Extensive dry heating-induced changes in physicochemical and immunological properties of whey proteins

SummaryCorrelations were identified between levels of the native whey proteins, β-lactoglobulin and α-lactalbumin and the surface and total hydrophobicities of cheese whey in response to different heat treatments. Heat-induced changes in the native βlactoglobulin content and surface hydrophobicity of whey exhibited the most significant linear relationship while correlations between total hydrophobicity and the native proteins were less significant because of an atypical rise in the n−heptane-binding capacity of whey after high-temperature treatment. The content of native β-lactoglobulin in whey was more sensitive to heating than the content of native α-lactalbumin, while heat-related changes in the total hydrophobicity of whey were generally greater than similar changes in surface hydrophobicity.

Download Full-text

Vibrational spectroscopic investigation of heat-induced changes in functional groups related to protein structural conformation in camelina seeds and their relationship to digestion in dairy cows

Animal Production Science ◽

10.1071/an14400 ◽

2015 ◽

Vol 55 (2) ◽

pp. 201 ◽

Cited By ~ 14

Author(s):

N. A. Khan ◽

Q. Peng ◽

H. Xin ◽

P. Yu

Keyword(s):

Dairy Cows ◽

Molecular Spectroscopy ◽

Molecular Structures ◽

Significant Shift ◽

Protein Digestion ◽

Dry Heating ◽

Feed Protein ◽

Induced Changes ◽

Intestinal Digestibility

The objective of this study was to use Fourier transform/infrared-attenuated total reflectance (FT/IR-ATR) molecular spectroscopy to quantify the heat-induced changes in feed protein molecular structures in relation to protein digestion in dairy cows. Camelina seeds were evaluated in this study as a model for feed protein. The seeds were either heated in air-draft oven (dry heating) or in autoclave (moist heating) at 120°C for 60 min or kept as raw (control). The parameters evaluated were Cornell net protein and carbohydrate system (CNCPS) subfractions, in situ ruminal degradation kinetics, intestinal digestibility of rumen undegraded protein (RUP) and protein molecular structures. Moist heating decreased (P < 0.05) the content of total rumen degradable (RDP) crude protein (CP) subfractions and increased the content of total RUP subfractions compared with raw seeds, indicating a significant shift at the site of protein digestion from rumen to post-ruminal tract. The decrease in RDP was mainly related to the marked decrease in rapidly solubilised (PA) and degradable (PB1) fractions, whereas the moderately degradable (PB2) and slowly degradable (PB3) fractions increased, suggesting a decrease in degradation rate of RDP. The in situ rumen incubation study revealed that moist heating decreased (P < 0.05) RDP and increased (P < 0.05) RUP and its intestinal digestibility. The molecular spectroscopy study revealed that moist heating altered protein molecular structures. Except PA and lag time, dry heating did not significantly alter any of the CNCPS CP subfraction, in situ ruminal CP degradation parameters, intestinal digestibility of RUP, and protein molecular structures. The correlation analysis showed that the heat-induced changes in protein secondary structures, α-helix-to-β-sheet ratio, were positively correlated (P < 0.05) with the contents PA (r = 0.90), PB1 (r = 0.89), RDP (r = 0.72) and intestinal digestibility (r = 0.91) of RUP, and negatively correlated (P < 0.05) with PB2 (r = –0.90), PB3 (r = –0.85) and RUP (–0.87). These results showed that compared with dry heating, moist heating significantly changed protein subfractions, rumen degradability and intestinal digestibility, and these changes were strongly associated with changes in protein molecular structures.

Download Full-text

Properties of aseptically packed ultra-high-temperature milk: III. Formation of polymerized protein during storage at various temperatures

Journal of Dairy Research ◽

10.1017/s0022029900015120 ◽

1975 ◽

Vol 42 (1) ◽

pp. 89-99 ◽

Cited By ~ 44

Author(s):

A. T. Andrews

Keyword(s):

High Temperature ◽

Whey Proteins ◽

Gel Filtration ◽

Milk Proteins ◽

Dependent Manner ◽

Temperature Dependent ◽

Minor Significance ◽

Protein Components ◽

Induced Changes ◽

Ultra High Temperature

SummaryThe formation of protein polymers in ultra-high-temperature (UHT)-treated milk during storage at various temperatures was examined by gel filtration. The extent of polymer formation was found to depend on both storage time and temperature. After some months of storage at the higher temperatures of 30 and 37°C, the extent of polymerization of the caseins and whey proteins due to reactions of the Maillard type was several times greater than the heat-induced changes resulting from the UHT processing itself. After storage for 6 months the following proportions of milk proteins were found to exist in the form of covalently bound polymers: 50% at 37°C, 40% at 30°C, 26% at 20°C and 21% at 4°C. In addition, further amounts of polymer were formed by disulphide bonding, the contribution of such polymers diminishing gradually in a temperature-dependent manner during storage due to continuing polymerization reactions. It appeared that αs1-casein may be preferentially involved in these polymerizations with β-casein reacting at a somewhat slower rate. Polymerization and associated reactions modifying molecular charge led to the expected alterations in electrophoretic mobility and a loss of definition in the bands due to the various protein components. Measurements of proteolytic breakdown indicated only very small increases in trichloroacetic acidsoluble fragments, suggesting that proteolysis was of minor significance.

Download Full-text