Grading

9. 4. 5. 1 At harvest

The severity of damage appears to increase in proportion to increasing fruit velocities and it is likely that damage occurs even at low velocities (Sections 2.2.7.4, 4.3. 1 ). Fruit exiting a grader into a pack are usually fed out of grading machines by belts and ramps with the assistance of gravity, providing opportunity for fruit to be damaged and to soften prematurely (Sections 2.2.7.4, 5.3). Damage due to grading fruit needs to be identified and eliminated. Transfer of sorted fruit after grading into packs should involve fruit being exposed to nil impacts. The instrumented sphere offers a means of evaluating graders for their potential impacts (Section 2.2.7.4). Even an overall subjective assessment of a grader' s perceived potential to damage fruit appeared to provide a reasonable indication of the actual damage fruit would sustain during grading (Section 5.3 . 1 ). Currently used commercial graders should be quantified for their potential to damage fruit. This could be done by measuring drop heights on graders, and assessment of sites on graders where fruit may potentially increase in their speed of travel, followed by an impacts against static surfaces or other fruit.

Chapter 9 General D iscussion _{1 77}

9.4.5.2 After CA storage

Kiwifruit not graded and packed at harvest are bulk stored in wooden bins in either air or CA storage. Fruit are then graded some time after harvest when they have started to soften (Section 6. 1 ; Fig. 6. 1 ). The final firmness of fruit removed from CA is more influenced by their rapid rate of softening than damage due to grading. Kiwifruit softened rapidly after removal from CA (Fig. 6. 1 ) . Understanding of the process which causes rapid softening of whole fruit after removal from a CA atmosphere seems likely to permit a greater influence over fruit rate of softening than any effect mechanical damage would have (Fig. 6 . 1 ) .

9.4.6 Packing

The interaction between packaging and its effect on the long term storage potential of fruit has not been clearly defined in this study (Sections 2 .2.7.5, 5.3 .2). The factors which cause variation in the incidence of premature softening between different pack-types require further investigation so that packaging aspects of storage practices can be adapted to take advantage of any differences. At the moment, the industry is moving towards bulk storage and grading once fruit have softened, and those which have softened prematurely are removed. The benefits of storing fruit in bulk wooden bins, bulk packs, or in single layer trays depends on the relative costs of the packaging system themselves, and their effect on fruit softening behaviour, the cost of removing soft fruit prior to market sale, and the potential for impact, vibration, or compression to damage fruit in each system. Further work is required into the trade-offs that would be associated with alternative packaging strategies. This may include any variation between packs in their ability to maintain high humidity around the fruit during long term storage to prevent an enhanced fruit softening. Each pack -type may need different management practices to minimise loss of fruit quality during storage. Unfortunately, the benefits of grading softened fruit some time after harvest could be at the cost of the increased susceptibility of fruit to impact damage

9.4.7 Bulk storage

It is not known how much compression damage occurs to kiwifruit stored in wooden bins after the CA atmosphere is removed (Section 6.3.2).

Compression to fruit that are rapidly softening in wooden bins after the CA atmosphere is removed could promote softening of the whole fruit, similar to fruit in the LC and SL treatments (Section 3.3.2). Fruit temperature (Section 2.2.3 .2), rate of water loss (Section 2.2.2), and vibration (Section

2.2.7.3) could have been responsible for the observed differences between the top and bottom fruit layers of bins (Section 6.3.2). An alternative approach may be to bulk store fruit in less deep containers.

There was no comparison made with fruit held in bins with or without polyliners to reduce water loss. It is recommended by the NZKMB

( 1 996) that wooden bins have liners during storage to reduce w ater loss; this should probably be a required practice to prevent loss of firmness due to water loss (Section 2.2.2). However, further work in the relative costs and benefits of such a strategy should be done before a firm requirement could be made.

9.4.8 Coolstorage

Further work is required to understand how temperature influences development of soft patches and L TB in coolstorage, particuarly with respect to which phase of fruit softening could be most critical in

influencing fruit susceptibility to L TB or soft patch development (Sections

2.2. 1 , 8.3). If physiological soft patches are a form of localised premature fruit senescence then, once fruit are coolstored, factors such as temperature and time can be used to manage ripening and development of soft patches during coolstorage. This would make it useful to determine how prolonged storage of soft patch fruit at ooc influences the fruit rate of ethylene

production once removed from coolstorage and stored at ambient temperatures.

