Formation Pattern And Prevention Mechanism Of Fresh Wet Noodle Browning

In general,fresh wet noodles will be stored for a certain period of time before they are cooked or consumed.Browning occurs during storage.The color of fresh wet noodles will change from light yellow or creamy white to light gray,light brown or even dark brown.At the same time,dark spots will form on the surface of fresh wet noodles.Browning affects the appearance of fresh wet noodles,and it may cause consumers to worry about the fresh wet noodle quality and safety.The color protection of noodles is carried out by reducing agents such as ascorbic acid and physical methods.There are also studies on the color change pattern of alkali fresh wet noodles?However,there are few reports on the dark spots and the chemical mechanism of browning.To solve the above problems,the regularity and prevention mechanism of fresh wet noodle browning were studied.First,the formation pattern of fresh wet noodle browning was discussed from the angle of color change.Wheat flour of different bran particle content from different mill flows was used to prepare fresh wet noodles.Fresh wet noodles with different water addition and 10 metal ions were made.The color change of fresh wet noodle was measured and substitute into the equation.Base on the analysis results of low-field NMR and RP-HPLC analysis,the influence of raw material compositions,water binding state,and metal ions on the browning rate and degree was discussed.With the increase in PPO activity and total phenol content of the raw materials,the color of fresh wet noodles gradually darkened,and?L_0¹h increased first and then decreased.The color change degree within 24 h,?L_4²4h,and k₃ of fresh wet noodles made from wheat flour of high bran particle content increased with the increase in ash content,PPO activity,and total phenol content.As the water addition increased,the color of fresh wet noodle of low ash content darkened first and then lightened,?L_0¹h gradually increased,and?L_4²4h and k₃increased first and then decreased.Metal ions affected the browning of fresh wet noodles,which was mainly reflected in?L_4²4h and k₃.The presence of metal ions such as Ca²⁺,Zn²⁺,Mn²⁺,Mg²⁺,Fe³⁺,etc.,might be the factor that induces or accelerates the browning of fresh wet noodles.Meanwhile,the formation pattern of dark spots was discussed.It is generally believed that fresh wet noodles made of wheat flour with lower processing accuracy and higher ash content are prone to generate dark spots.However,it was found that even the fresh wet noodles made of wheat flour with low ash content would also generate dark spots during storage,which was hard to be prevented.To solve this problem,wheat flour with different bran particle content was used for the preparation of fresh wet noodles.By confocal laser scanning microscopy?CLSM?observation,dark spots on the fresh wet noodles were proved to be formed by wheat bran particles,and a bran particle,with melanins spreading around it,was the core of a dark spot.In the wheat flours with low ash content,there were a small number of wheat bran particles which could cause dark spots on fresh wet noodles,but the wheat bran particles could not be observed by naked eyes until the size was up to about 50?m.The browning caused by the oxidation of phenols catalyzed by polyphenol oxidase?PPO?is common in plant foods.PPO catalyzes the dehydrogenation reaction of phenolic compounds to generate quinones,and quinones generate melanins through non-enzymatic polymerization.The fresh wet noodles in different p H were prepared.The PPO-catechol systems were built with the crude PPO extracts from wheat flour and analytically pure catechol.The chemical formation mechanism of the dark spots on fresh wet noodles was discussed from the perspective of PPO browning.Base on the observation of the fresh wet noodles and analysis of PPO-catechol systems at different p H,the PPO browning process was investigated.Different from the overall color change of the fresh wet noodles,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 if the PPO was completely deactivated.The optimum p H for the phenolic dehydrogenation in fresh wet noodles was about7,and the alkaline condition was advantageous for the progress of the polymerization.Comprehensively,the dark spots formed at the maximum amount at about p H 9.Hexose oxidase is safe and efficient and can catalyze the oxidation of various hexoses and their oligosaccharides to generate acids or esters.Fresh wet noodles and PPO-catechol systems were prepared with hexose oxidase added.The chemical mechanism that hexose oxidase reducing the melanins of dark spots was discussed basis on the UPLC-TOF-MS analysis of the PPO-catechol systems.In the process of PPO browning,hexose oxidase catalyzed the oxidation of o-benzoquinone derivatives and their oligomers,hindering the formation of melanins.In the low ash content fresh wet noodle stored at 4°C for 6 days,40 ppm of hexose oxidase reduced the total area of dark spots by more than 80%,and 60 ppm of hexose oxidase could almost completely inhibit the formation of dark spots.In the presence of 1.5%Na Cl,0.03%Na₂CO_3,and other 9 metal ions,hexose oxidase could effectively prevent the formation of dark spots.Last but not least,fresh wet noodle browning was prevented through aqueous ozone mixing.Aqueous ozone mixing could increase the whiteness of the fresh wet noodles and reduce the total area of dark spots to a certain extent,in which physical factors and non-covalent bonds played a key role.The results of the dynamic rheology test and scanning electron microscope observation showed that aqueous ozone mixing strengthened the gluten network structure in the fresh wet noodles.The results of the low field nuclear magnetic resonance test showed that aqueous ozone mixing reduced the freedom degree of the water in the fresh wet noodle.This was because aqueous ozone had a moderate oxidizing capability,which was beneficial to promote the cross-linking of disulfide bonds in the dough.Thus,aqueous ozone mixing improved the fresh wet noodle gluten network structure and indirectly changed the water state in the fresh wet noodles.This could make the fresh wet noodle structure more compact and uniform,and reduce the browning rate of the fresh wet noodles.Aqueous ozone mixing combined with hexose oxidase could effectively prevent the browning of the fresh wet noodles.When the ozone concentration reached 2.35 mol/L,the amount of aqueous ozone addition was 20%to 32%,and the hexose oxidase solution was added 30 to 120 s after the start of mixing,the browning of fresh wet noodles could be effectively prevented.Combined with aqueous ozone mixing,compared with hexose oxidase only,the dark spots could still be prevented effectively when the amount of hexose oxidase was reduced by 10?20 ppm.