Nisin in special medical purpose foods

Food for Special Medical Purposes (FSMP) refers to a category of food products designed to provide precise nutritional support for populations with restricted eating ability, digestive and absorption disorders, metabolic disturbances, or specific disease conditions. Its core requirements not only include "nutritional adaptation" but also strict control of microbial contamination risks. This is because the target populations (such as cancer patients, post-surgery recovery patients, infants and young children, and frail elderly individuals) generally have weakened immune function and impaired intestinal barrier function. Once contaminated by pathogenic bacteria, they are highly susceptible to infectious complications (e.g., sepsis, intestinal infections). As a natural, safe, and targeted antibacterial agent, nisin is well-suited to meet the "safety-first" principle of FSMP while adapting to specific needs in different scenarios. Currently, it has formed clear application directions in various types of FSMP.

From the perspective of application scenarios, the use of nisin in FSMP mainly focuses on two core needs: "control of high-risk microorganisms" and "protection of nutritional stability," with adjustments to its application method based on the physiological characteristics of the target population.

First, it is most widely used in enteral nutrition preparations (e.g., short peptide-type, amino acid-type, and total nutrient formula powders/liquids). Enteral nutrition preparations serve as the primary source of nutrition for most people unable to eat normally by mouth (such as post-surgery fasting patients, stroke patients, and intensive care patients). These preparations are typically rich in nutrients like protein, carbohydrates, and fats, and are often in liquid form or as easily soluble powders. During storage, after opening, or during continuous infusion, they are highly prone to contamination by Gram-positive pathogenic bacteria (e.g., Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus). These bacteria not only cause spoilage of the preparation but also produce toxins (such as Staphylococcus aureus enterotoxin) that can trigger acute reactions like vomiting and diarrhea. For individuals with weakened immunity, such infections may progress to severe conditions. Nisin can specifically inhibit the growth of these Gram-positive bacteria and the germination of their spores. Moreover, it can be decomposed into amino acids by human digestive enzymes, without increasing the intestinal metabolic burden or reacting with nutrients like vitamins and minerals in the preparation. Therefore, it is often added to enteral nutrition preparations, especially those requiring long-term use after opening (e.g., formula powders for multiple reconstitutions) or short-term storage at room temperature (e.g., ready-to-use nutrient solutions). It not only extends the usable period after opening but also avoids nutrient loss (e.g., destruction of heat-sensitive vitamins) caused by excessive heat sterilization, balancing the contradiction between "sterilization effectiveness" and "nutrient retention."

Second, in FSMP for specific disease states, the application of nisin needs to achieve "precision adaptation" based on disease characteristics. For example, in FSMP for cancer patients: cancer patients often have compromised immune function due to chemotherapy and radiotherapy, accompanied by intestinal mucosal damage, resulting in significantly reduced resistance to pathogenic bacteria. Meanwhile, such formulas need to be rich in high-quality protein and immune-regulating nutrients (e.g., glutamine, ω-3 fatty acids) to support body repair, and the high nutrient content also increases the risk of microbial growth. The addition of nisin can specifically control Gram-positive bacteria that may cause infections (e.g., Listeria monocytogenes—this bacterium can multiply even in low-temperature environments, is difficult to inhibit with conventional refrigeration, and has a high mortality rate in immunocompromised populations). Additionally, its natural properties do not cause antagonistic effects with immune-regulating components in the formula, nor do they increase the metabolic burden on the liver and kidneys (cancer patients often have abnormal liver and kidney function), meeting the requirement of "low metabolic load." Another example is FSMP for infants and young children (e.g., formulas for premature infants, special formulas for amino acid metabolism disorders): the intestinal barrier and immune system of infants and young children are not yet fully developed, making them extremely intolerant to microbial contamination. Moreover, components like lactose and whey protein in the formula are prone to attracting pathogenic bacteria. The use of nisin in such products requires strict dose control (in compliance with national standards for food additives in infant food), mainly to inhibit Staphylococcus aureus and Staphylococcus epidermidis—bacteria that may cause sepsis in infants. Since nisin can be rapidly decomposed by proteases in the infant digestive tract, it does not interfere with the normal establishment of the infant intestinal flora (unlike antibiotics, it does not cause flora imbalance) nor trigger allergic reactions (its molecular structure has no cross-reactivity with common allergens in infants), making it the preferred choice that balances safety and antibacterial effectiveness.

