Massey Research Online - Browsing by Author "Yang Z"

Browsing by Author "Yang Z"

Now showing 1 - 20 of 23

Application of Absorption and Scattering Properties Obtained through Image Pre-Classification Method Using a Laser Backscattering Imaging System to Detect Kiwifruit Chilling Injury
(MDPI (Basel, Switzerland), 2021-06-22) Yang Z; Li M; East AR; Zude-Sasse M; Ruiz-Altisent M; Diezma B
Kiwifruit chilling injury (CI) damage occurs after long-term exposure to low temperature. A non-destructive approach to detect CI injury was tested in the present study, using a laser backscattering image (LBI) technique calibrated with 56 liquid phantoms for providing absorption coefficient (µa) and reduced scattering coefficient (µs'). Calibration of LBI resulted in a true-positive (TP) classification of 91.5% and 65.6% of predicted µs' and µa, respectively. The optical properties of 'SunGold™'and 'Hayward' kiwifruit were analysed at 520 nm with a two-step protocol capturing pre-classification according to the LBI parameters used in the calibration and estimation with the Farrell equation. Severely injured kiwifruit showed white corky tissue and water soaking, reduced soluble solids content and firmness measured destructively. Non-destructive classification results for 'SunGold™' showed a high percentage of TP for severe CI of 92% and 75% using LBI parameters directly and predicted µa and µs' after pre-classification, respectively. The classification accuracy for severe CI 'Hayward' kiwifruit with LBI parameter was low (58%) and with µa and µs' decreased further (35%), which was assumed to be due to interference caused by the long trichomes on the fruit surface.
Comparative study on the rheological properties of myofibrillar proteins from different kinds of meat
(Elsevier Ltd, 2022-01) Wang H; Yang Z; Yang H; Xue J; Li Y; Wang S; Ge L; Shen Q; Zhang M
In this study, the gel properties of myofibrillar proteins (MPs) from four meat sources (fish, beef, sheep, and pork) were compared. Oscillatory rheology measurements including temperature sweep, frequency sweep, and strain sweep were conducted to characterise the small and large deformation rheological properties of the MPs. In addition, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and scanning electron microscopy (SEM) were used to evaluate differences in the molecular weight distribution as well as the microstructures in gel among different MPs. Frequency sweep measurements showed that all MP gels were weak gels. MPs extracted from pork exhibited the highest gel strength and most compact gel structure, whereas those from fish exhibited the lowest gel strength and loosest gel structure. In addition, the MP extracted from pork (PSM) had the highest content of myosin heavy chain (MHC) and actin. In conclusion, the MPs extracted from fish source and mammalian sources varied significantly in terms of rheological properties and microstructural characteristics. These results provided useful information for developing mixed gel products with different gel strengths.
Comparison of Cd(II) adsorption properties onto cellulose, hemicellulose and lignin extracted from rice bran
(Elsevier Ltd, 2021-06) Wu C; Ren M; Zhang X; Li C; Li T; Yang Z; Chen Z; Wang L
Rice bran, an underutilized by-product obtained from outer rice layers, has received wide interest due to its abundance, eco-friendliness, and low cost. In this research, cellulose, hemicellulose and lignin as the main components of rice bran were fractionated, and their Cd(II) adsorption capacity, behavior and mechanism were further studied. The adsorption capacity of cellulose for Cd(II) was 5.79 mg/g within the equilibrium time of 10 min, which was 1.8 and 3.6 times those of hemicellulose and lignin, respectively. The Cd(II) adsorption onto cellulose exhibited monolayer surface behavior, whilst the heterogeneous adsorption behavior was observed for hemicellulose and lignin. These differences were related to the discrepancy of morphology and chemical composition in three polymers. The multi-hole sticks morphology of cellulose and porous blocky structure of hemicellulose were observed, while lignin showed compact and agglomerated blocky structure. Cellulose had numerous available adsorption sites including the oxygen-containing functional groups, which bonded with Cd(II) driven by chemical interaction. In conclusion, it highlights that cellulose from rice bran has the great potential of being applied as adsorbent for the Cd(II) removal.
