Effect of pH on the formation of serum heat‐induced protein aggregates in heated yak milk

Serum heat‐induced protein aggregates at various pH levels were isolated from heated yak milk by size‐exclusion fast protein liquid chromatography. Analysis by reversed‐phase high‐performance liquid chromatography showed that β‐lactoglobulin and κ‐casein were the two main proteins in these aggregates. The amount of serum heat‐induced protein aggregates increased from pH 6.6 to 7.4, whereas the content of β‐lactoglobulin in aggregates decreased from 61.9% at pH 6.6 to 50.4% at pH 7.2, and then increased to 51.3% at pH 7.4. The content of κ‐casein, αs₁‐casein and β‐casein increased from pH 6.6 to pH 7.4. These results show that serum heat‐induced protein aggregates are pH dependent.     

Effects of pH and salt concentration on functional properties of rambutan (Nephelium lappaceum L.) seed albumin concentrate

Searching new protein sources is essential due to an increase in protein demand. In this study, rambutan seed albumin concentrate (RSAC) with the protein content of 80.8% was isolated from defatted rambutan seed meal. The effects of pH and sodium chloride concentration on solubility and functional properties of RSAC were investigated. RSAC had minimum solubility at pH 4. Water absorption capacity at pH 7 and oil absorption capacity of RSAC were 0.79 and 6.13 mL g^?1, respectively. Both foaming and emulsifying capacities achieved maximal levels at pH 12. In sodium chloride solution, foaming capacity and stability achieved maximal levels at the concentration of 0.6 mol L^?1, while the highest emulsifying capacity and stability were noted at the concentration of 0.2 mol L^?1. The least gelation concentration of RSAC was 100 g L^?1 and this value decreased by five times as salt concentration in the protein solution was 0.6 mol L^?1. RSAC was a potential functional ingredient in food processing.     

Changes in bioactive compounds and antioxidant activity during convective drying of murta (Ugni molinae T.) berries

Murta (Ugni molinae T.) berries were air‐dried at five temperatures (40, 50, 60, 70 and 80 °C), and the changes in β‐carotene, phenolic acids, total phenolic and flavonoid contents and antioxidant capacities (DPPH and ORAC) were investigated. The berries showed a high content of β‐carotene, which decreased during drying temperature between 40 °C and 80 °C. Free and bound phenolic acids were also determined, showing gallic acid to be the prevalent phenolic acid. Total phenolic and flavonoid contents in the dried berries showed a higher decrease at lower temperature due to longer drying time. The radical‐scavenging activity also showed higher antioxidant activity at higher drying temperatures (70–80 °C) than at lower drying temperatures (40–50 °C). Total phenolic content (TPC) and flavonoids showed good correlation with antioxidant capacity. Murta berries proved to be an excellent source of antioxidants and bioactive compounds and are therefore a potential ingredient for new functional food products.     

Development of novel pea flour‐based nanofibres by electrospinning method

The aim of this study was to produce pea flour and hydroxypropyl methylcellulose (HPMC)‐based novel nanofibres using electrospinning method. The effects of pH, pea flour and HPMC concentration on apparent viscosity, electrical conductivity of electrospinning solutions and nanofibre characteristics were studied. Solutions were prepared at different pH values (7, 10, 12), with different pea flour concentrations (1%, 2% w/v) and HPMC concentrations (0.25%, 0.5%, 1.0% w/v). For all pea flour concentrations, k values increased significantly with increase in pH and HPMC concentration. It also increased with increase in pea flour concentration for basic solutions. Pea flour concentration increased diameter and water vapour permeability (WVP) values of nanofibres. This study showed that electrospinning was a promising method for fabrication of homogenous pea flour and HPMC‐based nanofibres to be used in packaging industry.     

Changes in phosphorylation of myofibrillar proteins during postmortem development of porcine muscle

A gel-based phosphoproteomic study was performed to investigate the postmortem (PM) changes in protein phosphorylation of the myofibrillar proteins in three groups of pigs with different pH decline rates, from PM 1 to 24 h. The global phosphorylation level in the group with a fast pH decline rate was higher than that in the slow and intermediate groups at early PM time, but became the lowest at 24 h. The protein phosphorylation level of seven individual protein bands was only significantly (p < 0.05) affected by PM time, and two protein bands were subjected to a synergy effect between PM time and pH decline rate. A total of 35 non-redundant highly abundant proteins were identified from 19 protein bands; most of the identified proteins were sarcomeric function-related proteins. Myosin-binding protein C, troponin T, tropomyosin and myosin regulatory light chain 2 were identified in the highly phosphorylated protein bands with the highest scores. The results indicate that the phosphorylation pattern of myofibrillar proteins in PM muscle is mainly changed with PM time, but only to a minor extent influenced by the rate of pH decline, suggesting that the phosphorylation of myofibrillar proteins may be related to the meat rigor mortis and quality development.     

