Factors to consider when ripening avocado Mary Lu Arpaia Univ. of CA Riverside, CA mlarpaia@ucanr.edu Limitations to avocado postharvest handling v Time after harvest (fruit age) v Stage of ripeness more difficult to handle ripe fruit v Mismanagement at any point in the handling chain v Fruit maturity Time after harvest influences the percentage of unsound fruit % Unsound fruit (% threshold) 1 9 8 7 6 4 3 2 1 2 21 22 y = +.2762*exp(days/.23) r 2 =.82, n=, p<.1 22 24 26 28 3 32 34 36 38 4 42 44 Age when ripe (days) Dixon, Pak and Cutting What we know about the avocado and why it responds to ethylene A climacteric fruit showing an increase in respiration and ethylene production during ripening Influenced by maturity, time after harvest, temperature and atmosphere Adapted from Eaks (1978) for Hass ml CO 2 /kg/hr 1 1 Carbon Dioxide Ethylene 1 2 3 4 6 Days at 68F 4 3 2 1 ul C 2 H 4 /kg/hr 1
Susceptibility to low storage temperatures Body Rot Postharvest Diseases Stem End Rot External Chilling Injury Internal Chilling Injury Relationship between dry matter (maturity) and final peel color Why Ripen Avocados? Final Peel Color = 3.6261-.264DW +.2DW 2 where DW = Dry weight R2 =.621 *** Untreated, fruit ripening may range from a few days to even weeks within a carton 6... Peel Color 4. 4. 3. 3. 2. Actual Final Color Predicted Final Color 2. 1. 1. 1. 22.8 Dry Matter (%) Increase Uniformity Decrease Checkerboarding 2
18 16 14 12 1 8 6 4 Eaks, 198, JASHS (Harvest August - June) Maturity and days to ripe 2 Days to Soft 1 ppm propylene 1 2 3 4 6 7 8 9 1 11 12 13 14 1 16 17 Oil Content (%) no yes Average Days to Eating Ripeness (<1. lbf) in response to 24 hour treatment of 4 ppm ethylene. Days 1 1/2/ 3/7/ 4/18/ 6/1/ 7/11/ 8/22/ Harvest Date Ethylene hastens ripening regardless of stage of maturity 1 RAIN Ethylene NO YES Hass Seasonality/Quality Early Season Mid Season Late Season Ethylene treatment is highly recommended (checkerboarding) Fruit more prone to: Shriveling when ripe Decay Internal disorders Most susceptible to low temperature After ripe fruit may be: Not fully colored Watery texture Bland or grassy flavor Responds well to ethylene treatment Best fruit quality: No shriveling Little decay except when harvested after rain Most tolerant of long term storage After ripe fruit will be: Green-black to black in color Creamy texture Good to excellent flavor Little or no ethylene needed Fruit more prone to: Decay Internal disorders Difficult to store long term Uneven ripening Germinated seed After ripe fruit may be: Black in color Difficult to Peel Creamy to dry texture Full to rancid flavor Time after harvest Time after harvest 1 Ethylene has maximum benefit within 1-2 weeks of harvest Imported fruit if conventional shipment will need less time (24 hours or less) Imported fruit if CA shipped or 1-MCP treated may need longer treatment times Days to < 1. lbf 1 hr 24 hr 48 hr days 7 days 14 days Days at C 28 days Time after harvest decreases the impact of ethylene California Hass ; average of 3 harvests; 3 grower lots per harvest, 26 3
Even within lots of fruit there is variability in ripening a way to control this is sorting by degree of ripeness into different categories Suggested treatment times for California Hass avocados Early season fruit (November February) 36 72 hours Mid-season fruit (March June) 24 36 hours Late season fruit (July October) 8-24 hours +/- ethylene g 3 3g Management Issues Factors under your control Temperature Ventilation/Air exchanges ücareful Monitoring üprompt Movement of fruit üwhat is the proper stage of ripeness? üwhere do you ripen the fruit? Educate yourself about the potential differences between varying sources of fruit there are differences Pre-ripening inspection Ripening management Postripening management 4
Ripening Management Uniform heating and cooling is ABSOLUTELY ESSENTIAL Refrigeration needs to control the heat (6 BTU per pallet) Forced air ripening is critical (1 cfm/pallet) Venting (preferably flow through, keep CO 2 below 1%) Source of Ethylene as low as possible; physiologically you only need ~1 ppm but practically use 6-1ppm Fruit needs to be easily accessible in ripening room for monitoring; especially if fruit is of varying arrival condition or multiple lots of fruit Keep good records Can I use a banana ripening room for avocado ripening? Some considerations Peak Respiration (mg/kg-hr) Refrigeration Load (BTU/T-day) Can I use a banana room.. With some practical modifications 3 3 2 2 1 1 7 6 4 3 2 1 Refrigeration during ripening and cooling of fruit likely to be insufficient in a banana room Hot spots within pallet Uneven ripening Do not to overload the room Banana at 14C Banana at 18C Avocado at 2C Banana at 14C Banana at 18C Avocado at 2C
Ethylene dose considerations How much to apply? Ethylene concentration >2 ppm; no more than 1 ppm Fruit Maturity Less mature; longer treatment Time after Harvest With increasing time after harvest; shorter durations needed 1, 1 ppm 1 ppm ppm Source: I. L. Eaks, UC, Riverside Short exposures to ethylene can trigger ripening; threshold is believed to be around 1 ppm Commercial application of 6-1 ppm is recommended Temperature Management Avocados have a VERY high rate of respiration during ripening = HEAT Efficient warming/cooling of fruit essential Airflow essential to maintain proper pulp temperature (2C) Impact of high temperatures Delayed/uneven ripening Increased decay The impact of Temperature (24 or 48 hours) on ripening performance of Hass avocado Days to Ripe 16 14 12 1 8 6 4 2 d c The outcome is delayed or 2inhibited 2 3 3 Temperature (C) during 24 or 48 hr Holding 2 2 3 3 b Keep temperatures below 2 21 C Temperature (C) during 24 or 48 hr Holding a High temperatures are DETRIMENTAL ripening and increased decay No significant difference due to duration Stem End Rot (%) Body Rot (%) 3 3 2 2 1 1 2 1 1 c b bc b ab ab 2 2 3 3 Temperature (C) during 24 or 48 hr Holding a a 6