Controlling starch surface characteristics - Impact on dough formation in a reconstituted dough system
(Elsevier Ltd, 2022-06-15) Lu F; Zhu X-F; Tao H; Wang HL; Yang Z
The effects of starch granule-surface proteins (SGSPs) on dough formation and breadmaking quality were studied in a reconstituted dough. After removing the SGSPs by NaOH and SDS treatment, the dough development time, stability time, and resistance to extension were increased. CLSM exhibited a coarse and discontinuous gluten network in the dough containing NaOH- and SDS-treated starches. Meanwhile, gelatinization temperatures were shifted to higher values while the gelatinization enthalpy decreased. Removing SGSPs prevented the formation of gluten network and reduced dough extensional deformability, which showed that the dough structure became worse. Compared with the control group, the firmness of the bread sample without SGSPs was significantly increased (p < 0.05), which was manifested by small and dense pores in the bread. LF-NMR showed that the distribution of relative water content shifted from T21 (0–1 ms) to T22 (1–100 ms), indicating that removing SGSPs decreased the water-holding capacity of the bread. This study suggested that starch surface characteristics were essential to maintain the structure and mechanical properties of dough and bread.
Corrigendum to "Kinetics of pepsin-induced hydrolysis and the coagulation of milk proteins" (J. Dairy Sci. 105:990-1003)
(Elsevier Inc on behalf of the American Dairy Science Association, 2023-11) Yang M; Ye A; Yang Z; Everett DW; Gilbert EP; Singh H
In equation [3] (page 994), “1−” was placed incorrectly. The corrected equation reads as follows: [Formula Presented] The authors regret the error.
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 H
Pepsin-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.
Fibrillisation of faba bean protein isolate by thermosonication for process efficacy: Microstructural characteristics, assembly behaviour, and physicochemical properties
(Elsevier Ltd, 2024-09) Hu Y; Cheng L; Gilbert EP; Loo TS; Lee SJ; Harrison J; Yang Z
The effect of thermosonication (TS) (90 °C, 10–30 min) on the fibrillisation of faba bean protein isolate (FPI) was studied. The self-assembly behaviour, microstructural characteristics and techno-functional (gelation and emulsification) properties of FPI fibrils obtained from TS treatment were compared with those obtained from conventional prolonged heating (CH) at 90 °C up to 8 h. Compared to CH treatment, TS treatment was shown to significantly accelerate the formation of FPI fibrils with prominent β-sheet structures as revealed by Thioflavin T (ThT) fluorescence, Fourier-transform infrared spectroscopy (FTIR) and circular dichroism (CD). The characteristics of fibril building blocks were analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and liquid chromatography linked to tandem mass spectrometry (LC-MS/MS) to obtain the differences between TS and CH induced fibrillisation of FPI. Transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) showed that 4 h CH and 10 min TS treatments resulted in the fibrils with similar radius (from 5 to 10 nm). Furthermore, SANS indicated that TS treatment induced the formation of an entangled FPI fibrillar network, which could lead to the observed viscoelastic properties of FPI at a high concentration (10 wt%). Finally, high internal phase O/W emulsions (HIPE, φ = 0.75) stabilised by 30 min TS induced FPI fibrils (3 wt%) demonstrated a stronger gel strength and smaller oil droplet size compared to those prepared with untreated FPI, suggesting a superior emulsification capability of FPI fibrils. This finding demonstrates that TS treatment is a promising and efficient method for fibrillisation of plant proteins with the resultant fibrils generating excellent gelation and emulsification properties.
