Nectarine & Peach

MATURITY & QUALITY

Maturity Indices

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)
2. Well-Mature
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.

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

TEMPERATURE & CONTROLLED ATMOSPHERE (CA)

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)

Optimum Relative Humidity

90-95% R.H.; an air velocity of approximately 50 CFM is suggested during storage.

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

• < 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)
• 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% CO₂are suggested for reduction of internal breakdown during shipments, but the efficacy is related to cultivar, preharvest factors, market life and shipping time period.

Effects of Genotype and Cultural Practices on Postharvest Life

There are approximately 350 peach and nectarine cultivars in California. Market life varies among them and it is strongly affected by temperature management. Maximum market life is obtained when fruit is stored at approximately 0°C (32°F). Maximum market life varies from 1-7 weeks for nectarine cultivars and from 1-5 weeks for peach cultivars. Because internal breakdown is the main limitation to market life, minimum postharvest life occurs when fruit is stored at 5°C (41°F). Cultural practices have an important role in determining fruit quality and storage potential. Leaf nitrogen content between 2.6-3.0% is advised to obtain high red color development and maximum storage performance. Small size fruit grown in the outside canopy position have a longer market life than large size fruit grown in the inside position.