Effect of milk fat concentration and gel firmness on syneresis during curd stirring in cheese-making

An experiment was undertaken to investigate the effect of milk fat level (0%, 2.5% and 5.0% w/w) and gel firmness level at cutting (5, 35 and 65 Pa) on indices of syneresis, while curd was undergoing stirring. The curd moisture content, yield of whey, fat in whey and casein fines in whey were measured at fixed intervals between 5 and 75 min after cutting the gel. The casein level in milk and clotting conditions was kept constant in all trials. The trials were carried out using recombined whole milk in an 11 L cheese vat. The fat level in milk had a large negative effect on the yield of whey. A clear effect of gel firmness on casein fines was observed. The best overall prediction, in terms of coefficient of determination, was for curd moisture content using milk fat concentration, time after gel cutting and set-to-cut time (R² = 0.95).     

The effect of pectin concentration and degree of methyl-esterification on the in vitro bioaccessibility of β-carotene-enriched emulsions

Soluble fibers, like pectin, are known to influence the physicochemical processes during the digestion of dietary fat and may therefore affect the absorption of lipophilic micronutrients such as carotenoids. The objective of the current work was to investigate whether the pectin concentration and degree of methyl-esterification (DM) influence the bioaccessibility of carotenoids loaded in the oil phase of oil-in-water emulsions. The in vitro β-carotene bioaccessibility was determined for different oil-in-water emulsions in which 1 or 2% citrus pectin with a DM of 99%, 66% and 14% was present. Results show that pectin concentration and DM influence the initial emulsion properties. The most stable emulsions with the smallest oil droplets (D(v,0.9) of 15–16 μm) were obtained when medium or high methyl-esterified pectin was present in a 2% concentration while gel-like pectin structures (D(v,0.9) of 114 μm), entrapping oil droplets, were observed in the case where low methyl-esterified pectin was present in the aqueous emulsion phase. During in vitro stomach digestion, these gel-like structures, entrapping β-carotene loaded oil droplets, significantly enlarged (D(v,0.9) of 738 μm), whereas the emulsion structure could be preserved when the medium or high methyl-esterified pectin was present. Initial emulsion viscosity differences, due to pectin concentration and especially due to pectin DM, largely disappeared during in vitro digestion, but were still significant after the stomach digestion phase. The observed differences in emulsion structure before and during in vitro digestion only resulted in a significant difference between emulsions containing low methyl-esterified pectin (β-carotene bioaccessibility of 33–37%) and medium/high methyl-esterified pectin (β-carotene bioaccessibility of 56–62%).     

Effect of processing on droplet cluster structure in emulsion gels

The fat droplet cluster structure in acidified and neutral emulsion gels is investigated after storage at fixed temperature or after temperature cycling. Amongst other techniques, the novel non-invasive Spin-echo Small-angle Neutron Scattering (SESANS) technique is applied to probe the structure of emulsion droplet aggregates up to a length scale of ∼10 μm.The SESANS data show that fat droplet clusters in non-cycled emulsions become smaller with increasing homogenisation pressure (next to the droplets themselves getting smaller as well), and that the emulsion gel becomes more homogeneous as a result. Upon temperature-cycling, it is found that the fat droplet clusters increase in size (next to the droplets themselves getting larger as well). The presence of these more lumpy aggregates is not the direct cause of the higher firmness of the emulsion gels, but the rearrangement process itself may promote the partial coalescence that causes an increase in firmness of these emulsion gels upon temperature-cycling.     

Effect of composition and antioxidants on the oxidative stability of fluid milk supplemented with an algae oil emulsion

The oxidative stability of an algal oil emulsion dispersed in water, or fluid milk of varying fat contents, was assessed from measurements of lipid hydroperoxide and propanal concentration. All of the milk samples, independent of their milk fat content, were stable compared to the aqueous samples. The extent of oxidation was unaffected when sodium azide (200 ppm) was added to inhibit microbial growth. Added iron (100 ppm) accelerated the oxidation rate in the aqueous samples, but had no effect on the milk samples. The antioxidant properties of milk were ascribed to the iron binding of casein. Added protein antioxidants (0.8 wt%) [i.e. sodium caseinate, whey protein isolate (WPI) and thermally denatured WPI] had minimal effects whereas EDTA and ascorbic acid (160 ppm) were effective antioxidants.     

