Structure rearrangement during rennet coagulation of milk modifies curd density

Abstract

Milk curds are a semisolid structure resulting from the enzymatic coagulation of milk, consisting mainly of paracasein micelles, fat globules, and whey. This gel undergoes a series of changes in its composition and structure during setting and curing, affecting curd density. The present study investigated the composition and density of inoculated and noninoculated milk curds during a 60-min curing period conducted at 30, 35, and 40°C. The purpose of the study was to determine the density changes occurring in the protein phase of curds during curing under different conditions of temperature and pH to understand the nature of the structural changes happening in the paracasein matrix. Noninoculated curd density values oscillated between 1.0247 and 1.0294 g/cm 3 after 60 min of curing, whereas inoculated treatments showed values between 1.0222 and 1.0321 g/ cm 3 . This small difference in density between the studied samples was surprising because the whey content of samples differed greatly. Density of the protein phase reached values of 1.8002 and 1.4388 g/cm 3 for noninoculated and inoculated curds, respectively, after 60 min of curing. Two independent mechanisms involved in the development of the protein-based structure of curds were identified upon comparison of the development of protein phase density in inoculated and noninoculated curds. Although the larger increase in protein phase density observed in noninoculated curds was probably due to the concurrent action of calcium-mediated electrostatic bonds and temperature-dependent hydrophobic bonds, inoculated curds showed a lower protein phase density caused by calcium solubilization and by a decrease in the net charge of paracasein micelles induced by pH reduction.

Effect of pH on the coagulation properties of Tenebrio molitor coagulant

“…The determination of whey OD value refers to the method of Amaro‐Hernández et al . (2020). Ten millilitres of coagulant were added to 100 mL of milk samples, and then coagulated at 35°C for 1 h and collected the whey.…”

Nutritional Value of Yogurt as a Protein Source: Digestibility/Absorbability and Effects on Skeletal Muscle

“…Milk protein is broadly divided into casein and whey proteins. Traditionally, when cheese is produced from milk using rennet, the protein in the solidified part of the cheese body is casein, and the protein in the residual water, called whey, is whey protein [12]. Total milk protein is composed of casein and whey proteins at an approximate 8:2 ratio.…”

Structural dependence of concentrated skim milk curd on micellar restructuring

“…Several studies have attempted to explain why milk composition and processing conditions affect gel structure. These include, for example; the dependence of curd strength on native casein micelle size [ 9 ], demineralisation of Ca and a lower net charge reported as the reason for a reduced density of the protein network during renneting of milk with decreasing pH [ 10 ] and a higher gelation temperature reported to be responsible for an unstructured and coarse network of larger casein aggregates [ 11 ]. Rearrangements in rennet gels from pre-heated milk were found to be limited due to crosslinking by denatured whey proteins [ 6 ], while using a fractal scaling model, Mellema [ 12 ] reported that the structure of skim milk curd at various pH and temperatures is related to rearrangements thought to be caused by particle fusion.…”