a short production time and large production capacity. In addition, the reaction conditions of the present invention are under normal pressure, and the raw material oil does not need to be dehydrated in advance, and a solvent-free system is adopted, so that the subsequent separation is simple, the reaction process complies with the green principle, and can effectively reduce resource waste and reduce environmental pollution. In addition, the present invention adopts the transesterification method to synthesize frying oil, which is simple and easy, has low raw material cost, can quickly synthesize target oil under the catalysis of specific lipase, and is suitable for industrial large-scale production of edible oil products; at the same time, after the catalytic reaction is completed, the immobilized enzyme is easy to recover and can be reused, and the cost required for the whole production process is low.

[0030] (2) In order to prepare frying oil with high nutritional value and reasonable cost, it is necessary to select suitable oil species. The cyperus juncea oil used in the preparation method of the present invention is a special oil crop that has been vigorously developed in my country in recent years, and has high nutritional value and health care functions. However, for the cyperus juncea oil with rich nutritional value, the popularity of related products in the consumer market is still not high, and there are many gaps in the research on the high-value utilization of its back-end industrial chain (such as functional food ingredients, commercial frying oil, nutritional supplements, etc.). Therefore, vigorously developing the downstream functional value research of cyperus juncea oil is conducive to strengthening its market acceptance, expanding the production scale of the entire industrial chain, promoting the cultivation and development of emerging oil crops in the country, and also conducive to solving the problem of insufficient oil crops in my country and high external dependence. In the present invention, cyperus juncea oil is used as the preparation raw material of frying oil for the first time, and the preparation process of new frying oil is explored, which not only provides a new raw material source for synthetic functional frying oil, but also expands the application prospect of cyperus juncea oil, and also helps to enrich the types of edible oils and improve the self-sufficiency rate of edible oils in my country.

[0031] (3) The cyperus oleifera oil-based frying oil prepared by the present invention has a moisture content, an acid value, and a peroxide value that all meet the national food safety standards. In particular, the triglyceride purity is relatively high, reaching more than 99%, and the MLCT content is more than 60%. It has a high nutritional value, is also beneficial for reducing the metabolic burden of the liver, promoting digestion and reducing obesity, and can effectively meet the new era development needs of consumers for healthy and nutritious frying oil.

[0032] (4) The present invention uses jatropha oil and coconut oil to react quickly to synthesize frying oil rich in medium and long carbon chain structural fats. Thanks to the special structural composition of the raw materials and the better adaptability of the lipase catalytic active site, the transesterification reaction can be accelerated, and more transesterification products can be obtained in a short time, and the content of MLCT in the product is high. In particular, after the frying oil of the present invention is used as high-moisture starch-based food frying oil, the frying stability characteristics of the frying oil can be effectively improved, not only to bring more abundant nutrition to fried foods, but also to reduce the foaming, acid value increase, color deepening and other phenomena during the frying process, while having the effect of reducing fat accumulation by medium and long chain fatty acids, and reducing the viscosity of the oil, reducing the generation of polymers, slowing down the increase of total polar compounds, especially effectively reducing the oil absorption rate of food, and being very suitable for use as a high-quality frying oil for healthy fat reduction.

[0033] In summary, the present invention uses cyperus oleifera oil and coconut oil as raw materials and immobilized lipase as a biocatalyst to greenly and efficiently produce a novel frying oil with high nutritional value and fat-reducing effect, which can provide a new idea for the efficient production of fat-reducing frying oil in industry, and can also broaden the application scope of cyperus oleifera oil, and has extremely broad development prospects and huge application potential in the field of high-quality frying oil preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The figure shows the effect of each immobilized lipase (Lipozyme RM C, Lipozyme TLIM, Novozym 435) on the MLCT yield at different time points in the present invention;

[0035] Figure 2 The infrared spectra of the reaction raw materials and target oil involved in the preparation method of Example 1 of the present invention;

[0036] Figure 3 The results of the acid value changes of the oils and fats provided in Example 1 and Comparative Examples 1 to 6 during frying;

[0037] Figure 4 The viscosity change results of the oils provided in Example 1 and Comparative Examples 1 to 6 during frying;

[0038] Figure 5 The results of the change of the total polar component (TPC) content of the oils provided in Example 1 of the present invention and Comparative Examples 1 to 6 during frying;

[0039] Figure 6 The results of the oil absorption rate changes of the food materials provided by the oils in Example 1 and Comparative Examples 1 to 6 at the beginning and end of frying are shown. DETAILED DESCRIPTION

[0040] In order to make the purpose, features and advantages of the above technical solution of the present invention more obvious and easy to understand, the specific implementation of the present invention is described in detail in combination with specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from this description, and those skilled in the art can make equivalent substitutions without violating the connotation of the present invention, so the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0041] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the raw materials used are all commonly used in the art, available to the public or commercially available, unless otherwise specified.

