Grapefruit

MATURITY & QUALITY

Maturity Indices

Color (more than 2/3 of fruit surface showing yellow color) and a minimum soluble solids/acid ratio of 5.5 or 6 (depending on production area). Grapefruit do not continue to ripen after harvest so they should be harvested fully-ripe (with good flavor).

Quality Indices

• Color intensity and uniformity
• Firmness
• Size
• Shape
• Peel thickness; smoothness
• Freedom from decay and defects, such as freezing injury, rind staining, pitting, scars, and insect damage
• Flavor is related to soluble solids/acid ratio and concentration of compounds that impart bitter flavor (limonin and naringin)

TEMPERATURE & CONTROLLED ATMOSPHERE (CA)

Optimum Temperature

12-14°C (54-57°F) depending on cultivar, production area, maturity-ripeness stage at harvest, and storage & transport duration (up to 6-8 weeks).

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 ?l/kg·hr at 20°C (68°F)

Responses to Ethylene

Exposure of mature-green grapefruits for 1-3 days to ethylene (1-10ppm) at 20-30°C (68 to 86°F) accelerates loss of green color and appearance of yellow color (degreening). This is accompanied by faster peel senescence and greater susceptibility to decay-causing pathogens.

Responses to Controlled Atmospheres (CA)

• Low O₂ (3-10%) and high CO₂ (5-10%) concentrations delay senesence and maintain firmness of grapefruits kept at 13-15°C (55-59°C).
• Exposure to O₂ levels below 3% and/or CO₂ levels above 10% may result in off- flavors due to accumulation of acetaldehyde, ethanol, and ethyl acetate. This precludes the use of fungistatic levels of CO₂ (>10%) for longer than a few days.
• Commercial use of CA during transport and/or storage of grapefruits is very limited.