Acid Gelation Research Articles

The impact of calcium sequestration on the material and structural properties of acid milk gels and corresponding cream cheeses

SummaryWe report on the role of ethylenediaminetetraacetic acid (EDTA) in addition to the structural and material properties of acid milk gels formed via addition of glucono‐delta‐lactone (GDL) and these properties of corresponding analogue cream cheeses prepared from these gels. Increasing addition of EDTA to cheese milks prior to acidulation reduced the concentration of insoluble calcium in the milks. Acid gelation of milks, as measured by small deformation rheology, showed a decreased rate of gelation and lower relative elastic modulus of gels with increasing EDTA concentration. The sequestration of colloidal calcium phosphate from the casein micelle by the addition of EDTA led to the lower gelation rate and elastic modulus. The lower extent of ionic binding is considered the causative mechanism for formation of weaker gel structures. Cream cheeses prepared using acid gels with GDL acidulant were compositionally unaffected by EDTA concentration. However, variations in G′ observed in the acid gels containing increasing levels of EDTA correlated with large deformation material property changes in cream cheese analogues. In addition, the increasing inclusion of EDTA in cheese milks translated to reduced water‐holding capacity of the cream cheeses prepared from those milks. These results provide insights on the specific role of milk calcium on the structure, material and physical properties of acid milk gels and corresponding cream cheese analogues.

Acid gelation of high-concentrated casein micelles and pea proteins mixed systems

The increased demand for plant-based products brings a new challenge to the food industry. Especially, proteins from soy, chickpea, and pea are being highly demanded as food ingredients. However, they still present some drawbacks such as poor techno-functional properties and remarkable beany flavor that hamper their wider application. Contrarily, milk products such as yogurt and cheeses are highly consumed and accepted worldwide. Therefore, the association of plant proteins, such as pea with milk proteins is an interesting strategy to incorporate more plant-based proteins into people’s diet. However, this strategy can largely impact gel formation and final structure. This study aims to develop mixed casein micelles (CMs) and pea proteins gel at high concentrations in four protein ratios, 80:20, 60:40, 40:60, and 20:80 by acidification. The effect of a thermal treatment before gelation was also evaluated. The replacement of CMs for pea proteins disturbed the gel formation at the beginning of acidification, demand more time to increase the G*, being this effect more pronounced as more casein is replaced in the system. Despite of this effect, the final gel elasticity was higher in the presence of pea proteins for the ratios 80:20 and 60:40, probably due to the formation of pea network. It is hypothesized that pea proteins can form a network when surrounded by CMs, however, CMs restrict pea proteins aggregation. This study describes that the final characteristics of mixed gels can be tailored by changing protein ratios and applying thermal treatment before acidification, opening the possibility for the development of innovative food products.

Tunable circularly polarized luminescence of hybrid supramolecular nanofibers based on a cinnamic acid gelator and spiropyran by photoisomerization

Tunable circularly polarized luminescence of hybrid supramolecular nanofibers based on a cinnamic acid gelator and spiropyran by photoisomerization

Influence of Heating Temperature and pH on Acid Gelation of Micellar Calcium Phosphate-Adjusted Skim Milk.

Micellar calcium phosphate (MCP) plays an important role in maintaining the structure and stability of the casein micelle and its properties during processing. The objective of this study was to investigate how heating (10 min at 80 or 90 °C) at different pH levels (6.3, 6.6, 6.9, or 7.2) impacted the acid-induced gelation of MCP-adjusted milk, containing 67 (MCP67), 100 (MCP100), or 113 (MCP113) % of the original MCP content. The unheated sample MCP100 at pH 6.6 was considered the control. pH acidification to pH 4.5 at 30 °C was achieved with glucono delta-lactone while monitoring viscoelastic behaviour by small-amplitude oscillatory rheology. The partitioning of calcium and proteins between colloidal and soluble phases was also examined. In MCP-depleted skim milk samples, the concentrations of non-sedimentable caseins and whey proteins were higher compared to the control and MCP-enriched skim milk samples. The influence of MCP adjustment on gelation was dependent on pH. Acid gels from sample MCP67 exhibited the highest storage modulus (G'). At other pH levels, MCP100 resulted in the greatest G'. The pH of MCP-adjusted skim milk also impacted the gel properties after heating. Overall, this study highlights the substantial impact of MCP content on the acid gelation of milk, with a pronounced dependency of the MCP adjustment effect on pH variations.

