As reducing sodium across the population is debated, the food industry is pressured to reduce the salt content of its products.

Kathie Wrick, Contributing Editor

Few researchers doubt high blood pressure is a leading contributor to heart disease and stroke. However, a simple cause-and-effect epidemiological linkage is undermined by physiological complexity, since many other factors are involved in blood pressure regulation. Some people with high blood pressure can bring it down with a sodium-restricted diet, but most hypertensive people do not respond to low sodium intakes and require medication. Additionally, one study of people with normal blood pressure showed no blood pressure rise until over 18g sodium was consumed (Sagnella, GA, et al. 1989. Am J Physiol. 256:R1171 –R1175). In another study of young men, over 24g--the equivalent to over 61g (10tsp) of salt--had to be consumed before blood pressure finally rose (Luft, FC, et al. 1979. Circulation. 60:697-706).

 However, although controversy over the appropriateness of low-sodium diets continues, the advice to reduce sodium content remains compelling, because it could have an important impact on public health.

Current U.S. Dietary Guidelines (2005) make recommendations for adults to consume no more than 2,300mg sodium/day (equivalent to about 1tsp of salt). Individuals at high risk for hypertension should not exceed 1,500mg/daily of sodium, and meet their 4,700mg/day potassium need through the consumption of high-potassium foods. In 2006, the American Medical Association urged and eventually petitioned the FDA to remove salt from the GRAS list, and called for the food and restaurant industry to lower the sodium level of the U.S. food supply by 50%.

An analysis of the most recent National Health and Nutrition Examination Survey (NHANES) data (2003-2004), commissioned by the International Life Sciences Institute (ILSI), shows Americans average just over 3,400mg/day overall. The same ILSI analysis estimated 65.6% of sodium came from processed ingredients entering the food supply.

Product Development Approaches
Before sodium can be reduced, thought needs to be given to what roles these sources play, since their functions need to be replaced, also. (See charts “Typical Sources of Sodium” and “Salt--A Functional Ingredient.”)

For example, salt (sodium chloride) is mankind’s oldest preservative. In addition, salt has a complex effect on flavor. Salt can enhance sweetness, mute acidity and alter mouthfeel. The taste of salt is never exactly the same, when used in different foods, because of the modifying effects on flavor from different food components. Additionally, the majority of approaches to sodium reduction are highly application-specific. Here are some to consider.
* A stealth reduction program. Many global packaged food companies have announced they will be gradually reducing the sodium chloride level in their branded products over a period of years. This approach is based on the concept that people can adapt to a less salty note in foods over time, and an extended timetable for salt levels may allow for the formulation changes, without consumers noticing. This approach, however, does not address other sodium sources in products that do not directly contribute to salty taste. The many flavor nuances created by sodium chloride, along with its other functionalities, force food technologists to take a systems approach. The best development efforts using all the tools available may not result in a perfect sensory match to the current product standards, but achieving consumer acceptance means a better product has been developed because of the lower sodium benefit.

* Use of salt with unique crystal shapes. Salt is available in a variety of salt crystal shapes and particle sizes that influence bulk densities, caking resistance, flowability, fryability, dissolution rates, surface area and the ease of blending, and salty taste perception. Does the salt crystal dissolve quickly on the tongue for a quick, clean salt “hit,” or does it melt more slowly and exert its influence on the overall savory flavor perception? The crystal shape and particle size of salt will affect flavor profiles, especially when salt is applied in topical applications, such as chips or breadsticks.

Sodium chloride crystals typically have a cubic shape. Tiny cubes can bind together through ionic bonding of the sodium, and further processing can provide specific sizes. These salts can range from a fine, pulverized four-microns-diameter product, to coarse, rock salts greater than 1,000 microns in diameter. Salt crystals also can be compacted into flakes.

Alternatively, they can use the Grainer or Alberger evaporation process to form three-dimensional, pyramid-shaped, hollow crystals. These crystals with irregular shapes cling to surfaces more effectively than traditional salt, while dissolving more rapidly in the mouth. This provides a big, salty burst with less salt. If this salt is broken into flakes with a light bulk density and uneven surface, it can have enhanced cling and solubility.

