Addition of sodium caseinate to skim milk increases nonsedimentable casein and causes significant changes in rennet-induced gelation, heat stability, and ethanol stability

Abstract

The protein content of skim milk was increased from 3.3 to 4.1% (wt/wt) by the addition of a blend of skim milk powder and sodium caseinate (NaCas), in which the weight ratio of skim milk powder to NaCas was varied from 0.8:0.0 to 0.0:0.8. Addition of NaCas increased the levels of nonsedimentable casein (from ∼6 to 18% of total casein) and calcium (from ∼36 to 43% of total calcium) and reduced the turbidity of the fortified milk, to a degree depending on level of NaCas added. Rennet gelation was adversely affected by the addition of NaCas at 0.2% (wt/wt) and completely inhibited at NaCas ≥0.4% (wt/wt). Rennet-induced hydrolysis was not affected by added NaCas. The proportion of total casein that was nonsedimentable on centrifugation (3,000 × g, 1 h, 25°C) of the rennet-treated milk after incubation for 1 h at 31°C increased significantly on addition of NaCas at ≥0.4% (wt/wt). Heat stability in the pH range 6.7 to 7.2 and ethanol stability at pH 6.4 were enhanced by the addition of NaCas. It is suggested that the negative effect of NaCas on rennet gelation is due to the increase in nonsedimentable casein, which upon hydrolysis by chymosin forms into small nonsedimentable particles that physically come between, and impede the aggregation of, rennet-altered para-casein micelles, and thereby inhibit the development of a gel network.

Effect of heat treatment, evaporation and spray drying during skim milk powder manufacture on the compositional and processing characteristics of reconstituted skim milk and concentrate

“…Skim milk samples were assayed for TS and fat using the CEM SMART Trac II (CEM, Matthews, NC, USA), lactose using the FOSS MilkoScan™ FT+ (N. Foss Electric A/S, Hillerød, Denmark) and ionic calcium [Ca 2+ ], using a sensION+ 9660C Calcium Combination Ion Selective Electrode (Hach Lange, Barcelona, Spain), as described by Lin, Kelly, O'Mahony, and Guinee (2017).…”

“…Serum was prepared by ultracentrifugation of skim milk at 100,000 × g at 25 °C for 1 h and filtration of the supernatant, as described by Lin et al (2017). Skim milk and serum were analysed for total protein, non-casein nitrogen (NCN), non-protein nitrogen (NPN), calcium (Ca), phosphorus (P), and protein profile using reversed-phase high performance liquid chromatography (RP-HPLC) using methods described previously by Lin et al (2017).…”

“…(Malvern Instruments Ltd, Malvern, UK), as described by Lin et al (2017). Casein hydration was measured by lyophilisation of the pellet obtained on ultracentrifugation, and expressed as g water g -1 sedimented casein (Lin et al, 2017).…”

“…frequency of 1 Hz, as described by Lin et al (2017). The storage modulus, G', was measured dynamically as a function of time over h (G' ); the gelation time (GT) was defined as the time for G' to reach a threshold value of ≥0.2 Pa and the maximum curd firming rate as the maximum slope of the G'/time curve.…”

“…Samples of skim milk (SM, LHSM, HHSM, LHE-SM, HHE-SM, LHP-SM and HHP-SM) and skim milk concentrates with 15-25% TS (LHP-SMC, HHP-SMC) were adjusted to pH values in the range from 6.2 to 7.2 (in increment of 0.1 pH unit) at room temperature using 0.1 N HCl or NaOH. The HCT of the skim milk and skim milk concentrate samples was measured at 140 and 120 °C, respectively, as described by Lin et al (2017). Preliminary trials indicated that skim milk concentrates with 15-25% TS were sometimes prone to instantaneous coagulation at 130 or 140 °C depending on pH, while concentrates with ≥25%…”