Field

The invention pertains to apparatus and methods for pasteurizing and drying of organic materials, such as food and pharmaceutical products. Background

Dehydration of organic materials is commonly done in the food processing and pharmaceutical industries to preserve the products for storage, to concentrate non-volatile components, or to create products that are used in the dehydrated form, for example dried herbs and various kinds of chips. It is known to dehydrate food and pharmaceutical products by vacuum microwave dehydration. Examples of this in the patent literature include WO 2009/049409 dated April 23, 2009, WO 2009/033285 dated March 19, 2009, WO 201 1/085467 dated July 21 , 201 1 , WO 2013/010257 dated January 24, 2013, and WO 2014/085897 dated June 12, 2014. Vacuum microwave drying is a rapid method that can yield products with improved quality compared to air-dried and freeze-dried products. Because the drying is done under reduced pressure, the boiling point of water and the oxygen content of the atmosphere are lowered, so food and medicinal components sensitive to oxidation and thermal degradation can be retained to a high degree. Despite being dehydrated, many organic products have bacterial contamination or contain deleterious enzymes that reduce storage life. In the prior art, separate treatment processes additional to drying are required to address these problems. It is known to process food products by increasing the pressure in a vacuum microwave chamber to atmospheric or greater than atmospheric pressure, thereby elevating the temperature of the product to a sterilization temperature. See Yaghmaee et al.,“Efficacy of Vacuum Microwave Drying in Microbial Decontamination of Dried Vegetables,” in Drying Technology , 25:6, 1099-1 104 (2007). However, heat treatment at such elevated temperatures is not suitable for materials that are subject to thermal degradation. In thermal processing of organic materials such as food products, distinctions are made between different levels of heat treatment in terms of the types of microorganisms that are targeted. A distinction is made between: 1 ) heat processes that kill all viable organisms, termed“sterilization;” 2) processes that kill all viable organisms of public health concern, termed“commercial

sterilization;” and 3) relatively milder heat processes that only kill some of the less heat-resistant pathogenic organisms, termed“pasteurization.” Sterilizing with heat requires temperatures well above 100°C, which are achieved at or above atmospheric pressure, not under vacuum pressures. The present disclosure pertains to an apparatus and processes for treatment of materials under vacuum conditions, so the processes pasteurize rather than sterilize. There is a need for a cost-effective apparatus and method for treating food and pharmaceutical products to improve their quality, safety and storage life.

Summary of the Invention

The invention provides an apparatus and method for pasteurizing and drying organic materials under vacuum conditions. The invention permits both drying and pasteurizing to be done in a single vacuum chamber in a continuous throughput process.

According to one aspect of the invention, there is provided an apparatus for dehydrating and pasteurizing an organic material, comprising: a vacuum chamber having a first zone (a pasteurization zone) and a second zone (a drying zone); means for loading the organic material into the vacuum chamber; means for unloading the organic material from the vacuum chamber; means for conveying the organic material from an input end of the vacuum chamber, through the first zone and the second zone to an output end of the vacuum chamber; means for reducing pressure within the vacuum chamber to a first pressure below atmospheric; means for periodically changing the pressure within the vacuum chamber to a second pressure below atmospheric and higher than the first pressure; means for irradiating the organic material with microwave radiation within the first zone and the second zone at a first microwave power level; means for periodically irradiating the organic material within the first zone with

microwave radiation at a second microwave power level higher than the first microwave power level; and means for controlling the changing of pressure to the second pressure and the irradiation of the organic material at the second microwave power level to occur within the same time interval.

According to another aspect of the invention, there is provided an apparatus for dehydrating and pasteurizing an organic material, comprising: a vacuum chamber having a first zone and a second zone; an apparatus for loading the organic material into the vacuum chamber; an apparatus for unloading the organic material from the vacuum chamber; a conveyor for conveying the organic material from an input end of the vacuum chamber, through the first zone and the second zone to an output end of the vacuum chamber; a vacuum apparatus for reducing pressure within the vacuum chamber to a first pressure below atmospheric; an apparatus for periodically changing the pressure within the vacuum chamber to a second pressure below atmospheric and higher than the first pressure; magnetrons for irradiating the organic material with microwave radiation within the first zone and the second zone at a first microwave power level; magnetrons for periodically irradiating the organic material within the first zone with microwave radiation at a second microwave power level higher than the first microwave power level; and a controller for controlling the changing of pressure to the second pressure and the irradiation of the organic material at the second microwave power level to occur within the same time interval.

