Research Overview

Research Background: What Problem Did This Study Address?

Postharvest fruit and vegetable losses are a serious challenge in low- and middle-income countries. In sub-Saharan Africa, more than 40% of fruit and vegetables can be lost after harvest before reaching consumers. For smallholder farmers and local traders, these losses directly reduce income and limit food availability.

Cooling fresh produce after harvest is one of the most effective ways to slow quality degradation. Lower temperature can reduce respiration, moisture loss, softening, shriveling, microbial growth, and visible decay. However, refrigerated storage and refrigerated transport are often unavailable or too expensive for smallholder tomato supply chains in countries such as Uganda. As a result, tomatoes are commonly stored under natural shade and transported to market without active cooling.

This study tested a low-cost passive cooling solution called the charcoal cooling blanket, or CCB. The blanket uses evaporative cooling: water is added to charcoal-filled burlap compartments, and evaporation lowers the surrounding air temperature while increasing relative humidity. The researchers evaluated the CCB in laboratory conditions and in a real Ugandan tomato supply chain, including storage under a shelter, motorbike transport, and market storage.

UbiBot WS1 Pro sensors were used to monitor temperature and relative humidity inside and outside the CCB. These environmental data helped the researchers quantify the cooling effect and connect storage conditions with tomato quality changes.

The Specific Role of UbiBot in the Study

In this study, UbiBot WS1 Pro was used as an IoT temperature and humidity monitoring device for the passive cooling system. The paper does not state that UbiBot itself reduced tomato losses. Instead, the research team used UbiBot sensors to record the real hygrothermal conditions inside and outside the charcoal cooling blanket, and then used those data to evaluate cooling performance and interpret tomato quality changes.

The field experiments were conducted at Makerere University Agricultural Research Institute Kabanyolo, about 20 km north of Kampala, Uganda. The researchers tested tomatoes stored in plastic crates wrapped with charcoal cooling blankets and compared them with tomatoes stored in plastic crates under ambient shaded conditions.

UbiBot WS1 Pro Wi-Fi hygrothermal sensors equipped with probes were used to record temperature and relative humidity inside and outside the blanket. This placement allowed the researchers to compare the microenvironment created by the CCB against the surrounding shelter or market environment. The paper also used Sensirion Bluetooth hygrothermal sensors inside crates and Tinytag temperature probes inserted into tomatoes to measure fruit core temperature. UbiBot’s role was specifically to provide real-time monitoring of the cooling system’s air temperature and relative humidity.

The monitored data were used in several ways.

First, UbiBot data documented whether the CCB produced cooler and more humid storage conditions than natural shade. In the field ripening-stage experiment, the CCB maintained average internal temperatures around 23 °C, about 1.5 °C below ambient, and increased internal relative humidity to roughly 86%–89.5%.

Second, the temperature and humidity data were used to calculate evaporative cooling efficiency. The paper calculated cooling efficiency from dry-bulb temperature, blanket temperature, and wet-bulb temperature. This helped quantify how effectively the blanket used evaporation to approach the theoretical cooling limit.

Third, the monitored conditions were linked to tomato quality measurements. The researchers measured weight loss, firmness, color, pH, and soluble solids content during storage. UbiBot-supported environmental records helped explain why tomatoes stored in the blanket lost less weight, changed color more slowly, and retained marketable quality longer.

Fourth, UbiBot data supported the farm-to-market supply chain test. During transport and market storage, temperature monitoring helped show how the CCB affected the tomato environment beyond the farm, including during motorbike transport and five days at a local market.

Therefore, UbiBot’s role was environmental monitoring and data support. It supplied the temperature and relative humidity records needed to evaluate the CCB as a practical passive cooling technology for tropical tomato supply chains.

Research Methods and Data Collection Approach

The study included laboratory testing in Switzerland and field experiments in Uganda.

The laboratory experiment was conducted in two climate chambers at Agroscope in Wädenswil, Switzerland, from April to July 2023. The chambers were set to 23 °C and 60% relative humidity to simulate average Ugandan conditions. Tomatoes were stored in plastic crates, woven baskets, and wooden crates, either wrapped with charcoal cooling blankets or kept as controls. The purpose was to compare packaging types and cooling performance before field deployment.