Formation and characterisation of concentrated emulsion gels stabilised by faba bean protein isolate and its applications for 3D food printing
(Elsevier BV, 2023-08-20) Hu Y; Cheng L; Lee SJ; Yang Z
Concentrated emulsions were prepared at a fixed oil concentration (50 wt%) using faba bean protein isolates (FPI) as an emulsifier and texturizer. Effects of FPI concentration (1, 3 and 5 wt%; at pH7), pH (pH 3, 5, 7, and 9; 3 wt%) and addition of salts (200 mM NaCl and 40 mM CaCl2; at 3 wt% FPI and pH 7) on the emulsion formation were studied. The oil droplet size and microstructural characteristics were examined by static light scattering and confocal laser scanning microscopy (CLSM), and the viscoelastic behaviours of emulsions were characterised by oscillatory rheology. At all different FPI concentrations, the emulsions formed viscoelastic gels with different gel strengths and stability due to network formation and interactions between jammed oil droplets and protein aggregates. The oil droplet size, rheological properties, and 3D printability of emulsions were not significantly changed by the presence of salts. The storage modulus G′ (1 Hz) values were higher at higher FPI concentrations, and higher pH values (i.e., pH 7 and 9) as the droplet size was smaller and the droplet packing was more compact, resulting in a better 3D printing performance. Furthermore, the heat treatment (90 °C for 30 min) remarkedly improved gel strength and the 3D printability because of protein denaturation and oil droplet aggregation. This finding demonstrated that the emulsion gel formed with FPI was tuneable for food 3D printing. Most of samples displayed high printing precision with great self-supporting capability, which may find potential applications in creating specialised diet.
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 H
70% (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 or
Formation of by high power ultrasound aggregated emulsions stabilised with milk protein concentrate (MPC70)
(Elsevier BV, 2021-12-03) Zhang R; Luo L; Yang Z; Ashokkumar M; Hemar Y
In this work, oil-in-water emulsions stabilised by milk protein concentrate (MPC70) were investigated. The MPC70 concentration was kept constant at 5% (close to the protein content found in skim milk) and the oil volume fraction was varied from 20 to 65%. Sonication was performed at 20 kHz and at a constant power of 14.4 W for a total emulsion volume of 10 mL. Under certain oil concentration (≥35%) and sonication times (≥3s) the emulsion aggregated and formed high-viscosity pseudo plastic materials. However, the viscosity behaviour of the emulsion made with 35% oil reverted to that of a liquid if sonicated for longer times (≥15 s). Confocal laser scanning microscopy showed clearly that the oil droplets are aggregated under the sonication conditions and oil concentrations indicated above. An attempt to explain this behaviour through a simple model based on the bridging of oil droplets by the MPC70 particles and, taking into account the oil droplet and MPC70 particle sizes as well as the oil volume fraction, was made. The model fails to describe in details the aggregation behaviour of these emulsions, likely due to the inhomogeneous protein layer, where both free caseins and casein micelles are adsorbed, and to the packing of the oil droplets at concentrations ≤55%. Nonetheless, this work demonstrates the potential of ultrasound processing for the formation of dairy emulsions with tailored textures.
Heterogeneous firm-level responses to the US 2018 tariff announcement
(Emerald Publishing Limited, 7/12/2020) Qin Y; Yang Z; Bai M; Yawson, A
Purpose This study examines the impact of the $60 billion tariff announcement of the US government on the Chinese exporting firms. In particular, we focus on firms whose revenues are highly dependent on the US economy. Design/methodology/approach This study uses an experimental analysis and event study methodology. The sample includes firms listed in mainland China and Hong Kong stock exchanges that have the highest revenues from exporting to the US. The data are obtained from CSMAR and DataStream. Findings We find that the tariff announcement has significantly negative impacts on stock performance both before and after the announcement, and the impacts are heterogeneous across our sample firms. For A-shares listed in Mainland China, firms with more revenues from the US experience greater price drops on the announcement day, regardless of being in the targeted industry or not. But such a finding is absent from H shares listed in Hong Kong. We also find that for all the firms, greater pricing power can alleviate the impacts of the tariff announcement. Originality This is the first study documenting the heterogeneity of the impact of the tariff announcement and thus contribute to the prosperous studies on the varied firm-level responses in the Chinese stock market, and to the burgeoning literature by filling the gap of the financial market responses to the protectionist policy announcement.