[0042] The present invention provides a method for preparing cyperus oleifera oil-based frying oil, comprising the following steps:

[0043] Under the catalysis of immobilized lipase, cyperus oleiferus oil and coconut oil are subjected to transesterification reaction, the immobilized lipase is separated after the reaction, and then molecular distillation is used for purification to obtain cyperus oleiferus oil-based frying oil;

[0044] The molar ratio of cyperus oleifera oil to coconut oil is (1-2):(1-2); the fatty acid composition of the cyperus oleifera oil contains oleic acid ≥65%; the fatty acid composition of the coconut oil contains medium-chain fatty acids ≥50%; and the immobilized lipase is one of Lipozyme RM C, Lipozyme TL IM and Novozym 435.

[0045] The method for preparing cyperus oleiferus oil-based frying oil of the present invention does not specifically limit the source and fatty acid composition of the raw material cyperus oleiferus oil and coconut oil. The technicians can obtain them from conventional commercial channels or prepare them by themselves according to the oil preparation process. The index of the raw material oil only needs to meet the national standard and the basic requirements of "the fatty acid composition of cyperus oleiferus oil, the content of oleic acid ≥ 65%; the fatty acid composition of coconut oil, the content of medium-chain fatty acid ≥ 50%" specified in the present invention. Since the fatty acid compositions of cyperus oleiferus oil and coconut oil from different sources are generally similar and are within the standard range, they can achieve the preparation effect of frying oil equivalent to that of the present invention.

[0046] More specifically, as a preferred embodiment of the present invention, the raw materials cyperus oleifera oil and coconut oil used in the following examples are all from conventional oil manufacturers (the relative molecular weight of cyperus oleifera oil is 889.12, and the relative molecular weight of coconut oil is 673.98). Further, the present invention uses gas chromatography to test the fatty acid composition and Sn-2 fatty acid composition of the raw material oil, and uses the area normalization method to analyze the relative content of each fatty acid. Wherein, the fatty acid composition of cyperus oleifera oil (TNO) is shown in Table 1. The fatty acid composition of coconut oil (VCO) is shown in Table 2. The Sn-2 fatty acid composition in cyperus oleifera oil, coconut oil and cyperus oleifera oil-based frying oil prepared in Example 1 of the present invention is shown in Table 3.

[0047] Table 1. Fatty acid composition of cyperus oleifera oil (%)

[0048] FA C16:0 C18:0 C18:1 C18:2 C18:3 Cyperus oleifera oil(TNO) 12.64 4.12 69.6 12.36 1.27

[0049] Table 2. Fatty acid composition of coconut oil (%)

[0050] FA C8:0 C10:0 C12:0 C14:0 C16:0 C18:0 C18:1 Coconut Oil (VCO) 6.57 5.87 49.63 19.31 9.28 3.71 5.63

[0051] Table 3. Sn-2 fatty acid composition of cyperus oleifera oil, coconut oil and frying oil of Example 1

[0052]

[0053] As shown in Tables 1 to 3, the content of unsaturated fatty acids in jatropha oil is relatively rich, reaching more than 80%, of which oleic acid (C18:1) has the highest content, reaching more than 65%, followed by palmitic acid (C16:0) and linoleic acid (C18:2), and unsaturated fatty acids are mainly distributed at the sn-2 position, which is easier to digest and absorb. Medium-chain fatty acids (C8 to C12) in coconut oil account for more than 50% of the total fatty acid content, of which lauric acid (C12:0) reaches more than 45%, and saturated fatty acids are mainly located at the sn-1 or sn-3 position, accounting for more than 50%.

[0054] In the following embodiments of the present invention, the immobilized lipase involved is Lipozyme RM C, Lipozyme TL IM, and Novozym 435, which are commercial lipases derived from Thermomyces lanuginosus or from Candida antarctica, and can be obtained by technicians through commercial channels. Specifically, Lipozyme RM C, Lipozyme TL IM, and Novozym 435 used in the present invention are from the Danish Novozymes brand.