According to another aspect of the invention, there is provided a method of pasteurizing and dehydrating an organic material in a vacuum chamber having a pasteurization zone and a drying zone, comprising the steps of: loading the organic material into the vacuum chamber; conveying the organic material from an input end of the vacuum chamber, through the pasteurization zone and the drying zone to an output end of the vacuum chamber while exposing the organic material to microwave radiation at a first microwave power level and to a first vacuum pressure; periodically exposing the organic material to microwave radiation in the pasteurization zone at a second microwave power level higher than the first microwave power level and to a second vacuum pressure higher than the first vacuum pressure, whereby said exposing pasteurizes the organic material within the pasteurization zone; and unloading the pasteurized and dehydrated organic material from the vacuum chamber. According to another aspect of the invention, there is provided a method of pasteurizing and dehydrating an organic material in a vacuum chamber having a pasteurization zone and a drying zone, comprising the steps of: (a) loading the organic material into the vacuum chamber; (b) conveying the organic material from an input end of the vacuum chamber, through the pasteurization zone and the drying zone to an output end of the vacuum chamber, (c) exposing the organic material to a first vacuum pressure and microwave radiation at a first microwave power level during step (b) to dehydrate the organic material; (d) increasing the pressure within the vacuum chamber from the first vacuum pressure to a second vacuum pressure higher than the first vacuum pressure; (e) increasing the microwave power level within the pasteurization zone from the first microwave power level to a second microwave power level that is higher than the first microwave power level; (f) exposing the organic material to the second pressure and to microwave radiation at the second microwave power level in the pasteurization zone for a plurality of time intervals during step (b), whereby the exposure of the organic material to the second vacuum pressure and to microwave radiation at the second microwave power level pasteurizes the organic material within the pasteurization zone, wherein each of said time intervals is separated by a period of exposure to microwave radiation at the first microwave power level in the pasteurization zone and to the first vacuum pressure; and (g) unloading the pasteurized and dehydrated organic material from the vacuum chamber.

These and other aspects and features of the invention will be apparent from the following description and drawings of the specific embodiments.

Brief Description of the Drawings

Figure 1 is a schematic diagram of a vacuum microwave dehydration apparatus according to one embodiment of the invention.

Figure 2 is a flow chart of a method for making a pasteurized and dehydrated product according to one embodiment of the invention.

Figure 3 is a graph of the increases in vacuum pressure and microwave power level during the pasteurization and dehydration process described in Example 1 . Detailed Description of Preferred Embodiments

Figure 1 schematically illustrates an embodiment of the vacuum microwave drying apparatus 10. It has a vacuum chamber 12 through which a tray of organic material is conveyed for dehydration and pasteurization. A loading module 14 is positioned at the input end 16 of the vacuum chamber for introduction of trays 18 of organic material 19 into the vacuum chamber 12. A discharge module 20 is positioned at the output or discharge end 22 of the vacuum chamber for removal of the trays of material. The loading module 14 and discharge module 20 each have a pair of airlock doors, respectively 24, 26 and 28, 30 (their open position being shown by dotted lines in Figure 1 ). These permit the trays to be loaded into and unloaded from the vacuum chamber, while maintaining the vacuum chamber at the reduced pressures required for the pasteurization and

dehydration process. The loading and discharge modules 14, 20 have motor- driven conveyors 32, 34, respectively, for moving the trays.

The vacuum chamber 12 is connected via a vacuum conduit 36, a condenser 38 and a shut-off valve 40 to a vacuum pump 42 or the vacuum system of a plant. The loading and discharge modules 14, 20 are connected via a vacuum conduit 44 and shut-off valves 46, 48 and 50 to a vacuum pump 52. The loading and discharge modules are vented by discharge shut-off valves 54 and 56

respectively. A further discharge valve (not shown) is provided for venting the vacuum chamber. The loading and discharge modules 14, 20 are connected to the vacuum chamber 12 for pressure equalization by means of equalization conduits 58 and 60 and the associated shut-off valves 62 and 64, respectively.

The vacuum chamber 12 has a motor-driven conveyor 66 extending longitudinally through it and arranged to support and convey the trays 18. The conveyor runs on rollers 68 adjacent to the inlet and the outlet ends of the vacuum chamber.

