Alternative sweetener research advances.

The sugar beet, the major crop for producing sucrose in temperate climes, may be on its way to becoming more healthy. Genetic technologists in Holland (Institute of Molecular Plant Sciences, Leiden University, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands) have engineered the sugar beet to produce fructan, a low-calorie sugar alternative, instead of sucrose.

By introducing genes encoding the enzymes for an entirely new metabolic pathway, the scientists have succeeded in generating transgenic sugar beets that are capable of producing large amounts of low-molecular-weight fructans. The transgenic sugar beet could represent a potential new source of fructans that rivals commercial strategies.

Fructans are polymers of fructose that cannot be digested by humans. They are very attractive as low-calorie food ingredients, sweeteners and fat substitutes. Some plants naturally convert sucrose to fructan by the activity of the enzyme fructosyl transferase.

Because it is difficult to harvest fructans, and their yield and quality of product are poor, the Dutch researchers hypothesized that sugar beets could be a better source of fructan. When they introduced a fructosyl transferase gene into the sugar beet, their theories were confirmed. Not only did the beets grow and appear normal, they converted virtually all of their sucrose to low-molecular fructans. Thus the fructan beet might replace expensive semi-synthetic methods of preparing this alternative sweetener. You also may recall that researchers at the University of Wisconsin (College of Agricultural and Life Sciences, Department of Animal Health and Biomedical Science, 1635 Linden Dr., Madison, WI 53706) isolated a protein sweetener from the pulp of the West African fruit Pentadiplandra brazzeana. The alternative sweetener, which they've named brazzein, is 2000 times as sweet as sugar. Some companies have taken out licenses on this technology, and academic research is continuing.

The brownish berry measures about 2 in. across and has a large seed surrounded by sweet red pulp with the consistency of avocado. In tests, investigators found that unlike sugar, which loses its intensity almost immediately, there is a momentary delay before the taste buds recognize brazzein. Then the taste lasts longer and is more steady than sugar.

Sweet proteins neither introduce non-natural metabolites into the body nor disturb the balance of the amino acid pool. Other sweeteners when decomposed may cause adverse effects. Brazzein is a naturally-occurring, low-calorie sweetener. About 30 g, or 1 oz, of brazzein equals 60 kg, or more than 130 lb of sugar in terms of sweetness. Not much of the protein is needed to sweeten a product, so brazzein does not add many calories. Unlike other naturally-occurring sweet proteins, brazzein is thermostable and will not decompose or change flavor when boiled. Its thermostability makes this protein more useful than other sweet proteins. With its heat stability, it may be possible to use brazzein as a practical protein sweetener to replace or partly replace currently-marketed carbohydrates or nontoxic sugar substitute organic sweeteners to create risk-free diet foods.

Further information. On the sugar beet: Paul J. J. Hooykaas; phone: [phone]; fax: [phone]. On brazzein: Goran Hellekant; phone: [phone]; fax: [phone].