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Item 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 ZGelation 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.Item 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 MIn 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.Item 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 ZThis 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.Item A study on the mechanisms of calcium-induced gelation in skim milk : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Albany, New Zealand(Massey University, 2019) Lin, LiangjueThe destabilisation and aggregation of milk proteins is the first step towards the gelation of milk. The addition of calcium to milk is known to destabilise milk proteins and may result in gelation on heating. However, the mechanisms involved in gelation induced by heating calcium-added milk was not well understood. Therefore, this project aimed to determine the fundamental mechanisms involved in the development of a calciuminduced skim milk gel. Skim milk was selected as the model system and gelation was induced in-situ by heating the calcium-added skim milk at the rheometer. The changes in the storage modulus, G′, were monitored to study the development of the gel network. This project examined the impact of the following factors on the rheological properties of a calciuminduced skim milk gel: the type of soluble calcium salt added (calcium chloride, calcium lactate, calcium gluconate, calcium lactobionate and calcium iodide), pH, holding temperature during gelation (70°C to 90°C), preheat treatment, ionic strength (by addition of sodium chloride) and the contribution of casein and whey proteins. A higher calcium ion activity (aCa 2+), which indicated a higher calcium ion (Ca2+) concentration, and a lower pH favoured the formation of a stronger gel. An increase in ionic strength by addition of sodium chloride decreased the final G′ of the calciuminduced skim milk gel due to reduced calcium bridging and increased hydration repulsion. A higher heating temperature also resulted in gels with higher final G′ due to more frequent particle collisions. Casein micelles and whey proteins were both responsible for the structure of the gel network. The contribution of whey proteins towards the gel network was dependent on if they were denatured prior to heating, on the concentration of calcium ions available, and on the ratio between the casein and whey proteins present. At lower added calcium concentrations (10 mmol L-1) where the available calcium ions were limited, interactions and aggregation amongst denatured whey proteins via hydrophobic and disulphide bonds may have resulted in the formation of a stronger gel. However, at higher added calcium concentrations (20 and 40 mmol L-1), where sufficient calcium ions may be available for binding, interactions between casein and calcium dominated over the self-aggregating effect of denatured whey proteins. In conclusion, the results demonstrated that the final gel properties of a calcium-induced skim milk gel were dependent on the net effect of all the factors involved in the stability and interactions of the milk proteins, including the calcium salt concentration, pH, preheat treatment, ionic strength, and the protein composition in solution. These findings provide alternative methods for texture modification in milk.Item Cryogelation of egg white protein : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatū, New Zealand(Massey University, 2017) Huang, ZitongGelation of egg white protein (EWP) solutions can be induced as a consequence of freezing and thawing in the presence of a denaturant (urea). This mechanism of cryogelation can be affected by the relative concentrations of protein and urea, as well as freezing conditions including freezing temperature and freezing duration. The compression peak force (CPF) of the obtained cryogels was measured using large deformation texture analysis to indicate the gel strength of samples. In the range of added urea concentration from 1M to 6.6M the CPF of samples was seen to decrease, whilst increasing EWP concentration from 5% (w/v) to 15% (w/v) resulted in a strengthening of gel structure with increasing CPF. Lower freezing temperatures (e.g. -30oC) caused a decrease in CPF of samples compared to -18oC and samples stored for 68 hours had higher CPF than those stored for 20 hours (at 1M added urea). Water holding capacity (WHC) of cryogel was determined by measuring the amount of released water from samples gravimetrically. With increasing concentration of urea the WHC of samples was seen to initially decreased, followed by a progressive increase as the concentration of urea was raised. This trend was observed for most protein concentration with the exception of 5% EWP which showed a significant increase at 4M urea, followed by a drop at higher urea concentrations. Increasing EWP concentrations tended to result in higher WHC in general, although samples with 10% and 12% EWP had relatively similar WHC values. WHC of samples frozen at -30oC was higher than those frozen at -18oC at high urea concentrations. However, increasing the frozen storage time did not appear to affect the WHC. The microstructure of EWP cryogel was observed using scanning electric microscopy (SEM) and transmission electric microscopy (TEM). The SEM data showed a porous structure for all samples. The increase in the concentration of added urea and the decrease in freezing temperature seemed to reduce the porosity and connectivity of the structure especially at low EWP concentrations. There was also some observed difference of the gel wall thickness between some different samples. The TEM data provided a clear distribution of protein and pores within the gel phase. The effect of urea on the thermal stability of protein molecules was studied using nano differential scanning colorimetry (nano DSC). Results showed that the addition of urea progressively denatured the protein with increasing urea concentration. Proteins appeared to be further denatured as a consequence of the freezing-thawing process. The effect of urea addition on freezing point depression and ice content was calculated, allowing the protein content in the unfrozen phase to be determined. The relative concentrations of protein, urea, frozen and unfrozen water in the frozen state provided some indications as to how the extent of denaturation coupled with freeze concentration in the unfrozen phase contributed to the cryogels structures being formed. A number of correlations were determined that assisted in developing a mechanistic understanding of the cryogelation effect. Findings demonstrate a potential means of creating food gel structures with novel structural and material characteristics.Item Characterisation of food fibres and their effect on starch digestion in an in-vitro system at physiological shear rates : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Anatomy and Physiology at Massey University, New Zealand(Massey University, 2017) Yap, Sia-YenThe fast pace of life promotes the excessive consumption of processed starchy food containing high levels of sugar, salt and oil; which can increase the prevalence of type II diabetes, colon and cardiovascular diseases. The addition of dietary fibres in the diet increases the viscosity of digesta, delays mixing in the gut, and promotes laxation. However, few studies attempt to quantify the possible physical and chemical effects of either soluble (food gums) and insoluble (largely cellulose) fibre in the diet. These effects may encompass the retention of water inside the fibre particles, between particles in the fibre mass and direct effects of the chemical nature of the fibre on the digestion process. In this study, the fractions of water held in the various partitions of insoluble particulate dietary fibres are quantified. The relationship between the volume fraction of soluble and insoluble dietary fibres in simulated digesta at physiological concentrations and the rheological properties of the suspension at physiological shear rates is determined. Furthermore, the impact of fibre and shear rates on the digestion of starch in-vitro at physiological shear rates was measured. This work provides the first quantitative assessment of the effects of the physical attributes of dietary fibre on the digestion of starch in-vitro, at physiological shear rates. In this work, four insoluble fibre types were used to construct aqueous suspensions containing solid volume fractions similar to those of pig digesta from the small intestine; these suspensions also were shown to have similar rheological properties to those of pig digesta at physiological shear rates. In addition, a soluble fibre (Guar gum) was used to construct solutions with viscosities comparable to those of the particulate suspensions. Gelatinised and partially gelatinised starch was added to these suspensions and its rate of digestion at 37°C under simulated small intestinal conditions was measured at shear rates covering the reported physiological range. Important results from this work include: - The proportion of water retained by a given volume of hydrated mass of large fibre particles (AllBran®) was double that of smaller particles (wheat fibre). For all of the solid particles used, the proportion of water sequestered by the intra-particulate voids was less than 4% of the volume of the particles, similar proportions were determined for indigestible particles recovered from the colon of pigs and from human faeces. - Food fibre systems containing less than 20% by volume (solid volume fraction, φ = 0.20) of insoluble dietary fibres showed Newtonian rheological properties and the viscosity of these suspensions could be predicted from φ by the Maron-Pierce model. Starch/fibre suspensions prepared with φ below 20% (φ = 0.68-0.98) had a similar