literature review salt; health, functionality and...

Literature Review Salt Taste

June 1, 2010

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Literature Review

Salt; Health, Functionality and Flavor

Nu-Tek Products

Dr. Russell Keast

Centre for Physical Activity and Nutrition (CPAN)

School of Exercise and Nutrition Sciences

Deakin University

Australia


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Setting the Scene The April 2010 release of the Institute of Medicine report (Medicine, 2010) on salt (sodium

chloride, NaCl) levels in processed foods sends a strong warning to the food industry about

future changes in their use of sodium. Food companies will need to reduce levels of sodium

in foods as mandatory national standards have been recommended. Excessive salt

consumption is a major health problem for developed Nations. What follows is a brief

summary of the IOM report including it’s recommendations.

Institute of Medicine Report on Salt 2010

Americans consume unhealthy amounts of sodium in their food, far exceeding public health

recommendations. Consuming too much sodium increases the risk for high blood pressure, a

serious health condition that is avoidable and can lead to a variety of diseases. Analysts

estimate that population-wide reductions in sodium could prevent more than 100,000 deaths

annually. While numerous stakeholders have initiated voluntary efforts to reduce sodium

consumption in the United States during the past 40 years, they have not succeeded. Without

major change, hypertension and cardiovascular disease rates will continue to rise, and

consumers will pay the price for inaction.

In 2008, Congress asked the IOM to recommend strategies for reducing sodium intake to

levels recommended in the Dietary Guidelines for Americans. In this report, the IOM

concludes that reducing sodium content in food requires new government standards for the

acceptable level of sodium. Manufacturers and restaurants need to meet these standards so

that all sources in the food supply are involved. The goal is to slowly, over time, reduce the

sodium content of the food supply in a way that goes unnoticed by most consumers as

individuals’ taste sensors adjust to the lower levels of sodium.


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Strategies to Reduce Sodium Intake in the United States from IOM Report

Recommendation 1: The Food and Drug Administration (FDA) should expeditiously initiate

a process to set a mandatory national standards for the sodium content of foods.

Recommendation 2: The food industry should voluntarily act to reduce the sodium content

of foods in advance of the implementation of mandatory standards.

Recommendation 3: Government agencies, public health and consumer organizations, and

the food industry should carry out activities to support the reduction of sodium levels in the

food supply.

Recommendation 4: In tandem with recommendations to reduce the sodium content of the

food supply, government agencies, public health and consumer organizations, health

professionals, the health insurance industry, the food industry, and public-private partnerships

should conduct augmenting activities to support consumers in reducing sodium intake

Recommendation 5: Federal agencies should ensure and enhance monitoring and

surveillance relative to sodium intake measurement, salt taste preference, and sodium content

of foods, and should ensure sustained and timely release of data in user-friendly formats.


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1.0 Introduction

Sodium chloride (NaCl) is the prototypical stimulus that elicits salty taste. Sodium chloride is

a commonly used food ingredient which provides many technological functions such as

flavour enhancement, preservation and texture modification (Hutton, 2002). Sodium (Na+)

also performs a number of vital roles in the body including maintaining the volume of

extracellular fluid, osmotic pressure, acid-base balance and transmission of nerves impulses

(Geerling & Loewy, 2008). Unlike other essential minerals such as calcium, we do not have

large stores of sodium in the body and need to constantly replenish sodium via the diet

(Reddy & Marth, 1991).

While sodium is essential for normal human functioning, current sodium intakes far exceed

recommendations for good health (Brown et al., 2009). This is a problem because there is a

strong positive relationship between sodium intake and blood pressure. Raised blood

pressure is a major cause of cardiovascular disease, responsible for 62% of stroke and 49% of

coronary heart disease (He & MacGregor, 2010). Excess sodium consumption has also been

linked to numerous other negative health effects including gastric cancer (Tsugane et al.,

2004), decreased bone mineral density (Devine et al., 1995) and possibly obesity (He et al.,

2008).

In general, attempts to reduce dietary sodium intake through sodium restricted diets have

shown short term success but have lacked long term sustainability and practicality for large

populations due to high levels of sodium in processed foods and the significant contribution

of processed foods to our diet (James et al., 1987; Hooper et al., 2002b). Also, a reduction of

sodium chloride in foods is accompanied by a loss of palatability of those foods (Mattes,

1997; Karanja et al., 2007a). The ideal solution would be to reduce the concentration of

sodium in the food while retaining optimum saltiness for palatability. One strategy to reduce

sodium is to replace with potassium salts, and while potassium chloride elicits weak saltiness,

at higher concentrations it also elicits metallic and bitter taste limiting its utility in foods

(Ainsworth & Plunkett, 2007). However, minimising those ‘off-flavors’ means potassium

could be an effective salt taste replacer.


