International Journal of Dairy Technology最新文献

Whey protein hydrolysates (WPH) possess unique functional properties, including bioactivity, improved solubility and enhanced heat stability. These characteristics make them valuable for food applications. While it is known that enzymatic hydrolysis and heat denaturation influence the technological properties of WPH, their impact on functional characteristics has not been fully explored. This study aimed to comprehensively evaluate the technological properties of WPH obtained through enzymatic hydrolysis of native and heat-denatured whey protein concentrates (WPC). WPC was hydrolysed using a protease complex (subtilisin, chymotrypsin) under varying conditions. The study assessed particle size, wettability, solubility, hygroscopicity and heat stability of the produced WPH. The influence of hydrolysis time, pH conditions and preliminary heat denaturation of proteins on these properties was analysed. Enzymatic hydrolysis improved WPH wettability and solubility but increased hygroscopicity at 65% and 85% relative humidity. The highest heat stability was observed after 90–180 min of hydrolysis at neutral pH, allowing WPH to withstand 95°C for 60 min and 137°C for 10 min. Lowering pH to 4.5 reduced heat stability. Preliminary heat denaturation of proteins before hydrolysis enhanced peptide bond accessibility but promoted protein aggregation, leading to decreased solubility, increased hydrophobicity and alterations in heat stability and water interactions. These findings suggest that both enzymatic hydrolysis and heat denaturation play an important role in modulating the functional properties of WPH. Optimising the balance between these processes could help tailor WPH properties for specific food applications, such as heat-stable protein formulations. Further research is needed to refine processing conditions and enhance the functional performance of WPH in industrial applications.

Somatic cell count (SCC) is a test used for mastitis control in ewes, but there is no consensus on the cut-off value. Other markers of subclinical mastitis (SCM) have been proposed as potentially more efficient, sensitive and specific, such as differential somatic cell count (DSCC). Several studies have been conducted on cow milk DSCC application, especially since the development of a method (Foss DSCC method) that allows the rapid and simultaneous determination of both SCC and DSCC in cow milk. The aim of this study was to investigate the Foss DSCC method in ewe milk. We first calculated a SCC cut-off for sheep half-udder milk samples from three dairy breeds to be used with bacteriological analysis to define SCM; second, we validated the Foss DSCC method following the validation conducted on bovine milk; and finally, the DSCC cut-off study was conducted for the sheep SCM milk. For this purpose, 4074 ewe half-udder milk samples from three breeds were analysed for bacteriological, SCC and DSCC investigation. The validation of the Foss DSCC method followed that previously conducted on cow milk, while the optimal cut-off values were chosen based on the Youden method after generating receiver operating characteristic curves and calculating the relative area under curve values. The specificity, repeatability and robustness of the Foss DSCC method for sheep milk were comparable to those of the method for bovine milk. The optimal cut-off resulted in 500 × 10³ cells/mL and 71.5% for SCC and DSCC, respectively. For the first time, the Foss DSCC method was validated in sheep milk, and SCC and DSCC cut-off values were determined for three important dairy milk breeds of ewes in Italy. These results will allow developing further studies to improve mastitis screening and will help farmers, veterinarians and technicians to identify SCM in flocks.

