RASPBERRIES AND RELATED FRUIT
Dr. Marvin Pritts, Department of Horticulture,Cornell University’s College of Agriculture and Life Sciences, Ithaca, NY 14853
(For more information visit www.fruit.cornell.edu)
Raspberries are a high-value crop due to their unique flavor, exacting climatic requirements, high costs of production, and perishability.
Handling and Storage of Fresh Produce
Post-harvest Considerations
The objective of post-harvest handling of raspberries is to slow the respiration and transpiration rate of fruit. Respiration and transpiration result in shrinkage and reduced sweetness. Conditions that slow the respiration process are low temperatures, high carbon dioxide levels, and low oxygen in the storage chamber. Transpiration is slowed by high humidity.
Temperature is the easiest environmental variable to modify for extended storage of raspberries. A 5oC reduction in temperature reduces the respiration rate by approximately 50%: at 0oC the respiration rate is 24 mg of carbon dioxide per kg of raspberry per hour; at 5oC the rate is 55; at 10oC the rate is 92; at 15oC the rate is 135; and at 20oC the rate is 200.
Rapid movement of cold, humid air through the berries is essential during the first few hours after harvest to slow respiration and prevent deterioration. Large growers may have a precooling facility specifically designed for removing field heat, and an additional storage cooler. For every hour delay in cooling, shelf life can be reduced by one day. Growers take advantage of natural night cooling by harvesting fruit as early in the morning as possible. Mechanical harvesting is often done at night.
Once the berries are cool, containers are wrapped in plastic to prevent water loss from the fruit and condensation on the berries when they are removed from the cooler. The plastic is not removed until the temperature of the berries warms to near the ambient temperature.
The storage room can be maintained as low as -1oC. Berries will not freeze at or above this temperature because the sugars in the fruit depress the freezing point. When temperature is lowered, the amount of moisture in the air is reduced.
For raspberries, it is critical to maintain a humid atmosphere (90-95%) simultaneously with low temperature to prevent water loss from the fruit. Special cooling units designed to maintain a high humidity are required for raspberries. At 25oC and 30% relative humidity, fruits lose water 35 times faster than at 0oC and 90% relative humidity.
Harvest Considerations
Raspberries have one of the highest respiration rates of any fruit. This, coupled with their thin skin and sugary interior, makes them among the most perishable of all fruits. With any given variety, fruit on a bush will ripen over a period of several weeks. Harvesting the same planting frequently (once every two days) is critical. Fruit harvested before it is fully ripe will have a much longer shelf life than fully ripe or overripe fruit, but will be lower in sugar and anthocyanins. The optimum stage of maturity for the raspberry occurs when the berry first becomes completely red, but before any darker hues develop.
Fruit quality for fresh market raspberries usually declines as the season progresses. Marketing channels must be open before the first berries ripen, as these are likely to be the highest quality and have largest size for the season. Berries should not be touched before harvest, and only undamaged berries with good appearance should be placed in the pack. The magnitude of injury caused by human pickers can be so great as to mask any other causes of deterioration.
Overripe or damaged berries should be harvested and discarded because they are susceptible to moulds. Botrytis is the most common pathogen of raspberry fruit. Once the mould growing on overripe berries sporulates, large amounts of inoculum will be present to infect other ripening fruit. Overripe berries also attract ants, wasps, and other pests.
Containers holding approximately 150 g of raspberries are typically used.
Wide, shallow containers are preferable to deep containers.
Bibliography
Crandall PC and Daubeny HA (1990) Raspberry management. In: Galletta GJ and Himeirick DG (eds) Small Fruit Crop Management, pp 157-213. New Jersey: Prentice Hall.
Green A (197 1) Soft fruits. In: Hulme AC (ed) The Biochemistry of Fruits and their Products, vol. 2. pp 375-410. New York: Academic Press.
Jennings DL (1988) Raspberries and Blackberries – their Breeding, Diseases, and Growth. New York: Academic Press.
- Kader AA (1997) A summary of CA requirements and recommendations for fruits other than apples and pears. In: Kader AA (ed) Proceedings of the Controlled Atmosphere Research Conference 3:1-34. Davis, Calif.
- Ourecky DK (1975) Brambles. In: Janick J and Moore J (eds.) Advances in fruit breeding, pp 98129. Indiana: Purdue University Press.
- Pritts M and Handley D (1989) Bramble Production Guide. Northeast Regional Agricultural Engineering Service Bulletin 35. Cornell University, New York.
Table 1. Reported values or ranges of nutrient content in 100 g of fresh raspberries
| Nutrient | Amount |
| Water (g) | 84-87 |
| Food energy (kcal) | 31-49 |
| Protein (g) | 0.42-1.40 |
| Fat (g) | 0.20-0.55 |
| Carbohydrate (g) | 5.8-11.6 |
| Fiber (g) | 3.0-7.4 |
| Ash (g) | 0.40-0.51 |
| Minerals | Amount (mg) |
| Calcium | 22-50 |
| Iron | 0.57-1.20 |
| Magnesium | 18-30 |
| Phosphorus | 12-50 |
| Potassium | 130-221 |
| Sodium | 0-2.5 |
| Zinc | 0.46 |
| Copper | 0.07-0.21 |
| Manganese | 1.01 |
| Sulphur | 17.3 |
| Chlorine | 22.3-22.8 |
| Boron | 71-125 |
| Vitamins (mg) | Amount (mg) |
| Carotene | 0.05-0.08 |
| Thiamin | 0.01-0.03 |
| Riboflavin | 0.03-0.10 |
| Pantothenic acid | 0.24-0.30 |
| Nicotinamide | 0.20-1.00 |
| Vitamin B6 | 0.06-0.90 |
| Vitamin C | 13-38 |
| Tocopherols | 0.3-4.5 |