Changes in Glycoalkaloid Composition During Potato Processing: Simple and Reliable Quality Control by HPTLC

An HPTLC method has been established for analysis of α-solanine and α-chaconine in potatoes during industrial processing. Chromatography is performed on silica gel plates in a horizontal developing chamber. Post-chromatographic derivatization by dipping the plates into antimony(III) chloride solution and subsequent heating results in red chromatographic bands. The reaction products are detected and quantified densitometrically by reflectance scanning at 560 nm. The limit of quantification is approximately 30 ng per zone. Depending on the matrix of the sample, the detection limit for both compounds is between 5 and 20 ng per zone. The calibration plots for α-solanine and α-chaconine are linear in the range 30 to 700 ng. Polynomial regression with low relative standard deviation is possible from 30 to 1500 ng. Easy sample preparation, ruggedness, and high selectivity are outstanding advantages of this method. The method is applicable to samples at all stages of processing - raw, peeled, blanched, cooked, and dried potatoes, and byproducts such as peel, waste mash, and processing waters. After steam-peeling, the total glycoalkaloid (TGA) concentration in the analyzed cultivar Karlenawas reduced to approximately 25% of its original content in the whole potato, which can increase to more than 1000 mg TGA kg-1fresh weight. Because of further leaching during processing, the commercial potato flakes tested contained less than 6 mg TGA kg-1reconstituted mashed potatoes. Food with TGA concentrations of up to 100 mg kg-1is regarded as completely safe. The ratio of α-chaconine to α-solanine was between 4:1 to 2:1 for all the samples analyzed.