Effect of calcium-sequestering salts and heat treatment on the rheological and textural properties of acid gels from blends of skimmed buffalo and bovine milk

The influence of adding 5 mm trisodium citrate (TSC) or disodium hydrogen phosphate (DSHP) and heat treatment (85 °C or 95 °C for 5 min) on the acid gelation properties of blends of skim buffalo and bovine milk (0:100, 25:75, 50:50, 75:25, 100:0) was investigated. Significant increases in gelation pH, final G′ values, firmness, and water-holding capacity of gels were observed with increasing proportion of buffalo skim milk and with higher heating temperature. Differences in gel firmness were linked to gel microstructure, where milk blends containing higher proportion of buffalo skim milk formed gels with denser protein network clusters. The addition of TSC or DSHP reduced the gelation pH, final G′ values and gel firmness, but increased gel water-holding capacity. These results provide a better understanding of acid gelation of buffalo and bovine milk blends which will subsequently promote the potential of using milk mixtures in modulating the gel texture.

Interpreting the “twice gelation” mechanism of a novel egg-based yoghurt through the dynamics of rheology, microstructure, and intermolecular forces

In this paper, we interpreted the “twice gelation” mechanism of egg-based yoghurt through the integrated multidimensional dynamic change analysis of rheology, microstructure, and intermolecular forces. The results showed that during the first gelation stage (i.e., thermal gelation), egg proteins underwent heat denaturation and formed crosslinks, with the main intermolecular forces involved in gel formation being disulfide bonds (∼84%). After homogenization by the colloid mill, the heat-induced gel transformed into a smooth, viscous fluid state, which subsequently turned into a weak gel as the pH continuously decreased under the effect of lactic acid bacteria fermentation. In the second gelation stage (i.e., acid gelation), the proportion of hydrophobic interactions increased from ∼12% to ∼49%, whereas the proportion of disulfide bonds decreased from ∼74% to ∼45%, indicating that hydrophobic interactions played a crucial role in the second gelation, while disulfide bonds still showed great importance in stabilizing the gel structure, although their percentage decreased significantly. In summary, egg proteins form a hard gel by heating, and this heat-induced gel has the ability to gel twice after homogenization, making it possible to form egg-based yoghurt with a fine texture and good taste under the action of lactic acid bacteria fermentation.

A semiconducting supramolecular novel Co(II)-metallogel based on 5-aminoisophthalic acid gelator: Toward efficient microelectronic device application

A novel ultrasonication method was successfully employed to prepare a metallogel using 5-aminoisophthalic acid as a low molecular weight gelator and cobalt(II)-acetate in N,N-dimethyl formamide at room temperature. Mechanical properties were analyzed through rheological analysis, microstructure through scanning electron microscopy and EDX mapping, and formation strategy via FT-IR and Raman spectroscopy. Crystalline nature was confirmed by PXRD analysis. The gel exhibited a strong semiconducting nature, supported by optical band gap estimation, electronic device characterization, and charge carrier mobility assessment. Remarkably high electron mobility, potentially surpassing reported metallogels, was observed.

Effect of atmospheric cold plasma treatment on acid gelation properties of skim milk: Rheology and textural studies

Cold plasma processing is a non-thermal food processing technique that has been shown to improve the gelling properties of plant proteins by altering their structure through oxidation and crosslinking. This study aimed to investigate the effects of cold plasma treatment on the rheological properties of skim milk under different conditions, focusing on the impact of feed gas and treatment time on skim milk's sulfhydryl content, flow properties, and acid gelling behavior. Results showed that free sulfhydryl content decreased with treatment time, with a notable reduction observed after 2 min of N2-O2 plasma treatment. Skim milk treated with N2 plasma experienced a more gradual decrease in free SH content. Cold plasma increased skim milk viscosity over time. N2-O2 plasma treatment significantly affected G′40 and G′4 storage moduli, with an increase observed after 2 min of exposure but no change beyond that time. Acid gels' greenness (a* value) decreased with increasing treatment time compared to the control. Acid gel firmness of milk treated with N2-O2 plasma for 1 min significantly increased from 1.804 N to 1.912 N, and further to 2.072 N after 2 min of treatment. However, longer exposure times led to lower firmness in gels. N2 plasma treatment also significantly impacted acid gel firmness. Syneresis in acid gels decreased from 63.4 % to 57.7 % and 58.7 % after 1 and 2 min of N2-O2 plasma treatment, respectively, but increased to about 70 % after 4 min. Acid gels made from milk treated with N2 plasma experienced considerably less syneresis. The cold plasma treatment under different conditions significantly affected the properties of skim milk, with various impacts on sulfhydryl content, flow properties, and acid gelling behavior. These findings demonstrate the potential applications of cold plasma processing in the food industry to improve product properties.

