The influence of harvest date on the volatile composition of ‘Starkspur Golden’ apples

Postharvest

Biologyand Technology

ELSEVIER

Postharvest Biology and Technology 6 (1995) 225-234

The influence of harvest date on the volatile composition of ‘Starkspur Golden’ apples Maristella

Vanoli a**, Costanza

Visai a, Anna Rizzolo b

a Istituto di Coltivazioni Arboree, Universitrf degli Studi, via Celoria, 2, 20133 Milano, Italy b Istituto per la Valorizzazione Tecnologica dei F’rodotti Agricoli (I. YTPA.), via Venezian, 26, 20133 Milano, Italy

Accepted 8 February 1995

Abstract The effect of harvest date on the volatile composition of ‘Starkspur Golden’ apples (M&s domestica Borkh.) was studied. The fruits were picked 158, 172 and 181 days after

full bloom (DAFB). Volatile substances were sampled by dynamic headspace on intact fruits and analysed by capillary gas chromatography. Qualitative and quantitative differences were found among the harvest dates. Apples picked 172 DAFB showed the highest amount of volatiles, as well as the best volatile composition; they had a low content of high boiling-point esters and alcohols and a high content of low boiling-point esters, which are responsible for the characteristic ‘Golden’ aroma. Apples picked 158 and 181 DAFB showed a volatile substance composition typical of immature and overripe apples, respectively. Keywords:

Apple; Volatiles; Aroma; Harvest date; Ripening

1. Introduction Volatile compounds are responsible for the odour formation which is an important criterion of fruit quality. There has been much research concerning the separation and the identification of apple volatiles, and it is known that there are more than 300 volatiles produced by apples. Apple aroma is due to a complex mixture of alcohols, aldehydes, C1-C6 esterified acids, estragol and terpenes (Dimick and Hoskin, 1983; Rizzolo et al., 1995). Among these compounds, only about 20-40 are directly associated with the characteristic apple-like aroma; the main components are: hexanal, (E)-Zhexenal, butyl acetate, hexyl acetate, hexanol, ethyl 2-methyl-butanoate, /I-damascenone, butyl-, 3-methyl-butyl- and hexyl-hexanoate, *Corresponding author. Fax: +39 (2) 236-5302. 0925-5214/95/$09.50 Q 1995 Elsevier Science B.V. All rights reserved. SSDI 0925-5214(95)00012-7

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along with ethyl-, propyl- and hexyl-butanoates (Flath et al., 1967; Cunningham et al., 1986; Rizzolo et al., 1989). Fruit maturity at harvest is a critical factor which affects ripening and flavour development after harvest and determines the post-harvest utilisation of fruits. In most countries, a major part of apple production is stored, but the choice of harvest date for apples intended for storage is usually based on the development of appropriate firmness, colour, soluble solids and titratable acidity rather than on the optimisation of aroma. Because these quality attributes gradually change during ripening, the interpretation of their changes during ripening can be difficult, whereas the main volatiles produced by apple fruit can characterise the stage of fruit ripening. De Pooter et al. (1987) found that preclimacteric ‘Golden Delicious’ apples were particularly rich in Cl-C6 aldehydes, which decreased to trace amounts in climacteric fruits. In ‘Rome’ apples, ester concentration increased with advancing harvest date, butyl acetate and 2-methyl-butyl acetate being the main compounds (Fellman et al., 1993). Likewise, in ‘Bisbee’ apples, acetates increased with picking time, as well as butanoates, ethanol and butanol, while hexanal and propanol markedly decreased (Fellman et al., 1990). Hansen et al. (1992) for ‘Jonagold’, and Dirinck et al. (1989) for ‘Golden Delicious’ apples followed the volatile production during the post-harvest ripening in normal atmosphere at 20°C. These authors found that the onset of the volatile production was delayed in early picked apples and the production was lower compared to later picked apples. In a previous work on volatile substance development during growth [from 33 to 145 days after full bloom (DAFB)] of ‘Starkspur Golden’ apples, we found a decrease of total volatiles, a progressive disappearance of aldehydes [hexanal and (E)-2-hexenal] and a gradual appearance of acetate and butanoate esters (Rizzolo et al., 1988). In the present study we investigated the volatile composition during the post-harvest ripening of ‘Starkspur Golden’ apples picked at different harvest dates in order to provide an accurate assessment of harvest maturity and possibly to determine, via aroma analysis, the most suitable way whereby picked ‘Starkspur Golden’ apples could be utilised. 2. Materials and methods Plant material