High-coverage genomes to elucidate the evolution of penguins
(Oxford University Press and BGI, 2019-09-18) Pan H; Cole TL; Bi X; Fang M; Zhou C; Yang Z; Ksepka DT; Hart T; Bouzat JL; Argilla LS; Bertelsen MF; Boersma PD; Bost C-A; Cherel Y; Dann P; Fiddaman SR; Howard P; Labuschagne K; Mattern T; Miller G; Parker P; Phillips RA; Quillfeldt P; Ryan PG; Taylor H; Thompson DR; Young MJ; Ellegaard MR; Gilbert MTP; Sinding M-HS; Pacheco G; Shepherd LD; Tennyson AJD; Grosser S; Kay E; Nupen LJ; Ellenberg U; Houston DM; Reeve AH; Johnson K; Masello JF; Stracke T; McKinlay B; Borboroglu PG; Zhang D-X; Zhang G
BACKGROUND: Penguins (Sphenisciformes) are a remarkable order of flightless wing-propelled diving seabirds distributed widely across the southern hemisphere. They share a volant common ancestor with Procellariiformes close to the Cretaceous-Paleogene boundary (66 million years ago) and subsequently lost the ability to fly but enhanced their diving capabilities. With ∼20 species among 6 genera, penguins range from the tropical Galápagos Islands to the oceanic temperate forests of New Zealand, the rocky coastlines of the sub-Antarctic islands, and the sea ice around Antarctica. To inhabit such diverse and extreme environments, penguins evolved many physiological and morphological adaptations. However, they are also highly sensitive to climate change. Therefore, penguins provide an exciting target system for understanding the evolutionary processes of speciation, adaptation, and demography. Genomic data are an emerging resource for addressing questions about such processes. RESULTS: Here we present a novel dataset of 19 high-coverage genomes that, together with 2 previously published genomes, encompass all extant penguin species. We also present a well-supported phylogeny to clarify the relationships among penguins. In contrast to recent studies, our results demonstrate that the genus Aptenodytes is basal and sister to all other extant penguin genera, providing intriguing new insights into the adaptation of penguins to Antarctica. As such, our dataset provides a novel resource for understanding the evolutionary history of penguins as a clade, as well as the fine-scale relationships of individual penguin lineages. Against this background, we introduce a major consortium of international scientists dedicated to studying these genomes. Moreover, we highlight emerging issues regarding ensuring legal and respectful indigenous consultation, particularly for genomic data originating from New Zealand Taonga species. CONCLUSIONS: We believe that our dataset and project will be important for understanding evolution, increasing cultural heritage and guiding the conservation of this iconic southern hemisphere species assemblage.
Impact of incorporations of various polysaccharides on rheological and microstructural characteristics of heat-induced quinoa protein isolate gels
(Springer Science+Business Media, LLC, 2022-09) Patole S; Cheng L; Yang Z
This study aimed to investigate the properties of heat-induced gels (85 °C for 30 min) of quinoa protein isolate (QPI) in the presence and absence of various polysaccharides including guar gum (GG), locust bean gum (LBG), and xanthan gum (XG) at pH 7. For this purpose, samples with three gum concentrations (0.05, 0.1, and 0.2 wt%) at a fixed QPI concentration (10 wt%) and a fixed ionic strength (50 mM NaCl) were studied in terms of their gelation behaviour, small and large deformation rheological properties, water holding capabilities, and microstructural characteristics. Rheological measurements revealed that all polysaccharides incorporation could improve gel strength (complex modulus, G*) and breaking stress, accelerate gel formations, and more stiffer gels were obtained at greater polysaccharide concentrations. The XG exhibited the most gel strengthening effect followed by LBG and GG. Incorporation of 0.2 wt% XG led to a 15 folds increase in G* compared to the control. Confocal laser scanning microscopy observation revealed that the polysaccharides also altered gel microstructures, with the gels containing XG showing the most compact gel structures. The findings of this study may provide useful information for the fabrication of novel QPI based food gel products with improved texture.
