Zinc protoporphyrin IX formation in relation to the colouring of nitrite-free dry fermented sausages

Promovendus/a: Hannelore De Maere

Promotor(en): Prof. dr. Ilse Fraeye, Prof. dr. ir. Hubert Paelinck, Dr. Sylvie Chollet, Prof. dr. ir. Christiaan Michiels

During processing, nitrite salt is traditionally used in meat products. In addition to an antimicrobial and anti-oxidative effect, nitrite contributes to a desirable aroma and it is responsible for the typical red colour of unpasteurized meat products. In spite of the many advantages, the use of nitrite is strongly discouraged in view of its toxicity (lethal oral dose of: 33-250 mg / kg body weight). Moreover, nitrite, in the presence of secondary amines, may be involved in the formation of carcinogenic N-nitrosamines. Consequently, the addition of these additives (KNO2 (E249), NaNO2 (E250), NaNO3 (E251), or KNO3 (E252)) in processed meat products are legally restricted to 150 mg/ kg (expressed as NaNO2 / kg).

A few years ago, it has been found that during the time of ripening, zinc protoporphyrin IX (Zn(II)PPIX) is formed in dry cured hams. It was assumed that this pigment gives the ham its red colour without the addition of nitrite. Hence, it has been thought that alternative colouring of other meat products than dry cured hams and without the addition of additives, should be possible, even though it still remains unclear which variables are important in the formation of Zn(II)PPIX.

The aim of this doctoral study was to assess whether Zn(II)PPIX can be formed during the production of nitrite-free dry fermented sausages. Also the relation between Zn(II)PPIX formation and product redness was investigated. The influence of pH and production time, as important process parameters in fermented meat products, were included in the study. In addition, the importance of eight intrinsic parameters in different meat sources on the in vitro endogenous formation of Zn(II)PPIX was estimated in order to investigate finally the influence of product parameter, meat source, on the formation of Zn(II)PPIX and product redness in nitrite-free dry fermented sausages.

The feasibility of Zn(II)PPIX in nitrite-free porcine dry fermented sausages was investigated and related to product redness. The formation of Zn(II)PPIX was demonstrated at pH values > 4.9 and at long production times (up to 177 days), indicating the importance of process parameters pH and time. Specifically, a high increase in Zn(II)PPIX was seen at the later phase of the production process, reaching even higher concentrations of Zn(II)PPIX in comparison with dry cured ham. In addition, a statistically significant relationship between Zn(II)PPIX formation and product redness was established.

These results were promising for the production of red coloured dry fermented sausages without addition of the undesirable nitrite. However, since the formation of Zn(II)PPIX was found to be still too slow - and as such not yet applicable in meat industry - another route was investigated for accelerating Zn(II)PPIX formation in dry fermented sausages, namely the influence of product parameter meat source.

The in vitro endogenous formation of Zn(II)PPIX in various meat types, namely chicken, turkey, pork, lamb, beef, veal, horse and porcine liver was determined and related to eight intrinsic parameters. The highest Zn(II)PPIX formation was achieved in porcine liver, but also horsemeat was found to have a very good ability to form Zn(II)PPIX. Zinc chelatase activity appeared to be the most important intrinsic parameter.

Next, it was hypothesized that the use of horsemeat in the production of nitrite-free dry fermented sausages may be promising to accelerate Zn(II)PPIX formation. Nitrite-free dry fermented sausages were prepared based on pork, horsemeat and a 50/50 combination of pork and horsemeat at two different pH conditions. Pigment and colour formation were evaluated in function of meat source, pH and production time. The use of horsemeat in nitrite-free dry fermented sausages significantly promoted Zn(II)PPIX formation. By combining pork and horsemeat, similar formation of Zn(II)PPIX was established. Also in this study, Zn(II)PPIX formation was pH dependent. The highly increased Zn(II)PPIX concentration at the later phase of the production process, however, as was seen before, did not occur in this study. In this study, however, Zn(II)PPIX had no effect on product redness. In contrast to the Zn(II)PPIX formation, redness was most pronounced in the sausages based on pork followed by the 50/50 combination of pork and horsemeat. As such, the higher concentrations of Zn(II)PPIX obtained when horsemeat was used, did not act as a natural colouring agent.

The results obtained in this work demonstrated that formation of Zn(II)PPIX in nitrite-free dry fermented sausages is feasible. Zn(II)PPIX formation is highly pH dependent, with increased formation in sausages with a minimal pH decline upon fermentation. However, even at the high pH conditions, Zn(II)PPIX formation in meat products needs time, which is still disadvantageous for the production of dry fermented sausages with shorter production times compared to dry cured hams. By the selection of horsemeat, having more optimal intrinsic parameters for the formation of Zn(II)PPIX, an enhanced Zn(II)PPIX formation in the nitrite-free dry fermented sausages was established compared to porcine nitrite-free dry fermented sausages. However, the relation of Zn(II)PPIX formation with product redness was found to be very complex and could not be directly assigned to a single pigment.