Seventeen-year-old apple trees, of ‘Starkspur Golden’, grafted on MM 111 and grown in the Experimental Orchard of the University of Milan (Montanaso Lombardo, PO Valley), were used. Twenty apples were picked 158 (commercial harvest), 172 and 181 DAFB (full bloom occurred on April 16th, 1989), when soluble solids were about 11”Brix and titratable acidity was 6.3 meq 100 ml-’ of juice for early picked apples and about 2 meq 100 ml-’ of juice for the apples of the other two harvest dates. Intact apples were analysed for headspace volatile substance evolution during the post-harvest ripening at 18°C till the fruit skin reached the No. 8 yellow of the calorimetric chart for ‘Golden Delicious’ apples set up by Gorini (1983). The No. 8 yellow corresponds to a fully ripe apple (ready-to-eat) but without showing water loss and shrivelling.

M. tinoli et al. I Postharvest Biology and Technology 6 (1995) 225-233

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Volatilecompound analysis Headspace volatiles were sampled daily by placing intact apples (ca. 1.5-2 kg) into a 5-l desiccator and passing purified air through the desiccator at 36 1 h-’ for Table 1 Volatile compounds

identified

in ‘Starkspur

Golden’

apples

Compounds Esters

Alcohols

Aldehydes

Butyl acetate Hexyl acetate Pentyl acetate 3-Methyl-butyl acetate (‘2)3-Hexenyl acetate Butyl propanoate Butyl butanoate Ethyl butanoate Hexyl butanoate Butyl hexanoate 3-Methyl butyl butanoate Hexyl 2-methyl-butanoate

Butanol Hexanol 3-Penten-2-01

Acetaldehyde (E)-Z-Hexenal Hexanal

A

10

20

30

40

50

days at 18OC Fig. 1. Post-harvest total volatile production from ‘Starkspur (158 DAFB o; 172 DAFB q; 181 DAFB A).

Golden’

apples

picked

on different

dates

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1 h to collect headspace volatiles on 100 mg of coconut charcoal (20-40 mesh, ORBO-32, Supelco). The system was maintained at 18°C. Trapped volatiles were desorbed from the charcoal in a 4.5ml vial by addition of 0.5 ml dicholoromethane and agitated for 40 min; 3 ~1 were then analysed by capillary gas chromatography using a 12 m x 0.33 mm i.d. Carbowax 20 M column (0.5 pm film thickness; SGE, Australia) following the conditions described by Rizzolo et al. (1992). After concentration in a micro Kuderna Danish apparatus (Supelco), the desorbed volatiles were identified by gas chromatography/mass spectrometric analysis using a Hewlett-Packard 5870B Quadrupole Mass Spectrometer operated in the electron ionisation mode at 70 eV. Identification was via the National Bureau of Standards, Washington, D.C. library match and by comparison with known compounds. Volatile compounds were quantified using flame ionisation detection and were expressed as pmol kg-’ h-l. All values represent the averages of duplicate sampling of groups of ten apples. 3. Results The volatile compounds identified and quantified from ‘Starkspur Golden’ apples are listed in Table 1. The total volatile production, representing the sum of the

20

30

days at 18T Fig. 2. Post-harvest production of hexyl acetate from ‘Starkspur Golden’ apples picked on different dates (158 DAFB 0; 172 DAFB CI; 181 DAFB A).

