Influence of pre-treatment and storage temperature on the evolution of the colour of dried persimmon

Drying could be a way of increasing in the value of the large quantity of persimmon that is rejected for fresh consumption, being the colour one of the main attributes of the product. Although the use of sulphites is one of the most widely extended methods of preservation their undesirable effects on asthma sufferers currently limit their application. An interesting alternative could be to use citric acid combined with an adequate storage temperature. To that end, dried persimmon slices were stored at 4 temperatures (2, 10, 18 and 28 °C) for 409 days. Before drying, one group of samples was pre-treated (15 min) in a solution of potassium meta-bisulphite (3% w/w), other two groups (15 and 35 min respectively) in a solution of citric acid (3% w/w) and the last group (control) was untreated. The L, a and b CIE-Lab coordinates were measured during storage and the colour change, ΔE, was estimated. The experimental results were modelled using first-order kinetics and Peleg’s model. The citric acid pre-treatment turned out to be an interesting alternative to SO2 taking into account that its effect was more effective at temperatures lower than 18 °C. No significant differences were found between the two citric acid pre-treatments, being, therefore, the shortest pre-treatment the most interesting one. More experiments are necessary to establish an optimum content of citric acid in samples.