| ‘Yali’pear has delicate meat,thin juicy skin,sweet and delicious,rich in polysaccharides,tannic acid,vitamins and trace elements,suitable for processing canned,pear juice,pear preserved and other series of products.Among them,pear paste has a fresh taste,moderate sweetness and fragrance,and has various effects such as relieving cough and asthma,anti-inflammation and anti-bacteria.It is one of the popular pear deep processing products.In this study,the comprehensive evaluation model of Z-score（Z value）method was established.The response surface method was used to optimize the color preservation process of pear paste.The effects of different concentration methods and concentration temperatures on the quality of pear paste were compared,and the rheological properties of pear paste were measured systematically.The results were as follows:（1）Taking Z value as evaluation index,the color protection process of‘Yali’pear paste was optimized through single factor experiment and response surface experiment.The optimum process conditions for color protection were added amount of sodium ascorbate 0.02%（W/V）,citric acid 0.05%（W/V）and potassium metabisulfite 0.02%（W/V）.Under these conditions,the sensory score of‘Yali’pear paste was 9.38,the browning degree was 0.201,the contents of total phenol and total flavonoid were 59.80μg/m L and 80.10μg/m L,respectively,and the comprehensive evaluation score of Z-value method was 5.14.The electronic nose technology made a perfect distinction on flavour between the optimized condition and without color protection of‘Yali’pear paste.The electronic tongue analysis showed that‘Yali’pear paste prepared under optimized conditions aroused stronger signals than paste without color protection in taste richness and sour sensors.（2）The effects of different concentration methods and temperatures on physicochemical indexes,sensory quality,antioxidant capacity and volatile components of‘Yali’pear paste were studied.‘Yali’pear paste prepared by vacuum concentration method had better quality.The optimum vacuum concentration temperature was 65℃,and the comprehensive evaluation score of Z-value method was the highest,10.49.On this condition,the browning degree and soluble quinones were the lowest in all tested temperatures,and the contents were 60.12%and 72.88%compared with the heating method,respectively.While the values were 148.29%,209.44%,310.86%,120.37%,106.24%,and 181.26%of total phenol,total flavonoid,vitamin C,DPPH,·OH radical scavenging rates and total reducing power,respectively.The electronic nose can effectively distinguish the vacuum concentrated pear paste from the traditional heating concentration pear paste.The electronic tongue tests showed that the vacuum concentrated pear paste had larger freshness and richness kurtosis.（3）HR-10 rheometer was used to determine the fluid type,viscosity and thixotropy of Yali paste,and to investigate the changes of thixotropy and viscosity of the pear paste after artificial addition of sugar and glue.‘Yali’pear paste belonged to non-Newtonian fluid,which was subdivided into pseudoplastic fluid infinitely closed to Newtonian fluid,with shear thinning and normal thixotropy characteristics.The relation between shear rate and shear force fitted the Power Law equationτ=KDn,and the fitting effect was gorgeous（R2>0.99）.The effect of temperature on viscosity was consistent with the Arrhenius equationη=Ke-Ea/RT,and the fitting effect was good（R2>0.95）.The viscosity was dependent on SSC,and the effect of SSC on viscosity could be accurately expressed by the exponential functionη=K2exp A2C,with great fitting effect（R2>0.99）.The thixotropy and viscosity of pear paste were significantly weakened by different SSC,adding sugar,gum.This study can provided reference for the optimization of color protection and concentration process of pear paste in industrial production,as well as multi-index comprehensive evaluation,and provided theoretical basis for the viscosity prediction,quality control and adulteration detection of pear paste. |
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