Predicting sediment formation in ultra high temperature-treated whole and skim milk using attenuated total reflectance-Fourier transform infrared spectroscopy

Establishing accelerated shelf-life testing using Fourier transform infrared spectroscopy (FTIR) as a tool for prediction of stability requires pre-assessment of correlations between spectral changes and instability development during storage at room temperature. Comparison of results with those at elevated temperatures would establish appropriateness of accelerated shelf-life testing. UHT skim milk (SM) and UHT whole milk (WM) were stored at 20 °C for 9 months to investigate the feasibility of identifying spectral markers to predict sedimentation (a measure of instability). Marker variables corresponding to changes in structure and interactions of lipids, proteins and carbohydrates successfully predicted sedimentation in SM (R² = 0.92) and WM (R² = 0.60). Low predictability in WM may be due to influence of fat. These markers were similar to those observed during accelerated shelf-life testing, hence affirming its application with further work required to develop a model able to forecast sedimentation and other instabilities in UHT milk.     

Combined effects of high-pressure treatment and storage temperature on the physicochemical properties of caprine milk

The effects of high-pressure (HP) treatment (200–500 MPa for 25 min at 25 °C) combined with storage temperature (25 and 4 °C) on the physicochemical properties of raw caprine milk were studied. Storage of HP-treated and untreated milk samples at 25 °C considerably affected the changes in the conformation of milk proteins, which were reflected by changes in the protein sedimentation rate, gradual decreases in the soluble calcium and phosphorus contents, a slight decrease in pH, an insignificant decrease (P > 0.05) in viscosity, and a decrease in the casein hydration level of milk at the end of the storage time. In contrast, the HP-treated and untreated milk samples stored at 4 °C demonstrated different characteristics than the samples stored at 25 °C. These results could be due to calcium and phosphate association with caseins, which screen charges and reduce the repulsion of micelles during the storage time.     

Electrophoretic characterization of protein interactions suggesting limited feasibility of accelerated shelf-life testing of ultra-high temperature milk

Accelerated shelf-life testing is applied to a variety of products to estimate keeping quality over a short period of time. The industry has not been successful in applying this approach to ultra-high temperature (UHT) milk because of chemical and physical changes in the milk proteins that take place during processing and storage. We investigated these protein changes, applying accelerated shelf-life principles to UHT milk samples with different fat levels and using native- and sodium dodecyl sulfate-PAGE. Samples of UHT skim and whole milk were stored at 20, 30, 40, and 50°C for 28 d. Irrespective of fat content, UHT treatment had a similar effect on the electrophoretic patterns of milk proteins. At the start of testing, proteins were bonded mainly through disulfide and noncovalent interactions. However, storage at and above 30°C enhanced protein aggregation via covalent interactions. The extent of aggregation appeared to be influenced by fat content; whole milk contained more fat than skim milk, implying aggregation via melted or oxidized fat, or both. Based on reduction in loss in absolute quantity of individual proteins, covalent crosslinking in whole milk was facilitated mainly by products of lipid oxidation and increased access to caseins for crosslinking reactions. Maillard and dehydroalanine products were the main contributors involved in protein changes in skim milk. Protein crosslinking appeared to follow a different pathway at higher temperatures (≥40°C) than at lower temperatures, making it very difficult to extrapolate these changes to protein interactions at lower temperatures.     

Inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide

This study assessed the inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide (HPCD) at 10–30 MPa and 20–50 °C for 20–70 min. The log reduction of microorganisms increased as raw bovine milk was exposed to higher pressures and temperatures and longer treatment times. The maximum reduction of aerobic bacteria (AB) was 4.96‐log at 25 MPa and 50 °C for 70 min. At lower temperatures and treatment times, a complete inactivation of yeasts and moulds (Y&M) and coliform bacteria (CB) was obtained at 25 MPa. Changes in microorganisms naturally present in raw bovine milk during storage were also assessed. There were 1.83‐log survival of AB, 0.65‐log survival of Y&M and a complete inactivation of CB in raw bovine milk when subjected to HPCD at 25 MPa and 40 °C for 50 min. Moreover, the AB, Y&M and the CB in raw bovine milk exhibited insignificant alterations during storage at 4 °C for 15 days, indicating a potential capability of HPCD to extend the shelf life of milk.     

