Total glycoalkaloids

Table 6.2 contains a survey of glycoalkaloid content in potatoes analyzed using the above HPLC NH2 column technique. None of the whole potatoes exceeded the 200 mg total glycoalkaloids per kg of potatoes (see A + B column). However, this was not the case for potato peel. Five of the eight samples exceeded this benchmark. The high content of peels should not be of concern, unless consumers ate large amounts of peel, as they sometimes do in some commercial products, such as potato skin appetizers. 

Morris and Lee1 analyzed potato alkaloids on octyl and octadecyl-type stationary phases. Using a mobile phase consisting of acetonitrile - water that contained small amounts of etha-nolamine (less than 0.1%), detection at 200 nm was possible. The separation of a-chaconine and a-solanine could be achieved on an octadecyl column with acetonitrile - water - ethanol-amine (45 55 0.1)(Fig.10.9e) or on an octyl column with the same solvent in the ratio (55 45 0.l)(Fig,10.9f). The alkaloids could also be separated on silica gel with this mobile phase in the ratio (77.5 22.5 0.05)(Fig,10.9g). In the case when solanidine was present in the extracts, the silica gel column was preferred. Hydrolysates of the a-chaconine and a-solanine could also be analyzed with the octadecyl column (Fig.10.9a-d). The systems could also be used for the analysis of potato extracts (Fig,10.9e-g). For a total glycoalkaloid analysis, the normal-phase system gave the fastest results (Fig.10.9h). 

A few data on total glycoalkaloid concentration in ripe fruits are mentioned in the study of Levin et al. in connection with a potential correlation between seed-dispersal and these metabolites S. mammosum L. showed almost 50 times more than S. capsicoides All., S. myriacanthum Dun. a much higher content than S. viarum Dun., and S. acerifolium Humb. Bonpl. a low content . It might be assumed that these alkaloids are also solasodine-based in case of S. myriacanthum as proven for the remaining four species however, this is speculative. 

The estimated highest safe level of total glycoalkaloids for human consumption is about 1 mg/kg body weight, a level that may cause gastrointestinal irritation (13). The acute toxic dose is estimated to be about 1.75 mg/kg body weight (4). A lethal dose may be as low as 3-6 mg/kg body weight (14). 

Fragoyiannis, D. A., McKinlay, R. G., D Mello, J. P. F. (2001). Interactions of aphid herbivory and nitrogen availability on the total foliar glycoalkaloid content of potato plants. J. Chem. EcoL, 27, 1749-1762. 

The solasodine-based glycoalkaloids solamargine and solasonine were isolated from ripe fruits of 5. acculeatissimum. The total solasodine content of these fruits was 3.8%.35 The same glycoalkaloids were found in tissue cultures of S. acculeatissimum,36 while solasodine was isolated from tissue cultures of five Solanum... 

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