Homogenisation improves the microstructure,syneresis and rheological properties of buffalo yoghurt

Homogenisation is known to improve the textural properties of bovine yoghurt but the potential of this processing step has not been systematically explored for buffalo yoghurt. In this study, buffalo milk was homogenised at 80 bar or 160 bar and the effect on the properties of buffalo yoghurt examined. The microstructure of both buffalo yoghurt samples produced from homogenised milk was significantly altered, forming a more interconnected protein network with smaller embedded fat globules. These structural changes resulted in a significant decrease in syneresis and hysteresis area and led to a considerable increase in the storage modulus, gel firmness and flow behaviour index. A higher homogenisation pressure of 160 bar resulted in a lower gel firmness and storage modulus, possibly due to the presence of bigger fat–protein clusters within the homogenised milk. A homogenisation pressure of 80 bar could be optimal for improving the quality of buffalo yoghurt.     

The Effect of Fermentation Temperature on the Microstructure,Physicochemical and Rheological Properties of Probiotic Buffalo Yoghurt

The properties of buffalo and bovine milk differ and the procedures developed to make bovine yoghurt may require optimisation for the production of buffalo yoghurt. This study aimed to apply cryo-scanning electron microscopy and confocal laser scanning microscopy to determine the optimal temperature for processing buffalo yoghurt. Milk was fermented at three different temperatures (37, 40 and 43 °C), stored for 28 days and the yoghurt microstructure, physicochemical and rheological properties assessed. Yoghurt fermented at 37 °C had a compact microstructure and the probiotic Lactobacillus acidophilus La-5 was more viable on storage. In contrast, yoghurt produced from a faster fermentation at 43 °C was firmer with a more porous microstructure that exhibited a higher degree of syneresis. The rheological properties during storage including the thixotropy, consistency coefficient and flow behaviour index were not significantly affected by temperature nor were the concentration of lactose, ionic calcium or titratable acidity. This study shows how changes to processing can be used to alter the microstructure of buffalo products and suggests that a decrease in fermentation temperature could be used to improve the quality of buffalo yoghurt.     

Effect of Emulsion Droplet Size on Foaming Properties of Milk Fat Emulsions

Foamability and foam stability of dairy-based emulsions, as a function of emulsion droplet size ranging from micron- to nanometre-scale, were investigated. Fat phase (10 % w/w of anhydrous milk fat, stearin or olein fraction) was mixed with 2 % w/w protein solution (sodium caseinate or whey protein concentrate) and homogenised at 3, 10 and 35 MPa to obtain emulsions having particle sizes of about 1.20, 0.60 and 0.20 μm, respectively. The emulsions were cooled down and aged at 4 °C for 48 h to promote crystallisation. No fat coalescence was observed in any of the emulsions, as particle size distribution remained the same upon aging and whipping. It was shown that the smaller the particle size, the higher was the apparent viscosity and the lower was the solid fat content. Higher solid fat content tended to yield better foamability and foam stability. Destabilisation of air cells happened fastest with nanosized fat particles, resulting in shorter half-life of foam.     

The effect of milk fat globules on adherence and internalization of Salmonella Enteritidis to HT-29 cells

Milk fat globules were extracted from bovine and goat milk and incubated with HT-29 human adenocarcinoma cells to assess the attachment and internalization of Salmonella Enteritidis. Because the expression of bacterial adhesins is highly affected by the presence of antibiotic, the attachment was studied with and without antibiotic in the cell growth medium. Although no inhibitory effect of the fat globules was observed in the presence of the antibiotic, milk fat globules significantly inhibited the binding and internalization of Salmonella in medium free of antibiotic. The fat globules from both bovine and goat milk markedly reduced bacterial binding and invasion compared with controls, and the cells treated with goat milk-derived fat globules demonstrated greater protective properties than those derived from bovine milk. The effect of heat treatment on bovine fat globules was also investigated, and it was shown that the fat globules from heated milk had a higher degree of inhibition than those from unheated milk.     

