Journal Articles
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Item Heat-set gelation of milk- and fermentation-derived β-lactoglobulin variants(Elsevier Ltd, 2025-08) Pan Z; Kornet R; Hewitt S; Welman A; Hill JP; Wubbolts M; Mitchell S; McNabb WC; Ye A; Acevedo-Fani A; Anema SGMilk-derived β-lactoglobulin (mβ-LG) and fermentation-derived β-lactoglobulin (fβ-LG) may slightly differ in their amino acid sequences. This study aims to investigate the heat-set gelling behaviour of mβ-LG (variants A, B, and C) and fβ-LG A variants. Differential scanning calorimetry indicated similar denaturation temperatures for mβ-LG A and fβ-LG A (∼75 °C), with mβ-LG C highest (∼81 °C) and mβ-LG B intermediate (∼78 °C). All fβ-LG A formed translucent gels with a fine-stranded structure, whereas mβ-LG A, B, and C formed opaque gels with a coarse particulate structure. fβ-LG A exhibited delayed gelation onset and lower gel stiffness compared to mβ-LG A. Among mβ-LG's, mβ-LG A showed the highest gel stiffness, followed by mβ-LG B and then mβ-LG C. Rheological analysis showed that fβ-LG A gels were more elastic and ductile compared to mβ-LG A gels, indicated by smaller tan δ values and delayed increases in energy dissipation ratio at higher strain amplitude; mβ-LG B and mβ-LG C gels were less elastic but more ductile compared to mβ-LG A gels. The more elastic and ductile nature of fβ-LG A gels indicates their potential for applications requiring these specific textural properties. By selecting mβ-LG variants from milk and/or utilizing precision fermentation to engineer additional differences, it is possible to tailor the gelation characteristics of β-LG to meet specific functional requirements.Item Formation and properties of highly concentrated oil-in-water emulsions stabilized by emulsion droplets(Elsevier Ltd, 2023-12) Cheng L; Ye A; Yang Z; Hemar Y; Singh H70% (v/v) concentrated emulsion has been prepared using Ca2+-cross-linked sodium caseinate particles (Ca-CAS) or Ca-CAS coated nano-sized primary emulsion droplets as emulsifiers. The primary droplet-stabilised emulsion (DSE) was compared with the conventional Ca-CAS stabilised-emulsion (PSE) in terms of viscoelasticity as affected by aging (30 days) and heating (80 °C, 30 min) at pH 5.8 and 7.0. DSE at pH 5.8 showed the highest complex modulus (G* = 1174 ± 39 Pa), approximately was six-times higher than other emulsions (G* ≤ ∼250 Pa) due to the thick emulsifier layer consisting of primary droplet increasing the effective volume faction of core droplets by a factor of ∼1.21. After aging, G* of DSE at pH 5.8 increased to 1685 ± 68 Pa, while G* of other three emulsions were ∼400 Pa. After heating, G* of DSE reached 1801 ± 69 Pa and 1312 ± 205 Pa at pH 5.8 and pH 7.0, respectively, while G* of PSE were ∼600 Pa at both pHs. The possible mechanism for aging-induced gelation was the gravity-driven microphase separation, in which the droplets flocculate together with the entrapped aqueous phase increasing the effective volume fraction. The heat-induced gelation was attributed to the increase in droplet interactions through protein aggregates and/or primary droplets forming three-dimensional networks at elevated temperature. This study suggests that the mechanical strength of food-grade concentrated emulsions can be effectively improved using nano-sized primary emulsions as emulsifying agent and can be further modulated by aging orItem Acid and rennet gelation properties of sheep, goat, and cow milks: Effects of processing and seasonal variation(Elsevier Inc on behalf of the American Dairy Science Association, 2023-03) Li S; Delger M; Dave A; Singh H; Ye AGelation is an important functional property of milk that enables the manufacture of various dairy products. This study investigated the acid (with glucono-δ-lactone) and rennet gelation properties of differently processed sheep, goat, and cow milks using small-amplitude oscillatory rheological tests. The impacts of ruminant species, milk processing (homogenization and heat treatments), seasonality, and their interactions were studied. Acid gelation properties were improved (higher gelation pH, shorter gelation time, and higher storage modulus (G') by intense heat treatment (95°C for 5 min) to comparable extents for sheep and cow milks, both better than those for goat milk. Goat milk produced weak acid gels with low G' (<100 Pa) despite improvements induced by heat treatments. Seasonality had a marked impact on the acid gelation properties of sheep milk. The acid gels of late-season sheep milk had a lower gelation pH, no maximum in tan δ following gel formation, and 70% lower G' values than those from other seasons. We propose the potential key role of a critical acid gelation pH that induces structural rearrangements in determining the viscoelastic properties of the final gels. For rennet-induced gelation, compared with cow milk, the processing treatments of the goat and sheep milks had much smaller impacts on their gelation properties. Intense heat treatment (95°C for 5 min) prolonged the rennet gelation time of homogenized cow milk by 8.6 min (74% increase) and reduced the G' of the rennet gels by 81 Pa (85% decrease). For sheep and goat milks, the same treatment altered the rennet gelation time by only less than 3 min and the G' of the rennet gels by less than 14 Pa. This difference may have been caused by the different physicochemical properties of the milks, such as differences in their colloidal stability, proportion of serum-phase caseins, and ionic calcium concentration. The seasonal variations in the gelation properties (both acid and rennet induced) of goat milk could be explained by the minor variation in its protein and fat contents. This study provides new perspectives and understandings of milk gelation by demonstrating the interactive effects among ruminant species, processing, and seasonality.Item Kinetics of pepsin-induced hydrolysis and the coagulation of milk proteins(Elsevier Inc and the Federation of Animal Science Societies on behalf of the American Dairy Science Association, 2022-02) Yang M; Ye A; Yang Z; Everett DW; Gilbert EP; Singh HHydrolysis-induced coagulation of casein micelles by pepsin occurs during the digestion of milk. In this study, the effect of pH (6.7–5.3) and pepsin concentration (0.110–2.75 U/mL) on the hydrolysis of κ-casein and the coagulation of the casein micelles in bovine skim milk was investigated at 37°C using reverse-phase HPLC, oscillatory rheology, and confocal laser scanning microscopy. The hydrolysis of κ-casein followed a combined kinetic model of first-order hydrolysis and putative pepsin denaturation. The hydrolysis rate increased with increasing pepsin concentration at a given pH, was pH dependent, and reached a maximum at pH ~6.0. Both the increase in pepsin concentration and decrease in pH resulted in a shorter coagulation time. The extent of κ-casein hydrolysis required for coagulation was independent of the pepsin concentration at a given pH and, because of the lower electrostatic repulsion between para-casein micelles at lower pH, decreased markedly from ~73% to ~33% when pH decreased from 6.3 to 5.3. In addition, the rheological properties and the microstructures of the coagulum were markedly affected by the pH and the pepsin concentration. The knowledge obtained from this study provides further understanding on the mechanism of milk coagulation, occurring at the initial stage of transiting into gastric conditions with high pH and low pepsin concentration.