Researchers at Leatherhead Food International have also been manipulating salt’s physical characteristics to maximize flavor. They have demonstrated that smaller salt crystals produced by a freeze-drying method make for a more fast-acting and, therefore, altered salty sensation on the tongue. The June 1, 2009, issue of Chemical and Engineering News quotes Cindy Beeren, sensory and consumer manager at Leatherhead, as saying sodium chloride must dissolve before humans perceive it, and that physical process is intimately linked to the crystals’ shapes and sizes.

n Salts with different mineral contents. Sea salts from various global locations are growing in popularity. Many are naturally evaporated, along with other minerals unique to the local seawater that can impact taste. The soup category was the first to take the lead in using a specific type of sea salt in its products in 2006, allowing claimed sodium reductions from 25-40%. Some sea salts are blends of sodium and potassium chloride (KCl). Some have been naturally evaporated by wind and sun and contain all of the salts found in seawater, including sodium chloride at approximately 78%, along with other mineral salts. These other salts, usually magnesium salts, may impart bitter notes and may preclude the ingredient from meeting FCC standards for sodium chloride for purity.

* Salt substitutes, plus masking agents. Reducing sodium by over 25% has often been accomplished by replacement of sodium chloride with KCl. Blends with 25-40% (or even more) potassium appear to work well in some applications. Food scientists must consider where their products will be marketed, since some countries limit or prohibit potassium chloride use altogether.

Bitterness also remains problematic. Many flavor houses with strong R&D capabilities have proprietary molecules that mask these bitter notes and help round out the overall flavor to which salt contributes. Bitterness blockers are also available, such as one that combines the sulfonic acid taurine with nucleotides, such as adenosine 5’-monophosphate (AMP). They are thought to reduce taste-cell activation by bitter compounds, while enhancing salty and umami (often described as savory) tastes.

The supplier of one KCl-based, salt-replacement ingredient that is coated with a proprietary flavor system says it enhances any salt that is present in the product and changes the way the palate perceives the potassium chloride. The system brings the perception closer to the beginning of the flavor response curve; that is, potassium chloride has a bit of a late onset of perception, unlike salt, which is immediate.

The flavor houses have been working on sodium reduction for years, also, and, unlike years ago, they now have some proprietary molecules that mask KCl’s bitter notes very well. “But, I can’t emphasize enough that success is very formula-specific,” says Linda Kragt, technical sales manager of a well-known sodium and potassium chloride supplier. “We have been addressing sodium reduction for decades at our company, since the 1960s. Successful salt reduction depends not just on the food category, but on the specific nature of a given product within a category. Formulation strategies depend on the starting composition, the role sodium chloride already plays in the product, the desired sodium reduction level and the target sensory profile.”

* Low- and no-sodium leavening agents. Leavening ingredients, such as sodium bicarbonate (baking soda), sodium acid pyrophosphate and sodium aluminum phosphate (among others) have long contributed significant quantities of sodium to diets. Innovative phosphate leavening system options are now available. For example, calcium acid pyrophosphate provides a sodium-free means of controlled leavening and potential textural improvement via calcium-protein interactions. Other options include monocalcium phosphate monohydrate, monocalcium phosphate anhydrous and potassium bicarbonate. In addition to knowing the appropriate usage level and understanding the rate and time course of gas release, so that the baking process can be fine-tuned, watch to see if new flavors are imparted to the finished product that should be addressed.

* Dairy protein-based systems. Researchers are looking into dairy-derived ingredients captured from the whey stream during cheese-making that contain relatively low levels of sodium (between about 2.8-3%). They induce a salty flavor perception that belies their actual sodium level. A paper published on the innovatewithdairy.com site advises that whey permeate, with a 0.6% sodium content and a naturally salty flavor, means salt may be reduced or eliminated in some baked goods formulas. They also offer a very clean label (i.e., “natural flavor” or “contains milk”). Dressings, sauces, soups and baked goods are potential application areas, because these ingredients are liquid.

* AYEs, HVPs, amino acids, peptides and nucleotides. Autolyzed yeast extracts (AYEs) and hydrolyzed vegetable proteins (HVPs) can replace a portion of the salt in some formulations. Newer technologies have allowed development of specialty yeasts rich in glutamates and nucleotides that also are considered “all-natural” and can be listed simply as “yeast.” These ingredients help compensate for lower sodium chloride levels, because they are good sources of free amino acids, certain peptides and nucleotides, among other flavor and umami taste-enhancing compounds. (See sidebar “Umami Update.”)

