What is Lysozyme?
Lysozyme, also known as muramidase, is a naturally occurring enzyme that acts as a potent antimicrobial agent by breaking down the peptidoglycan layer in the cell walls of many bacteria, particularly Gram-positive types. This lysis, or breakdown, causes the bacteria to die, making lysozyme an important component of the innate immune system in humans and animals. It is found in various bodily fluids, such as tears, saliva, and milk, serving as a first line of defense against pathogens. Beyond its biological role, purified lysozyme, primarily from hen eggs, is widely used in the food industry as a safe, natural preservative to extend shelf life and enhance food safety.
The Richest Natural Food Sources
While lysozyme is present in many living organisms, a few food sources are particularly rich in this antibacterial enzyme.
Egg Whites
Hen egg white is, by far, the most concentrated and well-known food source of lysozyme. The enzyme makes up approximately 3-4% of the total protein content in egg white, providing a natural defense to protect the developing embryo from bacterial contamination. This high concentration and easy availability have made chicken egg white the primary industrial source for producing commercial lysozyme. Other avian eggs, such as those from ducks and geese, also contain high levels of lysozyme, though generally in lower concentrations than hen eggs.
Milk and Dairy Products
Lysozyme is naturally present in the milk of mammals, where it plays a protective role in the developing gut of infants. The concentration varies significantly by species. While human milk contains high quantities of lysozyme (55-75 ppm), providing vital immune support to infants, cow milk has much lower levels (10-15 ppm). Interestingly, donkey milk is an exception among domesticated animals, containing a very high lysozyme content, comparable to human milk, making it a noteworthy source. Lysozyme is also added as a preservative (E 1105) during the cheesemaking process, particularly for hard and semi-hard cheeses like Gouda and Parmigiano. This is done to prevent a defect called "late-blowing," caused by the bacterium Clostridium tyrobutyricum.
Plant-Based Sources
Though not as concentrated as in eggs or certain milks, some fruits and vegetables have been found to contain detectable levels of lysozyme activity. Studies have identified lysozyme in the juices of several plants, although the concentrations are typically much lower. Some notable plant sources include:
- Cauliflower: Detected levels range around 25-28 ppm in the juice.
- Cabbage: Cabbage juice has shown lysozyme activity, though in smaller amounts (7-8 ppm).
- Papaya: The latex of papaya plants contains lysozyme, with research showing it possesses antibacterial properties, though with less lytic activity than hen egg white lysozyme.
- Radishes: Various types of radish have displayed lysozyme activity.
Lysozyme as a Food Additive
Purified lysozyme, most often from hen egg white, is a widely used food preservative approved for use under the code E 1105. Its primary function is to inhibit the growth of spoilage and pathogenic bacteria in a variety of foods, thereby extending shelf life and enhancing safety.
Lysozyme is commonly added to:
- Cheeses: Used to control the growth of spoilage-causing bacteria in both hard and soft cheese varieties.
- Wine and Beer: Inhibits lactic acid bacteria that can cause unwanted malolactic fermentation and spoilage.
- Ready-to-Eat Meats and Seafood: Applied directly or incorporated into packaging to reduce microbial contaminants like Listeria monocytogenes.
- Tofu and Seafood: Helps to preserve freshness and prolong shelf life.
Comparison of Lysozyme Concentrations
The following table compares the typical concentrations of lysozyme found in some natural food sources. Note that concentrations can vary based on factors like breed, processing, and age.
| Source | Lysozyme Concentration (ppm) |
|---|---|
| Hen Egg White | 2,500–3,500 |
| Duck Egg White | 1,000–1,300 |
| Goose Egg White | 500–700 |
| Donkey Milk | 500–1,000 |
| Human Milk | 55–75 |
| Cauliflower Juice | 25–28 |
| Cow Milk | 10–15 |
| Papaya Juice | 8–9 |
| Cabbage Juice | 7–8 |
The Benefits and Considerations of Dietary Lysozyme
While lysozyme's function as a preservative is clear, its potential health benefits when consumed through diet are still being explored. For infants, the high levels of lysozyme in human milk are understood to provide a key defensive component for their immature immune systems. However, the digestive process and processing methods can affect the enzyme's activity, and for many adults, dietary lysozyme may not have a significant impact on internal bacterial populations.
For most people, the lysozyme content in commonly consumed foods is low. For individuals with egg allergies, consumption of foods containing egg-derived lysozyme (E 1105) can pose a risk and requires careful label reading. Conversely, sources like donkey milk, which have a very high concentration, trigger fewer allergies compared to egg-derived lysozyme and may offer additional nutraceutical benefits.
Conclusion
When considering what foods are high in lysozymes, hen egg white stands out as the most abundant natural source. However, other animal-derived foods like donkey milk and some fermented dairy products also contain notable concentrations. While some plants have detectable lysozyme, the levels are significantly lower. For the consumer, understanding which foods are naturally rich in this antimicrobial enzyme and where it is added as a preservative can help inform dietary choices. For food manufacturers, the efficacy and safety of lysozyme, particularly hen egg white lysozyme, make it a reliable tool for enhancing product safety and extending shelf life.
Learn more about lysozyme and its applications in the food industry in this detailed review: Use of Hen Egg White Lysozyme in the Food Industry.
