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Food Structure

Abstract

Freeze-fracturing can be used effectively to study pasta microstructure both in the dry and cooked state. Aft er a walerglycerol soaking. conventional raw wheat pasta shows an uncoagulated protein matrix in which the starch granules are uniformly dispersed. Starch granules appear unswollen with a spherulitic structure. Extensive protein denaturation and starch swelling may occur during processing when a temperature greater than 60°C is attained in drying. Extensive structural transformations take place in cooking. A fibrillar protein network which envelops gelatinized starch is the typical structure observed in cooked durum wheat spaghetti. Whereas. in soft wheat products, there is a less extensive protein framework with more diffuse starch particles.

Pasta cooking quality is determined by a physical competition between protein coagulation into a continuous network (I) and starch swelling with spherulite scattering (II) during cooking. If the former (I) prevails, starch particles are trapped in the network alveoli promoting firmness in cooked pasta : Whereas if the latter ( II) prevails, the protein coagulates in discrete masses lacking a continuous framework and pasta will show softness and usually stickiness. High temperature-low moisture (HT-LM) drying partially overcomes this competition by producing a coagulated protein framework in dry pasta without starch swelling.

HT-LM treatment induces protein-starch interactions and conformational changes in the starch granule fine structure during cooking. Linear and branched chain-like fibrils appear in the core of the granules and particle groupings in the outer area. The better understanding of the role of controlled starch modification which optimizes pasta processing permits better use of non-conventional raw materials in pasta preparation.


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