Kiwifruit

MATURITY & QUALITY

Maturity Indices

• Minimum of 6.5% soluble solids content (SSC) at harvest.
• Minimum flesh firmness of 14 lbf (penetration force with an 8-mm = 5/16 inch tip). Late harvested kiwifruits retain their firmness better than early harvested fruit and have higher SSC at harvest and when ripe.

Quality Indices

• Freedom from growth cracks, insect injury, bruises, scars, sunscald, internal breakdown, and decay.
• Minimum of 14% SSC when ripe (ready to eat); a kiwifruit at 2-3 lb flesh firmness is considered ripe.
• Kiwifruits are a good source of vitamin C.

TEMPERATURE & CONTROLLED ATMOSPHERE (CA)

Optimum Temperature

0°C (32°F); highest freezing point is -1.5°C (29.3°F).

Optimum Relative Humidity

90-95%

Rates of Respiration

To calculate heat production multiply ml CO₂/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

Less than 0.1 µl/kg·hr at 0°C (32°F), 0.1-0.5 µl/kg·hr at 20°C (68°F) for Production unripe kiwifruit. Ripe kiwifruit (less than 4 lbf firmness) produce 50-100 µl/kg·hr at 20°C (68°F).

Responses to Ethylene

• Kiwifruits are extremely sensitive to ethylene. As little as 5-10 ppb ethylene will induce fruit softening.
• Avoid exposure of unripe kiwifruits to ethylene during harvest, transport, and storage.

Responses to Controlled Atmospheres (CA)

Optimum CA 1-2% O₂ + 3-5% CO₂.
CA delays ripening and retains flesh firmness.
CO₂ levels above 7% can cause internal breakdown of the flesh.
CA must be established within 2 days after harvest to maximize benefits; ethylene concentration should be kept below 20 ppb to avoid accelerated flesh softening and incidence of white core inclusions.