1. Effect of spectral characteristics of different retail lightings and residual oxygen on cured meat products
Nadine Böhner, Wolfgang Danzl, Klaus Rieblinger Fraunhofer Institute for Process Engineering and Packaging IVV, Giggenhauser Straße 35, Freising, Germany
Introduction
Light in combination with oxygen can cause irreversible discoloration to meat and meat products. Especially cured boiled sausages are strongly affected, since the main coloring pigment, the denaturated nitrosylmyoglobin acts as a photosensitizer. Different retail lighting sources emit specific light spectra, which can promote discoloration of different levels if the emission maximum matched with the absorption maximum of the photosensitizer [1]. The aim of this study was to investigate the influence of different illuminating devices and residual oxygen concentration on discoloration and oxidation of cured meat products.
Materials and Methods
“Lyoner”-type sliced sausages were stored at 5 °C for 24 h in oxygen measuring cells with 100 % nitrogen in the headspace for degassing of the sausage. Afterwards the measuring cells were flushed with 0.5 % O2 in nitrogen to simulate a gastight package with 0.5 % residual oxygen in the packaging. The sausage slices were exposed to daylight fluorescent tubes, white LEDs and metal halide lamps and also to six single-colored LEDs: blue (emission maximum at 452 nm), verde (506 nm), green (520 nm), yellow (590 nm), amber (620 nm) and red (635 nm), covering a main part of the visible spectrum (Fig. 1 & 2). The spectral irradiance of each light source was 3 W/m2. References were stored in the dark. Before and after storage, the oxygen content in the headspace was determined and the color was measured as L*a*b*values.
Figure 2: Emission spectra of colored LEDs and absorption spectra of nitrosylmyoglobin (MbNO) [4]
Results and Discussion
The oxygen absorption increased with light of shorter wavelength (Fig. 3). The samples illuminated with blue LED light absorbed 0.60 mg O2 / 100 g, whereas the sausages exposed to red LED light absorbed 0.44 mg O2 / 100 g. The dark stored references showed a minimal increase in headspace oxygen. The sausage slices exposed to fluorescent tubes showed the highest oxygen absorption of 0.81 mg O2 / 100 g and the samples exposed to metal halide lamps showed the lowest oxygen absorption. Also the discoloration of the sausage, measured as a*value, decreased stronger at shorter wavelengths. Blue LED illuminated sausages showed a drop in a*value from to 4.13, whereas the red LED illuminated samples showed a drop to 7.93 after 24 h storage. Dark stored references showed a small indecrease in redness. Higher oxygen absorption and higher discoloration of cured boiled sausages were caused by light of shorter wavelength.
Nitrosylmyoglobin (MbNO) is a light sensitive substance acting as a photosensitizer like the denaturated form of cured boiled sausages and is promoted to an excited state upon absorption of light [2]. The activated state of MbNO* reacts with triplet oxygen (3O2) and forms metmyoglobin and other products. Metmyoglobin formation causes the grey brown color of illuminated cured sausages and therefore the decrease in a*value [3]. The absorption spectra of nitrosylmyoglobin is congruent with a main part of the emission spectra of the blue LED and of the daylight fluorescent tube and leads therefore to an increased fading of the sausage exposed to those wavelengths.
Figure 3: Changes in a*value (red bars) and oxygen absorption (blue bars) of cured boiled sausage during 24 h storage at 5 °C and exposure to different lamps and different colored LEDs [4]
Conclusions
The results showed that wavelengths of higher energy of the visible spectra, which match with the absorption spectra of the sausage pigment, have a strong negative impact on sausage quality during storage. The best packaging approach would be non-transparent or without residual oxygen. Also the avoidance of shortwave visible light (blue and verde) during illumination would enhance sausage quality during illuminated storage in retail shelfs. Since this is not desired by the costumer or technically unfeasible, these results could be used for the development of new specific LED lights with a lower shortwave ratio in the visible spectra in order to prevent greying.
References
1 Böhner, N. et al. (2014). Food Packaging and Shelf Life,1(2),
[2] Sandmeier, D. (2003). Symposium: Aktive und Kommunikative Verpackungen, Freising, Germany
3 Andersen, H.J. & Skibsted, L.H. (1992). Journal of Agricultural
and Food Chemistry, 40(10), 1741–1750.
4 Fraunhofer Institute for Process Engineering and Packaging, Freising, Germany
Nadine Böhner
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Figure 1: Emission spectra of fluorescent tubes, white LEDs and metal halide lamps and absorption spectra of nitrosylmyoglobin MbNO [4]
28th EFFoST International Conference November 2014, Uppsala, Sweden