The lysis (breakdown) of various protein-based starting materials releases peptides and amino acids--and, in the case of the yeast-based products, cellular contents such as monosaccharides, nucleotides and mineral salts--that can heighten a food’s savory notes. Starting materials to produce AYEs include proprietary strains of Saccharomyces cereviciae or protein derived from them. Soy or vegetable protein sources are used for HVPs.

“Soups, sauces and processed cheeses use AYE quite often in salt replacement,” says Kevin McDermott, product manager of a well-known AYE and HVP supplier. “Special replacements have been developed for bakery applications, because the presence of inactive yeast cells can sometimes inhibit the live yeast fermentation rates.”

* Proprietary flavor/taste modifiers. Flavor companies are making new ingredients available to help all aspects of food flavor development, including sodium reduction. Flavor modifiers have little to no taste of their own, but have shown the capability of modifying how flavor is perceived by the consumer. They can achieve these effects by fatiguing the palate for a particular taste or flavor; changing the perception threshold for one or more substances; blocking a taste bud’s ability to respond to a tastant; or changing the taste perception of a flavor.

Jeff Cousminer, now a consulting culinologist after a professional career exclusively in the flavor industry, says, “Absolutely no one has developed a compound or group of compounds that do a near perfect job of duplicating the flavor impact of salt, nor are they likely to.” An ingredient solution that works extremely well can likely cost a great deal more than sodium chloride, a low-cost, commodity ingredient. “This makes marketing finished products that may be more expensive to the sizeable segment of consumers who do not consider high blood pressure to be ‘their personal issue’ a real problem.”

Cousminer is convinced that most all the flavor houses have developed their own technologies to partially replace sodium-containing ingredients and enhance overall product sensory profile. “The inquiries were enormous a couple of years ago, and now companies are further along the sodium reduction learning curve,” he says. Cousminer has years of experience in systematically evaluating the application potential of experimental products intended for flavor enhancement, including products targeted for sodium-reduced foods, in conjunction with professionally trained and consumer taste panels. One issue that often is overlooked is that the same taste acuity cannot be generalized across all consumers. “This makes flavor development an art as well as a science,” Cousminer says.

A number of new, proprietary compounds that help enhance savory flavors by stimulating umami taste receptors are coming onto the market. (See sidebar “Umami Update,” along with a chart of compounds.) This new generation of umami-enhancing ingredients and other flavor potentiators and modifiers will certainly add value to the product development toolbox. They will have to do a better job of enhancing salty perception, independent of any contribution from potassium chloride, in order to compete with other available sodium reduction and flavor development tools. Newer, even more “natural” ingredient strategies uncovered by high throughput screening methods that actually utilize human taste receptor cells will become more important in the future. They will likely become food formulator’s “gold,” should there be yet another round of attempts to lower the salt and sodium content of foods even further. The medical nutrition science communities may, in a few years, reveal that Americans still consume too much sodium. Might today’s newer, proprietary flavor enhancers be just the beginning for the food industry to “change the way America perceives salt?” Stay tuned... pf

SIDEBAR

The discovery helped stimulate increased scientific sophistication about taste. When the umami receptors (known as G-protein-coupled receptors, or GPCRs) bind a tastant, such as glutamate or a 5’ nucleotide, a G-protein called gustducin turns on a sequence of signals that lets the brain physiochemically acknowledge the umami taste (Zhang F, et al. 2008.  Proc Natl Acad Sci U S A.52:20930-4). These signals work through an ion channel known as TRPM5, also located on the taste cells. Transgenic mice lacking this ion channel cannot taste umami, sweet or bitter, but can taste salt and sour.

Umami taste is provided by its long-known stimulants (glutamate and aspartic acid, MSG and the 5’ ribonucleotides), lesser known organic acids, as well as a host of proprietary molecules offered by flavor companies, who have the technical expertise to identify, develop, manufacture and commercialize them. An interesting review of umami and the history of some industry developments in the search for umami enhancers appeared in Chemistry & Biodiversity (Winkel, C, et al. 2008. Chem Biodivers. 5:1195 – 1203). It notes that umami stimulants can come from many disparate compounds.