Mechanism Underlying Green Discolouration of Myoglobin Induced by Atmospheric Pressure Plasma

Hae In Yong,Hyun-Joo Kim,Cheorun Jo,Mookyoung Han,Jeong-Yong Suh

doi:10.1038/s41598-018-28096-4

Hae In Yong, Hyun-Joo Kim + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-28096-4

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Abstract

In this study, we elucidated the mechanism underlying atmospheric pressure plasma (APP)-induced green discolouration of myoglobin. Green-coloured pigments are produced upon conversion of myoglobin into sulphmyoglobin, choleglobin, verdoheme, nitrihemin, or nitrimyoglobin. We exposed myoglobin dissolved in phosphate buffer to APP for 20 min and found a decrease in a* value (+redness/−greenness) and increase in b* value (+yellowness/−blueness) (P < 0.05). In the ultraviolet absorption spectrum, myoglobin treated with APP for 20 min showed absorption peaks at 503 and 630 nm, a spectrum different from that of sulphmyoglobin or choleglobin. The secondary structure and molecular weight of myoglobin were unaffected by APP treatment, excluding the possibility of verdoheme or nitrihemin formation. After APP treatment, nitrite was produced in myoglobin solution that provided a positive environment for nitrimyoglobin formation. However, the addition of 0.5% sodium dithionite, a strong reducing agent, to myoglobin solution resulted in the formation of deoxymyoglobin, which was subsequently converted to nitrosomyoglobin upon APP treatment to yield a desirable red colour. Thus, APP-induced green colouration in myoglobin solution is associated with nitrimyoglobin formation. The addition of the antioxidant resulted in the production of red colour in myoglobin solution after APP treatment owing to nitrosomyoglobin formation.

Highlights

Meat colour is the most important quality attribute because it influences the first impression and purchasing decision of the consumers
We observed a significant decrease in L* and a* values of myoglobin in both phosphate buffer and distilled water (DW) with an increasing atmospheric pressure plasma (APP) treatment time (Table 1)
While the values of b* and chroma for myoglobin dissolved in phosphate buffer decreased with an increasing APP treatment time (P < 0.05), those for myoglobin dissolved in DW decreased only up to 10 min of APP treatment and slightly increased after 20 min of APP treatment (P < 0.05)

Summary

Introduction

Meat colour is the most important quality attribute because it influences the first impression and purchasing decision of the consumers. Green discolouration of meat caused by APP treatment should be investigated and controlled. The factor associated with the meat colour is myoglobin, a monomeric protein composed of a globin protein and haeme group. An iron atom is centrally located in a porphyrin ring to form six bonds. Four of these bonds coordinate with pyrrole nitrogen atoms in the porphyrin ring and one is associated with the proximal histidine of globin protein. We hypothesised that APP treatment affects myoglobin in raw meat, resulting in meat discolouration. We elucidate the mechanism underlying APP-induced green discolouration of myoglobin (Experiment I) and demonstrate a control measure (Experiment II)

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