Chemical characteristics,oxidation and proteolysis in cheese produced from fresh or stored milk subjected to heat treatments

Cheese produced from fresh, stored or heat pretreated (65°C for 15 s) milk subjected to pasteurisation (72°C or 77°C for 15 s) was studied for chemical characteristics and proteolysis after 4 and 21 days of storage. Antioxidant activity was higher in cheese from fresh milk than in cheese from stored and heat pretreated milk. Malondialdehyde content as an index of lipid oxidation increased in cheese made with pretreated and preserved milk than in cheese made with fresh milk. Antioxidant activity and lipid oxidation were not significantly affected by pasteurisation temperature. Proteolysis increased during cheese maturation regardless of milk heat treatments.     

Inactivation kinetics of γ-glutamyltransferase during the heating of milk

The inactivation of γ-glutamyltransferase (GGT, E.C. 2.3.2.2) during the heating of milk to between 65.0°C and 76.0dgC for periods of 5 s to 1000 s follows a first-order reaction (energy of activation 457 kJ/mol) and can be used to monitor the process of milk pasteurisation. GGT activity in raw milks from individual cows showed only little variation (5.92±0.59 units). Residual GGT activity in 17 commercial milks ranged between 1% and 20%, indicating a heat treatment at the upper limit of the permitted pasteurisation conditions.     

The effects of heat applications on macrocyclic lactone-structured antiparasitic drug residues in cows’ milk

ABSTRACT

The study aimed to evaluate the effects of heat on macrocyclic lactone residues in cows’ milk. Ivermectin, abamectin, doramectin, eprinomectin and moxidectin were added to raw milk in three concentrations. The milk was then pasteurised (40 seconds at 74°C or 1 minute at 80°C) and boiled (10 minutes at 100°C). The analyses were performed with a validated method: LC-MS/MS. Thermal treatment resulted in a statistically significant decrease in the abamectin, eprinomectin, and moxidectin concentrations in the milk; however, the residues did not completely degrade. Boiling resulted in a greater decrease in the moxidectin concentrations than was observed with pasteurisation. The high pasteurisation and boiling processes had a greater effect on the eprinomectin residues than did the low pasteurisation process. The pasteurisation and boiling processes did not have an effect on the doramectin and ivermectin. The study concluded that the macrocyclic lactones are generally resistant to such processes.     

Heat resistance of Lactobacillus paracasei isolated from semi-hard cheese made of pasteurised milk

Nine strains of non-starter Lactobacillus paracasei isolated from semi-hard cheese made of pasteurised milk were selected for their anticlostridial activity. Resistance to thermisation (60 °C, 5 min) and pasteurisation (73 °C, 15 s) was investigated using a submerged-coil apparatus. MRS broth-grown cultures of all nine strains survived thermisation in buffer. The level of resistance to thermisation was strain dependent and lower for freshly grown cells (stationary phase cells) than for resting cells (freshly grown cells kept diluted 10-fold in MRS broth at 17 °C for 6 days). None of the nine Lb. paracasei strains survived or recovered after pasteurisation in buffer when grown in MRS broth, while seven of the nine strains survived pasteurisation in UHT whole milk when grown in milk. Identity of the strains was successfully confirmed during the experiments using repetitive-PCR analysis. The potential of Lb. paracasei strains to survive pasteurisation of cheese milk was demonstrated.     

Composition of volatile compounds in bovine milk heat treated by instant infusion pasteurisation and their correlation to sensory analysis

Volatile compounds in skim milk and nonstandardised milk subjected to instant infusion pasteurisation at 80°C, 100°C and 120°C were compared with raw milk, high temperature short time pasteurised milk and milk pasteurised at 85°C/30 s. The composition of volatile compounds differed between infusion pasteurisation treated samples and the reference pasteurisations. The sensory properties of skim milk subjected to instant infusion pasteurisation were described by negative attributes, such as cardboard sour and plastic flavours, which are not associated normally with fresh milk. Partial least squares modelling showed good correlation between the volatile compounds and the sensory properties, indicating the predictive and possible causal importance of the volatile compounds for the sensory characteristics.     

