Zinc protoporphyrin IX formation in relation to the colouring of nitrite-free dry fermented sausages.
The colour of fresh meat is mainly determined by myoglobin, which is found in large quantities in mammalian muscles (≈ 30% of the total muscle proteins). Myoglobin has a globular structure and consists of one chain of 153 amino acids enclosing a non-protein heme group. This heme group, an iron-containing protoporphyrin IX, is the active center of myoglobin and directly responsible for the colour of meat.
Traditionally, sodium nitrite and/ or potassium nitrate are used for the colouring of meat products. Nitric oxide (NO), formed after the reduction of the added nitrite and/ or nitrate, is bound to heme. This resulting nitrosyl myoglobin gives raw meat products their characteristic red colour.
Consumers are increasingly aware of the impact and the importance of a healthy lifestyle and therefore have a growing interest in healthy food. Because of this increasing awareness, the use of "chemical" additives is becoming less obvious. Especially sodium nitrite (E250) and potassium nitrate (E252) are controversial. Although nitrite also increases the microbial shelf-life and safety, this additive is nevertheless considered to be undesirable as it is involved in the formation of carcinogenic N-nitrosamines. Therefore, strict regulations were formulated to limit the use of nitrite and nitrate. Under current European legislation, the maximum allowed amount of sodium nitrite for all meat products is only 150 mg / kg [Directive 2006/52 / EC].
For a long time nitrosyl myoglobin was regarded as the only molecule that could give meat products their attractive red colour. In contrast to this generally accepted idea, however, it was established in 2004 that the red colour of Parma ham, a traditional Italian dried ham, was not due to the formation of nitrosyl myoglobin but zinc protoporphyrin IX was identified as the colour-forming pigment. Similar to heme, zinkprotopofyrine IX has a protoporphyrin IX structure, but instead of iron zinc is complexed in the pyrrole ring.
Until now, the formation mechanism of zinc protoporphyrin IX has not yet been clarified sufficiently. More knowledge about this red pigment, however, would be interesting to replace sodium nitrite or potassium nitrate in other meat products with regard to the colour formation, such as, for example, in dry fermented sausages. The purpose of this doctoral study is to assess whether zinc protoporphyrin IX can be formed during the production of nitrite-free dry fermented sausage and what effect it has on colour formation. Additionally, investigation will be done on the influence of product and process factors on formation of this natural pigment, in order to obtain an attractive colour in meat products without any addition of additives.