Effect Of Tea Extracts On Quality Characteristics Of Chinese Dried Noodles And Physicochemical Properties Of Wheat Starch

Chinese dried noodle is a popular staple food due to its convenience.Nowadays,its limited functional property and low nutritional value influence consumers purchasing behavior.As the most biologically active group of the tea components,tea polyphenols have great potential in preventing or reducing the risk of oxidation-linked chronic diseases.Incorporation of tea polyphenols may be expected to nutritionally enhanced quality of wheat-based products.And the physicochemical quality of products would also be affected by complicated interaction between polyphenol and macronutrients(starch and protein).In order to provide effective information for Chinese dried noodle innovation,different tea polyphenol resources(green tea extract,black tea extract,and oolong tea extract)were added into hard red winter flour to study their effects on starch pasting and dough mixing property.The three tea extracts were then applied in two different noodle systems(white salted noodle and yellow alkaline noodle).Their effects on starch pasting,dough mixing and noodle making quality in different pH systems were explored and the underlying mechanisms were discussed.A detailed polyphenol-starch interaction under different pH conditions was illustrated.The main research contents and conclusions were summarized as follows:The effect of different TPs supplements(green tea extract,black tea extract,and oolong tea extract)on the pasting,aggregation and mixing properties of hard red spring flour was firstly investigated.All the tea extracts hindered granule swelling,amylose leaching and starch retrogradation.Peak maximum time was prolonged,and maximum torque and aggregation energy were decreased for each tea extract when the addition level was increased from 0.5%to 2.0%.During mild mixing,tea extracts gave rise to the limited water absorption,delayed dough development and strengthened dough network,which may increase dough handling difficulity in noodle processing.Among three tea extracts,black tea extract was more effective in reducing paste viscosity,inhibiting gluten aggregation and strengthening dough network.Three tea extracts were then added into noodle formulation at 0.5-2.0%levels(based on flour weight)to produce dry Chinese white salted noodles(WSNs)and yellow alkaline noodles(YANs).Tea extracts had negative effect on texture of WSNs,but positive on YANs.Tea extracts induced more pronounced starch pasting and dough strengthening effects in alkaline environment than in saline environment.With 2.0%tea extracts,the dry WSNs exhibited darker and yellower color,and higher breaking force than control dry WSN,while YANs exhibited darker and redder color and lower breaking force than control dry YAN.Both texture profile analysis and stress relaxation tests confirmed that tea extracts exhibited opposite effect on the viscoelasticity of cooked WSN and YAN,which was related to the different polyphenol-starch-gluten interaction in different pH environments.To investigate the mechanisms underlying quality differences between WSNs and YANs,starch gelatinization,noodle microstructural,water distributional,and protein polymerization properties were determined.Meanwhile,the antioxidant capacity and in-vitro starch digestibility of WSNs and YANs were also explored.In WSNs,tea extracts addition resulted in a decrease in peak temperature,gluten netword strengthening,a slightly decrease in the intensity of a protein band,an increase in parallel ?-sheet content and water mobility enhancement.In YANs,tea extracts addition resulted in decrease in peak temperature,end temperature and the gelatinization enthalpy,gluten structure weakening,an obvious decrease in the intensity of the protein bands,increase in parallel and anti-parallel ?-sheet contents and limited water mobility.Tea extracts addition showed effective DPPH scavenging and starch digestion inhibition capacities for both WSNs and YANs.The interactions between wheat starch and tea polyphenols(TPs)in different pH systems(3,7 and 11)were investigated.TPs reduced peak viscosity,breakdown,setback,storage modulus,loss modulus and flow behavior index of wheat starch in three different pH systems due to the cross-linking between starch granules and TPs.The polyphenol-starch interactions were more pronounced in acidic and alkaline systems,which may be related to the depolymerization of starch chain in acidic condition and the modification of ionic charge in alkaline condition.A porous three-dimensional gel matrix was transformed to one-dimensional lamellar structure when TPs were added in three pH systems.The structure transformation was firstly initiated in acidic environment.By TPs addition,the average height of bundles formed by starch chain aggregation was decreased by 0.5 nm,0.9 n,and 0.2 nm in acidic,neutral and alkaline conditions,respectively.1H NMR studies of gelatinized starch containing TPs in acidic system showed the most obvious signal shifting and relative signal intensity modification.