Sample Preparation of Paste/Purée for Tomato Color Measurement

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FAQ: "I have another rather basic question - is there an International agreed dilution in which to measure tomato colour? I am using 8.3 brix." 

FAQ: “We are processing tomato fruits to produce tomato paste (28/30°Bx – 36/38°Bx), in all products with different brix values we reconstitute the sample to 12°Bx to measure color value.”

FAQ: “The product that we are talking about is tomato paste with varying brix levels from 19 through to 36 brix, depending on specification. Is there a preparation convention on dilution of tomato paste/purée for color measurement?”

First level processed tomato products tomato paste/purée, sauce, catsup and juice are sufficiently uniform such that small redness color differences can be visually seen by a human observer. When you apply color quality measurement of redness (Hunter L, a, b; a/b ratio, USDA Tomato Scores) to these uniform processed tomato products, sample preparation for translucency becomes important to ensure a repeatable measurement.

All tomato products are translucent to some degree but tomato paste/purée has a higher level of solids than sauce, catsup and juice. To keep the degree of translucency relatively even and consistent among all 4 classes of processed tomato products, there is a reference in the original USDA Tomato Scores study that states that tomato paste/purée should be diluted from their original tomato soluble solids (NTSS) to 8.5 +/- 0.1 Brix using de-aerated, distilled water. Tomato sauce, catsup and juice should be measured at the same solids level as found in the can.

Reference:

George Marsh, James Buhlert, Sherman Leonard, Teri Wolcott and Julie Heil,

“Color Scoring Tomato Products Objectively”

University of California, Davis, CA USA

July 15, 1980

Our advice on sample preparation for processed tomato products would be to dilute tomato paste/purée to 8.5 brix and use tomato sauce, catsup and juice as found in can.

Other more non-uniform tomato products such salsa and pizza sauce that have added extra ingredients (onions, green and red peppers, spice blends etc.), typically have product color tolerances that are not as tight. Sample preparation for these derivative tomato products is typically as found in can.

Please not that some companies, particularly in Europe, dilute their paste/purée to 12 Brix. The key point is that for a translucent product such as tomato paste/purée, the color values are dependent on dilution this factor along with temperature and how measured should be reported with the color values.

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