Influence of Drying Processes and Pretreatments on Nutritional and Bioactive Characteristics of Dried Vegetables: A Review

Abstract

Drying has been applied to vegetables in order to preserve, store and transport these food products. However, drying implies not only physical changes, easily detectable by the consumer through visual assessment, but also chemical modifications. These are not always visible, but are responsible for alterations in colour, flavour and nutritional value, which compromise the overall quality of the final product. The main chemical changes associated with drying are related to the degradation of phytochemicals, such as vitamins, antioxidants, minerals, pigments and other bioactive compounds sensitive to heat, light and oxygen. Moreover, nutrient losses are inevitably associated with leaching as a result of the water removal from the vegetable during the drying process. In order to prevent or reduce nutrient losses and thus improve the quality of dried products, pretreatments are often applied. In this review, an overview of the procedures developed for dehydration of vegetables applying heat by convection, conduction or radiation is presented. The influence of pretreatments on nutritional and bioactive characteristics of dried vegetables is discussed. Blanching with steam, water or chemical solutions is the most commonly used, but power ultrasound, ohmic blanching, osmotic and edible coatings pretreatments have also been reported. The influence of the drying processes and conditions on nutritional contents and bioactive characteristics is also presented.

Application of non‐thermal pretreatment techniques on agricultural products prior to drying: a review

“…The application of OD pretreatment is another strategy to improve the quality of agricultural products by inactivating enzymes and modifying the texture of their tissues preceding drying. Moreover, due to its chelating properties, some acids have the ability to retain product colour . In general, OD is being used as a pretreatment technique preceding further drying in order to retain the functional, sensory and nutritional properties of food .…”

“…Moreover, due to its chelating properties, some acids have the ability to retain product colour. 67 In general, OD is being used as a pretreatment technique preceding further drying in order to retain the functional, sensory and nutritional properties of food. 68 Osmotic agents commonly used in the OD of foods include salt, alcohol, sucrose, ethanol, calcium, corn syrup, fructose and their combinations.…”

Natural Pectin Polysaccharides as Edible Coatings

“…However, this method implies important physical changes in color and texture, as well as chemical modifications related to the degradation of bioactive compounds sensitive to oxygen, light and heating, such as vitamins, antioxidants or minerals. Edible coatings have been proposed as a possibility to prevent the nutrients loss while improving the organoleptic quality of dried products after different pre-treatments, such as blanching and osmotic dehydration [83].…”

Effects of ultrasound-assisted osmotic dehydration as a pretreatment and finish drying methods on the quality of pumpkin slices

“…Drying is a common food preservation process. It is well known that the drying process affects the quality of the dried fruits and vegetables (Oliveira, Brandao, & Silva, 2016). For this reason, there are many studies in literature focusing on the effect of different drying techniques on product quality (Bonazzi & Dumoulin, 2011).…”

“…Freeze drying and vacuum drying are also among the most widely studied methods for drying of fruits and vegetables (Junlakan, Tirawanichakul, & Yamsaengsung, 2017;Kamiloglu et al, 2016). Another way to improve the quality of dried product is the application of pre-treatment before the drying process (Oliveira et al, 2016;Turgut, K€ uç€ uk€ oner, & Karacabey, 2018). One of these pretreatment methods is the application of ultrasound assisted osmotic dehydration (UAOD).…”