Aeration of low fat dairy emulsions: Effects of saturated–unsaturated triglycerides

Three dairy emulsions containing 10 wt% anhydrous milk fat (AMF), alone or in mixture with its low or high melting temperature fraction (olein- or stearin-rich fraction, respectively), were aged at 4 °C for 24 h and then submitted to a whipping test at this temperature. We observed that the AMF/olein emulsion presented less crystalline fat content, and a higher ability for air incorporation than the other two emulsions. In addition, air bubbles formed in the AMF/olein-rich emulsion presented a more uniform size distribution, a smaller proportion of bubbles higher than 50 μm, and they appeared to be coated with a thicker layer of fat droplets. These results indicated that foam-structure forming properties in reduced milk fat emulsions can be enhanced by lowering the proportion of saturated triglycerides.     

Addition of olein from milk fat positively affects the firmness of butter

Butter is highly valued for its characteristic flavor and aroma; however, it has the disadvantage of unsatisfactory spreadability at low temperatures. The functional characteristics of butter can be modified by changing its composition or physical structure. The objective of this study was to evaluate the effect of olein on structure and composition of butter. Olein was obtained by two stage dry fractionation process of the anhydrous milk fat (AMF) and added to commercial cream prior to butter manufacture. The fractions were characterized for triacylglycerols composition, solid fat content, crystallization isotherm, and thermal behavior. Butter was manufactured using commercial cream or cream containing 50% olein. Butter samples were characterized for physicochemical composition, instrumental color, crystallization parameters, and firmness after 1 and 7 days of storage at 10 °C. The firmness of butter subjected to room temperature was also evaluated. Butter containing olein differed significantly from the control and had darker yellow color, higher crystallization time, and lower solid fat content after 120 min at 15 °C, and hence lower firmness after 1 and 7 days of refrigerated storage. Although lower firmness was observed over time for all samples at room temperature, butter containing olein exhibited lower firmness after both 1 and 7 days, thus suggesting changes in organization of solid fat crystal network in the liquid fat. The addition of olein to butter allowed obtaining a softer product, with more intense color and possible nutritional benefits due to the medium chain triglycerides and higher carotene levels.     

Production of conjugated linoleic acid enriched milk and dairy products from cows receiving grass silage supplemented with a cereal-based concentrate containing rapeseed oil

Opportunities for the production of milk and dairy products enriched with cis-9, trans-11 conjugated linoleic acid (CLA) were investigated. Eighteen mid-lactation cows were used in a continuous-design for 7 weeks. During the first week, cows received grass silage ad libitum supplemented with 10 kg per day of a cereal-based concentrate (control) that was replaced with a concentrate containing 50 g kg⁻¹ of rapeseed oil (RO). Changes in milk fatty acid composition were monitored on a weekly basis and milk produced was used to manufacture Edam cheese and butter. Inclusion of RO in the concentrate supplement increased the mean levels of trans-octadecanoic, monounsaturated, CLA and polyunsaturated fatty acid in the milk fat from 1.6, 25.7, 0.46 and 2.8 to 4.3, 35.3, 1.02 and 3.9 g 100 g⁻¹ total fatty acids, respectively. In contrast, the mean level of saturated fatty acids decreased from 71.4 to 60.7 g  100 g⁻¹ total fatty acids. Changes in milk fatty acid composition due to RO occurred within 7 days, with responses reaching a plateau after 21 days. Furthermore, the CLA concentrations in the milk fat from individual cows ranged between 0.37 and 0.65 and 0.43 and 2.06 g 100 g⁻¹ total fatty acids for the control and RO diet, respectively. CLA enriched milk was used successfully to manufacture of Edam cheese and butter with softer textures but with acceptable organoleptic and storage properties. Processing milk into butter or cheese had no effect on the CLA concentrations indicating that enrichment of dairy products is dependent on the content in raw milk fat.     

