Citrus fruit injury test

Physical injury testing for citrus fruit

Dr SP Singh NSW DPI Research | Centre of Excellence for Market Access

October 2015

Physical injury to citrus can occur during preharvest, harvest and in the postharvest supply chain. In the packing house, while major injuries are easily noticed and the fruit are removed during sorting, minor injuries in the form of cuts, bruises and punctures can go unnoticed along the packing line and become a hidden cause of fruit losses. These physical injuries also serve as the point-of-entry for the fungal pathogens responsible for postharvest rots and breakdown. Invisible injuries such as punctures and cuts can allow fungicides and foodborne pathogens to penetrate the fruit, elevating the risks of chemical and microbial contamination. The acidic nature of citrus fruit is not conducive for the survival and growth of foodborne pathogens. However, fungicide penetration into the edible portion of the fruit can lead to chemical residues above the maximum permitted levels. To minimise the physical injury to citrus fruit, regular and accurate assessment of the causes and extent of these invisible injuries is essential.

Detecting physical injuries

The physical injury test involves using a colourless solution of 2,3,5-triphenyltetrazolium chloride (TTC) to detect the invisible physical injuries to citrus fruit. TTC reacts with injuries on the skin, making them red and readily visible to the naked eye (Figure 1).

To conduct this test, follow these steps:

Step 1: Collect your samples: The test can be conducted at least twice in a season; at the beginning and in the middle. Any major change in the packing line (e.g. brushes or conveyor belts) should be followed by the physical injury test. At least 12 fruit per sampling point should be collected from different areas in the packing shed where there is any likelihood of physical injuries such as before (harvest bins) and after dumping, before and after washing, before and after wax/fungicide application, and packed fruit ready for despatch.

Step 2: Make your TTC solution: Wear safety glasses and gloves, and follow safe handling, disposal and other instructions on material safety data sheet (MSDS) for TTC. : Prepare a 0.5% solution of TTC in potable water by dissolving 20 grams of TTC powder in 4 L of water in a plastic bucket. Place the fruit in the bucket containing the TTC solution and keep submerged for at least 30 minutes. The TTC solution should be poured back into the jug through a layer of cheesecloth to remove debris and can be reused.

Step 3: Pour fresh water into the bucket and again submerge the fruit, this time for five minutes. Transfer the fruit into paper bags and keep at room temperature overnight. The next morning, assess the fruit and grade the severity of damage as slight, moderate or severe. Keep records for future reference.

Minimise physical injuries

The test is useful to assess the areas in the packing line where fruit are being injured and enabling corrective action to reduce future injuries. The condition and length of the packing line, the number of times fruit drops from a height or hits right-angle curves along the line affect the frequency and severity of physical injury.

Precautions to minimise physical injuries include careful dumping, removing trash, twigs or stems during pre-grading, clipping stems from fruit, pre-conditioning the packing line brushes before use, optimising brushing speed and time, minimising fruit drop damage, avoiding right-angle curves in the packing line, and avoiding overloading the packing line and overfilling cartons.

The test can also be used to detect chilling injury symptoms in cold-stored fruit and post-cold disinfestation treatment.

For more information, email Dr SP Singh or phone 02 4348 1935.

Reference

Ismail, M.A., 1993. The hidden causes of fruit losses in a citrus packing house. Florida Cooperative Extension Service, University of Florida.Packing House Newsletter, No 169. pp. 2–4