Magnetrons (microwave generators) or groups of magnetrons 70A to 70G are mounted below the vacuum chamber 12 and are arranged to radiate microwave energy into the vacuum chamber through waveguides 72 and microwave- transparent windows 74. Each magnetron group 70 comprises one or more magnetrons, for example six or eight magnetrons, depending upon the power requirements for a particular dehydration apparatus 10. The magnetrons are connected to a conventional power source (not shown) which provides the required electric power. The magnetrons are cooled by coolant pumped to circulate around them from a cooling liquid refrigeration unit.

A water load 76 is provided at the upper part of the vacuum chamber 12 to absorb microwave energy and thus prevent reflection of microwaves in the vacuum chamber. The water is pumped through tubing by a water load pump (not shown).

The vacuum chamber 12 has two zones. A pasteurization zone 78 is at the input end 14 of the vacuum chamber. In the illustrated embodiment it extends approximately one-fifth of the length of the vacuum chamber. The second zone is a drying zone 80. It extends approximately four-fifths of the length of the vacuum chamber, from the pasteurization zone to the output end 22 of the vacuum chamber. For example, in a vacuum chamber that is 10 meters in length, the pasteurization zone 78 is about 2 meters long and the drying zone is about 8 meters long.

The pasteurization zone may be of various lengths relative to the total length of the vacuum chamber other than one-fifth. In other embodiments it may be, for example, one-third, one-fourth, one-sixth, etc. of the length of the vacuum chamber.

The pasteurization zone 78 is preferably positioned at the input end 14 of the vacuum chamber, as in the illustrated embodiment, because the organic material has a higher water content at the beginning of the drying process and bacteria are more readily killed in material that is wet rather than dry. However, the pasteurization zone may instead be located at other positions within the vacuum chamber. It has been determined that for the processing of pastes or other materials that cannot withstand the high power intensity of a pasteurization zone at their initial moisture content, the pasteurization zone should be located downstream from the input end of the vacuum chamber, for example, midway between the input and discharge ends. This avoids undesirable splashing or foaming of such materials during pasteurization.

The vacuum chamber zone 12 is not partitioned into separate pressure zones and accordingly the pasteurization zone 78 and the drying zone 80 are at the same vacuum pressure. The distinction between the two zones is the maximum microwave power that can be produced per unit of length of the vacuum chamber. This may be accomplished, for example, by the number of magnetron groups 70 per unit of length of the vacuum chamber. In the illustrated

embodiment, there are three magnetron groups 70A, 70B and 70C in the pasteurization zone 78 and four magnetron groups 70D, 70E, 70F and 70G spaced apart along the drying zone. Since the pasteurization zone is about one- fifth of the length of the vacuum chamber and the drying zone about four-fifths, there are three times as many magnetron groups per unit of length in the pasteurization zone as in the drying zone. The microwave power in the pasteurization zone is therefore up to three times higher in the pasteurization zone than within an equivalent length of the drying zone. Alternatively, the higher microwave power level in the pasteurization zone can be produced by means of higher power magnetrons in that zone, rather than by a greater number of magnetrons.

As used herein, the term“pasteurization zone” means the section of the vacuum chamber capable of providing relatively higher microwave power levels, for example by having a relatively higher density of microwave generators. The term “drying zone” means the remaining section of the vacuum chamber capable of providing, relative to the pasteurization zone, a lower microwave power level, one that is suitable for drying. The higher temperatures required to effect

pasteurization are thus provided in the pasteurization zone, not in the drying zone. It will be understood, of course, that drying of the material without pasteurization also occurs in the pasteurization zone during the periods when the microwave power level in that zone is at the base level, i.e. the same power level as in the drying zone.

The dehydration apparatus 10 includes a programmable logic controller (PLC)

82, programmed and connected to control the operation of the system, including the pressure and temperature sensors, the conveyor drive motors, the airlock doors, the magnetrons, the water load pump, the vacuum pumps, the condenser, the refrigerant pump and the vacuum shut-off valves. The timed application of increased microwave power in the pasteurization zone and the higher vacuum pressure steps is achieved by programming of the PLC. It will be understood that the invention applies to vacuum microwave dehydrators having any of various means for feeding, conveying and discharging the organic materials. In one embodiment, as illustrated, the material is transported in trays which ride on a conveyor belt, with feeding into and discharge from the vacuum chamber being done by means of loading and discharge modules having airlock doors. In another embodiment, the organic material is fed into and out of the vacuum chamber by means of rotary vacuum valves rather than airlocks with doors, and is transported directly on the conveyor belt rather than on trays. In yet another embodiment, the material is transported through the vacuum chamber in a rotating basket, an arrangement of the type disclosed in WO 2009/049409 dated April 23, 2009. The present invention is independent of any particular means for moving the organic material into, through and out of the vacuum chamber.