[0055] In the preparation method of frying oil provided by the present invention, after the ester exchange reaction is completed, the immobilized lipase can be separated from the reaction system by conventional separation means (such as centrifugal separation, etc.), and the separated immobilized lipase can be simply treated, for example, rinsed three times with n-hexane, and then placed in a constant temperature drying oven at 45°C for drying for 3 hours, and then it can be put into the next ester exchange reaction system for repeated use.

[0056] At present, common purification methods of MLCT include extraction, column chromatography and distillation. Conventional chemical methods such as extraction and column chromatography inevitably use organic solvents, which increase the steps of solvent recovery and product purification, and there is also a potential risk of residual solvent in the obtained product. In addition, the chemical method also has the disadvantages of low separation efficiency, small processing capacity, and inability to be applied on a large scale. Molecular distillation is a kind of distillation method, which has the advantages of low operating temperature, high degree of separation, short material heating time, and suitability for industrial production. It can avoid high temperature treatment for too long, which may have a negative impact on the quality of structural lipids. Therefore, in the present invention, molecular distillation is used to purify the product obtained by ester exchange.

[0057] The product after the transesterification reaction of the present invention can realize the rapid preparation and factory application of structured fat through molecular distillation, and non-oil components such as fatty acids can be removed after molecular distillation, and finally frying oil rich in MLCT is obtained. The present invention does not specifically limit the equipment and distillation parameters of molecular distillation. The technician can conventionally select the molecular distillation equipment that meets the requirements of edible oil separation, and set the suitable molecular distillation process parameters according to the separation requirements. Further, in order to improve the purification efficiency, molecular distillation can adopt continuous feeding and discharging devices, so as to obtain frying oil products in large-scale production. Specifically, the model of the molecular distillation equipment used in the following embodiments of the present invention is KDL5 (German UIC company).

[0058] Example 1

[0059] This embodiment provides a frying oil based on cyperus oleifera oil, the preparation method of which comprises the following steps:

[0060] A 50 mL volumetric flask was used as the reaction system, and a mixed oil of 15 g of cyperus oleifera oil and coconut oil (in the mixed oil, the molar ratio of cyperus oleifera oil and coconut oil was 1:1) was first added, the temperature was preheated to 65°C, and then an immobilized lipase Lipozyme RM C with an addition amount of 8 wt% (the proportion of the total mass of cyperus oleifera oil and coconut oil substrates) was added. After sealing, the mixture was reacted for 4 hours under stirring conditions at 250 r / min, and the sample oil obtained by the reaction was transferred to a centrifuge tube and centrifuged at 3000 r / min for 5 minutes to separate the lipase and the oil to obtain a crude product.

[0061] The crude product was collected after 4 hours of reaction and subjected to molecular distillation purification operation. A molecular distillation device with continuous feeding and continuous discharging was used for purification. The evaporation temperature was set to 200°C, the feeding rate was 3 mL / min, the scraping speed was 220 rpm, the condensed water temperature was 25°C, and the feeding and discharging insulation were both set to 40°C. Distillation was started after the vacuum degree of the entire device dropped to 100 Pa. The purified oil sample was collected, which was the final jatropha oil-based frying oil.

[0062] Example 2

[0063] This embodiment provides a frying oil based on cyperus oleifera oil, the preparation method of which comprises the following steps:

[0064] A 50 mL volumetric flask was used as the reaction system, and a mixed oil of 15 g of cyperus juncea oil and coconut oil (in the mixed oil, the molar ratio of cyperus juncea oil to coconut oil was 1:1) was first added, the temperature was preheated to 65°C, and then an immobilized lipase Lipozyme TL IM was added in an amount of 8 wt% (the proportion of the total mass of cyperus juncea oil and coconut oil substrates), and after sealing, the mixture was stirred at 250 r / min and reacted for 4 h. The sample oil obtained by the reaction was transferred to a centrifuge tube and centrifuged at 3000 r / min for 5 min to separate the lipase and the oil to obtain a crude product.

[0065] The crude product was collected after 4 hours of reaction and purified by molecular distillation. A molecular distillation device with continuous feeding and discharging was used for purification. The evaporation temperature was set to 200°C, the feeding rate was 3 mL / min, the scraping speed was 220 rpm, the condensed water temperature was 25°C, and the feeding and discharging insulation were both set to 40°C. The vacuum degree of the entire device was reduced to 100 Pa before distillation was started. The purified oil sample was collected, which was the final jatropha oil-based frying oil.