Acid gelation functionality of casein micelles in concentrated state: Influence of calcium supplementation or chelation combined with enzymatic stabilization

The main structure-building component in gelled dairy products is the casein micelle (CM). It was previously shown that in concentrated state of CMs, the changes of their compositional and colloidal properties in response to the addition or chelation of calcium divers from the reactions at milk-like casein concentration. This study aimed to evaluate the relationship between these specifically induced properties of CMs and the acid gelation functionality of a micellar casein concentrate (MCC). A covalent stabilization of the structures of pre-modified and native CMs by treatment with transglutaminase (Tgase) prior to acidification with glucono-δ-lactone was additionally tested. During acidification, structure formation was monitored in a rheometer to gain insights on mechanistic changes in the course of structural changes during acidification compared to gelation of unmodified MCC. Gelation pH, gel firmness, and serum binding capacity were analyzed to characterize gel structures at a final pH of 4.6. The structure formation process was highly affected by prior changes in composition, integrity, and structural stabilization of CMs. Gelation pH and acid gel firmness were reduced by ionic strength. Thermal and Tgase treatment induced opposing effects, leading to compensation when combined with prior salt supplementation. A synergistic increasing effect on serum binding capacity was found for trisodium-citrate supplementation and subsequent Tgase treatment. New mechanistic insights on acid gel structure formation progression were gained. This study provides a better insight into the relationship between structural CM properties prior to acid gelation and the resulting acidification progress, as well as the final acid gel properties.

Influence of variation in calcium content on casein micelle stability and techno‐functional properties of buffalo milk

Changes in techno‐functional properties of buffalo milk were evaluated due to variation in calcium content. Decalcification resulted in significant variation in ζ‐potential, casein size, colour and ηapp. However, calcium addition only influenced ζ‐potential of milk. In case of acid gelation, the time and temperature required for coagulation decreased significantly for both calcium‐depleted and ‐added milks. However, during chymosin gelation, only 20%–30% of calcium‐depleted milk coagulated with an increased clotting time. Furthermore, calcium addition increased firmness, consistency and cohesiveness of both chymosin and acid‐induced gelation.

Rheological and microstructural characterisation of lotus seed milks and their glucono-δ-lactone induced acid-set milk gels: 1. Effect of protein content

The physicochemical and acid gelation properties of lotus seed milks (LSMs), total solid concentrations varying from 5 to 20 wt%, were investigated in comparison with bovine skim milk (10 wt%). LSM was prepared by soaking, blending and milling, filtering followed by α-amylose treatment to hydrolyse the starch in order to reduce its viscosity. The particle size of LSM revealed a multimodal distribution with two main size distributions, a smaller one (∼0.06 and ∼1.5 μm) from protein aggregates as a result of the heat treatment and a larger one (∼1.5 μm and ∼250 μm) likely due to the presence of undissolved protein and cellular materials. A slight shift toward higher sizes, due to further protein denaturation, can be observed after heating at 80 °C for 30 min. As expected, the viscosity of LSM depended on the total solid concentration, and was found to be similar to that of the skim milk when the LSM concentration was around 5 wt%. Addition of glucono-δ-lactone resulted in the formation of LSM gels, and the gelation of LSM occurred when the pH decreased to ∼6 while that of skim milk occurred at pH 5.2. Small deformation rheological measurements showed that it is possible to obtain a LSM acid-gels similar in viscoelastic behaviour (complex modulus G*≈300 Pa after 5 h acidification) to 10 wt% skim milk gel when the concentration of LSM is about 11.1 wt% (same dietary energy as skim milk). Confocal laser scanning microscopy showed that a similar microstructure to skim milk gel is observed for 5 wt% LSM gel, while a denser protein network with voids were observed at high LSM concentrations. The colour of these milk gels appeared white under the naked eye and their syneresis decreased sharply with the increase in concentration with a syneresis similar to that of skim milk when LSM concentration was ≥15 wt%. This study suggested for the first time the potential of LSM to be a strong alternative for the manufacture of non-animal acid milk gels.

