2012 grower manual - avocado industry council - new...

Avocado Growers Manual Postharvesting Handling

Postharvest

Handling

© Copyright NZ Avocado Growers Association August 2001 PG 1 of 10

Main Points

� Avocados are a �living� fruit that willdeteriorate very quickly if not handled gently

� Avocados are sensitive to ethylene, do notstore with other fruit such as apples orbananas

� For best quality ripen avocados �thecontrolled way�

� Storage temperature depends on stage ofripeness

� Avocados are packed and exportedaccording to market requirements

� Quality in the marketplace depends ongrowing history, how the fruit are handledduring transit to the market and retailhandling practices

Avocado fruit despite appearing hard and resilient

require careful handling after harvest, during packing

and while in transit to their point of sale. The postharvest

handling of the fruit is an important final step in the

overall process of growing avocado trees and producing

a crop. Once the fruit are harvested their quality is set;

the fruit quality cannot be improved but can be

successfully maintained after packing, in storage and in

transit to the market. Significant losses in fruit and fruit

quality can occur after harvest if the fruit are not handled

correctly. It is not enough to have a high yield of good

quality fruit that the market wants; the fruit also have to

get to the market in good condition. This chapter

describes the processes that avocados currently undergo

during packing and transport to export markets. In

addition the reasons why avocado fruit quality

deteriorates after harvest are explained.

RipeningTo understand the processes of how avocados deteriorate

after harvest it is important to understand the ripening

process of the fruit. Avocado fruit are unusual in that

they only ripen after removal from the tree. This is the

reason why fruit can hang on the tree for a long time

after they become �mature� and remain capable of

ripening to an acceptable eating standard.

Ripening is the term used to describe the changes that

occur when avocado fruit change from being hard and

inedible to soft and edible. While on the tree, a ripening

inhibitor prevents the fruit ripening by making the fruit

insensitive to ethylene (the fruit ripening gas). Once

harvested the influence of the ripening inhibitor is

removed. This is thought to be related to the fruit losing

a certain amount of water before they become sensitive

to ethylene which takes between one to three days after

which ripening can begin.

Many internal changes occur as the fruit softens.

Ripening can be affected by temperature and, to a lesser

extent, air circulation and gas exchange around the fruit.

During ripening avocados are respiring producing

carbon dioxide, using up oxygen and producing ethylene.

A build up of carbon dioxide can retard or inhibit normal

ripening while ethylene can promote ripening.

Ethylene is a gas produced naturally by plants that starts

the avocado ripening process. Once started, the ethylene

produced stimulates further ethylene production

speeding up the ripening process. Avocado fruit, once

sensitive to ethylene, can start ripening rapidly after

exposure to as little as 0.1 parts per million (ppm) of

ethylene. Once ripening avocado fruit can produce up

100 ppm of ethylene per hour and ethylene levels in

coolstore containing ripe avocados have been recorded

to range from 0.1 ppm to as high as 1.8 ppm. The

production of ethylene and response of avocados to

ethylene depends on temperature, for example ethylene

production is considerably greater at 20 to 21°C than at

cold storage temperatures of 5 to 6°C.

Avocados are also known as climacteric fruit, which

means that as part of the ripening process, they undergo

a period of very active metabolic activity (respiration)

that corresponds to softening. The climacteric period is

affected by fruit maturity (as measured by oil content),

water loss, temperature, levels of carbon dioxide and

oxygen in the fruits environment, exposure to ethylene

(which triggers and accelerates the process) and physical

Postharvest Handling Avocado Growers Manual

PG 2 of 10 August 2001 © Copyright NZ Avocado Growers Association

damage or presence of rot on the fruit. The climacteric

can be delayed for some time by coolstorage and

removal of ethylene sources. Once the climacteric is

initiated, which is required for the fruit to soften and

become edible, it cannot be stopped and may only be

slowed. The ripening process is irreversible and once

complete the fruit has a limited time in which it can be

consumed before it rots.

Stage of fruit ripenessThe ripening of avocados can be described in a number

of stages. They are:

� Green mature

� Ripening

� Sprung

� Ready-to-eat ripe

� Over-ripe

It is important to be able to identify the stage of ripeness

the avocado fruit has reached in the postharvest handling

chain, as the fruit require different handling and storage

at the various stages of ripeness.