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1.1 Significance

Excess sodium consumption has been linked to numerous adverse health conditions and is a

major public health concern in the USA and worldwide (Medicine, 2010). Previous

strategies to reduce sodium chloride consumption have shown to be effective in health care

settings but are not practical at the population level due to the large contribution of processed

foods to sodium intake. Strategies aimed at lowering the sodium content of processed foods

have the potential to decrease sodium in the food supply, thereby decreasing population wide

sodium consumption. Even small decreases in diastolic blood pressure (DBP) (-2 mmHg) as a

result of sodium reduction can reduce the prevalence of hypertension by 17% (Cook et al.,

1995). While decreasing sodium is causal in reducing hypertension (World Health

Organisation, 2003), the totality of existing evidence suggests that both low sodium and high

potassium intakes are necessary for the greatest protection against high blood pressure and

development of CVD (Intersalt Cooperative Research Group, 1988; Poulter et al., 1990;

Cook et al., 2009).


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2.0 Physiological roles, intake recommendations and current consumption

patterns of sodium and potassium.

2.1 Sodium

Sodium is responsible for regulating extracellular volume, maintaining acid-base balance,

neural transmission, renal function, cardiac output and myocytic contraction (Dotsch et al.,

2009). While there is variability in individual sodium requirements the World Health

Organisation recommends that an adult adequate sodium intake is <87 mM/day (<5g) (World

Health Organisation, 2003). The average US sodium intake is estimated to be 140-160

mM/day (8-9.5 g/day) (Wright et al., 2003; Cordain et al., 2005; Cook et al., 2007) and

United Kingdom (161 mM/day (9.5g/day). These studies illustrate we are consuming levels

well in excess of sodium required for optimum health.

2.2 Potassium.

Potassium is an essential dietary micronutrient responsible for smooth muscle contractility,

fluid balance, neural signal transduction and cardiac function (Wardlaw & Hampl, 2007).

Adequate intake for the prevention of chronic disease for potassium is 120 mM/day (4.6g)

(World Health Organisation, 2003; Champagne, 2006). The NHANES survey revealed the

median potassium intake to be 49.8 mM (g)/day (Bazzano et al., 2001). In contrast to

sodium, these studies demonstrate that we are consuming potassium below intake guidelines.

2.3 Inversion of potassium and sodium intake.

Arguably, the human diet has undergone more significant changes in the past 50 years than in

the past 10 million (Cordain et al., 2005). One such modification is the molar ratio

consumption of sodium to potassium. Historically hominid diets contained high potassium

and low sodium concentrations due to a diet consisting largely of fruits, vegetables and whole

grains (Cordain et al., 2005). Our evolutionary forebears had a need to consume sodium, and

as sodium was a scarce dietary element, we developed an appetitive response to sodium via

salt taste (Mela, 2006). Although the taste mechanism for sodium has not changed, the food

supply has developed to suit our appetitive desires and the modern western diet contains a

high proportion of processed foods with high levels of sodium, which is inherently appealing

to humans (Mattes, 1997). Moreover, fruit and vegetables are the main source of dietary


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potassium, however fruit and vegetables are not adequately consumed in a western style diet.

Overall consuming a western style diet has resulted in a decreased intake of potassium and

increased intake of sodium (Figure 1).

Figure 1 : Changes in sodium (Na) and potassium (K) intake in the transition from ancestral

(Then) to current (Now) diet (Frassetto et al., 2001). The graph demonstrates sodium

concentration increasing while potassium concentration declines during the transition from

the ancestral to the current diet.

mM

/day

Reduction in [Na/K] ratio


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3.0 Health effects of sodium and potassium intake

The excess sodium and insufficient potassium consumption that is associated with a typical

western style diet have been linked with several negative health effects which are outlined in

the following sections.