Acid and rennet gelation properties of sheep, goat, and cow milks: Effects of processing and seasonal variation

Gelation is an important functional property of milk that enables the manufacture of various dairy products. This study investigated the acid (with glucono-δ-lactone) and rennet gelation properties of differently processed sheep, goat, and cow milks using small-amplitude oscillatory rheological tests. The impacts of ruminant species, milk processing (homogenization and heat treatments), seasonality, and their interactions were studied. Acid gelation properties were improved (higher gelation pH, shorter gelation time, and higher storage modulus (G') by intense heat treatment (95°C for 5 min) to comparable extents for sheep and cow milks, both better than those for goat milk. Goat milk produced weak acid gels with low G' (<100 Pa) despite improvements induced by heat treatments. Seasonality had a marked impact on the acid gelation properties of sheep milk. The acid gels of late-season sheep milk had a lower gelation pH, no maximum in tan δ following gel formation, and 70% lower G' values than those from other seasons. We propose the potential key role of a critical acid gelation pH that induces structural rearrangements in determining the viscoelastic properties of the final gels. For rennet-induced gelation, compared with cow milk, the processing treatments of the goat and sheep milks had much smaller impacts on their gelation properties. Intense heat treatment (95°C for 5 min) prolonged the rennet gelation time of homogenized cow milk by 8.6 min (74% increase) and reduced the G' of the rennet gels by 81 Pa (85% decrease). For sheep and goat milks, the same treatment altered the rennet gelation time by only less than 3 min and the G' of the rennet gels by less than 14 Pa. This difference may have been caused by the different physicochemical properties of the milks, such as differences in their colloidal stability, proportion of serum-phase caseins, and ionic calcium concentration. The seasonal variations in the gelation properties (both acid and rennet induced) of goat milk could be explained by the minor variation in its protein and fat contents. This study provides new perspectives and understandings of milk gelation by demonstrating the interactive effects among ruminant species, processing, and seasonality.

Storage related changes in short-set cream cheese manufactured using thermophilicstarter culture and direct acidification technique

Cream cheese is a fresh acid curd variety with semi-soft body, manufactured by the gradual, quiescent acid gelation of milk. The typical flavour profile of cream cheese is cultured diacetyl with little bit lactic acid flavour as well as aroma. It is envisaged that demand of cream cheese will increase in upcoming years due to its application as spread and it having higher nutritional value compared to similar products available in the market. The purpose of the study was to observe changes in sensory, physicochemical and microbial quality during storage in short-set cream cheese samples manufactured by using thermophilic starter culture and direct acidification technique and was compared with control cream cheese manufactured using mesophilic starter culture. All the three samples i.e., control cream cheese made using mesophilic culture (MC), cream cheese made using thermophilic culture (TC) and cream cheese made using laboratory grade lactic acid (SLA) were stored in re-closable polypropylene tubs at 7 ± 2°C. During storage study, flavour score, FFA, tyrosine value were significantly affected by storage period (P), treatment (T) and the interaction of T × P. Moisture, pH, titratable acidity, sensory parameters (except flavour) were significantly affected only by storage period (P) and treatment(T). All the three samples had storage stability up to 15 days at 7± 2°C.

A coordination driven 'heat-set' Zr-gel: efficient fluorophore probe for selective detection of Fe3+ and nitrofuran-based antibiotics and smart approach for UV protection.