Third, in oral supplement-type FSMP (e.g., protein modules, fat modules, vitamin and mineral supplements), the application of nisin focuses on "extending shelf life and ensuring safety after opening." Most of these supplements are in powder or emulsion form for single or multiple doses. Some products need to be stored at room temperature after opening (e.g., when carried outside), and the target populations (such as frail elderly individuals and chronic kidney disease patients) often have long usage cycles and low frequency of use after opening, making the supplements susceptible to bacterial growth due to repeated exposure to air and saliva during opening. The addition of nisin can effectively inhibit the proliferation of Gram-positive bacteria during storage, particularly exerting a clear inhibitory effect on Staphylococcus aureus introduced by improper handling (e.g., using an uncleaned spoon to scoop powder). This prevents nutrient inactivation or health risks caused by excessive microbial levels in the supplements. At the same time, it does not affect the absorption and utilization of core nutrients (e.g., whey protein, fish oil, vitamin D) in the supplements, ensuring the dual goals of "nutritional supplementation" and "safety guarantee."

In terms of application advantages, the core of nisin’s suitability for FSMP lies in the dual alignment of its "safety" and "targeting." Compared with chemical preservatives (e.g., benzoates, sorbates), nisin’s natural origin and degradable properties make it more suitable for special populations who need to take FSMP for a long time—even with long-term intake, it does not accumulate in the body, impose a burden on liver and kidney function, or cause chronic toxic reactions, which is highly consistent with the "long-term nutritional support" demand of FSMP. Compared with broad-spectrum antibacterial agents (e.g., certain organic acids), nisin only targets Gram-positive pathogenic bacteria and has almost no impact on beneficial Gram-negative bacteria in the intestine (e.g., Bifidobacterium, Escherichia coli), avoiding intestinal flora imbalance caused by overly strong antibacterial effects. This is especially suitable for FSMP target populations with inherently fragile intestinal barrier function (e.g., patients with inflammatory bowel disease). Additionally, nisin has good thermal stability (it can withstand a certain degree of heat sterilization under acidic conditions) and is compatible with FSMP production processes (e.g., spray drying, ultra-high temperature instantaneous sterilization). It does not lose effectiveness during processing nor cause adverse reactions with other components in the formula, ensuring the stability and consistency of the product.

However, the application of nisin in FSMP must also adhere to strict principles of "dose control" and "scenario adaptation." On one hand, the added dose needs to be adjusted based on the type of FSMP (e.g., liquid vs. powder, ready-to-eat vs. reconstitutable) and the target population (e.g., infants vs. adults, normal vs. abnormal liver/kidney function) to ensure that while achieving antibacterial effects, it does not exceed the limits specified in national food safety standards for FSMP. On the other hand, excessive use of nisin in FSMP with "no clear microbial risk" (e.g., nutritional supplements for short-term use by healthy people) should be avoided. The core principle should always be "controlling necessary risks" rather than pursuing "absolute sterility," ensuring a balance between the "nutritional attributes" and "safety attributes" of FSMP.

With its characteristics of natural safety, targeted antibacterial activity, degradability, and compatibility with processing technologies, nisin has become an important auxiliary component for controlling microbial risks in FSMP. Its application scenarios cover core categories such as enteral nutrition preparations, disease-specific formulas, and oral supplements. It not only addresses the problem of high susceptibility to microbial growth in FSMP due to high nutrient content but also adapts to the "low burden, high safety" nutritional needs of special populations. It is a typical example of the combination of "safe preservation" and "precision nutrition" in the FSMP field.