Role of internal atmosphere on fruit ripening and storability-a review

Abstract

Concentrations of different gases and volatiles present or produced inside a fruit are determined by the permeability of the fruit tissue to these compounds. Primarily, surface morphology and anatomical features of a given fruit determine the degree of permeance across the fruit. Species and varietal variability in surface characteristics and anatomical features therefore influence not only the diffusibility of gases and volatiles across the fruits but also the activity and response of various metabolic and physiological reactions/processes regulated by these compounds. Besides the well-known role of ethylene, gases and volatiles; O2, CO2, ethanol, acetaldehyde, water vapours, methyl salicylate, methyl jasmonate and nitric oxide (NO) have the potential to regulate the process of ripening individually and also in various interactive ways. Differences in the prevailing internal atmosphere of the fruits may therefore be considered as one of the causes behind the existing varietal variability of fruits in terms of rate of ripening, qualitative changes, firmness, shelf-life, ideal storage requirement, extent of tolerance towards reduced O2 and/or elevated CO2, transpirational loss and susceptibility to various physiological disorders. In this way, internal atmosphere of a fruit (in terms of different gases and volatiles) plays a critical regulatory role in the process of fruit ripening. So, better and holistic understanding of this internal atmosphere along with its exact regulatory role on various aspects of fruit ripening will facilitate the development of more meaningful, refined and effective approaches in postharvest management of fruits. Its applicability, specially for the climacteric fruits, at various stages of the supply chain from growers to consumers would assist in reducing postharvest losses not only in quantity but also in quality.

Keywords: Endogenous volatiles; Fruit ripening; Gaseous exchange; Internal atmosphere; Postharvest; Postharvest management; Storage.

Fig. 1

Changes in various parameters during climacteric fruit ripening (Source: Nath et al. 2006)

Fig. 2

Ethylene biosynthesis, perception and response. SAM: S-Adenosyl-L-methionine, ACC: 1-Amino-cyclopropane-1-carboxylic acid, MTA: 5-Methylthioadenosine, HCN: Hydrogen cyanide

Fig. 3

Simplified pathway of ethylene biosynthesis in plants showing auto-inhibition (inhibiting its own production) and auto-induction of ethylene (inducing its own production). These two systems are referred as system 1 and system 2 of ethylene production respectively. In system 1, ethylene inhibits its own production by inhibiting () ACS (ACC-synthase) expression/activity. It may be noted that the ACO (ACC-oxidase) activity is enhanced during system 1 but due to the absence of any enhancement in the activity of ACS there is no auto-induction. In system 2, ethylene induces more of its own production by stimulating () the expression/activity of both of the enzymes (ACS and ACO) simultaneously and this thereby enhances the overall ethylene production (). 2, 4- norbornadiene and 1-MCP (1-methylcyclopropene) [action inhibitors of ethylene] and response mutants of ethylene block () the action/response of the ethylene and thereby inhibit the system 2 of ethylene production (Source: Adapted and modified from Srivastava 2001)

Fig. 4

Interaction of ethylene with plant/plant parts and its immediate environment (Source: Adapted and modified from Saltveit 1999)

Fig. 5

Cross section passing through a fruit showing how the concentration of O₂ and CO₂ can vary within different tissues of the fruit due to respiration and external and internal barriers to gas diffusion (Source: Kader and Saltveit 2003b)

Fig. 6

Different endogenous volatiles and other factors that play regulatory role in determining the production as well as the response of ethylene. The symbols , , >, < and indicate inducers, suppressors, higher, lower and possible interaction respectively. SAM: S-Adenosyl-L-methionine, ACC: 1-Amino-cyclopropane-1-carboxylic acid, SA: Salicylic acid, MSA: Methyl salicylic acid, JAs: Jasmonates, NO: Nitric oxide

Fig. 7

Pyruvate is produced during glycolysis. Under aerobic condition, this pyruvate enters into mitochondria for Krebs cycle. But under hypoxia or anaerobic condition, pyruvate is diverted for ethanolic glycolysis [where it is initially converted into acetaldehyde by the enzyme pyruvate decarboxylase (PDC) and then acetaldehyde is converted into ethanol by a reaction catalyzed by alcohol dehydrogenase (ADH)]. ADH basically catalyses bidirectional reaction for the inter-conversion of acetaldehyde and ethanol. The symbols , , >, <, and indicate inducers, suppressors, higher, lower and possible interaction respectively. NO: Nitric oxide