Dynamic water sorption for the study of amorphous content of vacuum-dried honey powder Bambang Nurhadi, Y.H. Roos ⁎ School of Food and Nutritional Sciences, University College Cork, Ireland abstract article info Article history: Received 1 February 2016 Received in revised form 18 July 2016 Accepted 22 July 2016 Available online 25 July 2016 Amorphous components in food powders are important as they often provide a solid structure. They also affect powder properties such as physical and storage stability. Quantification of amorphous components of food pow- ders may be challenging. We developed a dynamic water sorption by dynamic dew point isotherm (DDI) meth- od, which records the change of water activity and weight change (or water content) of a sample continuously. The research was aimed to study the amorphous content of vacuum-dried honey powder produced from differ- ent drying temperatures. The DDI method was calibrated using known amorphous contents of amorphous su- crose and mixtures of amorphous sucrose and maltodextrin. Amorphous materials often exhibit higher sorption of water than crystalline materials. In the new approach, water sorption data were differentiated numer- ically and plotted against water activity. The water sorbed by the sample during recrystallization was measured by integrating the area of the new derived water sorption curve against water activity. The water sorbed was cor- related with the amorphous content of the system. The honey powder also exhibited recrystallization of its amor- phous sugar during water sorption. The result showed that the higher the drying temperature, the higher the amorphous content of vacuum-dried honey powder. © 2016 Published by Elsevier B.V. Keywords: Amorphous Dynamic water sorption Sucrose Maltodextrin Honey powder 1. Introduction Powder components can be in pure amorphous, pure crystalline or partially amorphous structures (mixed amorphous and crystalline states) [3]. The differences in structure between amorphous and crystal- line order, crystalline structures have long range molecular alignment, while amorphous structures have short range molecular alignment of limited order [3]. Food processing, such as drying, may produce pure amorphous or partially amorphous structures [29]. Roos [29] stated that freeze-drying often results in pure amorphous materials as a result of freeze concentration of solutes and resultant removal of ice by subli- mation. Chiou, Langrish and Braham [8] reported that spray drying pro- duced lactose powders with various amorphous structures (partially amorphous) at different inlet drying temperatures. Amorphous and crystalline materials have different physicochemi- cal properties. Amorphous structures are thermodynamically unstable as compared to crystalline structures and as a result, amorphous struc- tures are metastable with reduced physical and chemical stability [12]. Powders with crystalline components have low porosities, easy to flow properties which make them easier to handle although hard to dis- solve [3,8]. Meanwhile, powders with amorphous structure are more hygroscopic, more cohesive, and difficult to flow and disperse [3,8]. Amorphous structures have larger porosity and volume and as consequence amorphous structures have a higher sorption capacity than crystalline forms [3]. In partially amorphous powders, the amor- phous fraction is mostly found on the surface of the powder [1,15]. Several methods can be used to detect amorphous powder compo- nents. Lehto et al. [12] used x-ray powder diffraction, differential scan- ning calorimetry (DSC), step scan DSC, isothermal microcalorimetry, solution calorimetry, Raman spectrometry and gravimetric water sorp- tion to quantify amorphous lactose in a dried lactose system. Chiou, Langrish, and Braham [8] used the water induced crystallization tech- nique to detect amorphous contents by recrystallization of amorphous fractions in partially amorphous materials. Recrystallization measure- ment as a basis to detect amorphous contents of materials was also used in gravimetric water sorption, solution calorimetry, Raman spec- trometry [12] and dynamic vapor sorption [15]. Vollenbroek et al. [32] and Burnett, Malde and Williams [5] used dynamic vapor sorption (DVS) to detect amorphous contents of components in dried materials. Vollenbroek et al. [32] determined the amorphous contents of partially amorphous lactose based on the corresponding BET (Brunauer-Emmet- Teller) monolayer water content. Lehto et al. [12] suggested using com- bined techniques in detecting amorphous content in dried materials. Dynamic dew point isotherm (DDI) is a recent technique developed along with dynamic vapor sorption (DVS) to measure water sorption properties of materials. The word ‘dynamic’ means that the measure- ment of water sorption variable (water content and water activity) is done continuously compared to conventional, static water sorption techniques which measure water content equilibrated materials at Powder Technology 301 (2016) 981–988 ⁎ Corresponding author. E-mail address: yrjo.roos@ucc.ie (Y.H. Roos). http://dx.doi.org/10.1016/j.powtec.2016.07.055 0032-5910/© 2016 Published by Elsevier B.V. Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec