CONTROL OF SENESCENCE IN FRUITS, VEGETABLES AND FLOWERS

Abstract: Senescence in perishable plant tissue is inhibited by the application thereto of an effective amount of a compound of formula (I), wherein R1, R2, R3, R4 and R5 are each selected from the group consisting of hydrogen, -OH or -OR7, provided that at least one of R1 to R5 is a hydroxyl group, R6 is selected from the group consisting of -OH, -OR8 and -NHR9, R7 is a substituent group, R8 is the residue of an ester-forming compound and R9 is the residue of an amide-forming compound. The compound may be prepared synthetically and, in some cases, can be isolated from natural sources, for example, the glucose ester of ferulic acid may be isolated from carnation petals.

Description: TITLE OF INVENTION CONTROL OF SENESCENCE IN FRUITS. VEGETABLES AND FLOWERS FIELD OF INVENTION The present invention relates to the inhibition of ethylene formation from perishable fruits, vegetables and flowers, thereby inhibiting the onset of senescence therein. BACKGROUND TO THE INVENTION Once fruits, vegetables and flowers are harvested, they are vulnerable to spoilage and must be consumed within a certain period of time. Some fruits and vegetables, for example, apples, can be stored under cold conditions for long periods without spoilage. Most fruits and vegetables, however, are perishable and cannot be stored for protracted periods. Studies have been made of the mechanism of senescence and post-harvest deterioration. Membrane deterioration mediated by lipoxygenase has been identified as an early manifestation of the onset of senescence. Senescence is accompanied by the evolution of ethylene and once ethylene evolution commences, the process of deterioration is accelerated. The biosynthetic path to ethylene formation has been identified as initial conversion of methionine to S-adenosyl methionine (SAM) , the conversion of SAM to 1-amino-cyclopropane-l-carboxylic acid (ACC) , and thence to ethylene. It has previously been observed that the cytosol fraction from extraction of the petals of senescing carnation flowers inhibited ACC to ethylene conversion activity of membranes isolated from the petals (Maya et al, Planta (1981) 153:49-55). We have now been able to isolate and identify the active material which provides the inhibition and have identified a class of compounds which are useful in the inhibition of ethylene production in vitro and ij situ from harvested fruits, vegetables and flowers. SUMMARY OF INVENTION In accordance with the present invention, there is provided a method of inhibiting senescence in perishable plant tissue, including fruits, vegetables and flowers, by the application thereto of an effective amount of a compound of the formula: wherein Rτ_, R 2 , R 3 , R4 and R5 are each hydrogen, -OH or -OR7 provided that at least one of R^ to R5 is a hydroxyl group, Rs is -OH, -ORβ or -NHRg, R7 is a substituent group, usually an alkyl group, or a sugar * via an ether linkage, s is the residue of an ester-forming compound, and Rg is the residue of an amide-forming compound. BRIEF DESCRIPTION OF DRAWING The sole Figure of the drawing is a schematic flow sheet of the procedure used to effect isolation of the active component and as set forth in detail in Example 1 below. GENERAL DESCRIPTION OF INVENTION As noted above, the present invention resides in the application to perishable plant tissue of an effective amount of a compound of formula (I) . In the compounds of formula (I) , R7 usually is a methyl or an ethyl group. Usually one only of the Rx to R5 groups is hydroxyl, while another of the Ri to R5 groups is alkoxy. Preferably, the organic acid, esterified or otherwise, is ferulic acid, i.e. the compound of formula (I) wherein R^, R2 and R5 are hydrogen, R3 is -OH and R4 is -OCH3. The organic acid also may be a benzoic acid derived by side-chain degradation of respective hydroxycinnamic acid precursors. In the compounds of formula (I) , the free acid may be used, i.e. R g is hydrogen, but it has been found that esters of the acids are preferred, especially esters having a plurality of hydroxyl groups. In one embodiment, R Q may be a glycosyl ester, such as a glucose ester, for example, the compound wherein R- is B-D-glucose, i.e.: Multiples and mixtures of sugars may comprise the glycosyl group. Another example of an R g group is the ester of quinic acid. The compounds used in the present invention may be isolated from natural sources. For example, the glucose ester of ferulic acid may be isolated from carnation petals by conventional isolation procedures involving chromatography. Such compound has been identified as the active compound achieving the inhibition reported in the previous work. Some of the compounds, for example, ferulic acid, are available commercially, while others and their esters may be synthesized from commercially-available materials. The compounds may be applied to the plant material with respect to which inhibition of ethylene production is desired in any convenient manner, usually from aqueous solutions thereof, for example, by infusion. Generally, only small amounts are required to achieve long term inhibition of lipoxygenase and ethylene production. The active compounds disclosed herein have been shown to inhibit ethylene formation and lipoxygenase activity in carnation petals. Since the same mechanism of senescence applies in fruits and vegetables, the compounds should have the same inhibitory effect on such other materials. Feruloyl glucose has shown promise as a full radial scavenger in tests with a chemical system and, therefore, this compound and other similar phenols may prove useful as processed food preservatives. EXAMPLES In the Examples, reference is made to the accompanying drawing (Figure 1) , which is a schematic flow sheet of the process steps used to effect isolation of the active component. Example 1 This Example illustrates the isolation of the glucose ester of ferulic acid from senescing carnation lowers. 50 g of senescing carnation petals were homogenized and centrifuged at ultraspeed (131,000 x g) . The supernatant (100 ml) , was freeze dried to a yellowish powder (2.5 g) . The lyophilyzed samples (250 mg) were extracted with 80% methanol at β C. Solid material was removed by centrifugation at top speed in a clinical centrifuge. After decanting, the pellet was resuspended in cold 80% methanol and centrifuged again. The washing procedure was repeated until the pellet was white and the supernatant was clear. The combined methanolic fractions were evaporated under vacuum to an aqueous volume (10 ml) , adjusted to pH 2.0 with 0.4 M HCl and immediately extracted four times with ethyl acetate. The combined ethyl acetate fractions were dried and the residue redissolved in 300 μl of absolute methanol and referred to as the crude ethyl acetate extract. The crude ethyl acetate extract was strip-loaded on 15 x 57 cm sheets of Whatman No. 3 filter paper and developed by descending chromatography with 15% (v/v) acetic acid. The inhibitory strip (Rf = 0.81) was eluted and rechromatographed using n-butanol:acetic acid:water (BAW, 4:1:5, v/v/v) . The inhibitor, purified by two systems of paper chromatography, was purified further by preparative TLC using ethyl acetate:iso- propanol:water, (65:24:11, v/v/v). The location and identity of the inhibitor was monitored by Rf values and UV fluorescence of the appropriate region on the chromatogram. Further confirmation was obtained from a complete UV scan of the eluates from each TLC plate. These procedures are illustrated in Figure 1. The inhibitor was identified as the glucose ester of ferulic acid. Example 2 This Example illustrates the inhibition of ethylene formation in vitro by the glucose ester of ferulic acid. Microsomes from senescing carnation flowers were treated with varying quantities of the glucose ester of ferulic acid, isolated as described in Example 1, and the production of ethylene was determined as a percentage of the control production of ethylene in the absence of added ferulic acid ester. The results obtained are set forth in the following Table I: Table I Reaction Mixture Ethylene Production % Control (nl.lOOμg"" 1 protein h -1 Control 0.962 ± 0.03 100 Control + 10 μM of Additive 0.518 ± 0.019 53.9 Control + 50 M of Additive 0.014 ± 0.005 2.0 Control + 100 / .M of Additive 0 0 As may be seen from this Table I, a concentration of only 100 μK of the glucose ester of ferulic acid was sufficient to decrease ethylene formation to zero. Example 3 This Example illustrates the use of the glucose ester of ferulic acid for in vivo prevention of ethylene formation in carnations. The glucose ester of ferulic acid (1 mM) , isolated as