Making a case for sesame seeds and konjac gum

Paul Boughton

While the benefits of fibre in the diet have long been known, food manufacturers are showing renewed interest in two particular food substances following the release of new research results from the Netherlands.

Published in the latest issue of the Society of the Chemical Industry (SCI) Journal of the Science of Food and Agriculture (88, pp2026-2035), the study by Petra Becker and others from Wageningen University and Research Centre in the Netherlands shows that konjac gum and sesame seed extract may offer protection against different strains of E coli and Salmonella bacteria.

Konjac is a plant of the genus Amorphophallus and is native to subtropical and tropical eastern Asia. It is often grown in these parts of the world for its starchy corm which is used to create a flour and jelly of the same name. Vegans can also used it as a substitute for gelatin.

Konjac is mostly made up of glucomannan, a polysaccharide formed when glucose and mannose are polymerised. According to one manufacturer, Acroyali in Qingdao, China, konjac glucomannan (KGM) is a high-quality soluble dietary fibre that has the function of “regulating the nutrient imbalance”. Acroyali highlights a number of ways in which this happens, including a “remarkable” reduction in blood sugar and cholesterol levels, improved regulation of lipid metabolism, and the prevention and treatment of constipation and obesity. KGM achieves this, says the company, as a result of its physicochemical properties including water solubility, thickening, stabilising, jelling and suspending, and film forming.

For its part, extracts of sesame seed are already used in various food supplements, often in conjunction with other fruit extracts such as those from olives. The claim here is that they help to slow down systemic inflammation associated with old age – notably those caused by cytokines and prostaglandins

The Dutch results show that these foodstuffs act as binders for E coli and Salmonella bacteria: the bacteria attach themselves to the fibrous foods instead of the gut cells of the host.

Becker says that eating a diet full of these foodstuffs may offer protection from gastro-intestinal infections or reduce the severity of symptoms caused by E coli or Salmonella.

 In the lab study that also included negative controls, the scientists looked at 18 food-related products including coffee beans, carrot, mango, fermented soya, and food stabilisers such as locust bean gum and konjac gum. All were subjected to in-vitro exposure to various bacteria that were allowed to attach themselves to the test products. The levels of bound bacteria were determined in a microplate-based method specifically developed for this purpose.

Bacterial adherence to host tissue is regarded as an important initial step for colonisation and infection. The first adherence specificity ever recognised in intestinal bacteria was binding to mannose-containing receptors. Even today, the most common binding ability described with bacteria is mannose-directed adhesion. As the authors highlight in their paper, almost all isolates of E coli, as well as other members of the Enterobactericeae, attach to mannose receptors by means of proteinaceous appendages called fimbriae. Other bacteria also possess different mannose-specific adhesins, too.

The results showed that sesame seed extract and konjac gum had the greatest number of adhered bacteria, leading to the conclusion that they may have a part to play in preventing certain E coli and Salmonella from latching onto the host.

Becker added: “The importance of fibre, particularly from certain foodstuffs, in maintaining a healthy gut and digestion cannot be underestimated. The study shows that these foods bind certain bacteria and may be a means of stopping bacteria from entering host cells thereby preventing disease.”

The study highlights the potential of different food and feed components as alternative binding matrices for enteropathogens. However, the authors caution that careful interpretation of the adhesion results is essential because of the magnitude of unknown factors involved, such as the expression of adhesins with a test strain, the relevance of the host in terms of an isolate’s niche, and the quality of the tested adhesion matrix. In this context, consciousness of the fact that the results were obtained with the products specified and treated as described is also important. In addition, only one product sample was tested in each case.

Despite these reservations, the in vitro test proved highly sensitive and discriminating, and hence useful for the screening of a high number of products and bacteria. The products that scored best, such as yeast mannan– oligosaccharide, pumpkin, sesame seed extract, palm kernel extract and konjac gum (against possibly zoonotic Salmonella), are worthy of further investigation in more detail with a choice of different product batches and selected bacteria, both in vitro and in vivo,” they conclude.