M. tinoli et al. /Postharvest Biology and Technology 6 (1995) 225-234

229

identified compounds, changed in relation to the harvest date (Fig. 1). Fruits picked 158 and 172 DAFB had a post-harvest ripening period of 40 days, while apples picked 181 DAFB took only 20 days to ripen. The maximum production of total volatiles occurred after 24 days of post-harvest ripening for 158 DAFB fruits and after 13 days for 181 DAFB apples, reaching 10 pmol kg-’ h-’ for both the harvests. Fruits picked 172 DAFB showed three maxima in volatile emission: the first occurred after 13 days of post-harvest ripening, the second after 22 days and the third, which represents the highest amount (19 pmol kg-’ h-t), after 33 days. Volatiles were arranged into groups according to their affinities. A first group, which included butyl acetate, hexyl acetate, 3-methyl-butyl acetate, butanol and hexanol showed a trend similar to the evolution of total volatiles. As an example, we reported the trend of hexyl acetate (Fig. 2). Fruits picked 158 DAFB gave off about 2.5 pmol kg-’ h-’ of hexyl acetate, 3 pmol kg-’ h-’ of butyl acetate, 1 wmol kg-’ h-’ of butanol, 0.6 pmol kg-’ h-t of hexanol and 0.8 pmol kg-’ h-’ of 3-methyl-butyl acetate. Fruits picked 172 DAFB produced about 5 pmol kg-’ hh’ of hexyl acetate, 4 pmol kg-l h-’ of butyl acetate, 1.5 pmol kg-’ h-’ of butanol and hexanol and 1 vmol kg-’ h-’ of 3-methyl-butyl acetate, while 181 DAFB apples produced 2 hmol kg-’ h-’ of hexyl acetate, 1 pmol kg-’ hh’ of butyl acetate, 1.3

1.2 ,

OS2 0-7r-r-z 10

50

days at I8T Fig. 3. Post-harvest production of ethyl butanoate from ‘Starkspur Golden’ dates (158 DAFB O; 172 DAFB 0; 181 DAFB A).

apples picked on different

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0.2

‘p 0

10

20

30

40

50

days at 18OC Fig. 4. Post-harvest production of pentyl acetate from ‘Starkspur Golden’ apples picked on different dates (158 DAFB 0; 172 DAFB 0; 181 DAFB A).

pmol kg-’ h-’ of butanol, 1.8 pmol kg-’ h-’ of hexanol and 0.3 pmol kg-’ h-’ of 3-methyl-butyl acetate. 3-penten-2-01 (a characteristic component of ‘Golden’ apple aroma) was detectable only in apples picked 172 DAFB (0.2 pmol). The amounts of butyl propanoate, butyl butanoate, 3-methyl-butyl butanoate and (Z)-3-hexenyl acetate fluctuated at low amounts (0.3 pmol kg-’ h-‘) during the post-harvest ripening period in all the samples. Ethyl butanoate increased according to the degree of ripening, reaching the highest value in 181 DAFB apples (Fig. 3). Also pentyl acetate increased with advancing harvest, showing the maximum production (1.2 pmol kg-’ h-l) in apples picked 172 and 181 DAFB and fluctuating in 158 DAFB fruits between 0.4 and 0.6 pmol kg-’ h-l (Fig. 4). Hexyl 2-methyl butanoate and butyl hexanoate+hexyl butanoate remained at almost constant levels (about 0.2 pmol kg-’ h-l) in apples picked 158 DAFB, and reached a maximum after 33 and 12 days of post-harvest ripening in fruits picked 172 and 181 DAFB. Both the maxima were about 0.4-0.5 pmol kg-’ h-’ (Fig. 5). Among the aldehydes, as with some of the esters, hexanal and (E)-Zhexenal did not change in apples picked 158 DAFB and ripened at 18°C (about 0.3-0.4 pmol kg-’ h-l), but they showed a maximum after 24 days of post-harvest ripening in

M. tinoli et al. /Postharvest Biology and Technology 6 (1995) 225-234

Ob0

10

20

30

231

40

days at 10OC

Fig. 5. Post-harvest production of hexyl-2-methyl butanoate different dates (158 DAFB O; 172 DAFB 0; 181 DAFB A).

from ‘Starkspur

Golden’

apples

picked

on

172 DAFB apples, reaching 1 pmol for (E)-2-hexenal and 0.5 for hexanal. In 181 DAFB apples the maximum production was achieved after 13 days of post-harvest ripening [0.5 Fmol for hexanal and 0.8 for (E)-2-hexenal] (Fig 6). Furthermore, the concentration of (E)-Zhexenal on the first day of post-harvest ripening increased according to the harvest date; this is particularly evident for 181 DAFB fruits. After 24 days of post-harvest ripening, acetaldehyde showed the highest amount in apples picked 172 DAFB and the lowest amount in apples picked 158 DAFB. In 181 DAFB fruits there was no emission of acetaldehyde between 7 and 12 days of post-harvest ripening (Fig. 7). 4. Discussion Headspace volatiles collected from ‘Starkspur Golden’ apples changed considerably with the harvest date. Fruits picked 158 and 172 DAFB produced the highest amount of total volatiles after 33 days of post-harvest ripening, while the maximum production of 181 DAFB apples was achieved after only 10 days. Moreover, fruits picked 181 DAFB were characterised by the highest amounts of butanoates and a high quantity of alcohols. This volatile composition is typical of overripe fruits and overripeness is correlated with the sum of ethyl butanoate, ethyl propanoate,

