Polyphenol oxidase browning in the formation of dark spots on fresh wet noodle sheets: How dark spots formed

• Published in: Food chemistry 2020-11, Vol.329, p.126800-126800, Article 126800
• Main Authors: Zhao, Yang, Huang, Ze-Hua, Zhou, Hui-Ming, Zhu, Ke-Xue, Guo, Xiao-Na, Peng, Wei
• Format: Article
• Language: English
• Subjects: Dark spots; Fresh wet noodle; Polyphenol oxidase browning; Wheat products
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2020.126800

[Display omitted] •The chemical formation mechanism of dark spots on fresh wet noodles was studied.•The melanins in dark spots were indirect products of polyphenol oxidase catalysis.•Polyphenol oxidase catalytic dehydrogenation was essential for dark spots.•The dark spots could form by further polymerization without polyphenol oxidase.•Comprehensively, the dark spots formed at the maximum amount at about pH 9. The role of polyphenol oxidase (PPO) in the browning of fresh wet noodle sheets (FWNS) was discussed. To release the chemical formation mechanism of the dark spots formed on FWNS, the reconstituted FWNS and PPO-catechol reaction systems were prepared. Different from the overall color change of FWNS, almost all the melanins in dark spots were indirect products of PPO catalysis. The PPO catalytic dehydrogenation was an essential step for the formation of dark spots, but once the phenol dehydrogenation products were formed, the dark spots could still form through a further polymerization process, even though the PPO was completely deactivated. The optimum pH for the phenolic dehydrogenation in FWNS was about 7, and the alkaline condition was advantageous to the progress of the polymerization. Comprehensively, the maximum amount of dark spots was formed at about pH 9.