Effects of Preconditioning Temperature and Duration on the Quality of 'Honeycrisp' after Storage
As more 'Honeycrisp' trees come into production and more fruit become available, there is a need to store this cultivar longer term. However, there are inherent quality issues with 'Honeycrisp'. For example, it is very prone to chilling injury, soggy breakdown and soft scald development. To control these storage disorders it is common to precondition the fruit prior to cold storage with delayed cooling. Postharvest application of 1-methylcyclopropene (1-MCP, SmartFresh), an inhibitor of ethylene action, has also been shown to reduce certain storage disorders in apples. Therefore, the effects of delayed cooling and SmartFresh on the physical and sensory quality of 'Honeycrisp' after storage were investigated.
'Honeycrisp' apples were harvested in Norfolk County, Ontario on September 16th, 2011. Fruit maturity was measured as: 19.5 ppm internal ethylene, 16.0 lb firmness, 13.1% soluble solids, 771 mg malic acid (per 100 ml of juice), and 6.4 starch index. Apples were transported to the Apple Research Storage Lab in Simcoe within 1 hour of harvest and cooled to ~10oC. Half of the apples were then treated with SmartFresh (1 ppm, 1-MCP) overnight for 24 hours. Three bushel boxes of each treated and non-treated fruit were subsequently held for 0, 5, 10, or 20 days at 10oC, 5 or 10 days at 20oC. After the appropriate time, all apples were then held in either air storage at 3oC for 4 and 8 months.
After 4 months of air storage, 'Honeycrisp' treated with SmartFresh had reduced internal ethylene concentration and peel greasiness. All preconditioning treatments, regardless of temperature or duration, substantially reduced the incidence of soft scald (Table 1). However, preconditioning at 20oC was less effective than at 10oC in apples not treated with SmartFresh.
Some bitter pit was observed after 4 months in air storage. Severe sunken dark lesions were also present, but only in apples that were preconditioned and/or treated with SmartFresh (Plate 1). It has been previously suggested that SmartFresh can aggravate the development of bitter pit, resulting in dark brown, large sunken lesions.
The highest amount of storage rots was found with preconditioning at 20oC for 10 days and the incidence was reduced with SmartFresh treatment.
Complementary sensory evaluations were performed at the Vineland Research and Innovation Centre (Bowen and Lesschaeve). Following removal from cold storage, the apples used for tasting were held at room temperature for 5 days prior to the sensory evaluations. SmartFresh-treated fruit preconditioned at 20oC for 5 days had higher mean ratings of "crisp texture" than those not treated with SmartFresh and held at 20oC for 10 days or 10oC for 20 days before air storage at 3°C. In addition, apples with no preconditioning (immediate storage at 3oC) and no SmartFresh treatment had higher mean ratings for "chewy texture" than those not treated with SmartFresh and held at 20oC for 5 days.
After 8 months of air storage, 'Honeycrisp' from all treatments had severe peel greasiness and there were little or inconsistent effects of preconditioning and/or SmartFresh on other physical quality attributes (i.e. firmness, soluble solids, acidity).
All preconditioning treatments, regardless of temperature or duration, continued to reduce the incidence of soft scald.
Some bitter pit was observed in fruit from all treatments, with the highest incidence found in non-SmartFresh treated fruit preconditioned for 20 days at 10oC. Severe sunken dark lesions (exacerbated bitter pit) were also observed and SmartFresh tended to increase the incidence.
High amounts of storage rots (up to 17%) were observed, but the incidence was often reduced by SmartFresh.
At this time, sensory evaluations revealed that panellists could
detect a difference due to SmartFresh in 'Honeycrisp' apples preconditioned
at 20oC for 5 days or 10oC for 10 or 20 days. In further analyses,
apples not treated with SmartFresh were described by more intense
"oxidized red apple", "earthy", and "honey"
flavors and were found generally less intense for "juicy, crisp"
textures. Conversely, SmartFresh-treated fruit were rated higher
for "fresh green apple" flavour and "acid" taste.
Plate 1: Severe sunken dark lesions (exacerbated bitter pit) in 'Honeycrisp'
Table 1: Disorders and rots of 'Honeycrisp' apples treated with or without SmartFresh and held at 10oC for 0, 5, 10, or 20 days or at 20oC for 5 or 10 days, followed by 4 months in air storage at 3oC, plus 8 days at ~18oC.
*, **, ***, **** = significant at P <0.05, P <0.01, P <0.001 or P <0.0001, respectively.
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