Properties Of Milk Gels Research Articles

Tribo-rheological properties of acid milk gels with different types of gelatin: Effect of concentration

We investigated the effect of low concentrations (0.1 to 1%, wt/wt) of gelatin (types A and B) on the properties of acid milk gels in terms of rheology, tribology, texture, and water-holding capacity to better understand the role of gelatin in yogurt. The 2 types of gelatin showed similar effects on the properties of milk gels, with some minor differences, such as lubrication behavior at low concentrations. During acidification, gelatin at ≤0.4% caused an increase in the gel strength, and at higher concentrations it showed a negative effect. However, during cooling and annealing, we observed a positive effect on gel strength with 0.8 and 1% gelatin. Gelling and melting occurred at 0.8 and 1% concentrations of both types of gelatin. The addition of gelatin tended to decrease the storage modulus of milk gels and increase the apparent viscosity, pseudoplasticity, consistency, and yield stress. The firmness of the gels was decreased by gelatin at medium concentrations, but increased at high concentrations. Gelatin significantly enhanced the water-holding capacity of the gels; we observed no serum at concentrations ≥0.4%. With the addition of gelatin at concentrations ≥0.4%, the particle size of gels was greatly reduced, and their lubrication properties were significantly improved. This study showed that 0.4% was an effective concentration in acid milk gel; above this concentration, the properties of the milk gels were greatly changed. Tribology provided important information for understanding the role of gelatin in milk gels.

The effect of Lactobacillus delbrueckii subsp bulgaricus proteinase on properties of milk gel acidified with glucono‐δ‐lactone

SummaryLactobacillus delbrueckii subsp. bulgaricus CH9‐3 proteinase is an enzyme that plays an important role in yogurt fermentation, by which its use is linked to gel properties of yogurt. In this work, a modified glucono‐δ‐lactone (GDL) acidification model was used to simulate the fermentation of yogurt and study the effect of CH9‐3 proteinase on GDL‐acidified milk gel. The results showed that the proteinase significantly improved the quality of milk gel by increasing its firmness, consistency, and viscosity index, while decreasing its syneresis. Furthermore, the proteinase could accelerate the formation of milk gel as indicated by the decrease in surface charge of milk gel. The findings demonstrate that CH9‐3 proteinase has a positive effect on the properties of milk gel, and thus may have promising applications in the yogurt making industry.

生姜プロテアーゼによる牛乳ゲルの調製におよぼす牛乳の種類と成分の影響

生姜プロテアーゼによる牛乳ゲルの調製におよぼす牛乳の種類と成分の影響

Effect of whey protein aggregates of various sizes on the formation and properties of rennet-induced milk gels

Whey protein (WP) aggregates that ranged in diameter from 41 to 299 nm but had the same composition were produced by varying the protein concentration at heating at neutral pH and low ionic strength, followed by dilution. The effect of WP aggregates on the formation and properties of rennet-induced milk gels were evaluated. Whey protein aggregates had no effect on the kinetics of caseinomacropeptide release during renneting but significantly affected the clotting of casein micelles and the properties of milk gels. The maximum clotting rate and the strength of rennet-induced milk gels decreased as the dose of WP aggregates added to milk increased. However, WP aggregates with larger diameter and higher voluminosity had a less detrimental effect on milk clotting than smaller aggregates did. The higher surface hydrophobicity and faster diffusion of smaller WP aggregates could have been responsible for adsorption onto renneted casein micelles, which reduced milk clotting rate and gel strength. The permeability of rennet-induced milk gels decreased as the dose of WP aggregates added to milk increased, but the protein concentration at heating had no effect. Whey protein aggregates reduced the contraction capacity of the gels during cooking (42 °C). Drained curd mass fraction and curd moisture increased as the dose of added WP aggregates increased and were affected less by larger WP aggregates. The results of this study suggest that small WP aggregates (<100 nm) interact with casein micelles and interfere with rennet gel formation and contraction.

The effect of transglutaminase on the properties of milk gels and processed cheese

The aim of this study was to investigate the influence of transglutaminase (TG) on rennet coagulation properties, and the impact on the properties of processed cheese. The TG was added before, at the same time as, and after the addition of rennet. The parameters moisture, total solids and proteins and physical parameters (syneresis index, wheying‐off and rheological behaviour) were measured. The manufacturing of the milk gels treated with transglutaminase after rennet addition was shown to be an effective means of improving the physical properties (reduced synereseis index and increased consistency index) of processed cheese, possible by the occurrence of enzymatic cross‐linking.

Controlled Proteolysis and the Properties of Milk Gels

Milk gels induced by partial proteolysis of the kappa-casein followed by acidification were studied, and their gelation behavior was compared to that of milk gels induced by simultaneous acidification and renneting, using dynamic rheology. There were generally two stages (at pH values below and above 5.0) in the gelation of the milk whose kappa-casein had been partially proteolyzed and acidified. The onset of gelation was at higher pH as the degree of kappa-casein proteolysis increased. The development of G' immediately after the onset of gelation was faster in the milk gels induced by simultaneous acidification and renneting, because of the continuing kappa-casein proteolysis. Preheat treatment caused the onset of gelation to occur at higher pH than for unheated milk. However, the maximum tan delta during gelation always occurred at the same pH (for a given concentration of acidulant), and its value and position were independent of the extent of renneting and whether the milks had been heat treated. The results are discussed in terms of the interactions between casein micelles occurring during gelation.

Carrageenan Gels in Skim Milk: Formation and Rheological Properties

Phase behavior and mechanical properties of gels of three (kappa-, iota-, and lambda-) carrageenans in skim milk are thoroughly studied. The measurements were performed with the aid of a dynamic rheology in different regimes including determination of frequency dependences of rheological parameters, creep, and critical strain and stress at which the gelled systems are destroyed. Temperature dependences of the rheological parameters were also measured. A set of obtained data allowed to quantitatively characterize the mechanical properties of milk gels and compare the gel-forming properties of various carrageenans. In addition to gels of individual polysaccharides, their mixed gels were studied for the first time. It is shown that kappa-carrageenan formed the most stiff and brittle gels. Its mixing with iota- or lambda-carrageenans made gels softer. This effect is observed when the degree of substitution of kappa-carrageenan was higher than 50% that indicates its prevalent role in the mixed systems. The gelation is explained by the formation of crosslinked structure where the nodes are the casein micelles connected by polysaccharide chains. Their binding occurs due to electrostatic interactions between the sulfo groups of carrageenans and amino groups of kappa-casein. In the case of kappa- or iota-carrageenans, network structure is additionally stabilized due to crosslinking of segments of their molecular chains by the double helices at the gaps between casein micelles.