Green mature: following harvest, avocado fruit pass

through a �lag� period where they do not undergo any

changes after which ripening begins. The length of the

�lag� period depends on fruit maturity and can last from

one to seven days. Early season fruit with low dry matter

has a longer green mature stage than later season fruit

with higher dry matter. Delaying the onset of ripening

can be achieved by prolonging the green mature stage

using coolstorage at 5 to 6°C. The cold room should be

well ventilated to prevent the build-up of ethylene.

Ripening: the green mature fruit are producing ethylene

and have an increased respiration rate until the fruit are

sprung. This takes from 3 to 4 days at temperatures

around 20°C. At this stage the fruit are more susceptible

to chilling injury than at the green mature stage. For

example, if the pulp temperature drops below 12°C for

more than a very short time chilling injury symptoms

will develop inside the fruit.

Sprung fruit: is when softening can be easily detected

by hand. Sprung fruit can be stored at 3 to 4°C for up to

2 weeks. At this stage avocados bruise easily but visible

signs of bruising cannot be seen until the fruit is cut. Do

not drop or knock trays, or handle fruit roughly to avoid

bruising. Just sprung fruit still take another 2 to 6 days

before they are eating ripe if held above 15°C.

Eating ripe: once the fruit feels soft and pliable it is

eating ripe. Avocados ready to eat can quickly become

over-ripe if they are kept too warm. Special care is

needed with soft, ripe avocados. The fruit bruise readily

and should be treated delicately and excessive handling

should be avoided. Fruit at the bottom of stacks or piles

will be bruised.

RECOMMENDED TEMPERATURE GUIDELINES

Maturity Stage Storage Temp Maximum Storage

°C Time

Green mature 5 - 6 28 days from harvest

During ripening 15 - 16 3 - 4 days

Sprung to eating ripe 3 - 4 7 - 14 days

ambient 1 - 3 days

Eating ripe 3 - 4 7 days

Ripening and temperatureThe rate at which avocado fruit ripen depends on two

factors: the temperature after picking and during

ripening, and the maturity of the fruit when harvested.

Ripening is faster the higher the temperature. For

example, fruit held at 17°C may take 14 days to ripen,

while at 25°C the ripening period would be reduced to

about 8 days.

The temperature during the various stages of ripening

has a major effect on disease development and eating

quality. Once avocados start to ripen, rots (usually

caused by the anthracnose fungus) that are dormant and

prevented from growing due to inhibitors in the fruit

begin to develop. The extent and rate of development

of rot depends on the temperature. The temperature at

ripening should be set at a level that allows the fruit to

soften more quickly than the rots grow. For this reason

a ripening temperature of between 16 to 18°C is

recommended when ripening New Zealand avocados.

Controlled ripeningControlled ripening of avocados is the process where

fruit are exposed to a controlled amount of ethylene at a

set temperature, relative humidity and air circulation in

a ripening room. Providing ripened fruit for retail can

increase sales of avocados. For many consumers, hard

unripened avocados are not an attractive or even

acceptable product.

Together, ripening temperatures and the presence of

ethylene greatly influence ripe fruit quality. Controlled

ripening using ethylene at temperatures from 15 to 16°C

enhances the ripening process. It reduces the

development, incidence and severity of ripe-fruit rots

and presents a ripe acceptable product to the consumer.

Controlled ripening also reduces abnormal and uneven

ripening problems by eliminating the random natural

ripening that occurs between avocados in the same tray

and allows for a shortening of the natural ripening time.



If the fruit are held at 3 to 4°C once sprung, shelf life

should not be affected. Care must be taken not to remove

sprung fruit to a high temperature as this causes an

increase in disease levels and abnormal ripening. If the

fruit are removed and cooled to temperatures below

12°C when ripening, but before they are sprung, the fruit

are susceptible to chilling injury. Ripening fruit should

be kept at the temperature at which they are ripening to

avoid development of disorders.

Softening of avocados treated with ethylene (red line) compared to

softening of untreated avocados (black line) at 15°C (adapted from

Woolf, McLeod, Roughan, Burdon and White, 1997).

The important points to note are:

� Two days of exposure to ethylene is sufficient to

trigger ripening in avocados

� After 2 days of gassing, firmness will vary from hard

to just sprung

� Avocados will not be eating ripe on removal from

the ripening room

� Fruit will be eating ripe after another 2 to 6 days

following the sprung stage if kept at 15 to 16°C or

above

� Sometimes the fruit are eating ripe 3 days after

gassing but the ripening time could be as long as 8

days if fruit maturity is not advanced

� After storage for 2 weeks or more, time from gassing

to eating ripe is less than that for unstored fruit

� The later ethylene is applied after harvest to green

mature fruit, the more uniform the ripening of fruit

within a tray

� Similar techniques of controlled ripening are used

for other tropical and subtropical fruits

� Ripening rooms used for bananas are also suitable

for avocados

Packing operationFollowing harvest fruit is transported to a Packhouse

where it typically goes through the process described

below. There are usually slight differences between how

each individual pack shed grades and packs avocados.

