Disorders
Phenolic browning
Phenolic browning (or surface browning) is seen as browning or discoloration of the surface of the carrot. It can develop when carrots are washed and stored in cool rooms for long periods before packing.
Abrasion caused by mechanical washing often removes the epidermal layer (outer skin), exposing the carrot tissue to oxidation of phenolic compounds, which turn brown, or black in severe cases.
Phenolic browning can be confused with ‘5 o’clock shadow’ or boron deficiency. The latter is seen as many small brown spots under the skin, causing the root to look dull.
Control
- Wash carrots as soon as possible after harvesting.
- Keep washed carrots moist.
- Don’t leave carrots in bulk bins in the cool room; pack them as soon as possible after cooling to maximise quality.
- Pack carrots into plastic-lined cartons or pre-pack plastic bags as soon as possible after harvest. Leaving carrots in bulk bins unprotected in cool store will lead to dehydration. Plastic bin liners will reduce dehydration if carrots are left for prolonged periods in bulk bins.
Bitterness
Carrots can develop off-flavours or bitterness in cool storage, caused by the production of compounds called isocoumarins. Isocoumarins develop when carrots are exposed to ethylene.
Ethylene is a gas produced naturally by many fruits and vegetables, such as apples, bananas and tomatoes, during ripening. Retailers, exporters and consumers should be aware that storing carrots with fresh products that produce ethylene can cause bitter flavours to develop in carrots. Store carrots in sealed plastic bags if domestic refrigerators contain ethylene producing fruit.
Control
Do not store carrots with fruit, vegetables or flowers that produce ethylene.
Silvering or scaling
Carrots can sometimes develop a scaly surface in storage. The carrot surface has a white, flaky appearance that looks similar to dandruff. This symptom appears when carrots become dehydrated.
Control
The use of brush polishing which removes the carrot’s outer layer (periderm) effectively removes the possibility of silvering developing.
Root breakage
Root breakage and splitting are common throughout the year. However, the proportion of breakages can increase under cooler conditions. Harvesting carrots from cold, wet ground tends to exacerbate the problem.
Control
- When possible in winter, let the soil dry out before harvest.
- Carrot varieties vary in their susceptibility to breakages. In general, Nantes types are more susceptible to breakage than Western Red and Imperator types. There are also differences among Nantes varieties in resistance to breakage. The Japanese Kuroda varieties have proved to be highly susceptible to breakage.