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    ABSTRACT: Expansion of biopolymer matrices is the basis for the production of a wide variety of cereal foods. A limited number of manufacturing processes provide practical solutions for the development of an impressive variety of expanded products, just by changing process variables. It is therefore essential that the mechanisms involved in expansion are well known and controlled. This paper summarizes the knowledge of nucleation and expansion in extruded and microwaved products available to date. The effect of processing conditions and properties of the biopolymeric matrix on nucleation and expansion are discussed. Moisture content enables the glassy polymeric matrix to turn into rubbery state at process temperatures, which allows superheated steam bubbles to form at nuclei and then expand, expansion being governed by the biaxial extensional viscosity of the matrix. Nucleation and expansion theories are presented along with quantitative data that support them.
    Comprehensive Reviews in Food Science and Food Safety 11/2006; 2(4):147 - 165. · 5.05 Impact Factor
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    ABSTRACT: The effects of starch origin (potato, corn, and rice starches) and hypochlorite level (NaOCl, 0.8% and 2% w/w) on the structures and physicochemical properties of oxidized starches were investigated. Carboxyl and carbonyl group contents of oxidized starches increased with increasing NaOCl level, with potato starch having the highest and corn starch having the lowest carboxyl groups content at both NaOCl levels. Oxidation generally reduced the pasting temperature and viscosity of native starches as demonstrated by using a Rapid Visco Analyser. The peak viscosities of oxidized rice and corn starches were higher than those of their native counterparts at 0.8% NaOCl. The morphology of starches was not altered and X-ray diffraction patterns of all the starches remained unchanged after oxidation. Oxidized starch batters exhibited greater adhesions than did native starch batters, with rice starch batter exhibiting the greatest adhesion. Carbohydrate profiles by high-performance size-exclusion chromatography indicated that both amylopectin and amylose were degraded during oxidation. The level of oxidation was largely dependent on the degree of crystallinity of starch and the degree of polymerization of amylose, whereas the adhesion property of oxidized starch was mainly attributed to its granular size and shape.
    Starch - Starke 05/2001; 53(5):211 - 218. · 1.22 Impact Factor
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    ABSTRACT: Extrusion cooking is one of the fastest growing food-processing operations in recent years due to several advantages over traditional methods. Apart from its main goal of improving the quality of intermediate and final processed products, it may incidentally also improve safety because of the potential to reduce mycotoxin levels in cereals. This review is focused on extrusion cooking and aims to give a general overview of its impact in reducing mycotoxin levels in cereals. Extrusion cooking generally decreases the mycotoxins levels at rates depending on different factors such as the type of extruder, the type of screw, the die configuration, the initial mycotoxin concentration, the barrel temperature, the screw speed, the moisture content of the raw material and the use of additives. Reductions of 100, 95 and 83% for fumonisins, aflatoxins and zearalenone, respectively, have been reported during extrusion cooking of cereals, while lower reductions were observed for deoxynivalenol, ochratoxin A and moniliformin, where maximum reductions did not exceed 55, 40 and 30%, respectively.
    Food Additives and Contaminants 03/2005; 22(2):150-7. · 2.13 Impact Factor

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