[0066] Example 3

[0067] This embodiment provides a frying oil based on cyperus oleifera oil, the preparation method of which comprises the following steps:

[0068] A 50 mL volumetric flask was used as the reaction system, and a mixed oil of 15 g of cyperus juncea oil and coconut oil (in the mixed oil, the molar ratio of cyperus juncea oil and coconut oil was 1:1) was first added, the temperature was preheated to 65°C, and then 8 wt% (the proportion of the total mass of cyperus juncea oil and coconut oil substrates) of immobilized lipase Novozym 435 was added, and after sealing, the mixture was stirred at 250 r / min and reacted for 4 h. The sample oil obtained by the reaction was transferred to a centrifuge tube and centrifuged at 3000 r / min for 5 min to separate the lipase and the oil to obtain a crude product.

[0069] The crude product was collected after 4 hours of reaction and subjected to molecular distillation purification operation. A molecular distillation device with continuous feeding and continuous discharging was used for purification. The evaporation temperature was set to 200°C, the feeding rate was 3 mL / min, the scraping speed was 220 rpm, the condensed water temperature was 25°C, and the feeding and discharging insulation were both set to 40°C. Distillation was started after the vacuum degree of the entire device dropped to 100 Pa. The purified oil sample was collected, which was the final jatropha oil-based frying oil.

[0070] Comparative Example 1

[0071] This comparative example provides a cyperus oleifera oil, which is the cyperus oleifera oil raw material used before the transesterification reaction in Example 1 of the present invention.

[0072] Comparative Example 2

[0073] This comparative example provides a coconut oil, which is the coconut oil raw material used before the transesterification reaction in Example 1 of the present invention.

[0074] Comparative Example 3

[0075] This comparative example provides a physical mixed oil of cyperus oleifera oil and coconut oil, which is prepared by physically mixing the cyperus oleifera oil and coconut oil raw materials used before the transesterification reaction in Example 1 of the present invention at a molar ratio of 1:1.

[0076] Comparative Example 4

[0077] This comparative example provides an olive oil, which is a bulk frying oil obtained from commercial channels.

[0078] Comparative Example 5

[0079] This comparative example provides a palm oil, which is a bulk frying oil obtained from commercial channels.

[0080] Comparative Example 6

[0081] This comparative example provides a soybean oil-based frying oil, the preparation method of which uses commercially available soybean oil as raw material instead of the cyperus oleifera oil in Example 1, and other processes and parameters are the same. The specific preparation process is as follows:

[0082] A 50 mL volumetric flask was used as the reaction system, and a mixed oil of soybean oil and coconut oil with a total weight of 15 g (in the mixed oil, the molar ratio of soybean oil to coconut oil was 1:1) was first added, the temperature was preheated to 65°C, and then 8 wt% (the proportion of the total mass of soybean oil and coconut oil substrates) of immobilized lipase Lipozyme RM C was added. After sealing, the mixture was reacted for 4 hours under stirring conditions at 250 r / min, and the sample oil obtained by the reaction was transferred to a centrifuge tube and centrifuged at 3000 r / min for 5 minutes to separate the lipase and the oil to obtain a crude product.

[0083] The crude product after 4 hours of the above reaction was collected and subjected to molecular distillation purification operation; during purification, a molecular distillation device with continuous feeding and continuous discharging was used, the evaporation temperature was set to 200°C, the feeding rate was 3mL / min, the scraping speed was 220rpm, the condensed water temperature was 25°C, and the feeding and discharging insulation were both set to 40°C. After the vacuum degree of the entire device dropped to 100Pa, distillation began, and the purified oil sample was collected, which was the soybean oil-based frying fat of Comparative Example 6.