The field study took place at Makerere University Agricultural Research Institute Kabanyolo from August to November 2023. Three charcoal cooling blankets were made of burlap and divided into compartments filled with charcoal. Each blanket measured 3.5 m × 0.6 m and contained 10 kg of charcoal. The blanket was wrapped around a plastic crate containing tomatoes. Bricks were placed between the blanket and crate to create an air gap, and a leaf cover was added for insulation. Water was added to the blanket several times per week to drive evaporative cooling.

The researchers tested tomatoes at three ripening stages: green, breaker, and red. Each storage treatment lasted 14 days. Tomatoes stored inside the CCB were compared with tomatoes stored in plastic crates under natural shade. Quality measurements included weight, firmness, color, pH, and soluble solids content.

A second field experiment examined irrigation treatments before harvest. Tomatoes grown under different irrigation schedules were harvested at the green stage and stored in CCB conditions. This allowed the researchers to examine how preharvest water management interacted with passive cooling during storage.

A third experiment tested the CCB across a local supply chain. Tomatoes were harvested, stored under shelter for two days, transported 2 km by local motorcycle to the Kabanyolo market, and then stored for five days at the market. Sensors measured environmental conditions and fruit core temperature during transport and market storage.

The study also used a kinetic quality-loss model based on fruit core temperature to estimate quality loss and remaining shelf life with and without the CCB.

Key Research Findings

The CCB reduced storage temperature and increased relative humidity. In the Uganda ripening-stage experiment, average ambient temperature was 24.5 °C, while the average temperature inside the blankets was about 23 °C. During hot daytime periods, the temperature reduction could be much larger; the paper reports reductions up to about 20 °C during maximum daytime temperature conditions.

The blanket also stabilized the storage environment. Ambient temperature fluctuated strongly during the day, while the temperature inside the CCB varied much less. Relative humidity inside the blankets averaged about 86%–89.5%, and daily fluctuations inside the blanket were much smaller than those in the ambient environment.

The CCB reduced tomato weight loss, especially for green tomatoes. After 14 days, green tomatoes stored inside the blanket lost about 7% of their initial weight, while green tomatoes stored outside lost about 19%. In the conclusions, the authors summarize that CCB storage reduced weight loss by about 5%–10% for green and breaker tomatoes compared with ambient storage.

The CCB also affected firmness and ripening. Red tomatoes stored in the blanket showed significantly lower firmness loss than those stored outside. Green and breaker tomatoes stored in the CCB showed slower reddening, indicating delayed ripening. The paper also reports 15%–20% lower firmness loss in breaker and red tomatoes after storage in the CCB.

The irrigation experiment suggested that preharvest water management can influence postharvest performance. In some treatments, tomatoes grown under smart or deficit irrigation showed lower weight loss during storage, although the authors note that heavy rainfall and fungal disease made it difficult to isolate the true irrigation effect.

The supply chain experiment showed practical value during transport and market storage. Tomatoes transported and stored with the CCB had lower core temperature than tomatoes without the blanket. By the second day of market storage, the maximum difference in tomato core temperature reached about 10 °C. Visual inspection showed that tomatoes stored with the CCB remained sellable longer, while many tomatoes stored without the blanket shriveled or cracked.

The kinetic model estimated that CCB use reduced tomato quality losses by about 10% after three days and extended remaining shelf life by about two days.

What This Means for Postharvest Tomato Cooling

This study shows that a low-cost passive cooling system can improve postharvest tomato handling in tropical local supply chains where refrigerated infrastructure is unavailable.

For smallholder farmers and traders, the main benefit is practical accessibility. The CCB does not require electricity, refrigeration equipment, or advanced construction. It can be made from locally available materials and used around plastic crates during storage and transport.

For tomato quality, the study shows why temperature and humidity monitoring matter. Reduced temperature slows respiration and quality degradation, while higher relative humidity reduces moisture loss. Together, these conditions can reduce shrinkage, slow softening, delay visible ripening, and preserve marketable quality.

For local markets, even a short extension in shelf life can have economic value. In the farm-to-market test, tomatoes stored without the blanket deteriorated sooner and created greater losses for the vendor, while the CCB allowed tomatoes to remain sellable for longer.

