Preserving the nutritional quality of packaged foods

The Nutrition Facts label is under scrutiny by consumers and FDA. Shoppers look at the label as they make dietary choices. The agency dictates the format and what nutrients must listed on the label. Compliance is enforced through random sample collection and testing for accuracy.

Yet, packaged foods are subject to processing methods that can alter the nutritional quality of a product. Pasteurization, high-pressure processing (HPP), ultra-high temperature (UHT) and freeze-thaw treatments expose foods to high levels of heat, light and/or oxygen that can diminish the nutritional quality of a product. What’s more, certain ingredients such as vitamins, minerals and botanicals are prone to degradation. Then there’s nutrient loss during storage. However, brands can ensure products remain nutritionally sound from factory to fork.

Although FDA provides guidance documents, there’s no rule of thumb for achieving this. Although similarities may exist among categories, every product and every process is different. “For example, cereal-based foods may be more or less refined, fractionated and recombined with added salt, sugars and fats, yielding a panoply of products with very different nutritional values,” authors pointed out in a study published in Advances in Nutrition.¹ “The same is true for other food groups.”

The writers suggested beyond chemical composition, food health potential is related to food structure, “which involves nutrient interactions, starch structures (degree of complexation with lipids and of gelatinization or the amylase/amylopectin ratio), and matrix porosity and density.” Food structure characteristics affect the feeling of satiety and nutrient bioavailability. They proposed considering the effect on food structure because the more food is processed, the more its structure is generally fractionated and/or destroyed. Yet, they acknowledged that measuring the impact of processing on food structure is complex, and more data is needed.

The good news is, “In general, the content of macronutrients like proteins, carbohydrates and fats will not be altered during processing and shelf life,” said Joe Farinella, vice president of product development, Imbibe. The form of the macronutrient may change. Fats may rise to the surface of a beverage or proteins may settle out to the bottom of the package; however, the actual amount of these ingredients will not change.

Protein

Proteins are delicate macromolecules that undergo denaturation or coagulation when subjected to different formulation systems or processing conditions such as changes in temperature, pH, pressure or agitation. Denaturation changes the shape of a protein and results in diminished protein solubility, according to Qin Zhao, Ph.D., associate, global plant-based proteins research and development (R&D), Ingredion Inc. “Coagulation causes protein molecules to clump together. However, in most cases, denatured or coagulated proteins will not lose their nutritional values, as our bodies still absorb the exact same amino acids from the protein, even if they are denatured or coagulated.”

But in some cases, food processing can potentially reduce the bioavailability of specific amino acids. One common example is lysine, which can undergo the Maillard reaction with reducing sugars or other aldehyde compounds during heat processing such as in heated skim milk powder.²

Other changes associated with alkaline and/or heat processing include the racemization of L-amino acids, and the formation of crosslinked peptide chains such as lysinoalanine, which result in a loss of lysine, cysteine and threonine, together with reduced protein digestibility.^2,3

Lysine and threonine are essential amino acids. They—along with histidine, isoleucine, leucine, methionine, phenylalanine, tryptophan and valine—cannot be produced by the body, so they are required in the diet. Other amino acids, such as arginine, are considered conditional because they are required by the body under some circumstances, such as when fighting certain diseases.

Because all proteins are not alike, protein quality is an important tool to measure the ability of a food protein to meet the body’s metabolic demand for amino acids, the digestibility of the protein and the bioavailability of the individual amino acids.⁴ Protein Digestibility Corrected Amino Acid Score (PDCAAS) is used to determine the protein quality and to support protein content claims.

With the current trend toward plant-based proteins, it’s worth looking at pulses, which are made from beans, lentils, chickpeas and peas. “Pulse proteins offer a balanced amino acid profile,” Zhao said. Compared to other protein sources, pulses are abundant in amino acids such as leucine and arginine, which can contribute to muscle protein synthesis. Pulse proteins are typically limited in either tryptophan or sulphur amino acids, such as cysteine and methionine. And cereal proteins are usually limited in lysine. “Therefore, blending pulse proteins with cereal proteins or other complementary sources is a good strategy to improve the overall protein quality of the final product,” he explained.

