Małgorzata Jakubowska

The influence of myoglobin on the colour of minced pork loin

The influence of the total and chromatic absorbance at wavelengths of 525 nm (A525 and A525p) and 700nm (A700), and the relative content of oxymyoglobin (MbO2), metmyoglobin (MetMb) and deoxymyoglobin (Mb), on the value of the colour parameters (L*, a*, b*, C* and h°) of minced pork loin, were evaluated. Lightness (L*) depended almost entirely on variation in total absorbance at a wavelength of 525 nm. Redness (a*) depended on the forms of myoglobin and A525p, while yellowness (b*) depended mainly on the proportions of the reduced form (Mb), the oxygenated form (MbO2) and the oxidised form (MetMb). Yellowness (b*) significantly increased with a decrease in the relative amount of Mb and an increase in relative amounts of MbO2 and MetMb, although a greater impact was exerted by fluctuations in MbO2 than MetMb. Variability of chroma (C*) depended mainly on proportions of the forms of myoglobin. Hue angle (h°) depended primarily on chromatic absorbance at 525 nm (A525p).

A comparison of two methods of determining colour change in the assessment of the quality of pork

BACKGROUNDnThe colour of pork is one of the most important measures of meat quality. For the consumer, it is a sign of freshness, crucial for the decision to buy a product. The storage of meat results in constant col- our changes. Differences can be found in all colour parameters, especially chromatic ones, such as redness (a*) and hue angle (h°), as these changes are significantly correlated with a number of quality traits. Colour change can be determined not only by evaluating changes in colour parameters, but also by establishing the change in absorbance of specific wavelengths of light. The aim of this study was to compare the usefulness of these two methods of determining colour change: parameters measured on the CIELAB and CIELCh scales and colour change (%CC) determined based on the absorbance of selected wavelengths of light, i.e. 505, 540, 560, 580 and 630 nm. In this paper, we analysed two methods of measuring colour change in terms of their relevance for meat quality assessment.nnnMETHODSnThe study involved 150 samples of the longissimus lumborum muscle collected from 150 carcasses of pigs slaughtered on an industrial line, weighing 65-107 kg, with an average carcass weight of 86.1 kg. Meat sensory analysis (colour, wateriness, firmness), physicochemical assessment (colour, WHC, pH48) and proximate analysis (moisture, total protein, fat, ash) were carried out. The methods included the determination of (I) changes in colour parameters measured on the CIELAB and CIELCh scales, and (II) colour change (%CC) based on the absorbance of selected wavelengths: 505, 540, 560, 580 and 630 nm. Chromatic absorbance values of a wavelength of 525 nm (A525p) and the relative content of Mb, MbO2 and MetMb were calculated according to the method proposed by Krzywicki (1979).nnnRESULTSnBasic chemical composition - with few exceptions - was not significantly correlated with differenc- es in the values of colour parameters (ΔL*, ?a*, ?b*, ΔC*, Δh°) and colour change (%CC). With an increase in scores in the sensory evaluation of colour, wateriness, and firmness, and an increase in WHC and pH48, the differences in lightness (ΔL*) significantly increased and differences in chromatic value (?a*, ?b*, ΔC*, Δh°) and %CC decreased, for all tested combinations of wavelengths. The highest correlation coefficients were observed for ?a* and Δh° and %CC540/630 and %CC580/630, with colour change (%CC540/630 and %CC580/630) showing a stronger correlation with the tested meat quality traits than the differences in redness (?a*) and hue angle (Δh°). We found a very strong correlation between changes in the relative levels of MetMb (ΔMetMb) and colour change (%CC) based on the absorbance of wavelengths of 540 and 505 nm, and 580 and 505 nm (r = 0.950*** and r = 0.967***, respectively).nnnCONCLUSIONSnThe determination of colour change based on the absorbance of two combinations of wave- lengths, i.e. (I) 540 and 630, and (II) 580 nm and 630 nm, is more useful in the assessment of pork quality than changes in two most relevant parameters of the CIELAB and CIELCh scales, i.e. redness (Δa*) and hue angle (Δh°). Moreover, the determination of absorbance of a wavelength of 630 nm was more useful for determin- ing colour change (%CC) than 505 nm. Colour change (%CC) based on the absorbance of wavelengths of 540 and 505 nm and 580 and 505 nm reflect the changes in the relative amounts of MetMb very well.