Massey Research Online - Browsing by Author "Singh, Harjinder"

Browsing by Author "Singh, Harjinder"

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Breakdown of rice and wheat-based foods during gastric digestion and its implications on glycemic response : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
(Massey University, 2022) Nadia, Joanna
The composition and structure of starch-based foods determine their breakdown behavior in the digestive tract and consequently their glycemic response. The glycemic response of starch-based foods is known to be influenced by their gastric emptying rate. However, the role of gastric digestion in regulating this process has not been well-understood, especially on how food breakdown behavior in the stomach may be related to the glycemic response. In this project, the link between food structure, food breakdown during gastric digestion, gastric emptying, and glycemic response was investigated in vivo using a growing pig model. Durum wheat- and white rice-based foods of varying physical structures (semolina porridge, rice- and wheat couscous, rice grain, rice noodle and wheat noodle/pasta) were studied. It was found that the foods with smaller-sized particles (semolina porridge and couscous products) had faster gastric breakdown rate and gastric emptying rate, resulting in higher glycemic impact (maximum change from the baseline and the overall impact) compared to the foods with larger-sized particles (rice grain and noodle products). The faster gastric breakdown rate of the smaller-sized foods was related to their acidification rate in the stomach, which caused their dilution or dissolution by gastric secretions. For larger-sized foods, their gastric breakdown rate and gastric acidification rate were slower, which extended their contact time with salivary amylase in the proximal stomach. To elucidate further the role of the proximal and distal phases of gastric digestion in solid food breakdown, a static in vitro digestion was conducted with the same food products. In the smaller-sized foods, both the proximal and distal phases led to their dissolution. Meanwhile, for the larger-sized foods, the extended contact time with α-amylase in the proximal phase contributed to the leaching of starch particles from the food, which was important to aid their breakdown during gastric digestion. The distal phase contributed to the softening of the larger-sized foods, but its softening effect was limited. The knowledge on the contributions of the phases of gastric digestion and the identified link between food structure, gastric digestion, and glycemic response in this thesis may be useful for structuring starch-based foods with controlled glycemic properties.
Carbohydrate-based oil-in-water emulsions for delivery of short-chain fatty acids : Doctor of Philosophy in Food Technology at Riddet Institute, Massey University, Palmerston North, New Zealand
(Massey University, 2021) Le, Hoang Du
Short-chain fatty acids (SCFAs) are important functional metabolites. There is clinical evidence to show that they are useful in the prevention of the metabolic syndrome, bowel disorders and certain types of cancer. Therefore, supplementation of SCFAs to the daily diet brings benefits to human health. However, SCFAs are small and water-soluble molecules that are quickly absorbed in the upper gastrointestinal tract. This project aimed to develop carbohydrate-based systems to deliver tripropionin (TP, glycerol tripropionate) and tributyrin (TB, glycerol tributyrate) as sources of propionic and butyric acids into the colon. Two types of emulsion systems were employed, i.e. surfactant-stabilised oil-in-water (O/W) emulsions (single and double-layer systems) and particle-stabilised O/W emulsions (Pickering emulsions). The systems were characterised in terms of structural stability, surface charge, rheological properties, lipolysis degree and release of SCFAs under a static in vitro gastrointestinal digestion and an in vivo study with ileal-cannulated pigs. In the screening experiments, several potential carbohydrate materials were explored, i.e. three modified starches (GUM, N46 and N-LOK), four pectins (PEC) and hydrophobically modified inulin (M-IN), to produce single-layer O/W emulsions. A double-layer O/W emulsion was also produced by combining whey protein isolate (WPI) and chitosan (CS) as the first and second layers, respectively. The capacity of emulsion systems for colon-targeted delivery of SCFAs was then tested using a static in vitro gastrointestinal digestion. The results show that PEC displayed the poorest emulsifying capacity amongst all investigated carbohydrates, leading to an emulsion droplets size (d32) of around 7.3 µm. However, PEC-based formulation was the best system for protection against gastric and intestinal conditions. On the other hand, other single-layer systems and the double-layer system proved to be unstable in the intestinal phase with a significant SCFA release. Deeper investigation on the emulsifying capacity showed that PEC stabilised the O/W emulsion mainly through steric effects. In addition, PEC had the ability to form thick layer around the O/W interface, which was evidenced by confocal laser scanning microscopy and the quantification of adsorbed PEC on the interface. In