Preliminary Report on the Feasibility of ‘Snap’ Harvesting ‘Hass’ Avocado

 

Mary Lu Arpaia

Dept. of Botany and Plant Sciences, University of California, Riverside

 

Reuben Hofshi

Del Rey Avocado, Fallbrook, CA

 

Traditionally, the California avocado industry has ‘clipped’ harvested avocados.  It is possible, however, to detach the fruit from the tree by ‘snapping’, leaving the stem-end exposed.  This is accomplished by pulling or twisting the fruit at the stem.  The avocado industries in Israel and South Africa have adopted the commercial use of ‘snap’ harvesting ‘Hass’ avocado fruit and some other varieties.  The feasibility of ‘snap’ harvesting ‘Hass’ avocado is also being evaluated in New Zealand (Woolf et al., 1997).

 

The reasons for converting to ‘snap’ harvesting are numerous.  Most importantly, there can be a considerable labor savings since the process of ‘snap’ harvesting is more time efficient especially when harvesting without ladders or picking poles.  In this situation an estimated 30 to 50% can be saved in picking costs (Allan Woolf (New Zealand), H. Arditi (Israel), personal communication).  ‘Clip’ harvesting fruit can also result in mechanical injury at the stem-end, which can result in downgrading at the packinghouse.  During the early part of the commercial season many growers will repetitively size pick their groves.  This coincides to a time when the pool of potential pickers is limited.  ‘Snap’ harvesting could increase the efficiency of the worker since a fruit is picked with only one step rather than multiple movements.  Another reason to explore the feasibility of ‘snap’ harvesting is the likelihood that worker safety issues (carpel tunnel syndrome associated with prolonged repetitive motion) may trigger the banning of fruit ‘clipping’ in the future (J. Miles, Dept. of Agricultural Engineering, UC, Davis; personal communication).

 

Fruit quality concerns, however, have been raised concerning ‘snap’ harvested fruit, foremost, an association with the occurrence of stem-end rots following fruit ripening.  This has been documented to occur in New Zealand (Hartill and Sale, 1991, Woolf et al, 1997).  On the other hand, other researchers have found no increase in stem-end rots when fruit were ‘snapped’ rather than ‘clipped’ harvested (Muirhead, 1984, Zauberman et al., 1971 and Kohne and Kremer-Kohne, 1995).  Another possible problem is the potential for skin tearing resulting from ‘snap’ harvesting.  H. Arditi estimated that in Israel no more than 5% of ‘Fuerte’ fruit show tearing at the stem-end, while no ‘Hass’ fruit show tearing.  Finally, some CA industry representatives have raised the concern of the potential impact of ‘snap’ harvesting on the “Ripe for Tonight” program, since one of the tools currently employed to assess the progress of fruit ripening is “popping the button off.”

 

We undertook a preliminary study in July 1997 to evaluate the potential of ‘snap’ harvesting ‘Hass’ avocado fruit.  Fruit were obtained from five mature commercial groves in northern San Diego County.  These groves were of various ages and conditions and were located in Rainbow, Rainbow-Pala, Pauma Valley, and Bonsall (2 sites).  Equal numbers (60 fruit) of ‘clipped’ and ‘snapped’ fruit were obtained from the same group of trees in each grove.  ‘Green’ colored fruit of similar size and weight were selected at all sites.  All fruit were picked within a 6 hour period and then held at 5ºC (41ºF) overnight.  The fruit were then transported to the UC Kearney Agricultural Center in Parlier at ambient temperature the following morning.  They were sorted for defects and uniformity of size and randomly assigned to one of two postharvest treatments.  Twenty-five fruit per harvesting method per grower lot were treated with ethylene (50 ppm) for 24 hours at 20ºC (68ºF) and then allowed to ripen.  The remaining fruit were stored at 5ºC (41ºF) for 4 weeks then ripened at 20ºC without ethylene.  Relative Humidity during storage and ripening ranged from 85 to 90%.  Once placed at 20ºC, the fruit were monitored daily for the stage of ripeness (by touch).  Once determined as ‘ripe by touch’ the fruit were weighed to determine weight loss.  Their firmness was then measured using a UC Pressure Tester (7-mm tip) to verify ripeness.  Fruit were considered ‘firm ripe’ once they reached a firmness of 1.5 lbf.  Using this method, the average ‘ripe’ firmness ranged from 0.5  to 1.5 lbf.  At this point, the following fruit quality parameters were visually assessed: external and internal appearance (0 - 5), external shriveling (1 - 4), vascular discoloration (1 - 4), ease of peeling (0 - 4), flesh adhesion to the seed (0 - 4) and decay (presence or absence).  In all cases, a low rating is more desirable.  We also tallied the days to ripeness for individual fruit so that we could determine if the method of harvesting influenced the ripening rate. 

 

Table 1 reports the results of this one-year study.  The data is presented from two perspectives, harvesting method and storage duration.  When the harvesting method is considered, no significant differences were observed in fruit quality except for the incidence of decay.  In this study, we observed a significantly higher level of decay (primarily stem-end decay) in the ‘clipped’ fruit.  This contrasts with the data from New Zealand which reported an increase in stem-end decay following ‘snap’ harvesting (Hartill and Sale, 1991, Woolf et al, 1997).  These results also differ from the results of others (Muirhead, 1984, Zauberman et al., 1971 and Kohne and Kremer-Kohne, 1995) who reported no difference in decay levels between ‘snapped’ and ‘clipped’ fruit.

