Effect Of Three Refining Treatments On The Color And Rheological Properties Of Peach Pulp

The objective of this study was to evaluate the effect of refining treatments on the color stability and rheological properties of peach pulp.Processing methods included beater,colloid mill and wet ultrafine grinder with different frequencies（18,26,34,42 Hz and 50 Hz）.The analyses of Pearson correlation,stepwise linear regression and mathematical models were used to clarify the main factors affecting the color and rheological properties of peach pulp during the physical grinding process.In addition,the effects of different refining treatments on the structural characteristics of peach pulp WSP,CSP and NSP were also investigated.The results of this study provide a theoretical basis for the optimization of peach pulp processing technology and quality control.The main conclusions of the thesis were as follows:Results showed that L^*,b^*and a^*values of the unblanched peach pulp sample with ultrafine grinding at 50 Hz for 60 s were higher than those of beating treatment.Compared with the non-blanched peach pulp sample,the L^*,b^*andΔE values of the blanched samples increased,while the a^*value reduced.For blanched peach pulp samples,as the grinding frequency increased,the values of L^*,b^*andΔE increased,while the value of a^*did not change significantly.Further studies on the composition of related substances showed that blanching at 90℃for 1 min could inactivate the PPO activity and effectively inhibited enzymatic browning.The total phenol,soluble protein and reducing sugar concentrations of peach pulp sample with ultrafine grinding at 50 Hz for 60 s were 1.58 GAE·g^-1,0.093%and 2.741%,respectively.Pearson correlation analysis showed that with blanching treatment,L^*showed a significantly positive correlation with total polyphenol concentration of peach pulp,and significantly negative correlated with the concentration of reducing sugar and sucrose.Results of stepwise linear regression analysis showed that the apparent color of blanched peach pulp during different ultrafine grinding treatments were mainly correlated to the substances of non-enzymatic Browning substances.Compared with beating,the particle size distribution peak of the pulp after ultrafine grinding treatment shifted to the left,and the D50,D[4,3]and D[3,2]values of the pulp processed at 50 Hz and 60 s were reduced by 40.65%,39.1%and44.42%respectively.For colloid milling pulp,D50 and D[4,3]showed downward trends,with no significant difference（P>0.05）.The rheological data showed that the rheological curve of peach pulp conformed to the Power-Low model.Peach pulp was considered as pseudo-plastic fluid（0<n<1）and had a gel-like behavior（G′>G″）.With the processing of colloid mill and ultrafine grinding,apparent viscosity,G′and G″of the pulp decreased.The results showed that galacturonic acid（Gal A）content of WSP showed an increasing trend with the processing of colloid mill and ultrafine grinding.The highest content of NSP and CSP was found with ultrafine grinding at 34 Hz for 60 s.For the molecular weights of three different pectin,CSP was the highest,followed by WSP and NSP.The degree of methyl esterification（DE）of most pectins were below50%,indicating as low methoxyl pectin.The Fourier Infrared results showed that different refining treatments had no significant effect on the absorption peaks of the three pectins.Therefore,the refining treatments did not change the functional group composition of the three pectins.There were seven types of monosaccharides in the three refined samples,and arabinose（Ara）,galactose（Gal）and rhamnose（Rha）were three main neutral sugar.The pectin structure of WSP and NSP were mainly consisted of RG-Ⅰ,while CSP was dominated by HG and RG-Ⅱ.