STARCH DAMAGE .2. TYPES OF DAMAGE IN BALL-MILLED POTATO STARCH, UPON HYDRATION OBSERVED BY CONFOCAL MICROSCOPY

Confocal fluorescent microscopy was used to classify the types of damage in native and ball milled potato starch granules on the basis of their response on hydration. Damage to individual granules at room temperature was assessed using the integrity of the maltese cross and with two fluorophores, congo red and acridine orange. A variety of types of damage were found, ranging from granules that appeared physically intact with localised congo red fluorescence and a corresponding deficit in the maltese cross, to granules that had 'exploded: as hydration of the core ruptured the granule, leaving the outer layers of the granule split but ostensibly intact. Also found were granules with obvious fractures and apparently intact granules with fluorescent areas which sometimes exuded a puff of fluorescing material. When hydrated at room temperature the interior of granules sometimes forms a gelatinous mass while the exterior of the granules remained virtually unaffected. The differentiation of the outer layers of the potato starch granule from the inner layers suggests a macroscopic model of granule structure comprising an outer layer, that is resistant to both damage and gelation, covering a less resistant interior.