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M. Vanoiiet al. I PostharvestBiologyand Technology6 (1995) 225-234

0

10

20

30

40

50

days at 18% Fig. 6. Post-harvest production of (E)-Zhexenal from ‘Starkspur Golden’ apples picked on different dates (158 DAFB 0; 172 DAFB 0; 181 DAFB A).

ethyLZmethy1 propanoate, methyl butanoate, methyl-2-methyl butanoate, ethyl-2methyl butanoate and ethyl pentanoate (Patterson et al., 1974; Panasiuk et al., 1980; Paillard, 1981; Willaert et al., 1983). This indicates that apples picked 181 DAFB could be suitable for fresh marketing and not for storage. The apples picked at the commercial harvest (158 DAFB) produced the lowest amounts of aldehydes, alcohols and esters, thus showing a poor quality from the aroma point of view. After storage, the quality of these apples would worsen, because storing fruits in normal and controlled atmosphere depresses the production of volatiles (Dirinck et al., 1989; Visai et al., 1993). The full quality was reached 14 days later; in fact fruits picked 172 DAFB showed the highest amount and the best volatile composition. These fruits had a low content of butanoates and alcohols and a high content of acetate esters, responsible for the characteristic aroma of ‘Golden’ apples. Furthermore, only these fruits developed 3-penten-2-01 which is typical of ripe apples (Visai et al., 1993). Acetate esters are the major contributors for the perception of ‘Starkspur Golden’ apple flavor, and fruits picked 172 DAFB showed the highest amount of pentyl and hexyl acetate, whose odour thresholds are 0.005 and 0.002 ppm, respectively (Flath et al., 1967). From the organoleptic point of view, aldehydes are also important to apple aroma. The increasing quantity of (E)-Zhexenal that we found on the first day of post-

M. Vanoli et al. I Postharvest Biology and Technology 6 (1995) 225-234

0

10

20

30

233

40

days at 18T Fig. 7. Post-harvest production dates (158 DAFB 0; 172 DAFB

of acetaldehyde from 0; 181 DAFB A).

‘Starkspur

Golden’

apples

picked

on different

harvest ripening is particularly important for ‘Starkspur Golden’ apples because its amount is related with the aroma described as “ripe, aromatic and fruity” and has a relatively low odour threshold (0.017 ppm; Flath et al., 1967). In addition, we found that butyl and hexyl acetate reached their maximum when butanol and hexanol amounts were also maximal. Our data show, moreover, that butanol and hexanol concentrations affected the amounts of butyl and hexyl acetate produced by 158 and 172 DAFB apples. This relationship was not so evident for 181 DAFB fruits. The connection between alcohol and ester metabolism was studied by Knee and Hatfield (1981). They found that the lack of acetate formation in unripe and in controlled atmosphere stored Cox’s Orange Pippin apples were due to a deficiency of alcohols for ester formation, which could also be related to acetaldehyde concentration. Our findings show that when acetaldehyde was low in concentration, esters reached their maximum production. This relationship was observed at all the harvests, and in 181 DAFB apples acetaldehyde disappeared. De Pooter et al. (1987) explain this connection suggesting that apples are synthesizing esters also through aldehyde reduction. In conclusion, the analysis of volatile composition could give an accurate assessment of the ripening of ‘Starkspur Golden’ apples and it is able to provide some indication of the best use for these apples. In order to have good-quality apples, even after storage, an optimum harvest date of 172 DAFB should be aimed at.

