Inhibition of hexose oxidase on the dark spots in fresh wet noodle sheets: A feasible prevention of dark spots.

Hexose oxidase was a feasible prevention for the dark spots in the fresh wet noodle sheets (FWNS). The chemical mechanism that hexose oxidase recucing the melanins of dark spots was discussed basis on the UPLC-TOF-MS analysis of the polyphenol oxidase (PPO)-catechol system. In the process of PPO browning, hexose oxidase catalyzed the oxidation of o-benzoquinone derivatives and their oligomers, hindering the formation of melanins. Hexose oxidase was efficient in FWNS with low ash content when water addition was 24%~44% or pH range was 4 ~ 7.5. Hexose oxidase could inhubit dark spots in the presence of 10 metal ions. The recommended addition amount was 40 ~ 60 ppm, by which the dark spots could be compolitely inhibited. Hexose oxidase was also suitable for wholewheat and oat FWNS, ΔL6d of wholewheat and oat FWNS were reduced by 4 and 7.98, respectively.

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

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.