addition to the above systems, a Pickering O/W emulsion stabilised by hydrophobically modified cellulose nanocrystals (CNCs) was also investigated. The hydrophobic modification of CNCs was carried out, resulting in an increase in static water contact angle from 56o (untreated CNCs) to 80.2o (MCNCs). As a result, the emulsifying capacity of MCNCs was significantly improved. The emulsions prepared from MCNCs ≥ 0.20 wt% were stable against droplet coalescence for up to 4-week storage. In addition, the Pickering emulsions were prone to droplet flocculation at ionic strength ≥ 20 mM NaCl (pH 7.0) or pH < 4.0 (without addition of NaCl), which was due to the charge screening associated with the cellulose molecules at the surface. Similar droplet flocculation was also observed under in vitro gastric conditions, where the emulsions were exposed to low pH and high ionic strength. This gastric-induced structural changes improved physical strength of the emulsions and that enhanced resistance to bile-salt displacement and consequently delayed lipid digestion in the intestinal conditions. In addition, high desorption energy of the MCNC particles at O/W interface of the Pickering emulsion contributed to low lipolysis degree (30–35%). High proportions of SCFAs remaining after the intestinal digestion observed in both PEC and MCNC-based emulsions show a strong promise their use in the colon-targeted delivery of SCFAs. However, CNCs are currently not considered as food-grade materials; therefore, PEC was chosen for the in vivo study using female ileal-cannulated pigs. The in vivo study demonstrated significant higher intestinal lipolysis (~ 51–53%) and lower SCFA release (~ 15%) as compared to the in vitro digestion (~ 40 and 35% respectively). The main reason for the difference between the two models was the absorption of the SCFAs in the pig’s small intestine. However, high proportions of unhydrolysed triglycerides (~ 47–49%) and presence of oil droplets in the ileal-digesta demonstrated successful delivery of SCFAs. Based on the findings in this research, we propose the use of PEC-based emulsion for human trials by incorporating the system into a daily diet or dessert liquid/gel products, such as drinking milk or yogurt. We also believe that the application of MCNC-based Pickering emulsions for colon-target delivery of could be of interest if the regulatory status could be confirmed. The study identifies promising directions for researchers who are interested in improving gut health through delivery of SCFAs to the colon.
Emulsion-based delivery systems to improve gut and brain bioaccessibility of curcumin in relation to Alzheimer’s disease prevention : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
(Massey University, 2023) Lunelli, Taciana
Medium chain triglycerides (MCT) from coconut oil, omega-3 polyunsaturated fatty acids from fish, phospholipids from dairy milk, and curcumin from turmeric all have been recognized for their anti-inflammatory and antioxidant properties. Curcumin is also a potential candidate for Alzheimer’s disease (AD) prevention; however, curcumin is poorly bioavailable unless emulsified. The milk fat globule membrane (MFGM) has natural emulsifying properties. I aimed to design an emulsion-based delivery system containing functional oils to encapsulate and deliver curcumin to the brain. I evaluated three commercial MFGM components with coconut and fish oils to produce emulsions with improved curcumin bioavailability. The emulsion structures were characterised by particle size, zeta-potential at the surface, microscopic structure, curcumin loading efficiency, and phospholipid distribution. All emulsions showed stable to particle size changes over 40 days at 4°C. Emulsion particle size decreased significantly with increasing concentrations of emulsifier, and presented negative zeta-potential varying from -50 to -20 mV, with the MFGM fractions creating significantly different charges and curcumin loading efficiency based on phospholipid and protein composition. All MFGM fractions efficiently created stable emulsions with small particle size and encapsulated curcumin. After simulated in vitro digestion, the emulsion with the highest phospholipid content had significantly higher curcumin bioaccessibility compared to the others. Fresh and digested emulsions and their components were assessed in the BE(2)-M17 neuroblastoma cell model for amyloid-β (Aβ) toxicity. Emulsions composed of both fish and coconut oils provided greater protection against Aβ toxicity compared to coconut oil alone. Curcumin was transported in vivo across the intestinal wall to the bloodstream and across the blood-brain barrier to the brain in rats fed all curcumin delivery formats. The kinetics of curcumin in blood and brain varied depending on the emulsion format. MFGM emulsions significantly reduced the curcumin and its metabolites peak time in blood and brain compared to the commercial curcumin preparation Meriva®, and all emulsions improved overall curcumin bioavailability and accumulation in the brain compared to free curcumin. A novel ex vivo approach using rat plasma samples directly in the neuroblastoma cell model requires further optimisation but demonstrated a significant interaction between gender and treatment on cell viability.
