PhD student’s insights help fledgling pomegranate industry

The arrival of this season’s first consignment of pomegranates from the Porterville region on British supermarket shelves this week serendipitously coincided with Dr Oluwafemi Caleb receiving his doctorate from Stellenbosch University (SU). After all, advice leading from his studies have helped pomegranate producer Mr Fan Olivier decide on the best possible packaging for his export produce.

Dr Oluwafemi Caleb. (Foto: Anton Jordaan)

Dr Oluwafemi Caleb. (Photo: Anton Jordaan)

Dr Caleb’s research focused on helping fruit producers, suppliers and processors in the emerging South African pomegranate market to find a perfect fit for the packaging material and storage conditions they choose. This helps to ensure the optimal shelf life and best possible quality of ready-to-eat pomegranate products.

“When packaging new products, producers often have very much of a ‘pack-and-pray’ approach, and they hope that materials and containers that were used successfully for other types of fruits will also work for theirs,” says Dr Caleb, who hails from Nigeria and came to SU in 2007 to completed his postgraduate studies in microbiology, and ultimately also his PhD degree in food science.

Correct packaging and storage conditions increase shelf life

Fresh or fresh-cut fruit and vegetables continue all metabolic processes after being picked, and continuously deteriorate in quality because of processes such as transpiration and respiration.

Dr Caleb developed mathematical models to understand the physiological response of pomegranate fruit to storage conditions and the application of modified atmosphere packaging (MAP) technology.

MAP technology is a dynamic process of altering gas composition inside a package. It relies on the interaction between the respiration rate of the fresh or fresh-cut produce and exchange of gases and water vapour through the packaging material. These processes are further influenced by storage temperature, film thickness and surface area, produce weight as well as free headspace within the pack. If applied correctly, MAP technology can help slow down physiological processes, delay softening and ripening and reduced incidence of various physiological disorders and pathogenic infestations.

Advice to the pomegranate industry

Dr Caleb’s findings highlights how important it is to maintain optimal cold-storage condition for packaged arils or whole fruit along the supply chain, and the need to systematically approach the packaging of fresh or fresh-cut fruit and vegetables.

Advice leading from his study includes:

  • Storage conditions and duration crucially impact the physiological responses (i.e. respiration and transpiration rates) of fresh arils;
  • Arils are best kept at 5 °C and 96% relative humidity for more than 8 days;
  • With MAP technology and low storage temperature it is possible to further keep the quality of fresh arils for 10 days;
  • Packaging has a  significant effect on the changes in the headspace aroma compounds of arils, and off-flavour is perceived at about Day 10;
  •  At high storage temperatures the polymeric film over the packaging should be perforated so that it allows gasses that build up to escape. However, storage temperatures above 5 °C are not encouraged.

    Pomegranate arils. Photo: Fan Olivier

    Pomegranate arils. Photo: Fan Olivier

Pomegranate producer takes advice to heart
“Based on Dr Caleb’s findings I reconsidered the current trend to package fruits in tiny upright containers, and reverted back to the flatter containers which have more surface space,” says Mr Fan Olivier, who four years ago imported the first mechanised processing unit in the Southern Hemisphere to de-aril ripe pomegranates.

He says it is of great benefit to work with researchers of the South African Research Chair (SARChI) in Postharvest Technology at Stellenbosch University “as you simply cannot run a business these days without have science to back you up.”

Mr Olivier, a SU alumnus who completed his Hons BComm with Computer Science, worked in the IT industry before buying the orange farm Houdconstant in the Porterville district. He has since turned it into one of the first pomegranate producing farms in South Africa, to cater for the growing global niche market. He also operates the Pomegranate Fruit SA packhouse from Houdconstant.

“A few years ago people said blueberries were the ‘superfruit’, but studies on the health benefits of pomegranates show it is now the new ‘super-superfruit’,” he says of the growing demand for the ready-to-eat packages of this fruit in especially the UK, Asia and the USA. It is already the 18th most popular fruit in the world, and is preferred for its high antioxidant, anti-mutagenic, anti-hypertension activities and ability to reduce liver injury.   

South African Research Chair in Postharvest Technology
Dr Caleb’s research is part of a much broader focus on the emerging pomegranate fruit industry of the SARChI Chair in Postharvest Technology in the Department of Horticultural Science at Stellenbosch University.

SARChI Chair holder Prof. Linus Opara first worked on this high-end fruit as a researcher at the Sultan Qaboos University in Oman. Soon after moving to Stellenbosch University in 2009 to take up the SARChI Chair, his help was sought by producers in South Africa’s fledgling industry.

“I now have more students working on pomegranates than any other product,” he says of the research which has a value chain approach. Topics being studied include maturity indexing to help farmers predict when fruit are ready for harvesting, determining optimal storage requirements, controlled atmosphere storage, the development of modified atmosphere packaging, and determining the phytochemical properties and antioxidant activities of various cultivars. Some of these projects are done collaboratively with overseas colleagues in France and Oman.

“If I had to leave this job tomorrow, I’d like to be remembered for playing a small role in developing the local human capacity and knowledge base that contributes to the successful development of this emerging and high-value niche fruit industry,” muses this agricultural engineer, who defines ‘postharvesting’ as everything in the supply chain after a fruit has been harvested, including aspects of transport, storage and packaging.


Notes to the editors:

  • Almost all the world’s pomegranate is cultivated in the northern hemisphere, with India being the world’s largest producer.
  • The harvest dates of pomegranate in the northern hemisphere are between September and November. This opens a window of opportunity for producers in the southern hemisphere including South Africa to export to the northern hemisphere during the months of late February to July.

Released by:
Monika Basson, Faculty of AgriSciences, Stellenbosch University
+27 21 808 2978