Identification of factors involved and control of astringency in pears

The objective of the study for the 2012 to 2014 seasons was to assess the effect of harvest maturity, storage duration, SmartFresh^SM and CO₂ spiking on astringency in Cheeky and Forelle pears.

The revised objective of this study in the 2015 and 2016 seasons was to continue work on establishing a physiological profile of Cheeky with particular reference to the effects of harvest maturity and storage duration on fruit quality, and expression of astringency and internal browning.

2012 – 2014

Cheeky pears sourced from 2 orchards in Ceres over 3 maturities were stored for 6, 12 and 18 weeks at

-0.5°C, followed by a shelf life of 7 days at 20°C. Forelle pears sourced from an orchard with a history of astringency from the Vyeboom area were subjected to either CO₂ or SmartFresh^SM or left untreated and stored for 4, 8, 12, 16 and 18 weeks at -0.5°C, followed by 7 days at 20°C. All fruit were assessed for storage and shelf-life quality.

2015 – 2016

Fruit from three orchards in the Ceres area were harvested at 4 different maturities and cold stored at

-0.5°C RA for 6, 12, 16 and 20 weeks (6, 8, 12 and 16 weeks for 2015 season), to assess the effect of harvest maturity and storage duration on the expression of astringency and internal browning.

2012 – 2014

In the 2012 season astringency occurred in the later harvested (Harvest 3) Cheeky pears, and declined with longer storage. No mealiness was detected. During the 2013 and 2014 season results regarding astringency were inconclusive. Low levels of mealiness occurred after 6 weeks cold storage followed by a shelf life. At longer storage durations however, mealiness did not occur.

Astringency of Forelle pears decreased with longer storage periods. Fruit subjected to SmartFresh^SM did not exhibit any mealiness. In the 2013 and 2014 seasons high levels of mealiness occurred in the untreated control fruit up to 8 weeks and 12 weeks cold storage respectively.

2015 – 2016

No internal browning and very little astringency (only in 2015 season) were detected in the fruit. Although not always significant, fruit were greener after 4 (2015), 6 (2016) and 8 (2015) weeks cold storage compared to fruit stored for longer. Low incidence of superficial scald occurred on early optimum harvested fruit (Harvest 1, 2016) cold stored for 20 weeks. Mealiness was detected in only a small number of fruit in the 2015 season. None of these were cold stored for longer than 8 weeks. Early optimum fruit (Harvest 1) of the 2016 season did not ripen to such an advanced state following 6 weeks cold storage and a 7 day shelf life period compared to the other harvests.

CO₂ treatment after harvest did not decrease astringency in Forelle pears to such an extend to make it worthwhile. SmartFresh^SM prevented mealiness in Forelle pears. Mealiness in Forelle not subjected to SmartFresh^SM decreased with longer storage periods (12 weeks and longer).

Currently the average release for Cheeky pears is 7.0 kg. Optimum harvest maturity for Cheeky pears is between ±7.2 kg and 6.8 kg. Although very little to no mealiness was detected, fruit stored for 8 weeks had the lowest firmness after shelf life. The most susceptible time for pears to mealiness is at 8 weeks cold storage. Fruit should be monitored for mealiness susceptibility especially during this time. Fruit became overripe after 20 weeks storage. Consequently Cheeky pears should not be stored for so long.

TSS levels of ± 12.0% are currently acceptable according to industry standards. Pre optimum harvests up to 2 weeks after commercial harvest had TSS levels higher than 12.0%. Therefore TSS levels of pre optimum and late harvested Cheeky pears are not a susceptible to low levels.

Pre optimum harvested fruit can be stored 12 weeks with no colour break. Optimum and later harvested fruit should not be stored longer than 8 weeks to prevent colour break.

Superficial scald, senescent scald, flesh decay and senescent breakdown in fruit stored for 20 weeks render this storage duration as high risk and should rather be avoided.

Following the results from the 2012 to 2016 season, fruit can be harvested from 1 week before current release criteria up to 1 week after current release date. Only fruit harvested before current release date can be stored for up to 12 weeks. Later harvested fruit should only be stored for up to 8 weeks to avoid colour break. Care should be taken for mealiness susceptible orchards at 8 weeks storage. To avoid astringency fruit harvested before release should be stored for at least 8 weeks. In later harvested fruit no astringency was detected in fruit up to 8 weeks cold storage.