WO1994012062A1

WO1994012062A1 - High temperature, short time sterilization and sterile filling

Info

Publication number: WO1994012062A1
Application number: PCT/US1993/010846
Authority: WO
Inventors: Alan R. Dudleston; Frank Bing, Jr.; George L. Curtiss; John F. Grillo; Erling Carl Nelson
Original assignee: Abbott Laboratories
Priority date: 1992-11-25
Filing date: 1993-11-04
Publication date: 1994-06-09
Also published as: AU5598394A

Abstract

A process for the high temperature sterilization of liquids in a short period of time and an apparatus therefor. The liquid is heated to a sterilization temperature and is maintained within about two degrees of that temperature for a sufficient amount of time to be sporicidal. The apparatus (10) has a first heat exchanger (20) in which is placed a coil of tubing (21) through which the liquid to be sterilized is pumped. Steam is introduced into the first heat exchanger (20) via steam line (22) at a temperature sufficient to heat the liquid to a desired temperature in about 2 seconds. The length of the tube (21) is sufficient to ensure that the liquid is maintained at elevated temperature for a time period that is sporicidal. The liquid then flows to a second heat exchanger (28) where it is cooled to a temperature that is less than sporicidal. An automated fill zone is optionally provided wherein the sterile liquid is introduced into presterilized containers (42) in sterile atmosphere.

Description

HIGH TEMPERATURE, SHORT TIME STERILIZATION AND STERILE FILLING Technical Field

The present invention is directed to a high temperature, short process time sterilization and sterile filling process and apparatus, the apparatus consisting of a sterilization unit and a compact sterile fill zone unit. Background of the Invention

There is a great need for processes and apparatus for sterile filling of packaged articles. Microbial contamination of packaged foods and drugs is unacceptable and is sought to be avoided. Unfortunately, economies of scale dictate mass production of food and drug items. Mass production is difficult to accomplish under sterile conditions. Where possible, it is preferable to sterilize the product immediately prior to filling or otherwise packaging the product for shipment and sale, as opposed to maintaining sterility throughout the manufacturing process.

Representative processes for sterilizing products and the containers in which they are to be packaged are disclosed in U.S. Patent No. 3,579,631 to Stewart et al. and U.S. Patent No. 3,892,058 to Kanatsu et al. Current production methods require that products be sterilized and packaged quickly to ensure that a backlog does not develop at the sterilizer and to minimize the possibility of contamination of the product or container.

Microbial contamination in liquid products can be eliminated by heating the solution; the higher the temperature, the more quickly the sterilization is accomplished. There is, however, an upper limit to the temperature to which liquid products can be exposed before they begin to degrade or are otherwise adversely affected. Microbiological inactivation kinetics are first-order (log linear) while chemical degradation kinetics are zero-order (linear). Theoretically then, heat sensitive Uquids which degrade at longer low temperature cycles of around 115°C (239°F) can be sterilized at higher temperatures of about 127°C (260°F) to about 136°C (277°F) if a shorter cycle time is used, yet exhibit little chemical degradation using the process and apparatus of the present invention.

Furthermore, in order to ensure that microbial contamination is eliminated, the entire liquid must be heated to a uniform temperature. Prior art processes that sterilize Uquids or other products using heat are plagued by the problem of inadequate heating of those portions of the liquid or product that are remote from the surface to which the heat source is appUed, as heat must migrate to these remote portions. If the remote portions of the liquid or product are not heated to the desired sterilization temperature, microbial contamination is not eliminated and the liquid or product is not steriUzed.

After the liquid is steriUzed, it must be packaged for shipment or storage if it is not to be used immediately. The packaging of the Uquid must take place under conditions that will not reintroduce microbial contamination into the sterilized liquid.

