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If cabbage is anything to go by, South Africans waste too much food
Author: Engela Duvenage
Published: 30/05/2016

SA study monetises wastage, environmental impact of a specific type of food

If cabbage is anything to go by, stacks of money and litres of water are wasted when farmed produce goes uneaten in South Africa. This is the conclusion of a study by Stellenbosch University (SU) food scientists and postharvest experts, who placed a monetary value on how much cabbage is wasted nationwide each year. It amounts to over R16 million per year, and enough water to meet the needs of more than 195 000 people annually.

The study was recently published in the British Food Journal. It is the first research effort of its kind in South Africa to monetise wastage and to calculate the environmental impacts of a specific type of food after it has been harvested or produced. It forms part of research efforts by the Stellenbosch University Food Security Initiative to curb postharvest losses and food waste in South Africa. The publication forms part of the MSc thesis of Karen Munhuweyi. Her study leader is Prof Umezuruike Linus Opara, holder of the South African Research Chair (SARChI) in Postharvest Technologies in the Department of Horticultural Science, while Dr Gunnar Sigge of the Department of Food Science is the co-supervisor.

"It's not only worrying how much never reaches our plates, but also how much resources such as water and energy are wasted in the process of farming uneaten cabbages," Prof Opara summarises the relevance of their findings.

The Stellenbosch research team chose cabbage as a test subject, because it is a widely consumed vegetable worldwide and a staple in many South African diets. Fresh cabbages can be kept on retail shelves for at least three to five days. Depending on the quality, heads of cabbage are either trimmed, shrink wrapped or discarded.

Initial investigations
Munhuweyi bought cabbages from three retail outlets in Stellenbosch, when their shelves were fully stocked and consumers were picking through the display items. These were put through a series of tests three and seven days after purchase, to consider changes in colour, texture, weight loss and chemical balance. A batch was analysed before storage. Two others were kept at room temperature (between 22 and 25 degrees Celsius) and two more batches were stored at an optimal storage temperature of between 0 and 0.5 degrees Celsius. Data loggers were used to assess the temperatures and humidity conditions inside the retail outlets.  

The vegetables were also inspected for decay, insect damage and mechanical damage to ascertain how many heads of cabbage were already unfit on a shop level for consumption or further marketing. On average, 21% of cabbage heads were lost at purchase. The cabbages were purchased for between R0.53 and R0.82 per kilogram, which means that R0.68 was lost for every kilogram of cabbages purchased from the three retailers.

Mechanical damage led to up to 50% of losses, and is often caused when produce is roughly handled during harvesting, loading and offloading. Decay accounted for up to 35% of losses. The study reveals how maintaining an optimum cold chain can prevent up to 30% of the total losses that are observed when cabbages are stored at room temperature for seven days.

How much is lost?
The researchers extrapolated their results to calculate how much of South Africa's annual cabbage harvest of approximately 103 000 tons never ends up on a plate. They calculated that at least 21 950 tons of cabbage worth R16 million on average is lost annually at the national retail level.

The total volume of these physical losses could meet the daily dietary requirements of at least 84 000 people for a month, and is enough to ensure the daily Vitamin C intake of 73 000 people for a year.

Impact on the environment
The researchers are not only worried about how produce loss affects food availability and nutrition, but also how it impacts the environment in terms of greenhouse gases emissions and water and energy usage. Approximately 27 million megajoules (or 7.5 million kilowatts) of fossil energy and 4 million cubic meters of fresh water resources are unnecessarily used in the production of the lost produce.

The volume of cabbages dumped in the process on average leads to around 2.9 million tons of the greenhouse gas carbon dioxide being emitted. "At least 75 million trees need to be planted to offset these emissions," calculates Prof Opara and his team. "The fresh water lost could sustain more than 195 000 people daily for a year."

"Severe postharvest losses do not only add to poverty through lost food and income, but also contribute to environmental and unsustainable usage of resources and the emission of unwarranted greenhouses gasses that contribute to global warming," the authors conclude.