Hass Avocado Ripening Hass at different temperatures Ripening temperature influences final peel color Cox et al, 24, PH Biol. Tech. Days to Ripe 9 8 7 6 4 3 2 1 Days to Ripe Hue angle 1⁰C 18⁰C 2⁰C 23⁰C 2⁰C Ripening Temperature 8 83 81 79 77 7 73 71 69 67 6 Hue Angle Ripening Management When do you turn off the gas? You don t need the gas until ripe; a short duration treatment will trigger ripening Fruit may soften but may not color maturity and other factors involved The best way to gauge the rate of softening is with a penetrometer not your fingertips or buttons popping Fruit maturity is an important variable The penetrometer is a tool to judge the relative stage of ripeness How long can I hold ripe or partially ripe fruit? Fruit continue to soften in storage Partially ripened fruit held at F (1C) can develop pink staining especially if held longer than 1 week Fruit can be successfully held at 34F (1C) for up to a week Is there a difference in eating quality? 7
Managing Ripe Fruit Decay increases with increasing ripeness; accelerates in overripe fruit Don t hold fruit for long periods of time that are partially ripe increased chilling injury Bruising increases with advancing ripeness Protect fruit Peel color at slicing or guacamole ripe does not necessarily mean the fruit needs to be completely black! These are issues wherever fruit are ripened The outcome of ripe fruit Ripe fruit at retail level has greatly increased consumption, HOWEVER.. Greater challenge in temperature management Fruit sensitivity to damage greatly enhanced Considerations for successful avocado ripening Temperature management is CRITICAL Too high; ripening inhibited and increased decay Too low; ripening is slowed and lose benefit Fruit Maturity More mature; less time Time after Harvest After storage; less time Avoids delays in marketing Minimize fruit handling Checklist Know the history of the fruit Quality; don t use stressed fruit Standardize fruit size and maturity Uniform warming and cooling Careful monitoring; don t overripen CONSUMER/MARKET Education Additional information Contact me mlarpaia@ucanr.edu UC Davis Postharvest Center website http://postharvest.ucdavis.edu/ California Avocado Commission website http://www.californiaavocado.com/ripening-andhandling/ General information on avocados www.avocadosource.com 8
Hass Seasonality/Quality Early Season Mid Season Late Season Ethylene treatment is highly recommended (checkerboarding) Fruit more prone to: Shriveling when ripe Decay Internal disorders Most susceptible to low temperature After ripe fruit may be: Not fully colored Watery texture Bland or grassy flavor Responds well to ethylene treatment Best fruit quality: No shriveling Little decay except when harvested after rain Most tolerant of long term storage After ripe fruit will be: Green-black to black in color Creamy texture Good to excellent flavor Little or no ethylene needed Fruit more prone to: Decay Internal disorders Difficult to store long term Uneven ripening Germinated seed After ripe fruit may be: Black in color Difficult to Peel Creamy to dry texture Full to rancid flavor Back to the consumer - Flavor Relationship between oil and acceptability p p p Lee et al, 1983, J. Amer. Soc. Hort Sci. Minimum acceptable taste score = 7 Demonstrated close relationship between oil and dry matter p HASS variety n Oil content = 11.2% n Dry weight equivalent = 22.8% Taste and oil development during maturation of 'Fuerte' fruit grown at Irvine. Sensory panel analysis Avocado texture and acceptability Texture Flavor Overall acceptability Percent response 9
Avocado flavor and acceptability What is the effect of maturity on flavor and what drives these flavor changes? Harvests taken throughout the season Sweet also associated with higher hedonic scores but at lower levels of response (3%) Jan Avocado season All samples were ripened to a similar firmness Sept Analyzed samples from each harvest for sensory and quality attributes as well as aroma volatile content Changes in key sensory attributes and grassy volatile content associated with increasing maturity Summary 1. Avocados that were most liked by our sensory panelists were described as having a creamy, smooth, buttery texture with richness, nuttiness and a minimum of grassy flavor. 2. Avocados contain aroma volatiles that likely help determine the flavor 3. Aldehydes, such as hexanal, were clearly associated with grassy flavor 4. Ripening led to a decline in soluble carbohydrates and in a number of aroma volatiles, hexanal being the most prominent Avocados were more liked with increasing maturity This was associated with increased richness and creaminess and decreased grassiness The decrease in grassiness paralleled a decline in volatiles with grassy aromas 1