International Journal of Dairy Technology最新文献

Ambient yoghurt is susceptible to microbial contamination. Decreased viscosity adversely affects the quality parameters of yoghurt. Microbial contamination is the significant cause of viscosity reduction. Ambient yoghurt contains various additives, among which colloidal substances and microbial cells are particularly resistant to separation and purification, posing significant challenges for the detection and identification of contaminating microorganisms. In a batch of Ambient yoghurt, only a small subset of samples exhibited reduced viscosity, while routine microbial tests showed no abnormalities. In order to expeditiously determine the underlying factors responsible for yoghurt viscosity reduction and overcome critical technological limitations in quality monitoring methodologies, a thorough microbial traceability analysis was performed. The addition of NaOH facilitated the separation of colloids and microbial cells, enabling subsequent microscopic analysis and sequencing to identify potential microbial contaminants. Additionally, a starch hydrolysis test was performed to analyse the microorganisms responsible for the viscosity reduction. The yoghurt with reduced viscosity exhibited lower colloid content compared with normal viscosity samples. Under staining and microscopic examination, fungal hyphae were observed, and ITS sequencing revealed the highest similarity to Geotrichum candidum. Cultivation tests of retained raw materials showed that only granulated sugar formed white, fluffy colonies on the culture plate, demonstrating strong starch-degrading activity. ITS sequencing analysis revealed the highest homology with G. candidum, confirming it as the source of contamination. After enhancing the sterilisation of granulated sugar, the produced yoghurt no longer exhibited reduced viscosity. Comprehensive analysis indicated that the viscosity reduction in yoghurt was likely caused by G. candidum contamination in the granulated sugar. This study established a simple and rapid method for separating colloids and microbial cells from yoghurt, and a universal method for extracting microbial genomic DNA, enabling rapid and efficient analysis of the causes of viscosity reduction in ambient yoghurt.

Staphylococcus (S.) aureus and its increasing antimicrobial resistance pose a significant challenge to global health. The rapid emergence of antibiotic resistance and the risks associated with chemical preservatives are major global concerns. Consequently, there is an important issue of developing effective control strategies in the food industry. This study aimed to determine the prevalence of S. aureus isolated from dairy products in Egypt. Additionally, antimicrobial resistance profiling was assessed. Finally, the potential use and sensory attributes of essential oils, such as olive and black seed oils, along with d-amino acids as antimicrobial additives in Domiati cheese under osmotic stress, were evaluated for controlling methicillin-resistant S. aureus. A total of 150 dairy samples were examined, including 30 samples each of raw milk, ultra-heat-treated (UHT) milk, Karish cheese, Domiati cheese and frozen dairy dessert. The results revealed that 32% of the examined samples were positive for S. aureus, with more than 70% of the isolates exhibiting multidrug resistance to tetracycline, erythromycin and oxacillin. Molecular characterisation showed that 23 and 7 isolates harboured the enterotoxin genes sea and seb, respectively. Furthermore, 72 and 4 isolates carried the nuc and mecA genes, respectively. Among the 10 examined d-amino acids, d-tryptophan (40 mM) demonstrated the most potent antibacterial activity. Our study also revealed, for the first time, the significant inhibitory effect of d-tryptophan on methicillin-resistant S. aureus (MRSA) in contaminated cheese. The number of MRSA cells treated with olive and black seed oils (1%) and d-tryptophan (40 mM) was significantly reduced by 2 to 5 log cfu/g in cheese (P < 0.05). The used natural additives improved overall acceptability and other sensory attributes of the cheese. The combination of essential oils and d-tryptophan presents a promising eco-friendly solution for controlling S. aureus contamination in the food industry.

