Bellingham + Stanley
Application Bulletin
Bulletin No:
Title:
APP002
Uses of Refractometers and Polarimeters in the
Confectionery Industry.
There are many uses of refractometers and polarimeters within the confectionery industry.
Fondants – Concentration by Refractometer:
Most common is the use of refractometers to control the concentration of sugar blends used
as fillings for chocolates, boiled sweets and other confectionery products. In most cases,
repeatability is more important than accuracy as product specifications tend to be wide
(i.e. 76 to 78 °Brix). A rapid reading is often required in order to stop the cooking process at
the correct stage.
In the past, optical “Projection refractometers” (a.k.a. ‘Queen Mary’ or
‘battleships’) have been used in such applications as they require no
skill and have a ‘low sensitivity’ when looking at viscous samples.
These have typically been replaced by RFM730 digital refractometers.
Hand-held and Abbe refractometers can also be
used, however, due to cooking temperatures, care must be taken to select
the correct instrument type. Sometimes it is desirable to raise the
instrument temperature in order to keep high concentration products in
liquid state, as well as to provide faster results (by providing a lesser
cooling time). Abbe and RFM300 refractometers provide readings up to
60°C when connected to a waterbath.
Process refractometers are also suitable for such applications as they give real time °Brix
values without having to remove the sample from the vessel; thus
eliminating evaporation (skin formation) and the need to wait for the
product to cool. Fitted to a bypass loop around the outside of the
tank as part of the ‘exit’, process refractometers can provide a
control signal in order to automatically move the product to a buffer
tank at the end of the cooking cycle.
Pastilles & “Gums”:
During the cooking process, Eclipse Hand-Held,
Abbe and digital instruments may be used.
Similarly to ‘fondants,’ product temperature is a
critical parameter when choosing the right
refractometer.
A quality control check of finished product is
somewhat harder, as the sample is often solid (e.g. 90 °Brix). Some
producers adopt the technique of ‘slicing’ the pastille and placing the more ‘liquid centre’ on
the prism of the refractometer. Results to one-decimal may then be achieved.
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Chocolate:
Measuring the fat content of raw chocolate is an important QC parameter.
However, as refractometers measure dissolved solids, it is not possible to
make an analysis without some sample preparation to force the
undissolved solids (fat) into solution. This is done by adding the chemical
‘monobromonapthalene.’ The resultant solution, somewhere in the region
of 1.60 RI, can then be measured on an Abbe refractometer or a digital
instrument such as the RFM860 or RFM870. An example procedure is
shown in Appendix 1 of this document.
Fondants – Controlling the Blend of Sugar Mixes:
The texture and flavour of confectionery filling relies on the accurate blending of sugar types.
Invert sugar is often mixed with sucrose at a specific ratio in order to make a creamy centre
(Reference After Dinner Mints). As the relationship of RI to
sucrose and invert sugar is similar, although it is possible to
measure the concentration of the mixture, it is not possible to
control the ratio of the blend of sugars. However, different sugar
types (sucrose/inverts) have a very different specific rotation
and as such, a polarimeter can be used to check sugar blends
are to the correct pre-described ratios. The ADP410 is suitable
for such applications.
Additives & Raw Materials:
Both refractometers and polarimeters are used to check raw materials used in confectionery
products. The addition of Gum Acacia (Gum Arabic) is often employed as a thickener to
confectionery products (Appendix 2 refers). This raw material can be checked using a
polarimeter. Additionally, gelatine can be checked with a refractometer. Flavours such as
mint oils are also checked on a polarimeter.
Effluent:
Monitoring of waste streams exiting confectionery factories helps
prevent effluent plant (reverse osmosis systems) from becoming
damaged by high sugar levels. Process refractometers can be fitted
to monitor and in some cases control exit streams. Additionally,
these systems can help prevent fines imposed by water authorities.
Appendix 1-
EXAMPLE LABORATORY METHOD
DETERMINATION OF FAT CONTENT BY REFRACTOMETER
Appendix 2-
EXAMPLE LABORATORY METHOD
ACACIA –SPECIFIC ROTATION (OPTICAL ROTATION
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Appendix 1
EXAMPLE LABORATORY METHOD
DETERMINATION OF FAT CONTENT
BY REFRACTOMETER
Page: 1/3
INTRODUCTION
The fat in cocoa beans, cocoa mass or chocolate is extracted into 1-bromonaphthalene. The change in refractive index between pure 1-bromonaphthalene and that containing the fat is a measure of the fat content of the
initial sample.
SCOPE
Raw and roasted cocoa beans, cocoa nib and mass, chocolate.
