Post harvest Management of Horticultural Crops (2+1)

Ethylene Biosynthesis

Ethylene has been shown to be produced from methionine via a intermediates S-adenosyl-methionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC). The conversion of SAM to ACC by the enzymes ACC Synthase(ACS). In higher plants, ACC can be removed by conjugation to form malonyl ACC (MACC) or glutamyl ACC (GACC). Ethylene forming enzyme (EFE) or ACC oxidase (ACO) is required to convert ACC to ethylene. ACO is a liable enzyme and sensitive to oxygen and attached to outer layer of the plasmalemma. Factor that effect the activity of the ACS includes fruit ripening, senescence, auxin, physical injuries and chilling injury. This enzyme (ACS) is strongly inhibited by aminooxyacetic acid(AOA), rhizobitoxine and amino ethoxy vinayl glycine (AVG). ACO is inhibited by anaerobiosis, temperature above 350C and cobalt ions.

Among various chemical used for extension of shelf life fruits 1-MCP has been found to be very effective. The 1-methyl cyclo propene (1-MCP) has been shown to be highly effective inhibitors of C2H4 action. 1–MCP binds irreversibly to the C2H4 receptors in sensitive plants tissues and a single treatment with low concentration for a few hours at ambient temperatures confers protection against C2H4 for several days. Many fruits respond to 1-MCP in extension of storage life by retarding the process of ripening.

The pattern of C2H4 production in tomato is it rises before the onset of ripening, where as in, apple and mango it does not rise before increase in reparation. Immature tomato fruit has high rate of C2H4 production and it extremely tolerance to C2H4 but banana and melons can readily ripened with C2H4 even when immature.


Class	Range at 200 C (µ C2H4 release kg-1hr-1)	Commodities
VERY LOW	< 0.1	Artichoke, Asparagus, Cauliflower, Cherry, Citrus fruits, Grape, Cut Flowers, Leafy Vegetables, Pomegranate, Potato, Root Vegetables, Strawberry
LOW	0.1-1.0	Brinjal, Chilli, Cucumber, Green Capsicum, Okra, Pine apple, Pumpkin, Water melon
MODERATE	1.0 -10	Banana, Guava, Fig, Litchi, Melon, Mango, Tomato
HIGH	10-100	Apple, Apricot, Avocado, Kiwi Fruit (ripe), Papaya, Peach, Plum, Pear
VERY HIGH	> 100	Sapota, Passion Fruit

Ripening is a catabolic process wherein the fruit undergoes a chain of biochemical reactions involving changes in colour, texture and taste.