International Dairy Journal最新文献

Staphylococcus aureus is recognized for causing contagious mastitis in cattle. Elimination of the organism in affected animals is challenging due to its potential antibiotic resistance mechanisms and virulence factors. The aim of the study was the pheno- and genotypic epidemiological characterization of S. aureus isolated from bulk tank milk samples obtained from three municipalities in the northern region of Antioquia. Twenty-one S. aureus isolates from 150 bulk tank milk samples were characterized by evaluating antimicrobial susceptibility to 17 antibiotics using the VITEK 2, and identifying several genes encoding for virulence factors, enterotoxins, and the agr groups by conventional PCR. The clonal relationship between the isolates was assessed using macrorestriction fragment analysis (MRFA) of chromosomal DNA by pulsed-field gel electrophoresis (PFGE). Most of the isolates showed susceptibility to the tested antibiotics; 19% exhibited resistance to tetracycline and all isolates showed beta-lactamases. Molecular typing revealed that 76% carried the agrI and cap5 genes. Seven isolates harbored genes coding for staphylococcal enterotoxins (SE), with seh being the most identified gene. Furthermore, MRFA demonstrated high heterogeneity among the isolates, resulting in the assignment of 18 different MRFA patterns. These results indicate phenotypic resistance to tetracycline and beta-lactams, the presence of genes encoding for staphylococcal enterotoxins, and high heterogeneity among S. aureus isolates from bulk tank milk.

Milk (MP) and whey (WP) ultrafiltration permeates were obtained from different dairy processing plants. The effects of pH (4 or 6) and heat treatments (63 °C, 30 min; or 110 °C, 6 min) on permeate stability were measured by the increase of turbidity, and precipitation of nitrogen and calcium. The antioxidant activity and the production of volatiles compounds, as affected by heat treatments, was also evaluated. WP showed a higher sensitivity to heat treatments than MP. Increasing heating temperature reduced the stability of permeates, with an intensified effect at pH 6. Calcium precipitation was the main factor responsible for the increase in turbidity. Lowering the pH to 4 prior to heating strongly limited the development of turbidity. Sterilisation improved antioxidant activity of both permeates, with a greater effect on WP. Sterilisation had no effect on the concentration of volatile aldehydes but promoted the formation of volatile sulfur compounds, and more significantly in WP.

The addition of encapsulated bioactive compounds in food matrices allows obtaining foods with improved nutritional characteristics. In this study, chia oil (a source of omega-3) and astaxanthin were encapsulated in beads and added to commercial yogurt. Particles formulated using only sodium alginate (100SA) or mixed with whey protein aggregates (25WPA75SA) with incorporated chia oil and astaxanthin were added to yogurt. The stability of bioactive compounds added was evaluated, and consumer-based sensory analysis was applied using both a hedonic scale and Check-All-That-Apply method. The content of bioactive compounds in yogurts did not change after 28 days of storage. Yogurts exhibited good acceptability and the terms with high positive impact in all samples were sweet, pleasant flavor, smooth, creamy, pleasant particles, pleasant, and easy to swallow. Yogurt added with 25WPA75SA beads showed greater acceptance indicating that this matrix may be a good option to improve the consumption of astaxanthin and omega-3.

The effect of calcium content of fat-free and full-fat cheese curds on soluble proteins and minerals and the rheological and textural properties of processed cheese (PC) prepared from these curds using 60, 120 or 180 mEq kg⁻¹ of disodium phosphate (DSP), trisodium citrate (TSC) and sodium hexametaphosphate (SHMP) was studied. Levels of caseins and Ca in the water soluble extract (WSE) of PC were higher in PC prepared from low-Ca cheese curds. Levels of Ca in the WSE decreased with increasing concentration of DSP for PC from all type of cheese curds. Levels of Ca in the WSE were moderately correlated (R² = 0.58) with the protein content of the WSE of PC. Hardness of PC prepared with low-Ca fat-free and full-fat cheese curds was lower than that of PC prepared from their high-Ca counterparts. The melting tendency of PC followed the order SHMP < DSP < TSC.

Whey, a byproduct of cheese production, is valued for its high-quality proteins. Ultrafiltration concentrates these proteins but faces challenges such as membrane fouling. This study investigates the use of transglutaminase to improve ultrafiltration efficiency by reducing fouling and optimizing protein recovery. Whey was divided into samples of whey in natura (WIN) and whey partially demineralized (WPD). Both were treated with different concentrations of transglutaminase (0, 0.5, 1.5, and 2.5% relative to protein mass) and ultrafiltered using polyethersulfone membranes at 4 bar. Effectiveness was evaluated by permeate flux and protein concentration, as well as physicochemical and structural characterizations such as FTIR, TGA, and molecular weight analysis. Transglutaminase reduced membrane fouling, increasing permeate flux. The 2.5% enzyme concentration was most efficient for WIN, while 1.5% was ideal for WPD. Enzymatic treatment increased protein concentration and thermal stability of the concentrates. FTIR analysis indicated the formation of cross-links between proteins. Molecular weight analysis revealed larger and more stable protein aggregates, improving ultrafiltration performance. This study suggests that transglutaminase is promising for optimizing whey ultrafiltration, improving protein recovery and process efficiency, with potential large-scale application in the food industry.

This study assessed the antimicrobial effectiveness of artisanal lamb and goat rennet compared to industrial calf rennet against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Results showed all three rennets were more effective against E. coli than S. aureus. Only lamb rennet achieved complete inhibition of both bacteria at a minimum inhibitory concentration of 7000 ppm. An extensive peptidomics analysis was conducted to characterize these rennet samples and correlate their antimicrobial activity with the data on endogenous peptides. Moreover, a prediction of the potential antimicrobial activity of the peptides was carried out with specific bioinformatic tools available online, proving that the isolated peptides did have the tested biological activity. Lamb rennet was found to contain 73 antimicrobial peptides with bioactivity scores between 1 and 0.52, including casocidin-I, known for its broad-spectrum antibacterial activity. Further research is ongoing to explore the applications of artisanal rennet in cheese production.

This study investigated the impact of post-fermentation processing and fat content on the quality of stirred high-protein yogurts (6 wt% protein) during 13 weeks of storage. A rotor/stator device was used to apply two post-fermentation treatments (119W and 296W, 290 L^-1h) to yogurts containing 0 or 3 wt % fat, while a control yogurt did not undergo post-fermentation processing. Sensory quality was analyzed by Quantitative descriptive analysis (QDA) and Quality control (QC). QC results showed significant effects of post-fermentation processing on appearance, consistency, and odor/flavor. Post-fermentation processing significantly reduced whey separation, stickiness, thickness, sticky mouthfeel and mealiness, and increased shininess and smooth mouthfeel according to QDA results. Confocal laser scanning microscopy and darkfield microscopy revealed larger protein aggregates in the control samples compared to the post-processed samples. The post-processed yogurts maintained acceptable quality after 13 weeks of storage, contrasting with the control samples that had unacceptable quality throughout the storage period.

This study investigates low-fat camel milk and cow milk fermentation behavior by Lactobacillus helveticus, Lactobacillus delbrueckii subsp. bulgaricus, and Streptococcus thermophilus at 28, 35, and 42 °C. Bacterial counts, titratable acidity (TA%), pH, lactose, lactic acid, and proteolysis were followed for 96 h. Temperature and bacteria highly affected all these parameters (p < 0.001) while milk type affected bacterial counts and degree of proteolysis and lactose (p < 0.001), pH, and lactic acid (p < 0.01) but did not affect TA (%). Fermented camel and cow milk products showed similar negative correlations between TA (%) and pH suggesting comparable buffering capacities. In both fermented products, the behavior of L. helveticus was more comparable to that of S. thermophilus than L. bulgaricus. Principal component analysis (PCA) showed a negative correlation between bacterial growth and the degree of proteolysis. The results of this study provided insights into the complex dynamics of bacterial interactions with different milk substrates.

Biomimetic and bioinspiration have grown as burgeoning research frontier in many fields. But few studies have introduced such ideas into food preservation area. Herein, inspired by the cocoon shell, silk fibroin (SF), Poly (L-lactic acid) (PLLA) and polyvinyl alcohol (PVA) were respectively mixed and prepared into biomimetic nanofibers on the surface of Mongolian cheese via electrospinning technology. The morphology, mechanical property and water vapour permeability of prepared biomimetic nanofibers were characterized. The acquired results revealed that the addition of SF promoted the uniformity coefficient, and flexibility of composite nanofibers. The influence of biomimetic nanofibers coated Mongolian cheese on physicochemical and microbiological properties was evaluated during 8 d storage at (25 °C ± 1 °C). Mongolian cheese with PVA/SF_(in)/PLLA/SF_(out) nanofibers performed well in retarding proteolysis and fat precipitation, and exhibited the lowest total viable counts (5.9 log CFU/g) on the 8th day. Thus, this work provides a novel design to construct biomimetic packaging for Mongolian cheese preservation.

A rapid method to assess freshness is crucial for the safe handling of reconstituted infant formula (RIF) and prevention of food-borne illnesses in infants. This study explored the use of electrical impedance measurement (EIM) at a constant frequency for real-time freshness evaluation of RIF. Initial electrical impedance of 89.16 ± 0.47 Ω decreased to 74.29 ± 0.23 Ω within 48 h at room temperature (20 °C) storage. Under temperature abuse conditions (30 °C), the electrical impedance rapidly dropped from 75.48 ± 0.52 Ω to 60.15 ± 4.76 Ω within 18 h, indicating more rapid spoilage. Notable changes in the electrical impedance were observed during temperature abuse. Empirical model analysis revealed a strong positive correlation between electrical impedance and conventional freshness parameters such as pH, protein, and microbial growth. This study demonstrates the potential of EIM for the rapid detection of freshness changes in RIF, offering valuable insights into the prevention of food-borne illnesses in infants.