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Storage behaviour of avocados at low temperatures

Chaplin, Grantley Richard

Ph.D., University of New South Wales (Australia), 1985. 205 pages.

1985

บทคัดย่อ

STORAGE BEHAVIOUR OF AVOCADOS AT LOW TEMPERATURES.

Chilling injury was a major factor influencing the postharvest quality of avocados stored at low temperatures.  This thesis examined the effect of various treatments, and inherent fruit factors, on the storage behaviour and the chilling response of avocados.  A new method to quantitate chilling injury was developed.

 Chilling injury occurred as a discolouration in the mesocarp, and developed fully when the stored fruit was ripened.  Symptoms were first observed and/or were more severe in the stylar end of the fruit.  Endogenous calcium in the pedicel end of avocados was consistently higher than in the stylar end.  Treatment of avocados with calcium, before storage, reduced chilling injury.

 Chilling injury increased with time but was less severe in fruit stored at 1(DEGREES)C than in fruit stored at higher chilling temperatures.  Fruit that had climacteric-like respiration and ethylene production patterns during storage, began to soften, and had more chilling injury.  Those at 1(DEGREES)C had no climacteric-like responses, softening, and less chilling injury.

 Exogenous ethylene, applied during storage, induced climacteric-like respiration and softening in the fruit, and also increased chilling injury.

 Avocados stored at 5(DEGREES)C, and warmed every 7 days, softened.  Unwarmed fruit were firmer.  Chilling injury was more severe in fruit warmed for 6 hours than if warmed for 2 or 24 hours, or not warmed.

 Storage in air at high flow rates, and low relative humidity, caused loss in fruit weight, premature softening and chilling injury.  Fruit stored in humidified air remained firm but developed rots when ripened at 20(DEGREES)C.

 Application of Ethrel, cobalt, methionine, and silver resulted in climacteric-like respiration and ethylene production patterns and fruit softening during storage.  Application of calcium inhibited climacteric-like patterns and fruit softening.  Softening was inversely related to the time in storage to peak ethylene production, and chilling injury was directly related to the degree of softening at the end of storage.

 Avocados stored in sealed polyethylene bags had less chilling injury than fruit stored in air.  Modified atmospheres, comprising 2 to 6% oxygen and 3 to 7% carbon dioxide, developed inside the bags.  Accumulation of ethylene was prevented by an ethylene oxidant.