Purpose: Color is often used as an indication of quality and freshness for food products. This is the case for orange juice, where a red-orange color is preferred.
Originally, orange juice manufacturers used subjective methods for measuring color. This involved visually comparing orange juice in a standard glass tube to a set of United States Department of Agriculture (USDA) plastic comparators, also in glass tubes. As with any subjective method, the results were inconsistent. In the 1950s and 60s, research was conducted by several companies to produce an instrument for objective measurement of the color of orange juice.
HunterLab developed the D45 Citrus Meter which is still used in the industry today although it is no longer manufactured. The current HunterLab instrument meant for measurement of orange juice is the ColorFlex L2. This compact spectro-colorimeter can measure the color of fresh and concentrated orange, grapefruit, and lemon juice contained in the same kind of glass tube used for the visual comparison method. It can show citrus score values in accordance with the USDA D45 Citrus Meter through hitch standardization with a OJ4 plastic standard.
The ColorFlex L2 Citrus reports Citrus Red (CR), Citrus Yellow (CY), and Citrus Number (CN). These citrus values are calculated from XYZ CIE Tristimulus Values, allowing citrus producers to accurately evaluate the quality of their products.
Conditions for Measurement
Instrumental: ColorFlex L2 Citrus
Illuminant: C
Standard Observer Function: 2-degree
Transmittance and/or Reflectance: Reflectance only.
(Formulas)
Typical Applications
The citrus scores are employed by citrus growers and processors. The scales are most commonly used for measuring orange juice, but they may also be used on grapefruit, lemons, and other citrus fruits.
FAQ: Do you have an external source / part# for vials with cap that fits into the ColorFlex L2 Citrus holder?
Answer:
The Citrus Sample Tubes are a molded glass cylinder mass-produced for another purpose which is the main reason why they are also reasonably priced. HunterLab refers clients directly to the source for these consumables.
The tube is placed in a special D02-1011-127 OJ Tube Holder when the ColorFlex L2 Citrus is placed on its back and color measurement of orange juice is read through the middle for the tube.
The containers used to measure OJ Color Scores on the ColorFlex L2 Citrus are borosilicate glass tubes (25-mm O.D. x 200-mm L) with a black phenolic screw cap. These tubes have a 70 ml fill capacity to the top but 50 ml sample volume should be sufficient for the citrus. They are manufactured by:
Kimble Chase Glass, Vineland, NJ 08362 USA, + 865-717-2600
Kimax # 45066A-25200
These tubes can be obtained from Kimble Chase (see web site for world locations), or from the following two suppliers:
Daigger Scientific, Vernon Hills, IL USA 60061, +847-816-5060
Order EF23607H
Fisher Scientific, Pittsburgh, PA 15275 USA 15275, +800-766-7000
Order 14-930-10L
FAQ: Can Citrus or Orange Juice Scores be used to measure other juices?
Answer:
The Citrus or OJ Scores was designed and optimized for orange juice. To date, this is the only scale that has physical standards such as the OJ Tubes to check and validate the scale. There is a long history with orange juice color evaluation and product quality. Before orange juice color was evaluated instrumentally, these OJ Tube standards were used to evaluate the color visually.
Yes, Citrus or OJ Scores have been used to quantify the color of tangerine, red grapefruit. white grapefruit, lemon and lime juice because the color of these juices is a combination of yellow and red. They are not the intended use of the scale however, and the user has to find their own range of acceptability with these juices in terms of CR, CY, CN. It is a non-standard application.
FAQ: Does the USDA make color tubes, similar to the OJ plastic color tubes but for Grapefruit juice?
Answer:
No. The reason why there are no physical visual standards for these alternate juice types is cost. To develop and maintain any visual color standard system is costly. These days, the USDA does not have to budget to do it on their own but expect considerable help from industry. Industry has not stepped up. The Citrus Scores and OJ visual standards remain the only option for all to use in standard and non-standard applications of measuring juice color.
See attached pdf file for the complete article with formulas.
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