The results suggest that starch quality significantly determined the expansion coefficient, density, and physico‐chemical properties of the extruded starch mixtures. Unique properties of buckwheat starch were most important in this case. Attention should also be given to the effect of the extrusion conditions on chemical composition of the product, and especially to the decrease of starch and dietary fiber content.
Extrusion of the cereal mixtures with 25% addition of milk proteins induced several changes in the chemical and physico-chemical properties of starch. Coefficient of expansion was close to the coefficient of natural cereal flours, but the extrudates were characterized by higher water absorption. Starch was only slightly dextrinized, but it contained more nitrogen compounds and mineral salts, and less free lipids. Solubility and swelling power of the extrudates did not change in a way characteristic for cereal starch and flours. Attention should be given to higher content of dietary fibre, pointing to the formation of the starch-lipids and the starch-protein complexes, less susceptible to enzymatic hydrolysis used. Hence, it can be stated that the latter increase was apparent only. It can be said that a mixture of cereal starch and milk proteins can be used to modify quality of the extruded products of increased protein content. More attention should be devoted to biochemical characteristics of the protein added, as this largely determines quality of the extruded starch-protein products.
L'addition au lait de 1,8 à 5,4 mM/litre de chlorure de calcium avant chauffage à 75, 85 et 92°C pendant 15 s et 15 min provoque des changements dans les proportions de calcium (soluble, colloïdal et ionisé), en comparaison avec celles des échan-tillons de lait chauffés sans addition de sels de calcium.Dans le lait enrichi de 3,6 mM de CaCl z , par litre pasteurisé à 92°C/15 s, les pourcentages des diverses formes de calcium sont proches de celles du lait cru ou non, additionné de sel de calcium, bien que 25 % environ du calcium ionique aient été déplacés au cours de chauffage.On a constaté que les ions calcium, ajoutés au lait avant une pasteurisation haute et rapide, assurent le maintien de l'aptitude à la coagulation par la présure à un niveau comparable à celle d'un lait ayant subi une pasteurisation ménagée qui est d'usage en . fabrication fromagère.Mots clés: Lait -Calcium -Chauffage.
Summary
Influence of the addition of calcium salts and of heating on the various forms of calcium in milkBy adding 1.8 to 5.4 mM/dm 3 of calcium salts to milk before warming it at 75, 85 and 92°C for 15 sand 900 s changes, were caused in amounts of various forms of calcium (soluble, colloidal and ionie), as compared with milk samples to which calcium salts were not added before warming.In milk which was enriched by 3,6 mM of CaCl z , and pasteurized at 92°C for 15 s the percent age of various forms of calcium approximated their amounts in raw or mildly pasteurized milk, to which no salts of calcium was added, though about 25 % of ionie calcium was displaced in the soluble or colloidal form in the course of warming.The ions of calcium, as added to milk before HTST pasteurization caused the rennetability of milk to be maintained at the same level as in slightly pasteurized milk, as generally used in cheese manufacture.
SummaryStudies were carried out on the modification of the supermolecular structure of casein obtained from milk in the form of calcium paracaseinate, low-calcium (20 mg Ca/g dry weight) paracaseinate, acid casein and alkali-neutralized casein in the course of extrusion performed using a twin screw extruder "Clextral" BC 92. Due to the transformation of casein micelles, the extruded products showed anisotropic supermolecular structure. In the casein preparations neutralized to form caseinates, there was no change to anisotropic structure. It was shown that calcium bound to casein played an important role in stabilizing the structural modification of casein in the course of its extrusion.
Zusammenfassung
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