Process for producing liquid egg having reduced cholesterol content and food containing liquid egg thus produced

Abstract: A process for producing liquid egg having a reduced cholesterol content having flavor and taste comparable to conventional liquid egg having a normal cholesterol content comprises contacting liquid egg with a supercritical fluid to extract cholesterol from the liquid egg. The liquid egg having a reduced cholesterol content produced by the above process can be the raw material of a foodstuff.

Description: FIELD OF THE INVENTION The present invention relates to a process for producing liquid egg having a reduced cholesterol content and food containing the liquid egg thus produced. BACKGROUND OF THE INVENTION Demand for food having a low cholesterol content has increased not only as a diet for treating patients with arteriosclerosis, but also as a health food for normal healthy people. In this respect, although eggs are excellent food, they contain a large amount of cholesterol. Therefore, it is desirable to reduce the cholesterol content of eggs. As a means for reducing the cholesterol content of food, direct extraction of cholesterol with various solvents has been proposed. For example, solid-liquid extraction of cholesterol contained in liquid or powdered egg with an organic solvent has been known. Examples of this extraction are disclosed in Japanese Patent Kokoku No. 46-42944 and Japanese Patent Kokai No. 47-19062. However, there are various disadvantages in the above extraction with an organic solvent. For example, since cholesterol is normally extracted together with other fats and oils, the resulting food product has a very low fat and oil content. Particularly, in liquid or powdered egg, triglycerides, pigments and the like are extracted together with cholesterol and, therefore, its characteristic flavour is lost, which results in deterioration of its commercial value. Further, there is the possibility that remaining solvent influences the human body. Therefore, the above extraction is not particularly suitable for practical use. Krukonis et al, International Symposium on Supercritical Fluids, Nice, 1988, pages 541-56 mentions extraction, from egg lipids, of cholesterol using supercritical CO₂, but the method by which the lipids are first extracted from the liquid egg yolk is not disclosed. JP-A-61-74548 discloses the preparation of high purity egg yolk, including firstly extraction with an organic solvent, then with supercritical CO₂, while JP-B-62-51092 (JP-A-59-135847) proposes a process for removing cholesterol from powdered egg by contacting the powdered egg with supercritical CO₂. However, since powdered egg itself has an extremely inferior flavour in comparison with that of liquid egg, there is a disadvantage that the use of the resulting egg product is limited. EP-A-0416561, acknowledged under Art. 54(3) EPC, discloses a process for the removal of cholesterol from, for example, liquid egg yolk by firstly treating it with supercritical CO₂ to provide an extract containing cholesterol and other ingredients and then removing the cholesterol from the extract with aluminium oxide. Extraction of various organic materials with a supercritical fluid has been known and practical examples thereof include decaffeination of coffee and extraction of hop extract. However, it has been considered that extraction with a supercritical fluid would be ineffective for extraction of a substance from a material containing a large amount of water such as liquid egg. Under these circumstances, we have conducted intensive investigations in an attempt to find a process for reducing the cholesterol content of liquid egg without deterioration of its flavour. As a result, we found unexpectedly that extraction with a supercritical fluid is applicable to reduction of the cholesterol content of liquid egg, and in accordance with the present invention provide a process by which the cholesterol content of liquid egg can be reduced. According to the present invention, there is provided a process for producing liquid egg having a reduced cholesterol content which comprises contacting liquid egg with a supercritical fluid to extract cholesterol from the liquid egg. The present invention also provides food whose raw material is liquid egg having a reduced cholesterol content produced by the above process. The process comprises the steps of contacting liquid egg with a supercritical fluid to extract from it cholesterol and other fat ingredients, while leaving the remaining liquid egg components and then subjecting the extract to a two-stage separation in which temperature and pressure conditions of supercritical fluid in contact with the extract are, at each stage, adjusted so as to provide a first fraction containing 5 to 75% by weight of the fraction of cholesterol and a second fraction containing other fat ingredients. In particular, the process may comprise the steps of: (a) contacting liquid egg with a supercritical fluid to extract from the liquid egg cholesterol and other fat ingredients, leaving remaining liquid egg components, (b) in a first stage of separating the extract from the supercritical fluid, adjusting temperature and pressure conditions of the supercritical fluid to allow