Factors Affecting Rheological Characteristics of Fibril Gels: The Case of β-Lactoglobulin and α-Lactalbumin
(Wiley-Blackwell, 2009) Loveday, SM; Rao, M..A.; Singh, Harjinder; Creamer, Lawrence K.
Some of the factors that affect the rheological characteristics of fibril gels are discussed. Fibrils with nanoscale diameters from β-lactoglobulin (β-lg) and α-lactalbumin (α-la) have been used to create gels with different rheological characteristics. Values of the gelation time, tc, the critical gel concentration, c0, and the equilibrium value of the storage modulus, G, such as G'inf at long gelation times, derived from experimental rheological data, are discussed. Fibrils created from β-lg using solvent-incubation and heating result in gels with different rheological properties, probably because of different microstructures and fibril densities. Partial hydrolysis of α-la with a serine proteinase from Bacillus licheniformis results in fibrils that are tubes about 20 nm in diameter. Such a fibril gel from a 10.0% w/v α-la solution has a higher modulus than a heat-set gel from a 10% w/w β-lg, pH 2.5 solution; it is suggested that one reason for the higher modulus might be the greater stiffness of α-la fibrils. However, the gelation times of α-la fibrils are longer than those of β-lg fibrils.
In vitro gastric digestion of heat-induced aggregates of β-lg
(Elsevier Inc., 2012) Loveday, SM; Singh, Harjinder; Ye, Aiqian; Peram, Malleswara R.
An in vitro gastric digestion of heat-induced aggregates of β-lactoglobulin (β-lg) in simulated gastric fluid was investigated using sodium dodecyl sulfate-PAGE under nonreducing and reducing conditions, native-PAGE, 2-dimensional electrophoresis, and size exclusion chromatography. Heating at 90ºC significantly increased the digestibility of β-lg, with a high initial digestion rate followed by a relatively constant rate of digestion at a high enzyme:substrate (E:S) ratio of 3:1. At a low E:S ratio (1:6), the rate of digestion of β-lg was slower, and intermediate and low molecular weight species could be seen. The high molecular weight nonnative aggregates (pentamers, tetramers, trimers, etc.) were digested relatively rapidly, whereas some of the nonnative dimers were resistant to digestion and others were digested rapidly. The intermediate molecular weight species (21 to 23 kDa) were digested slowly. These results indicated that the digestibility of nonnative β-lg aggregates varied significantly depending on the E:S ratio and the types of aggregate. Further investigation is necessary to identify and characterize slowly digested dimers and intermediate molecular weight species.