Raw plant sources, e.g., pulse seeds, typically have lower digestibility “due to the encapsulating effect of the cell wall and the presence of anti-nutritional factors (ANFs),” Zhao cautioned. “Their digestibility can be improved with milling to remove the outer seed coat and to further concentrate or isolate the proteins. Pulse protein concentrates, which contain 50% to 60% protein, are usually obtained from dry milling and air classification; and pulse protein isolates, which contain higher than 80% protein, are typically obtained through wet milling. It has been reported in the literature that pea protein isolate has an intermediately fast intestinal bioavailability in between that of whey (fast digestible) and casein (slow digestible).” Pea protein- and dairy protein-containing meals were comparably efficacious in triggering gastrointestinal (GI) satiety signals.⁵

Many pulse proteins contain ANFs, “including phytate, enzyme inhibitors, polyphenolics, lectin, saponin and vicine/convicine (only in faba bean), which can also cause a reduction in protein digestibility and amino acids bioavailability,” Zhao continued. “However, many conventional and innovative food processing methods can be used to reduce the levels of ANFs in pulses. In general, thermal processing is most effective at reducing the activity of enzyme inhibitors and lectin, whereas germination and fermentation can effectively reduce phytate content, and dehulling can effectively reduce phenolics and tannins. The combination of thermal and nonthermal processes can be used to more effectively reduce or eliminate specific ANFs.⁶ More work is needed in the future to understand how processing of finished products containing pulse ingredients affects levels of ANFs and ultimately the protein quality, as this is highly dependent on the process and the food matrix involved.”

Soy is one of the most flexible and stable proteins. It can perform at different heat, shear and pH conditions. “Soy proteins are widely used in UHT, low-temperature long time (LTLT) and high-temperature short-time (HTST) pasteurization and sterilization processes. There are also soy protein options that perform very well in low acid conditions. The key is to choose the right soy protein,” said Dina Fernandez, global protein development manager, ADM Nutrition. The requirements for soy protein will vary for a protein bar (low water holding capacity), a meat alternative (high gelling and emulsification) or beverage (highly soluble, clean flavor). “From a nutritional perspective, soy proteins are the most nutritional plant-based protein and the best option to replace animal proteins 1:1 when nutritional claims are targeted,” she said.

Fernandez advised it’s important to consider post-processing stability. “Most protein ingredients have a shelf life of 18 to 24 months and their nutritional composition is fairly stable during that time,” she said.

Fat

During oil processing, the concentrations of minor components, like antioxidants (such as tocopherols and tocotrienols, as found in vitamin E), may decrease slightly. John Satumba, Ph.D., R&D director, global edible oils, North America, Cargill, advised that control of the refining process helps ensure minimal degradation. “The post-refining addition of mixed tocopherols or other antioxidants is a tool that Cargill scientists leverage to design fat solutions with enhanced oxidative stability,” he said.

Choice of packaging is also a consideration, because it provides a physical barrier between oils and accelerants of oil degradation like light, oxygen and metals.

Lipid oxidation can lead not only to development of off-flavor and off-odor, but also loss of a food’s nutritional value. “A typical example is food containing essential fatty acids (EFAs), especially the long-chain polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA),” said Y. Joy Zhong, Ph.D., senior application scientist, food protection, Dupont Nutrition & Biosciences. These omega-3 fatty acids are highly unstable and susceptible to oxidation due to their highly unsaturated nature. Antioxidants can help protect the omega-3 fatty acids from oxidation and preserve the nutritional value of the food, in addition to their role to control rancidity.

Products containing PUFAs should also be stored under cool temperatures and protected from light and oxygen.

Antioxidants inhibit oxidation through different mechanisms. Primary antioxidants, such as tocopherols and some other phenolic compounds, scavenge free radicals and break the chain reaction. “They act as hydrogen donors and/or free radical acceptors to neutralize the highly reactive free radicals and yield stable products that will not initiate new free radicals via a chain reaction,” Zhong said. Secondary antioxidants inhibit oxidation by deactivating oxidation promoters, and these include metal chelators, singlet oxygen quenchers, oxidant reducers, pro-oxidative enzyme binders, etc. Reducing agents are a type of secondary antioxidants that reduce lipid peroxides and related oxidants (e.g., molecular oxygen) through redox reactions and are also referred to as oxygen scavengers. Some secondary antioxidants, such as ascorbic acid, can regenerate primary antioxidants by replenishing hydrogen atoms, thus inhibiting depletion of the primary antioxidants.”

David Johnson, lead scientist, Kalsec, suggested that by including low-aroma, low-flavor rosemary extract at 0.2%, combined with ascorbic acid (vitamin C), the stability of these oils can be greatly extended so their nutritional benefits can be delivered in the body.

Beyond off-flavors and nutrient loss, oxidation creates more alarming issues. “While the main concern with lipid oxidation for the food industry is the negative impact on sensory, lipid oxidation does generate potentially toxic compounds that have shown some correlation with inflammatory diseases,” Johnson said. Examples of harmful components are acrolein and 4-hydroxy-trans-2-nonanal.⁷

Green tea and mixed tocopherols are naturally sourced antioxidants. Their composition “also makes them have biological properties in our bodies and provides protection from oxidative stress,” said Julio Lopez, global business manager, botanical extracts, ADM Nutrition. “For these products to be effective antioxidants, they need to have the right composition or be part of a system that maximizes that function. The same applies for their role as nutraceutical ingredients—their biological function is defined by the composition and bioavailability in the human body. Overall these ingredients are well positioned with consumers and their presence tends to help elevate the wellness profile of the application.”

