A comprehensive model for the prediction and analysis of internal potato tuber damage in postharvest processes

在从收获到最终消费者的农业过程链中，马铃薯块茎经历了无数的机械载荷，这些载荷经常导致内部结构和生理损伤。与外部损害相反，内部损害尤其令人担忧，因为它在分级阶段不易发现。通常，内部组织损伤会引发生化过程，随着时间的推移，这会导致黑色素黑色素的产生。这一过程通常被称为黑斑瘀伤。在整个马铃薯块茎的尺度上，人们对此进行了广泛的调查，主要是为了评估可调的工艺参数，如施肥、收获温度、品种和块茎成熟度对黑斑病易感性的影响。虽然许多研究人员强调块茎组织的力学特性与挫伤敏感性之间的联系，但由于应用人员的意识，尚未建立组织尺度上黑斑挫伤的应力-应变响应的详细物理力学模型。在本项目中，开发了一种综合了马铃薯块茎组织的非弹性本构关系和黑斑挫伤强度和发展过程的反应动力学的多场建模方法。应力-应变响应和变色动力学的本构参数是基于组织尺度实验确定的，更重要的是，包含/吸收了马铃薯块茎批次的预测试历史。实验活动包括压缩测试、呼吸测量和变色测量，以及对块茎组织中气体扩散速度的量化。从概念上讲，所得到的连续统力学模型可以用来模拟和分析马铃薯块茎组织对不同载荷模式的响应，并预测随着时间的推移马铃薯块茎组织的生理损伤响应。为了量化马铃薯块茎在典型采后过程中所受的载荷集体，提出了块茎-块茎和块茎-机械相互作用的离散元模型。农产品数字高程模型面临的主要挑战是建立可靠的接触力-渗透率定律和识别典型块茎形状。此外，在块茎表面，冲击力根据它们对黑点的贡献被整理成载荷集合，通过将这两个发展分支结合起来，提供了一种前所未有的预测方法来量化马铃薯块茎内部受损的比例以及给定的马铃薯块茎批次和装卸设备的受损程度的时间变化。在一系列专门的实验中验证了投影连续体模型和DEM的预测能力。

In the agricultural process chain leading from the harvest to the final consumer, potato tubers undergo a myriad of mechanical loads which frequently entail internal structural and physiological damage. Contrary to external damage, internal damage is particularly worrisome as it is not easily detectable in grading stages. Typically, internal tissue damage elicits biochemical processes which, over time, entail the inception of the black pigment melanin. This process is commonly referred to as blackspot bruising. On the scale of a whole potato tuber, it has been extensively investigated, mainly in order to assess the influence of adjustable process parameters such as fertilization, harvest temperature, cultivar and tuber maturity on the susceptibility to blackspot bruising. While many researchers have emphasized the connection between mechanical characteristics of tuber tissue and bruising susceptibility, a detailed physio-mechanical model relating the stress-strain response to blackspot bruising on the tissue scale is as yet absent, to the awareness of the applicants.In this project, a multifield modeling approach synthesizing inelastic constitutive relations for potato tuber tissue and reaction kinetics for the intensity and progress of blackspot bruising is developed. The constitutive parameters for the stress-strain response and the discoloration kinetics are determined based on tissue scale experiments and, importantly, encompass/absorb the pre-testing history of a potato tuber batch. The experimental campaign involves compression tests, respirometric and discoloration measurements as well as a quantification of gas diffusion rates in tuber tissue. Conceptually, the resulting continuum mechanical model can be used to emulate and analyze the response of potato tuber tissue to different load patterns and to forecast the physiological bruising response over time.In order to quantify the load collectives that potato tubers are subjected to in the course of a typical postharvest process, a discrete element model (DEM) for the tuber-tuber and tuber-machinery interaction is advanced. The main persisting challenges for DEM of agricultural produce are related to the construction of reliable contact force-penetration laws and the identification of a representative tuber shape. On a tuber's surface, moreover, impact forces are collated into load collectives according to the blackspots which they contribute to.By joining these two branches of development, an unprecedented predictive approach for quantifying the fraction of internally damaged potato tubers and the temporal change in damage extent for a given potato tuber batch and handling equipment is provided. Both the projected continuum model and the predictive capabilities of the DEM are validated in a series of dedicated experiments.