Effects of gelation temperature on the mozzarella-type curd made from buffalo and cows’ milk: 2. curd yield, overall quality & casein fractions

Buffalo curd gave higher amount of yield than cows’ curd at similar processing conditions. Curd moisture was decreased with the increase of gelation temperatures in both types of milk. Curd cutting time of 45 minutes was found optimum for Mozzarella cheese making from both milk samples. Centrifugation method is simpler, quicker and more reproducible than Buchner funnel method. Buffalo milk contains higher amounts of αs1- , β- and к-casein as compared to cows’ milk.

Effects of gelation temperature on the Mozzarella-type curd made from buffalo and cows’ milk. 1: Rheology & microstructure

The rheology and microstructure of Mozzarella-type curds made from buffalo and cows’ milk were measured at gelation temperatures of 28, 34 and 39 °C after chymosin addition. The maximum curd strength (G′) was obtained at a gelation temperature of 34 °C in both types of bovine milk. The viscoelasticity (tan δ) of both curds was increased with increasing gelation temperature. The rennet coagulation time was reduced with increase of gelation temperature in both types of milk. Frequency sweep data (0.1–10Hz was recorded 90 min after chymosin addition, and both milk samples showed characteristics of weak viscoelastic gel systems. When both milk samples were subjected to shear stress to break the curd system at constant shear rate, 95 min after chymosin addition, the maximum yield stress was obtained at the gelation temperatures of 34 °C and 28 °C in buffalo and cows’ curd respectively. The cryo-SEM and CLSM techniques were used to observe the microstructure of Mozzarella-type curd. The porosity was measured using image J software. The cryo-SEM and CLSM micrographs showed that minimum porosity was observed at the gelation temperature of 34 °C in both types of milk. Buffalo curd showed minimum porosity at similar gelation temperature when compared to cows’ curd. This may be due to higher protein concentration in buffalo milk.

Mozzarella-type curd made from buffalo, cows’ and ultrafiltered cows’ milk. 1. Rheology and microstructure

Rennet-induced curd was made from both natural buffalo and cows’ milk, and ultrafiltered cows’ milk (cows’ milk was concentrated such that it had a chemical composition approximately equivalent to that of the buffalo milk). These milk samples were compared on the basis of their rheology, physicochemical characteristics and curd microstructure. The ionic and soluble calcium contents were found to be similar in all milk samples studied. The total and casein bound calcium were higher in concentrated cows’ milk than in standard cows’ milk. Both cows’ milk types were found to have lower total and casein bound calcium than the buffalo milk. This is probably due to concentration of the colloidal part of milk (casein), during the ultrafiltration (UF) process. The rennet coagulation time was similar in UF cows’ and buffalo milk while both were shorter when compared with that of the cows’ milk. The dynamic moduli (G′, G″) values were higher in both the buffalo and UF cows’ milk than in the cows’ milk after 90 min coagulation. The loss tangent, however, was found to be similar in both the UF cows’ and buffalo milk curds and was lower than that observed for the cows’ milk (0.42, 0.42 and 0.48, respectively). The frequency profile of each type of curd was recorded 90 min after the enzyme addition (0.1–10 Hz); all samples were found to be “weak” viscoelastic, frequency dependent gels. The yield stress was also measured 95 min after the enzyme addition, and a higher value was observed in buffalo milk curd when compared with other curd samples made from both the natural cows’ milk and the UF cows’ milk. The cryo-scanning electron and confocal laser scanning micrographs showed that curd structure appeared to be more “dense” and less porous in buffalo milk than cows’ milk even after concentration to equivalent levels of protein/total solids to those found in the buffalo milk.

