ASTA Color and IC Color of Paprika and Oleoresin Spices

“The pungency for red peppers and the color value for the paprikas are the most

paprika dolce

Dried red peppers and ground paprika showing good color.

important parameters. Hot peppers, used as relishes, pickled or ground into a fine powder for use as spices, derive their pungency from the compound capsaicin (8-methyl-N-vanillyl-6-enamide), a substance characterized by acrid and burning taste, that is located in the internal partitions of the fruit. First isolated in 1876, capsaicin stimulates gastric secretions and, if used in excess, causes inflammation. It is a tasteless, odorless white crystalline substance. Its level varies widely in capsicum peppers, from less than 0.05% in the mildly pungent types to as high as 1.3% in the hottest chilies. The pungency level is usually represented in Scoville heat values. Pungency levels vary in the same variety, by geographical region, and in maturity levels. Volatile oil content is low in all capscicums. The pigment responsible for the color in paprikas is capxanthin, a carotenoid. Other carotenoids present are capsorubin, zeaxanthin, lutein, kryptoxanthin and alpha and beta-carotene.

The pigment content increases as the fruit ripens and continues after maturity. The extractable color of paprika is usually expressed in ASTA color value or in Color Units, which are 40 times the ASTA color.”

Industry Reference Methods for ASTA and IC Color

ASTA – American Spice Trade Association currently has two color methods listed referencing these metrics:

  • ASTA Method 20.1 Extractable Color in Capsicums and Their Oleoresins (revised October, 2004) based on absorbance at 460 nm is used for quantifying the color of paprika and oleoresin spices.
  • ASTA Method 18.0 – Curcumin Content of Turmeric Spice & Oleoresins (revised October, 2004) measures the curcumin content of turmeric by measuring the absorbance of curcumin color at 415-425 nm.

An extract is made from the paprika or oleoresin using acetone. Then the absorbance of the oleoresin solution is measured at 460 nm in a 10-mm cell using a spectrophotometer such as a HunterLab ColorQuest XT or ColorQuest XE.

As a quantification of the extractable color (strength) of this oleoresin:

ASTA Color = (Absorbance (460 nm) of Acetone Solution * 164 * I + C) / (Initial Sample weight in grams)

Absorbance (460 nm) = – log10 of Transmittance factor at 460 nm

Instrument Correction Factor (I) = (NIST Absorbance for glass filter at 465 nm/Measured Absorbance of glass filter at 465 nm)

Offset Correction Factor (C) serves to accommodate differences in cells

IC Color or International Color Units = ASTA Color Units * 40

  • Although paprika is dominant shade red, the quality indicator is the degree of yellowness in the red, which is why the absorbance at 460 nm is measured.
  • Typical ASTA Color values are around 2000 ASTA units with IC Color at around 8000 IC units.
  • Measurement of sample weight is critical and requires a very good scale for small quantities.
  • As the ASTA and IC metrics are based on physical absorbance at a spectral data point, it is possible to have two paprika samples with similar ASTA color values that look different in color. This is because of a difference between the samples in the 600 – 700 nm range. A CIE L*, a*, b* specification for color in addition to an ASTA/IC Color spec can be used to verify lot-to-lot color consistency.

Sample calculation for Spectrophotometric Color of Paprika per Method 20.1 – 1997 Spectrophotometric Color Assay – Oleoresin Paprika and Capsicum

For a typical paprika sample, transmittance value at 460nm is 6.57%, then the absorbance at 460 nm = – log10 (0.0657) = 1.18

Alternatively a HunterLab ColorQuest XT applet or ColorQuest XE with EasyMatch QC does allow display of spectral data in absorbance (A) units such that the absorbance value at 460 nm can be read directly from the display and entered into the formula.

ASTA Color = [(1.18*164*1)/0.09 g)] = 2154
ICU International Color = (2154*40) = 86186

For a second paprika sample, the transmittance value at 460 nm is 4.59% and the absorbance at 460 nm = – log10 (0.0459) = 1.34

ASTA Color = [(1.34*164*1)/0.09 g] = 2438
ICU International Color = (2438*40) = 97538

How HunterLab Instruments Meet the Requirements of this Method:

There has been insufficient market demand to implement the above metrics as standard in a ColorQuest XT applet or EZMQC software with a ColorQuest XE.

The need for ASTA/ICU Color can be met with a transmission measurement at 460 nm and cut-and-paste to Excel to perform the calculations.

To implement the ASTA/ICU method on a HunterLab sphere instrument, here are the steps:

  1. Standardize any of our sphere instruments, such as ColorQuest XT or ColorQuest XE with EasyMatch QC software, in TTRAN LAV using a 10-mm cell filled with clear, colorless acetone (the solvent for this method).
  2. As a PQ Performance Qualification step, read back the 10-mm cell + acetone. The %Transmittance should be 100% at 460 nm and all points along the spectrum.
  3. Measure the transmission or absorbance at 460 nm of an oleoresin solution, cut-and-paste to Excel and calculate the ASTA and ICU International Color following the calculations above.

FAQ: “We have a COA certificate of analysis that references ASTA Color as one of the quality characteristics of paprika. Can ASTA Color be determined measuring paprika powder in reflectance rather than transmission?”

Typical COA - certificate of analysis for paprika powder referencing ASTA Color.

Typical COA – certificate of analysis for paprika powder referencing ASTA Color.

The formal definition of ASTA Color is based on a transmission measurement of paprika powder in solution using a 10 mm path length cell (described above) rather than measuring the paprika in reflectance through the bottom of a sample cup.

The primary quality concern in measuring the color of paprika powder in reflectance would be to verify that the lot-to-lot color is the same.

I have seen references to correlating reflectance measurements of paprika powder and correlating them to ASTA Color in transmission using a metric called “PACI – Paprika Color Index”.

PACI relationship to ln(ASTA) units for paprika powder based on L*, a*, b*, h° (D65/10) values measured in reflectance.

PACI relationship to ln(ASTA) units for paprika powder measured in reflectance

PACI – Paprika Color Index relationship to ln(ASTA) units for paprika powder measured in reflectance

Reference for PACI – Paprika Color Index

José M. Nieto-Sandoval, José A. Fernández-López, L. Almela, José A. Munõz; Dependence between Apparent Color and Extractable Color in Paprika; Color Research and Application, Volume 24, Number 2, April 1999 pp 93 – 97.

The reader is cautioned using Paprika Color Index on the following points.

  • This correlation needs to be verified by the user with their own paprika powder samples.
  • The ASTA Color transmission measurement where the concentrated paprika powder is let down in acetone solvent is likely to be more sensitive to product quality differences than PACI Color.
  • ASTA Color determined in transmission is the final industry reference method when releasing paprika product.

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