Impact of thermosonication at neutral pH on the structural characteristics of faba bean protein isolate dispersions and their physicochemical and techno-functional properties
(Elsevier Ltd, 2024-09) Hu Y; Cheng L; Gilbert EP; Lee SJ; Yang Z
The effect of thermosonication (TS) (90 °C, 10–30 min) on faba bean protein isolate (FPI) at pH 7 was investigated. The microstructural and techno-functional properties of TS-treated FPI were compared with native FPI or FPI treated with conventional prolonged heating (CH, up to 8 h) at 90 °C. TS treatment effectively converted FPI to amorphous aggregates containing predominant β-sheet secondary structures, as determined by Thioflavin T (ThT) fluorescence and circular dichroism (CD). According to sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), these amorphous aggregates could be formed by disulfide bonds. Additionally, TS treatment is efficient in disrupting large protein aggregates of FPI, thus improving their solubility. Both TS and CH treatments induced formation of viscoelastic FPI hydrogels, whose gel strength depends on the type and time of treatment. Hydrogels formation is likely to arise from the entanglement and interaction of protein aggregates as revealed by small angle neutron scattering (SANS) and scanning electron microscopy (SEM). TS-treated FPI was also used to prepare O/W emulsions and whose structural and physical properties were compared with those stabilised by untreated FPI. At all oil volume fractions (φ = 0.2, 0.5, and 0.7) and FPI concentrations (1, 3, and 5 wt %), emulsions stabilised by TS-treated FPI exhibited smaller oil droplet size, greater mechanical strength and superior stability compared to those stabilised by untreated FPI. The study suggests that TS treatment is promising in improving techno-functional properties of FPI; further studies are needed to exploit TS-treated plant proteins as a novel food ingredient in food product development.
Impact of Ultrasound Emulsification on the Physicochemical Properties of Emulsions Stabilised by Quinoa Protein Isolates at Different pHs
(Springer Science+Business Media, LLC, 2024-03) Yang Z; Cheng L
Ultrasonication (20 kHz, 19.9 W/10 mL sample) was used to form O/W emulsions stabilised by quinoa protein isolate (QPI) particles at 3 wt%. Effects of pH (3, 5, 7, 9) and oil volume fractions (20%, 40%, and 60%) on rheological properties and microstructural characteristics of emulsions were investigated. All emulsions show viscoelastic behaviours and form a network structure comprising aggregated oil droplets and QPI particles. Emulsions stabilised by QPI at pH 5 showed largest droplet sizes and lowest gel strength due to extensive aggregation of proteins around the isoelectric point (pI ~ 4.5). The gel strength (G´(1 Hz)) were enhanced when the oil volume fraction increased and reached ~ 1100–1350 Pa at 60% oil volume fraction at different pH. This could be attributed to a tighter packing of oil droplets at 60% oil. Confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) revealed that interdroplets bridging and voids filling of QPI particles between oil droplets are critical in formation of aggregated emulsions network. Emulsions stabilised by QPI at pH 7 and 9 possessed thinner interfacial layers compared to those at pH 3 and 5. Finally, this study shows a potential of using ultrasonication to prepare gel-like emulsions stabilised by QPI, broadening applications of quinoa proteins in making dairy substitutes with semi-solid textural characteristics.
Impacts of sonication and high hydrostatic pressure on the structural and physicochemical properties of quinoa protein isolate dispersions at acidic, neutral and alkaline pHs
(Elsevier BV, 2022-12) Luo L; Yang Z; Wang H; Muthupandian A; Hemar Y
Herein, 1 wt% quinoa protein isolate (QPI) was exposed to sonication using a 20 kHz ultrasonicator equipped with a 6 mm horn (14.4 W, 10 mL, up to 15 min) or high hydrostatic pressure (HHP, up to 600 MPa, 15 min) treatments at pH 5, pH 7, and pH 9. The changes to physicochemical properties were probed by SDS-PAGE, FTIR, free sulfhydryl group (SH), surface hydrophobicity (H0), particle size and solubility. As revealed by SDS-PAGE, substantial amounts of 11S globulin participated in the formations of aggregates via Ssingle bondS bond under HHP, particularly at pH 7 and pH 9. However, protein profiles of QPI were not significantly affected by the sonication. Free SH groups and surface hydrophobicity were increased after the sonication treatment indicating protein unfolding and exposure of the embedded SH and/or hydrophobic groups. An opposite trend was observed in HHP treated samples, implying aggregation and reassociation of structures under HHP. HHP and sonication treatments induced a decrease in ordered secondary structures (random coil and β-turn) accompanied with an increase in disordered secondary structures (α-helix and β-sheet) as probed by FTIR. Finally, the sonication treatment induced a significant improvement in the solubility (up to ∼3 folds at pH 7 and ∼2.6 folds at pH 9) and a reduction in particle sizes (up to ∼3 folds at pH 7 and ∼4.4 folds at pH 9). However, HHP treatment (600 MPa) only slightly increased the solubility (∼1.6 folds at pH 7 and ∼1.2 folds at pH 9) and decreased the particle size (∼1.3 folds at pH 7 and ∼1.2 folds at pH 9). This study provides a direct comparison of the impacts of sonication and HHP treatment on QPI, which will enable to choose the appropriate processing methods to achieve tailored properties of QPI.
