Sustainability in the Postharvest Programme

Reducing loss and waste by implementing evidence-based solutions is the key to increasing sustainability in the Postharvest Programme. By Jenny Underhill.

“We want minimal loss of fruit on the farm so that growers can pack and sell more cartons of good-quality fruit,” says Dr Mariana Jooste, Postharvest Programme Manager at Hortgro Science. “We also don’t want consumers to throw away fruit because it’s decayed or too shrivelled to be edible.”

Food loss typically refers to produce that is lost during production and postharvest handling, whereas food waste refers to produce that consumers discard. “Ultimately, losses represent wasted resources,” says Jooste. “If you export fruit and you can’t sell it overseas — for example, if there are claims or the buyer rejects it — the packaging and transport costs incurred are astounding.”

For this reason, sustainable solutions are good for the environment and also save growers money.

One of the six objectives of the postharvest research programme is to increase the sustainability of all postharvest practices. Jooste emphasises that this applies to all four themes of the programme: managing fruit quality, mitigating physiological defects, refining packaging and storage techniques, and solving logistical problems.

To date, Hortgro-funded research has led to numerous sustainable solutions for postharvest challenges. These include projects that aim to prevent bruising, shrivelling, moisture loss and defects, as well as those that focus on sustainable packaging. The resulting best-practice guidelines and cultivar-specific protocols are published on the Hortgro website.

Jooste acknowledges that Hortgro Science is fortunate to have research partners such as Stellenbosch University, the Agricultural Research Council, ExperiCo Agri-Research Solutions, and Provar, among others.

“These partners enable us to conduct both basic and applied research, helping us to understand the underlying physiology and develop optimal, practical protocols for each problem,” she says.

Preventing bruising

Reducing bruising in pome and stone fruit increases the marketable tonnes of fruit delivered per tonne of fruit loaded. Willie Kotze, Technical Manager at Dutoit Agri, conducted a study that placed data loggers in apple bins to identify where bruising occurs in the handling chain from the orchard to the pack house.

Kotze showed that bruising can be significantly reduced by bin liners, torsion bars on bin trailers, pneumatic suspension on bin-on-the-ground trailers, slower truck speeds — especially on uneven roads and with light loads — and vibration dampers on forklifts.

“The research identified practical protocols that growers can follow during harvest to ensure more cartons of high-quality fruit are packed per bin,” says Jooste, “Attaching GPS loggers to the tractors, trucks and forklifts can monitor compliance to the protocols and incentivise drivers to drive carefully.”

Increasing marketable tonnes of Forelle Pears

Rigorous research, combined with astute marketing, can also increase marketable tonnes of fruit and reduce losses. For example, Hortgro-funded research successfully positioned Forelle pears to fill a market gap for blushed pears early in the season.

Research at ExperiCo and the Department of Horticultural Sciences at Stellenbosch University found that both mealiness and astringency — when the pears are harvested too early — can be avoided by storing optimally mature fruit for 12 weeks. This mandatory storage period created a market gap between summer blushed pears and the later availability of Forelle, which overseas competitors quickly filled.

To solve this dilemma, ExperiCo tested harvesting at a more advanced maturity for sweetness. “When the fruit is treated with 1-MCP [1-methylcyclopropene], it stays at that sweet, crisp maturity and doesn’t ripen any further because the ethylene binding sites are blocked,” says Jooste. The pear can be exported much earlier in the season, but must be marketed as crisp and sweet to match consumer expectations.

Mitigating heat damage in plums

“Some of our main plum cultivars reach maturity during January and February, when we have the highest number of heatwaves in the Western Cape,” says Jooste. Heatwaves cause internal heat damage such as pit burn and gel breakdown.

Protocols have been developed to adjust irrigation schedules in advance of heatwaves, thereby buffering against increased evaporative demand and cooling the fruit. However, water is scarce in South Africa, and some plum producers may not have enough water to increase irrigation.

“Harvested plums are usually kept for about four to six hours at 15 °C. Then the fruit is cooled to minus 0.5 °C within 24 hours,” explains Jooste, “However, in the case of harvesting during heatwaves, further research shows that we need to cool the fruit at a much slower rate — within 48 to 72 hours. If we cool the fruit in a slow, stepwise manner, we can reduce internal heat damage significantly.”

Preventing moisture loss and shrivelling

Hortgro has funded several projects to address shrivel, which is especially problematic in stone fruit. “While plastic packaging during storage and transport is part of the solution, the same amount of moisture loss occurs during a six-week storage period as during the 48 hours between harvest and the end of forced-air cooling,” says Jooste.

Research projects at the Department of Horticultural Science at Stellenbosch University identified protocols to minimise water loss early in the handling chain. These include managing the temperature and humidity during harvest, transport to the pack house, and packing and cooling to minimise vapour pressure deficits between the fruit and the environment.

Overcoming physiological defects

Hortgro has funded research to prevent physiological defects in pome fruit. These defects include superficial scald, internal CO₂ damage in Fuji apples, internal browning in Cripps Pink apples, lenticel spot, bitter pit, and soft scald.

“The research has determined optimal harvest maturities and different storage protocols for the different cultivars,” says Jooste, “Storage under low-oxygen conditions can prevent superficial scald and internal browning in Cripps Pink apples. We can also use stepwise cooling to prevent internal browning or immediate cooling to prevent bitter pit development.”

Reducing plastic packaging

Plastic packaging is still essential to minimise moisture loss and retain colour in certain pome and stone fruit cultivars. However, a major focus of the Postharvest Programme is reducing single-use plastics and prioritising recyclable plastics.

Recyclable plastics can potentially be embedded with ethylene absorbers, natural fungicides, and moisture-control agents to preserve fruit quality throughout the supply chain.

“We can reduce plastic usage by using thinner liners and potentially by covering entire pallets with a plastic shroud instead of using individual bags in each carton,” says Jooste.

In addition, less plastic is required if vents in integral shipping containers are closed. However, this is not possible for all deciduous fruit because some are sensitive to the high levels of CO₂ that may accumulate.