Rheological,microstructural and sensory characterization of low-fat and whole milk set yoghurt as influenced by inulin addition

The effect of inulin addition (0–4%) upon texture and microstructure of set yoghurt with different levels of fat (0.2%–3.5%) was investigated. A two-factor experimental design with four treatments was used for data analysis. Skimmed milk with various inulin and cream concentrations was standardized to 4% protein content, homogenized, heated to 92 °C and fermented at 42 °C until a pH of 4.6 was reached. The chemical composition, pH, consistency and microstructure properties of the yoghurts were analysed after 6 days of storage at 5 °C. The statistical analysis showed that inulin and fat significantly affected the rheological and sensory results. Higher yield stress, “firmness” and “creaminess” values were observed in yoghurt produced with higher inulin additions, whereas the pH value was not affected. A significant correlation was found between yield stress and sensory determined firmness (r = 0.91). The microstructure examined by confocal laser scanning microscopy (CLSM) was only slightly affected by the concentrations of inulin in the range studied, possibly due to weak protein interactions between the inulin and the milk protein network.     

Gel-Forming Characteristics of Milk Proteins. 1. Effect of Heat Treatment

Skim milk with or without preheating (60 to 80°C for 30 min) were acid coagulated at 60 to 80°C for 1 h with glucono-delta-lactone. Preheating below 70°C has no effect on gel firmness and water-holding capacity. When coagulated below 70°C, the gels were weak and had low water-holding capacity. When coagulated at 80°C, the gels were solid and had high water-holding capacity. Gels prepared from skim milks preheated to above 80°C had a different quality: when coagulated at less than 70°C, gel firmness increased slightly, and when coagulated at 80°C, gel firmness decreased sharply. Change in the accessibility of sulfhydryl groups in milk protein caused by heating, was also measured using Ellman's reagent. Changes in the gel-forming property of milk protein, caused by the heat treatment, were closely related to increase in available sulfhydryl groups in milk proteins, and also were related to heat denaturation of whey protein or the formation of β-lactoglobulin/κ-casein complex.     

Enrichment of the conjugated linoleic acid content of bovine milk fat by dry fractionation

This study investigated the effect of fat fractionation on the conjugated linoleic acid (cis-9, trans-11-C_18 : 2) content of bovine milk fat. Anhydrous milk fat was fractionated into hard and soft fractions using controlled cooling and agitation. Fractionation of milk fat pre-melted at 60°C using a temperature programme of 33–10°C and a cooling rate of 0.58°C h⁻¹ yielded a soft fraction containing 63.2% more conjugated linoleic acid (2.22 g 100 g⁻¹ FAME), which was also enriched in polyunsaturated fatty acids and vaccenic acid (trans-11-C_18 : 1) compared with the parent fat. Agitation following fractionation was found to have a negative effect on the conjugated linoleic acid content of the soft fraction. Refractionation of the soft fraction did not increase the yield of conjugated linoleic acid. The conjugated linoleic acid and trans fatty acid content of 26 selected food products ranging in milk fat content from 0 to 100% is reported. Conjugated linoleic acid concentrations ranged from 0 to 16.2 mg g⁻¹ fat and were generally lower than the trans fatty acid content which ranged from 0 to 155.7 mg g⁻¹ fat. Spreads containing vegetable oils contained higher trans fatty acid and lower conjugated linoleic acid contents than milk fat-containing products. This study highlights that a milk fat fraction enriched in conjugated linoleic acid may be achieved by dry fractionation.     