For postharvest research, the study also demonstrates the importance of tracking both produce temperature and the surrounding storage environment. UbiBot temperature and humidity data helped explain the environmental mechanism behind quality preservation, while fruit core temperature data supported shelf-life modeling.

Application Value of UbiBot Devices

UbiBot WS1 Pro demonstrated value as a monitoring tool for passive cooling and postharvest storage research.

First, it provided real-time temperature and relative humidity records inside and outside the CCB. These data showed whether the blanket actually created a cooler and more humid microenvironment than natural shade.

Second, the sensor data supported cooling performance evaluation. Temperature and relative humidity measurements were used to calculate evaporative cooling efficiency and assess how well the CCB performed under tropical conditions.

Third, UbiBot data helped connect environmental conditions with tomato quality. Weight loss, firmness loss, color change, and SSC/pH changes could be interpreted alongside recorded temperature and humidity.

Fourth, the Wi-Fi monitoring function supported remote observation of the cooling system. The paper notes that these sensors enabled real-time monitoring of cooling system temperature and humidity from any location.

Fifth, the UbiBot setup helped evaluate real supply chain conditions, not just laboratory performance. The data collected in Uganda during storage and market handling provided evidence from practical field conditions.

Overall, UbiBot’s value in this paper was not direct food preservation. Its value was providing the environmental data needed to quantify, explain, and compare passive cooling performance in postharvest tomato handling.

Extended Application Scenarios

The monitoring approach used in this study can be extended to several related scenarios:

1. Postharvest tomato storage
   Used to monitor temperature and humidity in low-cost storage crates, shelters, and market stalls.
2. Passive evaporative cooling systems
   Used to evaluate charcoal cooling blankets, clay coolers, brick coolers, wet pad systems, and zero-energy cool chambers.
3. Smallholder cold-chain alternatives
   Used to support practical cooling solutions where refrigeration is unavailable or unaffordable.
4. Fresh produce transport monitoring
   Used to track environmental conditions during motorcycle, truck, or local market transport.
5. Market shelf-life studies
   Used to compare quality changes under shaded, cooled, and ambient retail conditions.
6. Farm-to-fork supply chain research
   Used to connect harvest, storage, transport, and retail temperature data with quality outcomes.
7. Quality-loss modeling
   Used to provide temperature and humidity inputs for shelf-life prediction models.
8. Cooling system watering optimization
   Used to identify when evaporative cooling blankets need additional water to maintain high humidity and cooling performance.

FAQ

1. Which UbiBot product was used in the study?

The study used UbiBot WS1 Pro IoT Wi-Fi hygrothermal sensors equipped with probes.

2. What data did UbiBot collect?

UbiBot collected temperature and relative humidity data inside and outside the charcoal cooling blanket.

3. Where were the UbiBot sensors deployed?

They were used around the charcoal cooling blanket system in Uganda, monitoring conditions inside and outside the blanket during tomato storage and supply chain experiments.

4. What was the sampling frequency?

The paper does not explicitly state the raw UbiBot logging interval.

5. How long did the tomato storage experiment last?

The main ripening-stage storage experiment lasted 14 days. The supply chain experiment included transport from farm to market and five days of market storage.

6. How were UbiBot data used?

The data were used to monitor cooling system temperature and humidity, calculate evaporative cooling efficiency, compare CCB and ambient storage conditions, and interpret tomato quality changes.

7. Did UbiBot measure tomato quality directly?

No. Tomato quality was measured separately through weight, firmness, color, pH, and soluble solids content. UbiBot measured the storage environment.

8. Did UbiBot measure fruit core temperature?

No. Fruit core temperature was measured using Tinytag temperature data loggers with probes inserted into tomatoes. UbiBot measured air temperature and relative humidity around the cooling system.

9. What was the main result of the CCB?

The CCB reduced average storage temperature by about 1.5 °C, increased relative humidity, reduced tomato quality losses, and extended shelf life by about two days in the farm-to-market test.

10. Why is this research important?

It shows how low-cost passive cooling, supported by environmental monitoring, can help reduce tomato postharvest losses in tropical local supply chains where refrigeration is not accessible.