Effect of a CO2-acidification cycle on physicochemical and acid gelation properties of skim milk reconstituted with added pectin

The influence of a CO2-acidification cycle on the acid (glucono-δ-lactone, GDL) gelation properties of skim milk with and without added low-methoxyl pectin (LM-pectin) was assessed. Ionic calcium level, zeta potential, particle size, buffering properties and small amplitude oscillatory rheology moduli were monitored. The presence of LM-pectin in milk had an impact on the average size of the casein micelles and a large and dominant influence on its rheological behaviour during GDL acidification. The application of a CO2–pH cycle (pHtarget 4.9) as a milk pretreatment induced during GDL acidification a stabilization of the colloidal system in wide pH range (pH 6.0–5.1) with modifications of the structure of the casein micelles before the onset of gelation. These modifications induced a significant improvement on its acid gelation behaviour. The measurements of Ca2+ level during GDL acidification showed that an important and significant part of the Ca2+ released during the CO2–pH cycling was electrostatistically trapped by pectin molecules in the serum.