Microencapsulated Starter Culture During Yoghurt Manufacturing,Effect on Technological Features

The potential of living cell microencapsulation in sustaining cells’ viability, functionality and targeted release in gastrointestinal tract is relatively well documented. Differently, the effects exerted by the capsules on cell metabolic activities during fermentation of a food matrix as well as on cell physiology are poorly addressed. This paper aimed at studying the effects of chitosan-alginate capsules (matrix and core-shell) on metabolic activities of Streptococcus thermophilus and probiotic Lactobacillus delbrueckii during milk fermentation for yoghurt production. This food system has been used to monitor growth, acidification kinetics and strain proteolytic activity. Bacterial viability has been monitored during yoghurt storage at 4 °C for 28 days and an in vitro digestion to evaluate the protective effect exerted by the capsules. Furthermore, production of volatile metabolites associated with starter culture activity was monitored by headspace solid-phase microextraction-GC/MS to explore possible influence of microenvironment on cell metabolism. Results indicate that both kinds of capsules influenced at different extent cell functionalities (growth, acidification and proteolysis), while they improve cell viability during yoghurt storage and simulated gastrointestinal passage. The volatile pattern revealed that capsules influenced their production in yoghurt: 12 out of 28 volatiles recovered in yoghurt fermented by free and encapsulated starters had significantly different concentration. However, concentration of the main aroma constituents (e.g. acetaldehyde, diacetyl, acetoin) was not significantly affected. Due to the leakage of bacteria from microcapsules during fermentation, the final product resulted in co-existing of free and still encapsulated cells, with the main advantage of an increased viability during yoghurt storage and simulated digestion of the encapsulated counterpart.     

Buffalo vs. cow milk fat globules: Size distribution,zeta-potential,compositions in total fatty acids and in polar lipids from the milk fat globule membrane

Although buffalo milk is the second most produced milk in the world, and of primary nutritional importance in various parts of the world, few studies have focused on the physicochemical properties of buffalo milk fat globules. This study is a comparative analysis of buffalo and cow milk fat globules. The larger size of buffalo fat globules, 5 vs. 3.5 μm, was related to the higher amount of fat in the buffalo milks: 73.4 ± 9.9 vs. 41.3 ± 3.7 g/kg for cow milk. Buffalo milks contained significantly lower amount of polar lipids expressed per gram of lipids (0.26% vs. 0.36%), but significantly higher amount of polar lipids per litre of milk (+26%). Buffalo and cow milk fat globule membranes contain the same classes of polar lipids; phosphatidylethanolamine, sphingomyelin (SM) and phosphatidylcholine (PC) being the main constituents. A significant higher percentage of PC and lower percentage of SM were found for buffalo milks. The fatty acid analysis revealed that saturated fatty acids, mainly palmitic acid, trans fatty acids, linolenic acid (ω3) and conjugated linolenic acid were higher in buffalo milk than in cow milk. Such results will contribute to the improvement of the quality of buffalo milk-based dairy products.     

Influence of enzymatic cross-linking on milk fat globules and emulsifying properties of milk proteins

The enzyme transglutaminase (TGase) can modify dairy protein functionality through cross-linking of proteins. This study examined the effects of TGase treatment on milk fat globules and the emulsifying properties of milk proteins. The extent of TGase-induced cross-linking of caseins increased with incubation time, with no differences between whole and skim milk. Extensive clustering of fat globules in extensively cross-linked raw whole milk occurred on homogenisation at 400 or 800 bar. Considerably less clustering of fat globules was observed when recombined milk (90 g fat L^–1) was prepared from TGase-treated skim milk and homogenised at 400 or 800 bar. TGase treatment did not affect fat globule size in cream, but prevented coalescence of fat globules therein, possibly through cross-linking of milk fat globule membrane components. TGase-induced cross-linking of milk proteins affected their emulsifying properties and may increase the stability of natural milk fat globules against coalescence.     

Buffalo milk fat globules and their biological membrane: in situ structural investigations

Milk fat globules and their surrounding biological membrane (the MFGM) are not well understood despite the importance of these milk components in human nutrition and the role of fat globules in determining the properties of dairy products. The objectives of this study were to investigate these unique colloidal assemblies and the microstructure of the MFGM in buffalo milk, which is the second largest global source of dairy products. In-situ structural investigations were performed at room temperature using confocal microscopy with multiple fluorescent probes (Nile Red, Rh-DOPE, the lectin WGA-488). Microscopic observations showed cytoplasmic crescents around fat globules and the heterogeneous distribution of glycosylated molecules and polar lipids with the occurrence of lipid domains. The lipid domains in the buffalo MFGM appear to form by the segregation of lipids with a high phase transition temperature (e.g. sphingomyelin and saturated phosphatidylcholine molecular species) and cholesterol resulting in a gel phase or a Lo phase forming circular domains. The structure of the buffalo MFGM results from a non-random mixing of components, consistent with observations for other species. Structural heterogeneities of the MFGM could affect the processability of buffalo fat globules and the bioavailability of milk lipids.     

