Journal Articles
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Item Interfacial composition of coenzyme Q10 emulsions impacts coagulation of fortified milk during gastric digestion(Elsevier Ltd, 2025-02-01) Wang X; Zhu P; Ye A; Singh H; Acevedo-Fani AThis study aimed to investigate the gastric digestion behaviour of heat-treated enriched milk containing Coenzyme Q10-loaded emulsions with different interfacial compositions. Four enriched milk types were compared: pasteurized with a Tween 80 stabilised emulsion (PAST-TW80), or with a sodium caseinate-stabilised emulsion (PAST-NaCN), and UHT with a TW80-stabilised emulsion (UHT-TW80), or PAST with a NaCN-stabilised emulsion (UHT-NaCN); all loaded with Coenzyme Q10. An in vitro dynamic gastric digestion model (Human Gastric Simulator) was utilized and the kinetics of milk coagulation and emptying of protein, lipid and Coenzyme Q10 were monitored. Adding NaCN-stabilised emulsion to heated milk led to a largely fragmented curd with signs of extensive droplets coalescence, disintegrating rapidly and accelerating protein and lipid release. Heated milk with TW80-stabilised emulsion produced a compact and closely integrated curd with limited coalescence, slowing nutrient emptying. UHT milk showed more curd fragmentation than PAST milk, regardless of emulsion type. The release profiles of Coenzyme Q10 were similar between UHT-TW80 and PAST-TW80 or between PAST-NaCN and UHT-NaCN, indicating the emulsion's interfacial composition as a key factor in controlling lipophilic bioactive release from the food matrix, regardless of heat treatment. These findings demonstrate that the emulsion's interfacial composition (NaCN vs TW80) and the heat treatment (PAST vs UHT) can be combined as a strategy to modulate milk coagulation kinetics and the rate of nutrient delivery to the small intestinal stage. This study provides insights into the development of functional milk products fortified with lipophilic bioactive compounds, as well as strategies for optimizing the controlled release of these compounds upon consumption.Item Animal factors affecting the cheese-making properties and the heat coagulation time of milk from dairy sheep in a New Zealand flock(Taylor and Francis Group on behalf of the Royal Society of New Zealand, 2024-03-27) Marshall AC; Lopez-Villalobos N; Loveday SM; Weeks M; McNabb WThe objective of this study was to evaluate the effect of animal factors on the cheese-making properties and on the heat coagulation time of milk from individual dairy sheep in a New Zealand flock. A total of 521 individual records were obtained from a seasonal pasture-based flock of 169 ewes milked once-a-day, from 50 to 182 days in milk. A statistical model was used to quantify the effects of animal factors (coat colour variety, age, litter size and stage of lactation) on the studied traits. Stage of lactation, confounded with seasonality, strongly influenced all properties of milk investigated. With the advancement of lactation, the milk took longer to coagulate after rennet addition, and the curd was softer. Higher relative cheese yield was achieved towards the end of lactation. The milk was also less stable to high-temperature treatment in late lactation. Coefficient of variation for processability traits was high and ranged from 20.2% to 58%, which can be largely attributed to stage of lactation but could also indicate room for genetic improvement of traits. Further genetic studies are underway to define animal genetic variance, heritability, and the phenotypic and genetic correlations between these processability and milk composition traits.Item Effect of protein polymorphisms on milk composition, coagulation properties, and protein profile in dairy sheep(Elsevier Ltd, 2025-01-01) Marshall AC; Vigolo V; De Marchi M; Lopez-Villalobos N; Loveday SM; Weeks M; McNabb WThe objective of this study was to quantify the effect of protein polymorphisms on milk composition, coagulation properties, and protein profile in dairy sheep from a New Zealand flock. A total of 470 test-day records, from 147 lactating ewes, were used in the statistical analyses. Protein polymorphisms observed in the RP-HPLC were self-named for purposes of the present study. Data were analyzed using a mixed linear model, including the fixed effects of ewe age, litter size, coat-colour, and stage of lactation, and, as a covariate, deviation from the median lambing date of the flock. The effects of protein polymorphisms were added to the model, one at a time. Protein polymorphisms were significantly (p < 0.05) associated with milk composition and protein profile. Polymorphisms of β-lactoglobulin were significantly associated with milk heat stability, being AB type more heat stable than AA. The other processability traits were not significantly affected by protein polymorphisms. Further studies are required to confirm the protein variants and the properties of individual protein polymorphisms.Item Probing structural modification of milk proteins in the presence of pepsin and/or acid using small- and ultra-small-angle neutron scattering(Elsevier Ltd, 2025-02) Yang M; Ye A; Yang Z; Everett DW; de Campo L; Singh H; Gilbert EPAcid- and pepsin-induced milk protein coagulation plays a crucial role in the gastric digestion of milk. Real-time structural evolution at a nano- (e.g. colloidal calcium phosphate (CCP) and micelle) and micro- (gel network) level of unheated and heated (85 °C for 30 min) bovine milk was examined under acidic conditions and at low and high concentrations of pepsin using ultra-small- and small-angle neutron scattering (USANS and SANS), small-amplitude oscillatory rheometry and confocal scanning laser microscopy. Milk was treated with glucono-δ-lactone (GDL), pepsin or a combination of GDL and pepsin to induce coagulation. Heat-treated milk showed a faster increase in elastic storage modulus (G′) and scattering intensity (USANS and SANS) compared with unheated milk when coagulated with GDL or the combination of GDL and pepsin. At pH 6.3, heat treatment retarded pepsin (1.10 U/mL)-induced milk coagulation, with slower increases in G′ and scattering intensity. At a high concentration of pepsin (2000 U/mL) that mimics the concentration found in the stomach, general proteolysis followed coagulation. Heat treatment retarded coagulation but accelerated curd proteolysis. This study demonstrates how time-resolved USANS and SANS can be used to investigate the structural evolution of protein coagulation and degradation under gastric environment conditions at nano- and micro-metre length scales.Item Effect of ingestion temperature on the pepsin-induced coagulation and the in vitro gastric digestion behavior of milk(Elsevier Ltd, 2023-05) Yang M; Ye A; Yang Z; Everett DW; Gilbert EP; Singh HPepsin-induced protein coagulation occurs in the gastric environment when the milk pH is above the isoelectric point of casein proteins. In this study, the effect of milk temperature (4–48 °C) on the hydrolysis of κ-casein by pepsin and the consequent protein coagulation was studied at pH 6.0 for 120 min. Quantitative determination of the released para-κ-casein showed that both the κ-casein hydrolysis reaction rate constant and the pepsin denaturation rate constant increased with an increase in temperature. The temperature coefficient (Q10) of the specific hydrolysis of κ-casein was calculated to be ∼1.95. The coagulation process was investigated by the evolution of the storage modulus (Gʹ). At higher temperature, the milk coagulated faster but had a lower firming rate and Gʹmax with larger aggregates and voids were observed. The digestion behavior of the milk ingested at 4 °C, 37 °C, or 50 °C was investigated for 240 min in a human gastric simulator, in which the milk temperature increased or decreased to 37 °C (body temperature) over ∼ 60 min. The coagulation of the 4 °C milk was slower than for the 37 °C and 50 °C milk. The curd obtained from the 4 °C milk had a looser and softer structure with a significantly higher moisture content at the initial stage of digestion (20 min) which, in turn, facilitated the breakdown and hydrolysis of the caseins by pepsin. During the digestion, the curd structure became more cohesive, along with a decrease in moisture content. The knowledge gained from this study provides insight into the effect of temperature on the kinetics of pepsin-induced milk coagulation and the consequent digestion behavior.