Food Spoilage Bacteria Reduction or Removal
Final membrane filters, used in food spoilage reduction, are made from membranes and are associated with a specific integrity test value.
While filter membranes are often thought of as simple sieves or screens, they are actually complex matrices that create convoluted and tortuous pathways to entrap particles, food spoilage microorganisms or bacteria. In simple terms, under a microscope, instead of resembling a screen, the food spoilage reduction membrane looks more like a sponge.
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Food & Beverage
How are the food spoilage bacteria removal capabilities of a filter determined?
Typically, filter removal capabilities are determined by performing a bacterial challenge test. A bacterial challenge test is a process of validating a final membrane filter. It is a test that essentially exposes the final membrane filter assembly to a known suspension of a model microorganism (one that resembles common food spoilage bacteria).
Some of the typical microorganisms used in a bacterial challenge test for the food and beverage market are:
The microbial removal rating of a final membrane filter is related to the average cross-section of the microorganism it is being challenged with.
Filters are Qualified Under Controlled Conditions with Model Organisms
- A known number of microorganisms in a solution are pumped through a membrane filter.
- After the solution passes through the membrane filter, a sample is collected in an analysis membrane or disc.
- Then, the number of colonies in the analysis disc is recorded.
- Finally, the number of microorganisms, before and after filtration, is compared, and the results can be expressed using the following terminology:
a. Titer Reduction = Number of microorganisms before filtration, divided by the number of microorganisms after filtration.
b. LRV = This is a mathematical conversion (of a more complex number into a simpler number) of the titer reduction.
c. Microbial Removal Efficiency = What percentage of all microorganisms passing through the membrane filter will be retained (or filtered).
d. Probability = What is the probability that 1 cell of the model microorganism will pass through the membrane (or not get filtered).
All of the above expressions are used to describe how good a final membrane filter is at removing food spoilage microorganisms, or food spoilage bacteria, from a solution. They all mean the same but are expressed differently.
For example, if a final membrane filter is described with the expressions below, it can be interpreted in “common language” as follows:
What does this mean for you as a food and beverage processor?
It means that when you are shopping for a final membrane filter to help you control and remove food spoilage bacteria in your product, you can compare filters in the market based on their retention capabilities, regardless of how these are communicated or claimed. It is a way to compare “like-to-like.” This is very important because the bacterial retention differences can be significant, even if, on the surface, it does not appear that way.
For example, let’s say you are comparing final membrane filters X vs. Y. Let’s assume that everything between filter X and Y is exactly the same, except for their LRV’s. Filter X claims to have a spoilage bacterial retention expressed as LRV5 vs. that of filter Y of LRV8.
The question you should ask yourself is, is this significant? Well, let’s translate the bacterial retention claims into simpler language:
From a food safety perspective, the above means that contamination using filter X (0.001% probability of contamination) is 1000 times more likely than if you use filter Y (0.000001% probability of contamination).
If we further simplify this comparison, suppose that you fill 1 million bottles of your best-selling beer after filtering with filter X, then 1000 of them will show spoilage contamination.
Whereas if you fill the same 1 million bottles of the same product after filtering with filter Y, then only 1 bottle will show contamination!
Membrane filters can provide a microbial reduction or sterile effluent depending on customer requirements and application.
The main objective of a microbial retention membrane filter, also known as final membrane filters, is to reduce or eliminate the presence of a certain microorganism that may be present in the effluent of a product; more importantly for the food industry, spoilage bacteria.
Failing to do so may result in spoilage of the final product, therefore reducing its claimed shelf life, causing consumer complaints or even costly recalls.