High pressure homogenisation of raw whole bovine milk (a) effects on fat globule size and other properties

Although widely adopted by the chemical and pharmaceutical industries in recent years, little published data is available regarding possible applications of high pressure homogenisation for dairy products. The objective of this work was to compare the effects of conventional (18 MPa, two-stage) and single or two-stage high pressure homogenisation (HPH) at 50-200 MPa on some properties of raw whole bovine milk (approximately 4% fat). Fat globule size decreased as HPH pressure increased and, under certain conditions of temperature and pressure, HPH yielded significantly smaller fat globules than conventional homogenisation. Fat globule size was also affected by milk inlet temperature. The pH of all homogenised milk samples decreased during 24 h refrigerated storage. Total bacterial counts of milk were decreased significantly (P < 0.05) for milk samples HPH-treated at 150 or 200 MPa. Whiteness and rennet coagulation properties of milk were unaffected or enhanced, respectively, as homogenisation pressure was increased. Average casein micelle size decreased slightly when skim milk was homogenised at 200 MPa. Thus, HPH treatment has several, potentially significant, effects on milk properties.     

Modifying the microstructure of low-fat yoghurt by microfluidisation of milk at different pressures to enhance rheological and sensory properties

The effects of microfluidisation of milk at different pressures, prior to heat treatment, on structural and sensory properties of low-fat stirred yoghurt, were investigated. Low-fat yoghurts prepared from microfluidised milk were compared with low-fat (1.5%) and full-fat (3.5%) control yoghurts made with homogenised (20/5 MPa) milk. The microstructure of low-fat yoghurts prepared with microfluidised milk consisted of smaller and more uniform fat globules, well incorporated into more interconnected fat-protein gel networks, compared with those of control yoghurts. This modification in microstructure caused significant changes in gel particle size, sensory profile and rheological behaviour. Microfluidisation increased the gel particle size, gel strength and viscosity; marked beneficial effects were found at higher pressures (50–150 MPa). Microfluidising milk at 50–150 MPa increased the gel strength by 171–195% and viscosity by 98–103%, creating low-fat yoghurts with creaminess and desirable texture properties similar to, or better than, full-fat conventional yoghurt.     

Effects of Size and Stability of Native Fat Globules on the Formation of Milk Gel Induced by Rennet

Rennet‐induced gelation crucially impacts cheese structure. In this study, effects of the size and stability of native fat globules on the kinetics of rennet‐induced coagulation were revealed by determining the caseinomacropeptide release rate and rheological properties of milk. Moreover, the mobility and stability of fat globules during renneting was revealed using diffusing wave spectroscopy and confocal laser scanning microscopy. By use of a 2‐stage gravity separation combined centrifugation scheme, native fat globules were selectively separated into small (SFG, D_4,3 = 1.87 ± 0.02 μm) and large fat globules (LFG, D_4,3 = 5.65 ± 0.03 μm). The protein and fat content of SFG and LFG milk were then standardized to 3.2 g/100 mL and 1.2 g/100 mL, respectively. The milk containing different sized globules were then subjected to renneting experiments in the laboratory. Reduction of globule size accelerated the aggregation of casein micelles during renneting, giving a shorter gelation time and earlier 1/l^* change. The gel produced from LFG milk was broken due to coalescent fat globules and generated coarser gel strands compared to the finer strands formed with SFG milk. Structural differences were also confirmed with a higher final storage modulus of the curd made from SFG milk than that from the LFG. In conclusion, the size of fat globules affects the aggregation of casein micelles. Moreover, fat globule coalescence and creaming during renneting, also affects the structure of the rennet gel. A better understanding of the size of globules effect on milk gelation could lead to the development of cheese with specific properties.     

