Indigenous enzymatic activities in ovine and caprine milks

The Effect of Alpha s1 Genotype on Some Physiological and Chemical Milk Characteristics in Garganica Goat

In the present study individual milk samples were collected from 80 Garganica goats and the population was genotyped for CSN1S1. Seven different alleles were observed with the A allele found as predominant, followed by the F and B allele, and 14 different genotypes were observed. A proteomic approach was used to classify the individual milk on the basis of protein abundance: four levels of αs1-casein (CN) expression were identified as high (HAS-1), intermediate (IAS-1), low (LAS-1), and null (NAS-1). The present paper aimed to investigate the influence of the level of expression of αs1-casein fraction in milk on proteolytic activities, chemical composition, and renneting properties of individual Garganica goat milk. Results from the present study evidenced that the level of expression of αs1-casein fraction in Garganica goat milk affected chemical composition, curd firmness, and indigenous proteolytic enzymes. In particular, fat, protein, and casein content were higher in HAS-1 and IAS-1 compared to LAS-1 and NAS-1. The SCC decreased passing from the HAS-1 to the NAS-1 and the curd firmness displayed the highest value in HAS-1. The activity of plasmin (PL) was higher in HAS-1 and IAS-1 groups compared to the LAS-1 and NAS-1; whereas, PL plasminogen-derived (PG) activity was the highest in NAS-1 group. On the contrary, the activity of elastase was the highest in LAS-1, intermediate in the IAS-1 group, and the lowest in HAS-1 and NAS-1 groups. Present data demonstrated that the level of synthesis of αs1-CN reflects the efficiency of the mammary gland in the activation of the cellular mechanisms and influences the proteolytic activity in milk, especially the PL-PG system.

Changes in Native Whey Protein Content, Gel Formation, and Endogenous Enzyme Activities Induced by Flow-Through Heat Treatments of Goat and Sheep Milk

The aim of the present study was to assess the effects of different flow-through heat treatments—68, 73, 78, 85, 100 °C for 16 s—applied to in-line homogenized goat and sheep milk. Alkaline phosphatase (ALP) activity in raw goat milk was 324.5 ± 47.3 μg phenol/mL, and that of lactoperoxidase (LPO) was 199.3 ± 6.7 U/L. The respective activities in raw sheep milk were 7615 ± 141 μg phenol/mL and 319 ± 38.6 U/L. LPO activity was not detected in both milk kinds treated at 85 °C for 16 s. Residual enzyme activities at 73 °C for 16 s with respect to the initial levels in raw milk were higher in goat than in sheep milk. The whey protein fraction of sheep milk was more heat sensitive compared to goat counterpart. Sheep milk rennet clotting time (RCT) was not affected by the treatments, while curd firmness decreased significantly (p < 0.05) at 100 °C for 16 s. Treatments more intense than 73 °C for 16 s increased the RCT of goat milk significantly but inconsistently and decreased curd firmness significantly, while yoghurt-type gels made from 73 °C or 78 °C for 16 s treated goat milk exhibited the highest water-holding capacity.

Molecular mobility changes after high-temperature, short-time pasteurization: An extended time-domain nuclear magnetic resonance screening of ewe milk

This study presents an extensive investigation on the effect of pasteurization on raw whole ewe milk. Milk samples have been analyzed, throughout lactation (from February to July), by time-domain nuclear magnetic resonance (TD-NMR), collecting the characteristic TD-NMR relaxation parameters, proton longitudinal and transverse relaxation times (¹H T₁ and T₂). Collected data aim at integrating previous NMR works, mainly focusing on dairy model systems (casein and whey proteins solutions and gels, reconstituted skim milk) and cheese, with specific reference to the effect of heat treatments. Whole ewe milk, from a single flock (Sarda sheep breed), was daily analyzed both as untreated (raw) and heat treated with a laboratory-scaled high-temperature, short-time treatment (72°C for 15 and 20 s). Moreover, molecular dynamics in milk were investigated by TD-NMR in different periods of lactation for the first time. As a consequence of high-temperature short-time treatment, ¹H T₁ and T₂ consistently shifted to lower values with respect to raw counterparts. Statistical analysis indicated a significant decrease of T₂ in treated samples, to an extent dependent on the heat treatment duration. A subset of dedicated experiments demonstrated that the observed T₂ shift is largely ascribable to protein molecular rearrangements and, to a lesser extent, to the interaction of fat globules with proteins or other nonfat components (or both). In light of the crucial importance of detecting the application of a heat treatment to milk, the results reported here suggest TD-NMR relaxation parameters were able to describe heat-induced changes in molecular dynamics and interactions of milk components in a water-rich environment. The use of TD-NMR can be considered a potential suitable technique for quality control and assurance practices in the dairy industry. Upon statistical validation of methods, the application of TD-NMR in the dairy industry would take advantage of its low cost, reliability, and robustness.