APPARATUS
Coffee Grinder
Timer
Analytical balance (to 0.lmg)
Retsch S2 mill
50ml grinding cups with lids and Teflon seals
3 x 20mm diameter stainless balls
Digital Dispenser
Refractometer with temperature control @ 30 ± 0.2°C minimum
Glass vials, 20ml
Filter papers Whatman No 2V (folded)
Syringe -10ml disposable, polypropylene
Syringe Filters -0.45µm, disposable
Cotton wool
CHEMICALS
1-Bromo-naphthalene
Hexane
METHOD
SAMPLE PREPARATION
A.
Cocoa beans nib, or mass
1.
Grind the beans or nib in a coffee grinder, raw beans for 25 seconds,
roasted beans or nib for 10 seconds.
3
EXAMPLE LABORATORY METHOD
DETERMINATION OF FAT CONTENT
BY REFRACTOMETER
Page 2/3
2.
Accurately weigh approximately 5g of sample into a 50ml grinding cup.
3.
Add the three stainless steel balls.
4.
Using a dispenser accurately add I5ml of l-bromo-naphthalene.
5.
Grind in Retsch S2 mill for 20 minutes at 80% speed.
B.
Chocolate
1.
Accurately weigh approximately 1.5g of molten sample into a glass vial.
2.
Accurately add 3ml 1-bromo-napthelene via the dispenser.
3.
Mix well and place in 45 oC incubator for 15 minutes.
4.
Mix well again.
MEASUREMENT
1.
Place one or two drops of 1-bromo-naphthalene onto the prism.
Cover with lid, leave for about 30 seconds to allow naphthalene
to equilibrate to 30°C then record reading (RI blank). The reading should be
between 1.6535 -1.6540 - if not, repeat with a fresh sample and check the
temperature.
2.
Clean the prism and lid with hexane and cotton wool.
3.
EITHER:
Filter the sample through folded filter paper into a glass vial.
Discard the first three drops.
OR:
Filter the sample using a disposable syringe filter. Discard the
first three drops.
4.
Place one or two drops of sample onto a prism, directly from filter paper or
syringe, replace lid and allow time for temperature to equilibrate. Record reading
(RI sample).
5.
Each sample and blank should be measured at least twice.
4
EXAMPLE LABORATORY METHOD
DETERMINA TION OF FAT CONTENT
BY REFRACTOMETER
Page: 3/3
CALCULATION
y
where
%fat
=
a 2 x2 + a 1 x + a o
y = mg fat
x = (RI (blank) -RI (sample) x 10000
a2 = 0.001065
a1 = 1.3411
ao = 0.0131
= mg fat
wt of sample(g)x 1 0
A calibration curve has previously been created to give the
constants ao, a1 and a2.
RESULTS
Results should be recorded in accordance with company policy.
The duplicates should be within 0.5% of each other.
HEALTH AND SAFETY INFORMATION:
N.B. 1-bromo-naphthalene is flammable and has a strong odour.
Use in the fume cupboard. Read MSDS Data Sheets before use.
The above calculation is based on statistical analysis carried out in a
contract laboratory and is for example only. The writer accepts no
responsibility for its use outside the origin of the original data.
- End-
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Appendix 2
EXAMPLE LABORATORY METHOD
ACACIA – SPECIFIC ROTATION
(OPTICAL ROTATION)
Page: 1/1
Principle: Specific Rotation of Gum Acacia is calculated on the anhydrous basis,
determined on a 1.0% w/v solution.
Procedure:
Weigh out 1.00 grams of previously dried (105˚C at 5 hours) Gum Acacia into a 150ml
beaker. Add 99mls of deionised water with stirring (use either a stirring rod or magnetic
stirring bar) until dissolved.
Filter the solution using a #1 Whatman filter paper into another 150ml beaker. Solution
must be clean (free from specks).
Calibrate the polarimeter (which polarimeter is to be mentioned…..?) manufactured by
Bellingham + Stanley Ltd. using deionised water as the standard in a polarimeter glass sample
tube (10 centimetres long by 1 centimetre in diameter). Discard the deionised water and
replace with the 1% Acacia solution. Place the tube in the instrument; wait a few minutes,
read the result from the digital display. This is a direct reading and no further calculations
are necessary.
NOTE: The Seventh Supplement Optical Rotation requirement in the Acacia Monograph of
the Description and Solubility Section of USP XX11 and of NF XV11 includes the following as
an informational note: (Page 3168 November 15, 1992)
“Optical rotation values vary depending on the source of Acacia. For example, specific
rotation values calculated on the anhydrous basis and determined on a 1.0% w/v solution are
usually between -25˚ and -35˚ for Acacia Senegal and usually between +35˚ and +60˚ for
Acacia Seyal.
- End -
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