recovery therefrom of a fraction containing 5 to 75%, by weight of the fraction, of cholesterol and retention in the supercritical fluid of a fraction containing other fat ingredients, (c) in a second stage of separating the extract from the supercritical fluid, further adjusting temperature and pressure conditions of the supercritical fluid to allow recovery therefrom of the fraction containing other fat ingredients, and (d) optionally returning the fraction containing other fat ingredients from step (c) to the liquid egg components remaining from step (a). Embodiments of the invention will now be described in more detail. Liquid egg to be used as a raw material in the process of the present invention may be either liquid whole egg or liquid egg yolk, or a mixture thereof. The liquid egg may be in any commercially available form and frozen liquid egg can also be used by thawing it. As the supercritical fluid, CO₂, N₂O, ethane and propane can be used, but CO₂ is preferred in view of food safety considerations. Hereinafter, "supercritical CO₂" preferably used as the extraction solvent for cholesterol means CO₂ in a state, when conducting extraction, above its critical point, i.e., at about 31°C under a pressure of 72 kg/cm². In particular, CO₂ at a temperature of 32 to 47°C and at a pressure of 120 to 270 kg/cm² is preferred in a process embodying the present invention. For conducting the process, liquid egg is brought into contact with the supercritical fluid in a wetted wall column system rather than a normal packed column system because, when the latter system is employed, liquid egg is bubbled, which makes the operation difficult. By selecting the above conditions, it becomes possible to extract cholesterol from liquid egg which contains a large amount of water. On the other hand, other fatty ingredients are also contained in the extract in addition to cholesterol, and main components of the other fatty ingredients are, for example, neutral fats which have a large influence on flavour and taste. Accordingly, in the separation of the extract, it is preferred to separate selectively in a first stage, a fraction containing a large amount of cholesterol at a first stage under the conditions of a pressure of 50 to 200 kg/cm² and a temperature of not more than 40°C, followed by recovering a fraction which contains the other fatty ingredients as the main components at a second stage under conditions different from those in the first stage separation, i.e., normally, at a pressure lower than that of the first stage separation, preferably not more than 70 kg/cm², and at a temperature of 30 to 60°C. Preferably, the amount of cholesterol in the first stage fraction is 5 to 75% by weight of the fraction, and the amount of cholesterol in the second stage fraction is up to only a few %. The main components of the second stage fraction are other fatty ingredients. Then, if the second stage fraction is returned to liquid egg to be used as a raw material of the extraction, flow of liquid egg along the wetted wall column is improved. Further, if it is added to the resulting liquid egg having a reduced cholesterol content, flavour and taste can be further improved. Accordingly, in the present invention, a part or all of the second stage fraction can be re-used for either or both of the above purposes. According to the process of the present invention, it is possible to remove 50% or more of cholesterol contained in liquid egg used as a raw material. Nevertheless, the resulting liquid egg having a reduced cholesterol content of the present invention has good taste and flavour comparable to fresh eggs and can be used as it is, or it can be frozen for storage. Further, it can be dried by a conventional drying method such as freeze drying, vacuum drying, spray drying or drum drying for use as a raw material for other food products. The liquid egg of the present invention can be used in the same manner as that for fresh eggs and conventional egg products. Further, the liquid egg of the present invention can be used together with fresh eggs and/or conventional egg products. For example, the liquid egg of the present invention can be used for preparing various dishes such as scrambled egg, egg soup, egg with bacon, omelet, thick custard soup and coating for fried food. Further, the liquid egg of the present invention can be used as a raw material for various food products such as mayonnaise, egg custard, bread, biscuits, crackers, cakes, cookies, pies, ice cream, noodle, pasta, confectionary and drinks. As described above, according to the present invention, the liquid egg having a reduced choresterol content can be obtained without deterioration of flavour and taste and can therefore be used in a diet for treating patients with hypercholesterolemia as well as in health foods for normal healthy people. The following Examples illustrate embodiments of the present invention in still further detail. Example 1 Liquid egg yolk (1 kg)which had a cholesterol content of 1.2% and was obtained by thawing commercially available frozen liquid egg was fed into a wetted wall column 30 mm in inner diameter and 1500 mm in length from its top, and CO₂ at a temperature of 35°C and pressure of 200 kg/cm² was introduced into a