Summer 2001 Issue — Tagatose — A novel low calorie bulk sweetener with probiotic properties

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Introduction

Tagatose, commercialised by Arla Foods Ingredients Amba is a low calorie bulk sweetener with the following properties:

• It has 92% the sweetness of sucrose.
• It has a reduced caloric value of 1.5 kcal/g vs. 4 kcal/g for sucrose (approved in the US).
• It is non-cariogenic.
• It is a probiotic.
• It is suitable for people suffering from diabetes.
• It is a flavour enhancer.

D-Tagatose or Tagatose is a ketohexose in which the fourth carbon is chiral and is a mirror image of the respective carbon atom of the common D-sugar, fructose. The structural formula of tagatose is depicted in Figure 1, along with that of D-fructose.

Fig. 1. The structural formula of fructose and tagatose

Based on a similarity in sweetness and physical bulk to sucrose, tagatose is intended to be used as:

• A reduced-calorie bulk sweetener in confectionary.
• A probiotic sugar in breakfast cereals and functional foods and meal replacements.
• A sugar suitable for people suffering from diabetes in breakfast cereals and functional foods.
• A sweetener in low glycemic food formations.
• A flavour enhancer in soft drinks.

In the following, we will focus on the probiotic properties of tagatose as well as the positive effects observed for people suffering from type 2 diabetes.

Probiotic effect

The rather small difference in chemical structure of tagatose compared to fructose has large implications on the overall metabolism of the sugar. The fructose carrier-mediated transport in the small intestine has no affinity for tagatose, and only approximately 20% of ingested tagatose is absorbed in the small intestine. The absorbed part is metabolised in the liver by the same pathway as fructose. The major part of ingested tagatose is fermented in the colon by the indigenous micro flora resulting in the production of short-chain fatty acids.

In this respect, tagatose is a potential probiotic. In pig studies, tagatose altered the composition of colonic micro flora as evidenced by changes in the proportions of the short-chain fatty acids produced. When colonic material from pigs adapted to tagatose was incubated with 1% tagatose, 46 mol% of the short-chain fatty acids produced where butyrate. In comparison, colonic material from pigs adapted to sucrose yielded 17-mol% butyrate (Laerke & Jensen 2000).

In addition, concentrations of butyrate in the caecum and colon of pigs increased in a dose-response manner when they were fed tagatose (Bertelsen et al 1999). This showed that the micro flora favoured by tagatose consumption had the potential to produce large amounts of butyrate, which is believed to be of importance for colonic health.

Increased concentrations of butyrate were also observed in portal vein blood from both adapted pigs fed tagatose. The appearance of butyrate in the portal vein of unadapted pigs showed that adaptation to tagatose took place within the 12 hours of the experimental period (Bertelsen et al 1999).

Similar results were obtained in humans ingesting 3x10g tagatose per day for two weeks. In vitro fermentation of 1% tagatose with faecal samples from the human volunteers showed that the proportion of butyrate was higher when the volunteers were adapted to tagatose (35-mol% after 4 hours of incubation vs. 25 mol% in samples from unadapted volunteers). The human faecal micro flora also adapted to tagatose fermentation within the time span of the experiment (48 hours).

In addition, tagatose lead to changes in microbial population density in the faeces of the human volunteers. Pathogenic bacteria (such as coliform bacteria) were reduced, and specific beneficial bacteria (such as lactobacilli and lactic acid bacteria) were increased (Bertelsen et al 1999). These results were in accordance with a study screening pure strains of intestinal bacteria as well as dairy starter cultures for their ability to ferment tagatose. Included in the study were isolates of normal (34 strains) or pathogenic (11 strains) human intestinal bacteria, 22 additional intestinal isolates from healthy humans and 107 dairy-type lactic acid bacteria.

Tagatose was only fermented by a limited number of the intestinal bacteria and except for one Clostridium species; the strains that were able to ferment tagatose belonged to the lactic acid bacteria group, Lactobacillus and Enterococus. None of the pathogens were able to metabolise tagatose. The high frequency of tagatose fermentation between intestinal Lactobacillus and Enterococus were confirmed in the dairy-type lactobacilli and Enterococusspecies. None of the Bifidobacterium tested were able to ferment tagatose (Bertelsen et al 2001). Lactobacilli are important inhabitants of the intestinal tract of man and animals and they are believed to exert positive effects on intestinal function and health (Klaenhammer 1998). As the viability of live bacteria in food products and during transit through the gastrointestinal tract may be variable, an alternative approach is to stimulate the growth of beneficial colonic bacteria by non-digestible food, the probiotic concept (Gibson & Roberfroid 1995).

The stimulation of lactobacilli and the increase in butyrate production in vitro and in vitro indicates that tagatose has probiotic properties that could find important applications in functional foods.

Effects for people suffering from type 2 diabetes

The incidence of diabetes is increasing worldwide representing a serious threat to public health. Glycemic control - i.e. maintaining the blood glucose levels as close to the normal range as possible - has been shown to have positive effects against secondary complications such as retinopathy (The Diabetes Control and Complications Trial Research Group 1993). Intake of low glycemic foods, resulting in a lower blood glucose relative to a similar intake (50g) of digestible carbohydrates from white bread or glucose, has been shown to improve glycemic control (Brand-Miller 1994). In addition, avoiding obesity and increasing intakes of food rich in dietary fibre and low glycemic carbohydrate-containing foods have been advocated by WHO/FAO (1998) as the best means of reducing the rapidly increasing rates of type 2 diabetes. Similar types of foods have also been suggested to have beneficial effects against obesity and cardio-vascular diseases (Frost & Dornhorst 2000, Jenkins et al 2000).

Fig 2.

A trial was conducted at the University of Maryland Hospital, which studied the acute glycemic effects of tagatose ingestion alone or in combination with glucose in 8 persons with and 8 persons with type 2 diabetes. The human volunteers were given 75g of tagatose. In addition, 10 type 2-diabetes patients were given separate doses of 0, 10, 15, 20 and 30g of tagatose 30 minutes prior to 75g of glucose. Ingestion of tagatose alone did not influence plasma glucose or insulin levels in either healthy humans or patients with type 2 diabetes. Interestingly, tagatose significantly blunted the rise in plasma glucose following intake of glucose in patients with type 2 diabetes in a dose-dependant manner without significantly affecting insulin levels (see fig. 2, Donner et al 1999). The reasons for the positive effects are not fully understood, but one may speculate that the observed blunting is due to either an specific osmotic effect on gastric emptying and small intestinal transit time or a stimulating effect on net deposition of liver glycogen.

Although it may be debated whether tagatose is strictly speaking a low glycemic food as it is not digested in the small intestine to any large extent, the results presented above suggest that tagatose is well suited for making palatable confectionary, breakfast cereals, soft drinks and other products, which can also be enjoyed by people suffering from type 2 diabetes.

In this article we have tried to focus on some of the important nutritional advantages that tagatose may offer in various food applications in addition to sweetness delivery, calorie reduction, tooth-friendliness and flavour enhancing properties. Tagatose has obtained self-affirmed GRAS (Generally Recognised As Safe) status in the US permitting its use in foods. Approval procedures in the EU, Japan, Australia and New Zealand will soon be initiated.

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