viscosity to that of starch/guar suspension comprising 10% (w/v) starch and 0.4% (w/v) guar. During in-vitro digestion, the viscosity of the starch/fibre suspensions decreased logarithmically over the first 20 minutes during which about 30% of the starch was hydrolysed, this was followed by a prolonged period of slow digestion as the slowly digested starch (SDS) and resistant starch (RS) were hydrolysed. The rate of starch digestion was independent of the type of insoluble fibre and was not affected by suspension viscosities used providing shear rates could be maintained within physiological levels. For guar, rates of digestion were slowed probably due to non-competitive inhibition of the amylase by the guar. - When shear rates were below the physiological range (0.1 s-1) or gelatinisation was incomplete, the rate of digestion became linear over the first 20 minutes of digestion suggesting that the rate of digestion was limited by transport processes at low shear in viscous suspensions. - This study provides useful information regarding the limiting concentration of particles and hence viscosity of digesta in the gut if rates of digestion are to be maximised. Additionally, it is suggested that guar, even at low concentration may reduce glycemia by reducing rates of amylolysis.Item Properties of recombined milk protein composite gels : effects of protein source, protein concentration and processing time : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University, Palmerston North, New Zealand(Massey University, 2002) Findlay, Robyn RosemaryIncreased knowledge of the interactions involved in the manufacture of Milk Protein Composite Gels (MPCGs) is essential for the further development of dairy-based analogue and recombined products and the advancement of novel product development. This study investigated MPCG manufacture using four protein sources (Rennet Casein, skim milk cheese (SMC), milk protein concentrate (MPC 85), calcium-depleted milk protein concentrate (IX MPC 85)), three protein to water (P/W) ratios (0.4, 0.5, 0.6) and four processing times (0, 4, 8, 16 minutes). The properties of the products were investigated using confocal and transmission electron microscopy, as well as rheological and functional tests. Protein source was found to have the greatest impact on product characteristics, followed by P/W ratio with processing time having little, and often inconsistent, effects. Increased protein concentration resulted in a higher viscosity during manufacture, a decrease in fat droplet size, an increase in gel firmness, and a decrease in meltability. Increased processing time resulted in a decrease in fat droplet size, few significant changes in firmness (both small- and large-strain), and an increase in meltability Fracture property analysis showed that SMC produced softer, more elastic gels than Rennet Casein. The whey-containing samples produced softer, more brittle gels with little difference between them Small-strain analysis showed that all samples were weak gels but the results did not follow the same trend as the fracture properties. The samples increased in firmness in the following order: SMC < Rennet Casein < IX MPC 85 < MPC 85. Microstructure analysis showed the presence of whey protein aggregates in the MPC 85 and IX MPC 85 samples. These samples also demonstrated aggregation of the lipid droplets, which was attributed to the presence of whey proteins. Reduced levels of calcium resulted in lower levels of emulsification (larger lipid droplets) due to lower in-process viscosities. Correlations between large- and small-strain testing showed that the correlation coefficient was dependent on the protein source being used and that although the level of correlation was not high, there was a general positive trend The small-strain and UW Meltmeter tests did not agree on the order of increasing meltability except for the SMC samples, which were significantly more meltable than the other protein sources. The two tests were poorly correlated (R² = 0.446).Item Effect of biopolymer addition on the properties of rennet-induced skim milk gels : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University, Palmerston North, New Zealand(Massey University, 2003) Tan, YilingThe main objectives of this study were to determine the effect of adding different biopolymers (κ-Carrageenan, xanthan gum, guar gum, high-methoxyl pectin and gelatin) on the properties of rennet skim milk gels. A collection of techniques, namely strain-controlled rheometery, spontaneous whey separation measurements, confocal laser scanning microscopy and diffusing wave spectroscopy, were used. The effects of these biopolymers were investigated for rennet skim milk gels made under model system and cheesemaking conditions. However, only rheological measurements were performed for samples made under cheesemaking conditions. For samples made under model system conditions, the concentration of the biopolymer was varied from 0 wt% to 0.1 wt%. Experimental conditions, such as renneting temperature (30°C), total milk-solids (10 wt% reconstituted skim milk), pH 6.7 and rennet concentration (200 µL per 100 g sample) were kept constant. The rheological behaviour of these samples was affected by the addition of κ-carrageenan, xanthan, guar, high-methoxyl (HM) pectin and gelatin. Both rheology and diffusing-wave spectroscopy (DWS) showed that the aggregation and gelation time and the gel strength was affected by the addition of these biopolymers. It was also shown that the syneresis behaviour, as well as the microstructure of rennet gels as imaged by confocal laser scanning microscopy (CLSM), was altered upon adding these biopolymers. The rheological and microstructural properties of model renneted skim milk systems improved by adding small amounts (0.025 wt%) of κ-carrageenan, guar, HM pectin and gelatin, but not xanthan. Renneted skim milk containing HM pectin and gelatin had higher G*, decreased aggregation time and gelation time and lower syneresis values as the concentration of biopolymer was increased. On the other hand, lower G* and higher syneresis values were obtained for samples containing higher concentrations (> 0.025 wt%) of κ-carrageenan, xanthan and guar gum. Higher syneresis index was a consequence of the presence of larger pores in these samples, as shown from the CLSM micrographs. The effects caused by the addition of κ-carrageenan, xanthan and guar gum were believed to be due to phase separation in rennet skim milk gels containing polysaccharide, and was explained in termsof a depletion-flocculation mechanism. For rennet gels made under cheesemaking conditions (pH 6.2 with addition of 0.68 mM CaCl2), it was found that the addition of xanthan, guar, HM pectin and gelatin had similar effect to that when added to samples made under model system conditions. This was due to the fact that the differences in pH and salt were known to not affect the properties of the biopolymers. However, the addition of κ-carrageenan, which was very sensitive to ions such as calcium, improved the viscoelastic properties of rennet skim milk gels made under cheesemaking conditions. Overall, this work provides useful information on the effects of adding κ-carrageenan, xanthan, guar, high-methoxyl pectin and gelatin on the properties of rennet-induced gels.Item Aggregation and gelation of bovine b-lactoglobulin, a-lactalbumin and serum albumin : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University(Massey University, 1995) Gezimati, JacquelineGelation is one of the most important functional properties of whey proteins in food systems. The properties of whey protein gels are affected by the chemical and physical properties of its protein components, (β- lactoglobulin AB (β-Lg), α-lactalbumin (α-La) and bovine serum albumin (BSA). Heat-induced aggregation and gelation of individual whey proteins, (β-Lg, α-La and BSA and in mixture was studied by dynamic rheology and electrophoresis analysis. The proteins were dispersed in an ionic buffer containing 0.009 M CaCl , 0.012 M NaCl, 0.012 M K HPO and 0.007 M Nacitrate (pH 6.8) which was comparable to the ionic composition of 12% whey protein concentrate solution. Rheological properties of the protein solutions were measured using a Bohlin VOR rheometer after heating to 70, 75 and 80°C, holding at these temperatures for 60 min and after cooling to 25°C. Gel electrophoresis under non-dissociating (Native-PAGE in the absence of dissociating and reducing agents) and dissociating but non-reducing conditions (SDS-PAGE) was used to determine the extents of aggregation in some of the heated protein samples. Gelation temperatures of 10%, w/v, protein solutions were found to be in the range 82.5 - 84°C for β-Lg and 68 - 70°C for BSA while α-La did not gel even at 90°C. Gelation temperatures of protein mixtures containing β- Lg and BSA were dependent on the relative proportion of the two proteins in the mixture. In contrast, the protein mixtures containing β-Lg and α-La gelled at temperatures (~ 83°C) comparable to that of β-Lg alone. Rheological measurements on pure β-Lg and BSA showed that BSA solutions formed self-supporting gels at lower protein concentrations and lower temperatures. Increasing the heating temperature or protein concentration of either β-Lg or BSA resulted in higher values of the storage modulus (G'). It was apparent from the electrophoretic data that protein aggregates were formed as an intermediate prior to the formation of gel net-work. These aggregates appeared to be non-covalently linked initially and became increasingly disulphide-linked during heating. Analysis of mixtures containing β-Lg and BSA during heat treatment showed that at both 70 and 75°C the gelation time decreased with the increasing proportion of BSA. Similarly, the values of G' after 60 min of heating were greater for the gels containing more BSA. G' values