What is the best way to measure Liquid Concentrates?

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FAQ: “We have an enquiry from a liquid concentrate manufacturer. Currently they are using an instrument to check on the color quality of their chicken essence. The scale that they are using is EBC. As EBC scale is only up to 27 units, we have to dilute the chicken essence sample before measurement. The client is looking for a technique whereby dilution steps can be eliminated. Is this possible?

Beside chicken essence, they would also like to measure color of other new food and fruit essences. By observing the color, they hope to control the quality of those essences. So far they do not have any method/scale yet for those new products. What would you recommend us to do in this case? Is it necessary to use a scale such as EBC or ASBC for measurement? Can we measure L* a* b* values or L*C*h* for those samples and then determine the color acceptance level using delta E or delta H by comparing with standard value?

Hope you can advise us on this.”

“Chicken essence” is typically a concentrated commercial chicken stock similar to chicken bouillon. It is likely prepared as a liquid rather than the cube form of a bouillon cube which is dissolved in hot water.

These food and fruit concentrates basically come in two forms, or a combination of both:

  • The sample being transparent with high absorption of light, therefore not much signal getting through. Think of soy sauce as an example.
  • The sample is translucent with internal solids. Think of concentrated strawberry fruit juice.

When we standardize our instruments in TTRAN transmission, a light blocker is used to set 0% transmission and the cell + DI Water for set to 100% transmission. Our sphere instruments with powerful pulsed xenon flash lamps can measure any color within that range, so there is not a problem in measuring concentrated dark liquid concentrates such as these food and fruit essences, in a 10 mm (or 2 mm) cell in TTRAN LAV UVFilter Nominal mode in the concentrated form (no dilution).

The problem is that while your customer can make color measurements (such as L* = 6.5, a* = 0.5, b* = 1.1 D65/10) and can compare those values to a product specification, this measurement will not provide very much color quality information as there is little light coming through these dark and murky concentrate samples. Small lot differences in color are not discernable visually, nor do the color measurements (which quantify what is seen visually) reflect a significant change with small concentration differences from lot-to-lot.

Some concentrates are not highly chromatic and can be measured undiluted. My recommendation is that if the average spectral transmission (or Y Transmission value) of the liquid concentrate > 10% (relative to cell + DI water = 100), then your customer can measure the food or fruit concentrate in the undiluted form. My preference is an average spectral transmission (or Y Transmission value) of the liquid sample in the 30 – 40% range for optimal results in lot differentiation.

Typically, the transmission of food and fruit concentrates is < 10% (dark and murky) and the best option is to dilute them to whatever concentration level your client recommends for their customers (called a “working strength”). Measure the concentrates in a 10 mm path length cell (use thinner 2 mm cell only if Y transmission < 10% in working strength form). There will be lots of sample signal coming through allowing lot color differences to be differentiated and the measurements will reflect what the customer sees.

EBC (or ASBC) intended for beer color is based on absorbance at 430 nm will work to quantify for chicken essence, and perhaps some other yellow concentrates but not all colors. I would not recommend EBC as we have a better color quality measurement method that will handle all concentrate colors.

To Establish Concentrate Target Values for each Product Color

  1. Configure a Job for display of:
  • CIE L*, a*, b*; Y Transmission D65/10 (measures product color).
  • dL*, da*, db* (measures lot color differences relative to product target).
  • dEcmc (2:1) or dE2000 (2:1:1) D65/10 elliptical difference (value > 1 indicates that the lot difference is visually different from product color).
  • Average Weighted Strength (% Strength WSUM in Color Data Table/Differences) to indicate if lot concentration is stronger or weaker than product target.
  1. File/Save Template As to save as this Color Data view as the default template.
  2. Standardize HunterLab sphere instrument in TTRAN transmission, LAV, UVFilter Nominal using a 10 mm path length cell filled with DI water.
  3. As an optional but recommended PQ Performance Qualification step, read back the DI water as a standard. It should read L* = 100, a* = 0, b* = 0, Y Transmission = 100% D65/10 closely.
  4. Make measurements of several “good” quality lots of each concentrate color in diluted (working strength; typical) or undiluted form with Y Transmission > 10%.
  5. Average the lot results to establish a target product color for each concentrate.
  6. Save the average results as a product standard target in the Job or database for later recall.

Typical Measurement Method for each Product Color

  1. Standardize HunterLab sphere instrument in TTRAN transmission, LAV, UVFilter Nominal using a 10 mm path length cell filled with DI water.
  2. As an optional but recommended PQ Performance Qualification step, read back the DI water as a standard. It should read L* = 100, a* = 0, b* = 0, Y Transmission = 100%, % Strength WSUM = 100 D65/10 closely.
  3. Prepare Lot Sample (dilute to working strength) and fill 10 mm cell.
  4. Recall Product Target from Job or database.
  5. Measure Lot in 10 mm cell under Product Target.
  6. If dEcmc (2:1) or dE2000 (2:1:1) D65/10 elliptical difference < approximately 1.5, the customer is unlikely to see a difference relative to initial Product Target color and it should be good to ship.
  7. If dEcmc (2:1) or dE2000 (2:1:1) D65/10 > 1.5, look at % Strength WSUM D65/10.
    • If % Strength WSUM of Lot > 100 relative to Product Target, then add water to lot to weaken the strength to be closer to 100 (close enough if dEcmc (2:1) or dE2000 (2:1:1) D65/10 < 1.5).
    • If % Strength WSUM of Lot < 100 relative to Product Target, increase lot concentration.
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