Beverage formulators working on a new product must work within a matrix of needs encompassing technical formulation challenges, marketing department desires and cost considerations.
Do you want the drink to be all natural? Organic? GMO free? Do you need a fibre source? A clear or cloudy emulsion? What mouthfeel are you trying to promote? What oils are you trying to emulsify? What is the flavour oil concentration going to be? How shelf-stable does it need to be? Or might it be an instant beverage sold in a powder form for consumer reconstitution?
When formulators begin filling in the criteria for this multi-dimensional matrix, the answers will determine which of the different approaches should be taken in picking the emulsifier.
Gum acacia is widely known throughout the beverage industry as a robust multi-functional emulsifier. It lends itself well to beverages for a variety of reasons. It acts as the primary emulsifier for flavour oils, permitting dispersion of the oil into the water and stabilizing the beverage to avoid ringing and creaming. It is stable in low pH environments, often an important criteria for beverages. At the same time, it has a low viscosity response in water, so it can provide mouthfeel without any adverse effect on the original beverage texture.
From a nutraceutical-beverage perspective, it is a protective carrier of nutrients and a natural prebiotic fibre source. It also offers the power of a 'clean label' and can qualify as a natural and certified organic ingredient. It is widely compatible with other ingredients for everything from sports drinks, where it may play a role in electrolyte absorption, to fruit juices, dairy beverages and liquid-meal substitutes.
In the world of beverage emulsions, there are two product ranges of gum acacia. For shelf-stable beverages and emulsions with extended shelf life, gum acacia senegal (grade one) is the most popular material. The seyal, or grade two species of gum acacia, is widely used as a flavour or oil carrier because of its excellent film-forming characteristics. With spray-dried oils, the oils will oxidize over time and oxidative stability is developed by enrobing them in gum acacia rather than spray drying them onto another carrier. It performs best in emulsions that require a shorter shelf life.
When you make an emulsion, you are trying to disperse two nonmiscible fluids within one another: the oil and water emulsion of a homemade salad dressing is the classic example. The oil is turned into droplets and dispersed in the water, which is the matrix phase. You can create a simple form of this emulsion if you put water and oil in a jar, put a lid on it (noticing that the oil floats in the jar), and shake it up. You can see the oil droplets floating within the water. When you stop shaking the jar, you will quickly see the oil droplets begin to coalesce and, because oil is lighter than water, it begins to rise to the surface. When you let it sit for a while you go back to having a distinct oil layer sitting on top of a distinct water layer. That's an unstable emulsion.
In the beverage world, an emulsion must be designed in a way that addresses the various natural forces at work, including density differences between the water phase and the oil phase, and the mobility of the oil droplets. When the rough emulsion is passed through a homogenizer, fine oil droplets are created. Gum acacia is added to the water phase to function as an emulsifier and a surfactant to balance the energy between the two phases.
This is effective because gum acacia is a somewhat linear molecule that has two different natures. One portion is oleophilic, meaning oil loving, and the other end is hydrophilic, meaning water loving. If you imagine the gum-acacia molecule as a string, the oleophilic end adheres to the outer surface of the oil droplet while the hydrophilic end adheres to the water phase.
Beverage emulsions are kinetically active environments, where the isolated oil droplets are moving, bumping into one another, and trying to rise through the water phase. The oil droplets never actually touch because surfactants protect them and keep them isolated from one another. At the same time, the droplets rise because oil has a lower density than water. For this reason, weighting agents such as ester gum or brominated vegetable oil (BVO) are commonly used to densify the oil so that it matches the density of the water, greatly reducing the tendency of the oil to rise to the surface.
Formulators are familiar with Stokes' Law, a formula to determine the rate at which a particle suspended in a liquid will rise or fall. When oil levels increase, the weighting-agent balance becomes particularly critical. Concentrates can have oil levels upwards of 20 per cent; while other emulsifier options have oil-loading limits, gum acacia can work well up to a 20 per cent oil level. Each flavour oil, as well as the surrounding water-based liquid, has a slightly different density (consider, say, the difference between a diet beverage and one loaded with sugar). When formulating a beverage emulsion or, more correctly, an emulsion concentrate, many factors come into play and it can get pretty complicated.