Innovative yoghurts: novel processing technologies for improving acid milk gel texture
(Elsevier, 2013) Loveday, SM; Singh, Harjinder; Sarkar, Anwesha
Consumers are demanding low-fat yoghurts without hydrocolloid stabilisers, but they are unwilling to compromise on texture for the sake of a ‘clean label’. Producing high quality low-fat yoghurt without stabilisers is challenging, and there is a need for new processing technologies to address consumer demand. Here we examine four technologies that can potentially improve the texture of yoghurt: high-pressure processing (HPP), high-pressure homogenisation (HPH), ultrasonic processing (USP) and protein crosslinking with the enzyme transglutaminase (TG). The benefits of HPH and USP depend on fat content, whilst HPP and TG work best in combination with other processes, and have strong potential for improving protein ingredients.
Phase and Rheological Behavior of High-Concentration Colloidal Hard-Sphere and Protein Dispersions
(Wiley-Blackwell, 2007) Loveday, SM; Creamer, Lawrence K.; Singh, Harjinder; Rao, M. A.
Colloidal hard-sphere particles of narrow-size distribution exhibit crystalline and glassy states beginning at the particle volume fractions φ=0.494 and φG=0.58, respectively. Dynamic rheological data on the dispersions was strongly modified to solid-like behavior as φ approached φG. In addition, cooperative motion in structural relaxation has been observed microscopically in the colloidal dispersions near the glassy state. Very high viscosities and glassy states were also found in high-concentration dispersions of sodium caseinate, and the globular proteins: bovine serum albumin and β-lactoglobulin. Viscosity models developed for hard-sphere dispersions provided reasonable predictions of relative viscosities of colloidal protein dispersions. Dispersions of food colloidal particles may be employed in studies, in which volume fraction is the thermodynamic variable, for understanding the relaxation and transport processes related to first-order and colloidal glass transitions
Physicochemical changes in a model protein bar during storage
(Elsevier, 2009) Loveday, SM; Hindmarsh, Jason; Creamer, Lawrence K; Singh, Harjinder
High-protein snack bars (protein bars) contain high-quality protein, sugars and other low molecular weight polyhydroxy compounds (PHCs), high-energy confectionary fats, and a minimum of water (water activity ≤ 0.65). The consequence of the intimate mixing of these components in protein bars is that they can react together, creating sensory characteristics that are unacceptable to consumers. This study examined the changes occurring in a model protein bar during storage for 50 days at 20 °C. Over this time, fracture stress increased from 20.1 +/- 1.8 Pa to 201 +/- 75 Pa at a rate that decreased slightly over time. 1H nuclear magnetic resonance (NMR) showed that the molecular mobility of PHCs decreased dramatically over the first 5 days as the batter set into a solid bar. Over the first 17 hours after manufacturing, protein particles became more clustered, and soluble protein appeared to precipitate, as shown by confocal microscopy. Reactive lysine fell 38% in the first 10 days of storage and was approximately constant thereafter. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed little change in protein molecular weights. Following the initial ‘setting’ phase of 5-10 days, fracture stress continued to increase and the molecular mobility of PHCs decreased. Changes in PHC molecular mobility were consistent with glucose crystallisation. Chemical changes were minimal during this phase, which suggests that chemical reactions play little part in the hardening of protein bars and that changes in molecular mobility and changes in microstructure driven by moisture migration may be more important.
Physicochemical changes in intermediate-moisture protein bars made with whey protein or calcium caseinate.
(Elsevier, 2010) Loveday, SM; Creamer, Lawrence K.; Singh, Harjinder; Hindmarsh, Jason P.