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 H
Hydrolysis-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.
Limited Alcalase hydrolysis improves the thermally-induced gelation of quinoa protein isolate (QPI) dispersions
(Elsevier BV, 2022-11-01) Wang X; Cheng L; Wang H; Yang Z
Gelation is critical in many food applications of plant proteins. Herein, limited hydrolysis by Alcalase was used to promote thermally induced gelation of quinoa protein isolates (QPI). Mechanical properties of various QPI gels were characterised by small and large oscillatory shear deformation rheology while the microstructural features were observed by confocal laser scanning microscopy (CLSM). Both the gel strength and microstructure are strongly related to the hydrolysis time. The maximum gel strength (∼100 Pa) was achieved after Alcalase hydrolysis for 1 min, which was ∼20 folds higher than that of untreated QPI. Extended hydrolysis up to 5 min progressively decreased the gel strength. A string-like interconnected protein network was formed after proteolysis. The change of gel strength with hydrolysis time correlated well to the Gʹ 20°C/Gʹ 90°C value and results of intrinsic fluorescence and surface hydrophobicity. The Gʹ 20°C/Gʹ 90°C value is sensitive to hydrogen bonds formation while the intrinsic fluorescence and surface hydrophobicity are associated with protein unfolding and exposure of hydrophobic groups. Therefore, both hydrogen bonding and hydrophobic interactions are critical in improving the gel strength of QPI hydrolysates. Finally, FTIR analysis revealed that protein secondary structures are affected by the proteolysis and formation of inter-molecular hydrogen bonds between polypeptides. This study provides an efficient strategy for improving thermally induced gelation of QPI and enables a deep understanding of QPI gelation mechanism induced by Alcalase hydrolysis.
Pepsin-induced hydrolysis and coagulation of proteins in goat, sheep and cow milk
(Elsevier Ltd, 2024-06) Yang M; Ye A; Gilbert E; Yang Z; Everett D; Singh H
The kinetics of pepsin-induced κ-casein hydrolysis and coagulation in cow, goat, and sheep milk were investigated at 37 °C, pH 6.3 and 6.0. At a 0.1 U mg−1 pepsin-to-κ-casein ratio, sheep milk showed the fastest κ-casein hydrolysis, followed by cow and goat milk as assessed by quantifying the release of para-κ-casein using RP-HPLC. Sheep milk coagulated most rapidly, with κ-casein hydrolysis of 64% and 59% at pH 6.3 and 6.0. Goat milk required higher levels of κ-casein hydrolysis (90% and 86% at pH 6.3 and 6.0), before coagulation could occur. Sheep milk formed denser curds, whereas goat milk curd had a more porous structure. Additionally, small-angle neutron scattering showed differing rates of aggregate size growth among species. These findings indicate κ-casein hydrolysis and coagulation differences are not just due to casein content but also physicochemical characteristics such as casein micelle size. This study deepens our understanding of sheep and goat milk coagulation mechanisms compared to cow milk during the early stages of gastric digestion.
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 EP
Acid- 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.

Browsing by Author "Yang Z"

Results Per Page

Sort Options