Mozzarella-type curd made from buffalo, cows’ and ultrafiltered cows’ milk. 2. Physicochemical properties, curd yield and quality, casein fractions & micelles size

Buffalo milk contains (40–60 %) more protein, fat and calcium than cows’ milk. These constituents were enhanced by ultrafiltration (UF) of cows’ milk to give a product with similar levels to those found in the buffalo milk. Mozzarella-type curd was made from buffalo, cows’ and UF cows’ milk to compare the overall curd yield and quality. The curd yield on both dry and wet weight basis, curd moisture content and overall curd fat retention were found to be higher in the UF cows’ milk than for either the buffalo or the cows’ milk preparations. The minimum whey fat losses occurred in the UF cows’ curd when compared to the cows’ and the buffalo curd. The whey protein losses were found to be higher in the UF cows’ curd than those for the buffalo and the cows’ curds. The total mineral content of the curd was also higher in the UF cows’ milk than that found in either the buffalo or the cows’ milk. SEM micrographs showed that casein micelles sizes were different in the two different types of milk. Casein micelles were also observed to be deformed in the UF cows’ milk samples. UF cows’ milk contained higher amounts of both the αs1- and αs2-casein moieties than either the buffalo or the cows’ milk. Buffalo milk was found to contain a higher concentration of β-casein than either the UF cows’ or untreated cows’ milk samples. Gel strength was found to be higher in the resultant buffalo curd than for curds made from either native cows’ milk or those made from UF cows’ milk. The mineral distribution was also different in the three different types of bovine milk, measured by energy-dispersive X-ray (EDX) analysis. Differences in the curd quality observed between the buffalo and the cows’ milk appear to result from the differences in casein composition and overall micelle structure, rather than casein concentration alone.

Evaluation and comparison of SYBR Green I Real-Time PCR and TaqMan Real-Time PCR methods for quantitative assay of Listeria monocytogenes in nutrient broth and milk

Specific traditional plate count method and real-time PCR systems based on SYBR Green I and TaqMan technologies using a specific primer pair and probe for amplification of iap-gene were used for quantitative assay of Listeria monocytogenes in seven decimal serial dilution series of nutrient broth and milk samples containing 1.58 to 1.58×107 cfu /ml and the real-time PCR methods were compared with the plate count method with respect to accuracy and sensitivity. In this study, the plate count method was performed using surface-plating of 0.1 ml of each sample on Palcam Agar. The lowest detectable level for this method was 1.58×10 cfu/ml for both nutrient broth and milk samples. Using purified DNA as a template for generation of standard curves, as few as four copies of the iap-gene could be detected per reaction with both real-time PCR assays, indicating that they were highly sensitive. When these real-time PCR assays were applied to quantification of L. monocytogenes in decimal serial dilution series of nutrient broth and milk samples, 3.16×10 to 3.16×105 copies per reaction (equals to 1.58×103 to 1.58×107 cfu/ml L. monocytogenes) were detectable. As logarithmic cycles, for Plate Count and both molecular assays, the quantitative results of the detectable steps were similar to the inoculation levels.

Salmon consumption during pregnancy alters fatty acid composition and secretory IgA concentration in human breast milk

Fish oil supplementation during pregnancy alters breast milk composition, but there is little information about the impact of oily fish consumption. We determined whether increased salmon consumption during pregnancy alters breast milk fatty acid composition and immune factors. Women (n = 123) who rarely ate oily fish were randomly assigned to consume their habitual diet or to consume 2 portions of farmed salmon per week from 20 wk of pregnancy until delivery. The salmon provided 3.45 g long-chain (LC) (n-3) PUFA/wk. Breast milk fatty acid composition and immune factors [soluble CD14, transforming growth factor-b (TGFb)1, TGFb2, and secretory IgA] were analyzed at 1, 5, 14, and 28 d postpartum (PP). Breast milk from the salmon group had higher proportions of EPA (80%), docosapentaenoic acid (30%), and DHA (90%) on d 5 PP compared with controls (P < 0.01). The LC (n-6) PUFA:LC (n-3) PUFA ratio was lower for the salmon group on all days of PP sampling (P < 0.004), although individual (n-6) PUFA proportions, including arachidonic acid, did not differ. All breast milk immune factors decreased between d 1 and 28 PP (P < 0.001). Breast milk secretory IgA (sIgA) was lower in the salmon group (d 1–28 PP; P = 0.006). Salmon consumption during pregnancy, at the current recommended intakes, increases the LC (n-3) PUFA concentration of breast milk in early lactation, thus improving the supply of these important fatty acids to the breast-fed neonate. The consequence of the lower breast milk concentration of sIgA in the salmon group is not clear.