[0084] Experimental Example 1: Effect of various process conditions on the yield of MLCT in crude product

[0085] 1.1 Effect of lipase addition on MLCT yield in crude product

[0086] A 50 mL volumetric flask was used as the reaction system, and a mixed oil of 15 g of cyperus oleifera oil and coconut oil (in the mixed oil, the molar ratio of cyperus oleifera oil to coconut oil was 1:1) was first added, the temperature was preheated to 65°C, and then 2 wt% to 12 wt% of immobilized lipase Lipozyme RM C was added in different amounts (accounting for the total mass of cyperus oleifera oil and coconut oil substrates). After sealing, the mixture was reacted for 4 hours under stirring conditions at 250 r / min, and the sample oil obtained by the reaction was transferred to a centrifuge tube and centrifuged at 3000 r / min for 5 minutes to separate the lipase and oil to obtain a crude product, and the yield of MLCT in the crude product was tested. The yield of MLCT was determined by high temperature gas chromatography, and the heating program was as follows: initial temperature 100°C, then increased to 220°C at 50°C / min and retained for 2min, then increased to 290°C at 15°C / min and retained for 2min, then increased to 320°C at 40°C / min for 6min, and finally increased to 360°C at 20°C / min and retained for 16min. The relative content of MLCT was analyzed by area normalization method, the same below. The effect of different lipase addition amounts on the yield of MLCT is shown in Table 4.

[0087] Table 4 Effect of different lipase addition amounts on MLCT yield

[0088] Lipase (wt%) 2 4 6 8 10 12 MLCT yield (%) 35.23 43.65 47.70 48.56 48.09 47.54

[0089] As shown in Table 4, when the addition amount of immobilized lipase is 6wt% to 10wt%, the yield of MLCT in the crude product is high, reaching more than 47%. Among them, when the addition amount of immobilized lipase is 8wt%, the yield of MLCT is the highest, reaching 48.56%. Therefore, the optimal addition amount of immobilized lipase is 8wt%.

[0090] 1.2 Effect of substrate ratio on MLCT yield in crude product

[0091] A 50 mL volumetric flask was used as the reaction system. A total weight of 15 g of mixed oil of cyperus oleifera oil and coconut oil was first added (in the mixed oil, the molar ratios of cyperus oleifera oil TNO and coconut oil VCO were 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, and 1:4, respectively). The temperature was preheated to 65°C, and then 8 wt% (the proportion of the total mass of cyperus oleifera oil and coconut oil substrates) of immobilized lipase Lipozyme RM C was added. After sealing and reacting for 4 hours under stirring conditions at 250 r / min, the sample oil obtained by the reaction was transferred to a centrifuge tube, centrifuged at 3000 r / min for 5 minutes, and the lipase and oil were separated to obtain a crude product, and the yield of MLCT in the crude product was tested. The results of the effects of different substrate ratios on the yield of MLCT are shown in Table 5.

[0092] Table 5. Effect of different substrate ratios on MLCT yield

[0093]

[0094] As shown in Table 5, when the molar ratio of cyperus juncea oil to coconut oil is (1-2): (1-2), the yield of MLCT in the crude product is relatively high, reaching more than 42%. Among them, when the molar ratio of cyperus juncea oil to coconut oil is 1:1, the yield of MLCT is the highest, reaching more than 50%. Therefore, the optimal substrate molar ratio of cyperus juncea oil to coconut oil is 1:1.

[0095] 1.3 Effect of reaction temperature on MLCT yield in crude product

[0096] A 50 mL volumetric flask was used as the reaction system. A total weight of 15 g of mixed oil of cyperus oleifera oil and coconut oil was first added (in the mixed oil, the molar ratio of cyperus oleifera oil TNO and coconut oil VCO was 1:1), the temperature was preheated to different temperatures (45°C, 55°C, 65°C, 75°C, 85°C), and then 8 wt% (the proportion of the total mass of cyperus oleifera oil and coconut oil substrates) of immobilized lipase Lipozyme RM C was added. After sealing and reacting for 4 hours under stirring conditions at 250 r / min, the sample oil obtained by the reaction was transferred to a centrifuge tube, centrifuged at 3000 r / min for 5 minutes, the lipase and the oil were separated, and the crude product was obtained. The yield of MLCT in the crude product was tested. The results of the effect of different reaction temperatures on the yield of MLCT are shown in Table 6.

[0097] Table 6. Effect of different reaction temperatures on MLCT yield

[0098]

[0099] As shown in Table 6, when the reaction temperature is 55-85°C, the yield of MLCT in the crude product is relatively high, reaching more than 46%. Among them, when the reaction temperature is 65-85°C, the yield of MLCT reaches more than 48%, and the difference in the yield of MLCT is not large. Based on the consideration of reducing energy consumption, the reaction temperature is selected to be 65°C.

