Influence of the acidification process on the colloidal stability of acidic milk drinks prepared from reconstituted nonfat dry milk

Studies on the stabilization of acidic milk drinks with pectin require the availability of well-defined preparations of acidic milk drink, but traditional acidic milk drinks suffer from problems of reproducibility because of variations of milk quality and bacterial fermentation. The possibility of replacing bacterial fermentation of fresh milk by chemical acidification with glucono-Delta-lactone of reconstituted nonfat dry milk has been considered. The addition of 3% glucono-Delta-lactone and subsequent incubation at 30 degrees C provided acidic milk gels that were similar in texture to those obtained by fermentation with lactic acid bacteria. Despite different setting rates, as evidenced by continuous turbidimetric and rheological measurements, the acidic milk gels set at nearly the same pH for both glucono-Delta-lactone and microbial acidifications. On the addition of pectin, the corresponding acidic milk drinks exhibited similar rheological changes, indicating that the stabilization mechanism is probably the same for both acidification processes. Reconstituted NDM acidified with glucono-Delta-lactone, which provides reproducible preparations, can thus be accepted as a good material for studying the stabilization of acidic milk with pectin.