| pH levels | Determine optimal pH for ZnPP formation in porcine skeletal muscles. | Porcine skeletal muscles | Analyzed at pH 4.75 and 5.5 based on muscle fiber type. | pH 4.75 favored ZnPP formation in type I fibers, while pH 5.5 was better for type II fibers. | pH levels are crucial for optimizing ZnPP formation based on muscle fiber types. | Wakamatsu et al. (2019) |
| pH levels | Investigate ZnPP formation in nitrite-free fermented sausages. | Dry fermented sausages | pH adjusted via dextrose addition during fermentation. | ZnPP formation peaked at pH≥4.9 after extended drying (up to 177 d), demonstrating pH and time dependency. | Promoting pH≥4.9 facilitates ZnPP development for natural coloring in nitrite-free products. | De Maere et al. (2016) |
| pH levels | Investigate ZnPP formation in porcine heart extract under varying pH conditions. | Porcine heart extract | Anaerobic incubation at pH levels from 4.5 to 5.5. | Optimal zinc-chelatase activity occurred at pH 5.5, enhanced by ATP presence, while anaerobic conditions stabilized ZnPP formation. | pH 5.5 is critical for enzymatic ZnPP synthesis in porcine heart. | Ishikawa et al. (2006) |
| pH levels | Optimize ZnPP formation in porcine liver. | Porcine liver homogenates | Incubated at pH 4.2–5.4 with organic acid (ascorbic and acetic). | ZnPP formation peaked at pH 4.8, with 24-h incubation at 45°C enhancing yield. Microbial safety was maintained under these conditions. | Slightly acidic pH (4.8) enhances ZnPP production in porcine liver. | Llauger et al. (2023) |
| pH levels | Study post-mortem pH and salting time effects on ZnPP in nitrite-free Serrano dry-cured hams. | Ham slices from Serrano dry-cured hams | Ham slices with pH at 24 h post-mortem categorized into low (≤5.4), medium (5.4–5.9), and high (≤5.9). | Low pH (≤5.4) increased ZnPP formation but decreased heme content. Reduced salting had minimal impact on ZnPP, but fatty acid levels correlated positively with ZnPP. | Acidic conditions improve ZnPP synthesis in cured hams, despite heme reduction. | Bou et al. (2020) |
| Muscle type, meat source, and meat composition | Investigate ZnPP formation in different muscle fiber types under varying pH conditions. | Porcine skeletal muscles | ZnPP levels analyzed in type I (red) and type II (white) fibers at pH 4.75 and 5.5. | ZnPP formation was optimized in type I fibers at pH 4.75 due to high mitochondrial content, while type II fibers favored pH 5.5 due to distinct enzymatic pathways. | Muscle fiber type and pH are key determinants of ZnPP formation, guiding processing strategies. | Wakamatsu et al. (2019) |
| Muscle type, meat source, and meat composition | Evaluate ZnPP formation across various meat sources. | Chicken, turkey, pork, lamb, beef, veal, horse, and porcine liver | Compared ZnPP and Zn-chelatase activity in meat homogenates. | Liver and horsemeat showed highest ZnPP formation, due to high Zn-chelatase activity and heme content. | Zn-chelatase activity is a key factor in ZnPP formation across meat types. | De Maere et al. (2017) |
| Muscle type, meat source, and meat composition | Assess proteolysis and marbling impacts on ZnPP in Parma hams. | Parma ham | Analyzed proteolysis and fat content. | Greater marbling facilitated ZnPP stability, while proteolysis enhanced heme transmetallation efficiency. | Fat content and proteolysis enhance ZnPP formation in natural curing. | Bou et al. (2018) |
| Muscle type, meat source, and meat composition | Study ZnPP formation in red vs. light muscles in nitrite-free cured hams. | Dry-cured ham | Analysis at different curing stages. | Red muscles (Semitendinosus) showed consistently higher ZnPP levels compared to white muscles. | Muscle type influences ZnPP levels due to differences in enzymatic activity. | Parolari et al. (2009) |
| Muscle type, meat source, and meat composition | Explore ZnPP distribution between lean and fat tissues in Parma ham using imaging techniques. | Parma ham | Used autofluorescence imaging to map ZnPP distribution | ZnPP was more concentrated in fat than lean regions, particularly in anaerobic conditions. | ZnPP forms in lean meat but accumulates in fat tissues, affecting visual color. | Wakamatsu et al. (2006) |
| Processing temperature and time | Investigate effects of temperature on ZnPP formation in dry-cured hams. | Dry-cured hams | Compared cold (4°C) and warm (16°C) maturation conditions. | Warm temperatures (16°C) enhanced ZnPP formation by increasing enzymatic activity, resulting in a deeper red color. | Warmer conditions promote enzymatic ZnPP synthesis effectively. | Parolari et al. (2016) |
