NL2021877B1 - Improved emulsion spray-drying process and assembly for use in said process - Google Patents
Improved emulsion spray-drying process and assembly for use in said process Download PDFInfo
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- NL2021877B1 NL2021877B1 NL2021877A NL2021877A NL2021877B1 NL 2021877 B1 NL2021877 B1 NL 2021877B1 NL 2021877 A NL2021877 A NL 2021877A NL 2021877 A NL2021877 A NL 2021877A NL 2021877 B1 NL2021877 B1 NL 2021877B1
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- carbon dioxide
- dried fat
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Abstract
The present invention concerns an emulsion spray-drying process for preparing flee flowing spray-dried fat powder comprising: (a) Mixing water, one or more emulsifiers, one or more fats and optional constituents to form an emulsion A; (b) Spray-drying the emulsion A to generate a flow of droplets and drying the droplets with hot air B, thus forming spray-dried fat powder C, and (c) Collecting the spray-dried fat powder C and separating the spray-dried fat powder C from the hot air B, which process further comprises (d) mixing the spray-dried fat powder C with solid carbon dioxide D and cooling the spray-dried fat powder C to below the glass transition temperature of the powder, and preferably below the melting/crystallization temperature of the employed fat characterized in that step (d) is performed by injecting controlled amounts of solid carbon dioxide D homogeneously through the spray-dried fat powder with the use of 2 or more carbon dioxide inlets during transport of the powder. The invention also concerns an assembly for use in the above process, comprising a spray- dryer and a powder transport, wherein the powder transport is equipped with two or more inlets for solid carbon dioxide.
Description
Technical Field
The present invention concerns an improved emulsion spray-drying process. More in particular, the present invention concerns an emulsion spray-drying process with improved efficiency and hygiene, which therefore is ideal in producing free-flowing spray-dried fat powder used as food or medicament. It also concerns an assembly for use in said process.
Background Art
Emulsion spray-drying is a method of producing a spray-dried fat powder from an oil/water emulsion by rapidly drying with a hot air.
Methods for producing spray-dried powder containing oil or fat are known. In GB919193 and GB937564 a process is described wherein powdery products containing edible oil or fat are made from an oil-in-water type of emulsion wherein the emulsion is spray-dried. In GB2031937 an edible dry, friable powdered lipid composition for human or animal consumption is described, that consists of spray-dried particles each comprising fat and/or oil, protein, and emulsifier, in the absence of any additional particulate coating material on the particles. In W02008066380 a process is described for the preparation of powdered oils and more particularly to oil encapsulated in a protein containing matrix. The powdered oils obtainable by such processes may be used in the preparation of food compositions. Also from EP2052622 a method is described for the preparation of a spraydried fat powder from an oil in water emulsion.
An alternative method for producing powder containing oil or fat is known from EP0393963, which discloses a method and apparatus for cryogenic crystallization of fats. This alternative process involves introducing a fine, downwardly directed spray of atomized liquid fat into the upper portion of the mixing chamber while directing a plurality of fine jets of cryogenic liquid against the downward spray of liquid fat droplets so as to cause rapid conversion thereof to solid particles which fall into the dry ingredients at the bottom of the mixing chamber. As cryogenic liquid coolant liquid nitrogen or carbon dioxide are used. As a result, a homogeneous mix free of fat lumps is produced.
Of particular importance in the spray-drying process, is that the product so prepared may be further processed without difficulty. Subsequent steps may, for instance, include milling, sieving, and packaging. It is therefore required that the spray-dried fat powder is cooled to below their glass transition temperature. Conventionally this is done with air.
-2Methods for cooling are known in the food-processing industry. For instance, in WO9215828 a process for treating newly formed soft elastic gelatine capsules to avoid their sticking to one another and to remove matter in the form of oils, pastes, and solid particles from exterior surfaces of said capsules, comprising the steps of: cooling said capsules to aid in preventing capsule deformation and to aid in removing aqueous moisture from exterior surfaces of said capsules; and contacting said capsules with an absorbent material to remove said oils, pastes, and solid particles from said exterior surfaces of said capsules. However, it should be noted that the problems of WO9215828 are very much different from what is encountered when producing spray-dried powder containing oil or fat.
