Study On Color And Polyphenol Stabilization Of Green Tea Noodles

Green tea noodles（GTPN）has a long history.GTPN,buckwheat noodles and udon noodles are known as the characteristic noodles in Japan and welcomed by consumers.Modern dietary patterns lead to a high incidence of chronic diseases resulting in increasing consumer demand for functional foods.GTPN in Chinese market mostly depends on imports,and their high price directly affect the temptation to consumers.However,the basic studies on GTPN are still weak,basic research is the source of scientific and technological innovation.Therefore,the studies should focus on the key problems to realize the industrialization and large-scale production of GTPN.Firstly,the key problems in the quality of GTPN were clarified,and laws and mechanism for the color change of GTPN were explored.Results showed that green tea powder improved the thermo-mechanical properties of wheat flour and qualities of GTPN,but destroyed the continuity and tightness of gluten network structure in GTPN.GTPN’s color mainly come from green tea powder（GTP）,and its color stability during processing and storage was poor,and the loss of polyphenols was large during cooking.Studies found that PPO in wheat flour is a key factor affecting the color formation and storage stability of GTPN,the lightness value（L）and yellow-green value（︱a︱）of GTPN continuously decreased during the processing process.The increase of PPO in wheat flour decreased the L and︱a︱value of GTPN,and increased the loss of polyphenols and chlorophyll during processing.The influence of PPO in wheat flour on the color formation of GTPN mostly happened during the noodle mixing process,which gradually weakened during the resting and drying.The discoloration rate of the GTPN during storage at 30℃indicated that the discoloration process could be divided into two stages,being stageⅠ:0-7 d and stageⅡ:7-56 d.The discoloration rate curve of 0 to 7 d time period（StageⅠ）can be defined using a nonlinear exponential function,whereas in the second time period 7-56d（StageⅡ）the discoloration rate curve is considered as a linear function.Increased PPO activity accelerated the discoloration and chlorophyll degradation rate of GTPN during storage.Principal component analysis（PCA）showed that L value,free polyphenol,chlorophyll,a value,b value and theabrownin content were related to the discoloration of GTPN.Based on the above studies,a processing method has been found,which can improve the color stability of GTPN during processing and storage.In the study,different processing methods were used to compare and analyze the color stability mechanism of GTPN.Results showed that PPO strongly affected the degradation of chlorophyll during processing,the reduction of PPO activity in wheat flour can significantly improve the color stability of GTPN during processing and storage.Adding green tea residue to the dough after resting at high temperature effectively avoided the thermal degradation of liposoluble chlorophyll and the degradation of liposoluble chlorophyll by PPO,which significantly reduced the color loss during processing of GTPN,and improved the color stability of GTPN during storage.Different scanning calorimetry（DSC）and the texture（TPA）results showed that resting at high temperature can increase the hardness and chewiness of GTPN by affecting the gelatinization of starch.The results of confocal laser scanning microscopy（CLSM）showed that resting at high temperature developed the gelatinized starch gel wrapping the GTP,which improved the storage stability of GTPN.Secondly,the mechanism of thermal degradation and dissolution of polyphenols in green tea noodles were studied.The research concluded that the cooking loss,polyphenol compounds loss and textural properties of GTPN were related to GTP particle size and amounts via the microstructure.Small GTP particles distributed more on the surface of GTPN.The network structure of GTPN prepared with small GTP particles was looser.As a result,polyphenols were easier to loss after cooking.Electron scanning microscope（SEM）results showed that large GTP formed some holes in the noodles’network,resulting in increased cooking loss and reduced breaking strength,nevertheless polyphenol retention rate of GTPN prepared with large GTP particles was relatively high.These results concluded that the cooking loss of GTPN cannot reflect the loss of polyphenols.7 catechins and 12 flavonoids in GTPN were characterized by Ultra-performance liquid chromatography-time off flight mass spectrometry（UPLC/Q-TOF-MS/MS）,almost of which come from GTP.Cooking led to a 25.29%decrease of total free polyphenol,92.61%of which was caused by catechin loss.The loss rates of 19 compounds ranged from 6.71 to 100%,and that the loss rate was above 25%included catechin,epicatechin gallate,epigallocatechin gallate,kaempferol,myricetin,luteolin,proanthocyanidin B2.35.70%of the total free polyphenol fraction was dissolved in cooking water,of which the proportion of catechins was still relatively high at 98.32%.In addition to the polyphenols dissolved in cooking water,64.30%of polyphenols lost due to thermal oxidation degradation,of which the flavonoid compounds and catechins lost 91.91%and 62.09%,respectively.Finally,microwave treatment of dough was used to reduce the cooking loss of polyphenols in GTPN,and its effect mechanism on the loss of polyphenols in GTPN was analyzed.The results showed that the diffusivity of polyphenol compounds during cooking fitted in the Fick’s Second Diffusion Law,and the diffusion coefficient values and kinetic constants of polyphenol compounds in different microwave treatment（700 W 0 s～60 s）GTPN samples were estimated to be in the range of 6.17×10^-9～10.43×10^-9m²/s and 0.22～0.29 s^-1,respectively.The diffusion coefficient values and kinetic constants of polyphenol compounds significantly increased after microwave treatment,but the retention rate of polyphenol compounds in 30 s GTPN and 45 s GTPN samples was improved.These results showed that the diffusion rate of polyphenol compounds in GTPN was slower than the heat oxidation degradation loss rate.Comprehensive results of X-ray diffraction（XRD）,Fourier Transform Infrared Spectroscopy（FT-IR）and DSC speculated that microwave treatment in this study induced the rearrangement of broken molecular chain segments resulting in a more relaxed and loose structure formation of starch polymorphs.Magnetic resonance image（MRI）results showed that starch granules at the edge of GTPN absorbed water and swelled rapidly,microwave treatment decreased the swelling power of starch at the edge during cooking and provided enough space for water penetrated into the core of the noodles.The changes in starch structure and water migration were related to the reduction of cooking time.Timely microwave treatment can significantly improve the texture characteristics and ABTS^·+scavenging abilities of cooked GTPN.