Thermal Stability of Tagatose

Abstract

Tagatose is a minimally absorbed monosaccharide that has prebiotic properties. To achieve this prebiotic benefit, tagatose in foods and beverages must not be lost during processing. However, data on the thermal stability of tagatose are lacking. The objective of this study was to evaluate the thermal stability of tagatose in solutions. 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. A second set of similar solutions was also made, only differing from the first set in that they contained 0.05 M glycine. All of the solutions were held at 60, 70, and 80ºC for a minimum of 5 hours. At least 11 samples were removed at regular time intervals during the study for analysis. Tagatose analysis occurred via reverse-phase HPLC while browning was measured using a spectrophotometer at 420 nm.

In the solutions without glycine, minimal tagatose was lost at 60-80ºC in citrate and phosphate buffers at pH 3. For these solutions, slight browning was observed at all temperatures. At pH 7, tagatose loss was enhanced. The pseudo-first-order rate constants (kobs) for tagatose degradation at pH 7 were greater in phosphate buffer than citrate buffer. Higher buffer concentrations and higher temperatures also increased kobs. Enhanced browning accompanied the tagatose degradation in all buffer solutions at pH 7. In the solutions containing tagatose as well as glycine, tagatose degraded faster at pH 7 than pH 3. Tagatose degradation was again greater in phosphate buffer than citrate buffer, and at the higher buffer concentration. Temperature also affected tagatose degradation, with faster tagatose loss occurring as the temperature increased. With glycine present in the solutions, enhanced browning occurred, but tagatose degradation rates were similar to those of the solutions without glycine. For both the solutions containing tagatose as well as those containing tagatose and glycine, the most reactive solution was 0.1 M phosphate at pH 7. Using the activation energies for tagatose degradation, it was predicted that less than 0.5 and 0.02% tagatose would be lost during basic vat and HTST pasteurization, respectively, regardless of whether or not glycine was present. Based on the results from this study, it was determined that although tagatose does breakdown at elevated temperatures, the amount of tagatose lost during the times and temperatures associated with typical thermal processing conditions would be virtually negligible. Due to minimal tagatose degradation during typical thermal processing techniques, the majority of tagatose would remain present in a beverage after pasteurization, allowing its presence to provide the consumer with prebiotic benefits.