Immune factors and fatty acid composition in human milk from river/lake, coastal and inland regions of China

Breast milk fatty acid composition may be affected by maternal diet during gestation and lactation. The influence of dietary and breast milk fatty acids on breast milk immune factors is poorly defined. We determined the fatty acid composition and immune factor concentrations of breast milk from women residing in river & lake, coastal, and inland regions of China, which differ in their consumption of lean fish and oily fish. Breast milk samples were collected on days 3 to 5 (colostrum), 14 and 28 post-partum and analysed for soluble CD14 (sCD14), transforming growth factor (TGF)-β1, TGF-β2, secretory immunoglobulin A (sIgA) and fatty acids. The fatty acid composition of breast milk differed between regions and with time post-partum. The concentrations of all four immune factors in breast milk decreased over time, with sCD14, sIgA and TGF-β1 being highest in colostrum in the river & lake region. Breast milk DHA and arachidonic acid (AA) were positively associated, and γ-linolenic acid and EPA negatively associated, with the concentrations of each of the four immune factors. In conclusion, breast milk fatty acids and immune factors differ between regions in China characterised by different patterns of fish consumption and change during the course of lactation. A higher breast milk DHA and AA concentration is associated with higher concentrations of immune factors in breast milk, suggesting a role for these fatty acids in promoting gastrointestinal and immune maturation of the infant.

Synergistic effects of mixing cocksfoot and sainfoin on in vitro rumen fermentation: role of condensed tannins

Some bioactive secondary metabolites in forage legumes can cause digestive interactions, so that the rumen fermentation pattern of a mixture of forages can differ from the average values of its components. The objective of this study was to investigate the potential role of condensed tannins (CT) on the synergistic effects between one grass species, cocksfoot, and one CT-containing legume species, sainfoin, on in vitro rumen fermentation characteristics. Cocksfoot and sainfoin in different proportions (in g/kg, 1000:0, 750:250, 500:500, 250:750 and 0:1000) were incubated under anaerobic conditions in culture bottles containing buffered rumen fluid from sheep. Incubations were carried out using artificial saliva with and without polyethylene glycol (PEG), which binds and thus inactivates CT. Rumen fermentation parameters describing the degradation and the fate of the energetic and nitrogenous substrates were measured at 3.5 and 24 h. At the early fermentation stage, when the sainfoin level increased from 0 to 1000 g/kg, the ammonia concentration in the medium quadratically decreased from 3.20 to 0.53 mmol/l in absence of PEG (P<0.01) but not in its presence. This result demonstrates that sainfoin CT decreased the rumen degradation of the proteins in the whole mixture, including the proteins in cocksfoot, rather than just the proteins in sainfoin. Interestingly, the total gas and methane productions were lower in mixtures incubated in absence of PEG than in presence of PEG (P<0.001) while no significant PEG effect was observed on digestibility. At the late fermentation stage, a positive quadratic effect on dry matter digestibility was detected without PEG (P<0.05), indicating a synergistic action of cocksfoot plus sainfoin on plant substrate degradation due to CT. The presence of PEG increased gas production (P<0.001) and NH3-N concentration in the medium (P<0.001). Our results suggest that CT could allow a better utilization of plant substrates in mixtures by the rumen ecosystem by improving the partitioning of degraded substrates toward lower gas losses, and decreasing the protein degradation.

