Relationship between ethylene response manipulation and volatile production in Jonagold variety apples

Comparative Analysis of Metabolites of 'Hongro' Apple Greasiness in Response to Temperature

Greasiness in apple skin reduces its quality, and its level varies depending on the variety. In this study, low-temperature (1 ± 0.5 °C) stored 'Hongro' and 'Fuji', which had differences in the occurrence of greasiness, were moved to room temperature (20 °C) and untargeted metabolite and fatty acids for skin and flesh along with quality changes due to greasiness occurrence were compared. Ethylene production differed noticeably between the two varieties and increased rapidly in 'Hongro' until 9 d of room-temperature storage. The ethylene production did not differ significantly between the two varieties on day 20 when greasiness occurred. According to the PLS-DA score plot, while 'Hongro' had similar amounts of unsaturated and saturated fatty acids, 'Fuji' had approximately twice as much unsaturated-fatty-acid content. 'Hongro', after 50 d of low-temperature (1 ± 0.5 °C) storage, produced excessive ethylene during room-temperature storage, which was directly related to greasiness development. As a result, the primary wax components of greasy 'Hongro' were nonacosane and nonacosan-10-ol. As the room-temperature storage period elapsed, pentyl linoleate and α-farnesene contents increased significantly. Furthermore, these greasiness-triggering characteristics of 'Hongro' may have been genetically influenced by the paternal parent used during breeding.

Functional Characteristics of Aldehyde Dehydrogenase and Its Involvement in Aromatic Volatile Biosynthesis in Postharvest Banana Ripening

Butanol vapor feeding to ripe banana pulp slices produced abundant butyl butanoate, indicating that a portion of butanol molecules was converted to butanoate/butanoyl-CoA via butanal, and further biosynthesized to ester. A similar phenomenon was observed when feeding propanol and pentanol, but was less pronounced when feeding hexanol, 2-methylpropanol and 3-methylbutanol. Enzymes which catalyze the cascade reactions, such as alcohol dehydrogenase (ADH), acetyl-CoA synthetase, and alcohol acetyl transferase, have been well documented. Aldehyde dehydrogenase (ALDH), which is presumed to play a key role in the pathway to convert aldehydes to carboxylic acids, has not been reported yet. The conversion is an oxygen-independent metabolic pathway and is enzyme-catalyzed with nicotinamide adenine dinucleotide (NAD⁺) as the cofactor. Crude ALDH was extracted from ripe banana pulps, and the interference from ADH was removed by two procedures: (1) washing off elutable proteins which contain 95% of ADH, but only about 40% of ALDH activity, with the remaining ALDH extracted from the pellet residues at the crude ALDH extraction stage; (2) adding an ADH inhibitor in the reaction mixture. The optimum pH of the ALDH was 8.8, and optimum phosphate buffer concentration was higher than 100 mM. High affinity of the enzyme was a straight chain of lower aldehydes except ethanal, while poor affinity was branched chain aldehydes.

Aloe vera gel coating aggravates superficial scald incidence in 'Starking' apples during low-temperature storage

The effects of aloe vera (Aloe vera (L.) Burm. f.) gel treatment on the incidence of superficial scald in 'Starking' apples (Malus domestica Borkh. Var. Starking) during cold storage were studied. Apples were harvested at the pre-climacteric stage and treated with aloe vera gel. The treatment increased malondialdehyde content and membrane lipid damage. Furthermore, it inhibited the release of ethylene at the early stage but increased it in the later stage. The expression level of ACC synthase 1 (MdACS1) also increased, and the antioxidant capacity in apples, particularly, catalase, peroxidase, and superoxide dismutase activities, all decreased, while concomitantly, the content of α-farnesene and its oxidation product, conjugated triene increased, thereby aggravating superficial scald incidence during storage at low temperature.

Tools to Maintain Postharvest Fruit and Vegetable Quality through the Inhibition of Ethylene Action: A Review

Ethylene is a plant hormone controlling a wide range of physiological processes in plants. During postharvest storage of fruit and vegetables ethylene can induce negative effects including senescence, over-ripening, accelerated quality loss, increased fruit pathogen susceptibility, and physiological disorders, among others. Apart from the endogenous ethylene production by plant tissues, external sources of ethylene (e.g. engine exhausts, pollutants, plant, and fungi metabolism) occur along the food chain, in packages, storage chambers, during transportation, and in domestic refrigerators. Thus, it is a great goal in postharvest to avoid ethylene action. This review focuses on tools which may be used to inhibit ethylene biosynthesis/action or to remove ethylene surrounding commodities in order to avoid its detrimental effects on fruit and vegetable quality. As inhibitors of ethylene biosynthesis and action, good results have been found with polyamines and 1-methylcyclopropene (1-MCP) in terms of maintenance of fruit and vegetable quality and extension of postharvest shelf-life. As ethylene scavengers, the best results can be achieved by adsorbers combined with catalysts, either chemical or biological (biofilters).

Functional characterization of a melon alcohol acyl-transferase gene family involved in the biosynthesis of ester volatiles. Identification of the crucial role of a threonine residue for enzyme activity*

Volatile esters, a major class of compounds contributing to the aroma of many fruit, are synthesized by alcohol acyl-transferases (AAT). We demonstrate here that, in Charentais melon (Cucumis melo var. cantalupensis), AAT are encoded by a gene family of at least four members with amino acid identity ranging from 84% (Cm-AAT1/Cm-AAT2) and 58% (Cm-AAT1/Cm-AAT3) to only 22% (Cm-AAT1/Cm-AAT4). All encoded proteins, except Cm-AAT2, were enzymatically active upon expression in yeast and show differential substrate preferences. Cm-AAT1 protein produces a wide range of short and long-chain acyl esters but has strong preference for the formation of E-2-hexenyl acetate and hexyl hexanoate. Cm-AAT3 also accepts a wide range of substrates but with very strong preference for producing benzyl acetate. Cm-AAT4 is almost exclusively devoted to the formation of acetates, with strong preference for cinnamoyl acetate. Site directed mutagenesis demonstrated that the failure of Cm-AAT2 to produce volatile esters is related to the presence of a 268-alanine residue instead of threonine as in all active AAT proteins. Mutating 268-A into 268-T of Cm-AAT2 restored enzyme activity, while mutating 268-T into 268-A abolished activity of Cm-AAT1. Activities of all three proteins measured with the prefered substrates sharply increase during fruit ripening. The expression of all Cm-AAT genes is up-regulated during ripening and inhibited in antisense ACC oxidase melons and in fruit treated with the ethylene antagonist 1-methylcyclopropene (1-MCP), indicating a positive regulation by ethylene. The data presented in this work suggest that the multiplicity of AAT genes accounts for the great diversity of esters formed in melon.