It is an object of this invention to provide an apparatus and process for sterilizing a liquid in a short period of time . A sterile fill apparatus that fills containers in a sterile manner with the sterile liquid is also provided to ensure microbial contamination is not reintroduced into the sterile liquid during packaging. Summary Of The Invention

The present invention is directed to an apparatus and process for the steriUzation and sterile filling of Uquids. The process heats the Uquid to be sterilized to a high steriUzation temperature, for example to at least about 127°C (260°F), in a short process time, for example in about two seconds, and maintains the Uquid to within about two degrees or less of the sterilization temperature for a sufficiently sporicidal time. The liquid is then cooled to a temperature that is somewhat less than sporicidal.

The apparatus facilitates in-line sterilization of Uquids. The apparatus has a first and a second heat exchanger connected in series, each of which, in a preferred embodiment, contains about 50 Unear feet of 3/8 inch diameter coiled heat-conductive tubing. The first heat exchanger uses pressurized steam as a heating medium and the second exchanger uses water as a coolant. The liquid to be sterilized is pumped through the tubing by a variable speed magnetic gear pump.

Flow rates of liquid through the apparatus are from 0-5500 milliliters (ml) per minute. The volumetric capacity of the tubing is approximately 700 ml for each coil of tubing. Steam pressure capacity for the first heat exchanger is in the range of about 15 to 100 psig, which correlates to a temperature of approximately 121°C (250°F) to 170° C ( 338°F) for saturated steam. The system is optionally designed to allow in- place steam sterilization of the fluid path of all components prior to use.

The apparatus also includes a sterile fill zone attached thereto. The apparatus automatically fills sterile containers with the sterilized liquid from the sterilization apparatus in a sterile environment with _ minimal handling of the sterile containers prior to automatic fill. The fill zone is provided with an enclosure into which the sterile containers are conveyed. Sterile air is passed through the enclosure to keep air borne contaminants away from the containers while they are automatically uncapped, filled and recapped. The filled containers are then conveyed from the enclosure as the next batch of containers enters the enclosure.

The objective of high temperature steriUzation in a short process time is accompUshed by heating the solution to within about 2°C of the sterilization temperature in approximately 2 seconds and maintaining that temperature for a sufficient amount of time to be sporicidal. Sterile filling is accompUshed in the sterile fill zone.

Other features and advantages of the present invention wiU become readily apparent from the following description , the accompanying drawings, and the appended claims. Brief Description of the Drawings

FIGURE 1 is a schematic representation of the liquid sterilization apparatus;

FIGURE 2 is a front sectional view of the sterile fill zone portion of the apparatus prior to the uncapping and filling operation;

FIGURE 3 is a front sectional view of the sterile fill zone portion of the apparatus during the filling operation; and

FIGURE 4 is a side view of FIGURE 3. Description of the Preferred Embodiment

While the present invention is susceptible of embodiments in various form, there is shown in the drawings and presently described a preferred embodiment, with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated.

Referring to FIGURE 1, a Uquid to be steriUzed, for example, an aqueous suspension of biological material, an emulsion, or a solution is introduced into the steriUzation apparatus 10 from inlet 40 or can be recirculated from reservoir 12 via recirculation line 14. The Uquid is drawn from the inlet 40 or the reservoir 12 by a pump 16. For example, the pump 16 may be a variable speed magnetic gear pump with a capacity of up to 5.5 Uters per minute.

The liquid to be steriUzed then flows through line 18 to heat exchanger 20 of the apparatus 10. The solution flows through heat exchanger 20 via heating coil 21. In a preferred embodiment, coil 21 is made of at least 50 linear feet of coiled 3/8 inch diameter stainless steel tubing.

Steam is introduced into the heat exchanger 20 of the apparatus 10 via steam line 22. A controller (not shown) regulates the flow of steam by receiving a signal from pressure sensor 23 which is in fluid communication with the steam side of heat exchanger 20. In a preferred embodiment the steam is saturated steam in the range of 15 to 100 psig. Condensed steam exits the heat exchanger 20 through condensation line 24.

