“Non-nutritive” fibers are a group of food ingredients that are becoming more important and more complex at the same time.
In the 70s, fiber was simply described as the remnants of plant cell wall components that are resistant to breakdown by human digestive enzymes. The definition was then broadened to include all digestion-resistant polysaccharides. Methods were developed first for total fiber, then insoluble and soluble fiber. As of 1999, the definition of dietary fiber remained as “dietary fiber consists of the remnants of edible plant cells, polysaccharides, lignin and associated substances resistant to (hydrolysis) digestion by the alimentary enzymes of humans.” This definition identifies a macro-constituent of foods that include cellulose, hemicellulose, lignin, gums, modified celluloses, mucilages, oligosaccharides, and pectins and associated minor substances, such as waxes, cutin, and suberin. (DeVries JW, et al. 1999, Cereal Foods World 44(5):367)
But today, as the physiological effects of dietary fiber become better understood via the proliferation of clinical studies, and as ingredient manufacturers devise new offerings that provide functional benefits in both food systems and human digestion, debate rages as to whether fiber should be defined by its source material, its chemistry or its human physiological effect. For example, many new carbohydrates that do not have fiber labeling status, such as inulin and several naturally based oligosaccharides, still meet the general definition or concept of dietary fiber. (See www.AACCnet.org discussion page.) Formulators who are confused about fiber functionality, label and regulatory status and nutritional implications are not alone. The chart “Fiber Labeling by Analysis” clarifies the measurement issue, as dietary fiber labeling status is determined by measurement methods based on solubility in 78% ethanol.
There are two main reasons why fiber is included in food formulations today: for a functional effect in a food system or for a human physiological effect. The following text discusses considerations for both types of projects, as they are approached very differently.
Functional Applications: Maximum Function, Minimum ImpactSince fibers constitute a large class of widely different and very functional ingredients, they can be applied to solve a variety of food problems. The largest applications of fiber center on:
In general, in a functional application of fiber, the most functional fiber with the least impact on sensory and processing characteristics at the lowest cost is sought. In other words, what is desired is maximum function with minimum impact. Fibers used in this manner will appear on the ingredient statement, but may be used at such low levels that the nutritional panel is not affected. In this case, the ideal fiber is bland, contributes no adverse visual or textural effects, is used at low levels (and, hence, the function contributed per unit of weight is very high), does not require alterations in process and is inexpensive. Unfortunately, many fibers do not fit this description. Some fibers are limited to certain applications because of taste or appearance issues, such as fig paste (to flavor and color compatible systems) and unbleached sugar beet fiber (which, despite assisting quality, is seldom used in white bread--due to its impact on crumb color).
Examples of Functional, Low Fiber Level Applications Include:
Today, the larger portion of fiber (on a tonnage basis) focuses on nutritional properties. In this case, the consideration is the amount needed to provide a marketable benefit. As the chart “Filling Formulas with Fiber” demonstrates, this can result in a large substitution of fiber for other components of the food formula. The formulator's job is much easier if fibers offered for these applications are essentially “non-functional.” The same features--such as water-holding, viscosity-increasing and structure-building--benefits in the applications above, become serious issues when the level of fiber is significantly increased.
The chart also demonstrates that a substantial portion of the formula is affected to meet a high-fiber claim. For bread, pasta and masa-based products, this necessitates that 9% or more of the formula, or roughly 18% or more of the flour, be replaced with fiber. But the next column clarifies the “functionality” problem. If the fiber holds only two times its weight in water during the dough mixing stage (and many fibers are claimed to have water-holding capacities of eight times their weight or more), then the dilution of the flour in the dough is more pronounced. Alternatively, formulators might add less water to the dough than the fiber could absorb in this application, but the rheology of the dough would be significantly impacted, affecting mixing characteristics, machinability, fermentation, bake characteristics and finished product attributes. Also, when the product undergoes shear or heat, the fiber is unlikely to hold water the same way as in the original formula. Consequently, high-fiber products often exhibit greater sensitivity to mixing or sheeting and different bake characteristics. “Blotchy” crusts on baked goods result directly from a fiber's differences in holding water during baking, as compared to flour.
As noted, fiber has the potential to increase shelflife in breads by carrying additional water. The fibers used to enhance bread shelflife, such as apple, sugar beet, prune, date fibers or psyllium, often contain a significant soluble fiber component. However, the specific fibers selected to meet a “high fiber” claim are often insoluble fibers. Thus, it may take a blend of different fibers or careful selection of a particular fiber to achieve both the nutrient content claim and enhanced freshness.
With health bars, which often are formulated with a minimum of water, the fiber content is significant enough to contribute its own texture and flavor. But, again, water absorption--which was a benefit in the functional applications--may now be problematic in applications such as this, which may try to make a nutrient claim. The fiber will attempt to absorb the water present, altering the texture of the bar matrix and affecting the bar's cohesiveness (as well as other attributes).
Meeting the nutrient content claim for both dough products and bars is easiest when a compatible, yet essentially non-functional fiber is used. Digestion-resistant starches have been engineered to have these characteristics, which make them particularly easy to use in these applications. One minor difficulty with resistant starches is that one form (RS2) is processed to be non-nutritive, but can become nutritive (digestible) during food processing, due to starch gelatinization. Thus, when RS2 resistant starch is used for a fiber claim, finished food product analysis is required for the nutritional label data to confirm the expected non-nutritive fiber content is still present after processing.