Fruit with low calcium c ontents are more susceptible to L TB and soft patches (Section 8 .3.2.3). This is consistent with the concept that fruit

Chapter 9 General D iscus s i on 1 79

which are predisposed to soften quickly, due to low calcium, could also senescence first. Such fruit would possibly be more susceptible to prematurely develop disorders associated with tissue breakdown such as LTB and soft patches. Measuring calcium contents at harvest may enable prediction of orchard lines that will be more susceptible to L TB during storage. As LTB is a form of chilling injury, and is, therefore, temperature dependent (Sections 8.3. 1 .2, 8.3.2. 1 ; Lallu et al. 1 992), it is important to adequately monitor coolstore temperatures to avoid fluctuations below 0°C (Amos et al. 1 993). The more temperature falls below 0°C, the greater proportion of fruit would be susceptible to develop L TB (Lallu et al. 1 992).

9.4.9 Condition checking

It is important that fruit which have softened excessively during storage are identified and not exported or purchased by the consumer. Condition checking provides opportunity to identify fruit which have soft patches. Condition checking relies mainly on firmness being an accurate measure of overall fruit quality (NZKMB 1 996). Mostly, the checking of fruit quality is performed subjectively, by gently clasping the fruit for a second or so, and then making a decision about the whole fruit firmness (NZKMB 1 996). Subjective decisions can be confirmed by penetrometer measurements

(NZKMB 1 996). Accurate detection of soft patches involves feeling the fruit surface and is time consuming (Section 6 .2.4). Detection of soft patches by feeling the whole fruit surface may not be an economic option.

However, the cost of detecting soft patches needs to be considered against the potential loss of consumer confidence and future sales, due to purchase of kiwifruit with soft patches.

Premature softening resulting from physical handling at harvest is restricted to the localised damaged tissue on the fruit (Sections 3 . 3 . 1 , 4.3 . 1 , 7.3. 1 .3). Unless a penetrometer measures at the site of damage, the firmness measurement would suggest that the fruit had a similar firmness to

undamaged fruit. The penetrometer appears to be severely restricted in its usefulness for the detection of soft patches (Sections 2.3, 2.4. 1 ) . The actual

level of damage occurring at harvest may not be accurately detected by the current condition checking process. Mean firmness for an orchard line may give a good estimate of the likely proportion of fruit with soft patches due to physiological factors (Fig. 6.2). As commercial fruit are likely to be exposed to some level of handling damage this association would be likely to become lost. A quick and accurate non-destructive tool is required to assess for the presence of soft patches in kiwifruit. The 'SoftSense' appears to have the potential to be used on a commercial grading machine at time of condition checking, to identify kiwifruit which have become very soft and, therefore, be likely to have physiological soft patches (Hopkirk et al. 1 996).

Detection of soft patches w ould involve assessing a sample of fruit from an orchard line; the number of fruit required in the sample to give an accurate estimate of the incidence of soft patches in an orchard line would need to be determined.

9.4.10 Export

Fruit being exported late in the storage season are often in their final softening phase (Fig. 2. 1 ), and have a high susceptibility to impact and compression damage (Sections 3.3.2, 4.3.2). Fruit texture has changed dramatically from that at harvest (Section 2.2. 1 ₎, which could allow a greater expression of tissue damage. Dropping or damage to pallets during transportation is likely to result in loss of fruit quality (Section 2.2.7.5). It is very important that staff associated with movement of fruit have the knowledge and skills required to minimise handling damage. No work has been reported on how much handling damage fruit receive during export handling operations, and how much this damage subsequently affected fruit quality. The export part of the distribution chain should be investigated to identify if there is a need to eliminate compression and impacts which might cause fruit to soften prematurely. Workers that are responsible for the movement of packed fruit need to be educated and trained to ensure careful handling of fruit. Companies transporting fruit could be audited to