Post Harvest Management of Horticultural Crops

Irradiation

Radiation can be applied to fresh fruits and vegetables to control micro organism/insects/parasites and inhibit or prevent cell reproduction and some chemical changes. It can be applied by exposing the crop to radioisotope in the form of gamma-rays but X-rays can also be used from the machine which produces a high energy electron beam.
Unit of measurement

• Radiation doses are measured in Grays (Gy). One Gray = 100 rads.
• One Gy dose of radiation is equal to 1 joule of energy absorbed per kg of food material.
• In radiation processing of foods, the doses are generally measured in kGy (1,000 Gy).

Radiation helps in breaking the chemical bonds in the produce or micro organism. Ionizing radiation involves damage to DNA, the basic genetic information for life. Microorganisms can no longer proliferate and continue their harmfull or pathogenic activities. Insects do not survive, or become incapable of proliferation. Plants cannot continue the natural ripening or aging process.

Cobalt 60 is commonly used as a source of gamma-rays in food irradiation. Radioisotopes cannot be switched on or off so they are immersed in a pool of water to allow operators to enter the processing area. When food is to be irradiated the radioisotopes is raised out of the water and material to be irradiated is usually passed through radiation field on the conveyer belts. The whole processing area is surrounded by thick concrete to prevent the radiation out.

Advantages of Irradiation

• Reduce the spoilage
• Slowing down the rate of metabolism in the produce
• Delay ripening and senescence
• Controlling sprouting in potato, onion, garlic and yams – 0.05-0.3 kGy
• Extend shelf life of fresh produce
• Insect and parasite disinfestations- egg phase is most sensitive followed by larval, pupal and adult stages. Most insects are sterilized at doses of 0.1 -1.0kGy. And survived adults progeny are sterile.
Eg. Irradiation is being is used in Australia to produce sterile male Queensland fruits flies and in Hawaii it is being used in papaya for papaya fruit fly


Factors effecting Radiation

• Moisture content in foods and the surrounding environment during treatment influence the sensitivity of microorganisms to irradiation.
For eg. high RH and high water content in foods reduce the effectiveness of irradiation.
• Ultraviolet lamps are sometimes used in refrigerated storage for the control of bacteria and moulds.

Dosage

• In general, most vegetables can withstand irradiation dosages up to a maximum of 2.25 kGy; higher doses can, however, interfere with the organoleptic properties of food products.
• Combining irradiation + temperature control + gaseous environment + adequate processing conditions is one of the most effective approaches to vegetable preservation.
• The maximum absorbed dose delivered to a food should not exceed 10 kGy.