Due to the broad definition of fibre as a substance that resists digestion by the upper human digestive system, a wide variety of fibres with different functionalities are available for use as ingredients. They can exist in purified form, like inulin or fructooligosaccharide (FOS), or be left in its natural botanical form, such as wheat bran or citrus fibre, or perhaps even partially purified.
They can be soluble or insoluble, and quite often they exist in that transition area of solubility known as a colloidal phase, like β-glucan from oats and barley. Many pure fibre types are large polymers of sugars, such as guar gum or acacia, and some are substantially smaller such as resistant maltodextrins and fructans.
Fibre’s Health Benefits & Applications
The health benefits of fibre are multifold, but also vary somewhat based on the physio-chemical properties of the fibre, including both the composition and the structural form. Some acknowledged nutritional benefits include: promoting satiety, intestinal bulking, enhancing immune health by promoting growth of beneficial bacteria in the large intestine, the production of short chain fatty acids (SCFAs) that improve the health of the digestive lining, and increased bioavailability of micronutrients.
It is interesting that the natural form of a fibre impacts the way it is fermented in the gut. For example, resistant starches have plenty of exposure to amylases throughout the digestive track yet they avoid direct contact with the active sites of enzymes by making tight crystalline regions or by surrounding itself with a tight protein matrix.
Another example is pectin. Purified pectin is often reported to result in large amounts of acetate after fermentation in the gut, yet pectin-rich fruit pulps have a SCFA profile that often includes much more propionic and butyric acid.
Fibres are commonly used in various food products including but not limited to bakery, frozen foods, dairy, meats, sauces and beverages. In a beverage system, fibres are most commonly added to either boost the nutritional profile of the product, or to add texture, thickness or bulking to a beverage.
Even dissolved fibres like FOS can enhance the mouthfeel of a beverage to give it some body. Since many fibres are polymeric in nature, their properties are influenced by other beverage conditions such as the sugar content, salt content, acidity, available water, and presence of other fibres.
Going Beyond Cellulose—Citrus Fibre
Citrus fibre contains cellulose and hemicellulose in addition to the native pectin present in orange pulp. The cellulose and hemicellulose act as the backbone of the fibre. This structure forms a very cotton ball-like fibre with the pectin and cellulosics intertwined. This gives the fibre a unique mouthfeel.
The fibre drags across the tongue which can give a creamy texture to milky coffee beverages or with a larger grind size, can give a pulpy texture. The pulp extension can help formulators extend expensive fruit pulp without modifying or changing the mouthfeel of the beverage. It can also extend tomato solids in tomato-based sauces.
Conventional cellulose fibres more often come from dried grains and fibrous plants, which when compared to fruit fibres, often do not have the natural botanical architecture optimised for holding bulk water tightly.
As one might suspect from its name, citrus fibre itself is a good source of dietary fibre (comprising) 70-80 percent. It has been shown to be bifidogenic, meaning that it selectively promotes growth of health-associated Bifidobacterium at the expensive of less desirable bacteria species.
The quality of the citrus fibre depends somewhat on the source of the fibre material. Whole citrus fibre is taken as it is from the pulp or peel of a citrus fruit and is ideally not further processed beyond drying to a powder. Such citrus fibres are usually obtained from excess material in the juice industry and contribute to a very clean label.
This type of fibre has higher levels of soluble fibre, namely pectin. Some citrus fibre is generated from the process of purifying pectin as a separate ingredient so this type of citrus fibre has a much higher proportion of insoluble fibre, namely cellulose and hemicellulose.
Despite the high dietary fibre content, citrus fibre is rarely used at levels above one percent in food products. This is due to its high water holding capacity. High amounts of citrus fibre would eventually cause textural defects because it outcompetes many other ingredients for water.
Nonetheless, citrus fibre can be a valuable tool in high fibre foods and beverages as a complementary fibre that improves the palatability of the food by addressing common problems associated with health foods, such as lack of moistness and mouthfeel.
A Natural Solution With Many Benefits
Whole citrus fibre that has not been chemically modified or stripped of its pectin has many functional properties that make it a great tool for formulators. This fibre is comprised of natural pectin, cellulose and hemicellulose and some residual protein. This chemical make-up of the slightly hydrophobic pectin, plus the physical cellulose framed structure of the fibre, make it able to hold onto not only water, but fats and oil too.
When the particles have been roughened by mechanical input, citrus fibre becomes more porous with a greater surface area which, in turn, makes it a great oil and water binder. Therefore, if you have both oil and water on the same particle, you have succeeded in making a natural emulsion.
In the Asian market, there are emulsion beverages such as milk tea and coconut milk drinks. These will often use chemical emulsifiers such as DMG, and sometimes if there is no hydrophilic-lipophilic balance (HLB), separation will occur after processing.
The strong water holding capacity of citrus fibre makes it a useful tool for preventing freeze/thaw damage to frozen food products. The robust cellulose scaffolding also makes it thermally stable; it will not thin out or break down at high temperatures. These properties make it a great addition to meat products to retain water and fat for juicier meatballs and sausages. They can also help with moisture retention of meat fillings in steamed buns or dim sum type products.
The emulsification and water binding properties also make it a great addition to baked goods where it will help delay staling defects and extend the soft fresh texture over a longer shelf-life. These properties also make it a great addition to sauces where emulsification is desired without the use of chemical emulsifiers.
Using Citrus Fibre In Fruit-Based & Dairy Applications
Due to its natural pectin content, citrus fibres can form gels in high acid, high brix applications like fruit preparations for yoghurt, bakery or spreads. Citrus fibre can replace or extend pectin where it is traditionally used.
Whole citrus fibre contains about 40 percent pectin, so in order to reach gelling conditions, one would need to use roughly twice as much citrus fibre as would be used with pure pectin. Despite this, the ingredient cost in use is often cheaper and arguably provides a cleaner label. The different grind sizes available can also permit the formulator to choose a fine or pulpy texture to suit the target application.
Citrus fibre can help control syneresis in cultured dairy products as well. Low levels of citrus fibre can add a creamy texture to yogurt products and help control syneresis in fresh cheeses such as cream cheese. Citrus fibre can increase yields and help manufacturers make the most of the water and fat in the system.
Working with whole citrus fibre is similar to working with other hydrocolloids. Dispersion and hydration are key to their functionality. For most applications, it is recommended to disperse citrus fibre with other dry ingredients and then add the liquids. For applications where an emulsion is desired, it is recommended to disperse the citrus fibre in oil, before adding the other liquids and shearing to form a stable emulsion.
While high shear is not necessary, it can help accelerate hydration and emulsification. In intermediate moisture foods, additions of small amounts of water may be needed to prevent the citrus fibre from outcompeting other ingredients for water, thus avoiding corresponding textural defects.