[0100] 1.4 Effect of immobilized lipase type on MLCT yield in crude product

[0101] A 50 mL volumetric flask was used as the reaction system. A total weight of 15 g of mixed oil of cyperus oleifera oil and coconut oil (in the mixed oil, the molar ratio of cyperus oleifera oil TNO and coconut oil VCO was 1:1) was first added, the temperature was preheated to 65°C, and then 8 wt% (accounting for the total mass of cyperus oleifera oil and coconut oil substrates) of different types of immobilized lipase (Lipozyme RM C, Lipozyme TL IM, Novozym 435) were added respectively. After sealing, the mixture was stirred at 250 r / min and samples were taken at different times during the reaction. The sample oil obtained by sampling was transferred to a centrifuge tube and centrifuged at 3000 r / min for 5 minutes to separate the lipase and oil to obtain a crude product, and the yield of MLCT in the crude product was tested. Figure 1 The results show the effect of various immobilized lipases on MLCT yield at different time points.

[0102] Depend on Figure 1 It can be seen that different types of lipases have different substrate specificities. The immobilized lipase Lipozyme RM C was used to catalyze the transesterification reaction of jatropha oil and coconut oil. After 4 hours of reaction, the MLCT yield in the crude product had basically reached equilibrium. At this time, the MLCT yield was 48.56%, which was significantly higher than the immobilized lipase Lipozyme TL IM (yield 46.53%) and Novozym 435 (yield 37.46%). It can be seen that compared with Lipozyme TL IM and Novozym 435, the immobilized lipase Lipozyme RM C has the best substrate catalytic effect. It can specifically catalyze the transesterification reaction of fatty acids and promote the reaction in the positive direction, so that the acid value of the product is not too high, reduce the inhibitory effect of free fatty acids on the enzyme, and increase the yield of MLCT obtained by catalysis.

[0103] Test Example 2: Basic physical and chemical indicators and structural characterization of the product

[0104] The raw materials (crapeseed oil TNO, coconut oil VCO) and the structure of the products (crude MLCT is the product before purification in Example 1, and pure MLCT is the product after purification in Example 1) involved in the preparation method of Example 1 of the present invention were characterized by infrared spectroscopy. The results are as follows Figure 2 shown.

[0105] Depend on Figure 2 It can be seen that the jatropha oil-based frying oil prepared after ester exchange still maintains the triglyceride structure of edible oil and has the characteristic peaks of two raw oils at the same time, indicating that the frying oil rich in medium and long carbon chain triglycerides of the present invention is successfully prepared.

[0106] Further, the basic physical and chemical indicators of the nut oil-based frying oil prepared after purification in Example 1 of the present invention were tested and compared with the raw nut oil (TNO) and coconut oil (VCO). Among them, the moisture determination was carried out with reference to GB5009.236-2016 "Determination of moisture and volatiles in animal and plant oils and fats of national food safety standard"; the acid value (AV) determination was carried out with reference to GB 5009.229-2016 "Determination of acid value in food of national food safety standard"; the peroxide value (POV) determination was carried out with reference to GB 5009.227-2016 "Determination of peroxide value in food of national food safety standard"; the viscosity test was measured using a digital viscometer of model NDJ-5S; 3-chloropropanol ester (3-MCPDE) and glycidyl ester (GE) were determined by gas phase-mass spectrometry. The triglyceride content and MLCT content tests were all determined by high temperature gas chromatography in Section 1.1 of Test Example 1. The results are shown in Table 7.

[0107] Table 7. Basic physical and chemical indicators of cyperus oleifera oil-based frying oil and raw material oil prepared in Example 1

[0108]

[0109] As shown in Table 7, the acid value, peroxide value and moisture content of the frying oil based on cyperus oleiferus oil prepared by the present invention all meet the requirements of the "National Food Safety Standard for Vegetable Oils", and the contents of 3-chloropropanol ester and glycidyl ester are not detected, and the oil safety is high. In particular, in the frying oil obtained by the present invention, the purity of triglycerides reaches more than 99%, the content of MLCT reaches more than 60% (specifically 68.89%), and the total content of cyperus oleiferus oil and coconut oil is less than 35%. This shows that the frying oil prepared by the present invention is rich in MLCT, which is more conducive to improving the nutrition of oil and reducing obesity.