Emulsion concentrate failures
If an emulsion is not balanced properly, several failure mechanisms present themselves: breaking, creaming and ringing. A broken emulsion resembles the salad dressing mentioned earlier where the oil separates and rises to the surface. Creaming is the failure of an emulsion concentrate that occurs when individual oil droplets begin rising to the surface and remain floating as individual droplets. Ringing is the failure of a beverage manufactured from an emulsion, and occurs when oil droplets coalesce at the surface and form an oil ring at the neck of the bottle.
Creaming in and of itself may not be a disaster. If the material creams but becomes homogeneous with gentle agitation and the finished beverage does not demonstrate ringing, a little bit of creaming may be acceptable. There is not necessarily a relationship between creaming in the concentrate and ringing in the finished beverage made from that concentrate.
The beverage formulator will typically go through a series of tests to ensure a stable and long-lasting emulsion has been created. The most common test is done by analyzing particle-size distribution. Smaller droplets with a narrow size distribution are preferred and indicative of a stable emulsion. During shelf-life studies of concentrated emulsions and finished beverages, visual inspections are combined with particle-size distribution analysis to predict whether or not the emulsion will be stable. Emulsions tend to be evaluated on day one, day seven, day 14, day 30 and day 90 of storage. The degree of shift that occurs at each interval is indicative of emulsion stability, or lack thereof; a pronounced shift early on demonstrates that the emulsion is not stable. Some flavour manufacturers demand a shelf life of up to 180 days.
However, you can't really look at a particle-size distribution and say for sure that you have created a stable emulsion. You can get very strong indications but rarely can you say the one test is a perfect predictor of stability. For that reason, application-level testing under real-world conditions is a key component in determining shelf life.
Accelerated shelf-life studies are also helpful.
The ability to create an appealing cloud is another important functionality of gum arabic. Some beverages are very clear even though they have colour. Others are cloudy, meaning you can't see through them. An orange soda is a prime example of a beverage that is expected to be cloudy.
Cloud is managed by particle size and light refraction. We established earlier that the smaller the oil droplet, the more stable the emulsion tends to be. However, as the droplets get smaller their ability to scatter, absorb and reflect light is reduced. So when you create a cloud emulsion, you're doing two things: forming a stable flavour emulsion, and at the same time creating an emulsion with a particle size large enough to give a cloudy appearance to the emulsion itself.
Acacia is about 85 per cent by weight soluble dietary fibre. It's worth making the distinction between insoluble fibre and soluble fibre. Insoluble fibre adds bulk to the stool, speeds digestion and passes through the intestines without being digested. Soluble fibre forms a gel in the intestines, slowing the rate of carbohydrate absorption and binding with fatty acids to lower LDL cholesterol.
A source of soluble fibre, gum acacia can be used in beverages at relatively high levels without negative impact on the finished product. Because of its low viscosity response in water, fibre levels of 6-8g per serving are achievable with little to no effect on the body of the beverage. From a taste standpoint it has a slightly sweet taste, similar to but more subtle than honey.
All fibre sources are not created equal. Oat fibre is 85-90 per cent fibre, but less than three per cent of the fibre content is soluble. Oat bran is approximately 22 per cent fibre, with 50 per cent of the fibre being soluble. Wheat bran is approximately 50 per cent fibre, with about 5 per cent of the fibre being soluble. Acacia, in comparison, is almost entirely soluble fibre.
From a functional standpoint, acacia is being adopted by more manufacturers to replace the binding properties of high-fructose corn syrup in meal-replacement and granola-bar applications. It delivers a slight sweet flavour and is cost effective.
Some data suggest gum acacia, like all hydrocolloids, has a relatively low glycaemic index, which means it helps maintain a consistent glucose response in the healthy human body. This is important because foods with high glycaemic indexes can cause wide fluctuations in glucose response.
Finally, gum acacia is one of the few ingredients that can be all-natural, non-GMO and kosher. It is also available in a certified 100 per cent organic form. Truly, gum acacia is a multifunctional natural ingredient that offers formulators many benefits.
Scott Riefler is vice president of science and technology at TIC Gums.