wetted wall column from its bottom to bring CO₂ into contact with the liquid egg to conduct extraction. The CO₂ containing the extract effused from the top was firstly subjected to a first stage separation in a separator maintained at a temperature of 35°C and a pressure of 150 kg/cm² and, then, it was further subjected to a second stage separation in a separator maintained at a temperature of 45°C and a pressure of 50 kg/cm². In the first stage separation, a fraction of 13 g was recovered and, in the second stage separation, a fraction of 126 g was recovered. On the other hand, liquid egg yolk residue of 826 g was recovered from the bottom of the wetted wall column. As a result of analysis, it was found that the fraction recovered in the first stage separation contained 45% by weight thereof of cholesterol and the amount of cholesterol in the liquid egg yolk recovered from the bottom was 0.36%. The removal ratio of cholesterol was 75.0%. The fraction recovered at the second stage separation was admixed with the liquid egg yolk recovered from the bottom to obtain the desired liquid egg yolk having a cholesterol content of 0.64%. The liquid egg yolk thus obtained was admixed with commercially available liquid egg white so that the composition of the resulting mixture was the same as that of fresh egg and scrambled egg was prepared using the mixture. As a result, no difference in flavour and taste was found between the scrambled egg thus prepared and that prepared by using fresh egg. Example 2 According to the same manner as that described in Example 1, a fraction of 9 g was recovered from a first stage separation and a fraction of 86 g was recovered from a second stage separation except that liquid whole egg (1.5 kg) which had a cholesterol content of 0.4% was used instead of liquid egg yolk. As a result of analysis, it was found that the fraction recovered from the first stage separation contained 32.0% by weight thereof of cholesterol and the amount of cholesterol in liquid whole egg recovered from the bottom was 0.13%. The removal ratio of cholesterol was 70%. No bubbling liquid whole egg was observed during the operation. When scrambled egg was prepared using the resulting liquid whole egg recovered from the bottom, no difference in flavour and taste was found between the scrambled egg and that prepared made from normal liquid whole egg. Example 3 According to the same manner as that described in Example 1, the desired liquid egg yolk (8 kg) having a reduced cholesterol content was obtained using 10 kg of liquid egg yolk. The removal ratio of cholesterol was about 70%. Analytical data of the liquid egg yolk used as the raw material and the resulting liquid egg having a reduced cholesterol content are shown in Table 1. Items Liquid egg yolk used as raw material Liquid egg yolk having reduced cholesterol content Water (%) 50.0 58.9 Protein (%) 14.9 17.3 Lipid (%) 32.0 21.1 Carbohydrate (%) 0.7 0.8 Ash (%) 1.6 1.9 Cholesterol (%) 1.2 0.36 The following food was prepared using the liquid egg yolk having a reduced cholesterol content (hereinafter referred to as low cholesterol liquid egg yolk) thus obtained. Omelet Liquid egg white (270 g) and small amounts of sugar and salt were added to the low cholesterol liquid egg yolk (100 g) and the mixture was mixed with a beater. The mixture was baked on a frying pan with a small amount of salad oil to prepare an omelet (omelet A). Likewise, according to the same manner, an omelet (omelet B) was prepared except that fresh eggs were used instead of the low cholesterol liquid egg yolk and liquid egg white. The cholesterol content of omelet A was about 30% of that of omelet B. Flavour and taste of these omelets were organoleptically evaluated by 10 panelists. The results are shown in Table 2. The figures in Table 2 are the numbers of the panelists who agreed with the indicated evaluation. Evaluation Omelet A Omelet B Better flavor 6 4 Better taste 5 5 Better body 2 8 Better chewing 4 6 Better overall evaluation 5 5 As seen from Table 2, although omelet A had a somewhat plain flavour and taste in comparison with omelet B, no inferior flavour and taste was found. Sponge cake A mixture of egg white (300 g) and sugar (250 g) was frothed by agitating with a beater. Separately, a mixture of the low cholesterol liquid egg yolk (400 g), sugar (250 g) and water (100 g) was frothed by agitating with a beater. The frothed latter mixture was added to the former and they were mixed. Then, low gluten wheat flour (500 g) was admixed with the resulting mixture. A small amount of vanilla essence was added and the mixture was baked in an oven to prepare a sponge cake (sponge cake A). Likewise, according the the same manner, a sponge cake (sponge cake B) was prepared except that conventional liquid egg yolk was used instead of the low cholesterol liquid egg yolk. The cholesterol content of sponge cake A was about 30% of that of sponge cake B. Flavour and taste of these sponge cakes were evaluated according to the same manner as that described with respect to the omelet. The results are shown in Table 3. Evaluation Sponge cake A Sponge cake B Better flavor 7 3 Better taste 6 4 Better body 4 6 Better chewing 4 6 Better overall evaluation 6 4 As seen from Table 3, no substantial