Effect of harvest maturity on decay and post-harvest life of ‘d'Anjou’ pear

Scientia Horticulturae, 31 (1987) 131-139

131

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Effect of H a r v e s t M a t u r i t y on D e c a y and PostH a r v e s t Life of 'd'Anjou' Pear D. BOONYAKIAT, P.M. CHEN, R.A. SPOTTS and D.G. RICHARDSON

Department of Horticulture and Mid-Columbia Agricultural Research and Extension Center, Oregon State University, Corvallis, OR 97331 (U.S.A.) Oregon State Agricultural Experiment Station Technical Paper No. 7839 (Accepted for publication 3 September 1986)

ABSTRACT Boonyakiat, D., Chen, P.M., Spotts, R.A. and Richardson, D.G., 1987. Effect of harvest maturity on decay and post-harvest life of'd'Anjou' pear. Scientia Hortic., 31: 131-139. 'D'Anjou' pear fruits (Pyrus communis L. ) were harvested at 3 times, 24 August, 8 September (commercial harvest date) and 30 September 1982. Late-harvested over-mature fruits were more susceptible to storage decay than immature and optimum-mature fruits. Mucor piriformis caused the highest storage decay, Botrytis cinerea the second and PeniciUium expansum the least. Fruits continued to increase in size during the harvesting period, but fruits harvested at the optimum maturity contained the highest percentage of suitable sizes (i.e. between 80 and 120 fruits per 20kg box) for marketing. Flesh firmness of fruits decreased during the harvesting period and in storage. Immature fruits always had the highest values of flesh firmness, optimum-mature fruits had the next and over-mature fruits the lowest at each corresponding sampling period during storage. Optimum-mature and over-mature fruits developed acceptable flesh texture, juiciness, and flavor upon ripening until February. Immature fruits were incapable of developing acceptable flavor upon ripening throughout the storage period. Superficial scald began to develop on the ripened fruits when taken from storage in December, and increased thereafter. Immature fruits showed a very high incidence of scald (98%) as compared to optimum-mature fruits (37 % ), while over-mature fruits were free from scald in December. All fruits, regardless of maturity, developed scald symptoms after February. The study suggested that 'd'Anjou' fruits should be harvested quickly when fruits reached the optimum maturity in order to reduce the susceptibility to decay, to gain optimum fruit sizes, and to ripen with an acceptable quality after storage. Keywords: Botrytis cinerea; dessert quality; flesh firmness; Mucor piriformis; pear; PeniciUium

expansum; Pyrus communis.

INTRODUCTION

It is generally known that immature pome fruits are more resistant to decay organisms than mature ones. Spotts (1985) showed that 'd'Anjou' and 'Bart0304-4238/87/$03.50

© 1987 Elsevier Science Publishers B.V.

132 lett' pear fruits inoculated with different decay organisms 3 and 4 months before harvest were highly resistant to decay, but susceptibility increased during the month before harvest. This pattern of decay resistance was also observed in apple (Wright and Smith, 1954; Edney, 1958; Sitterly and Shay, 1961) and in bananas (Sommer, 1982). The decrease in decay resistance during fruit maturation was though to be associated with the decrease in phenolic compounds (Ndubizu, 1976) and polygalacturonase inhibitors (Abu-Goukh, 1982). Spotts (1985) also reported that immature 'd'Anjou' and 'Bartlett' pear fruits were generally more resistant to decay than optimum mature fruits during cold storage at - 1 . 1 ° C. Optimum maturity of 'd'Anjou' fruits is commonly determined by a flesh firmness between 62.7 and 57.8N ( i.e. 15 and 13 lb f) ( Hansen and Mellenthin, 1979). The commercial harvesting period for 'd'Anjou' pear fruits in the Pacific Northwest may last as long as 3 weeks within a similar climatic location, which implies that pears are harvested at different stages of maturation. In some heavy crop-loading years, growers tend to pick fruits about 1 week prior to the optimum maturity. Information concerning the effect of early and late maturity of'd'Anjou' pears on susceptibility to decay during cold storage is not available. Although it is generally recognized that the rate of fruit enlargement decreases dramatically when fruit approaches optimum maturity, quantitative analysis of changes in fruit sizes for marketing purposes has not been repeorted. Lateharvested 'd'Anjou' fruits developed the capacity to ripen earlier than fruits harvested immature or at optimum-maturity, but late-harvested fruits tended to develop coarser texture and had shorter storage life than optimum-harvested fruits (Chen and Mellenthin, 1981 ). The objectives of this study were to determine the susceptibility of immature, optimum and over-mature 'd'Anjou' fruits to 3 decay organisms during cold storage; to measure the changes in fruit sizes between 2 weeks prior to, and 2 weeks after, optimum maturity; and to investigate the changes in dessert quality after cold storage. An attempt was made to elucidate an optimum harvesting period for 'd'Anjou' fruits that would minimize storage decay, maximize the percentage of proper marketing sizes, and maintain a long keepability with acceptable dessert quality. MATERIALSAND METHODS Nine uniform, mature 'd'Anjou' pear trees were selected from the same orchard of the Mid-Columbia Agricultural Research and Extension Center, Hood River, Oregon, U.S.A. They were randomly assigned to be harvested at 3 dates with 3 trees in each treatment. Harvest groups were subsequently referred to as Harvest I (24 August), II (8 September) and III (30 September 1982). The initial date for commercial harvest was on 8 September, as determined by a flesh firmness of 62.3N. Therefore, Harvest I was referred to as

