Storage Stability of Tagatose in Buffer Solutions of Various Composition
Type of DegreeThesis
Nutrition and Food Science
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Tagatose, an epimer of fructose, is a minimally absorbed monosaccharide that has been shown to function as a prebiotic in the human body. For this prebiotic effect to be achieved, tagatose in food and beverage products must not be lost during their processing and storage. However, data on the storage stability of tagatose is lacking. The objective of this study was to evaluate the storage stability of tagatose in solutions as affected by buffer type, buffer concentration, pH and temperature. Tagatose solutions (0.05 M or about 1%) were prepared in 0.02 and 0.1 M phosphate and citrate buffers at pH 3 and 7. Triplicate vials were stored at 20, 30 and 40°C. These eight solutions were prepared again with the addition of 0.05 M glycine. Aliquots were analyzed at regular time intervals for nine months. Tagatose analysis occurred via reverse-phase HPLC while browning was measured using a spectrophotometer at 420 nm. In the solutions with no added glycine, no tagatose loss or browning was observed in 0.02 M phosphate and citrate buffers at pH 3. In 0.1 M buffers at pH 3 and 40°C, 5-10% tagatose was lost over nine months and slight browning occurred. Tagatose loss was enhanced at pH 7. Tagatose degraded in a biphasic manner, with a rapid initial decrease followed by a plateau. The pseudo-first order rate constants (kobs) for the initial tagatose degradation at pH 7 were greater in phosphate buffer than citrate buffer. Higher buffer concentrations also increased kobs. In phosphate buffers at pH 7, browning accompanied the tagatose loss, increasing to a maximum and then decreasing as tagatose loss plateaued. In solutions with added glycine, tagatose also degraded faster at pH 7 than pH 3. However, glycine did not enhance tagatose loss. Glycine did enhance browning as compared to solutions without glycine. Tagatose degradation and browning occurred faster at higher phosphate buffer concentrations and at higher temperatures. To deliver the prebiotic effect from tagatose, shelf-stable beverages should be formulated to the lowest buffer concentration and pH possible to optimize tagatose’s stability.