This study examined model protein bars made with whey protein isolate (WPI) or calcium caseinate and stored at 20 °C for 50 days. WPI bars remained very soft and, throughout storage, confocal micrographs showed a continuous matrix containing soluble protein and increasing quantities of glucose crystals. In contrast, calcium caseinate bars had a firm texture within 1−5 days of manufacture (fracture stress 199 ± 16 Pa) and hardened progressively during storage (final fracture stress 301 ± 18 Pa). Electrophoresis showed no evidence of covalent protein aggregation, but there were substantial changes in microstructure over the first day of storage, resulting in segregation of a protein phase from a water−glucose−glycerol phase. Proton nuclear magnetic resonance (1H-NMR) relaxometry and nuclear Overhauser effect spectroscopy (NOESY) experiments showed that water migration away from protein towards glucose and glycerol occurred 10−18 h after manufacture, lowering the molecular mobility of protein. Phase separation was probably driven by the high osmotic pressure generated by the glucose and glycerol. These results confirm that the hardening of protein bars is driven by migration of water from protein to glucose and glycerol, and microstructural phase separation of aggregated protein.
Recent advances in technologies for vitamin A protection in foods.
(Elsevier, 2008) Loveday, SM; Singh, Harjinder
Vitamin A deficiency affects many children in the developing world, and is preventable via food or pharmaceutical supplementation. The main technical barrier to the fortification of food with vitamin A is its susceptibility to oxidation and isomerization, which result in loss of nutritional efficacy. This review discusses recent technological avenues for stabilizing vitamin A in foods.
The release of lipids from dairy food matrices under in vitro gastrointestinal digestive conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, Palmerston North, New Zealand
(Massey University, 2022) Tai, Patrick
The milk fat globule membrane (MFGM) is a trilayer phospholipid and protein interface that separates the triacylglycerides from the serum phase. Consumption of MFGM phospholipids decreases serum cholesterol in adults with high risk for hypercholesterolemia and modulates serum cholesterol in healthy adults. The biochemical mechanism behind this putative effect is currently unknown. The large majority (~80%) of the cholesterol in the milk fat globule is localized in the MFGM in complexation with sphingomyelin to form liquid-ordered (Lo) domains. The nutritional and digestive implications of consuming Lo domains have been scarcely considered. Considering sphingomyelin strongly complexes with cholesterol, the MFGM is rich in sphingomyelin, and the consumption of MFGM material has shown to modulate serum cholesterol, there is a likely link between the presence of Lo domains and the nutritional benefit of consuming MFGM material. Model bilayer systems, phospholipid liposomes/vesicles, were created from phospholipids derived from natural sources: soy phosphatidylcholine (SPC), porcine brain phosphatidylcholine (BPC), egg sphingomyelin (ESM), milk sphingomyelin (MSM), milk fat globule membrane (MFGM) phospholipids extracted from bovine beta-serum, and ovine cholesterol. The structural and thermotropic properties of the vesicles were investigated under in vitro gastrointestinal conditions. First, a screening test was performed on MSM/cholesterol multilamellar vesicles (MLVs). Instruments were capable of detecting shifts in the vesicles from solid-ordered (So) and liquid-disordered (Ld) to liquid-ordered at 2 × the MSM concentration found in raw milk. Incubation with physiologically relevant concentrations of bovine bile demonstrated 3:2 mol/mol MSM/cholesterol MLVs were capable of resisting detergent-induced solubilization by bile salts. The SPC/cholesterol, BPC/cholesterol, and MFGM/cholesterol phospholipid vesicles were disrupted. At the endpoint of in vitro gastrointestinal digestion, 3:2 mol/mol MSM/cholesterol MLVs also experienced micellization – however there was no statistically significant difference in the total bilayer order of the vesicles, implying a degree of structure possibly remained. Further investigation on the detergent solubilization of MFGM phospholipid vesicles by bile salts revealed that although the vesicle was disrupted, the mixed micellar size growth was minimal. That is, there was a lack of phospholipid exchange between vesicle and micelle. These findings set the stage for further research into the bioactive potential of milk phospholipids.