The effect of convective heating and microwave heating on antioxidant enzymes in pooled mature human milk

The effects of convective and microwave heating at constant temperature (62.5, 66 and 70 °C) on the activity of antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPx) in pooled mature human milk were compared. Activities of the enzymes were determined using spectrophotometric kits. Activity of GPx decreased significantly in the first stage of heating when milk samples were warmed to pasteurisation temperature. CAT was the most thermolabile enzyme but microwave heating induced a smaller decrease in CAT activity than convective heating. SOD was most resistant to thermal pasteurisation, regardless of the heating method. SOD and GPx activity temporary increased during microwaves heating. Considering shorter pasteurisation period and lower demand for energy, it can be concluded that microwaves pasteurisation enjoys special merits. However, still there is no clear answer as to whether the microwave field itself can affect the antioxidant enzymes of human milk.     

Tetracycline antibiotics transfer from contaminated milk to dairy products and the effect of the skimming step and pasteurisation process on residue concentrations

The presence of antibiotics in raw milk and milk derivatives poses a threat to human health and can negatively affect the dairy industry. Therefore, the main object of this study was to investigate the transfer of oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC) and doxycycline (DC) from raw, experimental milk contaminated with tetracyclines (TCs) to different dairy products: cream, butter, buttermilk, sour milk, whey, curd and cheese. Additionally the effect of the skimming process on TCs concentrations was tested, as well as the influence of low-temperature long-time pasteurisation. The analyses of TCs in milk and dairy products were performed by an LC-MS/MS method. In order to determine TCs residues in dairy products, an analytical method was developed with the same extraction step for all matrices. TCs molecules were inhomogenously distributed between the milk derivative fractions. The highest concentrations were determined in curd and cheese in the ranges 320–482 µg/kg and 280–561 µg/kg, respectively. Low levels of TCs in butter and whey were observed (11.8–41.2 µg/kg). TCs were found in sour milk (66.0–111 µg/kg), cream (85.0–115 µg/kg) and buttermilk (196–221 µg/kg) at much higher levels than in butter and whey, but lower than in curd and cheese. During the skimming process, the highest yield of cream was obtained after the raw milk was held at 2–8°C for 24 h. The differences in concentrations of TCs between whole milk and skimmed milk, expressed as percentages of recovery, were below 19% (recoveries in excess of 81%). The highest content was observed in milk and cream skimmed at 2–8°C. The degradation percentages for TCs during the pasteurisation process (63°C for 30 min) were below 19%.     

Effect of cream aging temperature and agitation on butter properties

Aging of cream is an important process to manage production time and to produce butter with consistent quality. The objective of this study was to evaluate the combined effect of temperature (5, 10, and 15°C) and agitation rate (0, 40, and 240 rpm) during aging of cream on the physical properties of cream and butter in a model system. Cream's solid fat content (SFC), melting behavior, and droplet size distribution were measured during and after 90 min of aging. Butter physical properties such as melting behavior, water content, and hardness were measured. The effects of agitation on SFC and droplet size are dependent on aging and churning temperature. Solid fat content increased faster at 5°C, and the maximum SFC was the highest at this temperature. An effect of agitation on SFC was observed only when cream was aged at 15°C. Agitating cream at 40 rpm increased the droplet size regardless of aging temperature. Two melting peaks, medium melting fraction (MMF) and high melting fraction (HMF), were found in cream samples aged at 5 and 10°C, but only a HMF melting peak was seen in the cream aged at 15°C. The enthalpy of MMF in the cream aged at 10°C with 40 rpm and without agitation was significantly lower than that in samples aged at 5°C regardless of agitation rate. Butter can be formed only from cream aged under certain conditions during 14.5 min of churning, which are 5°C with high agitation and 10°C regardless of agitation level. Butter produced with cream aged at 5°C with high agitation showed significantly higher MMF and total enthalpy values. However, no significant difference in enthalpy values was observed among the butter samples made from the cream aged at 10°C. Further crystallization of MMF occurred in the butter produced with cream aged at 10°C during 24 h of storage at 5°C, whereas no further crystallization occurred in the butter made with the cream aged at 5°C with high agitation. The hardest butter was obtained when cream was aged at 5°C with 240 rpm and at 10°C with 40 rpm. Softer butter was obtained when cream aged at 10°C with 240 rpm was used. This butter also had the highest water content. This study shows that butter hardness can be tailored by changing the aging conditions of the cream. Cream can be aged at higher temperature with low agitation without altering the hardness of butter. These results will help dairy producers to optimize butter making processes to obtain desired properties in the final product.     

