Natural low-calorie sweeteners - Natural Food Additives, Ingredients and Flavourings - page 46

equivalent to that from the original route, and that tagatose in the EU may claim
the reduced calorie content of 1.5 kcal/g rather than the mandatory 4 kcal/g that
applies to other sugars.

Physico-chemical properties
D -Tagatose is a virtually odourless white or slightly off-white crystalline powder
similar in appearance to sucrose. It melts at 133-137°C, and is very soluble in
water (1600 g/l at 20°C) and slightly in ethanol (0.2g/l) (Bär 2004). The crystals
have marginally greater hygroscopicity than sucrose (Bertelsen et al. 2001) but
not such as to require special packaging.
Like other monosaccharides, D -tagatose is stable under the pH conditions
which are encountered typically in foods (pH >3). Minimal tagatose loss and
browning were observed in 0.02M phosphate and citrate buffers at pH 3. In 0.1M
buffers at pH 3 and 40°C, approximately 5% tagatose was lost over six months
and slight browning occurred. Tagatose degradation was enhanced at pH 7,
especially in phosphate buffer, where it occurred faster than in citrate buffer.
Higher buffer concentrations also enhanced tagatose loss (Dobbs and Bell 2010).
As a reducing sugar, D -tagatose readily undergoes Maillard reactions and
caramelises at elevated temperatures.

Metabolism
D -Tagatose and fructose are metabolised via the same biochemical pathway.
However, ingested fructose is absorbed quantitatively, while D -tagatose is
absorbed only to the extent of about 20%. About a fi fth of this is excreted in the
urine, the rest is metabolised. The unabsorbed 80% of ingested tagatose passes to
the colon, where it is completely fermented by bacteria, resulting in the production
of biomass and short-chain fatty acids. The latter are mostly absorbed and
metabolised. However, such are the energy losses in this process that the US Food
and Drug Administration (FDA) has accepted a calorifi c value of 1.5 kcal/g for
tagatose.
It is prebiotic, as evidenced by the increased level of butyrate that it engenders
and the increased presence of lactobacilli in faeces. Unadapted subjects show
some mild intestinal intolerance to tagatose. A single dose of 20 g D -tagatose
resulted in the same mild intestinal side-effects (e.g. fl atulence) as a single dose of
20 g of the polyol lactitol (Lee and Storey 1999).
Tagatose does not promote dental caries, neither does it affect blood glucose or
insulin.
The JECFA ADI for tagatose is 'not specifi ed', meaning that its use is limited
only by GMP (JECFA 2004).

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Sensory properties
D -Tagatose is almost as sweet as sucrose and has a potency in water of 0.92 at
10% SE (Levin et al. 1995). It is also a fl avour enhancer, and is claimed to be
synergistic with aspartame and to benefi t the sweetness quality of several other
synthetic HPS (Bertelsen et al. 2001).