BEET STIFFNESS DURING STORAGE

WHY:

For my mind, it is pretty clear that beet strength doesn’t change much during storage – I’ve taken enough penetrometer measurements of fresh and highly dehydrated beets to see no difference. That said, over longer storage periods, Nedomova et al (2017) did see beets get stronger. Beet stiffness, on the other hand and again “for my mind”, clearly changes. The circumstantial evidence I have is clear, but my factual evidence is limited. In one set of trials in which I measured weight and volume loss from exposure to dry and windy conditions, I also attempted to measure stiffness. It was clear that stiffness changed if the data is interpreted in a particular way, but the method I used wasn’t proven. Other research, for example Nedomova et al (2017), does use proven methods and showed clearly decreased stiffness of the beet during storage.

This matters because a softer beet will be subjected to lesser forces and pressures for any given impact, which may mean less damage. It also matters when it comes to clamp architecture. If beets get softer during storage they will become more tightly packed (bulk porosity decrease), which will reduce the air flow in the clamp (permeability decreases). There will also be greater beet-to-beet contact area, which might impact rates of rot.

HOW:

There are two proven methods that I would trust. The first is using a laboratory penetrometer that can measure the distance the plunger moves from the point of contact to the point of skin rupture (as per Nedomová et al 2017). The second is to use pressure mapping sensors to measure contact area, total force, and pressure distribution (as per Nilsson 2020). I think that both methods allow for repeat measurement of approximately the same point on the same beets, which would mean reliable data. I think that the pressure mapping would give more interesting data, but the system is expensive and harder to find. Plus, it doesn’t strictly measure stiffness as it would be defined in a material sciences sense – just the change in contact area for a given force.

An example experimental set up:

Plant material: 2 varieties – one strong/ high sugar content, one weak/ low sugar content. 2 sizes of beets: small (ca. 1000g), large (ca. 2000g). 10 beets per variety x size x storage condition (see below), for a total of 80 beets.

Storage: beets are stored for ca. 300 degree days in either a 95% RH no air movement condition (“wet”), or 80% light air movement condition (“dry”).

Stiffness measurement: Using a pressure mapping sensor, contact area and pressure distribution is measured both pre- and post-storage. At measurement, beets are placed on the sensor at a round, relatively smooth, and damage free point of the widest part of the beet. The contact point is marked in a non-destructive & reliable way. A 40kg weight is placed on the beets and measurement taken.

If the project wants to be ambitious, both instruments could be applied to the same beets, but at different points (on the beet, and in time, and on a map of Skåne – the measuring equipment is at different universities).

WHEN:

This project could be run any harvest campaign, subject to the availability of instrumentation.

COST STAB-IN-THE-DARK:

Labour will be the major cost of this project. Beets can be sources from any other field trial, and storage can happen in existing infrastructure.

The measuring equipment is so expensive (hundred of thousands of SEK), that the project would need to borrow it, maybe buying some desk time or new sensors. This would be ca.5000 SEK. Lunds food technology lab, part of the Skåne Open Lab network, has a penetrometer. There is a pressure mapping sensor system at SLU, but the owner is pretty busy.

WHY THIS MIGHT NOT HAPPEN:

Access to the equipment.

COMMENTS:

This would be a good student project. It is of high interest to NBR.

Nedomová, Š., et al. (2017). “Mechanical properties of sugar beet root during storage” International Agrophysics 31(4): 507-513.