of these mixtures were dependent on the heating temperature and the relative proportion of the two proteins. Gel electrophoresis data for a mixture of 5% β-Lg and 5% BSA heated at 70°C showed that prior to gelation most of the BSA had been transformed into aggregates while most of the β-Lg was essentially in the native form. Aggregates of both β-Lg and BSA were formed during heating at 75°C. At both temperatures, gelation commenced after most of the BSA had become covalently cross-linked but before all the β-Lg had become cross-linked. This effect was also apparent for other mixtures. Initially the aggregates appeared to be non-covalently linked and became increasingly disulphide linked with heating. From these results it is apparent that during heating at 70°C, BSA is the main protein forming the gel net-work and some β-Lg aggregates are probably attached to the net-work strand through either hydrophobic interactions or disulphide linkages. During heating at 75°C, two gel net-works are presumed to be formed independently, again with some interactions between the strands of the two net-works. The rheological properties of protein mixtures containing β-Lg and α-La showed that β-Lg was the dominant gelling protein. G' values decreased with increasing relative proportion of α-La in the mixture at both 75 and 80°C. Gelling times increased with increasing proportion of α-La in the mixture at both 75 and 80°C. No aggregate formation was observed during heating of α-La at 75 or 80°C. However, in the presence of β-Lg, α-La aggregated rapidly during heating. This aggregation appears to involve sulphydryl disulphide interchange reactions particulary when the mixtures were heated at 80°C. Almost all the proteins had aggregated through disulphide linkages before any significant increase in G'. It is suggested that during heating and prior to gelation co-polymers of both β-Lg and α-La were formed and this resulted in heterogeneous net-work strands being formed. The results presented in this study suggest that slight differences in the protein composition of WPC are unlikely to affect the gelation properties of WPC. Further studies into the effects of immunoglobulins (Igs) are needed in order to gain further understanding of the contributions of these proteins to rheological properties of WPC gels.Item Glucono-[delta]-lactone-induced gelation of some meat components at chilled temperatures : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology and Bioprocess Engineering at Massey University, Palmerston North, New Zealand(Massey University, 1994) Ngapo, Tania ManuIn this study, 1,5-glucono-δ-lactone, was used to achieve acid-induced gelation of meat, myofibrillar protein and myosin at 4°C. The mechanisms of gelation of myofibrillar protein and myosin were investigated. The effects of addition of sodium chloride and tetrasodium pyrophosphate to myosin and myofibrillar protein, with and without 1,5-glucono-δ-lactone, were also studied. In addition, the presence of other phosphates, orthophosphatc, tripolyphosphate and hexametaphosphate, in a myosin system were studied to aid in an understanding of the the observed effects of tetrasodium pyrophosphate on myosin. At about pH 4.5, it was observed that extraction of the A-band of myofibrillar protein occurred. It was suggested that an impregnated composite system of myosin reinforcing the myofibrillar structure had formed. At about pH 4.0, complete extraction of the A-band occurred. Dissolution of the myofibrillar structure was suggested to result in myosin network formation of weaker Young's Modulus than the impregnated composite system. Addition of 1,5-glucono-δ-lactone to myosin resulted in the exposure of hydrophobic sites as the pH decreased and it was suggested that acid-induced denaturation had occurred. Gel formation occurred parallel to denaturation. At pH 4.0, the gel became liquid-like and was suggested to be a result of excess repulsive electrostatic interactions. Hydrogen bonding and hydrophobic interactions were shown to be involved in gel formation, whereas sulfhydryl bonding appeared not to be involved in gelation. Sodium chloride was postulated to enhance gel rigidity through its effects on the isoelectric point of myosin. The inclusion of tetrasodium pyrophosphate resulted in network formation prior to acid-induced denaturation and was suggested to enhance hydrogen bonding. The acid-induced gels appeared to revert to myosin or myofibrillar protein when immersed in quiescent water, a condition where unimpeded diffusion of ions was obtained. However, a slow rate of ion diffusion resulted in the formation of a 'strong', translucent gel which was dense to the point of being effectively impermeable to ion migration. These gels were hypothesized to have formed through the displacement of sodium and potassium ions with protons, enhancing hydrogen bonding. Myosin was observed to have a stronger affinity for sodium than for potassium.