Ultra-high Temperature Milk Samples Research Articles

The impact of different temperatures on spore count and browning of UHT milk over a long storage period

One of the major microbiological challenges for the ultra-high temperature (UHT) milk industry is the presence of sporeformers in milk, which can survive pasteurization and the UHT process. The present study has aimed to investigate the spore populations in UHT milk stored at 20 °C and 35 °C for 14 months. Samples of bulk tank milk, pasteurized milk, and UHT milk were randomly assigned to different temperatures and storage times and were analyzed to study the mesophilic populations of aerobic spores and any color changes. The results showed that aerobic sporeformers can survive the UHT process. Bacillus licheniformis group and Bacillus pumilus group were the most isolated aerobic sporeformers. The b∗ value increased significantly in samples stored at 35 °C. These data provide information on the aerobic spore populations of bulk tank milk and UHT milk produced in different seasons and stored at different temperatures for 14 months.

Tahran, İran'da yüksek performanslı sıvı kromatografi ile süt ve süt ürünlerinde aflatoksin M1 içeriğinin değerlendirilmesi

Aflatoxin M1 (AFM1) is the most important aflatoxin in milk and dairy products, which is carcinogenic and hepatotoxic. This study aimed to evaluate the AFM1 content in the milk and distributed dairy products in Tehran. 75 samples, including 15 samples of raw milk, 15 samples of pasteurized milk, 15 samples of ultra-high temperature milk, 15 samples of pasteurized yogurt, and 15 samples of pasteurized cheese, were collected from October to December 2020 in Tehran by simple random sampling. The dietary exposure or estimated dietary intake (EDI) and hazard index (HI) were calculated for milk and dairy product consumers. The AFM1 content in the samples was determined by using high-performance liquid chromatography (HPLC) along with a fluorescence detector. AFM1 was observed in all samples. The values of AFM1 in all samples were higher than the acceptable range determined by the European Union. 100% of milk and yogurt samples and 82% of cheese samples exceeded the Iranian maximum limit (100 ng kg-1 in milk and yogurt, and 250 ng Kg-1 in cheese). Mean AFM1 content in raw milk samples, pasteurized milk samples, UHT milk samples, pasteurized yogurt samples, and pasteurized cheese samples were 337±17.7, 306±15.5, 305±17.4, 320±17.6, and 309±18.5 ng Kg-1, respectively. The highest value of HI was observed in children of Tehran, Iran. Based on the results, the aflatoxin content in milk and distributed dairy products in Tehran in the autumn is inconvenient. It is recommended that the aflatoxin levels should be measured at different times of the year, especially in raw milk, and feed monitoring is intensified for contamination with toxin-producing molds.

Occurrence of Aflatoxin M1 in Milk and Dairy Products Traded in São Paulo, Brazil: An Update

The aim of this study was to conduct an up-to-date investigation on the occurrence levels of aflatoxin M1 (AFM1) in samples of raw milk (n = 40), pasteurized milk (n = 44), ultra-high temperature (UHT) milk (n = 27), Minas cheese (n = 57), and yogurt (n = 44) traded in São Paulo state, Brazil. AFM1 was extracted from fluid milks and dairy products using immunoaffinity columns and determined by high performance liquid chromatography. AFM1 was detected at the mean level of 0.080 ± 0.071 µg/L or kg in 72 samples (34.0%) evaluated in the study (n = 212). Detectable levels of AFM1 were observed in five samples of raw milk (12.5%), 16 samples of pasteurized milk (36.4%), 13 samples of UHT milk (48.1%), 27 samples of cheese (47.4%), and 11 samples of yogurt (25.0%), although none of them had concentrations above the maximum permitted levels (MPL) for AFM1 adopted in Brazil. However, 11.7% (n = 13) of samples of raw, pasteurized, and UHT milks would have AFM1 concentrations above the MPL of 0.05 μg/L adopted in the EU. The maximum level was detected in one cheese sample containing 0.695 µg/kg. Although none of the samples exceeded the Brazilian MPL, the high frequencies of AFM1 in Brazilian milk products warrant concern about their contribution to the human exposure to aflatoxins. Because aflatoxins are among the most potent carcinogens known, the results of this trial stress the need for stringent measures in the milk production system to avoid AFM1 in milk and derived products.