Robust PCR‐based method for quantification of bovine milk in cheeses made from caprine and ovine milk

To prevent fraud and enhance quality assurance, credible analysis of dairy products is crucial. A common problem is the addition of cheaper bovine milk to caprine and/or ovine dairy products and when not declared addition of bovine milk constitutes fraud. The aim was to develop a rapid, robust and sensitive method for the identification of adulteration of caprine and/or ovine cheeses with bovine milk. New quantitative real‐time polymerase (qPCR) assays were designed for the specific determination of bovine DNA (Cow1) and bovine, caprine and ovine DNA (BoCaOv). These were applied to 17 samples of caprine cheese and 24 of ovine cheese. Results showed that 17% (7/41) of these cheeses contained >5% bovine milk. As bovine milk was not declared as an ingredient in any of the samples, this represents adulteration. Other cheeses that contained detectable bovine milk at ≤5% (22%; 5/41) might pose a health risk to people allergic to bovine milk.     

Determination of the relationship between oxalate degradation and exopolysaccharide production by different Lactobacillus probiotic strains

The aim of this study was to evaluate the protective effects of exopolysaccharide (EPS) production on resistance to gastrointestinal digestive conditions and oxalate by probiotic strains of the species Lactobacillus rhamnosus, Lactobacillus fermentum and Lactobacillus brevis. The oxalate‐degrading ability of the strains was determined using an enzymatic assay. The correlation between oxalate degradation rate and EPS production was not significant (P > 0.05); however, the high‐EPS‐producing L. fermentumIP5 and L. brevisYG7 strains showed high oxalate‐degrading activity, whereas the low‐EPS‐producing strain L. fermentumBP5 demonstrated low oxalate‐degrading activity. The present findings suggest that dietary supplementation with the probiotic strain L. fermentumIP5 could be a promising strategy for the prevention of oxalate stone disease.     

Formation and dispersal of biofilms in dairy substrates

The formation and dispersion of biofilms in the dairy industry is a problem because it increases cross‐contamination, affecting the shelf life of the products and their safety. The objective of this study was to evaluate the influence of different dairy substrates (cows’ milk and whey protein) on the formation and dispersion of Enterococcus faecalis, Listeria monocytogenes, Staphylococcus aureus and Bacillus cereus in two biofilm systems (mono‐species and multi‐species) on stainless steel at 25 °C. The dominant behaviour of E. faecalis occurred in most of the tests on mono‐species and multi‐species biofilms. A greater dispersion of biofilm cells was observed in skimmed milk.     

Changes during storage of dried Moringa oleifera leaves prepared by heat pump‐assisted dehumidified air drying

Moringa oleifera leaves contain phytochemicals that are retained during heat pump‐assisted dehumidified air drying. Changes in phytochemicals, antioxidant capacity and colour were evaluated at 15–35 °C, during storage of dried leaves in polypropylene (PP) or high barrier (PET/Al/PE) packaging for up to 6 months. The a_w of samples in PP increased from 0.373 to 0.669. Decreases in total phenolics were greatest at 35 °C in PP (48%) and least at 15 °C in PET/Al/PE (19%). There were few significant changes in DPPH inhibition after 2 months storage. There was little change in kaempferol and some increase in quercetin. During storage, samples became less green, suggesting breakdown in chlorophyll had occurred. The degradation of flavonoids followed first‐order kinetics. The half‐life for total flavonoids ranged from 2.13 to 1.47 months for samples stored in PP and from 2.59 to 1.83 months for samples stored in PET/Al/PE.     