The sterilized liquid exits the heat exchanger 20 via exchange line 26 and flows into cooling heat exchanger 28 via cooling coil 30. Heat exchanger 28 may be an open water bath heat exchanger or other known cooUng apparatus, for example. Cooling water at 15°-20°C (59°-68°F) enters the heat exchanger 28 via water inlet line 32 and exits the heat exchanger 28 via water outlet line 34. Cooled, sterilized liquid exits the heat exchanger 28 via Une 36 and flows via return line 38 to reservoir 12 or via product output Une 39 to sterile surge container 42.

In one embodiment for example, the shell 25 of heat exchanger 20 is enclosed in a seamless pipe with removable end caps. The pipe is made of stainless steel that is approximately sixty inches in length and six inches in diameter. The sheU 29 of heat exchanger 28 is enclosed by a stainless steel tank that is approximately twenty-four inches in length by ten inches in diameter.

The reservoir 12 is depicted as a carboy with a 5 liter capacity, but the reservoir can be a container of any capacity. A further feature of the apparatus is that steam traps (not shown) can be added to the inlet and outlet sides of the heating and cooling coils, 21 and 30, respectively, to permit in-place steam steriUzation of aU portions of the unit.

The liquid is pumped through heat exchangers 20 and 28 by means of pump 16. The flow rate is controlled by adjusting a throttle valve 52 located at the product line 36 of the heat exchanger 28 and by controlling pump speed.

At the start of the sterilization process, liquid may be initially recirculated to and from the reservoir 12. During production periods, new solution is introduced into the solution inlet 40 and valves 44 and 50 are closed and valves 46 and 48 are opened. The solution is drawn by pump 16 and circulated through the apparatus 10. After being circulated through heat exchanger 20 and 28, the sterilized solution flows via product output line 39 to sterile surge container 42 and ultimately to fill nozzle 100.

The liquid capacities of coils 21 and 30 are approximately 700 ml in both the heat exchanger 20 and 28. The reservoir 12 has preferably at least a 5000 ml capacity. Flow rates are adjustable, for example from 0 to 5.5 ml per minute. The maximum steam pressure of the system can be designed up to a range of 100 psig, which correlates to a temperature of l70°C.

Referring to FIGURES 2-4, steriUzed product from the sterile surge container 42 of the apparatus 10 is supplied to a sterile fiU zone 70 via fiU line 72. The steriUzed product may be pumped directly from the apparatus 10 to the sterile fill zone 70. Alternately, the steriUzed product from the apparatus 10 is stored in a sterile environment prior to being supplied to the sterile fill zone 70. The fiU zone 70 is enclosed in an acryUc chamber 74 and sterile air via sterile air Une 76 is introduced under positive pressure. The air is sterilized by filtration through a 0.2 micrometer pore size hydrophobic membrane cartridge filter 78. The sterile air enters the top of the acrylic chamber 74 and spreads evenly via baffles and diffusers 80 over product containers 82. The product containers 82 are conveyed in a carrier 86 into the sterile fill zone 70 via a conveyor 84, uncapped, fiUed with an aliquot of sterile liquid, recapped, and conveyed out of the acrylic chamber 74 via conveyor 84. As best seen in FIGURE 4, the carrier 86 stops at three positions: partially blocking the entrance 88; at the filling station 92; and partially blocking the exit 90.

The containers 82 to be filled are sterilized prior to being introduced into the sterile fill zone 70. The containers 82 are subjected to minimal manual handling prior to filling to reduce the amount of microorganisms introduced into the fill zone.

The sterile fill zone 70 utilizes the flow of sterile air to prevent microbial contamination during the uncapping, filling and capping of the containers 82, and to prevent the penetration of airborne microbes into the acrylic chamber 74 itself. Unwanted microorganisms are, in essence, blown from the filling area by continuous air displacement. Micro organisms are deterred from entering the chamber in the first instance by the constant flow of sterile air outward through entrance 88 and exit 90 from the acryUc chamber 74.

