Article: Smoother Smoothies and Frozen Desserts -- October 2007
“Smoothness is not a well-defined term,” states Ross Clark, distinguished research fellow at a well-known gum supplier. He says, “At least four things can make a frozen dessert or smoothie seem not smooth.” These are graininess from protein precipitation, ice crystal growth, a thin viscosity and insoluble materials such as pulp, seeds or added minerals (like in calcium fortification). The following are some ways gums can help maintain smoothness or creaminess.
Hydrocolloid Gum AdditionGums are typically used at a range of 0.025% up to approximately 0.5%—sometimes up to 0.8%, depending on the combination of ingredients used. At times, emulsifiers are used in gum blends and, in those cases, the use levels for the blend are significantly higher. In frozen desserts and smoothie-type applications, combining gums is more common than using a single gum, because each gum has unique functions; also, there is typically more than one issue to address in these products.
The functions of gums in frozen dessert or smoothie systems include inhibition of ice crystal formation; improvement of body and mouthfeel (especially in reduced-fat and -sugar products); suspension of insoluble minerals, seeds, pulp, cocoa or inclusions; and the protection of proteins from precipitation due to low pH.
“Gums stabilize emulsions prior to freezing and prevent ‘whey off’ after heat treatment. ‘Whey off’ is a condition where the casein and whey in the milk become separated. This can happen due to pH change, heating or other conditions that destabilize the casein. Gums can be used to stabilize the less stable casein fraction. Air cells are stabilized for consistent overrun and slower melt,” contributes Ray Valli, senior scientist at a major gum supplier.
“The most common gums used in smoothies are pectin, propylene glycol alginate (PGA) and cellulose gum. All three of these stabilize proteins at low pH. Each has its own unique mouthfeel attributes and label declaration that will help developers select which one is right for them. Pectin is well received by consumers and has a very light mouthfeel. Cellulose gum has a heavier mouthfeel, while PGA can sound negative to consumers on a label,” explains Wanda Jurlina, technical service manager at a major gum supplier. There is also more interest in suspension in these systems. Insoluble fibers and minerals create the need for different gum/hydrocolloid systems.
"For suspension of particulates in acidified protein systems, blends of gums are often required to achieve suspension and protein stability. At this time, the two main choices for these blended systems are gellan and cellulose gum or cellulose gel and pectin," adds Jurlina.
“For frozen desserts, any products that help control water will impact how ice crystals form and how they grow. Lots of smaller ice crystals will give a much smoother product than fewer larger ice crystals. The goal in stabilizing a product is to promote smaller ice crystal formation to ensure a smoother, creamier product through the shelflife and abuse,” Jurlina adds.
“In the case of graininess from protein precipitation, a cellulose gum or pectin is typically added to serve as a protective colloid, because they prevent complete precipitation of the protein. To inhibit ice crystal growth, locust bean gum or other galactomannans are especially effective. To make a thin or runny product thicker, adding xanthan, cellulose gum or pectin gums are preferred ways to add body. Gellan gum helps suspend insoluble materials such as pulp, seeds from berries and added minerals,” explains Clark.
Formulating and Processing Considerations“Fat in a formula always adds body and makes a more thick and rich mouthfeel. Low pH tends to make things seem harsher, while low moisture thickens. In most cases, these properties cannot be adjusted, due to the product identity. For example, more fat may improve texture, but in a low-fat or low-calorie product, this may not be possible,” adds Clark.
“Fruit is used mainly for flavor, but cooked or canned fruit is softer and less pulpy than fresh fruit, so the product will be smoother and less pulpy in the mouth. Some fruits promote creaminess (such as bananas), because they have high amounts of starch, which adds viscosity and creaminess,” says Valli. Added whey or soy protein usually increases creaminess as well, unless the proteins precipitate in a low-pH system, resulting in a powdery or grainy product. As more milk solids are added, protein reactions occur, especially with heat abuse. Carrageenans can protect the proteins at neutral pH, but they are less effective at low pH. Pectin and carboxymethyl cellulose (CMC) are better choices for low-pH products.
“While there is a lot of overlap in gum functionality in the final product, it is critical to match the gum properties with the processing requirements,” says Valli. “For example, the stability requirements for a mix depend on batch size and how long the batch sits before freezing. If a mix sits around a long time before freezing, then guar or locust bean gum (LBG) cannot be counted on to maintain the emulsion. Adding a low level of carrageenan will prevent ‘whey off,’ and then adding some xanthan gum will ensure that the emulsion doesn't break in the holding tank,” he states.
“Other gum considerations are that xanthan, CMC and guar are all cold-soluble, so they contribute to mix viscosity prior to pasteurization. But excessive mix viscosity can create a problem for effective heat transfer. By using some LBG, pectin or carrageenan, initial mix viscosity can be reduced. The heat of pasteurization will fully hydrate these gums so that the mix will develop added viscosity after pasteurization,” Valli shares.
Formulating with StarchIn general, the use level for starches can range from 0.5% to 4% in frozen desserts, depending on a number of factors. Fat content, processing product type and other ingredients all affect the amount and type of starch ingredients used.
Starches have a variety of functions in smoothies and frozen desserts, including creaminess enhancement in low-fat products and freeze/thaw stability. Starches are commonly modified by processing, chemical or enzymatic means, with the final starch properties determined by the specific starch modification. This helps achieve the desired properties and functions in finished products.
For example, cross-linking increases starch stability during heat and shear and in lower pH systems. Substitution increases the water-binding capacity of starch, which helps control syneresis in dairy and frozen desserts.
