Nutrient Stability

The issue of nutrient stability and bioavailability in foods and beverages is not new. In the past century, the expanding knowledge base of nutrition and food science enlightened scientists on the effects of processing, handling and storage on bioactive components. Restoration, standardization, enrichment, supplementation and fortification became the methods for ensuring the food supply's nutritive value and addressing health concerns. Today, the newer world of functional foods challenges product developers to identify what's important and how to deliver it effectively.

Simply put, the basic laws of chemistry are key to understanding and managing the potency of vitamins and minerals. Ram Chaudhari, Ph.D., senior vice president, research and development, Fortitech, Inc., Schenectady, NY says: "You have to take into account that vitamins, minerals and bioactives are chemical compounds that can react with each other." He cites copper, iron, zinc and water-soluble vitamins as examples of reactive nutrients affected by processing and storage conditions as well as pH and enzymes in food systems.

The vitamins C, A, D, B1, and B12 are generally considered to be the least stable. C, A and B1 tend to be more suseptable to oxidization in the presence of metal ions. In addition, interactions between certain vitamins - particularly C, B1, B2, B12 and folic acid - may accelerate the rate of breakdown of some vitamins.

In addition, the solubility and complex-formation characteristics of minerals frequently create problems in food systems. For example, copper sulfate added to milk with fat becomes insoluble and catalyzes fat oxidation, resulting in rancidity. Another factor that can affect stability is pH. For example, vitamin A is susceptible to oxidation when the pH is less than 5.

In addition to the ingredients in the food matrix, exposure to temperature, light, oxygen and water may affect stability during processing and storage, and consequently, the actual amount of nutrient delivered to the consumer. Minerals tend to be much more stable under extreme processing conditions than vitamins.

Chaudhari says processing conditions are very important - dry mixing has very little effect, but water, oxygen and heat are catalysts for many chemical reactions. Time of exposure to a damaging factor can help or hinder the rate of nutrient retention. Heat is a prime example. Various time/temperature combinations result in differing vitamin-retention levels during oven-, drum- and spray-drying. In general, lower combinations of time and temperature are better. Since drum-drying employs high heat and shorter exposure time, less loss occurs than in oven-drying. Spray-drying, however, exposes the nutrients to more oxygen, making additional controls necessary to limit oxidative damage.

A number of ingredients found in functional foods and dietary supplements present challenges to product manufacture and acceptability. According to Chaudhari, branched-chain amino acids, popular in sports drinks, are difficult to work with. And high processing temperatures cause omega-3 fatty acids to develop a fishy odor, as well as discoloring and caking/lumping with choline and carnitine. He adds that calcium carbonate, an economical ingredient used for calcium supplementation, becomes insoluble and chalky in some applications. But with the increase in nutraceutical fortification, other issues will arise. "Information is lacking on how things like lutein and lycopene will act in applications. There is no simple answer," he says.

Interactions, bioavailability, and wholesomeness all are factors to consider when designing a system for fortification, according to Chaudhari. "You must make sure the final product is cost-effective and that the customer is getting what they are paying for," he says. "To maximize a nutrient, think about the minimum exposure (to the factors that will destroy it). You must also consider the stability of each and every ingredient in the final application. You need to know their chemistry and characteristics-how they react, their compatibility." He adds, "Food systems are more complex. In general, shorter-chain compounds are less reactive. For example, hydrolyzed proteins react less than amino acids." He also says that stabilizing systems help with very reactive nutrients such as calcium, iron and vitamin C.

Food manufacturers can retain a greater level of nutrients in finished products simply by changing processing steps. For example, manufacturers can minimize exposure of heat-labile and oxygen-sensitive vitamins to high temperatures and air by using HTST processing, or by adding nutrients mixed with flavors as a final step after heat treatment, mixing and aeration. During storage, packaging with oxygen and light barriers can limit losses, as does temperature control.

Chaudhari says that encapsulation and time-release compounds offer other ways to ensure utilization of nutrients. "This is a very fascinating area. People are working on microencapsulation with mono- and diglycerides which withstand room and slightly elevated temperatures."

A number of nutrients and bioactive substances are candidates for encapsulation. Obvious choices include reactive minerals, such as iron, magnesium and copper, and heat- and oxygen-sensitive vitamins, such as A, C and E. However, microencapsulation of probiotics, choline, amino acids and B-vitamins also offers delivery and flavor-masking advantages.

Historically, manufacturers compensate for expected losses by adding more of a vitamin or mineral to the mix so the dose at the end of a product's shelf life will meet labeling claims. Thus, the formulated amount and the declared amount are different. "Overage" is the term for the extra amount of nutrient needed, expressed as a percent of the declared value. A thorough understanding of the kinetics of a nutrient's degradation allows manufacturers to predict the overage needed.

Chaudhari says: "there are three factors to figure in for overage - processing loss, analytical variation and shelf life." He adds that while there are guidelines to help predict losses, every product and its conditions are different, necessitating close work with customers during product development. "We get baseline data after processing, then we can predict shelf life. In powder products, vitamins A, D, and C loss is about 0.25% per month but in liquids, vitamin A loss can be 80% to 100% and C, 30%, 40% (or) 50%," he says.

Some of the latest ingredients typically found in supplements pose new challenges to ensure that customers get what they want. Steve Dentali, vice president, scientific and technical affairs, American Herbal Products (AHPA), Silver Spring, MD, says that when developers consider adding botanicals to foods, "there are two issues - what are you going to look at as the marker and do we know how to choose the product. Herbs are really not new - we just forgot how to use them." As an example, he cites the centuries-old practice of using spice to preserve food and current knowledge of the antioxidant properties of rosemary. However, before botanical stability can be addressed, he says: "There is a more fundamental problem - how to measure herbal ingredients. In some matrices, you won't be able to measure them because the marker compound is not always measurable." Additionally, many times the materials measured by markers are not actually the active compounds and biological assays should be developed instead of chemical ones. He recommends the recently published AHPA white paper (available for purchase at www.ahpa.org/book store.htm) on the standardization of botanical products, an authoritative reference that clarifies the meaning of standardized botanical products, as a first step to further understanding these ingredients.

Researchers continue to investigate ways to prevent losses and maximize stability. "We are moving in a positive direction to create more stability through different types of processing," says Fergus Clydesdale, Ph.D., distinguished professor and department head, department of food science, University of Massachusetts, Amherst. "An old example is going from old processing to high-temperature, short-time processing. And we have made progress in terms of packaging." He adds that current research on newer technologies, such as high pressure and ultrasound, may lead to future improvements.

Another newer approach is to include ingredients, such as antioxidants and emulsifiers, in a blend that protects vitamins, minerals and bioactive components and enhances their stability and bioavailability. Clydesdale says: "Research on actual matrices are identifying synergies between nutrients to provide increased bioavailability. Also Drs. Decker and McClements in our department are (doing research on) stabilizing omega-3s in emulsions."

No doubt the evolution of nutrition and food science will deepen our understanding of ingredients and technologies, spawning innovative functional foods and beverages. Most likely, each new discovery will include a fresh set of stability and manufacturing issues. While ensuring stability and the presence of nutrients in products is important, Clydesdale advises product developers to "make sure it's efficacious by doing clinical studies. It has to do what you say it's going to do."

Angela M. Miraglio, M.S., R.D., (ammiraglio @aol.com) is a Fellow of the American Dietetic Association from Des Plaines, IL. She has extensive experience in trade and technical communications, public and consumer affairs, and product development and nutritional assessment. Her firm, AMM Food & Nutrition Consulting, provides food and nutrition communications and technical support services to food and beverage companies and trade and professional associations.

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