Let the food live! Perishable foods and the cold chain – Fellows’ seminar by Matia Mukama

12 March 2024

Ever wondered about the complex processes involved in getting the juicy apple you buy in your local supermarket from the orchard to the shop in such pristine condition? Well looking at how to improve those processes and eliminate waste, particularly in Africa, is what concerns Matia Mukama of the Department of Food Science and Technology at Kyambogo University, Uganda. Mukama is an Iso Lomso fellow in his first residency at STIAS.

Iso Lomso Fellow Matia Mukama during his seminar on 27 February 2024

“The annual increase in the global population worldwide puts pressure on food systems to avail enough food for all global citizens. Within the foods consumed are those with a short life span, termed perishable foods that need special handling after harvest or slaughter. They include fish, meat, poultry, dairy products, eggs, fruit and vegetables. These easily spoil and become unsafe for consumption if not kept at recommended refrigeration conditions. The handling of perishables under refrigerated conditions during transit, storage and display is termed cold-chain handling. This seminar will focus on the efficiency, efficacy and availability of food cold chains,” he explained.

“The lingua franca of all living things is food,” he added.

He pointed out that it’s estimated that the global population will reach 11.2 billion by 2100 with this vastly increased population requiring all categories of nutrition including carbohydrates, proteins, fats and micronutrients.

“Our food system needs to be inclusive, environmentally sustainable; nutrition, health and safety driven; and, contribute to the achievement of the Sustainable Development Goals.”

“The food industry is a US$10 trillion-dollar industry and food loss last year was US$1 trillion – with perishables being the biggest contributor – mostly due to inefficiencies in or absence of cold chain.”

He explained that loss is usually defined as what happens between the field and the retailer caused by factors like spillage, physical damage and lack of temperature management. Then there’s waste that occurs at the retailer and consumer end when unused food is thrown away.

“High-income nations have relatively better developed food cold-chain systems compared to most low-income nations. Therefore, perishable produce of low-income nations is more prone to post-harvest losses and waste, and related costs on environment and climate. These losses have been reported as high as 40% of the produce in some instances, exacerbating food-security challenges of vulnerable populations.”

Perishable products and food chains

A food system proceeds in steps from agriculture to processing, distribution, retail and finally reaching the consumer. But at each step perishable food is easily spoilt by microbes, physical damage, enzymatic activities and chemical reactions – majorly respiration.

Efficient cold-chain systems aim to slow or eliminate these processes. When it comes to fruit the cold chain includes processes in the orchard and packing facilities, precooling, cold storage, refrigerated transport (local and international) and cold display in market outlets.

“Fruit is usually picked either early morning or late afternoon – before or after the main heat of the day,” explained Mukama. “It’s washed, graded and packaged, then rapidly pre-cooled to reduce the field heat as quickly as possible – with different ideal temperatures for different fruits. It’s then placed in cold storage in refrigerated transport and finally into cold displays in markets and shops.”

Mukama pointed out that without cold chain an apple lasts two weeks but with cold chain at -1°C it can last three to six months.

But this depends on the perfect combination of proper handling to prevent physical damage, temperature, packaging and humidity. ‘If this is not ideal it means damage, rotting and fruit that can’t be sold.”

“Cooling rates, uniformity and energy expenses in cold-chain handling are of paramount importance,” he said.

Bringing together computational fluid, thermal and structural dynamics, Mukama has modelled more effective temperature management and packaging designs and methods for the fruit industry using pomegranates – this holistic model considers all major aspects of fruit cooling. The model also includes kinetic modelling to predict fruit quality in time. The models were validated experimentally.

The work looks at ideal temperature and relative humidity, fruit morphology and fruit thermal properties, cooling rates and uniformity, airflow patterns and related energy expenditure, and the impact of different packaging methods all of which affect cold-chain efficiency.

“Fruit is heterogenous,” explained Mukama. “You need to know about the fruit’s morphology, thermal properties and expected temperature transitions to model the cooling process.”

Packaging also plays an important role. “The use of plastic crates versus cardboard boxes, the cardboard used and the holes in the boxes lead to different interactions between the cold air and fruit. We looked at the characteristics of different box designs, the way these are stacked and their structural integrity, how the boxes are aligned and orientated when placed on pallets which affects the overall pallet ventilation, as well as the impact of polythene liners.”

The work found substantial inadequacies in the current designs leading to the development of two ideal carton designs which were then manufactured into physical prototypes in collaboration with a carton company in Worcester outside Cape Town.

“Further experiments were then done to validate the modelling – which showed faster and uniform cooling and that the packaging was strong enough in cold conditions and held more fruit per container compared to cartons currently available,” said Mukama. “Market testing last year showed they worked perfectly on export to Germany.”

Mukama’s future work will focus in more detail on access, efficiency and efficacy of refrigeration systems in the perishable produce chain in sub-Saharan Africa. This will include aspects like refrigeration capacity, the refrigerants used, the type and thickness of insulation, presence and use of door-protection devices, the age and condition of facilities, and, importantly, the education and training of operators.

More investment needed in Africa

But he is also interested in understanding the broader multidimensional aspects of cold chains in the food system in reducing food loss and waste, and making post-harvest chains more efficient to meet present and future demand and supply of food. His work is looking at the state of the art of food cold-chain handling in sub-Saharan Africa compared to the rest of the world. “Preliminary findings show that sub-Saharan African countries have not invested enough in cold-chain infrastructure leading to huge losses and dumping. My work, specifically in Uganda, shows there is very little public investment in these important processes.”

“Cold chain is not a one man play but an amalgamation of different players,” he continued. “It needs public infrastructure like electricity and roads; private-sector investment; and, farmers’ groups and non-governmental organisations to advocate for policy change. We also need to educate consumers not to contribute to the stats on food waste.”

He also pointed to the need for more work comparing the cost of cold-chain cooling versus loss. “Food loss and waste contribute 8% to greenhouse gas emissions.  It’s estimated that food loss in 2013 equalled one billion tonnes of CO2 emissions. Emissions from cooling systems are about a third of that. But we need to look at improving efficiency of cooling systems and using greener energy technologies like solar, wind into the future.

“Humans like eating fresh produce due to better nutritional and health benefits and we must find solutions not to lose so much,” he concluded.


Michelle Galloway: Part-time media officer at STIAS
Photograph:  Noloyiso Mtembu

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