During operation of the vacuum microwave dehydrator 10, there are repeated cycles of higher microwave power in the pasteurization zone, and of higher vacuum pressure throughout the vacuum chamber, as the organic material is moved continuously and at constant speed through the vacuum chamber. For example, every 10 minutes during a total residence time of 50 minutes, the microwave power is increased in the pasteurization zone 78 (not in the drying zone 80, where it remains constant) and at the same time the vacuum pressure is increased. The pressure increase occurs throughout the vacuum chamber, since it is not partitioned. The combination of increased microwave power in the pasteurization zone and increased vacuum pressure has the effect of increasing the temperature of the organic material within the pasteurization zone and thereby pasteurizing the organic material as it travels through the pasteurization zone.

The operating parameters of the system can assume various values, depending upon the organic material and the desired product characteristics. In some embodiments, the base microwave power level in the vacuum chamber is in the range of 0.1 to 3 kW/kg of material, alternatively in the range of 0.1 to 2 kW/kg, alternatively about 2 kW/kg. The increased, pasteurizing power level, in the pasteurization zone only, is in the range of 2 to 10 kW/kg of material, alternatively in the range of 4 to 6 kW/kg, alternatively about 5 kW/kg. Each magnetron group may have a power output in the range of 0.1 to 10 kW. The base vacuum pressure is in the range of about 10 to 50 Torr (13 to 67 mbar), alternatively about 20 to 30 Torr (27 to 40 mbar), alternatively about 25 Torr (33 mbar). The increased, pasteurizing vacuum pressure is in the range of about 100 to 300 Torr (133 to 400 mbar), alternatively about 150 to 200 Torr (200 to 267 mbar), alternatively about 180 Torr (240 mbar). The duration of increased microwave power and vacuum pressure is in the range of 1 to 5 minutes, alternatively in the range of 2 to 3 minutes, alternatively about 2.5 minutes. The residence time in the vacuum chamber, as the material moves at constant speed from the input end to the discharge end, is in the range of 20 to 120 minutes, alternatively in the range of 40 to 60 minutes, alternatively about 50 minutes. The drying

temperature, i.e., the temperature of the organic material in the drying zone, is in the range of 15 to 100°C, alternatively in the range of 25 to 45°C. The temperature in the drying zone during the pasteurization step is in the range of 45 to 65°C. The pasteurizing temperature, i.e., the temperature of the organic material in the pasteurizing zone during the pasteurization step, is in the range of 65 to 85°C, alternatively in the range of 75 to 80°C. The material is dried to a desired moisture content, for example in the range of 1 to 15 weight %, alternatively in the range of 2 to 14 weight %.

In an embodiment in which the travel time through the pasteurization zone is about 10 minutes, having a microwave power and vacuum pressure increase every 10 minutes ensures that all the material is subjected to a period of increased heating, and therefore pasteurization, as it travels through the pasteurization zone.

The flow diagram of Figure 2 illustrates the basic steps of the method 100 of drying and pasteurization. First, the organic material is loaded 102 into the vacuum chamber. This is done on a continuous throughput basis and the material is conveyed 103 at constant speed through the vacuum chamber. The material is initially processed 104 at a drying vacuum pressure and base microwave power level. The pressure is then increased 106 to the pasteurizing pressure and at the same time the microwave power level in the pasteurization zone is increased. The material is processed 108 at this increased, pasteurizing vacuum pressure and, within the pasteurization zone, at the pasteurizing microwave power level, for a selected time period. Then, the microwave power level in the pasteurization zone and the vacuum chamber pressure are decreased 110 to their base levels. The material is further processed 112 at the base microwave power level and base vacuum pressure. Steps 106, 108, 110 and 112 are then repeated 114. This repetition 114 is done, for example, four more times during a residence time of 50 minutes to ensure that all the material is pasteurized as it passes through the pasteurization zone. After the last repetition, the process concludes, as indicated by process line 116, with unloading 118 of the pasteurized and dried product.

