A comparison of the formation, rheological properties and microstructure of acid skim milk gels made with a bacterial culture or glucono-δ-lactone

Gels were made by acidification of milk with glucono-delta-lactone (GDL) or a starter culture, at two gelation temperatures. Rheological properties and microstructure of these gels were determined using oscillatory rheometry, permeability and confocal laser scanning microscopy. On addition of GDL to milk the pH decreased rapidly and it stabilized at pH similar to 4.6. After the addition of starter culture to milk initially the pH decreased slowly and then decreased steadily but stabilized at pH similar to 4.0. GDL-induced gels had much shorter gelation times but higher storage moduli (GI), yield stresses and strains, permeability and whey separation than gels formed by a bacterial culture. Gels formed at 42 degrees C had shorter gelation times but higher pH at gelation, G', permeability and whey separation. Loss tangent of all gels increased to a maximum shortly after gelation. Microstructure of gels formed with a bacterial culture was not greatly affected by gelation temperature in contrast to GDL-induced gels. (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.