Synbiotic Microencapsulation from Slow Digestible Colored Rice and Its Effect on Yoghurt Quality

Lactobacillus plantarum was encapsulated by slowly digestible hydrolyzed heat-moisture-treated (hydrolyzed-HMT) black waxy rice and applied in yoghurt. Incorporating these microcapsules in yoghurt resulted in higher viability of Lactobacillus bulgaricus C49 and Streptococcus thermophilus C44, especially in prolonged storage. The viability of L. bulgaricus and S. thermophilus (7.98 and 8.28 Log CFU/g) in synbiotic yoghurt was higher than in the control (7.81 and 7.96 Log CFU/g). Thirty-two aromatic compounds were detected and classified into 4 groups: alcohols, carbonyls, organic acids, and sulfur. Synbiotic yoghurt produced higher carbonyl compounds, particularly acetaldehyde and diacetyl. On the other hand, higher organic acid especially hexanoic, dodecanoic, acetic, butanoic, and pentanoic acids was observed at the end of fermentation but did not differ from control after storage. Ethanol was also higher in the synbiotic yoghurt due to the breakdown of glucose from starch and acetaldehyde by lactic acid bacteria. Weak correlation was found concerning sulfur compounds. Rice starch granules were aggregated and still retained its hexagonal shape, indicating high resistance to acid fermentation during 28 days of storage. The resistant starch coating from rice could provide a good prebiotic ingredient and allow the design of synbiotic yoghurt with enhanced aroma.     

Effects of ultrasonication on the physicochemical properties of milk fat globules of Bubalus bubalis (water buffalo) under processing conditions: A comparison with shear-homogenization

Ultrasonication has been widely studied in bovine milk but the effects of ultrasound (US) on the buffalo's milk fat globules (MFG) are not well known yet. In this study, buffalo's milk samples were ultrasonicated at 20 kHz and physicochemical properties were assessed under different processing conditions. Shear homogenization was performed with 1188 J/mL energy density for the comparison. Results show that ultrasonication reduced the average volume-weighted mean diameter (D[4,3]) of MFG by 93% and increased the surface area by a factor of 8.5 compared to the native counterparts. The zeta-potential (ZP) of MFG are increased by ultrasonication compared to fresh milk (−26.37 vs. −18.22 mV) indicating better stability. Changing the pH of ultrasonicated milk to the isoelectric pH (pI) reduced the zeta-potential (ZP) by −19.8 mV and increased the (D[4,3]) > 0.4 mm indicating the gelation. The size of milk particles increased up to 76–586 μm and the ZP was reduced by 3.1 mV with the increase of ionic strength from 50 to 200 mM. Heating of milk at 90 °C for 30 min increased D[4,3] in US homogenized milk by 22%. Both ultrasonication and shear-homogenization increased the free saturated fatty acids by 2.75–3 g/100 g fat compared to raw buffalo's milk. Ultrasonication increased the gel hardness by 98% compared and shear-homogenized milks. The results of this study indicate that the ultrasonication reduced the size of buffalo's MFG up to sub-micron level with superior stability while improving (P < 0.05) the gels strength compared to shear-homogenization.Industrial relevanceBuffalo set-yoghurts made with unhomogenized milk exhibit higher syneresis and poor stability upon shear-induced breakdown, which are mainly due to the porous gel structure containing a large number of bigger fat globules. Under the large scale production, buffalo set-yoghurts are often fortified with dairy/non-dairy solids and stabilizers in order to prevent this problem. However, the use of some inexpensive, non-food grade alternatives are also reported in some parts of the world for the cottage or medium level production of buffalo yoghurts. In this work, it was shown that ultrasonication with the energy density of 1188 J/mL can be used to produce buffalo set-yoghurts with superior gel strength and therefore, can be used as an unconventional approach to improve the product quality.     

Nutritional,antioxidant, and antimicrobial assessment of carrot powder and its application as a functional ingredient in probiotic soft cheese

