[PDF] How to Use a Refractometer - Fruit & Vegetable Preservation PDF 237293.pdf

soluble sugar is measured using a refractometer, either analog (below) or digital is covered by an illuminator flap or cover When light passes through a sample containing dissolved solids (such as sugars), it is interrupted, slows down and is bent or 'refracted'

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Refractometry – in other words, the measurement of light refraction – has proven itself as a method of analysis in the laboratory time and time again There, refractometers are used daily to determine the purity, concentration, or density of liquids

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COMPENDIUM OF INTERNATIONAL METHODS OF ANALYSIS –OIV Place a small test sample on the lower prism of the refractometer, taking care (because

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It is possible to measure the Brix and HFCS content either with a density meter or a refractometer Both methods will give the same result if pure sucrose/HFCS

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How to Use a Refractometer

Fact Sheet

Prepared by Diane M. Barrett, PhD,

Fruit & Vegetable Products Specialist, UC Davis

Introduction

Soluble (dissolved) sugar (or solids) content (SSC or °Brix) is a measure of sweetness. In fruits, the typical range of soluble sugar content is 5-15%, while in vegetables it is typically 5% or below. See examples in figure below (Matthews et al., USDA 1987). % soluble sugar is measured using a refractometer, either analog (below) or digital.

Key Concepts:

Measurement of % sugar in fruit and vegetables provides information on quality and may be used as an indicator of harvest time, market value or use as a fresh or preserved product. Refractometers are composed of a glass measuring prism where the sample is placed, which is covered by an illuminator flap or cover. When light passes through a sample containing dissolved solids (such as sugars), it is interrupted, slows down and is bent or 'refracted'. Scientists have correlated the change in the refractive index, or bend of light, to % sugar. Temperature affects the reading (increases 0.5% SSC for every 5°C or 10°F). The reading is only correct if done between 20 -30°C (68-86°F). Otherwise use a correction table.

0.005.0010.0015.00Apple

O r a n gePeachPeasPineappleStrawberries

TomatoesWatermelon

% soluble sugar

How to Use a Refractometer

Fact Sheet

Prepared by Diane M. Barrett, PhD,

Fruit & Vegetable Products Specialist, UC Davis

How To

With small fruits or vegetables, use the whole

fruit, but with larger ones, cut a representative wedge from the stem end to the blossom end and to the center of the fruit. Crush using a blender, mortar and pestle or garlic press, or squeeze through cheesecloth. Remove pulp or seeds by filtering through a small piece of cheesecloth or filter paper.

Measurement Steps

o Open the plastic cover and make sure the glass prism is clean and not scratched. o If not clean, put a few drops of distilled water on the glass, shake the water off, and touch the edge of the glass with a soft clean cloth to wick the remaining water off. o Place few drops of sample on glass measuring surface using plastic pipette or spoon. o Replace cover. If trapped air exists, gently press down on cover. o Look through the eyepiece while holding the refractometer up to a natural light or incandescent light source.

Adjust the focus by twisting the eyepiece.

There is a scale inside showing % sugar.

o Read where the shadow boundary or contrast line (difference between blue and white areas) crosses the scale. Record the % SSC or

Brix value.

Clean between each reading with distilled water, which should be 0% SSC at 20°C or 68°F.

Calibration

o Calibrate to 0% SSC using distilled water at the beginning of use, and depending on how many samples are measured, periodically throughou t measurements. o Contrast line should cross the scale at zero. If not, the scale needs adjustment. o Refer to specific manufacturer instructions, but there is a calibration screw to adjust.

Materials Required:

Refractometer

Blender, mortar and pestle or garlic press

Distilled water

Plastic pipette or spoon to put sample on glass measuring surface.

References:

Kitinoja, Lisa and Hussein, Awad. February 2005. Postharvest tools and supplies kit. Utilization, calibration and maintenance manual. University of California, Davis. Matthews, Ruth H., Pehrsson, Pamela, R. and Farhat-Sabet, Mojgan. Sugar content of selected foods. United States Department of Agriculture Home Economics Research Report

48. September 1987, 41pp.

Refractometer image. http://www.refractometer.pl/hand-held-refractometer Ulfund. Refraction at interface. Own work. Licensed CC0 via Wikimedia Commons - n_at_interface.svg Vasquez, Steve and Mueller, Shannon. Refractometer calibration, use and maintenance.

University of California Cooperative Extension.

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[PDF] [PDF] How to Use a Refractometer - Fruit & Vegetable Preservation