International Dairy Journal最新文献

This study investigated the bioactivity of bovine and ovine proteose-peptone (PPT) fractions, specifically the proteose-peptone component 3 (PP3) and its enzymatic hydrolysate. The antioxidant capacity of the above fractions and their activity against Cronobacter sakazakii and rotavirus were evaluated. Results revealed strong interspecies differences on their bioactivity. Thus, antioxidant activity of bovine PPT decreased with the fractionation but increased for ovine PPT, the latter being more active in all cases. Moreover, the antibacterial activity of hydrolyzed bovine PP3 showed high concentration-dependence reaching a maximum of 6.82 logarithmic cycle reduction at 4 mg mL⁻¹, for 24 h of incubation. Conversely, neither intact nor hydrolyzed ovine PP3 were able to reduce the bacterial growth. Finally, both bovine and ovine PP3 neutralized rotavirus in a dose-response way, the former being more effective. Interestingly, the antiviral activity of bovine PP3 increased after hydrolysis, whereas the ovine counterpart lost almost all of its antirotaviral capacity.

Calcium ion binding to native and heat denatured β-lactoglobulin A, B and C genetic variants at pH 7.0 and 0.08 m NaCl was investigated. Native β-lactoglobulin bound calcium ions and the binding increased after denaturation. Small variations in calcium ion binding were observed for the three genetic variants. Analysis of the binding by the Scatchard model suggested about 10 binding sites in the unheated β-lactoglobulin and this decreased to about 5 in the heated samples. The association constants were low in the unheated samples and increased in the heated samples. Analysis of the binding by the Langmuir adsorption model indicated the maximum binding was about 10–13 calcium ions per β-lactoglobulin monomer in the unheated samples and this was about half in the heated samples, possibly due to aggregation making binding sites less available. The affinity constants were low for the unheated samples and increased substantially for the heated samples.

Stabilizer combination with varying concentrations of kappa-carrageenan (KCG) was employed to reduce hardness, control overrun and improve the overall sensory attributes. A stabilizer combination of guar gum and locus bean gum was used with varying levels of kappa-carrageenan to maintain the total stabilizer concentration in the ice cream mix at 0.15% (w/w). Ice creams having 4% (w/w) and 10% w/w protein prepared with commercial stabilizer and emulsifier blend were served as positive and negative controls, respectively. All the ice cream mix samples showed pseudoplastic behaviour. Increasing the KCG level (0–0.12% w/w) in ice cream mix resulted in decreased flow behaviour index (0.80–0.43) and increased consistency coefficient (0.23–4.21 Pa.sⁿ). Instrumental hardness values decreased and overrun increased significantly (p < 0.05) with KCG addition. Samples containing lower levels of KCG (0.03% w/w) had higher melting rates. All ice cream mix samples have shown bi-modal droplet distributions. Sensorial attributes were also altered with variation in the KCG level. The sample containing 0.12% (w/w) KCG was most preferred by the sensory panellists.

The milk clotting activity (MCA) analysis of coagulants used in the production of cheese is an important parameter used in the modern dairy industry. The MCA is calculated using the estimated milk-clotting time (MCT). The standard method used for estimation of MCT is presented in the ISO 23058/IDF 199 Standard using the Berridge's operator-based approach. In this paper a new method is presented to estimate the MCT using digital image acquisition and signal processing. The estimate is obtained by processing a sequence of images of the wall of a round bottom flask containing milk and the coagulant. Digital signal processing and filter techniques were used to remove interferences and artifacts and improve the clotting time estimation. A set of 28 samples of milk plus coagulant were processed. The method's accuracy is about 1/30 s and the average relative error, when compared to an experienced human operator, was με = 2.82%, according to the experimental results, with an associated standard deviation of σε = 3.07% and a median of mε = 1.92%. The method may be used to replace the human operator during the MCT estimation procedure.

This study aimed to assess the effects of ripening at refrigeration and ambient temperatures on physic-chemical and microbiological parameters of artisanal Minas cheeses (made from raw milk) and to model the kinetics of lactic acid bacteria – $LAB$, Escherichia coli – $Ec$, and coagulase-positive staphylococci – $Sa$ along the ripening. Cheese pH, acidity, and moisture, fat, and protein contents were quantified, as well as $LAB$, $Ec$, and $Sa$ concentrations. Richards and simplified Lotka-Volterra models were used to describe the microbial kinetic data. The fits were assessed by statistical indices, and the Monte-Carlo method was applied to identifiability analysis. Cheese moisture was reduced along the ripening, increasing protein concentration and acidity values. Cheese pH showed a reduction followed by an increase. $LAB$ concentration increased to the stationary phase after a few days; $Ec$ and $Sa$ concentrations increased and then decreased due to interactions with $LAB$ and low moisture content. Mathematical models successfully described the kinetics of $LAB$, $Ec$, and $Sa$ in cheese throughout ripening. Most parameters were not correlated to each other and were estimated with narrow confidence intervals.

