| Summary: | Industrial batters, which contain starches, are used to coat potato products. It is the mix of different starches and their ability to form films that contribute to the key eating characteristics. The major part of this study was to use commercial starches and batters to ascertain the different roles of the starches whilst the batter formulation rapidly changed from 60% moisture to very low levels. Materials studied included starches of different botanical origin, native or with various chemical and physical modifications, and other materials such as flour, stabilisers and salt. A group of stabilised crosslinked tapioca starches were examined in detail, but it was not possible to align the behaviour in excess water with the given levels of modification.
The theory for film creation was that structured swollen granules were embedded in starch polymers that formed a continuous network with the moisture content being critical for the transition from batter to film. To ascertain the starches’ characteristics in solution, a low moisture system, 78% N-methylmorpholine N-oxide (NMMO) - 22% water, was used and this revealed the complexity of modified starches. A major finding was that the NMMO-water system differentiated starches of the same origin (tapioca), which was not readily achieved by other techniques. To mimic film forming, starch formulations were assessed at moderate (10-50%) moisture levels using a “popping” and a hot press method. All the starches and combinations produced non-uniform, popped and interconnected films at 15% moisture (185°C for 4.6 s). This demonstrated sufficient starch polymer solubilisation to allow adhesion between the amorphous granular structures. Sorption isotherms may suggest an interaction between salt levels and processing of the starches. A critical factor for a coating is to act as a moisture barrier to maintain crispiness and therefore water sorption behaviour post processing is a key quality factor.
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