Nature creates definite architecture with fluorescence capabilities and superior visual adaptation in many organisms, e.g., cephalopods, which differentiates them from their surroundings in the context of colour and texture that allows them to use this in defence, communication, and reproduction. Inspired by nature, we have designed a coordination polymer gel (CPG)-based luminescent soft material where the photophysical properties of the material can be tuned using a low molecular weight gelator (LMWG) with chromophoric functionalities. Herein, a water-stable coordination polymer gel-based luminescent sensor was created using zirconium oxychloride octahydrate as a metal source and H3TATAB (4,4',4''-((1,3,5-triazine-2,4,6-triyl)tris(azanediyl))tribenzoic acid) as a LMWG. The tripodal carboxylic acid gelator H3TATAB with a triazine backbone induces rigidity in the coordination polymer gel network structure along with the unique photoluminescent properties. The xerogel material can selectively detect Fe3+ and nitrofuran-based antibiotics (i.e., NFT) in aqueous medium through luminescent 'turn-off' phenomena. This material is a potent sensor because of the ultrafast detection of the targeted analytes (Fe3+ and NFT), with consistent efficacy in quenching activity up to five consecutive cycles. More interestingly, colorimetric, portable handy paper strip, thin film-based smart detection approaches (under an ultraviolet (UV) source) were introduced to make this material a viable sensor probe in real-time applications. In addition, we developed a facile method to synthesize CPG-polymer composite material that can be utilized as a transparent thin film to protect against UV radiation (200-360 nm), with approximately 99% absorption efficacy.

Effect of hyaluronic acid on milk properties: Rheology, protein stability, acid and rennet gelation properties

Hyaluronic acid (HA) is gaining popularity and acceptance as a food ingredient. HA has certain properties such as water binding, viscosity manipulation which can be exploited in food products. However, there are limited studies available for the effect of HA on the properties of food, especially in milk and milk products. Studying the effect of HA treatments on milk properties such as viscosity, heat stability, phase separation, rennet, and acid gelation would be beneficial to the processors. The objective was to study the effect of HA at different concentrations on various physico-chemical properties of milk. Whole milk treated with HA showed increased viscosity as a function of HA concentration in both cold and pasteurized milk samples. The frequency sweep results indicated that only a higher HA concentration (0.5%) was able to achieve the viscoelastic solid behavior (G′ > G″), which was stable over the entire frequency sweep range of 10–150 rad/s. Heat stability of skim milk was negatively impacted as a function of HA concentration. The gravimetric protein phase separation during skim milk storage was also negatively impacted as a function of HA concentrations up to 0.25%. However, higher HA concentration (0.5%) reduced the phase separation. In the case of rennet gel and acid gel studies, the gelation properties and the gel structure was negatively impacted as a function of HA concentration. The negative effect of HA on rennet and acid gelation properties could be as a result of depletion–flocculation mechanism leading to micro-phase separation interference by HA polymer in the formation of continuous protein gel network.

Rheological and structural properties of acid-induced milk gels as a function of β-casein phenotype

This study aimed to investigate if differences in β-casein polymorphic structure would affect the acid-induced (glucono-δ-lactone) gelation behaviour of corresponding skim milks. Gels obtained from skim milk containing A2/A2 β-casein had significantly lower elastic modulus, water holding capacity, and gel permeability compared to A1/A1 and A1/A2 gels. Microscopy images also showed a denser microstructure and smaller pore size in acid-induced gels prepared with A1/A1 and A1/A2 milks compared to A2/A2 milk. A number of reasons may account for these differences in gelation, specifically, gels with A1 β-casein contained greater amounts of α-helixes and aggregated β-sheets in their secondary structure compared to A2/A2 gel that was comprised mainly of random coils or polyproline II helixes. In addition, compositional differences such as greater total and micellar calcium and higher levels of total κ-casein existed in A1/A1 and A1/A2 milks compared to A2/A2 milk and may have contributed to the difference in gelation and gel structure. Although the role of β-CN phenotype on skim milk gelation may need further investigation, findings from this study clearly indicate that A2/A2 milk was associated with poor acid gelation properties. • Effects of acidification on milks with various β-caseins were studied. • Gels carrying A1 β-casein possessed greater water retention and lower permeability. • Increased β-sheets in gels carrying A1 β-casein related to higher storage modulus. • A2/A2 gel possessed a high amount of polyproline II structures. • Gels prepared of A1/A1 and A1/A2 milks possessed a denser microstructure.