Effect of various storage conditions on the stability of quinolones in raw milk

Research on the storage stability of antibiotic residues in milk is important for method development or validation, milk quality control and risk assessment during screening, confirmation, qualitative or quantitative analysis. This study was conducted using UPLC-MS/MS to determine the stability of six quinolones – ciprofloxacin (CIP), danofloxacin (DAN), enrofloxacin (ENR), sarafloxacin (SAR), difloxacin (DIF) and flumequine (FLU) – in raw milk stored under various conditions to investigate if quinolones degrade during storage of milk, and finally to determine optimal storage conditions for analysis and scientific risk assessment of quinolone residues in raw milk. The storage conditions included different temperatures and durations (4°C for 4, 8, 24 and 48 h; –20°C for 1, 7 and 30 days; –80°C for 1, 7 and 30 days), thawing temperatures (25, 40 and 60°C), freeze–thaw cycles (1–5), and the addition of different preservatives (sodium thiocyanate, sodium azide, potassium dichromate, bronopol and methanal). Most quinolones exhibited high stability at 4°C for up to 24 h, but began to degrade after 48 h. In addition, no degradation of quinolones was seen when milk samples were stored at –20°C for up to 7 days; however, 30 days of storage at –20°C resulted in a small amount of degradation (about 30%). Similar results were seen when samples were stored at –80°C. Moreover, no losses were observed when frozen milk samples were thawed at 25, 40 or 60°C. All the quinolones of interest, except sarafloxacin, were stable when milk samples were thawed at 40°C once and three times, but unstable after five freeze–thaw cycles. Preservatives affected the stability of quinolones, but the effects differed depending on the preservative and quinolone. The results of this study indicate optimum storage protocols for milk samples, so that residue levels reflect those at the time of initial sample analysis, and should improve surveillance programmes for quinolones in raw milk.     

Changes in physicochemical characteristics of rice during storage at different temperatures

This study investigated the changes in the physicochemical properties of rice during storage at different temperatures. Milled rice stored at high temperatures showed higher fat acidity than rice stored at low temperatures. Although the moisture content of milled rice stored at 30 °C and 40 °C decreased below 15.5% (15.33% and 15.22%, respectively) after 1 month, adequate values were maintained with storage at 4 °C for 3 months (15.50%) and at 20 °C for 2 months (15.53%). Rice stored at low temperatures retained its white coloration, whereas low color retention values were obtained at higher storage temperatures. Peak viscosity increased during 4 months of storage and larger changes were found at higher storage temperatures. Breakdown decreased and setback increased with storage, regardless of storage temperatures. Storage at higher temperatures increased cohesiveness and hardness in compared with storage at lower temperatures. High temperatures also led to a decrease in adhesiveness with age. High temperatures (30 °C and 40 °C) significantly decreased all sensory values even after 1 month of storage. These results are similar to those obtained in an analysis of cooked rice texture. The results of this study indicate that storage temperature is an important factor affecting the physicochemical properties of rice. Short storage periods below room temperatures are recommended to maintain rice quality.     

Comparison between lipid and protein oxidation progress in the tail and claw muscles of signal crayfish (Pacifastacus leniusculus)

Microbial activity and then oxidation progress are the most important freshness indicators during post-mortem. In this study, we monitored proteomic and microbial changes, as well as biochemical degradation, in the tail and claw muscles of crayfish stored for 12 days at +4 °C. One specified protein band at 107 kDa in the claw muscle and two specified protein bands in the tail muscle at 140 and 36–40 kDa were identified. Western blotting indicated a higher amount of oxidised proteins in the tail compared to the claw muscle. Tail muscle showed higher oxidation progress and calpain activity than claw one. Both muscles were spoiled after 12 days with respect to total viable counts. In the first days, calpain activity is the main reason for protein degradation, while protein oxidation dominates for the rest of the time. Lipid–protein oxidation progress showed probably, protein oxidation started earlier than lipid oxidation in both muscles.     

