Mass transfer limitations during starch gelatinization

A relatively large volume of maize starch suspension (2.5–20% w/w solids) is heated to above its gelatinization temperature by two means: a microwave oven meant to provide a uniform global thermalization of the sample, and a conventional local electrical heater which, depending on agitation, yields different heating patterns on the sample. The progress of gelatinization is registered on-line by an electrical conductance technique. Contrary to what is observed in the conventionally heated samples, gelatinization is not completed in the microwave irradiated samples although the temperatures reached are as high as with conventional heating. This is attributed to poor mass transfer of water molecules during microwave irradiation as a result of the short processing period and the absence of mixing of water with starch components. The latter is in line with observations regarding the role of agitation in gelatinization under conventional heating.