Bins full of fruit are stacked in a cool area prior to tipping

fruit onto the packline. Once the fruit is gently tipped

out, a series of conveyor belts and rollers, transport the

fruit through a washer unit in some cases, a series of

soft brushes in others, or a combination of both, before

the fruit passes over the grading table. A few sheds also

apply wax to enhance the shine of the peel, but this is

not a statutory requirement.

Bins of fruit kept in a cool area before packing

Tipping of fruit onto grader

No ethylene

Ethylene

120

100

80

60

40

20

0

Fir

mo

mete

r valu

e

Days after treatment

0 2 4 6 8 10 12 14 16 18



Trained grading staff inspects individual fruit for external

defects and cull out any fruit found not complying with

the �Avocado Industry Export Grade Standards� (that is

set by a committee each year). Cull fruit are often graded

again for local market.

Export quality fruit then passes over a �singulator� that

separates and aligns fruit to pass onto the mass grader.

Mass graders can be between 1 and 6 lanes wide and

consist of a series of chain-mounted and driven weighing

cups, all moving parallel to one another with a variable

speed control. As each full cup passes over an electronic

weighing station early in the grader line, its weight is

measured and this information is fed into the grader

computer, which in turn activates a switch to tilt the cup

at the correct drop point.

Fruit are then either conveyed to bins or accumulate in

padded areas below the grader, while packing staff

places this fruit into single layer trays or double layer

lugs. Once filled, trays are stacked and strapped onto

pallets, which are then placed into cold rooms to await

transport to the port or arrival of containers.

Temperature managementEven under absolutely ideal handling and storage

conditions, avocados will eventually age (senesce) and

decay. Being such a highly perishable fruit, avocado

quality is therefore heavily affected by a combination

of time and temperature.

The shorter the time from harvest to arrival in the market,

the better the chance of good quality fruit. Combining

short storage time with correct temperatures during

storage (and in some cases, using controlled atmosphere

storage) will maximise the chances of maintaining good

fruit quality.

Air temperatures can vary enormously during the harvest

period and even during the course of the same day.

Avocado fruit, being dark-green skinned, can easily

absorb heat and this heat must be removed or reduced

after picking to delay the ripening process. Very hot fruit

take longer to cool to storage temperature and increases

the risk of �hot spots� occurring in pallet lots during

storage, which is why fruit should be kept cool in the

shade (refer to the �Harvesting� chapter). Once the fruit

temperature is brought down to the target level, it is

important to maintain this temperature and not allow

the temperature to vary widely from then on. Any

significant increase in temperature during storage

reduces shelf life after arrival in the market.

To maintain quality and prevent internal disorders, green,

unripened fruit should be stored in well-ventilated

coolrooms, at a pulp temperature of 5 to 7°C. Depending

on fruit maturity and their stage of ripening, avocados

can tolerate slightly lower temperatures, but there is a

risk of inducing cold damage to the peel.

Grading fruit

Packing fruit into trays

Pallet of fruit ready for shipping



AVOCADOS STORED FOR 28 DAYS

Storage Temperature °C Vascular Browning %

3.3 15.4

4.4 13.8

5.6 12.0

6.7 15.0

7.6 28.6

10.0 48.2

(South African Research)

Accurate monitoring of temperatures can only be done

using a probe thermometer to measure actual fruit pulp

temperature and temperature can be expected to vary

slightly within a pallet, depending on where

measurements are taken. It is advisable to take a range

of readings from top to bottom of pallets (Probes should

regularly be calibrated to 0°C in a water/ice slurry). Pulp

temperature will always be higher than the air

temperature of the coldroom. This is because the fruit

are alive and produce heat as part of the respiration

process.

Avocados should never be stored with other fresh

produce that is capable of generating ethylene such as

apples, bananas and kiwifruit or exposed to vehicle

fumes and cigarette smoke. Only electrically powered

forklifts should be allowed to operate inside avocado

coldrooms.

