Stress relaxation properties of bananas during drying

Bananas' mechanical properties are affected by the ripening and the drying processes since they induce profound microstructural changes. In this study, first, the interacting effect of the ripening and the drying processes on the mode of viscoelastic behavior of bananas was investigated. Second, the stress relaxation properties of fully ripe bananas were measured as a function of the hot air drying conditions. Finally, the two-element generalized Maxwell model was fitted to the experimental data. Thus, this study clarified the dependence of the mode of rheological behavior on both the ripening stage and the moisture content. It showed that bananas start softening at the onset of the drying when the fruit moisture content is high. The softening is reversed at a critical value, at which the bananas start regaining stiffness with further moisture reduction. The critical moisture content value decreases with ripening from 1.4 g/g solids for green bananas (5-11% Brix percentage) to 1.23 g/g solids for half-ripe bananas (15-20% Brix percentage) and eventually vanishes when the bananas are fully ripe (25-31% Brix percentage). The stress relaxation properties measured with fully ripe bananas substantiated the initial findings on the influence of the ripening stage on the mode of rheological behavior. The relaxation moduli displayed a decreasing trend with decrease in the moisture content for 40, 60, and 80 degrees C drying temperatures and decayed with time as expected for viscoelastic bodies. Lastly, the two-element generalized Maxwell model fitted well to the experimental data with the root mean square error varying between 0.06 x 10(-5) and 90.6 x 10(-5)MPa.

香蕉的力学性能受成熟和干燥过程的影响，因为它们会引起深刻的微观结构变化。在这项研究中，首先，研究了成熟和干燥过程对香蕉粘弹性行为模式的相互作用。其次，测量了完全成熟香蕉的应力松弛特性随热风干燥条件的变化。最后，将二元广义麦克斯韦模型与实验数据进行拟合。因此，这项研究阐明了流变行为模式对成熟阶段和水分含量的依赖性。研究表明，当果实含水量较高时，香蕉在干燥开始时就开始变软。在一个临界值时，软化趋势逆转，随着水分进一步减少，香蕉开始重新获得硬度。临界含水量值随着成熟度的增加而降低，从青香蕉的1.4克/克固体（白利糖度为5 - 11%）降至半熟香蕉的1.23克/克固体（白利糖度为15 - 20%），当香蕉完全成熟时（白利糖度为25 - 31%）最终消失。对完全成熟香蕉测量的应力松弛特性证实了关于成熟阶段对流变行为模式影响的初步发现。在40、60和80摄氏度的干燥温度下，松弛模量随着水分含量的降低呈下降趋势，并且像粘弹性体预期的那样随时间衰减。最后，二元广义麦克斯韦模型与实验数据拟合良好，均方根误差在0.06×10⁻⁵到90.6×10⁻⁵兆帕之间变化。