Carrots (the main source of carotenoids) have multiple nutritional and health benefits. The objectives of this study were to evaluate the compositional, antioxidant, and antimicrobial properties of carrot powder and to examine its effect on the sensory characteristics, chemical properties, and microbial viability of probiotic soft cheese at a rate of 0.2, 0.4, and 0.6%. The carrot was turned into powder before being analyzed and incorporated as an ingredient in making probiotic soft cheese. Probiotic soft cheese was made from buffalo milk. The buffalo milk (～6.9% fat, 4.4% protein, 9.2% milk solids not fat, and 0.7% ash) was pasteurized at 75 ± 1°C for 5 min and cooled to 40–42°C. The milk was then divided into 4 aliquots. Sodium chloride (local market, Assiut, Egypt) was added at a ratio of 5% followed by starter cultures. The carrot powder (4.5% moisture, 4.8% ash, 2.7% fat, 8.2% protein, 11.9% fibers, and 72.3% carbohydrate) was added at a rate of 0.2, 0.4, and 0.6%, followed by addition of 0.02 g/kg rennet. The cheese was cut again into cubes, pickled in jars filled with whey, and stored for 28 d at 6 ± 1°C. The results of this study illustrated the nutritional and antioxidant properties of carrot powder. Incorporation of carrot powder in probiotic soft cheese affected the moisture and salt content at 0 d. The total bacteria count decreased from 7.5 to 7.3 log cfu/g in the cheese when carrot powder was used at a rate of 0.6%. The reduction of total bacteria count was noticed during the 28 d of storage by adding carrot powder. Furthermore, lactic acid bacteria and Bifidobacterium longum counts elevated with adding carrot powder during the 28 d of storage.     

Comparison of the effects of high-pressure microfluidization and conventional homogenization of milk on particle size,water retention and texture of non-fat and low-fat yoghurts

The effect of high-pressure homogenization using a Microfluidizer^® on texture, water-holding capacity, and extent of syneresis on stirred yoghurts was compared with that of conventional homogenization. The effect of homogenization condition on particle size was also assessed in milk and in yoghurt. Stirred yoghurts were prepared from recombined milk samples (0 and 1.5% fat) heat-treated (95 °C, 2 min) and then treated by conventional valve homogenization at 25 MPa or microfluidization at 150 MPa. Homogenization conditions influenced the particle size in milk, gel particle size, and textural quality of stirred yoghurts in a manner dependent upon fat content. Milk microfluidized at 150 MPa had smaller particle size than homogenized milk, but resulted in larger particles in yoghurt. Microfluidization of low-fat milk modified the microstructure of yoghurt, giving more interconnectivity in the protein networks with embedded fat globules, but with similar texture profiles and water retention compared with yoghurt made from conventionally homogenized milk.     

Eliciting the Sensory Modalities of Fat Reformulated Yoghurt Ice Cream Using Oligosaccharides

In the present work, fat reduction of Greek strained yoghurt ice cream (YIC) was carried out in three proportional milkfat levels i.e. 30, 50 and 70% using three types of oligosaccharides namely long-chain inulin, oligofructose and maltodextrin 12 DE. Greek strained yoghurt was blended with ice cream mixes in ratios of 1:3 and 1:1. The physico-chemical, textural and thermal characteristics of the YIC mixes and their obtained frozen end products were determined. The sensory modalities (olfactory, gustatory, tactile and oro-tactile) of the YIC were monitored following 2 and 16 weeks of quiescent frozen storage at ?25 °C. Milkfat reduction impaired significantly (p?<?0.05) the perceived creaminess and mouthcoating sensation stimuli, whist it intensified the oral tissue friction associated sense stimuli such as astringency, wateriness and coarseness. Long-chain inulin- and maltodextrin-based samples received the highest scores for creaminess, mouthcoating, gumminess, hardness and iciness. The increase of the yoghurt to ice cream mix ratio escalated the friction/recrystallization-associated sensations e.g. astringency, sourness, coarseness and wateriness. Notwithstanding yoghurt supplementation reinforced the pseudoplasticity and macroviscosity of the ice cream mixes, it suppressed their aeration capacity leading to heavy-bodied ice creams. However, no significant effects of yoghurt supplementation level on the colligative and meltdown rate of the YIC formulations were identified. Partial least squares coupled discriminant analysis (PLS-DA) revealed that fat reformulation of YICs using oligosaccharides results in a substantially diversified sensory profile. Generally, a 50% fat reduction of YICs using long-chain oligosaccharides appears to be a technologically tangible solution.     