Similarly, W002100183 relates to a process for preparing micronised fat continuous particles comprising fat and non fat ingredients, wherein the process comprises a cryomilling step with a cryo coolant, such as liquid nitrogen or solid carbon dioxide and reducing them in size while cold, in particular while having a temperature of-20 to 10°C. This process is again very different from the process of spray-dried powder containing oil or fat.
Despite the knowledge in the general art of food-processing on cooling, improvement in respect of the preparation of spray-dried powder containing oil or fat remains desirable. Cooling, however, must be done carefully, so as to avoid risk of microbial contamination of the dry powder so produced. Moreover, in spray-dried powder containing oil or fat the cooling must be carried out appropriately, to control the degree of crystallization occurring in the spray-dried powder. More in particular, there is a desire for improvement of the lipid crystal structure within the spray-dried fat powder, which is difficult to obtain using ordinary cooling techniques. The aim of the present invention is to improve the process and/or the product functionality.
Summary of invention
Accordingly, the present invention provides an emulsion spray-drying process for preparing flee flowing spray-dried fat powder comprising:
(a) Mixing water, one or more emulsifiers, one or more fats and optional constituents for form an emulsion A (b) Spray-drying the emulsion A with hot air B, thus forming spray-dried fat powder C, and (c) Collecting the spray-dried fat powder C and separating the spray-dried fat powder from the hot air B, which process further comprises (d) mixing the spray-dried fat powder C with solid carbon dioxide D and cooling the same to below the glass transition temperature of the powder C and preferably below the melting/crystallization temperature of the employed fat characterized in that step (d) is performed by injecting controlled amounts of solid carbon dioxide D homogeneously through the spray-dried fat powder with the use of 2 or more carbon dioxide inlets during transport of the powder.
Also provided is an assembly for use in the process of the present invention.
Description of embodiments
As indicated, spray-drying is a common process for many products such as fat powders; creamers or Whiteners; milk powders/replacers; protein powders; colorants, antibiotics; blood products, and a variety of drugs for medication. The general process for spray-drying fat powder involves preparation of the feed, atomization, droplet air contact, droplet drying and separation. Drying is done in a spray-dryer at controlled conditions.
The preparation of the feed may involve the use of a homogenizer. Thus, an oil/water emulsion is typically heated to a temperature in the range of 50 to 95°C, and pumped through a homogenizer.
Typically a spray-dryer mixes heated air with the atomized (sprayed) emulsion within a drying chamber. The chamber may be in the form of a spray-drying tower, with adequate residence time and droplet trajectory distance for achieving the required heat and mass transfer to accomplish evaporation and produce a free flowing dry powder with a controlled average particle size. Various nozzles may be used to effect the atomization, including high pressure nozzles or even dual fluid nozzles, that use additional compressed gas. The heated air may be introduced in co-current or counter-current flow. By using counter-current flow it may be possible to reduce the height of the tower and still achieve adequate evaporation of the water from the droplets of atomized feed. It may also be possible to optimize the flow in the drying chamber with the use of additional hot air inlets, which moreover- may be oriented such that collision of the drying droplets with the inner wall of the drying chamber is avoided. The inner wall of the drying chamber may be coated to avoid contamination with collided droplets. Furthermore, the bottom part of the drying chamber is typically designed such as to facilitate the separation of the hot air. For instance, a perforated conveyor-belt may be used to collect the spray-dried fat powder and separate the same from the hot air. Similar means may be used to recover the solids from the gas stream, e.g., a cyclone or similar device. Thus, various modification are possible.
The temperature with which powders leave the drying chamber is a very important parameter, as it fully determines the functionality performance and mechanical handling of the ensuing powder. Thus, spray-dried fat powder has a matrix comprising carbohydrates with a glass transition temperature defined amongst others by the carbohydrates employed, and in that matrix a large amount of droplets comprising fat, with a melting temperature defined amongst others by the fat and other components contained therein. Especially
-4powders with a high fat content are very prone to be mechanically damaged when the fat is not sufficiently crystallized and thus remains (partly) liquid.
This problem of mechanical damage may be overcome with fast cooling. Also powders high in (small) carbohydrates may benefit from fast cooling as it may prevent them from being sticky when their temperature is lowered below the glass transition temperature. Other more specialized products may in their functionality also depend on the degree and speed of cooling.
