Evaluation of chilling injury index and handling techniques of guava fruits (Psidium guajava L.)
Date Issued
2008
Date
2008
Author(s)
Yeh, Szu-Wei
Abstract
Guava（Psidium guajava L.）, an important tropical fruit crop in Taiwan, is a highly perishable horticultural produce due to its rapid water loss and very susceptible to pathogen infection after harvest. Although cold storage is the most effective tool for extending the shelf life of fresh commodity, low temperature may cause chilling injury (CI) and, therefore, quality loss when guava fruit, a chilling-sensitive produce, is held below critical temperature. Therefore, how to assess CI occurrence and how to enhance chilling tolerance are pivot issues for postharvest and handling process of guava fruits.he first objective of this thesis is to define CI symptoms and threshold temperature of ‘Jen-Ju Bar’ guava fruits, the nonclimateric-type, dominate cultivar in Taiwan, as well as to investigate a quick and reliable CI assessment for the product by comparing different CI measurement methods. The CI symptoms, including grayish scald-like peel discoloration, surface pitting, increased susceptibility to decay, and, in severe cases, water-soaking core, of ‘Jen-Ju Bar’ guava fruits were noticeable after exposure to 0℃ for 4 days or 5℃ for 22 days. The lesions become more obviously upon transfer to 20℃ condition for 3 days. The CI threshold temperature for ‘Jen-Ju Bar’ guava fruit is estimated around 5℃. Because of large variations among samples and lack of quantitative correlation, transient increases of both respiration and stress ethylene release rates detected after CI fruit transferred to 20℃ were not evaluated as reliable CI measurements for guava. In contrast, CI rendered decrease of maximum quantum efficiency of Photosystem II photochemistry (Fv/ Fm) and increase of electrolyte leakage percentage and Hunter a* value of exocarp of ‘Jen-Ju Bar’ guava, and all these measurements showed a good quantitative correlation with the CI severity graded by vision assessment (CI index). After treatment at 0℃ for 4 days, a condition for trace CI induction in ‘Jen-Ju Bar’ guava, Fv/ Fm ratio significantly decreased from 0.77 to 0.71, but no difference was observed in electrolyte leakage measurement. Therefore, electrolyte leakage percentage was not a sensitive index for the very early stage of CI occurrence in guava fruits. In addition, the fact that Fv/ Fm ratio decreased more rapidly in ‘Li-Tzy Bar’ guava, a very chilling-sensitive cultivar, than that of ‘Jen-Ju Bar’ during 0℃ storage, chlorophyll inflorescences technique was sufficiently sensitive to discriminate clearly between two cultivars within a species. Fv/ Fm ratio was not only the most sensitive parameter among the techniques tested in this research for CI severity, but also could be used as a reliable parameter for CI occurrence prediction in guava fruits before any CI symptom appearance. When Fv/ Fm ratio dropped to 0.7 and 0.75 under 0℃ environment for ‘Jen-Ju Bar’ and ‘Li-Tzy Bar’, respectively, CI symptoms appeared after transfer at 20℃ for 3 days. These ratios implied the turning point between primary and secondary events of CI occurrence in the two guava cultivars. Hunter a* value of guava exocarp, instead, could not be used for prediction of CI occurrence in guava, since this parameter showed significant change only when visible symptom (brown discoloration) became obvious.either heat treatment nor salicylic acid/ methyl salicylate treatment used in this study affected CI severity of ‘Jen-Ju Bar’ guava fruits stored in 0℃ condition. However, ‘Jen-Ju Bar’ guava fruits with 100 mg/ L methyl jasmonate (MJ) fumigation treatment for 16 hours did effectively alleviate CI symptoms without affecting fruit quality, such as firmness, titratable acid, and ascorbic acid, at 0℃ storage for 14 days. The Fv/ Fm ratio, electrolyte leakage percentage, and Hunter a* value of the MJ treated ‘Jen-Ju Bar’guava were less fluctuated, namely 0.71, 20.79 and -10.3, respectively, when compared with 0.65, 31.15, and -2.95 in untreated control samples. Unlike fumigation treatment, MJ application by immersion or infiltration did not reduce CI severity in ‘Jen-Ju Bar’ guava fruits at 0℃.
Subjects
guava
chilling injury
chlorophyll fluorescence
methyl jasmonate
Type
thesis
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