Extending the shelf life of food products containing fruit

Products featuring real fruit appeal strongly to today’s health-conscious consumers, but significant technical obstacles have previously limited the use of fruit-based ingredients in many products with a long shelf life. Dry product applications such as biscuits, baked goods, cereals and snacks have been especially problematic.

Fruit taps into global trend for health and wellness

Health and wellness has been the biggest megatrend in the food industry in recent years and consumer appetite for healthy eating shows no sign of diminishing. Fruit ingredients provide a colourful, tasty and attractive way to tap into this trend and create a ‘health halo’ around products.

However, in products such as cereals, baked goods and snacks, incorporating fruit has previously presented a significant technical challenge, since introducing any additional moisture poses a threat to the texture and shelf life of the finished product.

Fruit solutions that mitigate moisture transfer in a range of long-shelf-life dry foods enable companies to develop products that include a variety of fruit pieces, flakes and pastes. In other words, they enable manufacturers to include fruit in products where it would otherwise be impossible without seriously compromising shelf life.

Taura Natural Ingredients uses its Ultra Rapid Concentration (URC) technology to concentrate fruit purees and blends to below 10% moisture in less than 60 seconds. However, it is not the absolute moisture content that decides whether ingredients can be used successfully in tricky applications. The crucial parameter is water activity (A_w), which is a measure of the ability of water to migrate from a given ingredient into the surrounding food matrix.

What is water activity and why does it matter?

Water is typically bound inside a material by a combination of hydrogen bonds, ionic bonds, dipole-dipole interactions and Van de Waals forces. With such complex forces at work, the absolute amount of water in the system may not relate to the ability of water within a food to escape. As a result, manufacturers require another means to measure the tendency of water to migrate into the surrounding food matrix.

Water activity provides this means. It measures the energy status of the water in a given system. High-energy water is more able to escape than low-energy water.

How do we define water activity?

At room temperature, water molecules move from the surface of a food to the atmosphere and back again until they reach equilibrium. The definition of water activity effectively compares the pressure generated by the vapour escaping from the surface of the food (p) with the vapour pressure of pure water under the same conditions (p_o):

A_w=p/p_o

The reason why water activity is such a critical parameter for food manufacturers varies depending on the application. In cereals, for example, fruit pieces need to exhibit the same water activity as the other components in order to prevent the cereal flakes from going soggy and the fruit pieces turning hard. In baked fruit-filled bars, cakes or cookies, the fruit paste must have the same water activity as the surrounding product to prevent moisture and colour leaching into the rest of the bar.

More generally, ensuring that fruit ingredients have the correct water activity can prevent shelf-life problems that might otherwise arise in one or more of the following areas:

Microbial growth

Microorganisms need access to water to grow. Bacteria will not grow if the water activity is below 0.70. Moulds will not grow if the water activity is below 0.60.

Physical properties

Water activity can have a major impact on colour, taste, texture and aroma.

Controlling moisture migration

Water activity is an important tool for controlling water migration in multicomponent foods. In other words, achieving the correct level of water activity can prevent soggy biscuits and cereals.

Chemical/biochemical reactivity

Water activity can play a significant role in determining the activity of enzymes and vitamin stability in foods. Water may influence chemical reactivity in different ways. It may act as a solvent or reactant, for instance, or it may change the mobility of a reactant by affecting the viscosity of the system. Water activity therefore influences a range of common chemical processes in foods, including non-enzymatic browning, lipid oxidation, degradation of vitamins and enzymatic reactions, which can all impact on shelf life.

Creating market opportunities

The ability to include meaningful amounts of real fruit creates excellent opportunities for new product development. It enables manufacturers to respond quickly to emerging trends in healthy eating.

This article was originally published as a white paper on the Taura Natural Ingredients website: www.tauraurc.com.