Temperature effects on Fossomatic cell counts in goats milk

In cows milk, analytical temperature has been identified as one of the possible factors affecting the somatic cell count (SCC). To establish the effect of the temperature used for SCC in goats milk, counts were performed on 45 goats milk samples using the Fossomatic counter. Tests were performed at two temperatures (40° and 60 °C) on preservative-free samples 3 h after collection, and on samples preserved with bronopol (BR) at 3 h, 1, 2, 3, and 4 d post-collection. The test temperature did not modify the SCC of the milk samples analyzed. Incubating samples 3 h post-collection at 60 °C failed to improve the SCC results. Similar counts were obtained for BR-preserved samples stored for 1–4 d at refrigeration temperature, suggesting the possibility of performing Fossomatic SCC in goats milk samples stored for this length of time.     

Impact of extended refrigerated storage and freezing/thawing storage combination on physicochemical and microstructural characteristics of raw whole and skimmed sheep milk

The impact of freezing (1 month + thawing at 7 or 25 °C) and extended refrigeration (4 days, 7 °C) on physicochemical and microstructural characteristics of raw whole and skimmed sheep milk were assessed. Refrigerated storage resulted in higher sedimentation and creaming (whole milk), possibly due to proteases and agglutinins. Freezing/thawing processes in whole milk increased the particle size and creaming when samples were thawed at 7 °C. Skimmed milk showed an increase in buffering capacity and a reduction in soluble calcium immediately after thawing at 25 °C, suggesting that although the changes in fat are the main alterations caused by slow freezing of sheep milk, minor changes in saline balance can occur. An evaluation of the results showed that frozen and thawed milk in domestic equipment (commonly found in smallholdings) alter the milk microstructure, and it is therefore preferable to use extended refrigeration to accumulate the milk before dairy production.     

Optimising water activity for storage of high lipid and high protein infant formula milk powder using multivariate analysis

High lipid and high protein infant formula milk powders were stored at water activity of 0.11, 0.33 and 0.53 for up to fourteen weeks at 40 °C to investigate the effect of storage water activity on physicochemical properties and formation of volatiles to thereby recommend optimal storage water activity conditions. Water activity of the powders was determined during storage together with surface colour, glass transition temperature combined with dynamic headspace sampling followed by gas chromatography/mass spectrometry. The principal component analysis (PCA) showed that the optimal water activity for storage of high lipid infant formula milk powder, for which lipid oxidation was found to be the critical quality parameter, is a_w = 0.33 with lowest lipid oxidation, while for high protein infant formula milk powder, for which protein degradation was found to be the critical quality parameter, a_w = 0.11 is optimal to limit formation of Maillard reaction products.     

Characterization and storage stability of spray dried soy-rapeseed lecithin/trehalose liposomes loaded with a tilapia viscera hydrolysate

Drying-induced stabilization is a challenge that delivery systems still face. This study aims to investigate the effects of adding trehalose to spray dried soy-rapeseed lecithin liposomes, and the storage stability of the dried liposomes loaded with a tilapia viscera protein hydrolysate, during 42 days at 4 °C and 23 °C, and at different relative humidity (RH). Particle size increased from 215 to 250 nm in fresh liposomes to 258–314 nm after spray drying according to trehalose concentration, all preparations showing a strong electronegative ζ Potential (−48.5 to −59.9 mV). Dried liposomes stored at 4 °C maintained lower polydispersity and higher solubility than those stored at 23 °C. Changes in water activity (A_w), FTIR and DSC revealed structural changes in samples stored at 23 °C and high RH. Spray dried hydrolysate-containing liposomes could be considered as a functional food ingredient due to the substantial antioxidant activity and angiotensin-converting enzyme (ACE) inhibitory capacity after in vitro simulated gastrointestinal digestion.Industrial relevanceThe availability of a natural liposomal preparation in dry powder form, capable to maintain its bioactive properties, is a great advantage for the functional food industry, since it favours the stability, transport and storage of the ingredient prior to use, and allows great versatility to be incorporated in solid restructured products.     

