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Study on the ZnPP formation mechanism in two different optimum pH at 4.75 and 5.5 in pork
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| Title: | Study on the ZnPP formation mechanism in two different optimum pH at 4.75 and 5.5 in pork |
| Other Titles: | 異なる2つの至適pH4.75と5.5における豚肉のZnPP形成機構に関する研究 |
| Authors: | AKTER, MOFASSARA Browse this author |
| Issue Date: | 25-Mar-2019 |
| Publisher: | Hokkaido University |
| Abstract: | Zinc protoporphyrin IX (ZnPP) is a bright red pigment formed in meat products without nitrate or nitrite. The two optimal pH values for ZnPP formation were 4.75 and 5.5. Moreover, the amount of ZnPP formed at pH 4.75 was much higher than that at pH 5.5 in pork. The number or kinds, of precursors or contributors for ZnPP formation at pH 4.75 might be different from that at pH 5.5. Although it is assumed that ferrochelatase (FECH), myoglobin as a heme donor and Zn ion play important roles in ZnPP formation, the exact mechanism is indistinct. It was reported that ZnPP formation is strongly influenced by protoporphyrin IX (PPIX) formation at pH 5.5. However, further investigations was hardly examined. Hence, it was hypothesized that ZnPP formation depends on the formation of PPIX at pH 4.75, multiple components in pork homogenate are essential to the formation of ZnPP and PPIX at pH 4.75 and 5.5, and the contributors and precursors are different between both pH conditions. Therefore, the purpose of this research was to examine ZnPP formation mechanism at optimum pH 4.75 and 5.5. The examined various factors on PPIX formation at pH 4.75 almost coincided with those of ZnPP, suggesting that ZnPP formation at pH 4.75 was strongly affected by PPIX formation. When pork homogenate was separated into the insoluble and two water-soluble fractions (>10 and <10 kDa) by centrifugation and ultrafiltration, ZnPP and PPIX formation were suppressed at pH 4.75 in the absence of one of those fractions. However, ZnPP and PPIX formation were rescued after mixing of all three fractions. Then, heating of the <10 kDa soluble fraction did not suppress ZnPP and PPIX formation as opposed to heating of the >10 kDa soluble fraction, suggesting that protein(s) presents in the >10 kDa and heat-stable component present in the <10 kDa2 soluble fraction contributed to ZnPP and PPIX formation. Furthermore, 10-30 kDa soluble fraction separated by ultrafiltration was important for ZnPP and PPIX formation at pH 4.75. Exogenous myoglobin assisted ZnPP and PPIX formation at pH 4.75. A gel filtration study showed that ZnPP and PPIX formation were significantly correlated with the endogenous myoglobin contents in the separated fractions at pH 4.75. Based on these results and previous reports, it was suggested that ZnPP is formed from myoglobin-derived heme via PPIX, and FECH from insoluble fraction, and heat-stable <10 kDa soluble component contribute to PPIX and ZnPP formation at pH 4.75 in pork. The study on ZnPP formation mechanism at pH 5.5 also revealed that three or more components i.e. the insoluble fraction, the >10 kDa and <10 kDa water-soluble fraction are also essential for ZnPP and PPIX formation at pH 5.5 in pork. Water-soluble protein(s) with higher molecular weight than that of myoglobin was involved in ZnPP and PPIX formation at pH 5.5. Water-soluble 42 and/or 60 kDa proteins separated by ion exchange chromatography are suggested to contribute for ZnPP formation at pH 5.5. Heat-stable components in the <10 kDa soluble fraction contribute to ZnPP formation at pH 5.5. Based on these results and previous reports, it was suggested that ZnPP is formed from PPIX with the contribution of 42 and/or 60 kDa soluble protein, and FECH from insoluble fraction, 10-30 kDa soluble protein and heat-stable <10 kDa component contribute to PPIX and ZnPP formation at pH 5.5 in pork. The present study revealed that the precursors, the contributors, and optimum temperature are different for ZnPP formation in the optimum pH at 4.75 and 5.5, thus the mechanisms are different. Although it is not clear how these two mechanisms contributed to the color formation in meat products, these findings will be helpful to elucidate the whole ZnPP formation mechanisms in meat products. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第13588号 |
| Degree Level: | 博士 |
| Degree Discipline: | 農学 |
| Examination Committee Members: | (主査) 准教授 若松 純一, 教授 玖村 朗人, 教授 西邑 隆徳, 助教 早川 徹 |
| Degree Affiliation: | 農学院（共生基盤学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/77166 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 農学院(Graduate School of Agriculture)
学位論文 (Theses) > 博士 （農学）
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