Effect of oxidoreduction potential and of gas bubbling on rheological properties and microstructure of acid skim milk gels acidified with glucono-δ-lactone

Evolution of (A) pH and (B) oxidoreduction potential (Eh₇) during the acidification of milk by glucono-δ-lactone (GDL). Different gaseous treatments were applied to milk: ungassed (U), gassed with air (G), gassed with N₂ (N), or gassed with N₂H₂ (H). Values are means from 3 experiments.

(A) Storage modulus (G′; ■) and loss modulus (G″; ○) for acid milk gels acidified by glucono-δ-lactone (GDL) under N₂H₂ conditions. (B) Mechanical spectrum of G′ (■) and G″ (○) for acid milk gels acidified by GDL under N₂H₂ conditions.

Flow curves (3 replications) for acid milk gels acidified by glucono-δ-lactone (GDL) under N₂H₂ conditions. Values at 500s⁻¹ were recorded to compare apparent viscosity in the different gels.

Confocal laser scanning micrographs (512×512) of acid milk gels acidified by glucono-δ-lactone. Different gaseous treatments were applied to milk: (A) ungassed, (B) gassed with air, (C) gassed with N₂, or (D) gassed with N₂H₂. The protein matrix appears white, whereas pores appear dark. Scale bar=20μm.