described in Example 1, was taken up transpiration- ally into petals of carnation flowers. Ethylene production was determined as a percentage of the ethylene produced by untreated control petals at various times after incubation with ACC. The results obtained are set forth in the following Table II: Table II Time after Treatment (hrs) % Inhibition 12 100 16 97.3 21 90.4 26 81.7 As may be seen from the data presented in Table II, the effectiveness of preventing ethylene formation is retained over a long period of time. Example 4 This Example illustrates the inhibition of lipoxygenase (LOX) activity by the glucose ester of ferulic acid. Lipoxygenase activity has been demonstrated in microsomal membranes of carnation (Lynch et al., Planta 1985, 164:121-125) and microsomes and cytosol fractions of bean cotyledon (Lynch and Thompson, FEBS 1984, 173:251-254). The addition of the glucose ester of ferulic acid, isolated as described in Example 1, to both membrane and cytosol preparations caused an inhibition of enzyme activity in all experiments when 100 μia concentrations were used. The results obtained are set forth in the following Table III: Table III Effect of feruloyl glucose on the activity of lipoxygenase in carnation and bean. All the experiments were repeated at least twice. The data reported are means from one experiment. where n = 3. Lipoxygenase Experiment Components in reaction activity (% mixture of control) l.a. control, containing 100 μg membrane protein from stage IV carnation 100 b. membrane plus 40 μM feruloyl glucose (FG) 1.8 l.a. control, containing 60 μg membrane protein of 9 d bean cotyledon 100 b. membrane plus 50 μM FG 46.3 100 μM FG 37.8 3.a, control, containing 10 μg cytosol protein of 9 d bean cotyledon 100 b. cytosol plus 50 μM FG 48.8 100 uM FG 35.9 As may be seen in Table III, feruloyl glucose was most effective against lipoxygenase activity derived from carnation, with almost complete inhibition of activity with a 40 μM solution of the inhibitor, but FG was also effective against LOX from several other plant systems including bean cotyledons. SUMMARY OF DISCLOSURE In summary of this disclosure, the present invention provides a novel method of inhibiting the onset of senescence in harvested fruits, vegetables and flowers by the application of small quantities of certain phenolic derivatives. Modifications are possible within the scope of this invention.

Claims: CLAIMS What we claim is: 1. A method of inhibition of senescence in perishable plant tissue, which comprises: applying thereto an effective amount of a compound of the formula: wherein Ri, R2, R 3 , R4 and R- are each selected from the group consisting of hydrogen, -OH or -OR7, provided that at least one of R± to R5 is a hydroxyl group, Rg is selected from the group consisting of -OH, -OR 3 and -NHRg, R 7 is a substituent group, Rs is the residue of an ester-forming compound and Rg is the residue of an amide-forming compound. 2. The method of claim 1 wherein R7 is selected from the methyl group and ethyl group. 3. The method of claim 2 wherein only one of the groups R^ to R5 is hydroxyl and another of the groups R^ to 5 is alkoxy. 4. The method of claim 1 wherein i, R2 and R 5 are each hydrogen, R 3 is -OH and R4 is -OCH 3 . 5. The method of claim 4 wherein Rs is glycoxyl ester. 6. The method of claim 5 wherein Rg is B-D-glucose. 7. The method of claim 5 wherein s is an ester of guinic acid. 8. A free-radical scavenging and antisenescence composition useful for application to perishable plant tissue, comprising an aqueous solution of a compound of the formula: wherein R^, R2, R3, R4 and R- are each selected from the group consisting of hydrogen, -OH or -OR7, provided that at least one of ^ to R5 is a hydroxyl group, Rg is selected from the group consisting of -OH, -ORs and -NHRg, R7 is a substituent group, Rs is the residue of an ester-forming compound and Rg is the residue of an amide-forming compound.

Inventors: DUMBROFF ERWIN B, SHIH CHING YU, STEWART MICHAEL IAN, THOMPSON JOHN E, DUMBROFF, ERWIN, B., SHIH, CHING, YU, STEWART, MICHAEL, IAN, THOMPSON, JOHN, E.
Applicants: DUMBROFF ERWIN B, SHIH CHING YU, STEWART MICHAEL IAN, THOMPSON JOHN E, DUMBROFF, ERWIN, B., SHIH, CHING, YU, STEWART, MICHAEL, IAN, THOMPSON, JOHN, E.
Application year: 1987
Main classification: A23B7
IPC codes: A01N37, A01N43, A23B7