Are we closer to understanding why viable cells of Mycobacterium avium subsp. paratuberculosis are still being reported in pasteurised milk?

Mycobacterium avium subsp. paratuberculosis (MAP) continues to be associated with Crohn’s disease. Following work in the 1990s that suggested that statutory pasteurisation of milk (72 °C, 15 s) was insufficient to destroy MAP, the UK Dairy Industry increased the holding time to 25 s. Since then, some plants have increased the lethality of pasteurisation further with a number using 78 °C for 27 s. Despite the increase in lethality, a recent survey of pasteurised milk in England found that 10.3% of pasteurised milk samples tested positive for viable MAP. This article discusses the significance of MAP and why viable MAP might be found in pasteurised milk.     

HEATING BEHAVIOR AND QUALITY FACTOR RETENTION IN A CANNED MODEL FOOD AS INFLUENCED BY THERMAL PROCESSING IN A ROTARY RETORT

Heat penetration data were obtained for a canned model food (gelatinized starch) during processing in a rotary retort under various conditions (retort temperature, 110–130C; rotation speed, 10–20 rpm, can headspace 6.4–12.8 mm and starch concentration, 3–4%) to establish thermal processes with an equivalent lethality (F₀ value) of 10 min. Apparent viscosity and Hunter L, a and b values were experimentally evaluated both before and after each run. The percentage of selected quality factors (nutrients, color) retained at each processing condition was estimated using the heat penetration data and documented kinetic parameters for each quality factor. The study indicated that the heating behavior was influenced (p < 0.05) by all factors except can headspace. Higher temperatures and higher rotation speeds favored better retention of quality factors and reduction in process times.     

Distribution of 45Ca between soluble and colloidal phases of buffaloes' milk as affected by processing

The distribution of ⁴⁵Ca between the soluble and colloidal phases of skimmed buffaloes' milk, and the effects of five processing treatments, was determined by the rennet coagulation technique. The five processing treatments consisted of pasteurisation (at 71.8°C for 15 s), pre-warming (at 96°C for 5 min), sterilisation (at 121.5°C for 15 min), and cooling (for 24 h at 4–6 and 0°C). The proportion of ⁴⁵Ca in the soluble phase of raw milk was about 44% (in vitro) and 37% (in vitro), while that of original Ca was about 21% (control). In vitro, pasteurisation, pre-warming and sterilisation progressively decreased the amount of ⁴⁵Ca incorporated into the soluble phase to about 39, 31 and 27%, respectively. The decline of incorporated ⁴⁵Ca was statistically significant (P < 0.01) for the prewarming and sterilisation of milk. In vitro, the decline of incorporated ⁴⁵Ca or the transfer of ⁴⁵Ca from the soluble to the colloidal phase due to the heat treatment, was small, irregular and not significant. Changes due to cooling were not significant for any of the experiments. Significantly different results were observed for the partitioning of Ca when comparisons were made between in-vitro introduced ⁴⁵Ca and original Ca, and between in-vivo incorporated ⁴⁵Ca and original Ca.     

Determination of insulin-like growth factor-1 and bovine insulin in raw milk and its casein and whey fractions after microfiltration and ultrafiltration

Insulin-like growth-factor 1 (IGF-1) and insulin were analysed from bovine milk during microfiltration (MF) and ultrafiltration (UF) processes using immunochemical methods. IGF-1 was found in the MF retentate and in the UF retentate. A very small fraction of IGF-1 was in the UF permeate. The results indicated that IGF-1 was present in milk as a complex molecule or bound to milk proteins. Insulin showed similar behaviour, but more insulin was found in the MF retentate than in the UF retentate. No insulin was found in the UF permeate. There were no differences in IGF-1 or insulin distribution between pasteurised or non-pasteurised milk. The stability of bovine insulin to heat treatments was also determined. The molecule was stable during pasteurisation at 65 and 72 °C, but lost some of its immunochemical activity at 90 and 135 °C.     