Cooling is commonly performed by exposure to cooled air. This method has the advantage that the cooling process is well controlled. However, this method has the disadvantage that the cooling process is slow. Direct, homogeneous cooling of spray-dried powders with a controlled cooling speed (slow or fast, optimized in respect to the spray dried powder) has not been performed before in an acceptable fashion. Thus, if a cooling agent is used, it should be non-toxic, food grade, and preferentially leave no traces in the product. Moreover, the cooling should be done such that no pockets are created with condensation as this may result in microbial contamination of the so produced powder. In addition, unnecessary cooling of machine parts, leading to condensation and concomitant microbial risks, should be avoided. Moreover, the cooling should be done gradually and homogeneously. In particular, there is a desire specifically for spray-dried powders to improve the lipid crystal structure within the spray-dried fat powder.
Surprisingly, it has been discovered that the process for preparing flee-flowing particles by spray-drying a feed may be improved by the addition of a cooling step, wherein solid carbon dioxide is used as cooling agent. Solid carbon dioxide has the advantage that it provides a well-controlled gradual cooling as it melts relatively slowly and draws the heat from the surrounding powder. This relative slow melting also allows proper mixing of the powder with carbon dioxide causing it to homogenously lower the temperature of the complete product. When properly mixed, solid carbon dioxide homogenously lowers the temperature of the complete product. Other cooling agents such as liquid nitrogen are prone to cause very fast, localized, and inhomogeneous cooling of the product, with an additional disadvantage lying in the severe risk of water condensation in the undercooled equipment leading to unacceptable microbial risk in the produced product. By using controlled amounts of solid carbon dioxide, and moreover through several inlets, and moreover directly after the drying step during the transport step, well controllable cooling is achieved, as the solid carbon dioxide mixes well with the spray-dried powder during the transport step, and as it melts relatively slowly, drawing heat from the surrounding powder. This homogenously lowers the temperature of the complete product at a rate which can be controlled to optimize the lipid crystal structure within the spray-dried fat powder.
-5Introduction of the solid carbon dioxide is preferably done by directly injecting small amounts of carbon dioxide into the collected spray-dried fat powder with use of an injection system working with two or more, preferably several injectors. By using several injectors for carbon dioxide, condensation of moisture onto the dried powder and/or on the inner walls of any part of the assembly is avoided, thus reducing the risk of microbial contamination and other disadvantages. The introduction of the solid carbon dioxide is preferably done with a cryogenic injection system, such as provided by Linde AG under the trademark LIXSHOOTER. For instance 2-10 injectors may be used to provide a very controlled homogeneous cooling. If less than 2 injectors are used, then the cooling may be insufficient or not be sufficiently homogeneous. More than 10 injectors may be used, e.g., around 15 injectors. The introduction of the solid carbon dioxide is done during pneumatic or mechanical powder transport, when the collected spray-dried fat powder is transported away from the drying chamber and prior to any of the subsequent mechanical handling of the powder (for instance, milling, sieving, packaging, etc.).
The spray-dried fat powder should be cooled to a temperature in the range of 040°C, preferably 5-20°C. Below 0°C the risk of condense formation increases. Above 40°C the risk of smearing and lump formation of the powder increases. Preferably sufficient solid carbon dioxide is introduced to cool the spray-dried fat powder to below the glass transition temperature of the powder and preferably below the melting temperature of the employed fat. The optimum temperatures therefore depend on the emulsion that is spray-dried. Moreover, the optimum amounts of solid carbon dioxide added to the spray-dried powder may be easily determined by experimentation. Typically this process is performed continuously. Generally between 0.02 and 0.2 kg of solid carbon dioxide per kg of spraydried fat powder is added at a rate sufficient to achieve appropriate cooling and optimize the lipid crystal structure within the spray-dried fat powder.
The product produced according to the process of the present invention has the advantage that it can be further processed by milling, sieving and packaging, without the risk of smearing or lump-formation. Moreover, the cooling can be fine-tuned such that the powder, despite the temperature increase in case of a milling operation, remains below the glass transition temperature, and preferably below the melting/crystallization temperature of the employed fat.
Claims (8)
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