Understanding microstructural changes of starch during atmospheric and vacuum heating in water and oil through online in situ vacuum hot-stage microscopy. http://dx.doi.org/10.1016/j.ifset.2012.11.006

Abstract

Starch gelatinization is a critical micro-scale phenomenon occurring during frying, which gets particular relevance during vacuum frying, where minimum conditions need to be fulfilled to get the required structure. The objective of this research was to understand the effect of water accessibility, temperature and vacuum level, in starch microstructural changes during heating in water and oil, in situ and in real time, using vacuum hot-stage microscopy. Potato starch was heated in water or in a pre-gelatinized corn starch solution, at different pressures (atmospheric, 6.5 kPa, 30 kPa). Also, a gluten–starch matrix immersed in oil was followed under the microscope. An increase in the heating rate as well as water inaccessibility increased the on-set gelatinization temperature. Under high vacuum no changes were observed, whereas under low vacuum, partial gelatinization occurred. Overall, this microstructural approach may help in explaining the high oil absorption of vacuum-fried formulated starchy products reported in previous studies.