Typical antimicrobial agents, difficult food matrices, and the significance of matrix confirmation
Whether they are purposefully introduced or occur spontaneously, microbial inhibitors are crucial to food safety. Numerous of these compounds have a reputation for inhibiting or inactivating microorganisms that could otherwise compromise the food product’s safety or quality. Even though they are not inhibitory, some food matrices have physical characteristics (such as thickening) that could make it more difficult to use analytical techniques. Because these matrices can prevent the target bacterium from being detected or quantified, they can present difficulties for analytical microbiology laboratories.
Understanding these inhibitory substances and how to appropriately enrich the product is crucial when working with newer ingredients or final product formulations in order to ensure effective target microorganism identification or enumeration. Inhibitory drugs and difficult matrices that are frequently encountered at NQAC Dublin will be covered in this article, along with the methods used to guarantee correct results.
Sugars and salts
As one of the most often used ingredients in concentrated flavor bases and seasoning blends, salt is perhaps the most prevalent microbial inhibitor in food items. Salt creates an isotonic solution in aqueous solutions when it is employed at the ideal concentration (0.85-0.90 percent), meaning that water flows equally from the microbe to the surrounding environment and vice versa. But at concentrations more than five percent, a process known as plasmolysis occurs where water exits the cell more quickly than it enters.1. This causes the cell to become dehydrated, which may restrict microbial development or possibly cause the cell to die.
The same amount of sugar (lactose, fructose, and sucrose) is needed to provide the same effect as salt; that is, six times as much sucrose is needed to produce the same amount of microbial suppression.1. To counteract the inhibitory effects of salts and/or sugars, an enhanced enrichment dilution, such as 1:20, may be adequate in most cases. However, the dilution may need to be increased to 1:200 based on concentration or the presence of other inhibitory chemicals.
agents that thicken
Although food matrices with thickening qualities may capture and separate target bacterial cells from the enrichment media, they are not intrinsically suppressive. In most circumstances, an enrichment in buffered peptone water (BPW) supplemented with α-amylase can be used at a ratio of for starchy items such as cereals, snack puffs, cookies, potato flakes, oats, fiber, and pure starch. The potency of the thickening properties, however, may require higher enrichment dilutions up to 1:100. Gums (xanthan, carrageenan, guar, etc.) might require supplementing with 1% cellulase to lower viscosity, or at least a enrichment dilution without it.
The thickening qualities of egg powders can differ; some goods just need a 1:10 enrichment, while others might require
Solid fats, oils, or goods with a high fat content
Although the goods in this category are not microbially inhibitory, the presence of microorganisms in the fat layer may hinder them from coming into touch with the aqueous enrichment broth. Products such as oils, solid fats (like tallow), cheeses, coffee creamers, dressings, flavor bases, coconut, legumes, seeds, nut butters, lecithin, and cooked (fried) or cured meats are examples of this category. An adequate enrichment dilution and BPW supplemented with one percent Tween 80 can be utilized to help the fat layer become more soluble in the enrichment media.
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Taste enhancers and extracts
Liquid flavourings can pose a challenge for the microbiology laboratory due to the proprietary formulations of the product, as well as their ingredients. These products can contain ethanol that serves as a carrier solvent and flavour enhancer. However, ethanol is well known for its lethal desiccant and denaturant effects on microorganisms.1 Another component of liquid flavours is propylene glycol, which is generally recognised as safe (GRAS) and is used to evenly distribute the flavour and maintain flavour quality.5 Propylene glycol is also known to be inhibitory to various microorganisms.
Vanilla, specifically its compound vanillin, is another common flavouring agent that is known to be inhibitory or even lethal to microorganisms by negatively affecting enzymatic processes, membrane integrity, or genetic material.1,7 Flavourings can vary in microbial inhibition depending on their composition; therefore, it is essential to determine the appropriate enrichment dilution. At NQAC Dublin, we have found that enrichment dilutions can go as high as , especially if vanilla or cinnamon are part of the flavouring components.
Herbs and spices constitute a large group of plant products with numerous food applications – as additives, flavourings, and even as antimicrobials/preservatives.3,4,8 Food items in this group that NQAC Dublin commonly encounters include onion, garlic, basil, thyme, oregano, clove, cinnamon, rosemary, sage, coriander, paprika, turmeric and ginger. Each herb or spice has its own unique constituents that provide antimicrobial characteristics, including phenolic compounds, essential oils, organic acids, aldehydes, ketones, alcohols, or sulphur-containing compounds, with essential oils and phenolics being the most potent.2