Oxidative status of Kefalotyri cheese during aerobic storage in the dark or under fluorescent light

Kefalotyri cheese made in December and April using milk from sheep grazing on pastures was aerobically kept, in the dark or under fluorescent light, for 40 days at 4°C. Unsaturated fatty acids, which were higher in April than in December cheese, were significantly (P < 0.05) decreased in all cheese samples under both storage conditions. According to lipid hydroperoxides, malondialdehyde and carbonyls changes, grated cheese samples stored under fluorescent light showed a higher protein and lipid oxidation as compared to samples stored in the dark. Sensory and colour characteristics were better for cheeses stored in the dark than those under fluorescent light.     

Osmodehydration assisted by ohmic heating/pulse vacuum in apples (cv. Fuji): retention of polyphenols during refrigerated storage

Apples are a widely consumed fruit and have a high polyphenol content. The aim of this study was to analyse the combined effects of osmotic dehydration (OD) and ohmic heating (OH) with a pulsed vacuum (PV) on polyphenol retention during the stored refrigeration of apple cubes. Treatments were performed using a 65°Brix sucrose solution at 30, 40 or 50 °C for 120 min, and then, samples were stored for 28 days at 5 °C. OH provides an electric field of 13 V cm^?1, and a pulsed vacuum was applied for 5 min at the beginning of the process. The results indicated that a lower temperature process (30–40 °C) resulted in the retention of more polyphenol compounds after treatment than a higher temperature process (50 °C). Nevertheless, during refrigerated storage, we observed that 50 °C preserved these compounds better due to polyphenol oxidase inactivation. PVOD/OH treatment at 50 °C was determined to be the best retention of polyphenols from the fresh apple for dehydrating apples.     

Concentrated whey protein ingredients: A Fourier transformed infrared spectroscopy investigation of thermally induced denaturation

Thermal denaturation of whey protein solutions was investigated from a structural perspective utilising attenuated total reflectance – Fourier transformed infrared spectroscopy (ATR‐FTIR). Solutions (100 g protein/L, pH 7) of commercial whey protein isolate (WPI) powders and enriched protein fractions of β‐lactoglobulin (β‐lg) and α‐lactalbumin (α‐la) were heat‐treated at temperatures of 50–90 °C. Subsequent analysis by ATR‐FTIR highlighted the structural changes occurring as a direct result of heat treatments. Molecularly, WPI dispersions exhibited pronounced differences in denaturation behaviour depending on their method of manufacture. ATR‐FTIR is an informative tool to discern the structural molecular interactions not apparent through physical analysis of concentrated ingredients.     

Effect of dissolved carbon dioxide on the sonocrystallisation and physical properties of anhydrous milk fat

The effects of dissolved CO₂ (0–2000 ppm) coupled with ultrasound (US; 20 kHz) on the physical properties of anhydrous milk fat (AMF) were examined. Carbonated AMF was sonicated at 28 °C for 5 s at various amplitudes and subjected to isothermal (28 °C) and non-isothermal (cooling from 28 to 5 °C) crystallisation conditions. AMF microstructure, thermal properties and hardness were evaluated after 48 h of storage. In general, carbonated AMF samples treated with the same US amplitude exhibited a slight decrease in endset-melting temperature, smaller fat crystals with denser fat crystal network. Dissolved CO₂ caused harder texture of sonicated AMF at 25 °C. However, when carbonated + sonicated AMF samples was stored at 5 °C, their texture appeared to be softer than that of the control sample. A protective effect of CO₂ against formation of primary oxidative products during 90 days of storage was evidenced in both non-sonicated and sonicated AMF.     