Listeriosis, caused by Listeria monocytogenes, is a severe foodborne infection, particularly hazardous for pregnant women and immunocompromised individuals. In Europe, L. monocytogenes was the fifth most reported zoonotic agent in 2022, with outbreaks frequently linked to ready-to-eat (RTE) foods. Addressing food contamination with innovative antimicrobial strategies is critical to enhancing food safety and reducing public health risks. This study evaluated the efficacy of two bacteriophage-derived endolysins, LP101_021 and PlyP100, in reducing L. monocytogenes contamination in Squacquerone, a traditional Italian soft cheese made from whole cow's milk. Squacquerone samples were experimentally inoculated with approximately 6 log₁₀ cfu/g of L. monocytogenes strain Lm-ID11. The samples were then treated with either LP101_021 or PlyP100, and viable bacterial counts were monitored over time. Reductions in bacterial load were measured at 1 and 24 h post treatment to assess the effectiveness of each endolysin. Endolysin LP101_021 demonstrated a significant reduction in L. monocytogenes counts, decreasing bacterial loads by more than 3 log₁₀ cfu/g within 1 h, with sustained effects over 24 h. PlyP100 exhibited a more moderate impact, reducing bacterial counts by approximately 0.5 log₁₀ cfu/g after 1 h and 1.38 log₁₀ cfu/g after 24 h. By comparing the effects of those two endolysins, these findings highlight the rapid and effective antimicrobial action in particular of LP101_021 in cheese matrices. The study underscores the potential of bacteriophage endolysins as targeted antimicrobial agents for food safety applications. Their specificity allows the biocontrol of harmful pathogens without disrupting beneficial microbial communities, making them a promising alternative to conventional antimicrobial strategies. Furthermore, the effectiveness in reducing L. monocytogenes contamination in dairy products supports their potential integration in food processing and storage protocols, addressing the global challenge of antibiotic-resistant bacteria.

Oil-in-water emulsions, such as dairy cream, can destabilise into an oily and an aqueous phase after freezing and thawing due to ice crystal formation. This work examined the freeze–thaw stability of dairy cream after isochoric cooling at subfreezing temperatures and conventional freezing (CF). Samples were processed under isochoric cooling conditions and under CF at −10°C, −15°C and −20°C. The stability of the emulsions was assessed by particle size distribution, visual appearance, confocal micrographs, amounts of destabilised serum, rheological properties and colour properties, as well as lipid oxidation and microbial growth after 14 days. Dairy creams conventionally frozen at these temperatures destabilised into a serum phase and a precipitate due to ice formation that caused partial and complete coalescence of the fat globules. In comparison, dairy cream samples stored under isochoric conditions showed greater stability than the control sample stored in refrigeration at 5°C, due to the absence of ice crystals and low processing temperatures. Also, no microbial growth, significant changes in flow behaviour, colour or lipid oxidation occurred for the isochoric samples. These results showed that isochoric cooling can be used to preserve dairy cream at subfreezing temperatures with no freeze–thaw destabilisation.

Skoglund T (2024) Minimising bubble-related fouling: How to improve performance at lower cost and increased product quality—A theoretical proposal for ultra-high-temperature processing of milk. International Journal of Dairy Technology 77 594–603. https://doi.org/10.1111/1471-0307.13037.

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Due to the strong stress resistance, causing food spoilage and toxin production of spore-forming Bacillus species, their presence will be detrimental to the quality assurance of dairy products. Impacts of five Bacillus strains (Bacillus licheniformis H1, B. licheniformis H2, B. subtilis Z2, B. cereus Z6-1 and B. cereus Z6-2) originated from dairy products on the quality of pasteurised yoghurt were investigated. Physiological characteristics of the strains, including growth, acid production, proteolysis, amylase production, extracellular polysaccharide and biofilm formation, were analysed. Additionally, changes in Bacillus-contaminated pasteurised yoghurt during a 60-day incubation at 28°C were observed. Physiological characteristics of the five Bacillus strains were strongly strain-specific. Both B. cereus strains had the highest growth rate and acid production in Brian Heart Infusion broth and the strongest proteolytic ability in skimmed milk. Bacillus subtilis Z2 exhibited the highest amylase activity, while the highest yields of extracellular polysaccharides and biofilm were obtained from B. cereus Z6-2 and B. licheniformis H2. The acidic environment (about pH 4.2–4.4) was not suitable for the growth of Bacilli, as the low survival rate after inoculation and the slow growth. Yoghurt contaminated with B. licheniformis H1 showed strong proteolytic activity, resulting in a gel with relatively low elasticity. Yoghurt containing H2 exhibited a high amylase activity, leading to the formation of many interspersed holes. The Z2 strain had the strongest effect on the rheological properties of yoghurt, resulting in the lowest viscoelasticity. Protease from Bacillus strains mainly interferes with the thickness of the protein matrix in the yoghurt, while amylase mainly affects the size of holes in the gel. The residual Bacillus strains may adversely affect the rheological properties of pasteurised yoghurt, particularly in products with a long shelf life.

