PREDICTING POTATO CRISP DARKENING - 2 METHODS FOR ANALYSIS OF GLUCOSE

Two methods were adapted to determine glucose concentrations in liquid expressed from potato tubers. Both methods are based on glucose oxidase. The first method is performed in multiwell plates such as used in ELISA assays and requires only 1-20-mu-g glucose/well. Using the multiwell plate method, glucose concentrations in 5-mu-litre samples of potato liquid could be tested without centrifuging or filtering. The colours of potato crisps made from the same groups of tubers, measured by reflectance (Agtron), were highly correlated with glucose concentrations (r2 = 0.89). Potatoes showing > 8 mM glucose (> 12-mu-g in 10-mu-l expressed sap) by this method were unsatisfactory for frying. An alternative assay using a commercial blood glucose strip (BM-Test 1-44) was used to estimate 1-11 mM glucose within 3 min. Results from this assay were equally well correlated with crisp reflectance after cooking. In this assay, potatoes showing > 4 mM glucose were unsatisfactory. The strip assay can be performed away from a laboratory, and may be useful for breeders, farmers, purchasing agents, and wholesalers.