Steviol glycosides are not altered during commercial extraction and purification processes

Steviol glycosides, sweet diterpenes extracted from the shrub Stevia rebaudiana Bertoni, are approved as sweeteners in many countries throughout the world. Former heat and pH‐investigations of these glycosides have established their stability. However, due to the complex purification process, the natural authenticity has still been discussed and challenged, recently. Thus, the objective of this work was to show that the steviol glycosides are not chemically modified during the commercial extraction and purification process. Therefore, samples of three independent commercial‐scale extraction and purification batches of steviol glycosides, each batch containing a sample of the untreated stevia leaves, the first water extract and the high‐purity end product, were analysed using HPLC‐UV and HPLC‐ESI‐MS/MS. The results show that the commercial powders of extracted steviol glycosides with an estimated purity of more than or equal to 95% contain the same steviol glycosides as the dried stevia leaves and their hot water infusions, demonstrating that steviol glycosides are not affected by the purification process.     

Analysis and mathematical modelling of the behaviour of Escherichia coli in the mascarpone cheese during cold storage

The aim of this work was to study the behaviour of E. coli in mascarpone cheese during storage at the temperatures ranging from 3 to 15 °C, as well as application of predictive microbiology to describe the experimental data. The Baranyi, Gompertz and logistic models were fitted at the stage of primary modelling. Although all applied primary models described the growth of micro‐organisms accurately, the most accurate goodness of fit was obtained for the Gompertz model and the growth rates generated by this model were used for secondary modelling. The polynomial model predicted accurately the influence of temperature on the growth rate of E. coli, reaching the adjusted coefficient of linear regression 0.99. Generated predictive model that describes the growth of E. coli in mascarpone cheese constitutes a valuable tool in assessing the microbiological stability of the food product with similar physicochemical properties.     

Effects of Mentha longifolia L. essential oil and Lactobacillus casei on the organoleptic properties and on the growth of Staphylococcus aureus and Listeria monocytogenes during manufacturing,ripening and storage of Iranian white‐brined cheese

This research evaluated the effects of Mentha longifolia L. essential oil (EO) in concentrations 0, 50, 150 and 300 ppm and Lactobacillus casei (10⁸–10⁹ CFU/mL) on the growth of Staphylococcus aureus and Listeria monocytogenes during the manufacturing, ripening and storage of Iranian white‐brined cheese. The growth of the two pathogens was significantly reduced (P < 0.01) by both EO concentrations ≥50 ppm and probiotic and their combination in the standard manufacturing and storage process conditions of the cheese. Furthermore, the treatment containing 150 ppm of this EO combined with probiotic had a favourable inhibitory effect on the growth of two pathogenic micro‐organisms and also was the most appropriate treatment in sensory assessment. The synergistic effects of the above‐mentioned concentration level between the essential oil and probiotic were significant compared to other treatments, including essential oil and probiotic only. Thus, a lower concentration of this EO can be used when it is combined with this probiotic.     

Stability of the antimicrobial activity of acetogenins from avocado seed,under common food processing conditions,against Clostridium sporogenes vegetative cell growth and endospore germination

Anticlostridial activity of acetogenins from avocado seed was further characterised, and their stability and effectiveness under food processing conditions, and in a model food system, studied for the first time. Isolated AcO‐avocadenyne (1) and AcO‐avocadene (2) showed anticlostridial potential, particularly the latter molecule. Enriched acetogenins extracts, obtained at laboratory scale (EAE) and semi‐commercially (Avosafe^®), presented similar MIC values (3.9–9.8 ppm) and a bacteriostatic effect. Extracts bioactivity showed resistance to heat (≤120 °C), high hydrostatic pressure (HHP; 300–600 MPa, 3–6 min, 25 °C) and salt (≤3% w/v). In addition, the extract was most stable at pH ≥ 7.0 and potency against endospores increased after HHP treatment and exposure to pH 9.5, suggesting a positive effect on solubility or structure of particular acetogenins. In a model food system processed by HHP, acetogenins were retained; however, initial quantities gradually declined by 63% and 32% at 25 and 4 °C, respectively, at the end of the storage period (42 days). Most stable molecules (persediene (4) > persenones > AcO‐avocadene (2)) possess a keto or trans‐enone group at C‐4 in the aliphatic chain, which could support hydrogen donation to surrounding carbon atoms and confer antioxidant activity. Active endospores were completely inhibited by 5000 ppm Avosafe^® in the model food system (37 °C, 72 h) and lower concentrations (500–1000 ppm) resulted in 1–2 log reduction of a 3 log inoculum target. Efficacy information generated in the present work is considered crucial to improve scientific knowledge on spore inhibition properties of avocado acetogenins.     