Modeling of particle size distribution of sonicated coconut milk emulsion: Effect of emulsifiers and sonication time

Coconut milk was extracted from grated coconut meat with addition of water by a hydraulic press. This milk was mixed with emulsifiers (Gum Acacia and maltodextrin) at different ratios of emulsifier to fat (4, 2.75, and 1.5) and different maltodextrin (MD) to Gum Acacia (GA) ratio (0.67, 1.085, and 1.5). The emulsion was sonicated for different time durations (0.5–3.0 min). Particle size analysis of the sonicated coconut milk emulsion revealed that the number fraction of fat globules below 2 × 10⁻⁶ m increased as the emulsifier to fat ratio increased. However, at the highest ratio of emulsifier to fat this trend reversed even at higher sonication times. Similar slump in the increasing trend of globules below 2 × 10⁻⁶ m were observed at the highest value of ratio of MD to GA (1.5) studied. Modeling of particle size distribution by Rosin–Rambler–Sperling–Bennet relation was found to be a good tool for prediction of uniformity of distribution n and statistical average globule diameter M. The n values varied between 0.981 and 1.318 where as M values lied between 2.11 × 10⁻⁶ and 4.12 × 10⁻⁶ m. Linear regression fitting of n and M values as function of ratio of emulsifier to fat, ratio of MD to GA and the sonication time resulted in a good fit with relative deviation of 3.96% and 10.77%, respectively. These linear regression equations provided a suitable model to predict the sonication time required to achieve certain degree of size reduction with a relative deviation of 2.33%.     

Effect of exopolysaccharides and proteolytic activity of Lactococcus lactis subsp. cremoris strains on the viscosity and structure of fermented milks

Two exopolysaccharide (EPS)-producing Lactococcus lactis subsp. cremoris strains (B35 and B891) were used to study the effect of the kinetics of EPS production and bacterial proteolytic activity on the structure of milk gels and the viscosity of stirred milk gels. Strains were grown at 20 °C in milk containing either yeast extract or casitone and at 30 °C in either milk alone or milk containing casitone. Lactococcal counts, pH decrease and production and molecular characteristics (molar mass and radius of gyration) of both EPSs were followed during milk fermentation. The level of proteolysis in the fermented milks was determined after 24 h of incubation. The results obtained showed that the yield of EPS and the timing of EPS production during milk-gel formation were the most important factors that influenced the structure of the milk gels and the viscosity of the stirred product. The proteolytic activity of the strains did not seem to play any significant role.     

Effect of genetic polymorphism of milk proteins on rheology of chymosin-induced milk gels

Individual milk samples from 121 cows in mid lactation of the Swedish Red and Swedish Holstein breeds with known protein genotypes of β- and κ-casein and β-lactoglobulin were analysed. Chromatographically pure chymosin was added to skim milk and rheological properties of the gels were measured using a Bohlin VOR Rheometer. Coagulation time (CT) and curd firmness after 25 min (G′₂₅) were registered for each sample. The B allele of κ-casein was associated with improved coagulating properties of milk, whereas the E allele showed a negative effect on these traits. The β-casein A²A² genotype was associated with inferior milk coagulation characteristics. Total protein concentration of milk was positively associated with curd firmness, but showed no association with milk coagulation time.     

Effect of genetic polymorphism of milk proteins on rheology of acid-induced milk gels

Individual milk samples from 80 cows in mid-lactation of the Swedish Red and Swedish Holstein breeds with known protein genotypes of β- and κ-casein and β-lactoglobulin were analysed for acid coagulation properties. Glucono-δ-lactone (1.5%) was added to defatted, heated (90–95 °C) samples and rheological properties of the gels were measured using a Bohlin VOR Rheometer. Coagulation time (CT) and curd firmness after 4, 8 and 10 h (G₄′, G₈′, and G₁₀′ were registered for each sample. Milk protein composition was analysed by reversed phase HPLC. Concentration of β-lactoglobulin in milk was found to be an important factor for the variation in CT and G′. The A allele of β-lactoglobulin was associated with higher concentrations of β-lactoglobulin in milk compared with B. When no adjustment for β-lactoglobulin concentration was made, there was a significant overall effect of β-lactoglobulin genotype on acid coagulation, where the AA and AB genotypes were associated with better curd firmness compared with BB, whereas at equal β-lactoglobulin concentrations a tendency in the opposite direction was found with a significant and positive effect of BB compared with AB. Lactose concentration of milk had a positive effect on acid coagulation and was shown to improve G′ in milk with low β-lactoglobulin concentrations.     

