Peach and Nectarine – In California, harvest date is determined by skin ground color changes from green to yellow in most cultivars. A color chip guide is used to determine maturity of each cultivar.
A three tier maturity system is used in California
1) US-Mature (Minimum Maturity)
3) Tree Ripe.
Measurement of fruit firmness is recommended in cultivars where skin ground color is masked by full red color development before maturation. Maximum maturity: The flesh firmness at which fruits can be handled without bruising damage is measured with a penetrometer with an 8 mm- (5/16″) tip. Bruising susceptibility varies among cultivars.
Peach and Nectarine Quality Indices
High consumer acceptance is attained on fruit with high soluble solids content (SSC). Fruit acidity, SSC/acidity ratio, and phenolic content are also important factors in consumer acceptance. There is no established minimum quality standard for peaches and nectarines.
Fruit with 2-3 pounds-force flesh firmness is considered “ready to eat”. Fruit below 6-8 pounds-force measured on the cheek are more acceptable to the consumer.
Peach and Nectarine Optimum Temperature
-1 to 0°C (30.5-32°F)
Freezing point varies depending on SSC from -3 to -2.5°C (26.5 to 29.5°F)
Peach and Nectarine Optimum Relative Humidity
90-95% R.H.; an air velocity of approximately 50 CFM is suggested during storage.
Rates of Respiration
2 – 3
8 – 12
32 – 55
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
< 0.01-5 µl/kg·hr (range)* at 0°C (32°F), 0.02-10 µl/kg·hr at 5°C (41°F), 0.05-50 µl/kg·hr at 10°C (50°F) and 0.1-160 µl/kg·hr at 20°C (68°F)
*The lower end of this range is for mature but unripe fruit; higher values are for ripe fruit.
Responses to Ethylene
In general peaches and nectarines harvested at Well Mature (higher than US-Mature) will ripen properly without exogenous ethylene application. Ethylene application to fruit harvested at the US-Mature maturity will only ripen the fruit more uniformly without speeding up the rate of ripening. A few cultivars may need to be exposed to ethylene to ripen properly.
Responses to Controlled Atmospheres(CA)
The major benefits of CA during storage/shipment are retention of fruit firmness and ground color. Decay incidence has not been reduced by using CA 1-2%O2+ 3-5 %CO2. CA conditions of 6% O2 + 17% CO2 are suggested for reduction of internal breakdown during shipments, but the efficacy is related to cultivar, preharvest factors, market life and shipping time period.