The method 100 of the invention may be carried out using the dehydration apparatus 10. The airlock doors 26 and 30 are closed and the vacuum pumps, water load pump, conveyor drive motors and microwave generators are actuated, all under the control of the PLC 82. Pressure within the vacuum chamber is reduced to the desired vacuum pressure for drying. The organic material 19 to be dehydrated is put into a tray 18 and the tray is placed in the loading module 14. The outer airlock door 24 and shut-off valve 52 are closed and the loading module is evacuated by the vacuum pump 45 to the pressure of the vacuum chamber. The inner airlock door 26 is then opened and the tray is transported, by the conveyors 32 and 66, into the vacuum chamber 12. Once the tray is fully inside the vacuum chamber, the loading chamber 14 is prepared for receiving a second tray, by closing the inner airlock door 26 and the shut-off valves 46 and 62, opening the shut-off valve 54 to vent the loading module to atmospheric pressure, and opening the outer airlock door 24. The dehydration apparatus is thus able to process multiple trays of organic material at the same time, in a continuous process. Inside the vacuum chamber 12, the tray is moved along the conveyor 66 and the microwave generator groups 70A, 70D, 70E, 70F and 70G irradiate the material and dehydrate it. Vapour given off by the material is conveyed to the condenser 40 to be condensed to liquid water. Repeated cycles of higher microwave power are applied in the pasteurization zone by actuation of magnetron groups 70B and 70C; and at the same time, the higher, pasteurizing vacuum pressure is applied by bleeding air into the vacuum chamber. The microwave power level and the vacuum pressure are then returned to their base levels. At the end of the residence time within the vacuum chamber, the tray 18 of material enters the discharge module 20, where it is conveyed toward the outer airlock door 30. The inner airlock door 28 is then closed, the shut-off valves 48, 64 are closed, the valve 56 is opened to vent the discharge module to the atmosphere, the outer airlock door 30 is opened and the tray is removed. The discharge module is prepared for the next tray to be removed from the vacuum chamber by closing the outer airlock door 30, evacuating the discharge module by means of vacuum pump 52 to the reduced pressure of the vacuum chamber, and opening the inner airlock door 28. Following either loading or discharge of a tray from the loading module or discharge module, the vacuum pump 52 draws gases from the loading or discharge module, through the vacuum conduit 64, without disturbing the vacuum in the vacuum chamber 12.

Examples of materials suitable for pasteurization and dehydration by the invention include fruit, either whole, puree or pieces, either frozen or un-frozen, including banana, mango, papaya, pineapple, melon, watermelon, pomegranate, apples, pears, cherries, berries, peaches, apricots, plums, grapes, oranges, lemons, grapefruit; vegetables, either fresh or frozen, whole, puree or pieces, including peas, beans, corn, carrots, tomatoes, peppers, herbs, potatoes, beets, turnips, squash, onions, garlic; fruit and vegetable juices; pre-cooked grains including rice, oats, wheat, barley, corn, flaxseed; cannabis; hydrocolloid solutions or suspensions, vegetable gums; frozen liquid bacterial cultures, probiotics, food culture, vaccines, enzymes, protein isolates; amino acids;

injectable drugs, pharmaceutical drugs, natural medicinal compounds, antibiotics, antibodies; meats, fish and seafoods, either fresh or frozen, either whole, puree or pieces; dairy products such as milk, cheese, whey proteins isolates and yogurt; and moist extracts of fruits, vegetables and meats.

Example 1

Cubed sweet potato is pasteurized and dried using a vacuum microwave drying apparatus of the type depicted in Figure 1 . The vacuum chamber is 10 meters long, with a pasteurization zone that is 2 meters long and a drying zone that is 8 meters long. The weight of product that is processed is 10 kg per tray and it has an initial water content of 80 weight %. The product remains in the vacuum chamber for a total residence time of 50 minutes in a continuous throughput process. The base microwave power level is 10 kW per meter. It is periodically increased in the pasteurization zone to 30 kW/m. Based on the weight of product being processed, this amounts to 1.6 kW/kg and 3.0 kW/kg, respectively. The vacuum pressure in the vacuum chamber is at a base level of 20 Torr (26 mba r).

It is periodically increased to 300 Torr (400 mbar). The duration of the increased power and pressure, which occur simultaneously, is 2.5 minutes, and is carried out every 10 minutes. Figure 3 graphically illustrates the timed, simultaneous increases in microwave power and vacuum pressure during the 50-minute residence time. The boiling point of water within the product is about 20°C at 20 Torr and is about 75°C at 300 Torr. The process pasteurizes and dries the product to a moisture content of about 10 weight %. The pasteurization reduces the total plate count from about 5,000,000 cfu/g to less than 100 cfu/g.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the following claims.