The air flow velocities are approximately 20 to 30 feet per minute (FPM) in the capping and fill area of the acryUc chamber 74 and from 100 to 500 FPM in the entrance 88 and exit 90 areas. A venturi effect at the entrance 88 and exit 90 of the chamber 74 is provided by the containers 82 and container carrier 86 largely obstructing both the entrance 88 and exit 90 while filling occurs. The venturi effect increases the velocity of the air flowing outward from the chamber 74 and reduces the available area through which microbes can pass into the chamber 74. Filtered air, as stated previously, is introduced into the chamber 74 at 76 and exits through the conveyor entrance 88 and exit 90 of plexiglass chamber 74.

In a preferred embodiment, the product containers 82 are test tubes that are 38 mm in diameter and 200 mm long. The tubes are filled in the sterile fill zone 70 at a rate of 6 tubes per minute. The fining rate is controlled to minimize foaming of the media. The filUng rate could be increased using known technology, however.

The containers 82 are held vertically in carriers 86 which hold a plurality of containers. The carriers are lightweight and durable. In a preferred embodiment the carriers 86 are made of a rigid plastic material such as polyvinyl chloride. The carrier 86 depicted in FIGURES 2-4 holds 4 tubes each. The carrier 86 moves with conveyor 84 until the first container 82 in the carrier 86 is approximately halfway through the entrance 88. The carrier 86 is then stopped, blocking most of the entrance 88. A relatively low volume of air flow provides a sufficient air velocity at the entrance 88 and exit 90 of the chamber 74 to disperse airborne microbial contamination away from the product containers 82. In an alternate embodiment, an electronically indexed rotary table could be utiUzed to provide a sterile filling zone enclosure with less exposure to the outside atmosphere.

Uncapping, filling and recapping of the containers 82 takes place at filling station 92. The carrier 86 is stopped and the containers 82 aligned by means of a positioning arm 94 which contacts the side of the carrier 86. At this point, the uncapping/capping head 96 is positioned over the slip caps 98 resting on top of the sterile containers 82. A vacuum is drawn by the head 96 which draws the caps 98 to the head 96 and retains them by suction. The head 96 raises the caps 98 to clear the containers 82.

The positioning arm 94, which aligns the carrier 84 for the uncapping operation, then tips the carrier 86 and the containers 82, as shown in FIGURE 3, so the uncovered tops of the containers 82 are aligned under product filler nozzles 100. A stop 102 prevents the carrier 86 from tipping too far forward. The fiUer nozzles 100 deliver a fixed volume of liquid, preferably about 105 ml, to each container 82. Because the containers 82 are tipped, the product runs down the side of the container 82 reducing the amount of foam produced.

After the containers 82 are filled, the positioning arm 94 retracts and allows the carrier 86, and the containers 82 therein to return to the vertical position under the head 96. The head 96 is then positioned over the containers 82, the vacuum is released and the slip caps 98 are thereby replaced onto the containers 82. The container carrier 86 is then transported by conveyor 84 to the exit hold position.

All of the movement of mechanisms other than the conveyor 84 in the chamber 74 is done by air cylinders (not shown) located externaUy from the acrylic chamber 74. The sequencing of operations is done by a simple programmable controUer that operates solenoid valves for control of air flow.

The following examples iUustrate the process and apparatus described generally above. The specific conditions under which the following examples were conducted are intended as representative and are not to be construed as limitations on the general principles enumerated herein.

EXAMPLE 1 Spore suspensions of Q__ sporogenes or B. subtilis 5230 were sterilized according to the process disclosed herein. The biological material was subjected to various heat inputs (Fo values) and the surviving population was determined. The results indicate that suspensions with a concentration of greater than 10⁵ spores per ml of either organism could be sterilized, i.e., the organisms rendered inactive, in a relatively short amount of time. The time that the liquid was in the coil of the heating section, (referred to herein as the dwell time) ranged between 11 and 27 seconds. The dwell times were varied with the temperature to deliver the necessary heat input to effect the desired sterilization. An apparatus as disclosed hereinabove was used to effect a sterile fiU of containers with the steriUzed biological material. The conveyor belt and various pieces of equipment with exposed surfaces associated with the linear conveyor system of the sterile fiU zone were disinfected prior to use. Excess disinfectant and other material were removed from the conveyor belt by wiping it with gauze. All connections between the sterilization unit, the reservoir, and the sterile fill zone were made aseptically. The sterile fiU zone was also sterilized by known procedures prior to use.