Whey is a main by-product generated during cheese manufacture. It contains abundant lactose and proteins and is a valued raw material in many countries. Pseudomonas putida KT2440 is a promising microbial strain for biobased chemical production. In our previous studies, this strain was confirmed owning high ability to oxidise galactose. Besides, we have constructed a recombinant strain P. putida KT2440 (pBB-GDH1) harbouring a novel glucose dehydrogenase that capable of oxidising lactose. Based on these, the potential of this engineered P. putida in whey utilisation deserves further exploration. This research aimed to establish a bioprocess to convert whey lactose into galactonic acid and lactobionic acid using engineered P. putida. Lactose in cheese whey powder was hydrolysed by Bacillus coagulans β-galactosidase into glucose and galactose. P. putida KT2440 (pBB-GDH1) was inoculated into the whey powder hydrolysate and galactose was converted into galactonic acid. Then, the bacterial cells were recovered and employed for lactobionic acid production from fresh whey powder solution. Three independent experiments were performed, and the mean value were taken as the results. Pseudomonas putida KT2440 (pBB-GDH1) exhibited a higher lactose-oxidising activity compared with the wild-type strain. It could utilise glucose and proteins in cheese whey powder hydrolysate for growth and convert galactose to galactonic acid. 25.45 g/L galactonic acid was obtained with a productivity of 1.06 g/L/h. The recovered cells maintained excellent lactose oxidation ability. After optimisation of biocatalytic reactions, 301.58 g/L lactobionic acid was obtained from cheese whey powder containing 300 g/L lactose in a 3 L bioreactor. The lactobionic acid productivity reached 2.28 g/L/h with a yield of 96.67%. This study established a sustainable and economic aldonic acids co-production strategy from cheese whey powder.

Casein (CN) is naturally a nanocarrier designed to deliver calcium and phosphate and hence has vast potential to be utilised for delivery of bio actives and therapeutics efficiently. The pH variation studies of MCC indicated that micelles open up at alkaline pH, exposing buried hydrophobic areas. Nanocapsules so designed had encapsulation efficiency of 95.80 ± 0.14% for curcumin. The in vitro digestions model showed a 98.12 ± 1.49% release of curcumin after 120 min of intestinal phase and only 6.12 ± 0.24% at end of gastric phase from nanocapsules. This indicates increased bioavailability of curcumin, without getting degraded. Global demand for functional food is increasing, and nanoencapsulation using native CN micelles could help in achieving differentiation and enhancing value of foods.

In recent years, probiotic products have received considerable attention. This study is aimed at utilising sugar beet pulp (SBP), a raw material potentially conferring health benefits, to enhance the stability of set yogurt. The study explored the influence of SBP on the fermentation performance and properties of set yogurt during 21-day storage at concentrations of 0.1, 0.5 and 1%. The incorporation of SBP led to significant decreases in pH, increased titratable acidity and modifications in the timing of peak hardness, adhesiveness and springiness. All samples demonstrated a predominance of the elastic component, which contributed to enhanced stability of the set yogurt during refrigeration. Furthermore, yogurts with 0.1 and 0.5% SBP exhibited superior performance in terms of syneresis and microstructure. This could be attributed to the soluble fibre in SBP, which binds more tightly to the protein aggregates in yogurt, thereby strengthening the network structure of the casein gel. The optimal sensory results were observed in yogurt containing 0.1% SBP. In conclusion, the addition of 0.1% SBP can effectively enhance the quality of set yogurt while increasing the intake of dietary fibre and bioactive compounds. As an agricultural by-product, SBP holds promise as a natural stabiliser in yogurt.