For effective cooling of fruit, temperatures should be

lowered towards the target temperature as quickly after

harvest and packing as possible. Pallets should be

stacked in coldrooms such that air can move freely

around each pallet and that the horizontal ventilation

holes in the pallet are aligned in the same direction as

the air-flow in the room.

Coldroom temperature monitoring is an important aspect

of cold chain maintenance. Temperature probes in the

rooms should be placed about 1.5m in front of the

delivery air coils and their accuracy checked regularly,

plus verifying the delivery air temperatures using hand-

held probe thermometers every day.

When transferring fruit to trucks or containers, fruit

temperature can rise surprisingly quickly, so speed of

loading is of the essence. Many trucks are not

particularly efficient at cooling and at best, only maintain

temperatures as a consequence the delivery air (DAT)

set-point in trucks should be set at 1 to 1.5°C lower than

the desired pulp temperature.

If loading fruit into containers for shipment, double-

check the DAT setpoint of the containers, as they are

often used for transporting frozen goods as well and

have been found sometimes to arrive at packhouses with

settings as low as �20°C.

HumidityAvocado fruit depending on maturity can contain more

than 75% water. Water lost during post harvest packing

and handling is a direct loss in saleable weight of the

fruit. Free water on the surface of fruit is also undesirable

in that it can promote the growth of rots. Therefore

understanding the role of water loss and humidity in the

postharvest handling chain is important to minimise fruit

quality losses.

Relative humidity (RH) is the term most often used to

describe the amount of water vapour in the air and is the

ratio of water vapour pressure in the air to the maximum

amount of water vapour the air can hold at a specific

temperature and is expressed as a percentage. The

smaller the RH the greater the driving force for water to

leave the fruit while RH values at 100% indicate that

water will condense out on any surface available.

Temperature and RH are directly related. If the

temperature increases by only 1 degree, the RH is

reduced by about 7% increasing the rate of water loss

from a fruit. It is worth remembering that the moisture

loss at 95% RH is one quarter the moisture loss at 80%

RH.

The difference between equilibrium RH of the fruit and

the RH of the air is important when cooling the fruit.

Even if saturated air at 100% RH is used to cool the

fruit, as long as the fruit is warmer than the cooling air,

the fruit will lose water. This highlights the importance

of cooling the fruit quickly to minimise water loss.

When moist air is cooled a temperature is reached at

which the air is saturated and water will condense out,

this is known as the dewpoint temperature. For example

air with an RH of 80% at 30°C reaches its dewpoint at

26°C that is when condensation will form on surfaces.

Loading fruit at the wharf



Condensation weakens packaging with the water being

absorbed into the wood or cardboard. At low storage

temperatures and high RH small changes in temperature

can result in excessive condensation and faster water

loss from the fruit.

Post harvest quality problemsThe postharvest quality problems typically found on

avocado fruit that has been coolstored and shipped to

market or after postharvest handling includes: rots,

bruising, uneven ripening, vascular browning, chilling

injury and mechanical damage.

Rots: are often the most common and severe problems

found in fruit at retail. The incidence and severity of rot

development in a line of fruit will often determine the

shelf life of the fruit. Rots can appear on the fruit when

they are green and unripe or once the fruit have changed

colour and softened to eating ripeness. Rots in green

fruit most commonly appear as spotting with or without

visible fungal fruiting bodies.

Most rot is caused by the anthracnose fungus

(Colletotrichum gloeosporioides), the symptoms of

which are, small, light brown circular spots that enlarge

rapidly changing colour to dark brown or black. The

centres of the spots may be slightly sunken and pink

bodies can develop within the spots. The rot penetrates

deeply into the flesh in a hemispherical shape.

Stem-end rot is characterised by a dark brown rot that

develops during ripening at the stem end and is often

associated with vascular browning where the water

conducting threads turn brown or black in strands to the

blossom end of the fruit. Usually, stem-end rot is not

visible until the fruit has been cut open.

Vascular browning can be found in immature fruit but

is most commonly associated with stem end rot. Small

increases in the size of a stem end rot can lead to large

increases in the severity of vascular browning.

Bruising: occurs in avocado fruit as a result of impact

damage, caused by dropping fruit during packing or

handling, or pressure where the fruit are crushed by over

packing, package base sag, package collapse or shifting

of loads during transport.

Damage in hard and sprung fruit is visible as small,

discoloured areas in the flesh between the seed and the

skin. Occasionally the bruised areas have cavities.

Bruising is usually more severe in soft, ripe fruit

compared hard, green fruit.

