基于流变特性的不同品种苹果果皮质地评价

为探究苹果果皮表面碎裂损伤的原因和评价不同品种果皮的质地。采用电子万能试验机对丹霞、红富士和新红星苹果果皮进行拉伸松弛和蠕变特性试验,得到了果皮松弛的初始应力、残余应力、应变保持和蠕变的初始应变、应力保持、蠕变量;建立了苹果果皮松弛和蠕变的数学模型,对松弛和蠕变特性参数进行了相关性和主成分分析。结果表明:松弛和蠕变试验结果揭示出不同品种果皮的流变特性和内部组织结构存在差异。不同品种果皮的初始应力较大时,松弛平衡后的残余应力较大;初始应变较大时,蠕变量较小。新红星果皮的弹性因子贡献率较高,而红富士果皮的黏性因子贡献率较高,反映出红富士果皮表面中较新红星和丹霞果皮表面容易碎裂损伤,在采收、运输等过程中红富士的果皮较新红星和丹霞的果皮易受机械损伤。研究结果可为苹果品种的优育及其质地评价体系的建立和完善提供参考。

Evaluation on peels texture of different apple cultivars based on rheological properties

In order to explore crack damage of apple peel in the process of naturally growing and evaluate quality of different peels varieties, peel samples coming the shadow side and sunlit side of three apple cultivars,Danxia, Fuji, Star-krimson were chosen for longitudinal tests of tensile stress relaxation and creep by means of electronic universal testing machine. Stress-time curve of relaxation test and strain-time curve of creep test were obtained from the tests; and initial stress, residual stress and strain holding of peel relaxation and initial strain, stress holding and creep value of peel creep were also gained. We then set up relaxation five component Maxwell model and creep Burgers model by use of experimental data; and established relaxation and creep characteristic parameters for correlation analysis; and used the relaxation and creep model parameters for principle component analysis. The results indicated that under the action of the same load, discrete degree of peel initial stress was far lower than that of peel residual stress. The standard deviation of initial stress was within 0.4 percent of the average, but the residual stress standard deviation reached about 10% of its average. Initial stress, residual stress, strain holding, initial strain, and stress holding of Star-krimson peel had significant differences (p<0.01) from Danxia and Fuji peels. For different varieties, peel relaxation initial stress, relaxation residual stress; and creep initial strain were large, but creep value was small. For relaxation model parameters of peel, the equilibrium modulus of Star-krimson peel was much larger (p < 0.01) than that of Danxia and Fuji peel; but its relaxation time were much less (p < 0.05) than that of Danxia and Fuji peel. Viscosity factors of Star-krimson peel showed a significant difference (p < 0.05) from that of Fuji peel. For creep model parameters of peel, the mean value of instant elastic modulus of Star-krimson peel was the greatest and that of Fuji peel was the lowest; but decay time and viscosity factors of Fuji peel were the largest. There was a significant (p < 0.05) difference between instant elastic modulus, decay time, viscosity factors of Star-krimson peel and that of Fuji peel. It was found that the relaxation and creep test can objectively describe internal tissue structure differences around different peels; and organization structure of Star-krimson peel had better fluidity and stronger elasticity and that of Fuji peel had weaker fluidity and stronger viscidity. When the principle component analysis was performed for relaxation and creep model parameters of peel, eigenvalue was more than 1 for selected principle component and accumulative contribution rate of Danxia, Fuji, and Star-krimson peel reached 85.13%、83.94% and 91.68%, respectively. Contribution rate of elasticity factor which was on behalf of peel quality was relatively larger in Star-krimson peel, but contribution rate of viscidity factor was relatively higher in Fuji peel, this reflected that Fuji peel surface was easier fragmentation than Star-krimson peel surface;and Fuji peel surface was also easy to injury including harvest, packaging, transportation and storage. The results have significances to provide better apple cultivation and perfect apple texture evaluation system.