CHILLING INJURY AND POSTHARVEST DECAY IN CITRUS

Authors: JOHN-KARUPPIAH, K - UF FT PIERCE FL; RITENOUR, MARK - UF FT PIERCE FL; BURTON, MICHAEL - UF FT PIERCE FL; BRECHT, JEFFREY - UF GAINESVILLE FL; McCollum, Thomas

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2004
Publication Date: 4/1/2005
Citation: John-Karuppiah, K., Ritenour, M.A., Burton, M.S., Brecht, J.K., Mccollum, T.G. 2004. Chilling injury and postharvest decay in citrus. Proceedings of Florida State Horticultural Society.

Interpretive Summary: Citrus fruit are typically treated with fungicides following harvest to reduce losses due to decay. Handling fruit at low temperature is another way to reduce decay; however, citrus fruit will develop a disorder know as chilling injury if held at low temperature. Treatment of citrus fruit with heated water has been show to reduce decay while at the same time increasing the resistance of the fruit to chilling injury thereby increasing shelf-life. Treatment with heated water has to potential to injure the fruit, therefore it is important do define the treatment conditions that are non-injurious, but effective. In the current study we determined the effects of treating grapefruit with water heated to 53 -59 degrees centigrade for 30 seconds. Effects of the treatments on fruit quality and shelf life were determined. We also determined the effects of waxing the fruit following treatment on the developing of injury due to the treatment. Results of this study indicate that grapefruit will tolerate being dipped in 56 degree centigrade water for 30 seconds and that such treatments reduce the development of chilling injury. This treatment also reduces decay, but not to the same extent as treatment with fungicide. By increasing the resistance to chilling injury it should be possible to hold the fruit at lower temperature which combined with the decrease in decay resulting from the treatment should reduce postharvest losses.

Technical Abstract: Hot water treatments have been studied and used as non-chemical methods to reduce postharvest decay and chilling injury (CI) in fresh citrus fruit. While many studies have been performed in Mediterranean climates, there exists relatively little work evaluating the effects of hot water on Florida grapefruit quality and quality retention during postharvest handling. In the current studies, 'Ruby Red' grapefruit dipped in water at 56 or 59 °C for 30 s developed 18% or 32%, respectively, less CI compared to fruit dipped at 25 °C after storage at 5 °C for 6 weeks plus 1 week at 16 °C. The fruit were not washed or coated with shellac and no fungicides were used. Hot water dip treatment (HWDT) had the greatest effect on reducing CI of less CI-sensitive inner-canopy fruit (32%) compared to more CI-sensitive outer-canopy fruit (10%). In a separate experiment, washing and coating the fruit with shellac (no fungicide) immediately after the 30 s HWDT significantly reduced scalding (i.e., hot water injury) by 45% or 37% in fruit treated at 59 or 62 °C, respectively, compared to unwashed and uncoated fruit. Fruit treated at 56 or 59 °C developed less total decay after 12 weeks of storage at 10 °C than did 25, 53 or 62 °C-treated fruit. None of the treatments resulted in consistent differences in total soluble solids or titratable acidity in grapefruit. Higher electrolyte leakage and lower peroxidase activity were observed in heat-treated 'Valencia' oranges, but there was no correlation with visible heat injury. HWDT did not affect total phenolics or total protein content of 'Valencia' oranges.