3.1 Blood Pressure

3.1.1 Sodium and blood pressure

The relationship between sodium intake and blood pressure is well established. Numerous

systematic reviews and meta analysis have been found to support a positive linear association

between sodium intake and increasing blood pressure (Intersalt Cooperative Research Group,

1988; Stamler, 1991; Stamler, 1997; He et al., 2002; Hooper et al., 2002b). This association

was depicted in the large worldwide epidemiological study INTERSALT which reported the

relationship between sodium and potassium excretion and blood pressure of 10,079 men and

women across 52 centres. A significant positive linear relationship was found between

sodium intake and systolic blood pressure (Figure 2) when adjusted for age, sex, BMI and

alcohol consumption (P<0.001) (Intersalt Cooperative Research Group, 1988).

Figure 2: The association between sodium excretion and systolic blood pressure (Intersalt

Cooperative Research Group, 1988). Depicted is a positive linear relationship between

sodium intake and systolic blood pressure.


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The linear relationship is supported by another meta-analysis which illustrate significant

reduction in blood pressure with a decline in sodium intake. He and MacGregor (2002) found

that a sodium decrease of 78 mM/day (4.5g) in hypertensive individuals equated with

4.96mmHg fall in systolic blood pressure (P<0.001). In addition, in normotensive individuals

a 74mmol/day (4.4g) reduction in sodium caused a decrease of 2.03mmHg (P<0.001). The

meta-analysis findings are supported by previous conclusions that reductions in sodium affect

hypertensive individuals to a greater degree than normotensive individuals (Geleijnse et al.,

1997; Sacks et al., 2001a; He & MacGregor, 2002; Geleijnse et al., 2003) Furthermore, these

findings were based on modest sodium reduced diets in adults over a minimum intervention

period of four weeks which demonstrates that there is likely to be a long term effect of

sodium reduction on blood pressure.

3.1.2 Potassium and blood pressure

Both epidemiologic and clinical studies have suggested that an increase in potassium intake

may lower blood pressure. A meta-regression analysis of randomised control trials by

Geleijnse, Kok and Grobbee (2003) found that a median potassium increase of 44 mM/day

(1.7g) corresponded in a fall of 2.2/1.6mmHg (systolic/diastolic) after adjusting for potential

confounders. These results appear conservative in comparison to an earlier meta analysis of

clinical trials by Cappuccio and MacGregor who witnessed a 6/3mmHg (systolic/diastolic)

decrease in blood pressure with oral potassium supplements (Cappuccio & MacGregor,

1991). The difference in results could be attributed to Geleijnse, Kok and Grobbee excluding

short term trials from the meta-regression and Cappuccio and MacGregor only using a

hypertensive population group for interventions.

3.2 The Sodium Potassium Ratio

Some studies have shown the effect of the sodium potassium ratio on blood pressure and

cardiovascular disease to be more significant than the effect of either electrolyte considered

individually (Khaw & Barrett-Connor, 1988; Poulter et al., 1990; Cook et al., 2009). The

consequences of increased sodium consumption in tandem with decreased potassium

consumption has been explored in populations moving from rural to urban areas.


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The Kenyan Luo Migration study showed rural farmers that traditionally consumed a diet

very low in sodium experienced increased blood pressure after an average of one month post

migration to urban areas (Poulter et al., 1990). As well as consistently having significantly

higher systolic and diastolic blood pressures than their rural counterparts, urbanised men and

women also had significantly higher urinary sodium and lower urinary potassium excretions

suggesting that both low dietary intake of potassium and high intake dietary intake of sodium

to be associated with increased blood pressure (Poulter et al., 1990). The Trials of

Hypertension Prevention (TOHP) follow up study found when urinary sodium potassium

ratio was tested for a relationship with CVD a significant, positive and linear relationship that

was similar for stroke and CHD morbidity and mortality and was not affected by age, sex,

race, baseline BMI or smoking (Cook et al., 2009).

Overall there has been limited research into the relationship of the sodium potassium ratio to

health. However, the totality of existing evidence suggests that both low sodium and high

potassium intakes are necessary for the greatest protection against high blood pressure and

CVD (Intersalt Cooperative Research Group, 1988; Poulter et al., 1990; Xie et al., 1992;

Dyer et al., 1994; Cook et al., 2009). Figure 3 shows the relationship between sodium,

potassium and blood pressure.


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Figure 3: Sodium and Potassium in the Pathogenesis of Hypertension. Adapted from (Androgue & Madais, 2007).

3.3 Cardiovascular Disease

High blood pressure is a strong risk factor for cardiovascular disease and stroke (World

Health Organisation, 2002). It has been estimated that a decrease in systolic blood pressure

of 2mmHg would result in a 4 % reduction cardiovascular disease risk and overall mortality

by 3% (Chobanian et al., 2003).


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Studies linking sodium intake and reduced cardiovascular disease risk have shown conflicting

results. A possible reason for this is the inconsistency of definitions used to describe

cardiovascular events, different methodological approaches used, differences in population

groups and sodium measurement methods (Hooper et al., 2002b). However, a meta-analysis

of prospective studies by Strazzullo et al (2009) found an association between higher sodium

intake and cardiovascular disease risk in a pooled analysis of 14 cohorts (Strazzullo et al.,

2009).

3.4 Stroke

A meta-analysis of prospective studies by Strazzullo et al. on the effects of sodium intake on

stroke and cardiovascular disease illustrated that a high sodium intake was associated with

greater risk of stroke (P=0.007) (Strazzullo et al., 2009). Results from prospective studies of

stroke risk and potassium intake have shown inconsistent findings however, a majority

support an inverse relationship between stroke risk and increased dietary potassium intake.

Bazzano et al. studied potassium intake and stroke risk of 9805 men and women who

participated in NHANES I epidemiologic follow-up study. It was found that those who had

insufficient potassium intake had a 28% greater risk of stroke (P=0.001) (Bazzano et al.,

2001). Potassium intake was obtained from 24 hour diet records which are prone to

confounding. A study of 43,738 male health professionals by Ascherio et al. also documented

an inverse relationship between risk of stroke and potassium intake (Ascherio et al., 1998).

3.5 Summary

Table 1: Summary of health effects related to sodium and potassium consumption

Health effect

Sodium

• ↑ Sodium intake = ↑ Blood Pressure

• ↑ Sodium intake = ↑ Risk of Cardiovascular Disease

• ↑ Sodium intake = ↑ Stroke Risk

Potassium

• ↑ Potassium intake = ↓ Blood Pressure

• ↑ Potassium intake = ↓ Stroke Risk


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4.0 Flavour Perception Flavour is a multimodal sensory experience incorporating inputs from all our senses: sight,

hearing, touch, smell and taste. While all sensory systems are involved in flavour perception,

it is the chemical senses, taste, smell and chemical irritation, that provide the majority of

information about the flavour of the food or beverage (Keast et al., 2004a). Arguably the

most important sensory system regarding the acceptance or rejection of food is the sense of

taste, as it is a proximal sense that determines whether a food carries potential nutrients or

toxins. To perform this task the taste system is subserved by five taste qualities: sweet, sour,

salty bitter and umami. Taste sensations are characterized by four separate attributes –

quality, intensity, temporal and spatial patterns (Keast et al., 2004a). Taste quality is the

most important defining feature of taste sensation and it is a descriptive noun given to

categorize sensations that taste compounds elicit (sweet, sour, salty, bitter and umami).

Intensity is related to the magnitude of the taste sensation and may be plotted against its

concentration to produce a psychophysical function. Temporal pattern is used to describe the

time course of taste perception and intensity. And spatial topography relates to location and

localizability of taste sensation (Keast et al., 2004a). Regarding spatial topography, it is

important to note the oft recited theory of the tongue map is incorrect, anywhere we have

papillae or taste receptor cells we can experience all tastes.

4.1 Taste Transduction and taste thresholds

Taste transduction is initiated when sapid compound activates taste receptors throughout the

oral cavity. Taste receptors are found on taste receptor cells, housed in groups of 50-100 cells

in taste buds. Taste buds themselves are housed in specialised epithelial structures named

papillae. Papillae have three different structural forms fungiform at the anterior tongue,

foliate at the side of the tongue, and circumvallate at the posterior tongue. Once the taste

receptor is activated, afferent nerve fibres then transmit this information to the gustoral cortex

of the brain where it is coded into a taste response (Chandrashekar et al., 2006).

As the concentration of a sapid compound increases, it may reach different levels of

perception. Taste is initiated when a sapid compound activates taste receptor cells but the

concentration may be too weak to produce a cognitively noticeable electrical impulse;

although the compound is present no taste is perceived. As the concentration of the

compound increases a level will be reached when an individual will be able to discriminate


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from water but unable to identify the taste quality, this is known as the detection threshold.

Taste identification occurs when the concentration of the sapid compound is enough to not

only activate the taste receptor but produce an electrical impulse which can be carried via

afferent fibres to the brain where it is decoded and the taste quality identified; this is known

as the recognition threshold (Keast & Roper, 2007). As the concentration of the tastant

increases further, the perceived intensity of the tastant also increases.

4.2 Salt taste

Recent advances in salt taste transduction illustrate the complexity involved in

chemoreception. Sodium and Lithium are the only two minerals known to elicit a pure salty

taste, other minerals can elicit some salt taste however it is often mixed with metallic or bitter

flavours. Lithium is toxic when ingested in moderate quantities and therefore is not added to

foods. Using an animal model, Chandrashakar et al (2010) demonstrated there are two

epithelial sodium channels on taste receptor cells, one that is permeable only to sodium, and

one that is non-specific and is activated by other mineral cations including potassium. The

sodium specific channel is believed responsible for the appetitive nature of sodium in foods,

while the non-specific channel may be responsible for some of the aversive nature of various

cations (Chandrashekar et al., 2010). It is thought that the ion channel for salt taste are not

located on the apical surface of the taste cell, but rather on the paracellular region between

taste cells (Keast & Breslin, 2002a).

5.0 Taste Interactions As a general rule, when we taste a solitary compound in water as the concentration of the

compound increases so too does our perceived intensity. However, singular taste stimuli are

rarely encountered in everyday life. A number of interactions can occur when two or more

taste stimuli are mixed. For example, mixture suppression can occur when two or more

suprathreshold stimuli of the same modality are mixed together, the intensity is less than the

sum of the individual (unmixed) intensities (Keast et al., 2004b). In other words suppression

results in a taste sensation which is less than the sum of its components (i.e 1 + 1 < 2).

Enhancement is in direct opposition of suppression and refers to when two or more supra

threshold stimuli are mixed together, the intensity is greater than the sum of the individual


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(unmixed) intensities (Keast et al., 2004b). Enhancement results in a sensation which is

greater than the sum of its components (ie. 1 + 1 >2).

5.1 Three levels of taste interactions

Interactions in taste mixtures such as mixture suppression and enhancement can occur at

three different levels – in a food/beverage prior to ingestion, oral physiological interactions or

central cognitive interactions (Keast et al., 2004a). Interactions in a food or beverage are

common and can result in tastants being trapped in a matrix and unavailable for taste

reception, such as happen with sodium in bread. Oral physiological interactions involves one

compound interfering with taste receptor cells or taste transduction mechanisms associated

with another compound and are classified as peripheral interactions as they occur at the

cellular/epithelial level (Keast & Breslin, 2005). Cognitive interactions refer to central

processing of taste stimuli after afferent signals are sent to taste processing regions of the

brain. Central cognitive interactions are generally responsible for mixture suppression and

caused during processing of signals in taste and smell processing regions of the brain (Kroeze

& Bartoshuk, 1985a; Keast & Breslin, 2005).

5.2 Taste interactions involving saltiness

Keast and Breslin reviewed salt taste interactions and reported at low concentration NaCl

saltiness was enhanced by KCl, while at higher concentrations it was suppressed (Breslin &

Beauchamp, 1995a; Keast & Breslin, 2003). Salt and sour mixtures symmetrically affect each

others’ intensity with enhancement at low intensity/concentrations and suppression or no

effect at high intensities/concentrations (Beebe-Center et al., 1959; Pangborn, 1960b; Kamen

et al., 1961; Pangborn, 1962; Kroeze, 1979; Kroeze, 1982; Lawless, 1982; Gillette, 1985;

Kroeze & Bartoshuk, 1985b; Schiffman et al., 1985; De Graaf & Frijters, 1989; Frank et al.,

1993; Schifferstein & Frijters, 1993; Frijters & Schifferstein, 1994; Breslin & Beauchamp,

1995b; Stevens, 1995; Breslin, 1996; Breslin & Beauchamp, 1997; Stevens & Traverzo,

1997; Prescott et al., 2001; Keast & Breslin, 2002b; Keast & Breslin, 2002c). Bitterness is

suppressed by salt while salt taste is not affected by bitterness. Salt enhances sweetness at

low concentrations, has variable effects through the moderate intensity/concentration range,

and is suppressive or has no effect on sweetness at higher intensity/concentration. Sweetness

suppresses salty taste at moderate intensities (Keast & Breslin, 2003).