[0110] Test Example 3: Frying Performance Test

[0111] Take 500 mL of the nut oil-based frying oil prepared in Example 1 or the oil samples provided in Comparative Examples 1 to 6 in a beaker, and conduct intermittent frying experiments to evaluate the frying performance of each oil. During the frying test, prepare 600 g of evenly cut potato slices (thickness 1 mm) in advance, preheat the oil temperature to 180°C, feed at a uniform speed when frying begins, fry until no bubbles appear, remove, stop feeding after frying for 15 minutes, and wait for the oil temperature to rise after 15 minutes. Fry intermittently for a total of 5 hours per day, and fry continuously for 6 days.

[0112] During the frying process, oil samples were taken at different time points (1 day, 2 days, 3 days, 4 days, 5 days, and 6 days) for acid value, viscosity, total polar component (TPC), and oil absorption rate tests. Among them, the acid value (AV) determination was carried out in accordance with GB 5009.229-2016 "National Food Safety Standard for the Determination of Acid Value in Foods"; the viscosity test was determined using a digital viscometer model NDJ-5S; the total polar component content was determined using a German Testo 270 polar component detector; the oil absorption rate was determined using the Soxhlet extraction method, referring to GB 5009.6-2016 "National Food Safety Standard for the Determination of Fat in Foods".

[0113] Test results such as Figure 3 to Figure 6 As shown. Figure 3 The results of the acid value changes of the oils in Example 1 and Comparative Examples 1 to 6 during frying are shown; Figure 4 The viscosity change results of the oils in Example 1 and Comparative Examples 1 to 6 during frying; Figure 5 The results of the change of the total polar component (TPC) content of the oil in Example 1 and Comparative Examples 1 to 6 during frying; Figure 6 The results are as follows: the changes in oil absorption rate of the materials in Example 1 and Comparative Examples 1 to 6 at the beginning and end of frying.

[0114] Depend on Figure 3 It can be known that using single cyperus oleiferus oil (Comparative Example 1) and cyperus oleiferus oil and coconut oil physical mixed oil (Comparative Example 3) as frying oil, in the frying process, the free fatty acid content rises, and the acid value rises rapidly. The frying oil prepared by the present invention has a slow rise in acid value in the frying process, and after frying for 6 days, the acid value is still lower than the national standard (2mg KOH / g), which is comparable to the effect of reducing acid value of bulk commonly used frying oils (palm oil, olive oil). It can be seen that the frying oil of the present invention is conducive to delaying the phenomenon of acid value increase, and is suitable for use as frying oil. In addition, the frying oil of the present invention does not have obvious bubbling and color deepening phenomenon in the whole frying process.

[0115] Depend on Figure 4 It can be seen that the frying oil provided by the present invention can significantly reduce the production of polymers, thereby reducing the viscosity of the oil, compared with single cyperus juncea oil (Comparative Example 1), cyperus juncea oil and coconut oil physical mixture (Comparative Example 3), olive oil (Comparative Example 4), and soybean oil-based oil (Comparative Example 6).

[0116] In the process of frying food materials, polar groups will polymerize through hydrogen bonds or other types of chemical bonds to form large molecular weight complexes, and a series of oil oxidation reactions will occur, thereby producing polar components and reducing the quality of frying oil. Figure 5It can be seen that the frying oil provided by the present invention has a relatively gentle change in the content of total polar components during frying, indicating that the frying oil has excellent frying stability. Compared with coconut oil (Comparative Example 2), cyperus oleifera oil and coconut oil physical mixed oil (Comparative Example 3), olive oil (Comparative Example 4), and soybean oil-based oil (Comparative Example 6), the frying oil of the present invention, single cyperus oleifera oil and palm oil all have excellent effects of slowing down the increase of total polar compounds.

[0117] Depend on Figure 6 It can be seen that the cyperus oleifera oil-based frying oil provided by the present invention has a significantly lower oil absorption rate in fried starch-based materials than the oils of Comparative Examples 1 to 6 during the entire process of frying the food materials. This indicates that the frying oil of the present invention can effectively reduce the oil absorption rate of fried food and is very suitable for use as a high-quality frying oil for healthy fat reduction.

