Learn why and how food manufacturers need to measure the sodium (Na+) and salt (NaCl) content in food samples.
Why we need to measure and control sodium content in food products:
- High dietary sodium intake increases the likelihood of developing high blood pressure and heart disease
- In 2010, 1 out of every 10 cardiovascular deaths were attributed to a too high salt consumption
- The World Health Organisation (WHO) recommends an intake of less than 2 000 mg of sodium or 5 g of salt per day (just under one tsp salt)
- Most people presently consume 9 – 12 g of salt per day, thus there is a drive to reduce salt content
- South Africa has introduced legislation to reduce sodium levels in many food categories
- Sodium is also an essential mineral that is needed in very small amounts for health
Where is sodium commonly found in foods?
- Found naturally in most foods, e.g. milk
- Table salt (NaCl) is the most common source of sodium and consists of 40% sodium and 60% chloride
- Other sources include monosodium glutamate, sodium nitrite, sodium saccharin, sodium bicarbonate and sodium benzoate
- Processed meats, snacks, condiments and stock cubes often contain very high levels of sodium
Did You Know?
Bread is the biggest contributor to non-discretionary salt intake in South Africa.
Maximum total sodium levels allowed in certain foodstuffs in South Africa as at June 2016 and June 20193
|Foodstuff Category||Maximum total sodium per 100 g per June 2016, mg||Maximum total sodium per 100 g per June 2019, mg|
|Breakfast cereals and porridges||500||400|
|Fat and butter spreads||550||450|
|Savoury snacks, not salt and vinegar flavoured||800||700|
|Savoury snacks, salt and vinegar flavoured||1 000||850|
|Processed meat, uncured||850||650|
|Processed meat, cured||950||850|
|Processed meat sausages, raw||800||600|
|Soup powder, dry||5 500||3 500|
|Gravy powders and savoury sauces, dry||3 500||1 500|
|Savoury powders with instant noodles, dry||1 500||800|
|Stock cubes, powders, granules, emulsions, pastes or jellies||18 000||13 000|
How to determine sodium content in food samples using the LAQUA Twin Sodium Ion Meter:1
1. Meter Set-Up and Calibration
- Make sure that the meter is set to 2 calibration points prior to calibration
- Calibrate the meter according to manufacturer’s instructions using 150ppm and 2000ppm sodium ion standards.
2. Sample Preparation and Measurement
- Liquid samples such as soups, sauces, brines, beverages, etc., can be placed directly onto the sensor. Dilute the sample with distilled or deionized water, if the results exceeded the meter’s calibration or measurement range (e.g. 5ml sample dilute to 100ml using DI water)
- Solid samples such as chips, cheese, ham etc. must be prepared to liberate the sodium. Mince or crush the sample in a blender. Weigh the crushed sample accurately, then add distilled or deionized water (e.g., 5 grams of sample in 100ml DI water). Mix the sample thoroughly. Place some drops of prepared sample onto the sensor and record the reading. To obtain accurate results, a uniform temperature should be maintained for the standard solutions and samples
- Clean the sensor with detergent and water (warm, if measured sample is oily). If the sensor is stained with sample residues, place a few drops of bleach onto the sensor and leave for 5 to 30 mins. Rinse the sensor with water and blot dry with soft tissue. Condition the sensor by soaking it with 2000ppm sodium standard for 10 minutes to 1 hour prior to next use
- For high accuracy measurement, prepare ionic strength adjuster (ISA) solution containing 4M NH4Cl and 4M NH4OH. Add equal volume of ISA to all samples and standards (i.e. 2ml ISA in 100ml samples or standards)2.
3. Results and Benefits
Foods contain varying amounts of salt. For processed or packaged foods, sodium is listed as milligrams (mg) per serving on the nutrition information panel of the food packaging rather than salt. To compute the sodium and salt (NaCl) contents in food samples from the results, use the formulas in the table.
Sodium and Salt Contents Computation
|Content per serving||Liquid||Solid|
|Sodium (mg)||Sodium (mg/L or ppm) x sample volume||Sodium (mg/L or ppm) x DI water volume (L) x original sample weight (g) / analysed sample weight (g)|
|NaCl (mg)||Sodium (mg) x 2.54||Sodium (mg) x 2.54|
|Example||Sample: 150 ml tomato sauce
1. Drops of tomato sauce give 1 500 ppm reading
2. 5 ml juice diluted to 100 ml gives 75 ppm (x 20 to account dilution). For 1 and 2, the sodium content is 225 mg while the salt content is 571.5 mg
|Sample: 28.4 g potato chips
Crush chips and weigh 5 g. Add the 5 g in 100 ml DI water and mix thoroughly. Drops of diluted chips give 250 ppm reading. The sodium content is 142 mg while the salt content is 360.68 mg
References and further reading:
1. Horiba Application Note: Determination of Sodium and Salt Content in Food Samples, Dec. 2015
2. Nielsen, Suzanne. Sodium Determination Using Ion Selective Electrodes, Mohr Titration, and Test Strips. Chapter 10. Food Analysis Laboratory Manual. 2nd Edition. USA: Springer. 2015
4. WHO Guideline – Sodium Intake for adults and children