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Peripheral interactions have an influence in multi-component mixtures. Breslin et al. (Breslin

& Beauchamp, 1997) examined the interaction between sodium, sucrose and urea. They

asked, What happens if a sodium salt is added to the bitter-sweet mixture, given that sodium

salts inhibit bitterness and bitterness and sweetness are mutually suppressive? The results

showed that addition of sodium to a bitter-sweet mixture suppressed the bitterness. As the

intensity of bitterness decreased, sweetness was enhanced due to release from cognitive

suppression of the bitterness. A similar study was performed with similar results by Keast

and Breslin (Keast & Breslin, 2005). These three-taste interaction studies illustrate the

complexity involved in understanding taste interactions and show how peripheral and central

cognitive effects can interact.

5.3 Taste Interactions in Food Matrices

The most influential researcher in the area of taste in various matrices or food systems was

Pangborn (Pangborn, 1960b; Pangborn, 1960a; Pangborn, 1961; Pangborn, 1962; Pangborn et

al., 1963; Pangborn & Hansen, 1963; Pangborn & Chrisp, 1964; Pangborn et al., 1964;

Pangborn & Trabue, 1964; Pangborn, 1965; Pangborn & Trabue, 1967; Pangborn et al.,

1973; Pangborn et al., 1978; Pangborn, 1987). Pangborn and colleagues performed a series

of experiments in the early 1960’s investigating sucrose, citric acid and NaCl taste

interrelationships. Several different food matrices were used, e.g., pear nectar (Pangborn,

1960b), tomato juice (Pangborn & Chrisp, 1964), and lima bean puree (Pangborn & Trabue,

1964). The results from the food matrix generally supported results mentioned in section 5.2.

Breslin et al, (1997) demonstrated that sodium salt suppressed bitterness and also increased

sweetness by releasing it from the mixture suppression exerted by the bitterness. This was

demonstrated in food matrices: Gillette (Gillette, 1985) reported that addition of NaCl to

three soups decreased bitterness and increases sweetness, while Fuke & Konosu (Fuke &

Konosu, 1991) reported that addition of umami tasting sodium salts of 5’-ribonucleotides

(which suppress bitterness) reduced bitterness and increased sweetness in an artificial prawn

extract.

Apart from the primary taste response of adding a compound (NaCl increasing saltiness), the

secondary and tertiary results such as suppressions, release of suppression, or enhancements


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can often be predicted. There are parallels between simple solutions used in psychophysical

studies and the more complex food matrices. However, sapid compounds added to a matrix

may behave differently than predicted, and matrix effects should not be underestimated

(Keast & Breslin, 2003).

6.0 Strategies for sodium reduction

6.1 Rationale, costs and benefits of a sodium reduction program.

The current sodium intake in developed Nations doubles exceeds the <87 mM/day (5g)

recommendation for disease prevention (World Health Organisation, 2003). High sodium

consumption is linked with both increased blood pressure and risk of cardiovascular disease.

The magnitude of potential health gains achievable through population based sodium

reduction are highly significant (Asaria et al., 2007; Webster et al., 2009). A report by Asaria

et al (2007). calculated that a modest 15% reduction in population sodium intake, could avert

8.5 million cardiovascular related deaths worldwide over 10 years (Asaria et al., 2007).

Decreasing sodium intakes would assist the prevention of age related rises in blood pressure

and therefore cardiovascular disease risk (Neal et al., 2006). Age related increases in blood

pressure and cardiovascular disease are likely to become more prolific with the current

ageing population.

A comprehensive meta analysis prepared by the WHO concludes that there is very strong

evidence for the cost effectiveness of national sodium reduction strategies (Neal et al., 2006;

Asaria et al., 2007). For example, cardiovascular diseases are the most expensive health issue

accounting for 11% of total health expenditure (AIHW, 2005). The average sodium reduction

strategy is expected to cost only a fraction of the cost to treat CVDs.

6.2 Methods of sodium reduction

The evidence supporting high sodium intake and negative health effects has lead to the

research on methods of sodium reduction which are discussed below.


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6.2.1 Sodium restricted diets

Sodium restricted diets have been shown to be effective at reducing blood pressure however,

support is often required in the form of extensive dietary counselling or in the provision of

low salt food products. Community based intervention trials have demonstrated that only 20-

40% of participants were able to reduce their sodium intake below the upper intake of

100mM/day despite intense counselling. (Karanja et al., 2007b). Due to the need for

counselling, this intervention would not be feasible at a population level. Sodium reduced

diets are often hard to maintain as they require a change in dietary behaviour, for example,

actively choosing low salt foods. This behavioural change is difficult to develop.