Beverages encounter a different set of problems. Hydration is no longer an issue, but particle size may lead to grittiness. Insoluble fiber may also settle out. The use of viscosity-increasing soluble fibers may prevent this problem. High-fiber claims can also be delivered in low-viscosity beverages if specialty fibers like hydrolyzed guar are used.
Flavor profiles often are significantly affected when high levels of fiber are used. This problem is best resolved by screening for fibers that have the least effect on flavor, then formulating the food with the selected fiber to meet the intended technical effect and, finally, re-balancing the flavor system to meet taste expectations.
Choosing a Dietary FiberBecause many types of fiber are commercially available from a variety of dietary fiber vendors, it can be difficult for formulators to find a starting point to identify their options. Additionally, rapid changes in the fiber area make many texts quickly out of date. The sidebar “Finding a Fiber Fix” serves as a quick reference for some current options.
When a formulator starts working with an application that may require dietary fiber(s) as a component, the first step is to identify the driving force for fiber use. Is the fiber for technical functionality or for nutritional functionality? Given that decision, the critical attributes the fiber must deliver should be described. Based on those criteria, the various options should be considered. For some nutritional or functional applications, these steps alone may narrow the options to a small number of choices.
Next, consider the physical attributes of the food system. Is it solid or fluid? If solid, was it a dough or batter prior to becoming a solid system? Is the finished product's moisture content critical to stability? Is there some critical element of the system that will lose functionality when diluted by the addition of fiber (and the water it may carry)? Can your system tolerate the addition of particles that some forms of fiber may add? Is it acceptable if the fiber alters the color or flavor of the finished product?
Also consider the chemistry of the system, including pH, concentration of electrolytes, sensitivity to oxidizing agents (many fibers are bleached, and may contribute unintentional oxidants), etc. Then, examine the chemistry and physical characteristics of different fiber options. If the fiber application is nutritionally driven, formulators will need to consider the nutrition questions first, followed by technical considerations. If the fiber application is technically driven, the nutrition considerations (essentially) are moot. Remember that fiber is a broad class of ingredients that includes cellulose, hemicellulose, lignin, gums, modified celluloses, mucilages, oligosaccharides and pectins.
Nutritional and Technical ConsiderationsWill the new product feature a nutrient content claim that it is a “good source” of dietary fiber (10%-19% of fiber DRV), or that it is “high in dietary fiber” (>20% of DRV)? Or, is the goal to be able to make a specific health claim that would require the presence of a specific fiber type (such as oat or beta glucan) or other soluble fibers? Is the new product's concept based on a benefit derived from a specific material? For example, insoluble fibers generally affect laxation, while soluble fibers, depending on their very specific chemistry, are implicated in heart and colonic health, and glucose response benefits.
A number of technical characteristics should also be considered. For example, is the fiber predominantly a single chemical entity or is it a mixture? Would the application benefit from a single fiber type or a mixture of fiber types? Is the fiber soluble, insoluble or a mixture of both? Is the fiber treated in some way that alters its properties and will that affect the product? Is the fiber finely ground or a more coarse material? Is the particle size important in the application? Is it compatible with present ingredient handling and processing systems? How much water does the fiber carry? Does it hold that water through processing and subsequent shelflife? Is it beneficial to the product to carry water or not?
Finally, the price of an ingredient is most always an issue. Depending on the food product and the specific product concept, cost often needs to be considered very early in the fiber selection process. Since fiber applications usually require additional formula adjustments than just adding the fiber itself, “cost in use” is the crucial calculation. Cost per pound of fiber is almost meaningless. When comparing the cost of a new versus an original formula, formulators should do so based on total cost of the finished products “as consumed,” since fiber addition may alter the formulation itself in many ways. Often, a purchasing agent may identify a fiber that has a lower cost per pound, but when that ingredient is fully applied to the food system, it may result in significantly higher product costs. Processing costs may also be impacted due to handling anomalies. If so, these additional costs should be considered in your fiber selection process.
Formulators embarking on a fiber application project should visit their regulatory advisor early in the development process. They should consult the Internet and other literature to locate the full range of options available, and take advantage of the technical applications resources offered by their suppliers. Excellent fiber application resources exist, but they are not concentrated in any one place.
Leslie Skarra is president of Merlin Development, which provides high-quality, cost-effective research and development services. Merlin specializes in all technical aspects of food product development from concept through commercialization, including prototype development, formulation, scale-up, quality system design and production start-up. Skarra can be contacted at 763-475-0224 or Lskarra@merlindev.com www.merlindevelopment.com.
Sidebar: Finding a Fiber FixThe range of ingredients that will analyze as dietary fiber and that provide nutritional and/or technical functionality in a food or beverage may seem overwhelming at times. Resistant starch, polydextrose, inulin/FOS, dextrins, and dietary fiber from grains, fruits, legumes and other plant sources are just some of the options. Prepared Foods magazine offers two annually updated ingredient catalogs. See the following online: