# Powdered Foods: Structure, Processing, and Challenges: A Review
## 7 Powdered Products: Case Studies
### Fruits and Vegetables  
Fruits and vegetable are known mainly for their potential to bring health benefits via the bioactive compounds present in them, reducing the risk of some chronic diseases. However, they have the disadvantage of being foods with a limited post-harvest shelf life, and an effective solution to overcome this challenge involves the production of powdered foods, this being an alternative to delay spoilage by significantly reducing the moisture content in food. The drying process for fruits and vegetables can include the production of instant juices and instant soups, including the dehydration of spices and herbs for cooking [73; 74]. Maintaining the stability and functionality of these powdered foods is one of the biggest challenges [73; 75]. [PERSON] et al. [76] investigated changes in the physicochemical properties of cabbage powder with different drying methods (air vacuum and freeze-drying). The authors found that the freeze-drying process obtained the best results among the different drying methods, with higher color retention and vitamin C (60.42%), justified by the reduced contact with oxygen and drying at low temperatures, besides better retained shape [76]. For spinach powder developed from different drying processes (sun-, freeze-, and tray-drying) [77], the authors obtained similar microstructures between the different drying methods, with an amorphous nature. Regarding bioactivity, the freeze-drying process showed the best results with a higher total phenolic content and antioxidant activity, compared to the sun and tray drying methods [77]. [PERSON] and [PERSON] [78] optimized the process to produce powdered beetroot juice from spray-drying, evaluating different feed rates, processing temperature, and maltodextrin concentration, in which the lowest maltodextrin concentration tested (20%) presented the best results of packed bulk density, moisture content, and betalain content. The morphology of the optimized powder was also evaluated, obtaining spherical particles with several dents on the surface, these dents being justified by shrinkage during the drying process [78]. With new trends in clean-label foods and the use of natural ingredients, the partial replacement of maltodextrin with vegetable fibers is an interesting alternative [79]. The utilization of fruit and vegetable powders (agus fiber, citrus fiber, and microcrystalline cellulose) obtained from spray-drying showed similar results in terms of physical properties, in addition to not having a harmful effect on the aroma profile of the powdered product. The authors also mention the limitation of the use of these fibers due to their low solubility, with a solution being a pretreatment of these fibers for their solubilization [79]. Due to the different chemical and physical characteristics of fruits, maintaining stability is one of the biggest difficulties of these powdered products. Fruits in general have a high concentration of low molecular weight sugars and some organic acids, giving the product the'sticky' characteristic after drying. Furthermore, they also have high hygroscopicity and water solubility, providing some undesirable effects during storage, and it is recommended to keep the powdered fruit below the glass transition temperature (Tg) [79]. To preserve the bioactive compound content of the fruits, the freeze-drying process is considered the best option, although it is not the most viable. Since fruits have several thermosensitive compounds, it is possible that there is a degradation of these compounds in drying processes that involves the application of heat. Furthermore, via freeze-drying, it is possible to maintain the color characteristics of the original food, such as maintaining a porous microstructure of the powdered food, facilitating its rehydration [73]. The application of a microwave drying pre-treatment can also leads to a faster dehydration of fruits and maintain their bioactive properties [80]. [PERSON] et al.