Fuzzy spotting

Anthracnose fungal bodies on a ripe fruit

Stem end rot and vascular browning



Uneven ripening: is where areas of flesh around the seed

remain hard as the fruit ripen. This problem occurs

frequently in export fruit and is most common in early

season fruit. However, as the fruit become increasingly

mature as the season progresses the incidence of uneven

ripening declines to insignificant levels. Uneven ripening

is also thought to be associated with water stress during

the growth and development of the fruit. Avocados

ripened at temperatures above 20°C can also have a high

incidence of uneven ripening.

Flesh discolouration: is where the flesh changes colour

to grey or black, appears to be decayed and has a foul

odour. Late season very mature fruit stored at too low

temperatures or prevented from breathing properly when

ripening can often exhibit blackened flesh around the

bottom of the seed. Avocados stored with other ethylene

producing fruit, such as apples, are also prone to flesh

discolouration. Flesh discolouration is also a symptom

of chilling injury especially in fruit stored for a long

time.

Chilling injury: can occur as an injury to the skin of the

fruit and as a blackening of the flesh. Damage to the

skin can appear to be similar to anthracnose spotting

but tends to be browner, sharply defined and superficial

not penetrating into the flesh. These fruit will often ripen

normally to acceptable eating quality. Internal chilling

damage makes the flesh look dirty and unattractive.

In Hass, chilling injured fruit will not colour normally

as they ripen, remaining green or a two-toned green to

black colour. Severe chilling results in irregular softening

of the flesh, off-flavours and an increase in ripe rots.

Avocados are most susceptible to chilling injury at the

start of ripening to the sprung stage.

Mechanical damage: is where the skin of the fruit has

been rubbed or abraded so that the tops of bumps or

nodules have been removed. The damage usually heals

leaving the fruit appearing spotted. Damage to the skin

makes the fruit more susceptible to fungal infection

especially if the fruit get wet or are dipped.

Bruising

Uneven ripening

Flesh discolouration

Chilling injury to the skin



Marketing the fruit in export marketsAt present, most New Zealand fruit is exported to either

Australia or the USA using a variety of transport systems:

air freight, container shipments (with or without

controlled atmosphere) and break-bulk shipments. The

choice of shipping method is based on distance to the

market, cost and the urgency of demand.

Each country has different phytosanitary and public

health requirements and regulations, to ensure that no

unwanted pests or pesticide residues are present on or

in the fruit. For Australia, a �pre-clearance� system is

generally used where Australian inspectors are based in

New Zealand for most of the season to inspect fruit at

packsheds before shipping to Australia.

In the USA, the US Dept of Agriculture, Plant Protection

& Quarantine and US Customs are all involved in

monitoring fruit quality, residue analyses and incidence

of pests. This is done in the USA, either at the docks or

at handler�s coolrooms. The cost of failure is high, which

is why so much emphasis is placed on spray diaries and

adherence to withholding periods.

There are a number of �different� avenues or markets in

each country, through which our fruit eventually reaches

the consumer by retailers, wholesalers and foodservice

suppliers. Each of these has slightly different ways of

distributing and presenting the fruit. In most cases

though, fruit will be supplied to these markets via an

intermediary handler who will store the fruit and then

prepare and arrange transport to the market�s or

customer�s specifications of size, packaging, stage of

ripeness etc.

While there is an increasing demand for pre-ripened

avocados, most points of sale are not geared to do the

ripening and so, this is often done by the specialist

handlers mentioned above. Ironically, while many

consumers prefer �ready to eat� fruit, handlers are very

specific in their requirement for having fruit rock-hard

and green on arrival. If fruit arrives soft or �breaking�,

the fruit then has to be moved relatively fast and

sometimes in an unprogrammed way, which can lead to

discounting and low prices.

The requirement for hard, green fruit on arrival, is the

real reason so much emphasis is placed on temperature

control, shipping systems and the other disciplines

mentioned elsewhere in this chapter. This urgency

continues overseas, when fruit is offloaded from vessels

or containers at the overseas ports and everything

possible is done to maintain the integrity of the cold

chain and get the product into the handlers coolstores

as quickly as possible.

Inventory management is important overseas, with older

fruit from each shipment generally requiring to be sold

first, leaving the youngest fruit for last.

Making the sale is not the end of the picture however,

as it is really only once the fruit has ripened, that post-

harvest rots and other physiological disorders start

manifesting themselves. Should problems like this occur,

claims can be lodged by customers which invariably

means a loss to the grower. This is one of the reasons so

much emphasis is placed on spray programs and fruit

handling practises in the orchard.

