April 30, 2021

Can you judge a potato by its cover?

Written by: Ed Hill-King

I am a PhD student with the Waitrose CTP in the first year of my four-year programme and beginning my laboratory research in the Lancaster Environment Centre. My research is focused on exploring novel approaches to detecting internal defects in intact potato tubers.

Internal defects in potato tubers pose a unique challenge to the potato supply chain. A tuber may visually appear healthy from the exterior, but be spoiled inside, which can lead to waste and customer dissatisfaction. Waste is a serious issue in the potato chain, with 53% of all potato being lost due to waste from all sources. [1]

Internal defects exhibit great diversity and have various causes. Some defects are caused by disease; bacterial, fungal and viral infections can all lead to rot and spoilage of tubers. Growth defects also affect potato tubers; changes in the rate of growth can cause a tuber to develop hollow heart. Storage conditions, such as temperature and air quality, can lead to spoilage; high carbon dioxide to oxygen ratios can lead to the development of black heart [2]. Additionally, direct damage can be a cause of tuber defects, either from pests, such as slugs, or through mechanical damage from agricultural equipment.

Traditional methods of detecting internal defects involve destructively cutting open a sample of tubers. There are some limitations to this approach: tuber destruction is wasteful and limits throughput, and individual tubers cannot all be screened. In addition to this, destructive approaches have limited applicability to prognostic applications. Traditional methods are inefficient, and novel and automatable approaches are needed for better tuber quality assessment.

Fast, reliable and non-invasive methods of detecting or identifying internal tuber defects could help to inform supply chain decisions to minimise loss and maximise consumer product quality. Assessing a crop post-harvest could give farmers crucial insights into defects on their farm and inform better predictions. Tuber assessment also informs storage and distribution decisions. If a tuber is likely to spoil within a few months, it could be sent to be made into crisps rather than go into storage and avoid the waste of spoilage.

In my research I am exploring how infra-red optical spectroscopy and bioimpedance, among other approaches, may be harnessed as tools to detect internal defects non-destructively. I am investigating how the spectral signatures of tubers change when they are subjected to defect-inducing environments. Stress signals of defective tubers may be detectable from the spectral signature of a tuber’s surface. The microbes in potato diseases may also be detected through changes in chemistry, for example by the breakdown of starch chains via amylase.

When deploying spectroscopic methods on vegetables, a sample usually requires multiple scans for an accurate and complete assessment. I am mapping how the spectral signature varies across a tuber’s surface, both in healthy and defective samples. This will inform scanning methodology optimisation: how many times to scan a tuber; where to scan a tuber; and the statistical significance of data, for example, whether outliers are more relevant as they may be indicative of a local defect.

Having a background in electronic engineering, I am fascinated by delving into electrical approaches to tuber quality assessment. Bioimpedance and electrical hysteresis offer promising potential for internal defect detection. I have planned some experiments to explore and develop these approaches.

Cavities, loss of turgor pressure and tissue breakdown will all affect the internal acoustics of a tuber. Thus, transudative acoustic methods could be deployed to assess internal tuber quality. In my research I am exploring whether Fourier convolution of sine sweeps could be used; however, there are some practical limitations to applying this approach in an industrial setting. Transudative methods require good coupling between the transducer and the sample, which is difficult with irregular-shaped potatoes, presenting noise and limitations on throughput. In addition to this, background noise of an industrial setting may be another source of noise, leading to unreliable results.

Undertaking a PhD with the Waitrose CTP is a fantastic opportunity to gain experience and expertise. I am excited to continue my research and dig deeper into fascinating field of potatoes.

[1] Tsolakis N, Kumar M. Investigating Wastage and Associated Mitigation Scenarios Across Fresh Potato Supply Chains in the UK: A Critical Literature Synthesis. Available at SSRN 3422067. 2019 Jul 18.

[2] AHDB, Blackheart knowledge library, [cited 30/04/2021]