Global launches of probiotic foods and beverages have steadily increased during the last 10 years. Although most of the foods launched have been dairy products, the number of nondairy probiotic foods introduced — such as juices, breakfast cereals, confectioneries, snacks, baby food, processed meats and desserts — has also been on the rise. When formulating any probiotic product there are many critical parameters to consider. Today, scientific experts and regulatory agencies agree that, because probiotics are micro-organisms, they must be delivered live (viable) in order to exert their beneficial health effects. Therefore, probiotics require that greater care be taken in adding them to foods and beverages compared to many other functional ingredients.
A variety of health benefits have been attributed to ingesting probiotics, including enhanced immune health and improved digestion. These human health benefits are known to be dependent on both the probiotic strain and dosage. When making claims on a finished product, use of a probiotic shown to be efficacious in human clinical studies is highly recommended. Such studies should be double-blind, placebo controlled and published in peer-reviewed journals. In addition, a reference to the strain and dose needed in order to deliver the health benefit should be identified on the package.
Optimising probiotic viability in the finished product requires that manufacturers take into account how all aspects of formulation, processing (including packaging), and storage conditions may affect viability. Understanding these factors in an application is essential to minimising probiotic loss and delivering a probiotic dose shown to be efficacious.
The most common formulation factors to consider include water activity, pH and organic acids, and food additives.
Water activity — The water activity (Aw) of individual ingredients and of the final product is a key factor in maintaining probiotic viability in low- and intermediate-moisture products. A shelf life of greater than one year can be achieved with freeze-dried probiotics in a low-moisture product (Aw < 0.2, eg, breakfast cereals, chocolate, instant dry beverages) when it is stored at room temperature. In intermediate Aw environments, however, the viability of most probiotics is more difficult to maintain. Options such as a micro-encapsulated probiotic may need to be explored for these types of products.
pH — pH tolerance, which varies by strain and specific application, is particularly important for high Aw products such as fermented dairy and beverages. Product developers may benefit from working closely with their probiotic suppliers in selecting appropriate probiotics for their specific applications. For example, probiotics chosen for addition to neutral milk or a fermented dairy product such as yoghurt may not be the best choice for a juice. It also is important to choose a probiotic that does not produce off-flavours during manufacture or storage.
Some probiotics can grow during storage (for example, those added to fluid milk) and cause changes in the flavour profile. When incorporating probiotics into juice and juice drinks, the organic-acid profile of the product is an important consideration. The undissociated form of organic acids is primarily responsible for their antimicrobial properties. As pH declines, the concentration of the undissociated organic acids increases, causing greater bactericidal activity, which can negatively affect probiotic survival.
Food additives — Most sweeteners, such as sucrose, dextrose and aspartame, have not been found to be detrimental to probiotic viability. However, some flavours and colours have been demonstrated to have either a beneficial or detrimental effect on probiotic viability, depending on their composition. This inconsistency is most likely a result of the diverse range of compounds found in flavours and colours. While these factors are important to consider in formulation, it may be prudent to conduct stability testing to confirm their effect on probiotic viability in each specific application.
Temperature — Because most probiotics are mesophilic microorganisms, they are sensitive to high heat used in processing. As a result, most probiotics (with the exception of spore-forming probiotics; see sidebar) must be added after any thermal processing such as pasteurisation. Probiotics' temperature tolerance can also vary depending on the matrix. Fat, for example, can improve probiotic tolerance to temperature, but in general, temperatures greater than 50°C begin to have a detrimental effect on viability.
Mixing — Shear forces experienced during some commercial mixing operations may decrease probiotic viability and should be kept to a minimum. Excessive mixing should also be avoided to minimise oxygen incorporation into the product. In fact, oxygen toxicity is considered a primary cause of probiotic loss during storage.
Packaging — Because exposure to oxygen can lead to decreased probiotic viability, packaging materials should also be considered. Some studies have shown that because glass bottles are more resistant than HDPE bottles to oxygen and moisture transfer, they are preferable for packaging probiotic products. Foil with a lower moisture vapour transfer rate can also be advantageous.
Storage and distribution
Conditions during storage and distribution can play an important role in sustaining probiotic viability in a product, primarily as they relate to temperature control and fluctuation. In general, lower temperatures improve probiotic stability. Limiting temperature fluctuation during storage and distribution improves stability in products as diverse as ice cream and powdered beverages. However, optimal manufacturing and storage conditions for a probiotic-containing food are frequently specific to the process or product.
The dynamic and complex interdependencies among the factors discussed above add to the challenge of achieving probiotic stability in foods and beverages. Obviously, it is not always possible to alter these factors without altering the organoleptic properties and shelf life of the food, so selection of product-specific probiotics is essential.
The universe of probiotic foods will continue to expand as researchers learn more about key factors affecting the survival of probiotics in food. Improved methods for enhancing probiotic viability will enable new food delivery vehicles to meet consumers' demand for these health-promoting functional products.
Connie Sindelar is the probiotics format development manager at Danisco, Inc where she works on probiotic product formulation for food, beverages and dietary supplements.
Peggy Steele is Danisco's global business director for probiotics utilised in food and beverages. She has 20 years food experience, from formulation and processing to starter-culture characterisation.
Score with spores
One way of avoiding many of the pitfalls associated with formulating probiotic foods is to use spore-forming probiotics. Spores "are analogous to a seed producing a tree," said Mike Bush at Ganeden Biotech, which supplies the GanedenBC30 spore-producing strain. "The spore protects the cell's delicate genetic material." When the spore enters an environment that is conducive to its growth — ideally found in the human GI tract and not in a processed food matrix — it germinates and grows, providing the probiotic benefit.
Spores are stable in intermediate-moisture products like chocolates, bars and confections, and also at a wide range of pH levels, said Bush. "Foods that are kept warm, moist and have lots of available nutrients may cause germination of the spores," he cautioned. "In such cases we may opt to use micro-encapsulated material to separate the spores from the substrate/moisture."