Detection and quantification of Escherichia coli and Pseudomonas aeruginosa in cow milk by near‐infrared spectroscopy

This work investigated the potential of NIR technology to be applied in the dairy industry for the detection of micro‐organisms. To this end, two types of cow milk samples were studied, one in which only bacterial biomass was considered and the other in which bacteria were cultured and grown in milk for 24 h. The study was carried out using two micro‐organisms Escherichia coli and Pseudomonas aeruginosa. Both types of samples with different counts of both micro‐organisms were analysed by a NIR analyser in the range 10 000–4000 cm^?1 based on transmittance measurements. Multivariate models indicated that a better discrimination between micro‐organisms was attained in those milk samples in which micro‐organisms have been grown.     

Protein lactosylation in UHT milk during storage measured by Liquid Chromatography–Mass Spectrometry and quantification of furosine

The initial stage of the Maillard reaction, protein lactosylation, occurs during heat treatment of milk and continues during subsequent storage. We compared the initial lactosylation as well as the rate of lactosylation of milk proteins during storage in UHT milk subjected to direct or indirect heat treatment using liquid chromatography (LC) coupled with electrospray injection mass spectrometry (ESI‐MS). Furosine content was used as an overall marker to allow for a quantitative correlation of lactosylation measured by LC‐ESI‐MS in the UHT milks. Protein lactosylation increased during the storage period of 6 months at 20 °C. Both the initial extent and the rate of lactosylation positively correlated with the number of lysine residues in the different proteins. An exponential or linear correlation with furosine concentration could be established for major and minor lactosylated proteins, respectively.     

Nutritional composition and sensory attributes of Alaskan flatfishes compared to plaice (Pleuronectes platessa)

Proximate composition, fatty acids profiles and other nutritional values were evaluated for fillets of Limanda aspera (yellowfin sole), Lepidopsetta bilineata (southern rock sole) and Lepidopsetta polyxystra (northern rock sole) and compared to North Sea plaice (Pleuronectes platessa). Additional information is given on the composition of fillets from arrowtooth flounder (Atheresthes stomias). Plaice (0.8% lipid) and Alaska soles (1.0–1.2% lipid) can be classified as lean species, resulting in low 0.3–0.5 g ∑EPA+DHA/100 g muscle, although the fatty acid profiles of the extracted lipids were characterised by high amount of n‐3 fatty acids (33.2–47.3%). Arrowtooth flounder belong to the medium‐fat species (4.3%). Taurine was the most prevalent free amino acid; mean values ranging between 221 mg100 g^?1 and 247 mg100 g^?1 wet weight. The selenium content varied between 130 and 310 μg kg^?1 ww. Sensory attributes of Southern and Northern rock sole were comparable to plaice.     

Effects of Mentha longifolia L. essential oil on viability and cellular ultrastructure of Lactobacillus casei during ripening of probiotic Feta cheese

The effects of Mentha longifolia L. essential oil during ripening and storage probiotic Feta cheese were studied, in relation to viability and cellular ultrastructure of Lactobacillus casei. The addition of the essential oil in the concentrations from 0.0 to 0.03% was trialled: the 0.03% treatment resulted in the highest viability of L. casei and the lowest pH value compared with other treatments (P < 0.05). Electron microscopy showed that essential oil caused no harm to L. casei. This study demonstrated the favourable effects of M. longifolia on optimal maintenance of L. casei at the end of cheese storage period.     

Development and validation of a SYBR‐Green I Real‐Time PCR test to detect bivalves including Mytilus species in foods

The incidence of allergy to seafood, and in particular to molluscs is second only to that of nuts. To protect consumers, the regulators of food products insisted on identifying molluscs as allergens. The aim was to develop quantitative assay for the presence Mytilus species in processed food products. The chosen platform was real‐time PCR (qPCR) targeting either the gene encoding mitochondrial cytochrome C oxidase I or the nuclear gene encoding β‐actin. Recombinant plasmids containing each of target regions were used as a reference for quantification purposes. Limit of detection (LOD) and of quantification (LOQ) were determined. Spiked food samples containing 50–500 μg g^?1 of Mytilus chilensis were analysed both by qPCR and by ELISA. The former assay gave a positive outcome over this range, whereas the latter was sensitive down to a concentration of 125 μg g^?1.