Water activity in bakery products

For bakery products, it is critical that they remain safe while maintaining their expected texture and sensory properties.

One of the most important factors influencing the quality and shelf life of bakery products is water activity. Water activity control in bakery products can help prevent or minimize various reactions such as rancidity, microbiological spoilage or changes in texture due to water migration.

Water activity in baked goods and microbial safety

Microorganisms need a favourable environment to grow in a product. The most important factors controlling growth are pH value and water activity. If they are below the growth limit for the organism, it will not grow. if a microorganism is in an environment where the water activity is lower than their own water activity, osmotic stress is the result and it begins to lose water to its environment. Water moves from high water activity (energy) to low water activity. Turgor pressure is therfore reduced and retards normal metabolic activity in the microorganism. To continue reproducing, the organism must lower its internal water activity below that of the environment. It tries to achieve this by concentrating solutes internally. The ability to reduce its internal water activity using these strategies is unique to each organism. As a result of that, every microorganism has a unique limiting water activity, is the water activity under this limit the microorgansim is not able to grow. This means that the ability to grow and reproduce for any organism is connected to the energy of water (water acitvity) and if it can access that water. It is not connected to how much water is in its environment (moisture content).

Water activity in baked goods and chemical stability

Sensory changes and nutritional loss due to chemical degradation one of the most likely causes of product failure for baked goods. Chemical reactions such as Maillard browning, lipid oxidation, staling, enzymatic, etc. can affect the taste, appearance, and nutritional value of baked products. Water activity influences reaction rates by reducing activation energy, increasing mobility, and increasing the rate constant. Consequently, reaction rates are better correlated to water activity than moisture content. In general, as water activity increases so do reaction rates, but specific correlations depend on the type of product and the reaction. Most reactions will reach a maximum in the range of 0.70-0.80 aw due to dilution at high water activities, but lipid oxidation is the only reaction that increases at low water activity.

Water activity in bakery products and texture/crispiness

Bakery products are known for their pleasing texture and taste and each product has its own unique organoleptic requirements. The most common mode of failure in baked products is an unexpected change in texture or flavor. For example a butter biscuit should be crispy, and a cake should show a good mixture of firmness and moisture. Changes in water activity will result in changes in texture and each baked product has an optimal water activity range where the texture and taste will be ideal. The key then to prolonging the shelf life of these products is to manufacture them to that ideal water activity and maintain that water activity in bakery products during storage and transport with effective packaging.

Many bakery products contain multiple components such as a cream filling or an icing covering. For these products, moisture migration between components can lead to undesirable texture changes or even susceptibility to microbial growth. Moisture moves from high water activity to low water activity, so the way to prevent moisture migration and its accompanying consequences is to match the water activity of the components. The icing, cake, and cream filling of a snack cake all need to be manufactured to the same water activity before being combined and then, even if their moisture content is different, there will be no moisture migration between the components.

The most important specification: water activity in bakery products

Most bakery products are sold on a weight basis, so maximizing the amount of water, the cheapest ingredient, that can be in a product while remaining safe and stable will maximize profitability. The key is to track water activity and end processing when the ideal water activity is achieved, thereby avoiding over drying and maximizing the final moisture content which will also maximize revenue. Check out Novasina´s latest aw-meters here.