Rheological Behavior of High-concentration Sodium Caseinate Dispersions
(Wiley-Blackwell, 2010) Loveday, SM; Rao, M. A.; Creamer, Lawrence K.; Singh, Harjinder
Apparent viscosity and frequency sweep (G’, G”) data for sodium caseinate dispersions with concentrations of approximately 18−40% w/w were obtained at 20°C; colloidal glass behavior was exhibited by dispersions with concentration ≥ 23% w/w. The G’−G” crossover seen in temperature scans between 60 and 5°C was thought to indicate gelation (low-temperature crossover). Temperature scans from 5 to 90°C revealed gradual decrease in G’, followed by plateau values. The gelation and end of softening temperatures of the dispersions increased with the concentration of sodium caseinate. From an Eldridge−Ferry plot, the enthalpy of softening was estimated to be 29.6 kJ mol−1.
Structural changes in milk of different species during digestion : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Food Technology), Massey University, Manawatū, New Zealand
(Massey University, 2021) Roy, Debashree
Cow milk is the most abundant type of mammalian milk produced in the world. It has been widely explored industrially as well as academically. However, non-cow milk (e.g. water buffalo, goat, and sheep milk) consumption is significant and forms an important nutritional source for people in many countries. The interest in non-cow milks has increased because of several anecdotal experiences reported about the nutritional and digestive benefits of these milks. However, there is very little scientifically validated information available. The overall objective of this PhD study was to investigate how some of the non-cow milks (such as goat and sheep milk) are structurally different (or similar) to cow milk, especially in their coagulation behaviour under the gastric environment. The potential implications of structural changes on the delivery of nutrients under dynamic gastric digestion conditions were also explored. Dynamic in vitro and in vivo gastric digestion models were employed for this study. It was found that milk from different species vary in their natural macronutrient composition, structure, and acid-gelation behaviour. The fundamental mechanism of coagulation of proteins under the dynamic in vitro gastric digestion conditions was found to be similar for different species milk. The in vivo gastric digestion studies revealed comparable results, although goat and sheep milk curds had relatively lower rates of strengthening and relatively more open microstructure. Both the dynamic in vitro and in vivo studies revealed that the release of fat globules from the coagulated curd was directly proportional to the breakdown (or hydrolysis) of the protein in the curd during gastric digestion. The studies clearly showed that the curd formation and its disintegration in the stomach is a key factor influencing the rate of delivery of macronutrients to the small intestine. The results from this thesis contribute to the knowledge of how composition along with structure impact the release of nutrients at various stages of gastric digestion of different mammalian milks. The information gained from this study might have important consequences for developing dairy products with improved structures for controlled delivery or release of nutrients to meet the special dietary needs of consumers.
Studies on the gastric digestion of plant-based alternative milks : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand
(Massey University, 2022) Wang, Xin
Plant-based alternative milks are colloidal dispersions consisting of extracted plant protein, oil bodies and other biopolymers that resemble cow milk in appearance. In recent years, plant-based alternative milks have become increasingly popular because of their sustainability and perceived health benefits. However, little is known about the structural changes and colloidal stability of these milks during gastric digestion and how these changes impact the delivery and absorption of nutrients. The aim of this PhD project was to understand the digestion behaviour of plant-based alternative milk in the gastric environment, with a focus on the changes in microstructure, colloidal stability, physiochemical properties and protein hydrolysis and their direct consequences on the kinetics of nutrient release and delivery. The impact of cow milk protein on the digestion behaviour of oat-based milk was also explored. State-of-the-art dynamic in vitro and in vivo gastric digestion models were employed for this project. The results demonstrated that plant-based alternative milks made with different plant materials (almonds, soybeans and oats) behaved differently under gastric conditions, in particular, in terms of changes in microstructures, colloidal stability and protein digestibility. Almond milk oil bodies flocculated, coalesced and then quickly layered into an upper lipid-rich layer and a lower aqueous phase upon gastric digestion. Soymilk coagulated and formed small-sized particles which sedimented rapidly. In contrast, no significant changes in the structure and colloidal stability were observed in oat milk. These variations in colloidal stability resulted in different gastric release profiles of protein and lipid. These results highlight the role of intragastric structural properties as a determining factor in controlling the kinetics of delivery of macronutrients. This study also clearly showed the influence of cow milk protein on the structural and colloidal stability of the oat milk-cow milk blend during gastric digestion. The findings from this thesis provide new knowledge and understanding of the gastric digestion of plant-based alternative milks and how their behaviours are different from cow milk. The knowledge gained from this PhD project may provide valuable information into the tailored design of novel plant-based alternative milk products or milk blended products for specific consumers' needs.