Microfiltration of Ovine and Bovine Milk: Effect on Microbial Counts and Biochemical Characteristics

The aim of this research work was to assess the effect of the microfiltration (ceramic membranes 1.4 μm, 50 °C) of partially defatted ovine milk (fat 0.4%) and bovine milk (fat 0.3%) characteristics. Feed milks, permeates and retentates were analyzed for microbial counts, gross composition, protein fractions, the indigenous enzymes cathepsin D and alkaline phosphatase and the behavior during renneting. It was showed that the microbial quality of both ovine and bovine permeate was improved by reduction of the total mesophilic microflora about 4 Log and 2 Log, respectively. The protein contents and the total solids contents of both permeates were significantly (p < 0.05) reduced. A further analysis of protein fractions by Reversed Phase -High Performance Liquid Chromatography (RP-HPLC) revealed lower αs1- and β-casein and higher κ-casein contents in permeates. The activity of alkaline phosphatase followed the allocation of the fat content, while activity of cathepsin D in permeates was not influenced, although somatic cells counts were removed. Regarding cheesemaking properties, the firmness of ovine curd made from the feed milk did not differ significantly from that made from the permeate. The obtained results suggested that microfiltration could be used for pre-treating of ovine milk prior to cheesemaking.

New insights into xanthine oxidase behavior upon heating using spectroscopy and in silico approach

Thermal dependent conformational changes of xanthine oxidase (XOD) were studied using sensitive and non-destructive methods like fluorescence spectroscopy and molecular modeling in the temperature range of 25-85°C. Intrinsic fluorescence studies showed that the microenvironment of tryptophan and tyrosine residues becomes more exposed to solvent as the temperature increased up to 85°C, whereas in case of flavin cofactor is rather conserved. At higher temperatures, the flavin adenine dinucleotide is displaced from the core of the protein, but is not fully released as shown by the Stern Volmer quenching constant and accessible fraction of the cofactor. Anyway, no significant changes in the structure of XOD monomer were identified after running molecular dynamics simulations at temperatures 25°C, 65°C and 85°C. Therefore, we can conclude that the most important changes in the protein structure at thermal treatment mainly consist on molecular aggregation and dissociation events.

Activities of indigenous proteolytic enzymes in caprine milk of different somatic cell counts

Individual caprine milk with different somatic cell counts (SCC) were studied with the aim of investigating the percentage distribution of leukocyte cell types and the activities of indigenous proteolytic enzymes; proteolysis of casein was also studied in relation to cell type following recovery from milk. The experiment was conducted on 5 intensively managed dairy flocks of Garganica goats; on the basis of SCC, the experimental groups were denoted low (L-SCC; <700,000 cells/mL), medium (M-SCC; from 701,000 to 1,500,000 cells/mL), and high (H-SCC; >1,501,000 cells/mL) SCC. Leukocyte distribution differed between groups; polymorphonuclear neutrophilic leukocytes were higher in M-SCC and H-SCC milk samples, the percentage macrophages was the highest in H-SCC, and levels of nonviable cells significantly decreased with increasing SCC. Activities of all the main proteolytic enzymes were affected by SCC; plasmin activity was the highest in H-SCC milk and the lowest in L-SCC, and elastase and cathepsin D activities were the highest in M-SCC. Somatic cell count influenced casein hydrolysis patterns, with less intact α- and β-casein in H-SCC milk. Higher levels of low electrophoretic mobility peptides were detected in sodium caseinate incubated with leukocytes isolated from L-SCC milk, independent of cell type, whereas among cells recovered from M-SCC milk, macrophages yielded the highest levels of low electrophoretic mobility peptides from sodium caseinate. The level of high electrophoretic mobility peptides was higher in sodium caseinate incubated with polymorphonuclear neutrophilic leukocytes and macrophages isolated from M-SCC, whereas the same fraction of peptides was always the highest, independent of leukocyte type, for cells recovered from H-SCC milk. In caprine milk, a level of 700,000 cells/mL represented the threshold for changes in leukocyte distribution, which is presumably related to the immune status of the mammary gland. Differences in the profile of indigenous lysosomal proteolytic enzymes in caprine milk may influence the integrity of casein based on proteolysis patterns of sodium caseinate incubated with isolated and lysed leukocyte types.