133

immature fruit, Harvest II as optimum-mature fruit and Harvest III as overmature fruit. Fruit sizes were manifested into Size 50 or larger, Sizes 60, 70, 80, 90, 100, 110, 120, 135, 150 and 165, and Size 180 or smaller, based on counts to fill a standard 20-kg box. The number of fruits in each size category were counted for each tree at each harvest, and the percentage of fruits in each size category was calculated. The mean percentage of each size category from 3 trees at each harvest was used to compare the changes in fruit sizes among 3 different harvest dates. Fruits were then stored in 20-kg wooden boxes with perforated polyethylene liners at - 1.1 °C in air until used. On 30 September, 8 boxes of fruits from each tree at each harvest date were divided into 4 groups with 2 boxes per group. Fruits from each group were separately immersed into each of the following decay fungal inoculum: Penicillium expansum Lk ex Thorn., Botrytis cinerea Per ex Ft. and Mucor piriformis Fischer, all isolated from decaying pear fruits, with distilled water as a control. Each inoculum had a concentration of 1 X 104 conidia ml-1. After a 1min immersion, fruits were air-dried at room temperature and put back into the wooden boxes with polyliners and stored at - 1.1 ° C in air. The numbers of decayed fruits from each tree at each harvest date were evaluated on 1 December 1982, and 1 February and 1 April 1983. Decayed fruits were discarded at each evaluation date. The number of decayed fruits were pooled from the 3 evaluation dates for each treatment at each harvest date. The incidence of fruit decay caused by each decay organism was expressed as percentage of fruits decayed for each harvest group. A split-split plot design was used for analysis of the decay incidences. Types of inoculum were the main plot and harvest dates were sub-plots. Each effect and interaction was tested by analysis of variance. Treatment means were separated by Duncan's multiple range test. Beginning on 1 October 1982 and continuing on the first of each calendar month, 20 fruits per tree at each harvest date were removed from cold storage to evaluate fruit condition and ripening quality. Ten fruits from each tree at each harvest date were used to determine flesh firmness immediately after removal from cold storage. The remaining 10 fruits were ripened at 20 ( + 1 ) ° C and 92 ( + 2 ) % relative humidity for 10 days. After 10 days of ripening, the development of superficial scald symptoms on each fruit was evaluated and categorized into 5 ranks of severity: clear; very slight; slight; moderate; severe. Any fruit ranked from slight to severe was considered as commercially unacceptable and the percentage of scalded fruits in each harvest group for each evaluation period was determined. After the evaluation of scald symptoms, flesh firmness of each ripened fruit was measured by a UC firmness tester with an 8-mm plunger and 3 punches per pared fruit. After the determination of flesh firmness, 5 ripened fruits per tree were randomly selected for the evaluation of dessert quality. Dessert quality of ripened fruits was evaluated organoleptically by the authors and rated for flesh texture,

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Fig. 1. Percentagefruit decayamongthree harvest groups in 1982 after storage for 6 months at 1.1°C. Valuesfollowedby the same letter(s) are not significantlydifferentaccordingto Duncan's multiplerangetest (P=0.05). Harvest I, 24 August;Harvest II, 8 September;Harvest III, 30 September. -