Sweetened condensed milk (SCM) is a widely consumed dairy product used in desserts. However, lactose crystallisation during storage creates a sandy texture, a quality defect. The traditional approach to controlling crystal size involves adding pure lactose to induce microcrystallisation. A cost-effective alternative is milk permeate, a by-product of milk ultrafiltration with up to 90% lactose. This study evaluates milk permeate as a nucleating agent compared with pure lactose, aiming to improve SCM texture and reduce costs. This study assessed the ability of milk ultrafiltration (UF) permeate to induce lactose crystallisation in SCM compared with pure lactose powder. The influence of micronised and non-micronised forms on crystal size, number and viscosity over 30 days was also examined. The samples were produced using whole milk and sucrose in a laboratory-scale rotary evaporator. Four treatments were applied: (T1) non-micronised lactose, (T2) micronised lactose, (T3) non-micronised UF permeate and (T4) micronised UF permeate. Crystallisation was monitored using optical microscopy and analysed with ImageJ software at 1, 7, 15 and 30 days. Viscosity was measured with a rotational viscometer and a Ford cup viscometer. Statistical analysis was performed using Tukey's test (P < 0.05). Micronised ingredients (T2 and T4) formed smaller (~11 μm) and more numerous (~700 crystals/microscopic field) crystals than non-micronised treatments (~15 μm, ~200 crystals/microscopic field). UF permeate showed similar nucleation capacity to pure lactose without altering viscosity. Viscosity increased over time, with T4 showing the highest values at day 30. Smaller, more numerous crystals in micronised treatments reduced the risk of a sandy texture. Milk UF permeate can replace pure lactose as a nucleating agent in SCM, offering a cost-effective alternative without compromising quality. Micronised permeate is especially effective, producing a smooth-textured product like traditional formulations. This innovation could enhance industry competitiveness by reducing costs and waste while maintaining quality.

Crossbreeding can be utilised in animal husbandry to increase genetic diversity and improve health and fertility in the next generation. In dairy herd management, a common strategy involves crossbreeding Jersey (JE) cows with Holstein-Friesians (HF), resulting in Jersey-Holstein-Friesian (JFX) progeny. This study investigated the impact of these genotypes on processing efficiency and product quality within Cheddar manufacturing. Raw JFX cows’ milk had significantly higher protein (+5.68%) and fat (+13.20%) than HF cows, but no significant differences in coagulation properties or cheese yield resulted. All cheese manufactured had macro-compositions within the range of expected values for Cheddar, with no meaningful differences in texture, proteolysis, pH, volatile organic compounds and fat profile. From a due-diligence perspective, it was not evident from any of the analyses performed that JFX phenotypes cause practical negative impacts to the cheesemaking ability of milk or adversely influence final cheese quality. Furthermore, cheese derived from JFX milk was more yellow in colour, with significantly higher b* values, which is indicative of preferable sensory and nutritional quality.

Whey protein concentrate (WPC) undergoes microfiltration (MF) to produce whey protein isolate (WPI), generating a lower value MF retentate as a co-product. Higher-than-expected protein retention in the retentate, attributed to protein aggregation, has been shown to limit WPI yield. Strategies to reverse or reduce aggregation would be expected to increase protein transmission during MF. This study investigated the effects of pre-treating WPC with 5 mM trisodium citrate (TSC), a calcium-binding salt and high-pressure homogenisation (HPH) at 650 bar, both individually and in combination, on protein transmission during MF. A WPC solution (2.4% protein) was pre-treated with TSC, HPH, TSC followed by HPH (TSC + HPH), or HPH followed by TSC (HPH + TSC). Microfiltration was performed using a 1000 kDa polyethersulfone membrane. Processing time, component partitioning and chemical composition in feed, retentate and permeate were analysed. Protein profiles were assessed using SDS-PAGE and RP-HPLC, in addition to whey protein denaturation. Data were obtained from three independent trials, with all analyses conducted in triplicate. Treatment significantly reduced processing time and increased protein permeation (P < 0.05). Processing time decreased by 6.4–11.0%, with TSC and HPH having the strongest effects. Compared with the control, protein retention in MF retentate from pre-treated samples decreased by 7.5–11.5%, with HPH + TSC showing the greatest effect, while permeate protein content increased by 5.45–9.64% (P < 0.05). SDS-PAGE confirmed lower levels of protein aggregation, particularly in HPH + TSC, coinciding with the lowest sedimented protein level (43.4%). Trisodium citrate pre-treated samples showed significantly lower (P < 0.05) calcium and magnesium levels, providing evidence that cations are involved in mediating protein aggregation. The results indicate that WPC treatment can modify protein permeation, improving the yield of WPI while also generating an MF retentate further enriched in polar lipids, supporting more sustainable dairy processing.

