Fahima Khatun, IIAST
A refractometer is a simple instrument used for measuring concentrations of aqueous solutions. It requires only a few drops of liquid, and is used throughout the food, agricultural, chemical, and manufacturing industries. This instrument is used to measure the index of refraction of a substance in any one of several ways, such as measurement of the refraction produced by a prism, measurement of the critical angle, observation of an interference pattern produced by passing light through the substance, and measurement of the substance’s dielectric constant.
International Institute of Applied Science and Technology (IIAST) Rangpur is using a modern refractometer to test and produce quality food sample in the lab at the Department of Food Science and Technology.
Determination of total soluble solids (TSS) or 0brix in supplied sample using refractometer.
Material Required:
- Supplied sample
- Distilled water for calibration
- Digital Refractometer
- An electrical blender
Procedure
- At first verified the instruments had been calibrated before taking the measurement.
- The prism surface located at the bottom of the sample wall was wiped off.
- Then the blended supplied food sample was poured on the prism surface until the sample wall was filled with sample.
- If the temperature of the sample differs significantly from the temperature of the instrument, waited approximately 1 minute to allow thermal equilibrium.
- After the read button was pressed, reading was displayed on the primary display as ⸰ brix.
- Then the reading was recorded.
Applications of Refractometers in the food industry, agriculture and crop production
In general, Refractometer is used for the purposes of quality controlling and quality management of food products.
- Refractometers are used to assess the ripeness of fruits, vegetables, sugar cane and beet before harvesting – i.e., it serves to find the maturity index. This is mainly used for grapes in vineyards. It measures the sugar content of the fruit in °Brix. A liquid has one degree Brix (=1% Brix) if it has the same refractive index as a solution of 1g sucrose in 100g of sucrose water solution.
- They are used to check the alcohol content of wine and beer during fermentation in breweries. For this purpose, special refractometers with scales calibrated to give the alcohol content directly are available.
- Quality of honey can be checked using special kind of refractometers which directly give the amount of water in honey. Low water content in honey is preferable as it ensures better shelf life to the product. If the % of water is high (>20%) then it leads to fermentation by wild yeasts. This kind of refractometer is preferred by bee keepers.
- The salinity meter is used in the food industry to measure the percentage of salt in condiments such as soy sauce, ketchup, mayonnaise and in canning industries for brine solution.
- Refractometers are used to monitor and control the quality of yoghurt, jam, fruit extract, syrup, coffee extract, chocolate, milk, baby food etc. by measuring the total solids in them during processing.
- The refractive index is an indicator of purity in products such as vegetable oils and animal fats.By comparing the values with that of the standard the purity of the product can be assessed.
- Since the refractive index of a pure substance is constant at constant temperature and pressure, it can be used as a means of identification.
Furthermore,In diagnostic and veterinary medicinerefractometer is used to measure the total plasma protein in a blood sample and specific gravity of urine.
Advantages of refractometers
- Refractometers give instant results.
- Refractometers are versatile – available as bench top, hand held and in line models.
- Hand held refractometers are portable and hence can be taken to the spot.
- They are relatively inexpensive with low initial cost and low level of maintenance.
- Refractometers, especially the hand held models are easy to operate. Hence they do not require much skill to operate.
- Also refractometerscan give direct readings such as °Brix or salinity.
Writter: Fahima Khatun (Nutritionist)
Lecturer, International Institute of Applied Science and Technology. Rangpur