juiciness and flavor. Each quality category was divided into a 5-point scale according to Cloninger and Baldwin (1976), with 5 representing the highest quality and 1 the lowest. Statistical analysis for flesh firmness, scald and dessert quality was done using a 3 X 7 X 2 factorial experiment including 3 harvest dates, 7 sampling periods and 2 states of ripening ( except for scald and dessert quality which had only one state of ripening). Each tree was considered as a replicate, and therefore each treatment had 3 replicates. Each effect and interaction was tested by analysis of variance. Treatment means were separated by Least Significant Difference (LSD) at the 5% level. RESULTS AND DISCUSSION Storage decay. - Fruit maturity and the type of decay organisms significantly affected storage decay of 'd'Anjou' pear fruits ( Fig. 1 ). M. piriformis (mucor rot) caused the highest percentage (about 27% ) of decay in fruits immersed in inoculum. Primary infection usually occurred at the stem end of the pear. Secondary infection occurred at the point of contact between sound and decayed pears. B. cinerea caused 15% and P. expansum caused 7% decay. The secondary spread of Mucor rot may have occurred more rapidly than that of B. cinerea and P. expansum because Mucor-infected pear tissue broke down and released liquid which was full of Mucor conidia. Bertrand and Saulie-Carter (1980) suggested that secondary infection occurred when the liquid produced from the disintegration of decaying tissues contacted sound fruits. Decay of inoculated fruits was highest in Harvest III groups for all three fungi (Fig. 1 ). Wallace et al. (1962) suggested that the water-insoluble material in immature fruits

135 TABLE I Distribution of fruit sizes in 3 harvest groups in 1982 expressedas a percentageby number of fruits Size (fruit number per 20-kg box)

Harvest I (24 August) {To)

Harvest II (8 September) (To)

Harvest III (30 September) (To)

50 60 70 Sub-total

0.0 0.0 0.3 0.3

0.7 0.8 7.0 8.5

1.1 11.5 30.2 42.9

80 90 100 110 120 Sub-total

0.8 5.7 13.8 22.5 24.8 67.6

18.3 25.1 21.8 13.7 8.7 87.5

27.9 18.9 6.5 2.2 1.2 56.8

135 150 165 180 Sub-total

18.7 8.3 4.0 1.1 32.1

2.5 1.0 0.4 0.2 4.1

0.2 0.1 0.0 0.0 0.3

was greater t h a n in mature fruits, indicating t h a t pectin from immature fruits was more "sterically hindered", or less accessible, t h a n from mature fruits. Therefore, pectin from immature fruits would be less readily utilized by fungi as a carbon source. Furthermore, premature fruits might also contain higher amounts of anti-fungal substances such as phenolics and polygalacturonase inhibitors ( Ndubizu, 1976; Abu-Goukh 1982 ). This could account for less storage decay in immature fruits t h a n in mature ones. Percentage decay in noninoculated (control) fruits in this study was low (Fig. 1 ). s i z e . - The premium sizes from commercial pack-out ranged from Size 80 to 120 for the best marketing price. Harvest II fruits had 87.5% fruit in the premium sizes, while Harvests I and III fruits had only 67.6 and 56.8%, respectively, with more fruits in the sizes larger t h a n 80's for Harvest III ( Table I). Therefore, most of the fruits contained in the Harvest II group were of suitable size for marketing. Fruit

- Flesh firmness (FF) decreased with harvests, from 70 newtons for Harvest I to 55 newtons for Harvest III (Fig. 2 ). During cold storage, FF of Harvest I fruits declined at a higher rate t h a n those of Harvests II and III, and reached an FF similar to Harvest II after the storage m o n t h of March Flesh firmness.

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Fig. 2. Changes in flesh firmness during storage at - 1.1 °C of 'd'Anjou' pears harvested at three dates, and after 10 days ripening at 20 ° C. (Fig. 2 ) . FF o f H a r v e s t III w a s a l w a y s l o w e r t h a n t h o s e o f H a r v e s t s I a n d II t h r o u g h o u t t h e storage period. FF o f H a r v e s t III at h a r v e s t w a s b e l o w t h e optim u m r e c o m m e n d e d range. Fruits f r o m H a r v e s t III were easily w o u n d e d a n d therefore m i g h t be m o r e susceptible to i n f e c t i o n . R e g a r d l e s s o f h a r v e s t m a t u rity a n d storage period, fruits s o f t e n e d to b e t w e e n 12 a n d 7 n e w t o n s u p o n ripe n i n g (Fig. 2 ) . !

