Comparison of 2° and 10° standard observers used with C and D65 illuminants in measurements of colour in raw minced pork loin

Abstract

Background. Colour measurement plays a key role in assessing the quality of pork meat. However, relatively little research has been conducted on the standard observer, one of the several factors influencing colour parameters. Therefore, in this study we examine the usefulness of 2° and 10° standard observers in combination with C and D65 illuminants for pork colour measurement, based on CIELAB and CIELCh systems. Materials and methods. The study involved 180 samples of the longissimus muscle collected from 180 carcasses from pigs slaughtered on an industrial line, with the average carcass weighing 91.3 ±5.7 kg. Total water, total protein, total fat, and pH 48 of the meat were determined. Measurements of colour (including colour changes) of the raw pork meat were carried out using CIELAB and CIELCh scales, and the following illuminant/observer combinations: C/2°, C/10°, D65/2° and D65/10°. Chromatic absorbance at 525 nm (A 525p ) and the relative content of Mb, MbO 2 and MetMb were calculated according to the method proposed by Krzywicki (1979). Results. Pork colour parameters (L*, a*, b*, C* and h°) and changes in these parameters (ΔL*, ∆a*, ∆b*, ΔC*, Δh°) during illumination were weak, and often statistically insignificant, correlating with total water, total protein and fat levels. Higher and statistically significant correlation coefficients were found for pH 48 . The 2° standard observer provided higher correlation coefficients than the 10° observer between pH 48 and hue (h°), pH 48 and changes in redness (Δa*), and pH 48 and changes in hue (Δh°). Conclusion. The use of a 2° standard observer compared to a 10° observer for pork meat colour measurements increased the effect of the relative amount of myoglobin chemical forms on hue (h°), which increases the correlation coefficients between hue (h°) and pH 48 . In addition, the effect is greater with a higher proportion of MetMb and a lower proportion of MbO 2 . When the 2° standard observer is used, higher correlation coefficients between pH 48 and redness (Δa*) and between pH 48 and hue (Δh°) are found in the colour change measurements. These results indicate that, in assessing the quality of raw pork meat, the 2° standard observer may be more useful for colour measurement, especially with regard to colour stability.

Recent advances in meat color research

“…Among those reported, 10° continues to be the most popular observation angle (35.1%) compared to the similar study published by Tapp et al [40] a decade ago. Most recent investigation suggest that 2° standard observer may be more useful for color measurement especially with regard to color stability [41]. Share of manuscripts not reporting observation angle at all has decreased from 65.9% to 48.7%.…”