Pilot-scale β-casein depletion from micellar casein via cold microfiltration in the diafiltration mode

The aim of this study was to produce pilot scale batches of β-casein concentrate and micellar casein concentrate with reduced β-casein level. The isolation of β-casein was done using membrane filtration at cold temperatures (≤5 °C). A micellar casein concentrate was obtained from skim milk by means of warm microfiltration (MF) at 50 °C (0.1 μm pore size, ceramic membranes). The concentrate was stored at 2–3 °C for approximately 40 h to induce temperature-dependent dissociation of β-casein from casein micelles. β-casein was separated from the cold-stored concentrate using MF (0.3 μm pore size, organic membranes) at ≤5 °C. β-Casein permeate was warmed up to 50 °C to lead self-association of β-casein micelles before ultrafiltration at 50 °C (10 kDa cut-off, organic membranes). Two streams, a β-casein-depleted and a β-casein concentrate, were generated. A purity of 92.64% and a yield of up to 18.07% were achieved for β-casein.     

Protein Stability of Frozen Milk as Influenced by Storage Temperature and Ultrafiltration

Milk and milk concentrates containing 12–35% total solids were stored at 0, –2, –4, –6, –8, –12, and –20°C and protein stability of the thawed products was evaluated periodically. Samples stored at –4 to – 12°C exhibited poorer protein stability than samples stored at higher or lower temperatures. Ultrafiltered (UF) skimmilk with permeate: retentate ratios of 10:90, 20:80, and 30:70 were stored at –8°C and they remained stable at least three times longer than frozen control samples of UF skimmilk stored at the same temperature. When the extent of UF was increased to 40:60, protein stability in the frozen retentate declined somewhat as compared to that of less concentrated retentates.     

Effects of homogenisation pressures on physicochemical changes in different layers of ultra‐high temperature whole milk during storage

The objective of this study was to investigate the effects of homogenisation pressures (10, 20, and 30 MPa) on the physicochemical changes in top, middle and bottom layers of ultra‐high temperature whole milk stored at 25 °C for 6 months. Fat separation, fat globule sizes, fat and protein contents, viscosity, free amino acids content and pH were analysed at an interval of 15 days. Results showed that higher homogenisation pressure retarded the differentiations of milk fat globule sizes, fat and protein contents and viscosity in different milk layers, but did not affect the final fat separation, proteolysis and pH.     

High temperature storage of infant formula milk powder for prediction of storage stability at ambient conditions

Hexanal formation and pentanal formation were found to be early signs of quality deterioration of both a high lipid infant formula milk powder and a high protein infant formula milk powder with similar lactose and water content; these aldehydes were sensitive predictors for shelf-life at ambient conditions using short term storage at temperatures up to 55 °C. Higher temperature loads such as 70 °C were found to induce rapid lactose crystallisation entailing a rising water activity, higher levels of free radicals, rapid browning and formation of Strecker aldehydes from protein degradation, of which all were found to be unsuitable for shelf-life prediction. Advanced glycation end products were not detected during storage at 25 °C for up to 18 weeks and the rate of oxygen consumption for the reconstituted milk drink was not affected by storage of the infant formulas at 25 °C; neither can be recommended for shelf-life prediction.     

Mass spectrometry-based electric nose system for assessing rice quality during storage at different temperatures

A mass spectrometry-based electronic nose (MS e-nose) was used to measure changes in rice quality during storage at different storage conditions. Rice was stored for 4 months at four different temperatures (0 °C, 20 °C, 30 °C, and 40 °C) and tested for fat acidity, sensory characteristics, and flavor pattern analysis using the MS e-nose. When the rice was stored for long durations at higher temperatures, fat acidity increased and sensory quality was low. Flavor volatile profiles of the rice determined by MS e-nose revealed a tendency for the results to separate into three groups (months 1 + 2, 3, and 4). Volatile profile changes in rice during storage depended on the storage time, regardless of storage temperature. It is likely that the fat acidity and sensory evaluation results, which were related, could be distinguished by their volatile-producing metabolic activities. Accordingly, MS e-nose system was successfully used to screen and qualitatively evaluate stored rice.