Microbial and enzymatic changes in natural soursop puree during storage

Microbial and enzymatic comparisons were made on natural soursop puree stored at 15, 4 and −20°C without pasteurisation and with pasteurisation at 79°C for 69 s. Results showed that pasteurisation caused significant decrease in microbial count in soursop puree from 6.4×10³ to 8.5×10¹ cfu per g. Generally, storage at −20°C exhibited greater stability of samples as compared to those kept at 4 and 15°C. In contrast to microbial reduction, pasteurisation caused significant increase in cloud from 0.318 to 0.529 and completely inactivated the pectinesterase enzyme. The puree packed into foils kept at 4°C exhibited decreased cloud loss as compared to others packed in cans and bottles kept at 15 and −20°C. No pectinesterase enzyme regeneration was observed for pasteurised puree in this study during 12 weeks of storage time.     

Contribution of proteolytic activity associated with somatic cells in milk to cheese ripening

The effect of proteolytic enzymes from somatic cells on cheese quality was studied. In preliminary experiments, milk and two sodium caseinate systems (pH 6.5 and pH 5.2, the latter in the presence of 5% NaCl) were used as substrates to investigate the proteolytic activity of somatic cells recovered from mastitic milk. Urea-polyacrylamide gel electrophoretograms of hydrolysates suggested that somatic cell extracts contributed directly to proteolysis both in buffer and in milk, but that such activity was reduced by batch pasteurisation (63 °C for 30 min). Sodium caseinate was readily hydrolysed by somatic cell extracts; hydrolysis of α_s1-casein was greater at pH 5.2 and increased with level of somatic cells, suggesting that somatic cells contain proteolytic enzymes which are more active at acidic pH values. Subsequently, miniature Cheddar-type cheeses were made from batches of milk to which somatic cells were added (at levels of levels of 3×10⁵ or 6×10⁵ cells mL⁻¹), either before or after pasteurisation. Proteolysis during ripening of cheese (as measured by levels of pH 4.6-soluble nitrogen) increased with somatic cell addition, although this effect was reduced by pasteurisation after cell addition. Somatic cells may also have directly influenced cheese moisture content, which has been established as a principal indicator of quality of Cheddar-type cheese. Proteolytic enzymes of somatic cells from milk were shown to contribute directly to proteolysis in milk and cheese.     

Effects of different saccharides on the microstructure and functional properties of protein in goat milk during processing

This study investigated the changes in the characteristics of goat milk protein in the presence of trehalose, chitooligosaccharide and pectin during two practical dairy processing operations of pasteurisation and spray drying. The highest denaturation temperature and the largest particle size of milk protein were found in goat milk added with pectin after pasteurisation. And particles with more uniform and compact morphology were observed in goat milk protein with these three saccharides. An elevated emulsifying activity index of 24.37 m/g⁻² was observed in protein after spray drying due to chitooligosaccharide. And the foam stability was also improved significantly in the presence of trehalose and pectin during pasteurisation. During spray drying, saccharides showed the stabilizing effect on goat milk protein. This study revealed a complex interplay between the type of saccharides and the processing operation applied to goat milk, which might be of great significance for the production and processing of goat milk.     

Vitamin Retention, Color and Texture in Thermally Processed Green Beans and Royal Ann Cherries Packed in Pouches and Cans

Thiamin (B-1) ascorbic acid (AA) and vitamin B-6 (B-6) were determined in pouched and canned green beans immediately after processing and after storage at 24–26°C or 38°C. AA and B-6 were also determined in pouched and canned cherries before and after storage at 24–26°C. There was significantly more B-1 and AA in drained pouched green beans, and more AA in drained pouched cherries than in canned ones. B-6 values in the solids of the pouched and canned products were not significantly different. These three vitamins were significantly reduced in drained pouched and canned green beans after storage at 38°C. B-6 was significantly reduced in the stored cherries. Compared to canned, the pouched products were brighter and firmer in texture.     

