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February

From soup to tomatoes (and back again)

Using satellite meteorology to determine the deterioration in tomato quality during transport

Tomato road transport obstacles
Fig. 1. Road-transport obstacles to regional trade in four (4) West African countries (modified after USAID (2008)). Click here to enlarge

To determine the deterioration in tomato quality during low-cost tomato transport in West Africa, spatial agro ecologists from the Faculty of Geo-Information Science and Earth Observation (ITC) of the University of Twente present a spatial–temporal simulation model in a recent paper that links the prevailing outside weather conditions, estimated using satellite meteorology, to the microclimate observed inside truck trailers (crypto climate).

Unfit for human consumption
Transporters are key players in the West African trade of tomatoes, valued at 60 million USD/year of trade between Burkina Faso and Ghana alone, and quality-related marginal differences are essential to keeping these imports attractive. But this potentially viable horticultural value chain is in jeopardy. Not only price fluctuations but also postharvest losses leave traders with uncertain returns, and sometimes even losses. Several studies estimate that postharvest losses in West Africa may be anywhere from 20% up to 50%; sometimes half of vegetable produce is unfit for human consumption once it arrives at the market. Sadly, these postharvest losses tend to be highest in countries with the greatest food shortages. These losses are further aggravated by delays at border crossings, (illegal) toll stops, police controls, or poor road and truck conditions. Fig. 1 shows road obstacles and their impact charted for several West African countries.

Reduce postharvest losses
“The spatial-temporal simulation model we present in this paper, say the authors, “will help planners to simulate the cost–benefit of various measures to reduce postharvest losses ahead of implementation, e.g. by semi-controlling cargo conditions (e.g. pre-cooling treatment), different transport scheduling, or what net gains can be expected if delays along the transportation route are reduced.” Supercomputing facilities at ITC and open source geospatial software were modified for the purpose, producing regional maps of environmental conditions (see example in Fig. 2) known to reinforce or reduce postharvest losses, uniquely for each GPS locations visited by the trucks transporting the produce.

Fig. 2. Example of observed crypto temperatures (Tincargo, °C) during a forward trip from Ghana to Burkina Faso showing a peak (±38 °C) at the border crossing. Click here to enlarge

Reduce total transport time
“Simulation results suggest that losses in tomato firmness could be reduced to 27% if the total transport is reduced from 43 to 24 h, and could be as low as 15% if the produce arrives at the destination points 12 h after harvest. This, however, may not be achieved in the short-term given the lack of cross-border trade policies regulating the sector”, says Valentijn Venus, researcher at the department of Natural Resources and lead author on the study. “The key to effectively identifying where cross-border trade regulation efforts are most likely to have an impact is finding areas where high marketing margin and high postharvest losses intersect”. Using a wide array of publicly available data (including road conditions and satellite observations), a branch of mathematics known as Generalized Estimating Equations (GEEs) insensitive to spatial and temporal autocorrelation, and kinetic tomato physiology and vegetable-environment interactions, the researchers arrived at estimated postharvest losses.

Packaging, handling, and cooling
When compared to actual losses, the tomato firmness model explained 77% of the variance observed during transports. “In the short-term, what is controllable is that the rough handling of the produce should be minimized by educating key players on appropriate packaging, packing and handling techniques, etc. Another direction to reduce postharvest losses could be through pre-cooling treatment of the produce through the use of Modified Atmosphere Packaging (MAP) or by semi-controlling the crypto climate of the cargo, particularly around midday (before and after solar noon) when quality attributes deteriorate quickest, using low-cost techniques such as hydro cooling.”

Soup or tomatoes?
The authors hope the study will help ignite new programs that aim to stimulate this potentially viable horticultural value chain by reducing losses that occur as produce is transported or by encouraging the production and marketing of processed agricultural products (soups, purée, etc.).

Study highlights
We simulate postharvest losses in tomatoes, as they are transported between two West African countries. ► Conditions in trucks were linked to ¼ hourly geo-stationary satellite observations (MSG/SEVIRI). ► Results indicate we can accurately model the crypto climate conditions of the cargo; Tincargo r2 = 0.77 RMSE = 4.18 °C, RHincargo r2 = 0.84 RMSE = 19.59%, LIincargo r2 = 0.9 RMSE = 137.31 Lux. ► The tomato firmness model explained 77% of the variance observed during transports (r2 = 0.92 climate chamber).


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