Tuning heat-‐induced colloidal aggregation of whey proteins, sodium caseinate and gum arabic: effect of protein composition, preheating and gum arabic level
(ELSEVIER SCI LTD, 2014) Loveday, SM; Ye, Aiqian; Anema, Skelte G; Singh, Harjinder
Heating can drive the colloidal complexation of negatively-‐charged proteins and polysaccharides by strengthening hydrophobic interactions and denaturing proteins, thereby exposing reactive sites for covalent and noncovalent bonding. We have previously shown that stable colloidal aggregates comprising whey protein, sodium caseinate and gum arabic can be produced by careful selection of heat treatment, pH and protein type. Here we tested how the size, composition, charge and morphology of colloidal aggregates are affected by the amounts of whey protein, sodium caseinate and gum arabic, as well as the thermal history of the proteins. Increasing amounts of whey protein resulted in larger particles, which were more prone to precipitate. Preheating whey protein slightly enhanced aggregation, and this effect was mitigated when sodium caseinate was present during preheating (chaperone effect). Increasing amounts of gum arabic produced larger particles with less charge, but the gum arabic effect was statistically confounded with ionic strength. We believe that both covalent (disulphide) and noncovalent interactions among protein molecules are required to overcome electrostatic repulsion at pH 7 and form stable aggregates.
Tuning the properties of b-lactoglobulin nanofibrils with pH, NaCl and CaCl2
(Elsevier, 2010) Loveday, SM; Creamer, Lawrence K.; Singh, Harjinder; Rao, M. A.; Wang, X. L.; Anema, S. G.
We investigated the effects of pH (1.6 – 2.4), NaCl and CaCl2 (0 – 100mM) on the kinetics of β-lactoglobulin fibril formation during heating at 80°C. The morphology of fibrils was also examined. At pH 1.8 - 2.4 fibril formation occurred slightly faster with decreasing pH. At pH 1.6 fibril formation during the growth phase occurred much faster than at any other pH. Fibril morphology was unchanged between pH 1.6 and pH 2.0. Addition of NaCl or CaCl2 accelerated fibril formation during the growth phase, and CaCl2 shortened the lag phase as well. Worm-like fibrils were seen at ≥ 60 mM NaCl or ≥ 33 mM CaCl2, and these had a persistence length which was much shorter than the long semi-flexible fibrils formed without salts. The efficiency of fibril formation can be substantially enhanced by varying pH and salt concentration.
Whey protein nanofibrils: kinetic, rheological and morphological effects of group IA and IIA cations
(International Dairy Journal, 2012) Loveday, SM; Su, Jiahong; Rao, M. Anandha; Anema, Skelte G.; Singh, Harjinder
Self-assembly of whey proteins into amyloid-like fibrils during heating at pH 2 and low ionic strength is sensitive to the presence of NaCl and CaCl2. Our earlier work established that at 10 - 120 mM of these salts speeds up self-assembly and favours short, flexible fibrils over long semiflexible fibrils in a way that depends on cation concentration and cation type. Here we explored how other mono- and divalent salts affected fibril morphology and the rheology of fibril dispersions. Divalent salts (MgCl2, CaCl2, BaCl2) had much stronger effects than monovalent salts (LiCl, NaCl, KCl) on gelation kinetics, and differences between salts of the same type were not large. No marked effects of salt type on fibril morphology were evident, but there were subtle differences in the size and extent of fibril networks with mono- vs. divalent salts, which may explain differences in bulk rheology.

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