[0118] Based on the above results, the present invention conducts a high-temperature frying experiment on the prepared frying oil, monitors the acid value, viscosity, and total polar compound content during the frying process, and measures the fat content of the fried starch-based raw materials to obtain the food oil absorption rate, and compares with a single cyperus juncea oil, coconut oil, a physical mixture of the two, a large class of frying oils (olive oil, palm oil) and soybean oil-based oils. It is thus confirmed that compared with a single cyperus juncea oil and coconut oil and a physical mixture of the two, the grease obtained by the present invention after the two are transesterified has better frying characteristics. The cyperus juncea oil-based frying oil prepared by the present invention is conducive to reducing the viscosity of the frying oil, enhancing thermal stability, and reducing the phenomenon of foaming and color deepening during frying. On the other hand, the frying stability of the frying oil is good, and the occurrence of oxidation reaction and polymerization reaction can be slowed down. The polar component content accumulates slowly during repeated frying, reducing the quality degradation rate of the frying oil, and the harmful substances produced are also less. Furthermore, compared with soybean oil-based oils obtained by ester exchange between soybean oil and coconut oil, and bulk frying oils such as palm oil and olive oil, the frying oil of the present invention has the same great advantage in frying resistance. It can effectively improve the stability of frying oil and significantly reduce the oil absorption rate of food on the basis of effectively improving the nutritional value of oil and giving it a fat-reducing function.

[0119] Therefore, the cyperus juncea oil-based frying oil provided by the present invention is a new type of frying oil with high nutritional value and fat-reducing effect, which can provide a new idea for the efficient industrial production of fat-reduced frying oil, and can also broaden the application scope of cyperus juncea oil, and has extremely broad development prospects and huge application potential in the field of high-quality frying oil preparation.

[0120] It should be noted that although the above embodiments describe the technical solutions of the present invention in detail, these embodiments are only illustrative examples rather than restrictive definitions. Those skilled in the art should understand that any modification or equivalent substitution made without departing from the spirit and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention. Therefore, the protection scope of the present invention shall be based on the content defined in the claims.

Claims

1. A method for preparing frying oil based on cyperus oleifera oil, characterized in that: The following steps are involved: Under the catalysis of immobilized lipase, cyperus oleiferus oil and coconut oil are subjected to transesterification reaction, the immobilized lipase is separated after the reaction, and then molecular distillation is used for purification to obtain cyperus oleiferus oil-based frying oil; The molar ratio of cyperus oleifera oil to coconut oil is (1-2):(1-2); the fatty acid composition of the cyperus oleifera oil contains oleic acid ≥65%; the fatty acid composition of the coconut oil contains medium-chain fatty acids ≥50%; and the immobilized lipase is one of Lipozyme RM C, Lipozyme TL IM and Novozym 435.

2. The method for preparing cyperus oleifera oil-based frying oil according to claim 1, characterized in that: The molar ratio of jatropha oil to coconut oil is 1:1; and the immobilized lipase is Lipozyme RM C.

3. The method for preparing cyperus oleifera oil-based frying oil according to claim 1, characterized in that: The fatty acid composition of the jatropha oil comprises 65% to 80% oleic acid, 10% to 15% palmitic acid and 6% to 14% linoleic acid; the fatty acid composition of the coconut oil comprises 5% to 10% caprylic acid, 4% to 8% capric acid and 45% to 55% lauric acid.

4. The method for preparing cyperus oleifera oil-based frying oil according to claim 1, characterized in that: The addition amount of the immobilized lipase is 6wt% to 10wt% of the sum of the mass of jatropha oil and coconut oil.

5. The method for preparing cyperus oleifera oil-based frying oil according to any one of claims 1 to 4, characterized in that: The temperature of the transesterification reaction is 55 to 85° C.; the time of the transesterification reaction is 4 to 8 hours.

6. The method for preparing cyperus oleifera oil-based frying oil according to any one of claims 1 to 4, characterized in that: The transesterification reaction is carried out under stirring conditions; the stirring speed is 200-400 rpm.

7. The method for preparing cyperus oleifera oil-based frying oil according to any one of claims 1 to 4, characterized in that: The molecular distillation process is as follows: the evaporation temperature is 180° C. to 220° C., the feed rate is 1 to 5 mL / min, the vacuum pressure is 20 to 200 Pa, and the film scraping speed is 100 to 300 rpm.

8. A frying oil based on cyperus oleifera oil prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The nut oil-based frying oil has a triglyceride content of ≥99% and a medium- and long-carbon chain structural fat content of ≥60%.

9. A use of the cyperus oleifera oil-based frying oil as claimed in claim 8, characterized in that: Use as frying oil in frying starch-based foods.

10. The use of cyperus oleifera oil-based frying oil according to claim 9, characterized in that: The frying temperature is 160-200°C.

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