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D-Tagatose is a naturally-occurring ketohexose which only differs from D-fructose at the fourth carbon atom ( fig. 1), the use of which has been proposed as a low-calorie, full-bulk sweetener [1]. D-Tagatose is produced from lactose in a two-step process ( fig. 2). Lactose is split into glucose and galactose. The latter is isomerized to D-tagatose by adding calcium hydroxide. At the end of the process, D-tagatose appears as a pure crystalline product (> 99%).The rather small difference in chemical structure has big implications on the overall metabolism of D-tagatose, as only 15±20% of ingested D-tagatose is absorbed in the small intestine ( fig. 3). The major part of ingested D-tagatose is fermented in the colon by indigenous microflora, resulting in production of short-chain fatty acids (SCFA).The first study investigating fermentation of D-tagatose indicated a change in the proportion of SCFA produced. In this study, one group of 8 pigs was fed a standard diet + 15% sucrose (unadapted) and another group of 8 pigs was fed a standard diet + 5% sucrose + 10% D-tagatose (adapted) for 17 days.On the 17th day, the pigs were killed 3 h after the morning feeding, and the entire gastrointestinal tract was sectioned. Contents from the mid-colon were used for in vitro fermentation assays. 20% slurries were incubated at 37°C under anaerobic conditions for 4 h with or without 1% D-tagatose added. The amount of SCFA produced by D-tagatose is calculated as the amount produced in the assay with 1% D-tagatose added subtracted the amount produced in the assay without D-tagatose.

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A number of 174 normal or pathogenic human enteric bacteria and dairy lactic acid bacteria were screened for D-tagatose fermentation by incubation for 48 hours. Selection criteria for fermentation employed included a drop in pH below 5.5 and a distance to controls of more than 0.5. Only a few of the normal occurring enteric human bacteria were able to ferment D-tagatose, among those Enterococcus faecalis, Enterococcus faecium and Lactobacillus strains. D-Tagatose fermentation seems to be common among lactic acid bacteria. Most of the analyzed dairy lactic acid bacteria fermented D-tagatose, and among those Lactobacillus, Leuconostoc and Pediococcus strains fermented most strongly, but also strains of Enterococcus, Streptococcus and Lactococcus fermented D-tagatose. None of the analyzed Bi dobacterium strains fermented tagatose.

Particle size distribution (PSD) is known to influence product properties such as flowability and compressibility. When producing crystalline lactose, different steps can affect the PSD of the final powder. The aim of this study was to investigate the influence of PSD on caking and the mechanisms involved. Smaller particles showed higher moisture sorption and a greater caking tendency, measured by dynamic vapor sorption and ring shear testing, respectively. Therefore, moisture sorption isotherms appeared as a valuable tool to predict the effect of PSD on humidity caking, as confirmed by the results of ring shear testing. Controlling the amount of fines, characterized by a higher content of impurities, a larger specific surface area and a broader span of the PSD, was found critical to limit caking. More precisely, both the total surface area and the span of the PSD require close attention as they can significantly influence humidity and mechanical caking.