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Fig. 4. Changes in flesh juiciness during storage at - 1.1 °C and ripening at 20 °C for 10 days of 'd'Anjou' pears harvested at three dates. 5=juicy; 4=moderately juicy; 3=slightly juicy; 2 = moderately dry; 1 = dry. I

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Fig. 5. Changes in flesh flavor during storage at - 1 . 1 ° C and ripening at 20°C for 10 days of 'd'Anjou' pears harvested at three dates. 5 = excellent; 4 = good; 3 = fair; 2 = poor; 1 = unacceptable. q u a l i t y . - Texture of ripened fruits was scored about 3 or above between the storage months of October and January, but decreased to about 2 or less after February (Fig. 3 ). Texture of ripened fruits from Harvest II was scored slightly higher than those from Harvests I and III between the storage months of October and January, perhaps due to a favorable balance between pectins and cellulose, but dropped to the same low score as Harvests I and III after February (Fig. 3 ). Juiciness of ripened fruits was also scored about 3 or above between October and January, but dropped rapidly thereafter, irrespective of the different harvests (Fig. 4). Flavor of ripened fruits from Harvest I was Dessert

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scored only about 2 or lower throughout the sampling period (Fig. 5). Flavor of ripened fruits from Harvest II improved from 2.5 to 4 between the storage months of October and January, but that from Harvest III maintained the score of 4 throughout the same sampling period (Fig. 5 ). Thereafter, flavor of ripened fruits from both Harvests II and III decreased rapidly and reached about 2 or lower after March (Fig. 5). - Fruits developed scald symptoms after about 3 months storage, and these symptoms appeared on fruits that were ripened at 20 QC for several days. Scald incidence of fruits from Harvests I and II first appeared on 10 December, at 93 and 33%, respectively ( Fig. 6). For Harvest III fruits, scald symptoms first developed on 10 January at 75% (Fig. 6). Beginning on 10 February 1983, all harvest groups showed 100% scald symptoms throughout the remaining storage period (Fig. 6). Our results clearly showed that storage time is involved in scald symptom development. Meigh (1970) suggested that the oxidation of a-farnesene, which accumulates in the epidermal layers of apple fruits during long-term cold storage, might cause scald. During the 3 months after harvest, the oxidation of a-farnesene may approach the level that can cause scald. Scald development.

CONCLUSIONS

Although Harvest I fruits had very low decay incidence, they developed poor dessert quality, especially poor flavor, and contained many undersized fruits. Harvest III fruits would require early marketing because this group had the highest incidence of decay and the softest flesh firmness in storage. Harvest II

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fruits appeared to be the optimum maturity for commercial harvest that would provide fruits with moderate decay resistance during storage, proper fruit sizes for profitable marketing, and good keepability with acceptable dessert quality. Therefore, the study suggested that 'd'Anjou' fruits should be harvested quickly when fruit reached optimum maturity.

REFERENCES Abu-Goukh, A.A., 1982. Polygalacturonase inhibitors in the 'Bartlett' pear. Ph.D. Thesis, University of California, Davis, 154 pp. Bertrand, P. and Saulie-Carter, J., 1980. Mucor rot of pears and apples. Spec. Rep. 508, Agric. Exp. Stn., Oregon State University, 21 pp. Chen, P.M. and Mellenthin, W.M., 1981. Effects of harvest date on ripening capacity and postharvest life of 'd'Anjou' pears. J. Am. Soc. Hortic. Sci., 106: 38-42. Cloninger, M.R. and Baldwin, R.E., 1976. Analysis of sensory rating scales. J. Food Sci., 41: 1225-1228. Edney, K.L., 1958. Observations on the infection of Cox's orange pippin apples by Gloeosporium perennans Zeller and Childs. Ann. Appl. Biol., 46: 622-629. Hansen, E. and Mellenthin, W.M., 1979. Commercial handling and storage practices for winter pears. Spec. Rep. 550, Agric. Exp. Stn., Oregon State University, 12 pp. Meigh, D.F., 1970. Apple scald. In: A.C. Hulme (Editor), The Biochemistry of Fruits and their Products. Academic Press, New York, pp. 555-569. Ndubizu, T.O.C., 1976. Relations of phenolic inhibitor to resistance of immature apple fruit to rot. J. Hortic. Sci., 51: 311-319. Sitterly, W.R. and Shay, J.R., 1961. Physiological factors affecting the onset of susceptibility of apple fruit to rotting fungus pathogens. Phytopathology, 50: 91-93. Sommer, N.F., 1982. Postharvest handling practices and postharvest diseases of fruit. Plant Dis., 66: 357-362. Spotts, R.A., 1985. Effect of preharvest pear fruit maturity on decay resistance. Plant Dis., 69: 388-390. Wallace, J., Kuc, J. and Duaudt, H.N., 1962. Biochemical changes in the water-insoluble materials of mature apple and their possible relationship to disease resistance. Phytopathology, 52: 1023-1027. Wright, T.R. and Smith, E., 1954. Relation of bruising and other factors to blue mold decay of Delicious apples. U.S. Dep. Agric. Circ. 935, 15 pp.