Bioactive amines in Mozzarella cheese from milk with varying somatic cell counts

The influence of somatic cells counts (SCC) in milk on bioactive amines in Mozzarella cheese was investigated. High SCC milk had lower lactose and higher pH compared to low and medium SCC. Low spermine levels were found in milk irrespective of SCC. The cheeses had similar characteristics, but the extension and depth of proteolysis increased with SCC. Cheese from all SCC categories contained spermine; whereas tyramine and tryptamine were only detected in cheese from high SCC milk. During 60-days refrigerated storage, significant positive effects were observed between SCC and proteolysis, storage time and pH and storage time and proteolysis. There was a significant positive effect of storage time on spermine and serotonin levels. Only cheese from high SCC milk showed significantly higher serotonin levels. Tyramine and tryptamine were found in cheese from high SCC milk.

Role of somatic cells on dairy processes and products: a review

Somatic cells are an important component naturally present in milk, and somatic cell count is used as an indicator of udder health and milk quality. The role of somatic cells in dairy processes and products is ill-defined in most studies because the role of these cells combines also the concomitance of physicochemical modifications of milk, bacterial count, and the udder inflammation in the presence of high somatic cell count. The aim of this review is to focus on the role of somatic cells themselves and of endogenous enzymes from somatic cells in milk, in dairy transformation processes, and in characteristics of final products overcoming biases due to other factors. The immune function of somatic cells in the udder defense and their protective role in milk will be primarily considered. Different characteristics of milk induced by various somatic cell counts, types, and their endogenous enzymes influencing directly the technological properties of milk and the final quality of dairy products will be discussed as well. By comparing methods used in other studies and eliminating biases due to other factors not considered in these studies, a new approach has been suggested to evaluate the effective role of somatic cells on dairy processes and products. In addition, this new approach allows the characterization of somatic cells and their endogenous enzymes and, in future research, will allow the clarification of mechanisms involved in the release of these components from somatic cells during dairy processes, particularly in cheese technologies.

Composition, indigenous proteolytic enzymes and coagulating behaviour of ewe milk as affected by somatic cell count

This study was undertaken to assess the effect of somatic cell count in ewe milk on i) composition and hygienic traits; ii) plasmin, cathepsin and elastase activities; iii) leukocyte differential count; iv) renneting parameters. Individual ewe milk samples were grouped according to somatic cell count (SCC) into five classes: SC300 (<300 000 cells/ml), SC500 (from 301 000 to 500 000 cells/ml), SC1000 (from 501 000 to 1 000 000 cells/ml), SC2000 (from 1 001 000 to 2 000 000 cells/ml) and SC>2000 (>2 001 000 cells/ml). Individual milk samples were analysed for pH, chemical composition, microbial features, indigenous proteolytic enzymes, differential leukocyte population, and renneting parameters. Milk yield, lactose, protein, non casein nitrogen, microbial features were affected by SCC level. Plasmin and elastase activities were the highest in samples with more than 1 000 000 cells/ml; plasmin had intermediate values in samples with 300 000 to 1 000 000 cells/ml and the lowest in samples with less than 300 000 cells/ml of milk. Cathepsin D showed significantly lower values in SC300 and SC1000 classes than in SC500, SC2000 and SC>2000 classes. The highest percentages of lymphocyte were found in samples with less than 1 000 000 cells/ml, while the highest levels of polymorphonuclear leukocyte were found in samples with more than 1 000 000 cells/ml of milk. Longer clotting time was found in SC>2000 samples, while reduced clot firmness was observed in SC500 and SC>2000 samples. Results on milk yield and on compositional parameters evidenced an impairment of udder efficiency in ewe milk samples starting from 300 000 cells/ml. Plasmin activity in milk can be considered as a marker of the synthetic and secreting ability of the mammary gland; furthermore plasmin and elastase were consistent with the health status of the udder. Finally cathepsin D played a role in the worsening of renneting properties of ewe milk.