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.     

Effects of somatic cell counts on the physicochemical and rheological properties of yoghurt made from sheep’s milk

In the present work, yoghurts were made from sheep’s milk with two different somatic cell count (SCC), at low (200 000 cells mL^?1) and high (750 000 cells mL^?1) levels. The characteristics of the final product were analysed for pH, acidity, protein, total solids, fat, syneresis, water holding capacity (WHC) and apparent viscosity. Samples were analysed on days 1, 7 and 14 after production of yoghurts. The SCC had no significant effect either on the acidity or pH of the yoghurt at 24 h (P > 0.05) but a significant effect (P < 0.05) was observed at 168 h. No effects of SCC were observed on total solids and fat content of the yoghurt after 24 and 168 h. High SCC (HSCC) yoghurt had higher protein content (P < 0.05). The yoghurt with the highest SCC had the highest level of syneresis. Viscosity of HSCC yoghurt was higher than that of the low SCC yoghurt on days 1, 7 and 14 of storage. The flow properties also showed that the low SCC yoghurt was softer than that from milk with high content in somatic cells.     

The effect of supplementing goats milk with whey protein concentrate on textural properties of set-type yoghurt

Yoghurt was manufactured from goat's milk and supplemented with 30 g L^?1 of whey protein concentrate (WPC). The textural properties of the yoghurt were evaluated during the shelf‐life of the product and the textural characteristics of yoghurt made from cow's milk were used as a reference. The instrumental analyses used were the puncture test, stress relaxation test and texture profile analysis. The addition of WPC to goat's milk enhanced the textural characteristics of yoghurt. These advantageous attributes included increased firmness, hardness and adhesiveness. These attributes were quantitatively similar (P > 0.05) to those obtained from yoghurt made from cow's milk. In addition, the textural properties were maintained constant throughout the shelf‐life of the product.     

Influence of enrofloxacin on the coagulation time and the quality parameters of goat's milk yoghurt

Three batches of yoghurts were made from goat's milk with different enrofloxacin concentrations (0, 50, 100 and 150 μg/kg). Quality parameters were analysed at 1, 7, 14 and 28 days at 5 °C. Drug residues were also quantified by HPLC. Coagulation time and most yoghurt properties remained unaffected by the presence of enrofloxacin in goat's milk. However, quality parameters were affected by the storage period. 74.9–99.2% of enrofloxacin initially added to goat's milk remained in the yoghurt throughout its entire shelf life, potentially posing a risk to consumer health. Therefore, an enrofloxacin maximum residue limit in yoghurt should be established.     

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.     

Evaluation of the peptide profile with a view to authenticating buffalo mozzarella cheese

Electrophoretic and chromatographic techniques were used to determine water‐soluble peptide profiles aiming to identify the adulteration of buffalo milk mozzarella cheese by the addition of cow's milk. Thus, cheeses were produced with contents of cow's milk varying from 0% to 100%, and the peptides extracted after production and after 20 days of refrigeration. Polyacrylamide gel electrophoresis under denaturing conditions in the presence of sodium dodecyl sulphate (SDS‐PAGE) identified a potential peptide marker of exclusively bovine origin with a size of about 21 kDa for the addition of cow's milk above 30%. Reverse‐phase high‐performance liquid chromatography (RP‐HPLC) indicated the existence of two potential peptides present in higher concentrations in buffalo milk and one exclusive for cow's milk, the latter making it possible to estimate the addition of cow's milk to buffalo milk. Six commercial brands of buffalo mozzarella cheese were evaluated, and indications of adulteration found in four of them.     

Flavour profiles and survival of starter cultures of yoghurt produced from high-pressure homogenized milk

Volatile carbonyl compounds, organic acids and yoghurt bacteria counts were investigated in yoghurts made from ultra-high pressure homogenized milk. Yoghurts were manufactured from milk treated using ultra-high pressure homogenization at 200 or 300 MPa and at 30 °C or 40 °C, and compared with those produced from heat-treated milk with 3% added skim milk powder. To study the evolution of these parameters, samples were analysed after days 1, 14 and 28 of storage. Yoghurts from milk heat-treated or treated at 300 MPa had very similar profiles of organic acids and volatile compounds, as well as similar bacterial counts of both starter cultures. In comparison, yoghurts from milk treated at 200 MPa at either 30 °C or 40 °C gave different profiles, together with a sharp decrease in counts of lactobacilli. During storage, only slight differences in flavour compounds and yoghurt bacteria counts were detected, except in those samples from milk treated at 200 MPa.     