Starch Applications“Frozen desserts have come a long way since the snow cone,” explains Joni Simms, manager, food ingredients technical service, Americas and Europe, at a well-known starch supplier. Consumers still want creamy taste and texture, often with the added benefits of low-fat and no-sugar-added. These considerations put demands on processors as they try to balance the fat, water and sugar in a formula, while maintaining the stability of the product. Maintaining stability requires managing the freezing point and temperature fluctuations during storage and distribution. Starches can be used in these applications to further improve texture. As an example, modified food starch has been used as a component in some premium texture ice cream stabilizer blends. The purposes of the stabilizer blends are to bind water, provide bulk and prevent ice crystallization.
Dairy desserts such as frozen mousses, which are aerated, may benefit from using an instant starch that holds moisture and provides viscosity. In this case, delayed hydration may be a necessary function in the chosen starch.
“For smoothies, different starches can be added to increase thickness, improve mouthfeel and lubricity of a beverage, without becoming slimy—as can be the case when using high levels of other hydrocolloids,” contributes Suzanne Mutz-Darwell, marketing manager for a starch supplier. Additionally, starch can act as a partial replacement for milk solids non-fat (MSNF) in products, delivering texture while saving costs.
Starch suppliers were showing plenty of smoothies at the recent IFT in Chicago, including a mango/passion fruit smoothie with appealing flavor and texture, plus added fiber. The proprietary blend of modified starches and fibers allowed the natural flavor to shine through and provided a creamy, pulpy mouthfeel, in addition to a “good source of fiber” claim. When adding nutritional ingredients to smoothies, texture can be affected.
Sensory Aspect of Creaminess“Creaminess or smoothness is often viewed as a bit of a vague consumer description, but even so, it can be improved by a variety of approaches,” explains Mutz-Darwell. She goes on to say, “Creaminess or smoothness is enhanced by starch in a number of ways. Maintaining a small ice crystal size in frozen products such as ice cream is one important aspect.”
“By controlling the glass transition temperature and the rheological characteristics of the unfrozen phase in a frozen dairy system, starch ingredients can control the size of ice crystal development, improve heat shock tolerance and maintain shape in frozen novelties—all of which contribute to the improved textural characteristics of frozen desserts. Additionally, there are other starch-based texturizers that can act as a fat mimic and enhance lubricity to further enhance the creamy eating experience,” Mutz-Darwell states.
Her company’s sensory department has been able to break down the “creaminess” experience desired into specific, well-defined, sensory texture attributes that become actionable targets for product developers to focus on when they seek to develop a consumer-preferred texture. Once the experience is mapped for a specific product, then the proper texturizing system can be selected from the vast toolbox of available texturizers that vary in origin, processing and, ultimately, in label declaration. Some examples of labeling would include tapioca maltodextrin, food starch-modified or physically modified native starches.
Co-texturizersDescribed as “co-texturizers,” one starch supplier provides a line of starch-based ingredients contributing a range of textures in a variety of dairy products, including frozen desserts and smoothies. These products are designed to work on top of an existing texture structure, hence the name co-texturizers. Many formulators think of starch as primarily a viscosifier, used to control the thickening aspect. However, co-texturizers do not add viscosity, but instead provide incredible texture versatility. “These products provide a new set of tools that are versatile, easy to use and cost-effective,” adds Mutz-Darwell.
Starch can aid in the dispersion and suspension of fruit pieces within a product; however, it does not usually interact with fruit ingredients. Typically, fruit pieces or preparations are blended into the dairy base at the end of the process. Food processors are offered flexibility in selecting starches that best suit their process, equipment and product needs. Some starches can be added at the beginning of a process, withstanding the heat from pasteurization and the shear from homogenization, or later in the process, when a starch must be dispersed in a cold liquid system (such as with an instant starch).
Sometimes ingredients in a formula, such as chocolate, nuts or soy powders, can affect creaminess. In these cases, starches are available to enhance the sensation of slipperiness in the mouth and promote a fast, clean melt-away. Others can enhance the full cream effect by delivering a full mouth-coating effect. Starches can mask the graininess and off-flavors of some powdery ingredients or of vitamin, minerals or other added ingredients in nutritional-type smoothies.
Chemical Property ConsiderationsOne must consider the chemical properties of a formula when choosing starches and other texturizers. Fat, pH, moisture and other properties affect texture and the choice of a texturant. Shear, pH and heating conditions affect how the starch cooks out. Therefore, it is important to select a starch that is stable enough for a specific process or pH to obtain optimum functionality.
When products are frozen, they often are exposed to varying temperatures and altitudes that cause expansion and shrinkage during shipping. Depending on what ingredients are present and the processing, shipping and storage conditions, a formulator may need a combination of starches, gums or other texturizers in one finished product.
A recent study published in Food Hydrocolloids indicated that xanthan gum could stabilize tapioca starch during freeze/thaw conditions, reducing the amount of syneresis. This research may offer formulators additional avenues into texture enhancement. The chemical structure of xanthan gum was most effective compared with other gums such as locust bean, guar and konjac-glucomannan for stabilizing tapioca starch gels. It was found that treatment conditions for reduction of starch retrogradation were optimized at a level of 0.5% xanthan gum with a freezing rate of 2.3°C per minute. Not only was xanthan gum found most effective in this study, it is also (according to the authors) one of the few hydrocolloids that have avoided price increases.
End users should carefully consider what they want from the final product and give clear guidelines to suppliers who can then suggest gums and blends of gums to meet customer expectations. Fat, milk solids and pH levels all are critical parameters that affect gum choice and stabilizer blend levels. As fat is reduced, stabilizers are typically added to maintain the mouthfeel. Different gum combinations often are needed to get the right mouthfeel.