The impact of the failure of a sterile air and gas filter can be potentially catastrophic for operators in the dairy industry. If a filter has failed, but the problem has not been identified, then microbiological contamination can occur. This can lead to decreased shelf life, product recalls and the potential for costly litigation. Non-conformance to health and safety standards - coupled with damage to reputation – can have a major financial impact. Parker Bioscience Filtration Division has been working with industry leading dairy producers to create a solution to this challenge.

So what causes a filter to fail?
The primary causes of a loss of filter integrity are related to Steam In Place (SIP) cycles.

In order to maintain aseptic conditions when processing microbially sensitive foods, the sterile gas filter system and its delivery pipework should be frequently sterilized. SIP is the industry method for achieving this.

A SIP cycle can put stress on the filter as it exposes it to aggressive temperature and pressure conditions.

In addition, in some sterile gas applications – particularly where steam is introduced to the filter in the reverse direction (for instance from a sterile tank, or the aseptic zone in a filling machine) – it is necessary for bulk liquid condensate to be drained away. However, this is undesirable from a process control perspective and it may have an impact on maintaining downstream sterility. Unless the process is tightly controlled, sterile filter cartridges may be damaged by the draining of bulk liquid concentrate.

Failure can also be caused by the hydrophobic nature of sterile gas filters.

The solution 
Parker Bioscience Filtration Division, working closely with the dairy industry, has developed ASEPT-X, a range of sterilizing gas filters which have been validated to withstand harsh reverse steam sterilization processes without the need for condensate management, as they have the ability to pass bulk liquid condensate.

The unique membrane composition of ASEPT-X is capable of withstanding reverse steam cycles without fail and, therefore, can offer a greater filter lifetime compared to other sterilizing gas filters.

ASEPT-X’s robust design helps to safeguard the sterile gas process and reduce the risk of contamination, as there is less risk of a process running with a damaged filter. 

The reduction in filter failure and consequential filter replacements also means that dairy producers can save on consumable costs.

ASEPT-X filters – put to the test
ASEPT-X filters are capable of withstanding 100 x Steam In Place (SIP) cycles in the reverse direction without the requirement to drain bulk condensate and are capable of withstanding aggressive differential pressures at steam temperatures in the reverse direction of up to 1.5 barg (21.8 psig) at 140°C (284 °C).

The filters also offer best in class microbial retention and are fully validated for bacterial, spore and bacteriophage retention.

 
SIP testing
To validate the ability of ASEPT-X filters to withstand aggressive SIP cycles without the need to drain condensate, multiple batches of ASEPT-X filters were exposed to multiple 30-minute SIP cycles in a specially designed test rig in both the forward and reverse directions with no condensate drainage across the filter system.

The integrity of the filters was determined before and after SIP testing by the aerosol challenge method using a calibrated Valairdata integrity test machine.

A solution for sterile gas filter failure in dairy applications - Figure 1-summary of forward SIP telemetry - Parker Bioscience

A solution for sterile gas filter failure in dairy applications - Figure 2-differential pressure and temperature exposures - Parker Bioscience

A solution for sterile gas filter failure in dairy applications - Figure 3-summary of reverse SIP telemetry - Parker Bioscience

A solution for sterile gas filter failure in dairy applications - Figure 4-summary of differential and temperature exposures during reverse SIP testing - Parker Bioscience

 
Aerosol challenge testing
This was used to determine the microbial retention efficiency of filters in their typical mode of operation when acting as sterile gas filters.

Two microorganisms were used to determine the microbial retention efficiency of ASEPT-X filters in the aerosol phase: Bacillus atrophaeus NCTC 10073 and MS-2 Bacteriophage NCIMB 10108.

The challenge apparatus was designed to challenge filters with high concentrations of airborne microorganisms for relatively short times. A suspension of microorganisms in aqueous solution was nebulised by a collison spray forming a fine aerosol containing viable microorganisms. The aerosol was then drawn through connecting stainless steel pipework leading to the filter housing containing the ASEPT-X test filters.

The efficiencies of the filters were calculated by determining the airborne concentration of viable microorganisms upstream and downstream of the filter using suitable aerosol sampling techniques and microbial assay methods.

The retention efficiency of the filters is expressed in terms of log reduction value (LRV) where:

LRV = log10 number of organisms challenging the filter
                    number of organisms recovered in filtrate
 

The results of the aerosol challenging testing are as follows:

Test organism

Total challenge level

Challenge level per cm²

Log reduction value (LRV)

Bacillus atrophaeus

2.38 x 1010 cfu

3.78 x 106 cfu

11.8

MS-2 Bacteriophage

2.06 x 1011 pfu

4.13 x 108 pfu

>11.3

Liquid challenge testing
Liquid bacterial challenge testing of ASEPT-X filters was carried out to determine the microbial retention efficiency when passing bulk condensate.

The testing was based upon methodologies outlined in ASTM F838 Standard Test Method for Determining Bacterial Retention of Membrane Filters Utilized for Liquid Filtration.

Under these test conditions, the test filter was challenged with a minimum of 107 viable Brevundimonas diminuta (ATCC 19146) per square centimetre of effective filtration area. Any organisms that passed through the test filter were collected and cultured on the surface of analytical discs. The filter retention was quantified by expressing the filter’s efficiency to remove the challenge organism from the challenge suspension as a Log Reduction Value (LRV).

The results of the liquid challenge testing are as follows:

Test organism

Total challenge level

Challenge level per cm²

Log reduction value (LRV)

B. diminuta

1.66 x 1011 cfu

2.65 x 107 cfu

10.6

Conclusion
The test work we have undertaken qualifies the suitability of ASEPT-X filters for use as sterilizing grade gas filters for critical gas filtration applications in food and beverage production. This solution provides greater confidence to operators in the dairy industry, reduces expenditure on consumables and crucially, reduces the risk of contamination in aseptic processing.

 Ian CurranThis post was contributed by Ian Curran, market development manager, Parker Bioscience Filtration Division, United Kingdom.

Parker Bioscience Filtration Division offers filtration solutions to protect the quality and taste of beverage products. By working with our application experts, manufacturers can develop a tailored solution to ensure their beverage is free from contamination, full of flavour and visibly clear.