Additionally, having an innate liking for salt taste in a food environment rich in sodium

makes compliance with low sodium diets difficult. Hooper and Sacks suggested that an

overall sodium reduction could be more effectively achieved by reducing the sodium content

of processed foods than by just giving dietary advice alone (Sacks et al., 2001b; Hooper et

al., 2002a; NHF, 2006).

6.2.2 Food industry strategy for sodium reduction

Processed foods contribute 75% to total sodium intake (James et al., 1987), therefore sodium

reductions within these foods could significantly contribute to an overall dietary decrease in

sodium. A World Health Organisation (WHO) report, Reducing Salt Intake in Populations,

underlines the need to work directly with food manufacturers as a cornerstone of any

successful national salt reduction campaign (World Health Organisation, 2006). A food

industry strategy is an important component of many sodium reduction programs worldwide.

6.3 Methods of sodium reduction in the food industry

Many countries now have implemented some kind of sodium reduction program, however the

United Kindom (UK) and Finland are the only countries to have strategies with proven

decreases on population sodium intakes (Webster et al., 2009). While the two strategies are

similar in their approaches using public health promotion and a sodium labelling system,

where they differ is in their methods of sodium reduction from within food industry.

6.3.1 The United Kingdom strategy - sodium reduction by stealth

The UK approach is based around stealth reduction methods which refers to a gradual

reduction of salt in processed foods that is unnoticeable to consumers (Kilcast & Ridder,


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2007). The foundation of the approach is based on setting sodium reduction targets for

different product categories which industry are expected to meet within an allocated time

period This strategy has been successful with the sodium content of most processed foods in

supermarkets being reduced by 20-30% in the past 3 years. These results are expected to be

duplicated when revised targets are set for a further 10-20% reduction to meet the UK’s daily

intake target of 6g/day by 2012 (He & MacGregor, 2008).

6.3.2 The Finnish strategy : Use of salt substitutes

The Finnish food industry has a different approach to reduce sodium in processed foods.

Companies have been reducing sodium in food products by replacing NaCl (salt) with

sodium-reduced, potassium and magnesium enriched mineral salt called Pansalt. Pansalt’s

composition is; NaCl 56%, KCI 28%, MgSO4.7H2O 12%, I-lysine-HCI 2%, anticaking

agents 2% (IMI Life Products, 2006). By 2002 the program has achieved a significant 3g/day

NaCl reduction from 12 to 9g/day (Laatikainen et al., 2006; He & MacGregor, 2008).

The significance of the success of using Pansalt in manufactured food products has sparked

an interest in the development and use of salt substitutes. Salt substitutes, are compounds or

ingredients that allow for the partial replacement of salt without affecting saltiness of

products. There are many different types of substitutes used within the food industry. The

most common types are; alternative minerals such potassium chloride, amino acids like

arginine, “salty” peptides and organic acids (Dotsch et al., 2009). Other types of salt flavour

enhancers are Hydrolysed Vegetable Proteins (HVP), yeast extracts and mono-sodium

glutamate (MSG) (Brandsma, 2006). Arguably salt taste is the most important function of

NaCl since our innate liking for salt taste in foods has an important role in food choice and

acceptance.

7.0 Concerns for food industry for sodium reduction The food industry is already responding to the need for sodium reduction with 3,000 global

low salt food and drink product launches in 2009, double that of 2006 (Katz & Williams,

2010). This underestimates the actual number of products as manufacturers will not label

their products as low salt due to possible consumer rejection.


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7.1 Loss of palatability and consumer acceptance

Taste is one of the most important factors in food choice. Humans have an innate liking for

salt taste and as a result, when large reductions in sodium content occurs there is a decline not

only in saltiness of the product but also in palatability and consumer acceptance (Beauchamp

et al., 1982; Mattes, 1997). This is an issue for the food industry as dramatic changes in

product flavour profiles could potentially alienate consumers and encourage them to choose

other product brands (Brandsma, 2006; Dotsch et al., 2009). Estimates by the Consensus

Action on Salt Health (CASH) show that a 10-25% reduction in sodium is undetectable by

humans senses (Consensus Action on Salt and Health, 2006). This estimate is supported by

an Australian study which demonstrated that consumers were not able to detect gradual

changes in sodium of up to a 25% in white bread (Girgis et al., 2003). However, with a

continual decline of sodium from products it is inevitable that a point will be reached where a

difference in flavour profile will be detectable by consumers. Therefore, to achieve large

sodium reductions in foods, an approach is required where the salt taste elicited by sodium

can be replaced so that the consumer acceptance is not negatively affected (Dotsch et al.,

2009).

7.2 Other functions of sodium

There are other functions of sodium in food including binding, flavour enhancement,

stabilisation and preservation (Lynch et al., 2009; Taormina, 2010). While it is thought that

sodium reduction in foods will affect the functionality of products, evidence presented by

Lynch et al demonstrated that reducing sodium level from 1.2% to 0.6% or 0.3% did not

significantly affect the functional properties of bread. The only significant difference

discovered was the taste qualities between the breads. Overall these results indicate that the

production of a lower level salt is technically feasible (Lynch et al., 2009). A number of

anecdotal case studies from industry were reported by the New York Times, where qualities

such as texture, colour, taste and flavor were negatively affected in various foods (Moss,

2010). It was reported that the food industry was not challenging the Institute of Medicine

recommendations on the link between sodium consumption and hypertension, rather that

decreasing sodium would increase food prices and also the level of sugars in foods (Moss,

2010).


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8.0 Potassium salts as potential sodium substitutes Although sodium and lithium are the only two cations which produce a true salt taste

potassium also elicits a salt like taste. Potassium chloride is currently the most commonly

used material to replace sodium in foods (Dotsch et al., 2009). In addition to producing a salt

like taste, potassium chloride also elicits a bitter/metallic taste (Van der Klaauw & Smith,

1995). This is thought to occur via the non-sodium specific channel of taste receptor cells

(Chandrashekar et al., 2010). When potassium chloride is used in high concentrations the

bitter/metallic taste dominates over the salty taste, often causing foods to become unpalatable,

thus limiting the utility of potassium chloride as a salt substitute (Ainsworth & Plunkett,

2007).

Studies have been conducted on the acceptability and liking of bread products containing

potassium chloride. In a partial substitution study replacing sodium chloride with potassium

chloride in white breads found that a 50% substitution of sodium chloride with potassium

chloride was considered to have an unpleasant flavour and aftertaste (Braschi et al., 2009).

The unpleasant taste associated with high potassium chloride levels is supported by Guy

(1986) and Salovaara (1986) who both demonstrated that breads containing potassium

chloride at levels of 0.36g and 0.29g/100g respectively were deemed unpalatable by

consumers (Salovaara, 1982; Guy, 1986).

These studies indicate that a salt substitute containing high concentrations of potassium will

be unpalatable in foods, therefore methods of masking the bitter/metallic tastes associated

with the use of potassium salts needs to be found. There have been advances in technologies

to reduce any off-flavors elicited by potassium salts and modified potassium chloride salts are

currently available in the market place. For example, Rao et al. reported the sensory and

functional characteristics of a modified potassium chloride in potato chips, French fries and

ham luncheon meat. Results showed replacement of 1/3rd of sodium using a modified

potassium chloride without any significant difference in sensory or functional properties of

the foods (Rao et al., 2010). Such results are encouraging because by increasing the utility of

potassium-salts in foods it is likely that the concentration of potassium in processed foods

will increase. Due to a high consumption of processed foods the dietary intake of potassium

will potentially increase, which is associated with many significant health benefits such as

reduced blood pressure and stroke risk.


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9.0 Summary In summary, excess sodium and insufficient potassium intakes are a major health concern in

the developed world as it plays a role in the manifestation of hypertension, stroke and

cardiovascular disease (Intersalt Cooperative Research Group, 1988; Bazzano et al., 2001;

Strazzullo et al., 2009). Processed foods provide in excess of 75% of sodium in the diet

(James et al., 1987) and thus the role of the food industry in a sodium reduction strategy is

vital (World Health Organisation, 2006). However, decreasing the sodium content of

products will also decrease salty taste and affect palatability and consumer acceptance

(Mattes, 1997) and many within the food industry are resistant to major change as

recommended in the Institute of Medicine report. If sodium is reduced in food products there

is a need to maintain saltiness and consumer appeal of those products and the use of salt

substitutes such as potassium-salts could allow for greater sodium reductions without any

perceived difference in taste properties.


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23

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