Approximately three liters of sterile water were processed through the sterilization unit before the biological material to be sterilized was introduced therein. The unit was then used to steriUze a soybean casein digest broth medium. AU the water and approximately one liter of the sterilized media liquid were sent to waste. The remaining media liquid was collected. The media liquid was sterilized at approximately 133°C with a dwell time of 20-22 seconds which translates to a heat input (Fo value) of 5.3-5.8. Fo is the number of

equivalent minutes at 121.11°C delivered to a product assuming a microbial Z value of 10, where Fo is mathematically defined as:

Fo = log -(T-T_ref)/Z,

where T = test temperature, (i.e. 127° C), T_ref = rerference temperature, (i.e. 121.11°C),

and Z = 10°C. After the media liquid was sterilized, the sterilization unit was shut down and the sterile fill process was commenced. Bags containing the sterile test tubes, which were 200 mm in length and 38 mm in diameter, were opened and the tubes hand-loaded onto the conveyor system carriers of the sterile fill zone.

Loaded carriers were then placed on the conveyor belt and conveyed into the sterile fill zone 70 where the tubes were filled. Approximately 100 ml of media Uquid was deUvered to each of the four tubes in the carrier. FiUed tubes were conveyed out of the sterile fill zone and the tubes removed from the carriers and placed into racks. Seventy-eight (78) tubes were filled using the above detailed procedures.

The fiUed tubes were incubated at 30°-35°C (86°-95°F) for 7 days and checked daily for signs of contamination. At the end of the incubation period, twenty tubes were selected at random and the contents of each tube tested for its ability to support the growth of low numbers of organisms. Ten tubes were inoculated with 10-100 spores of

B. subtilis var. niger per tube and ten were inoculated with 10-100 cells of

C. albicans per tube. The inoculated media were incubated at 20-25°C for seven days or until growth became discernible.

Media liquid that was processed through the sterilization unit and then introduced in a sterile manner into test tubes was found to be sterile at the end of seven days of incubation (Table 1). In addition, the media that were processed through the sterilization unit and sterile fill zone were determined to be capable of supporting the growth of B. subtilis var. niger and ______ albicans (Table 2). TABLE 1

Growth of Spores in Media Treated In SteriUzation Unit

Number of Positive (Turbid) Tubes vs. Day of Total No. of Tubes

Day of Incubation Positive Tests for

Indicator Organism vs. Number of Containers Inoculated

B. sub ili ni

1 2 3 4 5 6 7

EXAMPLE 2 Either a IL. subtilis 5230 suspension or a C. sporogenes _test suspension of an appropriate concentration was added to sterile water (about 700 ml).

For each test temperature, sterile water (about 630 ml) was added to the inlet port 40 of the steriUzation unit. This addition was followed by the addition of the spore suspension (about 700 ml) and then the addition of more sterile water (about 350 ml). In general, test temperatures of 121°, 124°, 127°, 130°, 133° and 136°C were used to treat the samples. In all experiments, temperatures were run in descending order beginning with the highest temperature. The Fo value accumulated by the test

suspension for each experiment at specific temperature was established by empirically determining the dwell time by measuring the flow rate of solution through the unit.

Table 3 (B. subtilis 5230) and Table 4 Q. sporogenes) indicate the sporicidal effect of the sterilization unit at various operating temperatures and constant dwell time. The dwell time at temperature of the suspension in the steriUzation unit was 11 seconds.

