Zinc-protoporphyrin IX promoting activity in pork muscle

Zinc-protoporphyrin formation in nitrite-free Parma Ham and its relationship with intrinsic parameters and red color profile of processed hams

A total of 134 fresh hams, assayed for Ferrochelatase (FeCH) activity and ultimate pH (pH48), were processed in compliance with the procedures established for PDO Parma ham and finally, analyzed for salt, moisture, Zinc Protoporphyrin IX (ZnPP), heme, iron and zinc contents, and proteolysis index (PI). The variation in ZnPP content was related to the intrinsic parameters of fresh and matured hams by a Partial Least Square Regression model. The most favorable factors on the formation of ZnPP were total iron content (representative of the initial hemoprotein content), and FeCH activity, demonstrating the main role played by these raw matter-specific predictors in the long matured dry-cured hams. To a lesser extent, zinc content and pH48 were involved with a positive and negative role, respectively. Salt content and PI of matured hams showed an inhibitory and a favorable influence, respectively, toward the ZnPP formation. Principal Component Analysis showed the associations between the sensory red color profile and the physicochemical traits of matured hams. The red color intensity increased in agreement with the red-violet and red-pink hues scores. The formation of a high amount of ZnPP was associated with the increased perception of the red-violet shade, with a lower lightness (L*) and Hue angle (h°). Moisture increase contributed to the shift in color perception to red-pink, while marked progress in PI strengthened the perception of the red-brown shade. ZnPP and final heme favored the red color of matured hams, although a high concentration of these pigments increased in particular the red-violet perception.

Effect of Overripening on the Physico-Chemical and Sensory Characteristics of Boneless, Salt-Reduced Iberian Dry-Cured Ham

The aim of this study was to evaluate the effect of extended maturation and temperature increase on the physico-chemical, biochemical, instrumental color and texture, sensory, and acceptability parameters of cured and boneless Iberian hams. Given the limited knowledge in this area, our objective was to develop a ham with enhanced proteolysis, potentially leading to increased bioactive peptide generation and superior sensory characteristics compared to salt-reduced counterparts. To achieve this, a batch of hams cured up to 38% loss at 30 °C and two batches cured up to 42% loss at 30 °C and 36 °C were evaluated. Results showed that the increase in processing time and temperature significantly enhanced (p < 0.05) ham proteolysis and amino acid content without adversely affecting its texture. No significant differences were observed in instrumental texture parameters or sensory attributes as evaluated by consumers. These processing conditions also increased the content of free amino acids, improving the product quality. Overall, these processing modifications resulted in hams with excellent sensory acceptability and enhanced bioactive potential despite the salt reduction.

Zinc protoporphyrin IX generation by Leuconostoc strains isolated from bulged pasteurized vacuum sliced hams

The colour of meat typically fades as it decays. However, it has been observed that certain vacuum-packaged spoiled hams can maintain a pink colour even when the packaging is bulged. A large amount of Zinc protoporphyrin IX (ZnPP) was found in these hams, compared to fresh red hams or spoiled and grey hams. Combined with high-throughput sequencing and cultural isolation, the potential cultures of Leuconostoc mesenteroides S-13 (LM), Leuconostoc citreum OCLC11 (LC), and Leuconostoc mesenteroides subsp. IMAU:80679 (LS) were selected based on their ability to produce ZnPP. Subsequently, these cultures were introduced into a fermented sausage model to assess their effect on colour conversion. The analysis of absorption and fluorescent spectra showed that Nitrite sausages contained nitrosyl heme pigment, while bacteria-inoculated sausages were predominantly composed of ZnPP. In addition, the a* value of the LS sausage was close to the Nitrite group at the end of fermentation, significantly higher than control, indicating the effect of bacterial metabolism on the redness. Meanwhile, the Ferrochelatase (FECH) activity of LM, LC and LS groups were 140 ± 13, 113 ± 16 and 201 ± 20 U/g sausage, respectively, providing a potential method on compensating for nitrite/nitrate substitution based on the presence of ZnPP in meat products.

Utilization of Porcine Livers through the Formation of Zn-Protoporphyrin Pigment Optimized by a Response Surface Methodology

There is a growing demand for clean-label products. This study aimed to obtain a food-grade coloring ingredient for meat products based on the formation of Zn-protoporphyrin from porcine livers, thus contributing to the development of nitrite-free products. First, the effects of sodium disulfite and acetic, ascorbic, and lactic acids on the formation of Zn-protoporphyrin and the total microbial count were studied. The combination of ascorbic and acetic acids resulted in a higher Zn-protoporphyrin content than acetic acid alone, and microbial levels were maintained (ca. 3 log CFU/mL). Second, a response surface methodology was used to maximize Zn-protoporphyrin while maintaining microbiological food standards. To that end, the effects of pH (4.2-5.4), incubation time (3-30 h), and temperature (25-50 °C) were studied. The selected conditions for Zn-protoporphyrin formation involved anaerobic incubation at pH 4.8 and 45 °C for 24 h. The safety was validated through challenge testing for relevant pathogens (Listeria monocytogenes, Salmonella spp., and Clostridium perfringens). A significant reduction (>6 log units) was observed in the selected conditions for L. monocytogenes and Salmonella, whereas C. perfringens spores remained at the inoculated levels. The optimized procedure is proven to be microbiologically safe, and may improve the color of nitrite-free meat products.

Evidence of the mechanism underlying zinc protoporphyrin IX formation in nitrite/nitrate-free dry-cured Parma ham

A large amount of zinc protoporphyrin IX (ZnPP) is found in nitrite/nitrate-free dry-cured meat products, such as Parma ham, and is known to contribute to the favorable bright red color of the latter. ZnPP is a metalloporphyrin, in which zinc is coordinated, instead of iron, in the porphyrin ring. ZnPP proved to be more stable than heme, and its formation should be favored in dried meat products to improve color without the addition of nitrites or nitrates. Toward that, understanding the mechanisms of formation of ZnPP in nitrite/nitrate-free dry-cured ham would be important. In this lecture, I introduce some of our research group's findings regarding the endogenous and exogenous factors contributing to the formation and distribution of ZnPP in Parma ham and why ZnPP formation is suppressed in common cured meat products.

Formation of Zn-protoporphyrin during the elaboration process of non-nitrified serrano dry-cured hams and its relationship with lipolysis

This study assessed the ZnPP content, heme content, salt content, and instrumental color in the biceps femoris and semimembranosus muscles during the elaboration of Serrano dry-cured ham manufactured without the addition of nitrate and nitrite for 15 months. The effects of lipolysis and lipid oxidation on the content of Zn-protoporphyrin were also investigated in the biceps femoris. We found that the maximum formation of Zn-protoporphyrin occurred between end of resting and 6 months of processing, which coincides with temperature increase during processing and the end of salt equalization. Zn-protoporphyrin further increased in the biceps femoris until 9 months of processing but remained unchanged in the semimembranosus. Free fatty acid content increased till 6 months and then remained unchanged until the end of the process. These findings and those from an in vitro study reinforced the idea that the release of free fatty acids can promote the activity of the endogenous enzyme ferrochelatase and contribute to the formation of Zn-protoporphyrin from heme. However, the content of Zn-protoporphyrin decreased at the end of the processing, which may be due to the progression of lipid oxidation.

Ultrasound intensification of Ferrochelatase extraction from pork liver as a strategy to improve ZINC-protoporphyrin formation

The enzyme Ferrochelatase (FeCH), which is naturally present in pork liver, catalyses the formation of Zinc-protoporphyrin (ZnPP), a natural pigment responsible for the typical color of dry-cured Italian Parma ham. The aim of this study was to evaluate the feasibility of using high power ultrasound in continuous and pulsed modes to intensify the extraction of the enzyme FeCH from pork liver. US application during FeCH extraction led to an improved enzymatic activity and further increase in the formation of ZnPP. The optimal condition tested was that of 1 min in continuous US application, in which time the enzymatic activity increased by 33.3 % compared to conventional extraction (30 min). Pulsed US application required 5 min treatments to observe a significant intensification effect. Therefore, ultrasound is a potentially feasible technique as it increases the catalytic activity of FeCH and saves time compared to the conventional extraction method.

Impact of salt levels on the sensory profile and consumer acceptance of Italian dry-cured ham

BACKGROUND

Reduction of the salt (NaCl) content in typical Italian dry-cured ham is intended to reduce sodium dietary intake to meet World Health Organization (WHO) recommendations for the prevention of serious diseases. This reduction is a complex issue because of the multiple roles that salt plays in the product. Hams that were processed to obtain a final product with target salt levels (hams with reduced salt concentration and controls) were analyzed using chemical parameters (salt, moisture, fat, and proteolysis indexes). Their sensory properties were described by a trained panel and 87 consumers evaluated the impact of salt reduction on their liking for the products.

RESULTS

The dry-cured hams under investigation are representative of Italian dry-cured hams, which are considered to be low and medium to high in terms of salt content. Consistent with the role of salt in proteolytic enzymes inhibition, there was an increase in the proteolysis index in fully matured dry-cured hams with reduced salt content. Salt level affected saltiness perception but also texture, color, and, to a lesser extent, flavor intensity in matured dry-cured hams. On average, reduced-salt dry-cured hams resulted in increased consumer liking. However, the resulting three consumer segments (37%, 27%, and 36% of the consumer cohort, respectively), differed in the acceptability ranking given to reduced-salt hams and controls.

CONCLUSION

The tested reduction in salt content, besides improving the nutritional profile of dry-cured ham, was effective in increasing consumers' acceptance. These results were useful for exploring the effect of reducing salt concentration on consumer liking for dry-cured hams. © 2020 Society of Chemical Industry.

Effects of post mortem pH and salting time on Zinc-protoporphyrin content in nitrite-free Serrano dry-cured hams

There is a growing demand for clean label products and thus the elimination of curing additives in various dry-cured meats is of interest while maintaining colour characteristics. This study was aimed to examine the effect of pH at 24 h post mortem (pH_SM24h ≤ 5.4; 5.4 > pH_SM24h < 5.9; pH_SM24h ≥ 5.9) and salting time (standard vs reduced) on zinc-protoporphyrin content, heme content and other physicochemical parameters of Serrano dry-cured hams manufactured without the addition of curing agents. Results showed that in those hams with higher post mortem pH heme content was increased whereas ZnPP content and proteolysis index were decreased. Reduced salting time decreased salt content whereas ZnPP and heme contents remained unaffected. Lower post mortem pH and reduced salting time led to a higher content in various free fatty acids which, in turn, were found to correlate positively with ZnPP formation. However, the observed changes in heme and ZnPP contents had no effect on the instrumental color of the final product.

Investigation of the post mortem zinc protoporphyrin IX fluorescence with respect to its protein-bound and unbound occurrence in aqueous meat extracts

Zinc protoporphyrin IX (ZnPP) is known to accumulate in most meat products during storage. However, the pathway of its formation is not yet completely clarified. To gain more insights into the specificity of ZnPP occurrence, a SEC-HPLC-UV-fluorescence setup was established to screen the proteins in aqueous meat extracts for their ZnPP fluorescence during incubation. In accordance with previous studies it was identified by SDS-PAGE and MALDI-TOF-MS that ZnPP formation takes place in myoglobin. In this study, valuable new insights into the ZnPP forming pathway were gained, as our results indicated that a significant part of ZnPP - after being formed within the protein - is transitioned into free ZnPP during incubation. Additionally, the obtained results implied that ZnPP may also occur in proteins of higher molecular weight (>100 kDa).

Investigation of contributors to zinc protoporphyrin IX formation at optimum pH 5.5 in pork

We investigated zinc protoporphyrin (ZnPP) formation in pork at pH 5.5, identified the contributors to ZnPP formation, and verified the involvement of myoglobin in this process. When pork homogenate was separated into two water-soluble fractions (>10 and <10 kDa) and an insoluble fraction, ZnPP formation was suppressed. ZnPP formation was rescued after mixing of all three fractions. Heating of the soluble <10 kDa fraction did not suppress the formation of ZnPP as opposed to heating of the soluble >10 kDa fraction, suggesting that protein(s) presents in the >10 kDa fraction contributed to ZnPP formation. Components of the soluble 10-30 kDa fractions separated by ultrafiltration were important in ZnPP formation. Exogenous myoglobin was not essential for ZnPP formation. A gel filtration study showed that soluble protein(s) with molecular weight higher than that of myoglobin was involved. Therefore, it was suggested that the soluble <10 kDa fraction, the insoluble fraction, and the soluble 10-30 kDa fraction (excluding myoglobin) are essential for ZnPP formation in pork at pH 5.5.

Effects of Processing Temperature on Color Properties of Dry-Cured Hams Made without Nitrite

Dry cured hams were investigated for their ability to develop red color even at low temperature (3–4 °C) and in the absence of added nitrites; results were compared with those obtained from nitrite-free hams made at conventional warm maturing temperatures. Colorimetric parameters (L*, a*, b*, and hue) and concentration of the main pigments Zn protoporphyrin IX (ZnPP) and heme were measured at three stages of preparation (six, nine, and 12 months), showing that red color was successfully formed at low temperatures, though at a slower rate and less intensively than under warm conditions. Major differences in the pattern of color development were found with the two processing temperatures. While the typical features of an enzyme-dependent mechanism, with a progressive drop in enzyme activity paralleling the synthesis of Zn protoporphyrin IX, were observed at warm temperatures, the same did not occur in cold-made hams, where the enzyme activity was almost unchanged throughout the process. These results, along with data from a descriptive sensory analysis, are supportive of a non-enzymatic mechanism leading to ZnPP (hence the red color) under cold conditions, with an estimated three-month delay compared with nitrite-free hams manufactured in a warm maturing regimen.

Formation of naturally occurring pigments during the production of nitrite-free dry fermented sausages

This study investigates the potential of producing red coloured dry fermented sausages without the addition of nitrite and/or nitrate. Therefore, the formation of zinc protoporphyrin IX (Zn(II)PPIX) as naturally occurring pigment, and the interrelated protoporphyrin IX (PPIX) and heme content were evaluated during nitrite-free dry fermented sausage production at different pH conditions. Zn(II)PPIX was only able to form in dry fermented sausages at pH conditions higher than approximately 4.9. Additionally, the presence of Zn(II)PPIX increased drastically at the later phase of the production process (up to day 177), confirming that in addition to pH, time is also a crucial factor for its formation. Similarly, PPIX also accumulated in the meat products at increased pH conditions and production times. In contrast, a breakdown of heme was observed. This breakdown was more gradual and independent of pH and showed no clear relationship with the formed amounts of Zn(II)PPIX and PPIX. A statistically significant relationship between Zn(II)PPIX formation and product redness was established.

Technological approach to reduce NaCl content of traditional smoked dry-cured hams: effect on quality properties and stability

The modification of the salting procedure (from a three- to a two-salt coverage steps) and its effects on quality and stability properties has been investigated to reduce NaCl content of traditional dry-cured ham. The study was applied on green hams of small-S and large-L weight classes. Results evidenced that a two-salt coverage steps salting could be applied to reduce significantly NaCl content of S-size hams and to reach the physico-chemical conditions required for microbial stability at the end of ripening. The final salt content of the products results (p < 0.05) to depend on salting procedure and initial weight of the hams, while limited differences on quality properties have been observed being the latter mainly associated to the pattern of the volatile compounds. In particular, aldehydes and hexanal content were lower in hams undergone to a 2-steps salting. Sensory analysis evidenced that the hams with reduced NaCl (2s-S and 2s-L) were less easy to chew, less salty and with a lower intensity of the smoky flavour in respect to the 3s- ones. The study confirmed the feasibility of salt content reduction of traditional dry-cured hams by modifying the salting process. However, the weight of the initial tights resulted a critical factor in affecting salting diffusion, salt content and water activity of the ripened products, their quality and stability properties.

Ferrochelatase catalyzes the formation of Zn-protoporphyrin of dry-cured ham via the conversion reaction from heme in meat

Ferrochelatase (FECH), the enzyme at the last step of the heme-biosynthetic pathway, is involved in the formation of Zn-protoporphyrin via an iron-removal reaction of heme. To improve the efficacy of the formation of Zn-protoporphyrin from heme, the use of recombinant FECHs from porcine, yeast, and bacteria was examined. Incubation of FECH with myoglobin in the presence of ascorbic acid and cysteine resulted in the efficient conversion of myoglobin-heme to Zn-protoporphyrin. Exogenously added recombinant yeast FECH facilitates the production of Zn-protoporphyrin from myoglobin-heme and heme in meat, via the replacement of iron in the protoporphyrin ring by zinc ions. A large amount of Zn-protoporphyrin was also generated by the catalysis of FECH using an intact piece of meat as a substrate. These findings can open up possible approaches for the generation of a nontoxic bright pigment, Zn-protoporphyrin, to shorten the incubation time required to produce dry-cured ham.