Our previous study suggested that bound phenolic acids of rice bran were converted into free phenolic acids during fermentation and these free phenolic acids improved the yogurt stability. Thus, this work investigated the effect of adding ferulic acid, the major phenolic acid of rice bran, on the yogurt stability. It was observed that the syneresis of yogurt was reduced by adding 100 μg/mL ferulic acid before fermentation, which suggested that ferulic acid increased the yogurt stability. Accordingly, adding ferulic acid made the yogurt gel more compact. However, 100 μg/mL ferulic acid had no significant impact on the pH, viscosity, and viscoelasticity of yogurt. Thus, the interaction between ferulic acid and milk protein was investigated. It was observed that ferulic acid interacted with milk protein through the hydrogen bond and van der Waals force. Therefore, it was speculated that ferulic acid interacted with milk protein molecules and induced the more compact structure of yogurt, thus improving the yogurt stability. However, adding ferulic acid after fermentation had no significant impact on the yogurt stability, because the gelation of milk protein caused by fermentation hindered the interaction between ferulic acid and milk protein.

Listeria monocytogenes is a serious pathogen with several serogroups that differ in virulence and distribution among countries. This study determined the serogroups and virulence of 116 L. monocytogenes from sheep milk (n = 52) and goat milk (n = 64) in Jordan by several multiplex PCR. The results showed that the L. monocytogenes isolates belong to five serogroups. Most isolates (37.9%) belonged to serogroup 4b (d, e), followed by serogroup 1/2a (3a) (31.9%), serogroup 1/2b (26.7%), and serogroup 4a/c (2.6%) and serogroup IV (serotypes 1/2c and 3c) (0.9%). All isolates carried the internalin (inlA, inlC, inlJ) and lmo 2672 genes. Additionally, 36.4% and 29.0 % of 4b and 1/2b isolates carried the Listeriolysin S gene (llsX). Therefore, L. monocytogenes in sheep and goat milk are potential public health hazards because they belong to the major listeriosis-causing serogroups (4b, 1/2a, and 1/2b), and carry major virulence genes. Small ruminants’ milk and cheeses should be considered high-risk foods for L. monocytogenes infection. Thus, safe production practices should be monitored and enforced in small dairy shops.

Enzymatic dephosphorylation of casein removes phosphate groups from serine residues and reduces the negative charge. In contrast, succinylation caps the ε-amino group of lysine residues and increases the negative charge on the caseins. The effect of these modifications on the self-association of α_s1-casein was studied using analytical ultracentrifugation. Dephosphorylation and succinylation have contrasting effects on α_s1-casein self-assembly. Native α_s1-casein was a mixture of dimers, trimers and higher order oligomers under these experimental conditions. Increasing the level of succinylation dissociated oligomeric α_s1-casein resulting in an increase in the monomeric protein. In contrast, dephosphorylated samples formed larger assemblies compared to the native α_s1-casein. Experiments performed at protein concentrations of 1, 2 or 3 mg mL⁻¹ provided consistent results indicating that across this concentration range there is no major difference in the assembly formation. This study demonstrated the utility of analytical ultracentrifugation to understand casein assembly, which will underpin the understanding of proteins structures in dairy foods.

Colostrum, the first food given to mammals after birth, plays a critical role in newborn nutrition. It is characterized by its high nutrient content, presence of immunoglobulins, and functional compounds. This study collected and freeze-dried colostrum from four different animals (Karayaka sheep, Saanen goats, Danish red cows and buffalo). Chemical and functional properties (total phenolic content and antioxidant capacity), mineral, as well as mineral content, amino acid composition, and fatty acid profile of the dried samples, were determined. Nutritional properties (protein efficiency ratio (PER), biological value (BV) and net protein utilization (NPU)) of powdered colostrum were also determined. It was found that buffalo colostrum had higher fat and protein content, while goat colostrum had high antioxidant activity. Buffalo and goat colostrums had a biological value (BV) of 94.96–97.78. Major minerals were more abundant in cow colostrum and minor minerals were more abundant in sheep colostrum. In terms of essential fatty acids, sheep and goat colostrums stood out. In conclusion, this comprehensive analysis of the composition of colostrum from different species sheds light on the different nutrient profiles and potential health benefits and provides a theoretical basis for the development of commercial products from goat, sheep, cow and buffalo colostrum.

This study is the first to screen of lactic acid bacteria strains with antimicrobial effect against spore outgrowth of Bacillus sporothermodurans and characterize their technological properties. Eighty strains were isolated from Tunisia raw milk but only 8 isolates were selected based on their antagonistic activity against germinated spores of B. sporothermodurans and nine pathogenic bacteria. Phenotypic and genotypic characterization allowed us to distinguish three different species, namely Lactiplantibacillus plantarum, Levilactobacillus brevis and Lactococcus lactis. The lactic acid strains able to produce protease and lipase enzymes. The important antagonistic activity was observed in presence of L. lactis TLAB6 strain which produced a bacteriocin and lactic acid. The bacteriocin produced by the L. lactis TLAB6 is heat stable and resistant to trypsin. The results suggest that the selected LAB with antibacterial activity against germinated spore and technological properties may be used to preserve the food and formulate of bioactive functional foods.