Abstract
Grapefruit is a cold-sensitive citrus fruit, and freezing can spoil the harvest when the fruit is still on the tree and even later during manufacturing and transport due to inappropriate postharvest management. This study performed a specific Electric Impedance Spectroscopy (EIS) analysis and statistical data treatment to obtain an EIS and Artificial Neural Networks (ANN)-based model for early freeze-damage detection in grapefruit showing a Correct Correlation Rate of 100%. Additionally, Cryo-Field Emission Scanning Electron Microscopy observations were conducted on both fresh and frozen/thawed samples, analyzing the different impedance responses in order to understand the biological changes in the tissue. Finally, a modified Hayden electric equivalent model was parameterized to simulate the impedance response electrically and link the electric behavior of biological tissue to the change in its properties due to freezing. The developed technique is introduced as an alternative to the traditional ones, as it is fast, economic, and easy to carry out.
Highlights
Academic Editor: Maria ConcettaGrapefruit (Citrus paradisi) is a citrus fruit of commercial interest due to its highly appreciated organoleptic and functional properties [1–3], with more than 9 million tons produced annually around the world
Freezing temperatures are problematic for grapefruit [6], as it is a coldsensitive fruit [7,8], with slight tolerance variations depending on the cultivar
The grapefruit were kept in the freezer at −9 ◦ C for 6–7 h until the temperature was in the range −0.9 ◦ C to −1.2 ◦ C exactly in the place where the Electric Impedance Spectroscopy (EIS) sensor had to be introduced to carry out the electrochemical measurements (1.5 cm inside the fruit)
Summary
Academic Editor: Maria ConcettaGrapefruit (Citrus paradisi) is a citrus fruit of commercial interest due to its highly appreciated organoleptic and functional properties [1–3], with more than 9 million tons produced annually around the world. Freezing temperatures are problematic for grapefruit [6], as it is a coldsensitive fruit (it is the second-most cold-sensitive citrus fruit after lemon) [7,8], with slight tolerance variations depending on the cultivar. It has been reported that white cultivars are more sensitive to freezing temperatures than red ones [9,10]. This problem appears both in the maturation phase on the tree and later during manufacture, transport, and storage, as well as in quarantine to control pests such as the Mediterranean fly (Ceratitis capitata) [11–13]. Some authors affirm that refrigerated storage of grapefruit and quarantine have minimal effects on fruit quality [14], inappropriate postharvest treatment, and freezing when the fruit is still on the tree, do have a noteworthy affect [15–17]
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