Chemical and Physical Stability of Powdered Tagatose as Affected by Temperature and Relative Humidity

Abstract

Tagatose is a reduced-calorie monosaccharide that displays prebiotic properties. Water can interact with powdered tagatose to varying extents, depending upon the storage environment. Adsorbed water can impact the physical and chemical stability of tagatose, altering its functionality and usability as an ingredient. Therefore, the objective of this study was to evaluate the physical and chemical stability of bulk tagatose powder as a function of relative humidity (RH) and temperature. Saturated salt solutions were used to create environments having RH values of 33%, 54%, 75% and 85% at 20°C. Tagatose (0.3-0.5 g) was placed in vials and stored in desiccators (i.e., relative humidity chambers) at 20°C, 30°C and 40°C. Duplicate vials were removed at regular time intervals for 12 months. Moisture contents (MC) and physical characteristics were monitored monthly. Samples were dissolved in water and analyzed using HPLC to quantify tagatose degradation. Early stages of browning were measured at 280 nm, whereas brown pigment formation was measured at 420 nm. Critical relative humidity was determined at 20, 30 and 40°C. Using saturated tagatose solutions, the critical RH associated with deliquescence (RH0) was 85% at 20°C. MC values below RH0 were all less than 2% (db). The average MC at 85%RH ranged from 53-80% (db), increasing as temperature decreased. At 33%RH/20°C tagatose remained free flowing. As either temperature or RH increased, varying degrees of physical caking occurred. At 85%RH, tagatose deliquesced at all temperatures. Browning occurred in all samples at 40°C. Despite physical caking and browning, tagatose degradation was only observed in the deliquesced sample at 85%RH/40°C, where a 20% loss occurred during the study. Although RH and temperature must become extreme for tagatose degradation to occur, intermediate RHs and temperatures promote physical caking and deliquescence, which create handling problems during product formulation. Tagatose should be stored in water impermeable packaging at 20°C rather than bulk storage bins in an uncontrolled environment.