Crossbred cow adoption and milk market participation in a multivariate count data framework

Cross-bred cow adoption is an important and potent policy variable precipitating subsistence household entry into emerging milk markets. This paper focuses on the problem of designing policies that encourage and sustain milkmarket expansion among a sample of subsistence households in the Ethiopian highlands. In this context it is desirable to measure households’ ‘proximity’ to market in terms of the level of deficiency of essential inputs. This problem is compounded by four factors. One is the existence of cross-bred cow numbers (count data) as an important, endogenous decision by the household; second is the lack of a multivariate generalization of the Poisson regression model; third is the censored nature of the milk sales data (sales from non-participating households are, essentially, censored at zero); and fourth is an important simultaneity that exists between the decision to adopt a cross-bred cow, the decision about how much milk to produce, the decision about how much milk to consume and the decision to market that milk which is produced but not consumed internally by the household. Routine application of Gibbs sampling and data augmentation overcome these problems in a relatively straightforward manner. We model the count data from two sites close to Addis Ababa in a latent, categorical-variable setting with known bin boundaries. The single-equation model is then extended to a multivariate system that accommodates the covariance between crossbred-cow adoption, milk-output, and milk-sales equations. The latent-variable procedure proves tractable in extension to the multivariate setting and provides important information for policy formation in emerging-market settings

Tobit estiamtion with unknown point of censoring with an application to milk market participation in the Ethiopian highlands

Data augmentation is a powerful technique for estimating models with latent or missing data, but applications in agricultural economics have thus far been few. This paper showcases the technique in an application to data on milk market participation in the Ethiopian highlands. There, a key impediment to economic development is an apparently low rate of market participation. Consequently, economic interest centers on the “locations” of nonparticipants in relation to the market and their “reservation values” across covariates. These quantities are of policy interest because they provide measures of the additional inputs necessary in order for nonparticipants to enter the market. One quantity of primary interest is the minimum amount of surplus milk (the “minimum efficient scale of operations”) that the household must acquire before market participation becomes feasible. We estimate this quantity through routine application of data augmentation and Gibbs sampling applied to a random-censored Tobit regression. Incorporating random censoring affects markedly the marketable-surplus requirements of the household, but only slightly the covariates requirements estimates and, generally, leads to more plausible policy estimates than the estimates obtained from the zero-censored formulation

Proportions of A1, A2, B and C β-casein protein variants in retail milk in the UK

The A1 variant protein of the β-casein family has been implicated in various disease states although much evidence is weak or contradictory. The primary objective was to measure, for the first time, the proportions of the key β-casein variant proteins in UK retail milk over the course of one year. In total, 55 samples of semi-skimmed milk were purchased from five supermarkets over the course of a year and the proportions of the A1, A2, B and C casein variant proteins were measured, using high resolution HPLC-MS. The results showed that β-casein in UK retail milk comprises approximately 0.58, 0.31, 0.07 and 0.03 A2, A1, B and C protein variants, respectively. The proportion of A2 is higher than some early studies would predict although the reasons for this and any implications for health are unclear

Acetone enhances the direct analysis of procyanidin- and prodelphinidin-based condensed tannins in lotus species by the butanol-HCl-iron assay

The butanol-HCl spectrophotometric assay is widely used for quantifying extractable and insoluble condensed tannins (CT, syn. proanthocyanidins) in foods, feeds, and foliage of herbaceous and woody plants, but the method underestimates total CT content when applied directly to plant material. To improve CT quantitation, we tested various cosolvents with butanol-HCl and found that acetone increased anthocyanidin yields from two forage Lotus species having contrasting procyanidin and prodelphinidin compositions. A butanol-HCl-iron assay run with 50% (v/v) acetone gave linear responses with Lotus CT standards and increased estimates of total CT in Lotus herbage and leaves by up to 3.2-fold over the conventional method run without acetone. The use of thiolysis to determine the purity of CT standards further improved quantitation. Gel-state 13C and 1H–13C HSQC NMR spectra of insoluble residues collected after butanol-HCl assays revealed that acetone increased anthocyanidin yields by facilitating complete solubilization of CT from tissue.