Exporting a perishable product is therefore a process

requiring attention to detail and all participants have an

important role to play, not least the grower � it can take

up to just over a month before the fruit is actually

consumed after it has been picked.

Mechanical Damage



FURTHER READING

Avocado Industry Council Ltd, 2001. Avocado fruit

assessment manual 2001.

Avocado Industry Council Ltd, 2000. Quality

Manual.

Avocado Industry Council Ltd, 2000. USA best

practice manual.

Binyamini, N., and Schiffmann-Nadel, M., 1972.

Latent Infection in Avocado Fruit Due to

Colletotrichum gloeosporioides. Phytopathology 62,

pp 592-594.

Chaplin, G.R., 1983. Chilling Injury in Stored

Avocados. Proceedings of the Second Australian

Avocado Research Workshop, pp 111-116.

Eaks, I.L., 1978. Ripening, Respiration and Ethylene

Production of Hass Avocado Fruit at 20°C to 40°C.

Journal of the American Society for Horticultural

Science 103, pp 576-578.

Hartill, W.F.T., Manning, M.A., and Allen, D.J., 1986.

Control of Post-Harvest Diseases of Avocado.

Proceedings of the 39th New Zealand Weed and Pest

Control Conference.

Hartill, W.F.T., Sale, P.R., and Sawden, D., 1991.

Post-Harvest Rots of Avocados and their Control.

Proceedings of the 44th New Zealand Weed and Pest

control Conference.

Kader, A.A., 1992. Postharvest Technology of

Horticultural Crops. 2nd Ed. Univ. California, Div.

Agric. Nat. Resources. Publication 3311. California,

USA. 296pp.

Kosiyachinda, S., and Young, R.E., 1976. Chilling

Sensitivity of Avocado Fruit at Different Stages of the

Respiratory Climacteric. Journal of the American

Society for Horticultural Science 101, pp. 665-667.

Muirhead, I.F., Fitzell, R.D., Davis, R.D., and

Peterson, R.A., 1982. Post-Harvest Control of

Anthracnose and Stem-End Rots of Fuerte Avocados

with Prochloraz and other Fungicides. Australian

Journal of Experimental Agriculture and Animal

Husbandry 22, pp 441�446.

Oppenheimer, C.A., 1969. Partial Non-Softening of

Avocado Fruit. Journal of the Agricultural Research

Station of Israel 10, pp 15-20.

Peterson, R.A., and Inch, A.J., 1980. Control of

Anthracnose on Avocados in Queensland.

Queensland Journal of Agricultural and animal

Sciences 37, pp 79-83.

Peterson, R.A., 1978. Susceptibility of Fuerte

Avocado Fruit at Various Stages of Growth, to

Infection by Anthracnose and Stem-End Rot Fungi.

Australian Journal of Experimental Agriculture and

Animal Husbandry 18, pp 158-160.

Sale, P.R., 1983. Avocados � Pests and Diseases.

Horticultural Produce & Practice 79 AgLink Series,

Media Services, MAF.

Sale P.R., 1983. Avocados � Yields, Maturity,

Grading, Packing and Storage. Horticultural Produce

& Practice 75, AgLink Series, Media Services, MAF.

Sale, P.R., 1983. Avocados � Yields, Harvest and

Post-Harvest Handling. Horticultural Produce &

Practice 75, AgLink Series, Media Services, MAF.

Schroeder, C.A., 1953. Growth and Development of

the Avocado Fruit. Proceedings of the American

Society of Horticultural Science 61, pp 103-109.

Wills, B.H., Lee T.H., Graham D., McGlasson W.B.

and Hall E.G., 1997. Postharvest: An Introduction to

the Physiology and Handling of Fruit and Vegetables.

4th Edition, New South Wales Univ. Press, New South

Wales, Australia. 174 pp.

Woolf, A.B., McLeod D.L., Burdon J.N. and White

A., 1997. Using the Anderson Firmometer.

HortResearch Client Report No. 97/119.

Woolf, A.B., McLeod D.L., Roughan S., Burdon J.N.

and White A., 1997. Avocado Postharvest Research:

1996/97 Ethylene ripening protocols for local and

export market avocados. HortResearch Client Report

No. 97/118.

Zauberman, G., and Fuchs, Y., 1973. Ripening

Process in Avocados Stored in Ethylene Atmosphere

in Cold Storage. Journal of the American Society for

Horticultural Science 98, pp 477-480.

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