Study On Mechanism And Inhibition Of Fresh Wet Noodle Browning

Noodles are one of the staple foods of Asian countries.According to water content,noodles are divided into dried noodles,semi-dry noodles and fresh wet noodles(FWNS),which have wonderful taste and short cooking time.However,FWNS is easy to brown,affecting the development of the FWNS industry.The purpose of this paper was to explore the law and factors of browning of FWNS and appropriate inhibitory measures.Firstly,the browning regularity and influencing factors of FWNS during storage(0-24 h)were explored.The color(?L^*,a^*,b^*),the activity of polyphenol oxidase(PPO),and the free polyphenol content of FWNS during storage were measured.The results showed that FWNS turned dark;The browning curve of FWNS was divided into stage I(0-4 h)and stage II(4-24h).The curve in stage I showed a non-linear exponential change trend,and the stage II was represented by a linear function;The PPO activity was almost unchanged during storage;The content of free polyphenols did not change significantly during 0-4 h,and dropped by 23.89%with 4-24 h.Effects of PPO,protein,pH and A_W on the browning of FWNS were explored.The?L^*of FWNS was significantly reduced after adding PPO inhibitors,of which?L^*_0-4h decreased by 7.91%,while?L^*_4-24h reduced by 40.69%,indicating that PPO browning mainly occurred in4-24 h.It was found that the?L^*increased significantly with adding 5%protein,indicating that protein promoted the browning of the FWNS.It was found that?L decreased when pH<6 or pH>10,while?L^*increased among pH 7-9,indicating pH was an important factor affecting the browning of FWNS.It was found that when A_w<0.90,?L^*did not change significantly;when A_w>0.92,?L^*increased.Secondly,the inhibitory effect of aspartic acid(Asp)on the browning of FWNS were explored.The?L^*,PPO activity and free polyphenol content of the FWNS were significantly reduced with adding Asp(P<0.05),indicating that Asp significantly(P<0.05)reduced the PPO activity of the FWNS and inhibited browning.Studies have found that the PPO by Asp was inhibited by lowering pH and chelating Cu²⁺of the active center of PPO.Through TOF-MS-HPLC analysis of the enzymatic browning products of the PPO-catechol system,it was found that the peak area of the enzymatic browning product decreased after the addition of Asp,indicating that Asp could reduce the final product of enzymatic browning.In addition,we explored the inhibitory effect and mechanism of L-cysteine on the browning of FWNS.The?L^*of the FWNS was significantly reduced after adding L-cysteine,By measuring the effect of L-cysteine on the PPO activity and pH of FWNS,it was found that L-cysteine significantly(P<0.05)reduced the pH,PPO activity.and the oxidation of free polyphenols.It was found that L-cysteine reacted with quinone to generate a stable light-colored substance according to the TOF-MS-HPLC analysis of enzymatic browning products.Subsequently,we explored the inhibitory effect of phosphate(TPP,SHMP,STPP)on the browning of FWNS.The study found that three phosphates significantly(P<0.05)reduced the?L^*of FWNS,and STPP had a better inhibitory effect.Experiments have explored the effect of phosphate(TPP,SHMP,STPP)on the browning of FWNS and the effect on moisture distribution.The results showed that phosphate reduced the T₂₂ and T₂₃,indicating that phosphate changed the state of free water and semi-combined water.The effects of three phosphates on the rheological properties of the dough sheet were determined,and found that the phosphates increased the G',G"and reduced Tan?,indicating that phosphate increased the overall elasticity and hardness of the dough sheet.IT was found that TPP and TSPP reduced PPO activity by changing pH,while STPP inhibited PPO activity by lowering pH and chelating Cu²⁺.Finally,we explored the?L^*,PPO activity and free polyphenol content of FWNS treated with ozone.The results showed that?L,PPO activity,the initial polyphenols and polyphenol changes of the FWNS after ozone treatment decreased significantly(P<0.05).Through the low-field NMR analysis of the noodles,it was found that the T₂₂and T₂₃ of the FWNS decreased after ozone treatment,indicating that the ozone treatment changed the state of free water and semi-bound water in the FWNS.On the other hand,we analyzed the rheological properties of the FWNS,and found that G'and G"of the sheet increased,while Tan?decreased,indicating that the elasticity of the dough sheet increased,and the overall the structure was tighter.After ozone treatment,the non-reduced SDS extractable protein and the reduced SDS extractable glutenin and gliadin reduced,indicating that ozone treatment improved the cross-linking of the protein in FWNS with disulfide bonds.