International Dairy Journal最新文献

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.

Using a metaproteomics approach, we showed that the initial milk quality impacts the proteome allocation of starter cultures used in cheese production and can be considered a fundamental source of cheese quality batch-to-batch variation. Raw milk was spiked with a highly proteolytic strain of Pseudomonas trivialis, previously isolated from raw milk, and incubated for 1, 3, and 6 days at refrigerated temperature. After incubation, the milk was heat-treated and then fermented with a mesophilic starter culture commonly used to produce Gouda-type cheeses. The development of metabolites was analyzed and a taxonomical and functional characterization of the starter culture was performed. Milk storage time impacted both the metaproteome of the starter culture, consequently affecting metabolite levels after fermentation and the level of protein expressed by the different taxa; Lactococcus protein was more abundant in samples made from milk stored longer with Pseudomonas while proteins expressed by Leuconostoc spp. decreased in abundance.

This investigation aims to explore the molecular epidemiological characteristics of the fosfomycin resistance gene, fosA5, in unpasteurized raw milk. A total of 385 unpasteurized raw milk samples were collected from dairy farms in Jiangsu province, China. From these samples, 102 strains of Klebsiella pneumoniae were isolated, with 9 of them testing positive for the presence of the fosA5 gene. Antimicrobial susceptibility testing revealed that K. pneumoniae carrying fosA5 exhibited high-level resistance to fosfomycin but also to other tested antibiotics, indicating multidrug resistance. The S1-PFGE and conjugation results indicated that the fosA5 gene was located on the chromosome. Furthermore, the analysis of PFGE patterns, MLST, and WGS elucidated the genetic diversity among K. pneumoniae strains harboring the fosA5 gene, indicating both clonal and horizontal transmission. This study highlights the prevalence and characteristics of the fosA5 fosfomycin resistance gene in large-scale dairy farms in Jiangsu province. Given its potential public health risks, these findings warrant significant attention.

Antibacterial substances have played a crucial role in food preservation. Herein, the inhibitory effects of potassium sorbate and ZnO nanoparticles (ZnO NPs) on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in milk-based beverages were examined through the determination of their minimum inhibitory concentrations (MICs) with an automated method for measuring bacterial growth curves. We revealed that the MICs of potassium sorbate and ZnO NPs against E. coli were 16.0 mg/mL and 8.0 mg/mL, respectively. While against S. aureus they were 24.0 mg/mL and 8.0 mg/mL, respectively. ZnO NPs demonstrated higher antibacterial efficacy compared to potassium sorbate. The combination of potassium sorbate and ZnO NPs showed an indifferent effect on E. coli, but an additive effect on S. aureus. The addition of 3 × MIC of either potassium sorbate or ZnO NPs resulted in a complete suppression of bacterial growth for 5 days. This study underscored the efficacy of potassium sorbate and ZnO NPs, either alone or in combination, in combating E. coli and S. aureus, highlighting their potential commercial utility in safeguarding milk-based beverages from spoilage.

This was a cross sectional study that examined the microbial ecology and aflatoxin M1 contamination in commercially produced Bongo, a traditionally fermented dairy beverage from Uganda. It also involved isolation and preliminary evaluation of defined starter cultures for Bongo. Microbial analyses were done by agar plating. Microbial identification was initially done by biochemical testing and microscopy. Followed by 16S rRNA and Internal Transcribed Spacer (ITS) region sequencing for bacteria and yeasts, respectively. Community DNA was studied using Next Generation Sequencing (NGS). Aflatoxin M1 was determined using Ultra High Pressure Liquid Chromatography - Triple Quadrupole Mass Spectrometry. (GTG)₅ Rep PCR fingerprinting was used to cluster candidates for starter culture evaluation. The rates of acidification of cow milk by candidate LAB coupled with sensory acceptability of the milk they fermented were the criteria for the selection of the starter cultures. Results indicated that lactic acid bacteria (LAB) and yeasts were the dominant groups. Molds, coliforms, enterococci and staphylococci were also detected. Aflatoxin M1 were insignificant. Based on agar plating technique, lactococci and lactobacilli were dominant, however, NGS showed Streptococci. Agar plating also showed Saccharomyces as dominant, but NGS showed Dipodascus. Cluster analysis identified 18 LAB, which were evaluated for starter culture properties. Three showed promise suggesting that they could be used for commercial production of cultured milks like Bongo.

UHT milk is stable towards spoilage for months, but chemical and enzymatic reactions occur during storage. This study evaluated whether changes over storage (at 4, 20 or 30 °C, for 30–90 d) of regular as well as lactose-reduced UHT milk were discernible by untrained and trained sensory panelists, and which physicochemical parameters they were associated with. Most changes were of low magnitude, such as significant increases in non-protein nitrogen (in both milk types) and lactulose (in regular UHT milk). However, the color of lactose-reduced UHT milk noticeably changed due to browning. Trained panelists evaluated lactose-reduced samples stored at 30 °C as significantly different in color than those stored at lower temperatures and untrained panelists correctly distinguished between fresh and stored lactose-reduced UHT milk in a tetrad-test already after 30 d. Further research is needed to evaluate if consumers detect such changes and therefore dispose of UHT-milk.

The techno-functional properties of dairy cheeses are often superior to their plant-based cheese alternatives. However, the constant increase in demand for plant-based cheese alternatives makes it important to achieve texture and functionality as in dairy cheeses. In this study commercial dairy cheeses and plant-based cheese alternatives were analyzed in regard to chemical composition, texture properties (unheated and heated state) and melting behavior with methods commonly applied to dairy cheeses. Especially, during an oscillatory temperature sweep, data did not show the “melting” the consumer notices while baking the product in an oven as done in the Schreiber test (2_CA, 3_CA). Therefore, a large amplitude oscillatory strain method (LAOS 60 °C) was applied and linked with the results obtained from the Schreiber test and the temperature sweep measurements. LAOS not only showed good correlation with the melting behavior observed in the Schreiber test but also allowed conclusions about the microstructure of the samples.