IES950791A2 - Method and apparatus for the production of a stable lactose product - Google Patents

Abstract

The present invention relates to a method and apparatus for the manufacture of stable, crystallized lactose powder to produce a crystallized lactose powder which will remain stable during long-term storage. The method comprises a treatment or conditioning step to prevent caking and formation of lumps, the step taking place after milling and prior to packing and storage wherein lactose crystals are exposed to humidified air followed by drying of the lactose crystals. The invention has resulted in a new process which is capable of producing, consistently, a lactose product which does not contain caked material or lumps, even after 18 months storage.

Description

METHOD AND APPARATUS FOR THE PRODUCTION OF A STABLE LACTOSE PRODUCT The present invention relates to a method and apparatus for the manufacture of stable, crystallized lactose powder and in particular to a method which is capable of producing a crystallized lactose powder which will remain stable during long-term storage.

Lactose is manufactured commercially by crystallization from whey concentrates. The method generally involves concentration of whole whey or deproteinized whey by evaporation, and controlled cooling of the resultant liquid concentrate in enclosed stirred tanks, in order to form lactose crystals. This is followed by centrifugal separation of the lactose crystals from the residual liquor and a subsequent washing step. The lactose crystals are then dried in a fluid bed dryer, milled, stored and packed.

One significant disadvantage with this process is the tendency of milled lactose to cake or harden and form lumps, varying in size and consistency, during storage. This can cause serious handling, capacity and quality problems and increases the overall cost of lactose manufacture, because, for example, it may subsequently be necessary to remill the lactose powder or break up the caked lactose in the bags before delivery to customers. 'I*?1 ..... ' OPEN TO PUBLIC INSPECTION WT SECTION 2« aNL· RULE 23 05O79T - 2 It is therefore an object of the present invention to provide a method of crystallized lactose production which produces a stable lactose product and which does not cake or form lumps during storage.

According to the present invention there is provided a method for the production of crystallized lactose powder comprising a treatment or conditioning step to prevent caking and formation of lumps, the step taking place after milling and prior to packing and storage wherein lactose crystals are exposed to humidified air followed by drying of the lactose crystals.

Preferably the conditioning step comprises exposure to humidified air which is at 80 to 95 % relative humidity, more preferably 85 to 90% relative humidity, at a temperature of 26 to 30°C, more preferably 28°C for about 10 to 15 minutes.

Preferably the lactose crystals are then dried at 30 to 36°C, more preferably 32 to 35°C for about 10 to 15 minutes, to 0.1% by weight moisture.

The invention also provides an apparatus to prevent caking of crystallized lactose during manufacture comprising a means to separate the lactose from the air transporting the lactose from a mill, a fluid bed onto which the lactose is fed and at least two heat exchange units, one having a means of humidifying the air, the heat exchange units passing air into the fluid bed.

Preferably the means to separate lactose from the transport air is a filter bag unit.

The apparatus may suitably be provided with a further filter bag unit for separating very fine lactose particles from the fluid bed exhaust air, and returning them to the main lactose powder stream.

This allows very fine lactose particles present in the exhaust drying air to be recovered.

Preferably an air filtration system is provided upstream of the heat exchange units. This prevents airborne contamination of the 0 7 9 1 - 3 lactose powder.

The present invention will now be described in further detail with reference to the accompanying drawings in which:Figure 1 is a schematic diagram of the prior art process for the manufacture of lactose.

Figure 2 is a schematic diagram of the process of the present invention for the manufacture of lactose.

Figure 3 is a diagrammatic representation of an apparatus in accordance with the present invention for the conditioning of the lactose after milling.

Figure 1 describes the prior art process flow. The initial steps in lactose production may involve the partial removal of proteins, minerals and lactic acid from the whey.

The whey concentrate is pumped to a crystallization tank where, after a predetermined time, it is cooled slowly at a rate of 2°C per hour down to 45°C and 3°C per hour thereafter to a temperature of 10°C + 2°C.

Agitation is constant while the whey concentrate is in the tank, to ensure uniform crystal growth and to keep the crystals in suspension. The agitation speed may range from 18-21 r.p.m. using propeller type or baffle/scraper type stirrers.

Lactose crystals are separated by means of horizontal centrifuges, washed and reseparated by a basket centrifuge. The resultant lactose slurry at 5-10% (by weight) moisture is dried in a two stage fluid bed drying process to give a moisture content of 0.1% (by weight) or less. Lactose crystals are then milled to the required particle size.

A feature of the process is that each particle of lactose has a layer of amorphous glass lactose on its surface. This layer, which is uncrystallized lactose, if untreated, will crystallize on storage, ί5θ7ί> - 4 resulting in caked or lumpy lactose. During the crystallization process, water is absorbed by the uncrystallized lactose. When crystallization is complete the water is released again and is available to dissolve more lactose thus making the crystals sticky and causing the actual caking. The combination of recrystallization and moisture release into the lactose will result in the ongoing formation of lumps and hardened, caked lactose, especially when the powder is stored, for more than two to three months, in bags on pallets, where the product is naturally subjected to compression which accelerates the caking process.

Figure 2 shows the process flow in accordance with the present invention. The process is similar to that shown in Figure 1 but it includes an extra process step after milling which has been termed a conditioning step.

The conditioning step consists of passing crystallized lactose powder through an environment with controlled humidity resulting in the crystallization of the surface amorphous glass layer of lactose thus stabilizing it.

