Influence of different pretreatments on the colour of dried pears

Abstract

As a physical property, colour is an important indicator of the product quality. The purpose of this paper is to examine the effects of different pretreatments on the pear colour alteration during and after combined drying. Combined drying entails both osmotic and convective drying. The osmotic drying was done in a sucrose solution with the temperature of 50 oC and the concentration of 50 oBx. The duration of osmotic drying was 120 minutes. The convective drying was performed by the air temperature of 50 oC during the period of 23 hours. The following protective agents were used: sulphur dioxide, ascorbic acid, citric acid, boiling water, and a solution of alcohol vinegar and water. The most significant change in the value of internal colour L*parameter was recorded in the blanched samples. After the convective drying, notable changes in this parameter were not recorded. All the samples showed an increase in the value of b*parameter following the convective drying. After the osmotic drying, the most significant change in the value of external colour L*parameter was also recorded in the blanched samples. However, in contrast with the internal pear colour, the changes in the external colour L*parameter following the convective drying were more significant. The slightest changes of all colour parameters were recorded in the samples treated with sulphur dioxide.

Keywords

• pear
• combined drying
• colour