Food Standards and Quality Control

Food Standard and Quality Control

Lesson 08 : Objective Methods - Chemical Methods

Physico-chemical methods

• The pH, acidity, total soluble solids, pectin etc can be measured using these methods. Hydrogen ion concentration can be estimated using pH meter. It consists of a glass indicating electrode and a reference elec­trode to complete the electrical circuit. Digital handheld pH meters also available for this purpose.
• The concentration of sugars in foods can be determined by refracto meter. Refractometers are instruments used to measure substances dissolved in water and certain oils. The refractometer works using the principle of light refraction through liquids.
• Refractometers use this principle to determine the amount of dissolved solids in liquids by passing light through a sample and showing the refracted angle on a scale. The scale most commonly used is referred to as the Brix scale. The Brix scale is defined as: the number of grams of pure cane sugar dissolved in 100 grams of pure water (grams sugar/100 grams of sugar solution).
• Brix or Balling hydrometer gives directly the percentage of sugar by weight in the syrup. It is always necessary to make a temperature correction since the hydrometers are usually calibrated at 20°C. Each instrument used by canners usually covers a range of only 10° Brix, e.g. 10-20, 20-30, 30-40, 40-50, 50-60 Brix respectively and are gradu­ated in 1/10th divisions. Brix is defined as percent sucrose measured by a Brix hydrometer.