Lactose,glucose and galactose content in milk,fermented milk and lactose-free milk products

Lactose, glucose and galactose contents in milk and fermented milk products and their lactose-free alternatives, were determined. Storage of products up to the best-before dates had no effect on carbohydrate composition. Total galactose content in yoghurt, i.e., free galactose plus the galactose moiety of lactose, was 2.3–2.4 g 100 g⁻¹ (94–95% of that in milk), whereas that in Swedish soured milk and kefir was 1.9–2.0 g 100 g⁻¹ (75–79% of that in milk). Lactose levels in lactose-free milk and fermented milk products were below or close to detection limits for all products. Only small differences in total galactose content existed for the lactose-free alternatives of milk, yoghurt and filmjölk, all with average total galactose contents of 1.3–1.4 g 100 g⁻¹ (55–60% of that in milk). In contrast, lactose-free kefir had the same galactose content as milk, 2.4 g 100 g⁻¹.     

Milk with different somatic cells counts and the physicochemical,microbiological characteristics and fatty acid profile of pasteurised milk cream: is there an association?

In this study, raw cow milk containing somatic cells counts (SCC) at mean levels of 39 000 cells mL^?1 (low), 349 000 cells mL^?1 (intermediate) and 1 297 000 cells mL^?1 (high) was used for the production of pasteurised cream. Physicochemical (pH, fat and fatty acid profile) and microbiological analyses (mesophilic and psychrotrophs) were performed in the obtained creams during 30 days of refrigerated storage at 5 °C ± 2. No interactions (P > 0.05) were found between SCC, storage time and the physicochemical and microbiological variables studied. Fatty acid profile was similar among the SCC creams, except for oleic acid (C18:1), which decreased (P < 0.05) in intermediate and high SCC creams. Considering the technological aspect, our findings suggest that milk cream manufacture can be an interesting option for the use of high SCC milk.     

Compositional profile of ovine milk with a high somatic cell count: A metabolomics approach

Ovine milk (Sarda breed) with high somatic cell count (SCC) (>1 × 10⁶ cell mL⁻¹) was compared with similar milk of low SCC (<150 × 10³ cell mL⁻¹) using a metabolomics approach, whereby the metabolite profile of milk was studied by gas chromatography coupled to mass spectrometry. Discriminant analysis indicated that high SCC milk samples have metabolite profiles from those of low SCC samples. Malic acid, ribitol, glucose and medium-short chain fatty acids were up-regulated in milk with high SCC, while stearic acid, oleic acid, scyllo-inositol, glutamine, threonine, and glycine were down-regulated. These differences may be related to metabolite release by somatic cells, inflammation status, altered permeability of the udder tight junctions, and changes in milk osmotic equilibrium. Moreover, high SCC milk samples showed higher levels of proteins, casein and fat, lower concentrations of lactose and urea, and a different fatty acid profile from that of low SCC milk.     

Available lysine,protein digestibility and lactulose in commercial infant formulas

Available lysine, in vitro protein digestibility and lactulose values were determined in 23 commercial infant formulas. The mean available lysine content of the formulas based on dairy proteins was 66.7±9.5 mg g⁻¹ protein, similar to that of human milk, while that of soy based formulas was considerably lower (45.0±8.3 mg g⁻¹ protein). In vitro protein digestibility values ranged 85.5–88.9% for soy-based formulas and 90.5–98.3% for formulas based on dairy proteins. Formulas based on milk enriched with whey had higher lactulose content than those based on cow's milk. However, all values were below the limit of 600 mg L⁻¹ recommended for UHT milk.     

Non-invasive monitoring of curd syneresis upon renneting of raw and heat-treated cow's and goat's milk

Molecular mobility of water during curd syneresis was investigated in raw and heat-treated cow's and goat's whole milk by Time-Domain ¹H Nuclear Magnetic Resonance (TD-NMR). Rennet was added to raw and heat-treated (72 °C) milk inside the NMR magnet at 40 °C, and curd evolution was monitored non-invasively over time. Distributions of ¹H NMR spin–spin relaxation time constants (T₂) were obtained at time zero (just after rennet addition), after 30 min (complete curd coagulation) and during serum expulsion (syneresis), every 10 min up to 70 min. Relaxation times and abundances of detected ¹H populations were calculated at each time point. Although further statistical validation would require a larger sample number, raw and heat-treated milk and the corresponding curd samples showed different NMR behaviour. It can be concluded that TD-NMR is able to identify differences between the molecular dynamics characterising raw milk and curd, and their heat-treated counterparts.     

