1/28/2024 0 Comments Water activityThe effects of water activity and pH can be combined through hurdle technology to control microorganisms more effectively. Water activity and pH-more powerful together Many chemical reactions are pH dependent and can be prevented or controlled by adjusting pH. This is often done through pickling or fermentation, which use microbial action, enzymatic reactions, or acids such as vinegar to induce the production of lactic acid. Additionally, some manufacturers adjust pH to change flavor. pH microbial growth limits for specific types of bacteria Microorganismsīecause of microbial growth limits, lowering pH is an effective way to preserve foods and prevent the growth of microorganisms and can also be used as a critical control point in HAACP plans. Historically, a pH of 4.6 was considered to be the lower growth limit, but portions of the food code were changed when it was discovered that some problematic microbes can grow in pH levels as low as 4.2. Some microorganisms can go as low as 4.6 and even down to 4.4. Most of them stop growing at a pH of 5.0. All microorganisms prefer a neutral pH for optimum growth, but they can grow in more acidic pH values. Table 2 shows the minimum pH limits for the growth of different types of microorganisms. Just as with water activity, microorganisms have pH limits below which they will not grow. Foods tend to be either neutral or acidic. Distilled water, which is neutral, has a pH of 7. Values between 0 and 7 indicate acidity values between 7 and 14 indicate alkalinity. PH is a measure of the degree of acidity or alkalinity of a solution. If the growth-limiting effects of lowered pH are combined with water activity control, however, microbial growth can actually be controlled at a higher water activity than shown on the chart. The growth limits in Table 1 assume that all other conditions (pH, temperature, etc.) are optimal for the growth of the organism. Microbial growth limits make water activity an excellent tool for assuring the safety of food products, and water activity measurement can be used as a critical control point in HACCP plans. Whole egg powder, cocoa, liquid center cough dropĬrackers, starch-based snack foods, cake mixes, vitamin tablets, suppositoriesīoiled sweets, milk powder, infant formula Jam, marmalade, marzipan, glace fruits, molasses, dried figs, heavily salted fishĭried fruits, corn syrup, licorice, marshmallows, chewing gums, dried pet foodsĬaramels, toffees, honey, noodles, topical ointments Sweetened condensed milk, aged cheeses (cheddar), fermented sausage (salami), dried meats (jerky), bacon, most fruit juice concentrates, chocolate syrup, fruit cake, fondants, cough syrup, oral analgesic suspensions Vegetables, canned fruit, canned vegetables Water activity growth limits for many common microorganisms As long as product developers keep the water activity below this limit, the microbe in question won’t replicate to high enough levels to cause infection or illness. Some types of molds and yeasts have adapted to withstand very low water activity levels.Įach organism has a specific water activity at which it will stop growing. That’s why there are different growth limits for each organism. Different organisms cope with osmotic stress in different ways. The microorganisms are not eliminated, they just become unable to reproduce. When water activity outside the cell becomes low enough, it causes osmotic stress: the cell cannot take up water and becomes dormant. This water movement mechanism depends on a water activity gradient-on water moving from a high water activity environment outside the cell to a lower water activity environment within the cell. They take up water by moving it across the cell membrane. Like all organisms, microorganisms rely on water for growth. How water activity prevents microbial growth Here’s how you can use the combined power of water activity and pH to increase microbial control using milder preservation techniques, which may result in improved product texture and quality. This synergistic effect is described in detail by hurdle technology for microbial control and is an intricate part of the FDA’s definition of potentially hazardous foods. Water activity and pH work synergistically, with their combined effects being more powerful at control than their individual effects. Water activity and pH are the two most important intrinsic factors that determine if a product will support the growth of a spoilage microorganism. Here's how food manufacturers can use hurdle technology to improve formulations. Using both pH and aW controls microbes more effectively than just one or the other.
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