*4.1. Mango Leather*

Fruit leathers are dried sheets of fruit pulp which have a soft, rubbery texture and a sweet taste [51]. Leathers can be produced from a variety of fruits, although mango, apricot, banana, and tamarind leathers are amongst the most popular. Mango leather is produced by spreading the pulp evenly in a thin layer on a tray coated with vegetable oil to a depth of 1 cm and drying in mechanical or solar dryers to a final moisture content of 15–20% [51,52]. Solar drying can take a much longer time, leading to discoloration of the pulp. Addition of guar gum, pectin, and ascorbic acid reduces the discoloration of the mango leather. Preservatives such as sodium metabisulfite can be added to extend the shelf life [51]. Incorporation of sucrose, pectin, and maltodextrin reduced the drying rate of mango leather [8].

Mango leather can also be produced by refractance window drying (RWD) which is synonymous with cast-tape drying (CTD) [53,54]. This drying method is characterized by the fruit pulp that is to be dried being spread on a transparent polyester film, commercially known as Mylar (DuPont®). The lower surface of Mylar is kept in contact with hot water which supplies the heat for the product drying. RWD is a drying technique developed for drying of food pulp and purees to retain nutritional quality at relatively low processing temperatures with reasonable capital costs [55]. RWD of mango resulted in much shorter drying times and the mango leather obtained had better quality with higher nutrient retention compared to conventional drying. In addition, scanning electron microscopy showed that RWD resulted in powder particles of irregular shape and smooth surface with uniform thickness. On the other hand, tray and oven drying resulted in powder particles of corrugated, irregular, and crinkled surface with uneven shape and thickness [13].