Vitamins and minerals

To further complicate matters, fat-soluble vitamins can become the substrates for oxidation and lose their nutritional value, even though they individually can function as antioxidants and protect other lipid components from oxidation. Fat-soluble vitamins include A, D, E and K.

Carrot oil color is a micronutrient that contains both alpha- and beta-carotene. Both are precursors of vitamin A. “It has been reported that beta-carotene is responsible for about 30% of the dietary intake of vitamin A in Western countries,” said Carol Locey, director of product management, colors, Kalsec. “One of the most widely used natural colors is oleoresin paprika. This coloring contains various carotenoids with vitamin A activity, as well as smaller amounts of other micronutrients such as tocopherol and ascorbic acid.”

Vitamin A is especially sensitive to light and certain oxidizing agents, such as oxygen, and quickly degrades in the presence of these elements.

The chemical stability of the vitamin or mineral, as well as the processing method, determine the outcome in the finished product. Leaching losses of vitamins and minerals occurs during blanching. Milling and extrusion can cause the physical removal of minerals during processing. The book, “The Impact of Food Processing on the Nutritional Quality of Vitamins and Minerals,” sheds more light. “The bioavailability of key minerals such as iron, zinc and calcium is known to be significantly affected by the fiber, phytic acid and tannin content of foods. Concentrations of these constituents are altered by various processing methods, including milling, fermentation, germination (sprouting), extrusion and thermal processing.” Authors Manju B. Reddy and Mark Love continued, “Vitamins, especially ascorbic acid, thiamin and folic acid, are highly sensitive to the same processing methods. The time and temperature of processing, product composition and storage are all factors that substantially impact the vitamin status of our foods.”

One way to preserve vitamins, fish oil and probiotics is to use physical means via encapsulation. This protects them from harsh environments, such as heat, light, moisture and antagonist ingredients in the formulation. “Most common encapsulation processes include spray drying, spray chilling and fluidized bed,” Zhong said. “A range of hydrocolloids (such as alginate or modified cellulose) and emulsifiers (e.g., lecithin) may be used as the wall material for encapsulation.” 

Advice for the developer

To combat losses during processing, formulators might add an increased amount to their products.  “Adding overages, protecting the functional ingredient or leveraging ingredients to stop degradation reactions are all recommended to protect the Nutrition Facts panel,” Farinella said.

Yet, he cautioned some vitamins and minerals may have off-notes that require masking, especially when used at high levels.

The experience of suppliers can also be helpful, but beware. “It’s important to vet ingredient suppliers to find an option that can withstand conditions based on the product type, pH, processing conditions and desired shelf life,” he pointed out. “Supplier recommendations are based on historical performance data and are relatively accurate; but, since every product is unique and so many variables can impact functional ingredient stability, it is strongly recommended to perform shelf-life testing on the final formula, process and package, measure actual content at the end of shelf life and reformulate as needed.”

Cindy Hazen has more than 25 years of experience developing seasonings, dry blends, beverages and more. Today, when not writing or consulting, she expands her knowledge of food safety as a food safety officer for a Memphis-based produce distributor. She can be reached at cindyhazen.com.

References

1 Fardet A et al. “Current Food Classifications in Epidemiological Studies Do Not Enable Solid Nutritional Recommendations for Preventing Diet-Related Chronic Diseases: The Impact of Food Processing.” Advances in Nutrition. 2015;6(6):629-638.

2 Gilani GS, Sepehr E. “Protein digestibility and quality in products containing antinutritional factors are adversely affected by old age in rats.” The Journal of Nutrition. 2003;133(1):220–225.

3 Sarwar G. “The protein digestibility – corrected amino acid score method overestimates quality of proteins containing antinutritional factors and of poorly digestible proteins supplemented with limiting amino acids in rats.” The Journal of Nutrition. 1997;127(5):758-764.

4 Boye J et al. “Protein quality evaluation twenty years after the introduction of the protein digestibility corrected amino acid score method.” British Journal of Nutrition. 2012;108(S2):s183-211.

5 Overduin J et al. “NUTRALYS pea protein: characterization of in vitro gastric digestion and in vivo gastrointestinal peptide responses relevant to satiety.” Food & Nutrition Research. 2015;59(1):25622.

6 Patterson CA et al. “Effect of processing on antinutrient compounds in pulses.” Cereal Chemistry. 2015;94(1):2-10.

7 Viera S et al. “Biological Implications of Lipid Oxidation Products.” Journal of the American Oil Chemists' Society. 2017;94(3).