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References Cunningham, D.G., Acree, TE., Barnard, J., Butts, R. and Braell, F!, 1986. Charm analysis of apple volatiles. Food Chem., 19: 137-147. De Pooter, H.L., Van Hacker, M.R. and Schamp, N.M., 1987. Aldehyde metabolism and the aroma quality of stored Golden Delicious apples. Phytochemistry, 26(l): 89-92. Dimick, P.S. and Hoskin, J.C., 1983. Review of apple flavor - state of the art. Crit. Rev. Food Sci. Nutr., 18: 387-409. Dirinck, I?, De Pooter, H. and Schamp, N., 1989. Aroma development in ripening fruits. In: R. Teranishi, R.G. Buttery and E Shaidi (Editors), Flavor Chemistry. Trends and Developments. ACS, Washington, D.C., pp. 23-34. Fellman, J.K., Mattheis, J.P., Patterson, M.E. and Chen, P.M., 1990. Volatile molecules within and around apples as a function of maturity. XXIII International Horticultural Congress, Firenze, 27 August-l September, 1990. Vol. 2, Abstract No. 3320. Fellman, J.K., Mattheis, J.P., Patterson, M.E., Mattinson, D.S. and Bostick, B.C., 1993. Study of ester biosynthesis in relation to harvest maturity and controlled atmosphere storage of apples (Malus domestica Borkh.). In: G.D. Blanpied (Editor), Proceedings, 6th International Controlled Atmosphere Research Conference, Cornell University, Ithaca, N.Y., June 15-17, 1993. pp. 500-507. Flath, R.A., Black, D.R., Guadagni, D.G., McFadden, W.H. and Schultz, TH., 1967. Identification and organoleptic evaluation of compounds in Delicious apple essence. J. Agric. Food Chem., 15(l): 29-35. Gorini, EL., 1983. Qualita e conservabilita delle mele. In: A. Monzini and E Lalatta (Editors), Monography No. D 6. Istituto per la Valorizzazione Tecnologica dei Prodotti Agricoli, Milano, pp. 45-47. Hansen, K., Poll, L. and Lewis, M.J., 1992. The influence of picking time on the post-harvest volatile ester production of ‘Jonagold’ apples. Lebensm. Wiss. Technol., 25: 451-456. Knee, M. and Hatfield, S.G.S., 1981. The metabolism of alcohols by apple fruit tissue. J. Sci. Food Agric., 32: 593-600. Paillard, N.M.M., 1981. Factors influencing flavour formation in fruits. In: P. Schreier (Editor), Flavour 81. Walter de Gruyter, Berlin, pp. 479-507. Panasiuk, O., Thlley, F.B. and Sapers, G.M., 1980. Correlation between aroma and volatile composition of McIntosh apples. J. Food Sci., 45: 989-991. Patterson, B., Hatfield, S. and Knee, M., 1974. Residual effects of controlled atmosphere storage on the production of volatile compounds by two varieties of apples. J. Sci. Food Agric., 25: 843-848. Rizzolo, A., Visai, C., De Micheli, L. and Rizzi, E., 1988. Sviluppo delle sostanze volatili durante l’accrescimento e la maturazione delle mele cv. ‘Starkspur Golden’. In: R. Jona (Editor), Proceedings, Symposium on Physiology of Fruit Drop, Ripening, Storage and Postharvest Processing Fruits, Torino, 3-4 October, 1988. pp. 174-178. Rizzolo, A., Polesello, A. and Teleky-Vamossy, Gy., 1989. CGC/sensory analysis of volatile compounds developed from ripening apple fruit. J. High Resolut. Chromatogr., 12: 824-827. Rizzolo, A., Polesello, A. and Polesello, S., 1992. Use of headspace CGC to study the development of volatile compounds in fresh fruits. J. High Resolut. Chromatogr., 15(7): 472-477. Rizzolo, A., Visai, C. and Vanoli, M., 1995. Volatile compounds during fruit ripening: state of the art. In: H. Bohling (Editor), COST 94 Workshop on: Ripening and Senescence, Federal Research Center for Nutrition, Karlsruhe, June 22-23, 1992 (in press). Visai, C., Rizzolo, A. and Vanoli, M., 1993. Sviluppo delle sostanze volatili nelle mele durante la conservazione. Riv. Frutticolt., 55(g): 57-60. Willaert, G.A., Dirinck, P.J., De Pooter, H.L. and Schamp, N.N., 1983. Objective measurement of aroma quality of Golden Delicious apples as a function of controlled atmosphere storage time. J. Agric. Food Chem., 31: 809-813.