Beschreibung:
<jats:title>ABSTRACT</jats:title><jats:p>Gels were prepared from fresh and reconstituted skim milk (10–30% total solids) using glucono‐δ‐lactone as the acid precursor within the pH range of 4 to 6.</jats:p><jats:p>Firmness of glucono‐δ‐lactone‐induced skim milk gels increased with (a) decrease in pH of skim milk having the same total solids content, (b) increase in total solids at a given pH, (c) pre‐heating skim milk to 90°C, and (d) adding glucono‐δ‐lactone at a higher temperature.</jats:p><jats:p>Electron microscopy revealed that in condition (a) larger sizes of casein micelles (particles) were associated with a higher firmness whereas in conditions (b), (c), and (d) the increased firmness was correlated with decreased micelle sizes. The relation between rheological behavior and microstructure of glucono‐δ‐lactone‐induced skim milk gels was more dependent upon the micellar arrangement than upon the size and shape of the casein micelles. Conditions which led to large casein micelle clusters and chains in conditions (b), (c), and (d) resulted both in severe syneresis and in weaker gels.</jats:p><jats:p>An unusual phenomenon was observed in skim milk gels made at pH 5.5, particularly at the lower total solids content (10%): the casein particles consisted of a solid core surrounded by an outer lining, 0.03–0.05 μm thick, which resembled a membrane‐line structure; there was a free annular space of 0.05 to 0.08 μm between the lining and the core. The existence of this structure was confirmed by thin‐sectioning and freeze‐fracturing techniques.</jats:p>