# Dehumidified Air-Assisted Spray-Drying of Cloudy Beetroot Juice at Low Temperature
## 3 Results and Discussion
### Glass Transition Temperature  
The glass transition temperatures (\(T_{g}\)) of the beetroot powders were presented in Table 2; the temperatures ranged from 58.46 to 70.06 \({}^{\circ}\)C. The value of \(T_{g}\) is an indicator of the quality and storage stability of food powders. [PERSON] et al. (2020) investigated the influence of carriers (maltodextrin and inulin) on the encapsulation process of beetroot powders [18]. \(T_{g}\) values of 18.34 \({}^{\circ}\)C, 61.63 \({}^{\circ}\)C, and 27.59 \({}^{\circ}\)C were presented for spray-dried beetroot powder without a carrier, with maltodextrin, and with inulin, respectively.  
The powder produced with maltodextrin (JMD 130) showed a higher \(T_{g}\) of 70.06 \({}^{\circ}\)C. The \(T_{g}\) of maltodextrin is depended on the dextrose equivalent (DE), which is related to the decrease in the molecular weight that decreases the \(T_{g}\)[19]. According to [PERSON] and [PERSON] (2020), maltodextrin with a DE from 36 to 5 is characterized by a \(T_{g}\) in a range from 100 to 188 \({}^{\circ}\)C [20]. The \(T_{g}\) of skimmed milk powder at 58 \({}^{\circ}\)C (water activity: 0.1) and 34 \({}^{\circ}\)C (water activity: 0.2) was obtained by [PERSON] and [PERSON] (1994) [21]. Higher values for the \(T_{g}\) of skimmed milk powder at 64.3 and 53.0 \({}^{\circ}\)C at the same \(a_{w}\) were presented by [PERSON] et al. (2007) [22]. The differences could have been caused by other parameters involved the drying process and the chemical composition of skimmed milk powder. The addition of nutriose (\(T_{g}\): 15 \({}^{\circ}\)C) and kleptose to beetroot powder as a carrier resulted in an increase of the \(T_{g}\) of beetroot powder to 68.52 \({}^{\circ}\)C and 69.22 \({}^{\circ}\)C, respectively [20]. Higher values for \(T_{g}\) were found in for powders with the addition of carriers.  
The use of lower inlet/outlet air temperatures makes it possible to obtain pure beet-root powders with higher \(T_{g}\). [PERSON] and [PERSON] (1999), [PERSON] et al. (2016), and [PERSON] (2017) have conducted extensive research on \(T_{g}\) phenomena [23; 24; 25]. The great problem during spray-drying is obtaining food powders from a material characterized by a low \(T_{g}\). The structural changes in food powders, like increased stickiness and caking susceptibility, depend on the differences between the \(T_{g}\) of the product and the particle surface temperature during spray-drying [23; 24; 25]. The outlet air temperature is even 10-20 \({}^{\circ}\)C higher than the temperature of the particle surface during spray-drying. At temperatures 10-20 \({}^{\circ}\)C higher than the \(T_{g}\), the material state changes from amorphous to rubbery. It can be concluded that the temperature of the particle surface during drying should not reach 10-20 \({}^{\circ}\)C above the \(T_{g}\)[26; 27]. Research on various carriers used in spray-drying has been undertaken, including maltodextrin, gum arabic, and inulin. [PERSON] and [PERSON] (2020) investigated honey and fruit juice powders, [PERSON] (2020) studied beetroot powder, and [PERSON] and [PERSON] (2008) examined tomato pulp [18; 20; 27]. The \(T_{g}\) of beetroot powder produced with different carriers explains the good quality of the powders obtained at 55 and 80 \({}^{\circ}\)C outlet temperatures.