Analysis of Raw Milk Quality at Reception and During Cold Storage: Combined Effects of Somatic Cell Counts and Psychrotrophic Bacteria on Lipolysis

The objective of the article was to analyze the influence of psychrotrophic bacteria counts (PBCs) and somatic cell counts (SCCs) on the extent of lipolysis in bulk samples of cow's milk at reception and during cold storage. Samples of milk were analyzed on the day of sampling and subsequently during cold storage. The acidity, fat, density, chloride content, electrical conductivity (EC), bulk milk SCCs (BMSCC), and PBC values were analyzed on the day of sampling and the levels of acidity, EC, SCC, and PBC were analyzed during cold storage at 4 °C for 72 h. The SCC value 869 × 10³ mL^?1 was higher than the recommended threshold. Lipolysis level at sampling day was related more closely with SCC than with PBC. There was no significant correlation between milk acidity and PBC among others parameters, while the milk mean density was only significant (P < 0.01) correlated with the fat content. The EC and chloride content were consistently correlated (P < 0.001) with BMSCC that allowed them to be used as indicators of mammary gland infection. The milk acidity, EC, PBC, and lipolysis levels increased in relation to the storage time at 4 °C. The lipolysis level during storage was in closer relation to the SCC, but not relation to the PBC. Effects of SCC and PBC on lipolysis decreased throughout the chilling period. It was concluded that initial lipolysis level and intrinsic milk lipoprotein lipase appear more effective than SCC and PBC on the development of lipolysis during storage.     

The free and total myo-inositol contents of early lactation and seasonal bovine milk

A high performance anion-exchange chromatographic method employing pulsed amperometric detection was applied to the determination of endogenous free and total myo-inositol in bovine milk, for which there is limited information. The contents and trend variability of myo-inositol in milk from extensively pasture-fed cows during early lactation and across a production season were therefore evaluated. Free and total myo-inositol in seasonal milk were within the ranges of 2.3–4.5 mg 100 g⁻¹ and 5.3–8.7 mg 100 g⁻¹, respectively. This novel information will both improve understanding of the expression of innate myo-inositol in bovine milk, and provide manufacturers with information that can enhance formulation capability related to the production of cow's milk-based products     

The effects of ratio of cow's milk to soymilk,probiotic strain and fruit concentrate on qualitative aspects of probiotic flavoured fermented drinks

The effects of proportion of cow's milk to soymilk (100:0, 75:25, 50:50, 25:75, 0:100), probiotic bacteria (Lactobacillus acidophilus LA‐5 or Lactobacillus casei L‐01) and natural fruit concentrates (strawberry, apricot, peach and pear) on quality characteristics of soy‐based probiotic drink were investigated. The parameters were analysed at the end of fermentation and during 21 days of storage at 5 ^°C. The highest viability was observed when the equal proportion of cow's milk and soymilk and L. casei was used (50:50‐CY). During chilled storage, the flavouring apricot had the highest stimulatory effect on the survival of L. casei in 50:50 treatment. In general, the treatment 50:50‐CY was realised as the best one overall.     

Dynamic changes in the volatiles and sensory properties of chilled milk during exposure to light

Exposure of milk to light causes photo-oxidation and off-flavour generation. To characterise these reactions, semi-skimmed (1.5% fat) and whole (3.8% fat) extended shelf-life cows' milk were exposed to light for 20–48 h at 4 °C and volatiles in the milk headspace were measured on-line using proton-transfer-reaction mass spectrometry (PTR-MS). The flavour of the whole-milk was assessed by aroma profile analysis on both orthonasal/retronasal odour and taste after 0, 0.25, 1, 6 and 24 h light-exposure. Sensory changes perceived in milk exposed to light for up to 6 h varied in intensity and between replicates, most notably a transient sensory defect being detectable after 0.25 h exposure, but these changes did not correspond to any volatile organic compound (VOC) generation detected by PTR-MS. After 24 h, several compounds showed enhanced release profiles. Principal components analysis related these VOCs to changes in the sensory properties of the milk, described as oxidised/rancid/hay-like.     

