Accurate Quality Assurance of Re-Constituted Orange Juice

Table of Contents

Challenges in Achieving High Accuracy °Brix Measurements
Solution from Bellingham + Stanley
Solutions Provided by Pro-Juice Refratometer
About Bellingham and Stanley


Refractometry is a low-cost method that provides rapid and simple measurement of the total dissolved solid content of a liquid sample. The sugar content of syrups and beverages are typically quantified by measuring the refractive index (RI) expressed on a °Brix scale, which is described as the percentage of sucrose weight for weight in water. For the past several years, beverage manufacturers have been using digital refractometers to measure the final dilution ratio (°Brix) of re-constituted fruit juice as a measure of product quality as well as a measure to minimize losses by ensuring total control over concentrate yields.

This method has been successful for most of the fruit types. However, the uncertainty of the Brix content always presents an analytical change in the case of orange juices. The RI readings measured on orange juice samples by modern electronic refractometers are sometimes both inconsistent and deceptive mainly because of the turbidity effect of the samples.

Challenges in Achieving High Accuracy °Brix Measurements

The high accuracy measurement provided by modern digital refractometers has revealed an unpredictable behavior within an orange juice sample that affects tighter dilution control. As a result, this eliminates any chance of cost reduction by means of decreasing target values without the risk of failing to meet minimum regulatory specifications. Since orange juice is a function food, tight control over its quality is imperative.

According to previous reports, difference between instrument, sample and ambient temperatures cause an unpredictable stabilization period between the analyses of samples, thus compounding the effects of the settling of solid particles onto the surface of the prism as being the root cause, as shown in Figure 1.

Figure 1. Insoluble solids in a sample gradually settle on an instrument prism

This causes a change in RI readings over time as depicted in Figure 2.

Figure 2. Continuous readings of three orange juice applications on a digital refractometer

The above also graph also shows the effects of temperature differential. As shown in App. 1, the readings drop at first because the sample temperature is below the standard 20 °C measuring temperature of the instrument, thus requiring a thermal stabilization period. Moreover, inaccuracies can be introduced even if there is a difference in temperature between samples being measured because of the change in thermal stabilization periods.

Other potential causes discussed include possible electro-static affects or absorption. Nevertheless, until now, no manufacturer is able to find a more practical solution for this problem.

Solution from Bellingham + Stanley

According to previous reports, a suitable technique to find the Brix value of orange juice has been developed. However, this method is a time-consuming process and requires multiple readings and extensive statistical analysis, making it not suitable for monitoring the Brix value on the filling line.

In order to achieve high accuracy results for orange juice samples like other fruit juices, Bellingham + Stanley, a unit of Xylem's analytics businesses, has developed an instrument based on its proven RFM340+ refractometer that provides a measurement with 0.01 °Brix accuracy for sucrose solutions and 0.02 °Brix reproducibility between orange juice samples irrespective of the temperature differential or the skill level of the operator.

The new device called Pro-Juice refractometer from Bellingham + Stanley handles the typical issues of refractometric analysis of orange juice measurement through the combination of dynamic measurement and intelligent thermal conditioning. It uses a peristaltic pump to prevent the settling of the solid particles onto the prism surface by keeping the sample in constant motion. Its on-screen menu helps the operator in every stage of measurement and the built-in software ensures cleanliness, which is essential to achieve a high accuracy result.

Filling machines are often put on hold during the establishment of final dilution before packaging a product. Hence, the turnaround time for off-line sample analysis plays a key role in plant efficiency. This latest instrument has been designed to deliver °Brix analysis within 2.5 minutes that include sample preparation and cleaning cycle, thus reducing downtime irrespective of the temperature difference between the instrument and sample.

The flow cell enables sample readings in constant motion its easy release arm facilitates calibration, measurement and cleaning of samples.

Figure 3. Flow Cell

The Pro-Juice automatically identifies the position of the flow cell arm. When up, the instrument serves as a standard high specification refractometer, thus providing quick, accurate and reproducible readings for all samples.

Figure 4. Flow cell up

Figure 5. Sample funnel

Repeated readings of verified orange juice samples in the Pro-Juice refractometer are shown Table 1.

Table 1. Repeated readings of verified orange juice samples in Pro-Juice

Batch 1 2 3
Verified Value 11.23 11.35 11.14
App 1 11.25 11.35 11.14
App 2 11.25 11.36 11.14
App 3 11.25 11.35 11.14
App 4 11.25 11.36 11.13
App 5 11.25 11.35 11.15
Average 11.25 11.35 11.14
Range 0.00 0.01 0.02
Error -0.02 0.00 0.00

The outstanding repeatability provided by the Pro-Juice refractometer can be demonstrated by taking multiple readings of an orange juice sample in the Pro-Juice, on a refractometer under factory conditions, and on a high specification digital refractometer under ideal conditions. The reading range can be compared by calculating the difference of each application from the average value of the readings, as shown in Figure 6.

Figure 6. Comparison of reading differential with different instruments

From the above graph, a range of 0.02 °Brix obtained from the Pro-Juice when evaluated at the extremes of its specification demonstrates the advantage of using the Pro-Juice over other digital refractometers for the analysis of orange juice samples.

Solutions Provided by Pro-Juice Refratometer

The following solutions are provided by the Pro-Juice refractometer

  • Keep sample in constant motion
  • Peltier controller maintains the sample temperature at 20 °C, thus eliminating the requirement for any extensive sample pre-conditioning before measurement
  • It is possible to obtain readings for any sample volume above the minimum requirement
  • Pre-conditioning gets rid of any stabilization concern
  • Pro-Juice readings are in line with values provided by the analysis of several applications on a refractometer under ideal conditions
  • Pro-Juice produces high accuracy results within 2 minutes
  • User friendly
  • It is possible to achieve 3s control limit tolerances of roughly 0.08 °Brix, thus providing improvements of up to 50% when compared to conventional measurement techniques


The Pro-Juice refractometer resolves all issues related to the orange juice measurement on a standard refractometer. Using the Pro-Juice refractometer, orange juice manufacturers can produce orange juice from concentrate with acceptance tolerances as low as possible, thus making significant savings and a quick return on initial investments.

About Bellingham and Stanley

For over ninety years Bellingham and Stanley has been one of the world's leading manufacturers of Refractometers and Polarimeters. Instrumentation is supplied to over 80 countries around the World and our products are considered by many global companies as the ultimate in quality and performance.

Our expertise in optical engineering, electronics and software design has enabled us to create instruments that are used extensively throughout the world's food, drinks, pharmaceutical, chemical and petroleum industries. Over 2000 digital refractometers have been supplied to customers within the USA!

This information has been sourced, reviewed and adapted from materials provided by Bellingham and Stanley.

For more information on this source, please visit Bellingham and Stanley.

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