difference in flavour and taste was found between sponge cakes A and B. Custard pudding Whole egg (100 g), the low cholesterol liquid egg yolk (120 g) and sugar (180 g) were mixed and milk (600 g) was added thereto while preventing bubbling. The mixture was stirred. Vanilla essence (0.5 g) and a small amount of rum were added thereto and 150 ml portions of the mixture were distributed into cups. The cups were in an oven and the mixture portions cooked at 150 to 160°C for 40 minutes to prepare a custard pudding (pudding A). Likewise, according to the same manner, a custard pudding (pudding B) was prepared except that conventional liquid egg yolk was used instead of the low cholesterol liquid egg yolk. The cholesterol content of pudding A was about 48% of that of pudding B. Flavour and taste of these puddings were evaluated according to the same manner as that described with respect to the omelet. The results are shown in Table 4. Evaluation Pudding A Pudding B Better flavor 6 4 Better taste 6 4 Better body 4 6 Better chewing 5 5 Better overall evaluation 6 4 As seen from Table 4, no substantial difference in flavour and taste was found between puddings A and B. Mayonnaise According to the formulation as shown in Table 5, a mayonnaise was prepared by uniformly mixing the low cholesterol liquid egg yolk, sugar, salt, powdered mustard, pepper, paprika and one half of vinegar, adding dropwise the remaining vinegar and salad oil to the mixture with agitating to obtain an emulsified mixture and then grinding the mixture with a colloid mill for several seconds to prepare a mayonnaise (mayonnaise A). Likewise, according to the same manner, a mayonnaise (mayonnaise B) was prepared except that conventional liquid egg yolk was used instead of the low cholesterol liquid egg yolk. The cholesterol content of mayonnaise A was about 30% of that of mayonnaise B. Ingredients Mayonnaise A (%) B (%) Conventional liquid egg yolk - 18.0 Low cholesterol liquid egg yolk 18.0 - Vinegar 9.4 9.4 Sugar 2.2 2.2 Salt 1.3 1.3 Powdered mustard 0.9 0.9 Pepper 0.1 0.1 Paprika 0.1 0.1 Salad oil up to 100 up to 100 Flavour and taste of these mayonnaises were evaluated according to the same manner as that with respect to the omelet. The results are shown in Table 6. Evaluation Mayonnaise A Mayonnaise B Better flavor 6 4 Better taste 6 4 Better body 4 6 Better smoothness 5 5 Better overall evaluation 6 4 As seen from Table, no substantial difference in flavour and taste was found between mayonnaises A and B. When both mayonnaises were allowed to stand at 50°C for 10 and 20 days, no substantial difference in appearance was found between mayonnaises A and B.

Claims: A process for producing liquid egg having a reduced cholesterol content, which process comprises the steps of: (a) contacting liquid egg with a supercritical fluid to extract from the liquid egg cholesterol and other fat ingredients, leaving remaining liquid egg components, and (b) subjecting the extract to a two-stage separation process in which temperature and pressure conditions of supercritical fluid in contact with the extract are, at each stage, adjusted so as to provide a first fraction containing 5 to 75%, by weight of the fraction, of cholesterol and a second fraction containing other fat ingredients, and (c) optionally returning the fraction containing other fat ingredients from step (b) to the liquid egg components remaining from step (a). A process according to claim 1, wherein the two-stage separation process of step (b) is carried out by (i) in a first stage of separating the extract from the supercritical fluid, adjusting temperature and pressure conditions of the supercritical fluid to allow recovery therefrom of the first fraction containing 5 to 75%, by weight of the fraction, of cholesterol and retention in the supercritical fluid of the second fraction containing other fat ingredients, and (ii) in a second stage of separating the extract from the supercritical fluid, further adjusting temperature and pressure conditions of the supercritical fluid to allow recovery therefrom of the fraction containing other fat ingredients. A process according to claim 1 or claim 2, wherein the liquid egg is liquid yolk or liquid whole egg. A process according to any preceding claim, wherein the supercritical fluid is CO₂. A process according to any preceding claim, wherein liquid egg is contacted with the supercritical fluid by means of a wetted wall column system. A process according to any preceding claim, wherein the first stage separation in step (b) is conducted under a pressure of 50 to 200 kg/cm² and at a temperature not higher than 40°C. A process according to any preceding claim, wherein the second stage separation in step (b) is conducted at a pressure lower than that of the first stage separation and at a temperature of from 30 to 60°C.

Inventors: HARIU HITOSHI, OGASAHARA JOHJI C O SUMITOMO S, TAKAHASHI MASAKAZU C O SUMITOM, HARIU, HITOSHI, OGASAHARA, JOHJI, C/O SUMITOMO SEIKA, TAKAHASHI, MASAKAZU, C/O SUMITOMO SEIKA CHEMICAL
Applicants: MITSUBISHI CORP, OTSUKA FOOD CO LTD, SUMITOMO SEIKA CHEMICALS, MITSUBISHI CORPORATION, OTSUKA FOODS CO., LTD., SUMITOMO SEIKA CHEMICALS CO., LTD.
Application year: 1990
Main classification: A23L1
IPC codes: A23L1