 

The data in Table 1 is also presented from the perspective of storage duration.  In this case, a number of significant differences were detected.  Not surprisingly, the fruit following 4 weeks of storage, even without the application of ethylene to stimulate ripening, took less time to ripen.  There was a slight but significant difference in weight loss following fruit ripening with the stored fruit having higher weight loss.  This difference, however, did not carry over to the amount of fruit shrivel that was observed following ripening.  Lower weight loss at 0 weeks also did not result in a lower percentage of fruit having difficulty in peeling.  The relative difficulty in peeling was assessed by peeling approximately ¼ of the fruit and rating the adhesion of the flesh to the peel and peel breakage during this process.  In this study we also noted significantly less external discoloration following ripening.  This discoloration is primarily associated with lenticel darkening.  The higher percentage of discoloration in fruit not stored but immediately ripened following harvest may be related to the fairly long ripening time (approximately 11 days).  In addition, some fruit without storage did not turn completely black with ripening; thus, any external problem would be more evident.  Flesh adhesion to the seed when the fruit halves were separated was a significantly greater problem following storage.  This may be due to the long storage duration (4 weeks), however, fruit were not evaluated at shorter intervals to adequately evaluate this aspect of quality.  A 4-week storage period is approximately the maximum time one would want to store avocados.  The fruit following 4 weeks of storage were ‘drier’ in appearance and did not appear as creamy.  This may have contributed to more flesh adhering to the seed.  Finally, we observed significantly less decay following storage.  This agrees with other data collected by M. L. Arpaia over the years where less overall fruit decay has been observed following 5ºC fruit storage.  The reason for less decay following storage has no clear explanation.

 

We did not detect any significant harvest - storage interactions, however, we did observe significant differences between grower lots pertaining to weight loss and difficulty in peeling.  The absence of significant ‘harvesting method’ by ‘weeks at 5ºC’ interactions implies that neither aspect of the study influenced the other. 

 

In conclusion, the results of this preliminary study indicated that it is possible to successfully ‘snap’ harvest California ‘Hass’ avocado fruit even during the latter part of the commercial harvesting season.  We expanded this project during the 1997 - 1998 harvesting season to include multiple harvests throughout the season, different growing areas (Ventura and San Diego counties) and varieties.  This continuation project has been funded through the California Avocado Commission Production Research Committee.  We will report the results of this study in an upcoming article.  If these results support the findings reported here, we will follow up with a commercial scale trial.  If ‘snap’ harvesting is successful, the California avocado grower will have a possible way to reduce harvesting costs.

 

References

 

Hartill, W. F. T. and P. R. Sale.  1991.  Report to the avocado growers research committee on a comparison of the incidence of post-harvest rots in plucked and clipped fruits.  DSIR Plant Protection Client Report, May 1991.

Kohne, J. S. and S. Kremer-Kohne.  1995.  Picking Hass avocados without pedicel.  South African Avocado Growers’ Yearbook.  18: 66.

Muirhead, I. F.  1984.  Effects of harvesting method on quality of ‘Hass’ avocados, with particular reference to stem-end rot.  Queensland Dept. Primary Industries Internal Report (Brisbane).

Woolf, A. B., McLeod, D. L., Roughan, S. and Yearsley, C. W.  1997.  Postharvest Research 1996/97: Effect of snap picking on fruit quality and shelf life.  HortResearch Client Report No. 97/52.

Zauberman, G., Schiffman-Nadel, M., Yanko, U. and Homski, S.  1971.  Experiments in storing avocado, mango and annona fruits.  The Volcani Institute of Agricultural Research, Preliminary Report 705.

 

 

Table 1.  Evaluation of the potential of ‘Snap’ harvesting of ‘Hass’ avocado.  Fruit harvested in July 1997 from San Diego County.  Average days to ‘firm ripe’, weight loss following ripening and the percentage of fruit exhibiting shriveling, difficulty in peeling, external discoloration, flesh adhesion to the seed and decay.
	Days  to Ripe	Weight  Loss  (%)	Shrivel (%)	Difficulty in Peeling (%)	External Discoloration  (%)	Flesh Adhesion to Seed (%)	Decay (%)
Harvesting Method
Clipped	7.7	4.6	11.2	45.8	20.8	48.8	38.3
Snapped	7.7	4.4	24.6	55.4	17.9	43.8	15.0
	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	**
Weeks at 5ºC (41ºF)
0	11.6	4.3	20.0	57.5	35.4	15.4	42.5
4	3.8	4.7	15.8	43.8	3.3	77.1	10.8
	***	**	n.s.	*	***	***	***
Harvesting Method x Weeks at 5ºC Interaction
	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.
Grower Effects
	n.s.	***	n.s.	***	n.s.	n.s.	n.s.
n.s., not significant; *, **, *** = Probability of statistical differences at P < 0.05, 0.01, and 0.001, respectively. Analysis of ‘Days to Ripe’ based on square root transformation. Data for ‘Harvesting Method’ represents average of both storage duration and all growers. Data for ‘Weeks at 5ºC (41ºF)’ represents average of both harvesting methods and all growers. Data for % Decay includes both stem-end decay and other decay lesions on peel and in flesh.