title: Rheological and structural properties of differently acidified and renneted milk gels.
abstract: In this study we assessed the rheological and structural properties of differently acidified and renneted milk gels by controlling pH value and renneting extent. Skim milk were exactly renneted to 4 extents (20, 35, 55, and 74%) and then direct acidified to the desired pH (4.8, 5.0, 5.2, 5.5, 5.8, and 6.2), respectively. Rheological properties were assessed by dynamic rheological measurements, structural properties were studied by spontaneous whey separation and confocal laser scanning micrograph, and protein interactions were studied by dissociation test. Results showed that minimally renneted milk samples (20 and 35%) formed weak gels with low storage modulus, and the acidification range within which gels could form was narrow (pH ≤ 5.2). Highly renneted milk samples formed more gels with high storage modulus. The results of this study revealed that acidification determined the structural properties of highly renneted milk gels. As pH increased from 5.0 to 6.2, highly renneted milk gels had lower loss tangent, decreased spontaneous syneresis, and smaller pores. For both the low and high rennetings, divalent calcium bonds contributed less at low pH than at high pH. In conclusion, renneting increased the pH range suitable for gel formation; acidification determined the spontaneous syneresis and microstructure of highly renneted milk gels.
authors.affiliation: Beijing Laboratory of Food Quality and Safety, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
authors.forename: X T
authors.initials: XT
authors.lastname: Liu
authors.affiliation: Beijing Laboratory of Food Quality and Safety, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Functional Dairy, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
authors.forename: F
authors.initials: F
authors.lastname: Wang
authors.affiliation: Key Laboratory of Functional Dairy, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
authors.forename: J
authors.initials: J
authors.lastname: Luo
authors.affiliation: Beijing Higher Institution Engineering Research Center of Animal Product, Beijing 100083, China.
authors.forename: H Y
authors.initials: HY
authors.lastname: Guo
authors.affiliation: Beijing Laboratory of Food Quality and Safety, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China. Electronic address: renfazheng@263.net.
authors.forename: F Z
authors.initials: FZ
authors.lastname: Ren
mesh_terms: D000818:Animals; D012085:Chymosin / Q000378:metabolism*; D005260:Female; D005782:Gels / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008892:Milk / Q000737:chemistry*; D012212:Rheology
chemical_list: D005782:Gels; C025350:rennet; D012085:Chymosin
keywords: acid; milk gel; rennet; rheology