Where we Least Expect them: Beneficial Micro-organisms in our Diet

03 July 2001

Foods made with fermentation technology have been around for thousands of years. In previous Food Today articles we explained the importance of yeasts and lactic acid bacteria. This time we focus on several less well known micro-organisms, also used in making common foods and food additives.

For example, most diets include vinegar, which is the mixed fermentation product of wine by yeasts and then by acetic acid bacteria. Acetic acid bacteria usually grow spontaneously when wine is exposed to the air, but commercial production involves the use of vinegar "towers". The name vinegar derives from vin aigre (French for sour wine). Not only wine, but any alcoholic beverage can be used as a base - for instance beer for malt vinegar - as well as certain fruits (raspberries, apples), vegetables and syrups.

Soy sauce, miso, tempeh

Soy sauce, miso and tempeh have been made in the Orient for centuries. Soy sauce production uses the mould Aspergillus oryzae and other micro-organisms to ferment a soybean/ wheat mixture. This gives it a strong aroma and a dark, reddish-brown colour. The process involves two stages and takes anything from 2-12 months. During this time, the proteins and sugars in the starting material are broken down and the products are in turn converted into a wide variety of flavour and aroma compounds.

Tempeh production also uses a mould, Rhizopus oligosporus. It is an important part of the diet in countries such as Indonesia, where it serves as a major source of protein and other essential nutriments. Miso, a fermented soybean paste used as a soup and sauce base, is made using a similar cocktail of micro-organismses. Different varieties can be produced by varying salt content, sweeteners and fermentation time.

Essential Aminoacids and Flavour Enhancers

Fermentation and thus micro-organisms are also used to make food additives. The flavour enhancing properties of glutamic acid (an amino acid used as monosodium glutamate) were discovered in Japan at the beginning of the twentieth century. As well as imparting flavour, amino acids are essential nutrients, as they are building blocks for protein. Certain foods such as cereals, contain protein which is relatively low in the amino acid lysine. Lysine can be added to improve the nutritional quality of the protein. Fermentation using the bacteria Corynebacterium glutamicum and Brevibacterium flavum produces both glutamic acid and lysine.

Citric Acid and Food Additives

Citric acid is added to soft drinks, confectionery and medicines. In the past, it was made from citrus fruits, but now nearly 99% of the world's production (more than 300,000 tons) comes from mould fermentation, using Aspergillus niger.

Micro-organisms are also used to make additives that improve food consistency. Several gums produced by micro-organisms are widely used in the food industry as thickeners, emulsifiers and fillers. These can stabilise food structure and improve appearance and palatability. The most common ones are xanthan and dextran gums, produced by species of Xanthomonas and Leuconostoc bacteria respectively.

In summary, beneficial micro-organisms are important elements of food processing. Without them, our diets would lose both flavour and variety and would be less nutritious.