Mango fruit quality selection and chilling injury prevention during ripening.
MSc-thesis abstract (submitted 10 December 2015): Mango is a tasty tropical fruit in demand of European consumers’ year-round. To supply them it has to be transported from distant places under low temperature, in order to postpone the ripening of the fruit. But storing the fruit below a threshold temperature, 10 °C to 0 °C, inhibits ethylene biosynthesis by enzymes, disturbing the ripening process, and induces oxidative stress by damaging cell membranes and inactivating antioxidants, which scavenges reactive oxidative species, resulting in discolorations and pitting on the peel, known as chilling injury (CI).
Mangos are treated with methyl jasmonate and ethylene to overcome or alleviate CI by inducing ethylene biosynthesis, to re-establish normal ripening. The consumer wants a damage-free, soft and sweet fruit. Retailers sell mango with a ‘Ready To Eat’(RTE)-label guarantying mangos to become soft in a few days. In order to also guarantee sweet fruits a ‘Ready To enJoy’(RTJ)-label has to be developed. The build-up of starch and dry matter (DM) during maturation of mango on the tree mostly determines how sweet a mango can become.
Therefore, selection based on starch and DM can be useful to separate potential RTJ from RTE mangos. Glucose, fructose, sucrose and starch contents in the pulp from peel to stone are measured with HPLC and followed during ripening to evaluate if the pulp ripens equally. So that near infra-red measurements, only protruding the first millimetres of the pulp, can be used to measure the contents in the mango.
DM is tested to correlate with density. So that a mango could simply be weighed under water or ethanol to separate potential RTE from RTJ mango. Ethanol has a lower density than water which facilitates mangos to sink. Internal air may disturb the correlation so a mild vacuum treatment is assessed to improve the correlation. Glucose and starch contents in pulp directly under the peel represented deeper lying pulp. DM correlated best with density when a mild vacuum was used regardless of the weighing method. Correlations differed between batches which could possibly be explained by that mango batches may vary in maturity at moment of harvest.
CI was not observed in any of the experiments so no conclusions can be made on whether CI can be alleviated or impaired with hormones or a heat shock, respectively. The fruit is more tolerant to chilling temperatures than was thought. It may be that the mangos were in an advanced stage of ripening when they were additionally stored at 4 °C after transportation making them tolerant to chilling temperatures.