TABLE 3

Survival of ft. subtilis 5230 Spores Dwell time - 11 Seconds

EXAMPLE 3 Spore suspensions for this example were prepared by adding a ]B, subtilis 5230 suspension (0.5 ml) to sterile water (about 140 ml). Sterile water (about 630 ml) was first added to the solution inlet port 40 of the sterilization unit for each test. The spore suspension (about 140 ml) was then introduced into the sterilization unit, followed by an additional aliquot of sterile water (about 350 ml).

^* Too numerous to count Tables 5 and 6 summarize two separate sterilizations of liquid suspension of B. subtilis 5230 spores. The unit was steam sterilized for approximately 20 minutes at 121°C before the steriUzation was commenced.

After the final addition was made, sterilized solution (about 1400 ml) was removed to a sterile two Uter Erlenmeyer flask from the product outlet Une 39 of the steriUzation unit. After all the test samples were taken, the suspensions were analyzed to quantify the number of surviving organisms. Soybean casein agar was used to recover spores of

B. subtilis 5230 and yeast extract agar was used to recover spores for C. sporogenes from the sterilized Uquids.

TABLE 5

Survival of B. subtilis 5230 Spores DweU Time = 20 Seconds

TABLE 6

Survival of B. subtilis 5230 Spores Dwell Time = 27 Seconds

The sterilization unit therefore can be used to sterilize solutions at high temperatures in a relatively short time. The unit, as illustrated by Tables 5 and 6, may be operated over a wide temperature range. The data presented in Tables 5 and 6 show the relationship between spore survival and the Fo values delivered to the test suspensions.

The organisms that were recovered at 136°C (277°F) in Table 6 were most likely the result of contamination that arose during sampling and subsequent handling of the test suspensions, since no organisms were recovered from samples sterilized at test temperatures of 130°C (266°F) and 133°C (271°F)

The foregoing examples are by way of illustration only and are not intended to limit the invention in any way, except in the spirit and scope of the appended claims.

Claims

We Claim:

1. An apparatus for the high temperature short process time steriUzation of a Uquid comprising: a pump means for circulating a Uquid; a first heat exchanger in Uquid communication with the pump means which is adapted to heat the circulating liquid to within about two degrees of a steriUzation temperature in about two seconds and maintain the Uquid within about two degrees of the steriUzation temperature over a period of time that is sufficiently sporicidal to result in a sterile Uquid; and a second heat exchanger in Uquid communication with the first heat exchanger which is adapted to cool the heated liquid to a temperature that is less than sporicidal.

2. The apparatus of claim 1 further comprising means in fluid communication with the second heat exchanger for filling a container with the sterile, cooled Uquid which does not reintroduce microbial contamination into the Uquid.

3. The apparatus of claim 1 wherein steam is introduced into the first heat exchanger.

4. The apparatus of claim 3 wherein the steam is in the range of 50 to 100 psig steam at a temperature of about 148°C (298°F) to 170°C ( 338°F).

5. The apparatus of claim 1 wherein cooling water is introduced into the second heat exchanger at a temperature of about 15°C (59°F).

6. The apparatus of claim 2 wherein the filling means comprises: a housing; means for automaticaUy conveying a container to be filled into the housing; means operatively connected to said housing for providing a sterile air atmosphere in the housing; means for automatically filling the container in the housing with the sterilized liquid; and means for removing a cap from the container to be filled in the housing prior to filling the container in the housing with the steriUzed Uquid and replacing the cap on the container after the container is fiUed with the sterilized Uquid.

7. A process for the steriUzation of a solution comprising: a.) heating a Uquid to within about two degrees of a sterilization temperature; b.) maintaining the sterilization temperature of step a) within about two degrees over a period of time that is sporicidal; and c.) cooUng the liquid of step b) to a storage temperature that is less than sporicidal.

8. The process of claim 7 wherein the sterilization temperature is about 127°C to about 136°C (about 261°F to about 277°F) .

9. The process of claim 7 wherein the Uquid is flowing in a conduit at a flow rate of about 0 to about 5500 ml/min.

10. The process of claim 9 wherein the period of time the Uquid is maintained at the steriUzation temperature is at least about 9 seconds.