HPLC of proteose peptones for evaluating ageing of packaged pasteurized milk

The proteolysis of casein (CN) occurring in packaged pasteurized milk (PM) during refrigerated storage was studied with relation to hygienic and microbiological characteristics of starting raw milk. Six batches of raw milk having standard plate count (SPC) from 1.5×10⁴ to 2.5×10⁵ cfu mL⁻¹ and somatic cell count (SCC) from 1.6×10⁵ to 4.4×10⁵ units mL⁻¹ were pasteurized (73 °C for 15 s), packaged and stored at 4 °C for 12 days. Capillary zone electrophoresis of CN showed breakdown of β-CN in all PM samples during storage. An HPLC method for monitoring proteose peptones (PP) formation was developed. Level of PP in PM samples increased, with keeping time from 667–789 to 947–1383 mg L⁻¹ and PP formation was significantly (P<0.05) related to SCC of starting raw milk. Electrospray ionization–mass spectrometry showed that PP were mainly represented by PP-5 from either A¹ or A² variants of β-CN. Five commercial samples of PM were analysed for PP formation during 14-day storage at 4 °C. Commercial samples prepared by microfiltration process or bactofugation combined with pasteurization showed the slowest formation of PP. The effect of storage temperature on PP formation was evaluated by keeping a conventional PM sample at either 8 or 12 °C for 12 days. Proteolysis of all major CNs upon action of plasmin and bacterial proteinases was observed under these conditions. PP level thus proves to be a reliable analytical index for evaluating the ageing of packaged PM during refrigerated storage.     

GC-MS metabolomics comparison of yoghurts from sheep's and goats' milk

In this study, the polar metabolite profile of commercial yoghurt samples produced in Sardinia (Italy) from milk of local sheep and goats was studied by GC-MS and multivariate statistical data analysis (MVA). Milks underwent the same manufacturing procedures and yoghurts were analysed one day post-manufacture. Results of discriminant analysis indicated that the two yoghurt types had very different metabolite profiles, with different levels of health promoting compounds. Goats' milk yoghurt was richer in free amino acids, γ-aminobutyric acid, pyroglutamic acid and β-phenyllactic acid when compared with yoghurt produced with sheep's milk. Sheep's milk yoghurt was characterised by higher levels of myo-inositol, N-acetylgalactosamine and N-acetylglucosamine. Comparing yoghurt metabolites with those of the original milk, it was found that goats' milk underwent stronger metabolite changes after inoculum. The comparison between the two yoghurt types gave us a deeper insight on the effects of manufacture on different milks.     

Composition and occurrence of aflatoxin M1 in cow's milk samples from Razavi Khorasan Province,Iran

The composition and occurrence of aflatoxin M₁ (AFM₁) were investigated in 60 samples of cow's raw milk samples from Razavi Khorasan Province of Iran. Only percentages of milk samples protein, lactose and total solids in samples collected during summer were slightly lower than the Iranian reference values. Compared with summer samples, higher percentages of milk samples components were observed in the winter. The overall mean AFM₁ level was 61 ± 8 ng/L, with 24 samples (40%) showing concentrations above the maximum permitted level established in Iran (50 ng/L). Control measures are urgently needed to avoid aflatoxin in milk samples produced in Razavi Khorasan Province.     

Effect of Soymilk Substitution on the Rheological and Sensory Properties of Salep (Traditional Turkish Milk Beverage)

Soymilk mixed at a proportion of 0%, 25%, 50%, and 75% (g/100 g total milk) with cow's milk to make a salep, a beverage prepared from the dried tubers of Orchis mascula. The values of the flow behaviour index, n, of salep samples decreased as the soymilk content in the beverage increased. All salep beverages exhibited a pseudoplastic behaviour. Among the samples, salep beverage containing 25% soymilk was scored the highest in terms of overall acceptance by sensory panellists. Statistically significant (p < 0.05) differences were determined for colour, odour, taste, mouthfeel, and overall acceptance as the concentration of soymilk increased in salep beverage. This study produced a beverage from cow's milk and soymilk to offer a promising nutritious and healthy alternative to the consumers with a reasonable acceptance. The rheological parameters of the cow's milk-soymilk salep blends obtained in this study may have useful implications for design and processing.