Fibre fortification is now not just a case of adding more grams on the nutritional label. For manufacturers of food products, the real problem is incorporating fibres into foods while maintaining the same handling properties, stability and consumer appeal.
This is because dietary fibre is a group of different functional ingredients. Resistant starch, beta glucan, arabinoxylans and inulin have different properties regarding hydration, viscosity, fermentability and reactivity to other ingredients. The performance of these ingredients is dependent on dose, processing parameters and the nature of food matrices.
For food developers, the choice of fibres will depend on two things – what function is the fibre supposed to play in the food and its behavior in the food product.
From Fibre Selection to Fibre Functionality
Resistant starch acts as a replacement for digestible starch fraction and simultaneously acts as dietary fibre. However, resistant starch can change water partition, dough development, and resistance in bakery formulations.
The role of beta-glucan is technologically quite different. Water binding capacity and viscosifying capacity can affect dough properties such as dough softness and texture. Arabinoxylans can also play a role in water partition and dough rheology depending on their concentrations.
On the other hand, inulin is used for the effect on the body, texture and serum retention in certain formulations of dairy products. Such effect, however, is not general. It depends on concentration of this component and composition of product.
It follows directly that good behaviour of some fibre in bread does not necessarily mean the same performance in yoghurt, drinks or nutrition bars.
Why Fibre Blends Need a Formulation Rationale
Importantly, the benefits of co-existence between fibres are not just in the addition of extra amounts of fibres but in the complementary roles these might play.
For instance, beta-glucan would increase water binding ability and affect dough softening whereas resistant starch could affect dough resistance and extensibility through the replacement of some of the digestible starch fraction. In the study of Mohebbi et al., both ingredients influenced water binding ability and rheological behaviour of the dough but not similarly. It was found out that a combination of beta-glucan and resistant starch resulted in favourable farinograph and extensograph properties, but it is only valid in the conditions of that study. It means that these ingredients are not always synergetic.
Such information is very important in the practical sphere. Beta-glucan could be chosen because of water-binding and viscosity properties while resistant starch could be used to increase fibre amount and to change dough structure. Therefore, the goal of such a mixture would be to manage certain formula needs but not just combine several types of fibres under general health statement.
It could be shown from patent intelligence by Mintel including beta-glucan and arabinoxylans in biscuits as well as resistant starch and prebiotic soluble fibre in cookies.
Bakery: Increasing Fibre Without Compromising Quality
Bakery products clearly demonstrate the technical challenges of fibre enrichment. Replacing part of the flour or digestible starch with fibre can affect gluten dilution, water absorption and dough development. These changes may influence gas retention, loaf volume, crumb structure, firmness and storage behaviour.
Water management becomes a crucial factor. Fibers with high water-binding capacity can compete with proteins for water molecules. Lack of water can lead to dense and dry crumbs, while excess water will make dough hard to process.
The results of the Mohebbi et al. experiment confirm that beta-glucan and resistant starch affect dough strength and extensibility, as well as bread firmness during storage. It means that instead of adding fibre as just another ingredient, it is necessary to balance its amount with flour quality and water.
Dairy: Fibre Performance Depends on the Matrix
The case of dairy is a good example where the effect of fibre on the product structure may be demonstrated. For instance, fibre may be used for enrichment not only from a nutritional perspective but also as an improver of such properties as viscosity, water-holding capacity, mouthfeel and structure.
The effect of barley beta-glucan, partially hydrolysed guar gum and inulin was investigated in low fat yoghurt by Brennan and Tudorica. It was shown that these ingredients had the ability to reduce syneresis and improve textural and rheological properties. Beta-glucan in the rather low concentration of 0.5% improved the properties of serum retention and viscoelastic properties of yoghurt, whereas inulin and guar gum usually needed concentrations over 2% in order to improve textural properties.
Further study of skimmed stirred yoghurt showed that inulin and galactooligosaccharides helped to reduce syneresis without losing such desirable characteristics as texture and sensory qualities. Beta-glucan and pectin made yoghurt more viscous and improved its gel strength. However, high concentrations of these fibres led to larger particle size, thus reducing smoothness and creaminess.
It may be seen from Mintel product intelligence that fibre combinations with probiotics, proteins and digestive-health claims become more popular. Product records do not contain much information on the interactions between proteins and fibres and on fermentation conditions and stability.
Therefore, the assessment of each combination has to be performed in the desired matrix from the viewpoints of hydration, protein–fibre interactions, viscosity, phase stability and sensory performance.
From Fibre Fortification to Fibre Design
The next phase of fibre innovation will be less about adding more fibre and more about designing the right fibre system for each application.
The kind of fibre, its chemistry, dosage, process parameters and ingredient interactions need to be looked into along with the nutritional outcome sought from it.
The key point of focus is not just how much fibre a product is supposed to have but what that fibre is supposed to accomplish.
