A preliminary AFL testing experiment was designed. To accelerate ripening of fruit a high temperature (20 °C) strategy was adopted, to be compared with fruit quality data recorded at optimal storage (0 °C). For each GL, 57 modular bulk (MB) packs (99 - 100
fruit/pack wrapped in polyliner) of count 36 ‘Hayward’ kiwifruit were sent in
temperature control transport from a commercial packing facility in Bay of Plenty to the Postharvest Laboratory at Massey University, Palmerston North. In total 20 GLs were collected by receiving two lines per day from Tuesday to Friday over the harvest season of 16 d, started from May 5, 2010 (ISO day 125) to May 21, 2010 (ISO day 141). International Standard Organization (ISO) date/day is a system used by the industry for time keeping and to track fiscal years. In this study, ISO day was used to define day of each fiscal year.
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At-harvest
Randomly divided into 3 groups
Optimal storage 27 MB packs - for 0 °C Remove 3 MB packs at 21 d intervals for 189 d Left overnight at 20 °C to equilibrate fruit temperature Following day: Recorded firmness (3 MBs) and SSC (15 fruit) 27 MB packs - for 20 °C
Accelerated fruit library (AFL)
Remove 3 MB packs at 3 d intervals for 27 d Recorded firmness (3 MB
packs) and SSC (15 fruit) 3 MB packs Left overnight at 20 °C to equilibrate fruit temperature Following day: Recorded firmness (3 MB packs), SSC and DM (30 fruit)
Each grower line (GL)
57 Modular bulk (MB) packs (99 fruit per pack)
of count 36
Upon arrival, MB packs of each GL were randomly divided into three (3) groups of fruit measurement; at-harvest, optimal storage and AFL (Figure 3.1). MB packs of each GL were randomly allocated a pre-printed label that dictated the storage condition and time (day) of measurement.
Figure 3.1: Fruit distribution and scheme of data collection for at-harvest, optimal storage and accelerated fruit library for each GL in 2010.
For at-harvest measurements, 3 MB packs per GL were left overnight at room temperature (20 °C) to equilibrate fruit temperature. Next day, firmness of all fruit in 3 MB packs, and soluble solids content (SSC) and dry matter (DM) of 30 fruit per GL were measured. For AFL, 27 MB packs per GL were stored at 20 °C for 27 d and fruit
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quality was monitored at 3 d interval. At each AFL measurement occasion, firmness of 3 MB packs and SSC of 15 fruit per GL were measured. For optimal storage, 27 MB packs per GL were stored at 0 °C for 189 d and fruit quality was assessed at 21 d interval. At each occasion, 3 MB packs per GL were removed from cool store and left overnight at room temperature (20 °C) for fruit temperature equilibration. Next day, firmness of all fruit in 3 MB packs and SSC of 15 fruit per GL were measured. For all measurement groups and occasions, incidence of rot, soft patches, bruise and any damage were also recorded.
Fruit temperature equilibration was performed for at-harvest and optimal storage data, to avoid errors in firmness measurement due to difference in temperature (Jeffery and Banks, 1994). During AFL and optimal storage monitoring, RH of >90% was maintained. Ethylene concentration in rooms was monitored intermittently during storage period. Room temperature was measured by thermocouples and was recorded in data loggers (Grant - 1200 Squirrel Digital Meter/Logger, Grant Instruments Ltd. Barrington, Cambridge, England). Large ethylene scrubbing sachets of Purafil® (Potassium permanganate - KMnO4) were also placed in rooms in order to minimise ethylene accumulation during storage.
3.2.1 Firmness
Firmness of kiwifruit was assessed by QALink Penetrometer (Willowbank Electronics Ltd., Napier, New Zealand), attached to a computer. A standard 7.9 mm Effegi probe was fitted with penetrometer. Fruit skin of 1 - 2 mm (approximately) thickness was removed from two locations, at 90° angle to each other, around the equator. Fruit area without skin was then subjected to puncture at 8 mm depth with the speed of 20 mm.s-1. Minimum measurable firmness was set at 0.1 kgf. The average peak force of two measurements per fruit was recorded.
3.2.2 Soluble solids content (SSC)
SSC of fruit was measured by a digital pocket refractometer (PAL-1, Atago, Japan), after calibration to 0% by using distilled water. Fruit juice was extracted from the blossom and stem ends after a 15 mm cut at each end. Approximately equal amounts of
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fruit juice from both tissues were mixed on refractometer prism. Data were recorded as percentage soluble solids.
3.2.3 Dry matter (DM)
Fruit DM was determined by careful removal of water through drying. First marked empty petri dishes or weighing boats were weighed by using a balance (Mettler PG- 503S, Toledo, Switzerland) with 0.001 g accuracy. A 2 - 3 mm equatorial slice was obtained from fruit. After placing fruit slice on the petri dish, it was re-weighed to record the fresh weight. Petri dishes were then placed in drying oven at 60 - 65 °C for 24 h. When weight of the dried sample was stable, each petri dish was weighed to record dry weight. DM was then calculated as percentage of fruit (Eq. 3.1).
1 . 3 Eq. 100 weight Fresh weight Dry DM u 3.2.4 Ethylene detection
For ethylene measurement ETD-300 (Sensor Sense, Nijmegen, Netherlands) was used, which is able to detect ethylene at very low concentrations (0.3 ppb). A sample pump (NMP 05B, KNF Neuberger GmbH, Germany) was used to suck air from different cool room locations and supply to the sensor at 5 L.h-1 using a continuous flow method. Sample air first passed through Drierite (self-indicating 8 mesh 2 mm granules, Acros Organics, Thermo Fisher Scientific, New Zealand) and soda lime to scrub moisture and CO2, respectively. For ethylene detection from each location, continuous flow of sample was maintained until a consistent concentration of ethylene was achieved. Between each location or sample, ethylene free air was used to standardise the sensor.