Honey is of interest as a prebiotic material because it contains many oligosaccharides and low molecular weight polysaccharides likely to resist degradation by host enzymes, and thus be available as a nutrient source for the microflora in the large bowel. In a recent review of functional foods honey was listed as a source of a functional component in the class/component 'prebiotics'. Various researchers have investigated the prebiotic effects of honey. Reports to date describe laboratory studies, ie in vitro tests, but no publications of human clinical studies.
Using pure cultures of bacteria, Ustunol reported that US honey enhanced the growth, activity and viability of commercial strains of bifidobacteria, which are typically used as in the manufacture of fermented dairy products. The reported prebiotic effect was strain-specific. That author also reported a synergistic effect for the carbohydrate components of honey in promoting growth and activity of bifidobacteria, on the basis that tests showed honey was more effective than an artificial combination of the purified major saccharides components of honey. Another interpretation of this result is, however, that the honey tested contained additional saccharides that were more effective at promoting the growth of bifidobacteria than those tested.
The reported effect of honey on the growth and activity of intestinal bifidobacteria was similar to that of commercial oligosaccharides (FOS, GOS, and inulin). This research provided promising results with respect to the growth-promoting and prebiotic activity of honey on bifidobacteria, but did not include a study of the effects on lessdesirable intestinal bacteria, nor attempt to quantify the prebiotic potential. Consequently, additional data are required before the anticipated benefits identified can be reliably estimated.
The effect of American honeys from sourwood, alfalfa and sage on the growth and activity of five strains of human intestinal bifidobacteria was studied by Shin at al. (2005). All three honeys enhanced growth and activity of the five bacterial species. In addition, the bifidobacteria inhibited the growth of some intestinal microflora.
Haddadin et al. investigated the effect of three different honeys from Jordan on the growth and SCFA secretions of two intestinal bacteria, Bifidobacterium infantis and Lactobacillus acidophilus, and found that all three honeys increased cell counts and levels of SCFA production. In addition, they found that different strains of bifidobacteria responded in a specific way to the addition of a given type of honey to the growth medium.
It has also been established that different honeys contain source-specific oligosaccharides. For example, Weston and Brocklebank showed that a New Zealand honey contained isomaltose and melezitose, while others reported the presence of raffinose in Italian honey. In order to apply the results from laboratory studies to quantify the prebiotic potential of honey, Sanz et al. studied the effect of honey oligosaccharides upon the growth of faecal bacteria. Before the oligosaccharides were added to cultures of the faecal bacteria, the monosaccharides in the honey (which included the glucose and fructose components, were removed to avoid any influence on bacterial populations in the fermentations. This procedure simulated what would have happened in the body, where the monosaccharides are digested and absorbed in the small intestine and only the oligosaccharides pass into the large intestine to serve as a potential food source for the indigenous bacteria.
Monosaccharides were removed by three different methods: nanofiltration, yeast treatment (Saccharomyces cerevisiae) and absorption onto activated charcoal. The researchers used the Prebiotic Index (PI) to compare the growth of beneficial faecal bacteria including bifidobacteria, lactobacilli and eubacteria, as well as of less desirable ones such as clostridia and bacteroides. The honey-derived samples were also compared to fructooligosaccharide (FOS), a commercial prebiotic). FOS was found to have the highest PI value (6.89); the three honey-derived oligosaccharide fractions returned similar PI values, with the highest being for the charcoal fraction (4.24), which contained the greatest oligosaccharide content. In addition, levels of the short chain fatty acids (SCFA) lactic acid and acetic acid were measured.
Natural honey, FOS and the charcoal-derived honey oligosaccharides showed the highest lactic acid values, while the charcoal fraction showed the highest acetic acid value. Those workers concluded that the tested honeys contained oligosaccharides which would function well as prebiotics.