| Processing temperature and time | Optimize ZnPP formation in porcine liver under varying conditions. | Porcine liver homogenates | Evaluated ZnPP formation across temperatures (25°C–55°C) and times (up to 30 h) | High ZnPP content achieved at 45°C for 24 h; longer times at lower temperatures also effective. | High-temperature curing optimizes ZnPP formation and maintains microbiological safety. | Llauger et al. (2023) |
| Processing temperature and time | Study temperature effects on ZnPP formation in Parma ham. | Porcine muscles and Parma ham | Modified curing model at optimal pH and 35°C. | ZnPP peaked at 35°C, with hemoglobin being a more efficient substrate than myoglobin due to its higher affinity for zinc incorporation. | Optimal temperature maximizes enzymatic and non-enzymatic ZnPP production in natural curing. | Zhai et al. (2022) |
| Processing temperature and time | Examine drying temperature impacts on ZnPP formation in pork liver. | Pork liver | Compared drying temperature at –10°C–70°C. | Moderate drying temperatures (10°C–20°C) preserved ZnPP levels and enzymatic activity by minimizing thermal denaturation. | Balancing drying temperature is key for maintaining ZnPP and enzyme functionality. | Abril et al. (2022) |
| Processing temperature and time | Evaluate ZnPP content changes at various curing stages (6–20 mon). | Parma ham slices | Sequential sampling during 6–20 mon of curing. | ZnPP levels steadily increased during the first 12 mon, stabilizing thereafter, indicating long-term pigment stability. | Longer curing durations stabilize ZnPP and improve final color in nitrite-free dry-cured meat products. | Parolari et al. (2009) |
| Oxygen levels | Investigate ZnPP formation by lactic acid bacteria (LAB) inoculation under aerobic and anaerobic conditions. | Fermented sausages | Tested Lactococcus lactis and other LAB strains under different oxygen conditions. | ZnPP formation was significantly higher under anaerobic conditions. L. lactis subsp. cremoris also formed ZnPP under aerobic conditions. | Highlights the potential of L. lactis as a natural nitrite alternative, effective under both oxygen conditions. | Kauser-Ul-Alam et al. (2020) |
| Oxygen levels | Evaluate the impact of oxygen on ZnPP formation in porcine skeletal muscles. | Porcine skeletal muscles | Incubated samples at different oxygen levels and pH conditions. | ZnPP formation was significantly inhibited in the presence of oxygen, with optimal production in anaerobic environments at pH 4.75–5.5. | Confirms oxygen as a major inhibitor of ZnPP formation, supporting the importance of anaerobic environments. | Wakamatsu et al. (2019) |
| Oxygen levels | Study the spatial distribution of ZnPP in relation to oxygen exposure. | Parma ham | Fluorescent imaging was applied to compare inner (anaerobic) and outer (aerobic) muscle layers. | ZnPP was concentrated in anaerobic inner layers, with reduced levels in oxygen-exposed outer sections. | Reinforces the role of oxygen exclusion in promoting ZnPP accumulation in Parma ham. | Wakamatsu et al. (2006) |
| Oxygen levels | Analyze the effects of oxygen on ZnPP formation using oxymyoglobin as a substrate. | Porcine heart extracts | Compared ZnPP production under aerobic and anaerobic conditions. | Anaerobic conditions doubled ZnPP formation compared to aerobic setups, but oxymyoglobin supported ZnPP formation. | Demonstrates that strict oxygen control enhances ZnPP yield even with oxygen-compatible substrates. | Ishikawa et al. (2006) |
| Oxygen levels | Investigate the ways oxygen levels and light exposure affect ZnPP stability in sliced Parma ham. | Sliced Parma ham | Compared storage in high (21%) and low (0.4%) oxygen atmospheres with or without light. | Low-oxygen, dark storage preserved ZnPP content and color stability, while high oxygen and light exposure caused rapid discoloration. | Supports the use of low-oxygen, light-protected storage to enhance product quality and shelf life. | Adamsen et al. (2004) |
| Presence of nitrites | Study nitrite’s inhibitory effects on ZnPP and protoporphyrin IX (PPIX) formation. | Pork loin homogenates | Tested nitrite-added and nitrite-free systems. | Nitrite significantly inhibited ZnPP and PPIX synthesis by blocking ferrochelatase (FECH) activity. | Nitrite-free curing allows natural ZnPP formation, supporting clean-label trends. | Wakamatsu et al. (2010) |
| Presence of nitrites | Compare ZnPP formation in nitrite-free Parma hams vs. nitrite-cured hams. | Parma ham, Iberian ham, and nitrite-cured hams | Matured hams under identical conditions with and without nitrite. | Higher ZnPP levels observed in nitrite-free hams; nitrite suppressed enzymatic activity required for ZnPP formation. | Supports nitrite-free methods as safer and more natural alternatives for cured meats. | Adamsen et al. (2006) |
