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Discussion Threads: Questions from the Field

Question:

In conversations concerning extending shelf-life, I have heard a food professional refer to the term, “competitive exclusion”. What were they talking about, and how does that help in shelf-life extension?

Answer:

Competitive exclusion is a term that refers to the situation where favorable bacteria are present in large numbers in a food and “compete” with spoilage bacteria for the same food source. Since the favorable bacteria are present in such a large number already and the microflora population is already established, they effectively “exclude” the spoilage bacteria to some degree. Consider the fact that if many millions of cells of favorable non-spoilage bacteria, such as lactic acid bacteria are already present in a dairy product, it makes it extremely difficult for spoilage bacteria to gain a foothold in the dairy product and spoil it.

One prime example is cottage cheese dressing. Cottage cheese dressing cultures are available that “seed” the dressing with many millions of lactic acid bacteria per gram of dressing. Because of their presence, it makes it difficult for other spoilage microorganisms to thrive and grow in the finished cottage cheese since the lactic acid bacteria population is already so high in the dressing. The spoilage bacteria compete with the lactic acid bacteria so they can grow and multiply. Since one competes with the other, we refer this type of method to extend shelf-life with the use of another culture as “competitive exclusion”.

The favorable bacteria culture effectively excludes the other based on competition for the same nutrients (lactose) that the bacteria need to thrive on. This type of food preservation in cottage cheese is considered just one of many tools or hurdles that you can use to extend shelf-life. As I discussed in a previous issue, if you combine a dressing culture with a chemical preservative or a natural one such as DuPont’s Microgard 100, 200 or 430, and with CO2 gas sparged right into the dressing, you have the most protection against spoilage microorganisms as you possibly can. This assures your dairy of the longest shelf-life possible for a cold packaged cottage cheese. In the past a 28-30 day shelf-life was the norm. Adding the “hurdles” described above can lengthen the shelf-life to 50-54 days or more. The preservation methods described above combine to create “growth hurdles” for the spoilage bacteria to overcome, and many times are referred to as “hurdle technology”.

Fig. 1 – Photo of CO2 gas spargers
Fig. 2 – Photo of CO2 being sparged into water
Fig. 3 and below – DuPont antimicrobial ingredients that can be used as part of hurdle technology (note – nisaplin is not approved for use in cottage cheese)

Product Benefit Application
MicroGARD® 100 Anti-Gram-negative bacteria, Anti-yeasts and molds Cultured skim milk-based Yogurts, cottage cheese, sour cream, dairy desserts, fresh cheese (quark), filled chocolate confections
MicroGARD® 200 Anti-Gram-negative bacteria, Anti-yeasts and molds Sauces, dressings, pasta, side dishes, baked goods incl. fruit applications
MicroGARD® 300 Anti-Gram-positive bacteria, Cultured skim milk-based Cottage cheese, flavored dairy drinks, custards and dairy desserts
MicroGARD® 430 Anti-Gram-positive bacteria, Anti-Gram-negative bacteria, Anti-yeasts and molds, Cultured skim milk-maltodextrin based Cottage cheese and other food products