Influence of water on potato starch-lipid interactions. An electron spin resonance (ESR) probe study

Electron spin resonance (ESR) was used in order to study the mechanism of i nteraction of potato starch with lipids in systems with different water con tents (40, 50 and 60% w/w) during heating and cooling. Different spin probe s were used, on the one hand spin-labelled stearic acids (5-DSA and 16-DSA) , which limited lipids, and on the other hand the water-soluble probe 4-hyd roxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol), which was sensitive to changes in the dynamic properties of the water phase associated with the te mperature-induced starch structural transformations. Whatever the water con tent in the hydration range considered, Tempol was observed to be relativel y mobile in the presence of potato starch, whereas a strong absorption of s pin-labelled stearic acids on potato starch granules took place at room tem perature for all investigated starch-water systems. Spin-labelled stearic a cids were expected to stick on the starch granules. The mobility of the spi n-labelled stearic acid was less upon cooling than upon heating as a result of starch gelation. The mobility of spin probes decreased with increasing starch concentration. Introduction of a doxyl fragment at position 16 of th e hydrocarbon chain leads to a lower degree of immobilisation of the spin p robe as compared with 5-DSA. This result suggests that there is a stronger interaction of polar sites of stearic acid with starch granules. (C) 2000 S ociety of Chemical Industry.