| Presence of nitrites | Investigate nitrite’s impact on ZnPP formation pathways. | Pork muscle homogenates | Evaluated nitrite’s interaction with zinc-chelatase and PPIX. | Nitrite altered heme enzyme activity, inhibiting ZnPP synthesis while promoting nitrosyl-heme pigments. | Nitrites suppress natural ZnPP production, emphasizing the need for nitrite-free curing methods. | Becker et al. (2012) |
| Presence of nitrites | Explore ZnPP formation in nitrite/nitrate-free meat systems using high ZnPP-forming bacteria. | Salted minced pork and meat homogenates | Screened 137 bacterial isolates and analyzed their ZnPP formation rates in nitrite-free environments. | Nitrite-free systems showed enhanced ZnPP formation when inoculated with L. lactis, Leuconostoc mesenteroides, and Enterococcus faecium. | Confirms that nitrites inhibit ZnPP formation, and nitrite-free curing with specific bacteria can mimic nitrite-cured coloration. | Asaduzzaman et al. (2020) |
| Presence of nitrites | Explore ZnPP formation in nitrite-free dry sausages. | Dry fermented sausages | Compared curing with and without nitrite across extended drying periods. | Nitrite-free sausages had higher ZnPP levels than nitrite-cured ones, particularly under extended curing periods and optimal pH (>4.9). | Long curing times in nitrite-free systems enhance ZnPP, supporting natural coloration alternatives. | De Maere et al. (2016) |
| Sodium chloride concentration | Investigate the effect of post mortem pH and salting time on ZnPP formation in Serrano dry-cured hams | Serrano dry-cured hams | Analyzed different salting times (standard vs. reduced) and measured ZnPP levels | Reduced salting time did not significantly affect ZnPP levels, but free fatty acid content correlated with ZnPP formation. | Optimal salt concentration is critical for ZnPP stability in dry-cured hams. | Bou et al. (2020) |
| Sodium chloride concentration | Examine the impact of refined salt vs. sea salt on ZnPP formation in Parma-like ham | Parma-like dry-cured ham | Evaluated ZnPP levels over 76 wk of processing using different salt types | ZnPP increased significantly after 40 wk, unaffected by salt impurities. | The type of salt (refined vs. sea salt) does not impact ZnPP formation, indicating minimal effect of trace minerals. | Wakamatsu et al. (2009) |
| Sodium chloride concentration | Analyze the role of LAB in ZnPP formation under different NaCl conditions | Minced pork inoculated with LAB strains | ZnPP formation analyzed in 3%–7% NaCl with LAB inoculation | LAB strains maintained ZnPP formation at 3%, but were inhibited at 5% salt. | Salt-resistant LAB strains could be used to optimize ZnPP formation. | Kauser-Ul-Alam et al. (2021) |
| Sodium chloride concentration | Examine ZnPP formation in different cured meat products | Parma ham, Iberian ham, nitrite-cured ham | Measured ZnPP content and correlated with NaCl and Zn levels | ZnPP formation was enhanced in non-nitrite cured dry hams but was inhibited in high nitrite and salt conditions. | High NaCl (≤9%) reduced ZnPP formation due to salt-protein interactions. | Adamsen et al. (2006) |
| Sodium chloride concentration | Study NaCl impact on Zn-chelatase activity in pork muscle | Pork muscle extracts | ZnPP enzymatic activity measured with different salt concentrations (0–80 g/L NaCl) | ZnPP-promoting activity increased with salt concentration up to 80 g/L. | Zn-chelatase enzyme remains active under high salt conditions. | Benedini et al. (2008) |
| Metal ions | Examine the role of Zn2+ in ZnPP formation | Meat and meat extracts | Evaluated ZnPP formation with Zn2+ supplementation | Zn2+ promotes ZnPP formation through enzymatic and non-enzymatic pathways, but high levels inhibit FECH. | Zn2+ is essential for ZnPP synthesis, but its optimal concentration is critical. | Becker et al. (2012) |
| Metal ions | Investigate Fe impact on ZnPP formation | Myoglobin, FECH | Studied Zn-Fe transmetallation | Fe2+ can be replaced by Zn2+ in heme, while Fe2+ inhibits ZnPP formation. | Fe2+ removal is a key step in ZnPP synthesis, whereas Fe2+ presence hinders formation. | Paganelli et al. (2016) |
| Metal ions | Investigate FECH inhibition by Zn2+ | Purified FECH | Studied Zn2+ effects on FECH activity | Excess Zn2+ inhibits FECH, reducing ZnPP formation. | Zn2+ serves both as a substrate and an inhibitor at high concentrations. | Hunter et al. (2008) |
| Metal ions | Evaluate ZnPP formation in nitrite-free dry-cured ham | Dry-cured ham | Analyzed ZnPP levels across different processing conditions | ZnPP formation is influenced by FeCH activity, total iron and salt content. | Proteolysis and iron availability are major determinants of ZnPP formation. | Schivazappa et al. (2024) |