Hot water treatment at 50 °C for 5 min could be a useful method to delay chlorophyll degradation in Thai lime fruit.
Citrus fruit can lose its colour awfully quickly. How many times have you seen fruit in the shop which seems to have lost its sheen and vibrancy after a few months storage. Post harvest treatments are designed to overcome these sensorial losses and there has been a recent study looking at minimising the loss of peel colour of Thai Limes (Citrus aurantifolia Swingle cv. Paan).
Hot water washing is a post harvest technology step that appears to be a simple solution to minimising chlorophyll (Chl) degradation and general loss of fruit quality during storage. Chlorophyll pigments provide the vibrant colour in the skin of limes and are prone to disappearing through enzymic catalysed breakdown.
Mature green lime fruit was treated with water at ambient temperature (control) or with hot water at 50 °C for 3 and 5 minutes and then kept at 25 °C in complete darkness. The study demonstrated that the hot water treatment at 50 °C for 5 minutes effectively delayed the decrease of hue angle values and the loss of Chlorophyll a.
Hot water treatments also halted the activities of those enzymes associated with chlorophyll degradation. These enzymes included chlorophyllase, a chlorophyll degrading peroxidase and pheophytinase as well as magnesium de-chelation activity in the fruit. Magnesium incidentally is the metal ion at the heart of the chlorophyll molecule and responsible for enhancing the strong green colour.
This reduction in enzyme activity was more pronounced in fruit treated by hot water for 5 min than in those treated for 3 min. It suggests that the longer the heat treatment the more penetrative the process. These heat treatments also extended storage life by 5 days in fruit treated for 3 minutes and by 10 days in fruit treated for 5 minutes. Hot water treatment at 50 °C for 5 min. maintained the highest total acidity and delayed the increase of total soluble solids contents during storage. Respiration rate and ethylene production were also reduced by the heat treatments.
There was no mention of any flavour or other effects associated with the keeping quality of the limes. It’s likely that treatments that extended beyond 5 minutes would have started to become detrimental to keeping quality.
In summary, these results suggest that hot water treatment at 50 °C for 5 minutes could be a useful method to delay chlorophyll degradation and to maintain postharvest quality in mature green lime during storage at 25 °C.
Kaewsuksaenga,S.,Tatmala, N.,Srilaong, V.,Pongprasert, N. (2015) Postharvest heat treatment delays chlorophyll degradation and maintains quality in Thai lime (Citrus aurantifolia Swingle cv. Paan) fruit. Postharvest Biology and Technology. 100 February pp. 1-7
DOI : 10.1016/j.postharvbio.2014.09.020
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