Rheological properties of model dairy emulsions as affected by high pressure homogenization

The aim of this work was to evaluate the effect of different homogenization pressures on the rheological properties of model dairy emulsions. Solutions of sodium caseinate and whey protein concentrate at 2% + 1% and 2% + 2% (w/v) were emulsified with milk fat at the final contents of 5%, 8% and 15% (w/v). Raw and pasteurized emulsions were subjected to conventional (15/3 MPa) and high pressure (97/3 MPa and 147/3 MPa) homogenization. Differences in viscosity were observed according to fat content, protein ratio, heat treatment and pressure homogenization conditions. Gel networks formed in 8% and 15% fat content emulsions after pasteurization and high pressure homogenization. Gel strength was mostly affected by protein and fat contents.Dynamic high pressure may be used to produce emulsion gels with modulated structures which could be exploited low fat formulations.Industrial relevanceTexture influences people's acceptance of food and may be more important than the flavor in some products. Gelation of emulsions was observed after pasteurization and high pressure homogenization treatments, depending on fat and protein contents. Dynamic high pressure may be an alternative tool to improve viscoelastic properties and mouth feel of emulsions by providing a weak gel structure in the system. These characteristics can be exploited for low fat and low additive formulations.     

Oil droplet release from emulsion-filled gels in relation to sensory perception

Oil droplet release upon shearing was studied in emulsion-filled gels containing oil droplets either bound or unbound to the gel matrix. At 20 °C no release was observed for gels containing droplets bound to the matrix, whereas the release measured for gels with unbound droplets related to the fat content and the size of the gel particles obtained after shearing. For gels with bound droplets and melting at the oral processing temperature, increasing the temperature of the determination to 37 °C resulted in an almost complete release of the oil droplets.An increase of the oil content induced an increase of the creaminess scores for all gels. These scores were somewhat higher for gels containing unbound droplets and gels melting at oral processing temperature. For these gels, the oil droplet release appears to correlate with creaminess. However, because a similar increase in creaminess at increasing oil concentration was also found for gels with oil droplets bound to the matrix, it is concluded that the release of oil droplets during oral processing is not the main mechanism causing creaminess perception in emulsion-filled gels.     

The increased viability of probiotic Lactobacillus salivarius NRRL B-30514 encapsulated in emulsions with multiple lipid-protein-pectin layers

Probiotics have demonstrated various health benefits but have poor stability to sustain food processing and storage conditions, as well as after ingestion. Biopolymer beads are commonly studied to encapsulate probiotic cells to improve their stability, but the millimeter-dimension of these beads may not meet the quality requirement of food products. The aim of this study was to enhance the viability of Lactobacillus salivarius NRRL B-30514 by encapsulation in emulsion droplets with multiple lipid-protein-pectin layers. Spray-dried L. salivarius was suspended in melted anhydrous milk fat that was then emulsified in a neutral aqueous phase with whey protein isolate or sodium caseinate to prepare primary solid/oil/water (S/O/W) emulsions. Subsequently, pectin was electrostatically deposited onto the droplet surface at pH 3.0 to form secondary emulsions. The encapsulation efficiency was up to 90%. After 20-day storage at 4 °C, the viable cell counts of bacteria in secondary emulsions at pH 3.0 and primary emulsions at 7.0 were 3 log higher than the respective free cell controls. After heating at 63 °C for 30 min, free L. salivarius was inactivated to be undetectable, while about 2.0 log CFU/mL was observed for primary (at pH 7.0) and secondary (at pH 3.0) emulsion treatments. Additionally, a 5 log-CFU/g-powder reduction was observed after spray drying free L. salivarius, while a 2 log CFU/g reduction was observed for emulsion treatments with capsules smaller than 20 μm. Furthermore, cross-linking the secondary emulsion with calcium enhanced the viability of L. salivarius after the simulated gastric and intestinal digestions. Therefore, the studied S/O/W emulsion systems may be used to improve the viability of probiotics during processing, storage, and gastrointestinal digestion.     