Interactive Effects of Milk Fat Globule and Casein Micelle Size on the Renneting Properties of Milk

The size of the casein micelles (CM) and the milk fat globules (MFG) vary depending on farming factors, such as seasonal variation and stage of lactation, and cow genetics. The MFG and CM size of milk can influence the renneting behavior and texture of manufactured dairy products. In this work, we investigated the combined effects of MFG and CM size on the onset of gelation, the maximum rate of gelation, the value for G′_60 min (the final storage modulus) and G″_60 min (the final loss modulus), and tan δ upon renneting. Fractionation of MFG on the basis of size was carried out using laboratory-based centrifugation, whereas milk of predominantly large (184–218 nm) or small (147–159 nm) CM was selected naturally on-farm. Casein micelle size had the dominant effect on curd firmness and gelation rates of milk, where small CM milk formed rennet gels earlier and resulted in a firmer gel than milk with large CM. However, MFG size also influenced the renneting properties. The strongest rennet gels were obtained when large MFG (3.88–5.78 μm) was combined with small CM (153–159 nm). Selecting milk on the basis of the microstructure of key milk components could be achieved by natural selection of dairy cows or via fractionation technologies. Selection may provide a useful tool for efficient manufacturing of different dairy products based on the desirable characteristics specific to each.     

Effects of somatic cell counts in milk on physical and chemical characteristics of yoghurt

The quality of plain stirred yoghurt produced from whole milk with somatic cell counts (SCC) at low (147,000 cells mL⁻¹), intermediate (434,000 cells mL⁻¹) and high (1,943,000 cells mL⁻¹) levels was examined. Each milk treatment was obtained from selected cows, according to its SCC status and milk composition. Yoghurt samples were analysed on days 1, 10, 20 and 30 after production. Analyses included pH, acidity, fat, lipolysis (expressed as free fatty acids, FFA), proteolysis and apparent viscosity. Viscosity of high SCC yoghurt was higher (P<0.05) than the low SCC yoghurt on days 10, 20 and 30 of storage. High SCC yoghurt also had higher FFA content (P<0.05). SCC did not affect pH, acidity, fat content and proteolysis of the yoghurt (P>0.05). Results indicate that SCC in milk increases the lipolysis in the resulting yoghurt during storage for 30 d.     

The effect of sonication and high pressure homogenisation on the properties of pure cream

The homogenisation of milk and cream has been widely studied but the effect of sonication on the structural and functional properties of cream is not well known. In this study, raw milk, ultrafiltration retentate and cream samples were sonicated at 20 kHz and the rennet and acid gelation properties of these sonicated samples investigated. High pressure homogenisation at 80 bar was also performed for comparison. Sonication of raw milk and retentate samples led to a decrease in the fat globule size. Conversely, the fat globules in cream samples sonicated at < 10 °C flocculated to form grapelike structures whereas the cream samples sonicated at 50 °C did not form such aggregates. High pressure homogenisation at 50 °C led to similar flocculated structures, but these were not observed at low temperatures. This suggests a potential benefit of sonication technology in allowing low temperatures to be utilised for cream homogenisation, reducing energy demand. However, a gel made using cheese-milk with sonicated cream resulted in separation of a fat layer rather than the incorporation of the fat globules into the gel matrix. Rennet gelation properties of both the sonicated or homogenised samples were significantly superior to a native control sample where the resultant gels had shorter coagulation times and decreased syneresis.Industrial RelevanceHomogenisation of dairy cream is normally carried out at temperatures of around 50 °C, to ensure that the fat is in the liquid state. In this work, we show that we can achieve comparable changes to the fat globules within the cream using ultrasound at much lower temperatures (< 10 °C). The ability to form flocculated fat particles at lower temperatures could lead to reduced costs through reduced energy demand.     

Deposit Generation During Camel and Cow Milk Heating: Microstructure and Chemical Composition

The aim of this study is to identify the chemical composition and the microstructure of the deposits obtained after heating camel and cow milks at 80 °C for 60 min using a laboratory-scale device. Like cow milk, camel milk was affected by heat treatment with the reduction of the non-casein nitrogen content reflecting the denaturation of camel whey proteins. The composition of the deposits generated during heating camel and cow milks at 80 °C for 60 min revealed that while camel deposit contained 57 % w/w protein, cow deposit showed a higher protein content of 69 % w/w. The mineral content was 35 % w/w for camel deposit which was higher than that of cow sample, which was 28 % w/w. SEM of both deposits showed a familiar structure of a protein deposit with large clumps composed of smaller aggregates. Camel deposit showed an amorphous structure due to its deficiency in β-lactoglobulin.