Forensic pathology in the citrus supply chain

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DURATION: Three years
LEAD INSTITUTION: University of Pretoria (Department of Microbiology and Plant Pathology)
BENEFICAIRY: The citrus industry

Despite the strict requirements and international standards that South African producers have to comply with, the farmer carries the final financial responsibility when a consignment of fruit is rejected in an overseas market due to quality problems. However, the farmer has little control over fruit handling and hygiene after it has left the country. The situation led to a forensic investigation of the citrus supply chain by Prof. Lise Korsten and her team at the Department of Microbiology and Plant Pathology of the University of Pretoria. The Post-Harvest Innovation (Phi) Programme and Citrus Research International financed the project.

Penicillium is the main culprit

Post-harvest pathogens, particularly Penicillium species, are mainly responsible for citrus post-harvest decay. Green mould (Penicillium digitatum) is one of the biggest contributors to economic losses in the citrus industry. Penicillium is a typical wound pathogen with aerodynamic spores (conidia) that can attach to almost any surface. It easily infects fruit through wounds, particularly due to poor handling. Infection can spread rapidly once packed and when the cold chain is not managed properly.

Local and international sampling

South African citrus fruit was followed, from the point of picking to European distribution centres and retailers. Hygiene standards in the supply chain were evaluated to identify critical control points that should be managed more efficiently to reduce decay and improve citrus post-harvest quality.

  • Over a few seasons, pathogen samples were taken at critical points along the supply chain, which were indicated on location maps.
  • Local sampling concentrated on two citrus export farms in Tzaneen. International sampling included the port of Rotterdam, distribution centres in Antwerp, Hamburg and Luxembourg and various retailers.
  • Microbiological surface and aerial samples were taken in fruit ripening rooms, cold rooms, storage areas and distribution areas of various facilities.
  • Swab sampling was performed on the surfaces of containers, pallets, crates, display tables, conveyer belts, bags, walls, floors and the hands of fruit pickers and packers. The Penicillium load in the air was determined by active and passive air sampling.
  • About five thousand Penicillium isolates were analysed and preserved at the University of Pretoria. The PCR-RFLP (restriction fragment length polymerase) method was used to identify the different species.

Outcome of study and benefits to industry

  • The aerial and surface microbial load in overseas distribution centres and repacking facilities indicated a high level of surface contamination, especially in containers and on walls and floors. Poor hygiene management systems and the mishandling of fruit were also observed.
  • The study confirmed Penicillium species dominance in various supply chain environments and a profile of their dynamics was documented.
  • The information can now be used to improve sanitation practices and standards – from South African pack houses to overseas retailers. This increases market compliance and market access.
  • Two articles have been prepared for publication.
  • René Jacobs will write up the research work as part of her PhD.
  • The Penicillium study provides a background for a new Phi-funded project (PHI-2) on the microbial dynamics of fresh fruit.