Yield and functionality of Cheddar cheese as influenced by homogenization of cream

Cheese milk was standardized (casein-to-fat ratio of 0.7) by blending 0.64% fat milk and 35% fat cream. Cream was homogenized at 0/0 MPa (CO), 3.5/3.5 MPa (H05), 6.9/3.5 MPa (H10) or 10.4/3.5 MPa (H15). Cream homogenization did not influence rennet-clotting time, but it increased rate of curd firming and increased curd firmness of cheese milk. Moisture and salt in moisture phase of cheese increased with homogenization. Moisture (37%) and salt (1.5%) adjusted yield increased 1.42, 3.44 and 3.85% in H05, H10 and H15, respectively, over CO. Homogenized treatment cheeses melted faster with age. Free oil in 1 week old cheeses was lowest in H10 and highest in H05 and increased in all treatments with age. Cheese hardness was not influenced by homogenization but decreased with age. Cheeses with homogenized cream had improved body and texture and flavor. Cream homogenized at 6.9/3.5 MPa was optimal for enhancing Cheddar cheese yield and functionality.     

Rheology of emulsion-filled alginate microgel suspensions

Emulsion filled polysaccharide gels can be used as carrier systems of lipophilic bioactives in the food, pharmaceutical and cosmetics industry. This carrier system can exist either as bulk or discrete gel systems. In this study the rheological properties of discrete emulsion filled alginate microgel suspension was examined as a function of volume fraction (ϕ) and oil content. Fine emulsion (220 nm) was encapsulated within alginate microgels (mean size 36.2–57.8 μm) by using the impinging aerosol technique. The microgels (containing 0–77% w/w oil total solids basis) produced were estimated to have particle modulus in the range of 150–212 Pa. An increase in oil content in the microgels led to more deformable microgels due to the reduction in gel density. The deformability of microgels influenced the bulk modulus and apparent viscosity of the concentrated suspension. At the same suspension volume fraction (ϕ), suspensions with more deformable microgels exhibited a lower bulk modulus. We also showed that the Carreau and Cross models were adequate in predicting the flow behaviour of the concentrated emulsion filled microgel suspension.     

Small and large deformation rheology and microstructure of κ-carrageenan gels containing commercial milk protein products

The rheological behaviour of commercial milk protein/κ-carrageenan mixtures in aqueous solutions was studied at neutral pH. Four milk protein ingredients; skim milk powder, milk protein concentrate, sodium caseinate, and whey protein isolate were considered. As seen by confocal laser microscopy, mixtures of κ-carrageenan with skim milk powder, milk protein concentrate, and sodium caseinate showed phase separation, but no phase separation was observed in mixtures containing whey protein isolate. For κ-carrageenan concentrations up to 0.5 wt%, the viscosity of the mixtures at low shear rates increased markedly in the case of skim milk powder and milk protein concentrate addition, but did not change by the addition of sodium caseinate or whey protein isolate. For κ-carrageenan concentrations from 1 to 2.5 wt%, small and large deformation rheological measurements, performed on the milk protein/κ-carrageenan gels, showed that skim milk powder, milk protein concentrate or sodium caseinate markedly improved the strength of the resulting gels, but whey protein isolate had no effect on the gel stength.