Modelling of Vitamin C Degradation during Thermal and High-Pressure Treatments of Red Fruit

Vitamin C is known for its potent antioxidant properties. Since humans lack one of the final enzymes in the biosynthesis of this vitamin, they are dependent on dietary sources for their vitamin C needs. Strawberries are good sources of vitamin C, but the vitamin is unstable during food processing, and high temperatures have shown to induce rapid degradation. As an alternative preservation technique, high-pressure processing is investigated for its potential to achieve pasteurisation and sterilisation conditions at lower process temperatures and shorter treatment times compared to thermal processing. The objective of the present study was to examine quantitatively the effect of processing on vitamin C in strawberry and raspberry matrices by comparing thermal treatments (80–140 °C) to treatments at 700 MPa (60 °C, 90 °C and 110 °C). To this end, a mechanistic model was proposed and tested to fit the degradation of ascorbic acid (AA) and the consecutive formation and degradation of dehydroascorbic acid (DHAA). AA degradation followed a biphasic course: the aerobic reaction was fast and most important, while the anaerobic reaction was slow and only perceptible at temperatures of 120 °C and up. The oxidation of AA to DHAA was slower than the subsequent degradation of DHAA in the strawberry matrix; the opposite was true in the raspberry matrix. Both temperature and pressure enhanced the degradation of vitamin C. The proposed mechanistic model provided reasonably good fits to the experimental data, only to a lesser extent for the DHAA evolution during high-pressure processing.     

Determining convective heat transfer coefficient during sterilisation of canned evaporated whole milk

The effect of retort temperature, rotation speed, headspace and radius of rotation on mean convective heat transfer coefficient during sterilisation of canned evaporated whole milk was studied. The mean total solids content of evaporated milk obtained in a pilot plant installation was 25.25 g/100 g. Processing variables used ranged as follows: retort temperature: 117-123 °C; speed of rotation: 10-20 rpm; headspace: 4-12 mm; radius of rotation: 3.5-16.5 cm. The model developed for heat transfer coefficient was adequate, showing no significant lack of fit and satisfactory coefficient of determination. Retort temperature, speed of rotation, headspace and radius of rotation have a significant effect. Dimensional correlations were developed for convective heat transfer coefficient, in terms of Nusselt number as a function of Reynolds number, Prandtl number and relative headspace; the best agreement was obtained using the diameter of rotation as the characteristic dimension.     

The effect of pasteurisation temperature on the CLA content and fatty acid composition of white pickled cheese

In this study, the effect of pasteurisation temperature on fatty acid composition of cheese was investigated. The fatty acid composition of raw and different heat‐treated milk, salt and salt‐free cheese were determined using cheese made from raw milk at temperatures varying between 70 and 90°C for 5 min. Generally, C 16:0 palmitic acid was the major fatty acid present in all milk and cheese samples. C 18:1 t11 vaccenic acid was the major trans fatty acid (TFA) in all samples. C 18:2 cis‐9, trans‐11 (Rumenic acid) was the major CLA isomer in these samples. Pasteurisation temperatures had no effect on TFA, CLA and fatty acid composition of the milk and cheese samples.     

Effect of mechanical treatments applied to milk fat on fat retention and lipolysis in minicurds

The aim of this work was to identify a treatment on milk fat, applicable to pretreat cheese milk, which could enhance lipolysis. Three factors were studied in milk fat mixtures: physical treatment (pumping and mechanical agitation), temperature (5, 15, and 45°C) and fat content (5%, 15%, and 30%). Damage to fat globule was estimated by assessing free fat and by phase contrast microscopy. Moderate damage was achieved in a mixture of 30% of fat, treated with mechanical agitation at 2800 rpm/2 min at 5°C. Applying this procedure to prepare minicurds did not modify values of fat content, moisture and lipolysis.