Foodborne pathogen Bacillus cereus is widely distributed in dairy products and the processing environment. Beyond its threat to human health, the production of thermostable protease also poses a significant challenge to the dairy industry, particularly in pasteurised or ultra-high-temperature (UHT) processed milk products. Despite this, our understanding of dairy spoilage caused by B. cereus is very limited. This study aimed to evaluate the spoilage potential of a thermostable protease produced by B. cereus 12–1 in fluid milk. Specifically, crude protease characterisation, including optimum pH and temperature, the influence of Ca²⁺ on enzyme activity and heat stability of protease, was studied. Moreover, the effects of this protease on the quality of both whole and skim UHT milk were evaluated, including zeta potential and particle size of milk, hydrolysis of milk protein, release of free amino acids and change of milk microstructure. This crude protease has relatively good stability at wide-ranging pH values from 5.0 to 10.0 (79.67–166.67 U/mL) and temperatures from 20°C to 70°C (92.67–165 U/mL), and maintained stability of 46.04% and 38.31% after heat treatment by 65°C/30 min or 100°C/10 min. Spoilage patterns in skim and whole UHT milk differ significantly due to variations in fat content. The protease caused protein hydrolysis in whole milk (15.25%) and skim milk (17.09%), effectively hydrolysed κ-casein and β-casein, caused the release of free amino acids (Lys, Val, Tyr, Phe, Ile, Met and Leu) in UHT milk and significantly increased particle size (increase by 940 nm for skim milk and 1319 nm for whole milk), and reduced zeta potential (reduction by 4 mV for skim milk and 3.83 mV for whole milk) of UHT milk. Results indicate the spoilage potential of crude protease from B. cereus and highlight the need to prevent dairy spoilage caused by B. cereus.

A1 and A2 milk differ in their beta-casein composition, with A1 milk containing a variant that releases beta-casomorphin-7 (BCM-7), a peptide that has been suggested to affect digestion. A2 milk, on the other hand, lacks the A1 variant and is marketed for its potential digestive benefits. However, there is limited research on consumer perceptions and experiences related to A1 and A2 milk, especially in terms of sensory and gastrointestinal attributes. This study aimed to evaluate consumer perceptions and consumption experiences of A1 and A2 milk, focussing on sensory characteristics and gastrointestinal effects. An online questionnaire was conducted with 200 participants to assess their awareness, attitudes, and preferences regarding A2 milk. Additionally, a diary-based consumption study was performed with 15 adult participants to document their sensory experiences and digestive perceptions when consuming A1 and A2 milk. Only 18.5% of the respondents had previously heard of A2 milk. Sensory attributes such as flavour, origin, brand and price were considered ‘very important’ when purchasing dairy products. In the consumption study, participants reported 11 sensory attributes and seven terms related to digestibility. A1 milk was more commonly associated with a ‘darker colour’ and ‘strong smell’, while A2 milk was linked to ‘regulated intestines’. These findings suggest that although A2 milk is marketed for its potential digestive benefits, consumer awareness remains low. Sensory attributes play a significant role in consumer decision-making when purchasing dairy products. Further research is needed to confirm the digestive advantages of A2 milk and to develop strategies to increase consumer knowledge and awareness of its benefits.

Milk and dairy products are essential food sources in human nutrition but can serve as reservoirs for pathogenic bacteria, such as Salmonella spp., posing serious public health risks. The increasing emergence of antimicrobial resistance in foodborne pathogens further complicates food safety and infection control. This study aimed to determine the presence of Salmonella spp. in milk and dairy products, analyse the virulence genes of the isolates and evaluate their antibiotic resistance profiles. A total of 300 milk and dairy product samples (150 raw milk, 60 village cheese, 50 curd cheese and 40 butter) were collected from family businesses and local markets in Samsun, Turkey. Salmonella spp. was detected using ISO 6579 culture methods, and PCR was used to confirm the presence of the oriC gene. The virulence genes (invA, hilA, avrA and stn) were identified by PCR. Antibiotic resistance was assessed using the VITEK 2 AST-GN97 system. Salmonella spp. was detected in 12 of 300 samples (4%), with the highest prevalence in village cheese (8.3%). Among 36 isolates, all (100%) harboured invA and hilA, while avrA (63.8%) and stn (55.5%) were less frequent. All isolates were resistant to at least two antibiotics, with the highest resistance to ampicillin (100%). The presence of Salmonella spp. in milk and dairy products, along with high rates of antibiotic resistance, highlights the need for enhanced food safety regulations, improved hygiene standards and stricter antimicrobial stewardship. Implementing effective pasteurisation and hazard control measures is crucial to reducing contamination risks and protecting public health.