In the conditioning step, lactose is passed over a fluid bed, through which humidified air is blown. This aids the crystallization of the amorphous glass lactose.

A second section of the fluid bed dries the lactose to less than 0.1% (by weight) moisture by passing heated air through it to remove the excess moisture released during crystallization.

The apparatus to prevent caking of crystallized lactose is shown in Figure 3. Milled dry lactose at an approximate moisture content of 0.1% (by weight) is transferred by suction, from a lactose mill (1) via a lactose powder transport line (2) to a filter bag unit (3). The filter bag unit (3) comprises a number of filter bags through which the exhaust air is pulled by means of an exhaust fan (4). Compressed air from an air compressor is applied to each filter bag in turn on a timed, rotating basis, using an electric timer and electromechanical valves, to remove excess lactose powder from the outside of the filter - 5 »5079f bag.

At the base of the filter unit (3) there is a rotary seal (5) powered by an electric motor which allows the lactose powder to pass into a fluid bed (6). The fluid bed (6) consists of a long, horizontal, cylindrical vessel with a perforated plate (7) running lengthways along the cylinder approximately 0.5 m from its base. The lactose powder is conveyed along this perforated plate (7). The fluid bed (6), which is sloped towards the product outlet and mounted on heavy springs, is vibrated using a mechanical device powered by an electric motor. The slope, vibration and air blown into the bed (6) from fans (10) and (16) below, all combine to convey the lactose, which is in a semi-fluidised state, along the perforated plate (7) towards the outlet.

Humidified air at 80 to 95 % relative humidity is blown through the first section of the fluid bed (6) via an air transport duct (8). The air in the transport duct comes from a heating unit (9) which comprises a supply fan (10) to blow air into the fluid bed, a heater (11) to heat the air, a humidifier (12) for the addition of water to the air via a very fine nozzle spray device (13) and a filter unit (14) to prevent any airborne contamination. This fluidizes the powder exposing each particle to a high humidity environment and a temperature of 28°C + 2°C for a period of about 10 to 15 minutes. This creates optimum conditions for crystallization of the amorphous glass lactose.

Heated dehumidified air is then blown through the second stage of the conditioning bed. A second heating unit (15) consists of a supply fan (16) which blows air through a heat exchanger (17) into the second section of the fluid bed, a filter unit (18) to prevent airborne contamination and a steam supply control unit (19) to maintain the air temperature at 30 to 36°C for 10 to 15 minutes. Air is supplied to the fluid bed (6) via a transport duct (20). This removes excess moisture and dries the lactose to less than 0.1% (by weight) moisture.

The powder then flows from the bed (6) into a rotary seal (21) powered by an electric motor. A powder transfer system comprising a filter unit (25) to prevent contamination, a blower (22) and a 950791 - 6 transport line (23) passing under the rotary seal (21) transfers the powder to a storage silo (24).

Exhaust air and very fine lactose particles (or fines) are pulled into a second filter unit (26) via ducting (27). The filter unit (26) consists of filter bags through which filtered air is pulled by means of an exhaust air fan (28). Compressed air pulses from an air compressor is applied to each filter bag in turn on a timed, rotating basis, using an electric timer and electromechanical valves, to remove excess build-up of lactose powder on the outside of the filter bags.

The recovered lactose fines powder is fed back into the main lactose powder stream via a rotary seal powered by an electric motor.

Compared to the prior art process, the present invention has resulted in a new process which is capable of producing, consistently, a lactose product which does not contain caked material or lumps, even after 18 months storage.

When the prior art process was in use, approximately 20% of the product, over 2-3 months old, had to be remilled before delivery to customers who needed free-flowing, lump-free lactose. Over 80% of the remaining 2-3 months old product had to undergo a process whereby each individual bag of caked lactose was put through a bag flattening device to break up the caked lactose into small manageable lumps for customers who did not need lump-free product. Furthermore, around 10% of the product less than 2 months old had to be remilled.

The new invention, therefore, has resulted in a process capable of producing, consistently, a high quality, stable product which will retain its free-flowing, lump-free properties during long-term storage. This means that lactose can be stored, if necessary, for up to 18 months and that customer complaints have been eliminated. The end result has been the realization of substantial financial savings in the cost of lactose powder manufacture.

Claims (5)

1. A method for the production of crystallized lactose powder comprising a treatment or conditioning step to prevent caking, the step taking place after milling and prior to packing and storage wherein lactose crystals are exposed to humidified air followed by drying of the lactose crystals.

2. A method as claimed in claim 1 wherein the conditioning step comprises exposure to humidified air at 80 to 95 % relative humidity, more preferably 85 to 90% relative humidity, at a temperature of 26 to 30°C, more preferably 28°C, for about 10 to 15 minutes.

3. A method as claimed in claim 1 or claim 2 wherein the lactose crystals are dried at 30 to 36°C, more preferably 32 to 35°C, to 0.1% by weight moisture.

4. An apparatus to prevent caking of crystallized lactose during manufacture comprising a means to separate the lactose from the air transporting the lactose from a mill, a fluid bed onto which the lactose is fed and at least two heat exchange units, one having a means of humidifying the air, the heat exchange units passing air into the fluid bed.

5. A method for the production of crystallized lactose comprising a treatment or conditioning step to prevent caking substantially as described herein with reference to figures 2 and 3 of the accompanying drawings.