Effect of pressure treatment of recombined whole milk on fat globule membrane composition and acid gelation functionality

Recombined whole milk was prepared by pressure treating skim milk (200 to 600 MPa/30 min) then homogenizing with milkfat (HPHO) or by homogenizing milkfat with skim milk then pressure treating the recombined whole milk (HOHP). β-Lactoglobulin denaturation increased at higher pressures. Low levels of α-lactalbumin were denatured at 600 MPa only. Denaturation was similar in the HPHO and HOHP milk. The HPHO milk had statistically similar levels of total protein, higher levels of whey protein and κ-casein and lower levels of αs-casein adsorbed to the fat globules compared with the HOHP milk. The HPHO milk had a higher proportion of β-casein directly at the interface at all pressures and a higher proportion of κ-casein and a lower proportion of denatured whey proteins at pressure up to 400 MPa than the HOHP milk. Acid gels prepared from the HOHP milk had higher final G′ and yield stresses than those from the HPHO milk. These differences are discussed in relation to the compositions of the proteins adsorbed to the fat globules and how these interact during acidification.

Acid Gelation Properties of Camel Milk—Effect of Gelatin and Processing Conditions

This study investigated the effects of glucono-delta-lactone (GDL) concentrations (0.8–1.2%, w/w), gelatin content (0.6–1.0%, w/w) and processing conditions on the properties of camel milk acid gels. Although the pH of camel milk reduced to 4.3 within 4 h of acidification at 1.0% GDL, it was unable to form a suitable gel for a yoghurt-like product unless gelatin was added. At 0.8% gelatin, camel milk gels had similar hardness, lower viscosity and rheological strength, and higher water holding capacity as compared to cow milk gels. Heating of camel milk (85 °C/15–20 min), 2-stage homogenization (150/50 bar) or their combination did not significantly affect the water holding capacity, hardness, viscosity, rheological strength and microstructure of camel milk gels. These processing conditions did not affect protein integrity as confirmed by sodium dodecyl-sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis.

In situ SAXS study of non-fat milk model systems during heat treatment and acidification

Small-angle X-ray scattering (SAXS) was used to monitor structural changes induced by heat treatment and acid gelation in milk matrices with added whey protein concentrates (WPCs) and nano-particulated whey protein (NWP). In general, heat treatment was found to mainly affect whey protein components while pure casein micelles remained largely unaffected. Conversely, acidification mainly affected caseins while leaving pure whey protein components intact. In mixed systems, the overall behaviour could be understood as a combination of the above effects, however, the type of the added whey protein components influenced the resulting structure formation and dynamics. NWP led to formation of larger structures compared to WPC components during heat treatment, although the latter showed faster aggregation dynamics. During acidification the NWP containing samples exhibited structural changes at slightly higher pH values than the WPC samples. The modeling of pure liquid whey protein (LWPC) samples showed that the heat induced denaturation and resulting aggregation of individual whey proteins is mainly a surface effect leaving the overall protein shape and dimensions unaffected. Schematic diagrams based on the current SAXS data and previous studies were constructed to illustrate the suggested interaction mechanisms between casein and whey proteins during both heating and acidification.

Acid gelation properties of fibrillated model milk protein concentrate dispersions

Whey proteins in milk are globular proteins that can be converted into fibrils to enhance functional properties such gelation, emulsification, and foaming. A model fibrillated milk protein concentrate (MPC) was developed by mixing micellar casein concentrate (MCC) with fibrillated milk whey proteins. Similarly, a control model MPC was obtained by mixing MCC with milk whey proteins. The resulting fibrillated model MPC and control model MPC contained 5% protein and a ratio of casein to whey proteins similar to milk. The objective of the current study was to understand the rheological characteristics of fibrillated and control model MPC during acid gelation, using Förster resonance energy transfer (FRET) to assess small amplitude oscillation and casein-whey protein interaction. The results from the FRET index images showed greater interactions between caseins and whey proteins in fibrillated model MPC compared with the moderate and uniform interactions in control model MPC gels. Rheological study showed that the maximum storage modulus of acid gel of fibrillated model MPC was 546.9 ± 15.5 Pa, which was significantly higher than acid gel made from control model MPC (336.9 ± 11.3 Pa), indicating that fibrillated model MPC produced a firmer gel. Therefore, it can be concluded that acid gel produced from fibrillated model MPC was stronger than control model MPC. Selective fibrillation of the whey protein fraction in MPC can be used to improve gelation characteristics of acid gel type products.