Antinutritional and nutritional compounds

The USDA-ARS has developed transgenic lines with reduced glycoalkaloid content by down-regulating the expression of a gene encoding solanidine UDP glucosyltransferase. Glycoalkaloids are natural compounds which can be harmful to humans and animals when consumed in high concentration. Transgenic tubers show up to a 40% reduction in glycoalkaloid levels in field trials. This provides opportunities to rescue advanced breeding selections with excellent commercial traits but which were previously discarded due to unacceptable glycoalkaloid levels. Further benefits would accrue from reduced glycoalkaloids in potato starch wastes, as a high residue content renders the wastes unsuitable for use as fodder. You can furthur read about it on the USDA-ARS website here

The production of transgenic crops containing proteins with improved amino acid composition should be of benefit to humans as well as to monogastric animals (pig, poultry, etc.) unable to synthesise all of the amino acids needed to sustain life. The potato is the most important non-cereal food crop in the world. However, it contains limited amounts of the essential amino acids lysine, tryptophan, methionine, and cysteine. Improvements in the nutritional value of food crops such as potato are especially important for people subsisting on a vegetarian diet in which the main source of protein comes from seeds, grains, tubers, etc., which contain limiting amounts of essential amino acids. Chakrabortyet al. (2000) reported improvements in the nutritive value of transgenic potato through the expression of a non-allergenic seed albumin gene (AmA1) from Amaranthus hypochondriacus. As a donor gene, the AmA1 gene has several advantages for genetic transformation experiments. First, this seed protein has a well-balanced amino acid composition, making it nutritionally superior to other proteins recommended by the WHO. Second, the purified protein has no known allergenic properties. Finally, the protein is controlled by a single gene, which facilitates integration into other species. The team showed a five- to ten-fold increase in AmA1 transcript levels in tubers of transgenic lines using the tuber-specific granule bound starch synthase (GBSS) promoter compared with the 35S CaMV promoter. Transgenic lines contained a significant two- to four-fold increase in lysine, methionine, cysteine, and tyrosine content in their protein amino acids. Data collected for two consecutive years revealed a 35 to 45% increase in total protein content in transgenic tubers, which corresponded to an increase in most essential amino acids. Grain amaranth is used in many foods throughout the world and amaranth forage has been used for centuries as an important component of the human diet throughout the tropics. The authors presented these facts as evidence of the non-allergenic nature of amaranth.

Fructans, or fructose-oligosaccharides, consist of short chains of fructose molecules. Inulin is a mixture of linear fructose-polymers with different chainlength and a glucose molecule at each C2-end. In over 30,000 plants (e.g. chicory, onion, asparagus, artichoke) inulin serves as a storage carbohydrate. Compounds such as inulin reduce the energy density of food and are used to enrich food with dietary fibre or to replace sugar and fat. When fructans are consumed, the undigested portion is reported to support growth of ‘friendly’ bacteria, such as Bifidobacteria and Lactobacillus species. Other benefits noted include increased production of beneficial short-chain fatty acids such as butyrate, increased absorption of calcium and magnesium and improved elimination of toxic compounds (van den Heuvel, 1999). Hellwege et al. (2000) have developed transgenic potato tubers which synthesise the full spectrum of inulin molecules naturally occurring in globe artichoke (Cyenara scolymus). High molecular weight inulins have been produced by expressing the sucrose:sucrose 1-fructosyl transferase and the fructan:fructan 1- fructosylhydrolase genes from globe artichoke. Inulin made up 5% of the dry weight of the transgenic tuber. This approach has the potential to enhance the value of staple foods such as potato with compounds giving additional benefits.