Loss of UHT milk quality: changes in compositional and physicochemical parameters triggered by different storage conditions

The objective of this study was to evaluate some compositional and physicochemical changes that occur during UHT (Ultra-high temperature) milk storage for up to four months. A total of 120 samples of UHT milk were collected from two dairy plants in the state of Minas Gerais, Brazil, and stored under two temperatures (20°C and 30°C) during five periods (0, 30, 60, 90 and 120 days). The experimental design was completely randomized, in a 2x2x5 factorial arrangement, with six replicates per treatment (six batches). Evaluated parameters included fat, total protein, casein, lactose, total solids, solids nonfat (SNF) and milk urea nitrogen (MUN) contents, as well as acidity, density, freezing point and indexes of lipolysis and caseinomacropeptide (CMP). When compared to the Brazilian requirements for UHT milk, the mean values ​​for acidity, fat and SNF contents were in accordance with the standards ​​until the last day of storage. The other parameters are still not covered by the specific UHT milk legislation in Brazil. There was no change of relative density and lactose content also remained constant, except for a decrease at the fourth month. A significant increase, over storage time, in acidity, MUN, lipolysis and CMP indexes occurred. On the other hand, there was a significant decrease in SNF and protein contents. The results showed that there was a gradual loss of quality during UHT milk storage, aggravated by the rise in temperature. These findings demonstrate that UHT milk legislation could be improved by adding parameters such as lipolysis and CMP indexes.

Dietary Exposure and Health Risk Assessment of Aflatoxin M1 in Dairy Products Consumed by Population of North Macedonia

Background: Aflatoxins (AFs), as secondary metabolites, are mainly produced by fungi of Aspergillus genus. The determination of contamination rate, dietary exposure, and health risk assessment for aflatoxin M1 (AFM1) was conducted aimed to estimate potential health risks for the population of North Macedonia.
 Methods: A total of 974 dairy samples, including 404 Ultra-High Temperature (UHT) milk, 291 ice cream, 178 yogurt, and 101 cheese were collected from the markets in North Macedonia. Analysis of AFM1 was done using Enzyme-Linked Immunosorbent Assay and High-Performance Liquid Chromatography with Fluorescence Detection.
 Results: The AFM1 incidence was highest in yogurt samples (93.8%) and lowest in UHT milk samples (67.8%). AFM1 concentrations were 49.1±68.4, 30.9±30.0, 35.1±40.4, and 40.1±90.1 ng/kg for UHT milk, ice cream, yogurt, and cheese samples, respectively. The Estimated Daily Intake (EDI) for the average population and high consumers (upper bound; samples with AFM1<Limit of Detection (LOD) were 0.150 and 0.456 ng/kg body weight (bw)/day, respectively. The Hazard Index (HI), Margin of Exposure (MoE), and the fraction of Hepatocarcinoma (HCC) cases per 100,000 inhabitants for the average population reached values of 0.33, 8533, and 0.004, respectively.
 Conclusion: To our best knowledge, this is the first report of dietary exposure and risk assessment of AFM1 in dairy products of North Macedonia, revealing a potential risk of AFM1 in population of this country.

Aflatoxin M1 in Ultra High Temperature Milk Consumed in Sharjah, United Arab Emirates

Background: Aflatoxin M1 (AFM1) is a mycotoxin found in milk that has a carcinogenic effect and poses significant public health risks. Since the human population's consumption of milk and milk products are quite high, thereby increasing the risk of exposure to AFM1 is of great threat. To assess public health hazards associated with the occurrence of AFM1 in Ultra High Temperature (UHT) milk, a survey was carried out in Sharjah, United Arab Emirates (UAE).
 Methods: A total of 42 UHT milk samples from different commercial brands were collected from January to April 2020. The occurrence and concentration range of AFM1 in the samples were investigated by applying the competitive Enzyme Linked Immunosorbent Assay (ELISA) method.
 Results: AFM1 was detected in four positive samples (9.5%) with a concentration range of 2.8-7.4 ng/L and a mean concentration of 5.2±1.9 ng/L. However, none of the positive samples had AFM1 levels exceeding the maximum permissible limit (50 ng/L) as set by the European Commission.
 Conclusion: AFM1 incidence in the samples selected from UHT consumed milk in Sharjah-UAE is very low and seems to be no serious public health problem at the moment. Frequent analytical surveillance by food control agencies is highly recommended to keep controlling of the incidence of mycotoxin contamination in dairy products consumed in the UAE.

Two-year survey of aflatoxin M1 in milk marketed in Albania, and human exposure assessment

Aflatoxin M1 (AFM1), a metabolite of aflatoxin B1 (AFB1), is detected in milk obtained from ruminants fed AFB1-contaminated feedstuff. Considering the potential risk of aflatoxin exposure for human health, the AFM1 content in milk and dairy products is regularly monitored. A survey on AFM1 contamination in milk from retail markets consumed in Albania was conducted in 2019–2020. A total of 119 cow milk samples, subjected to pasteurization and ultra-high temperature (UHT) treatment, were collected, and the AFM1 content was analyzed using a commercial enzyme-linked immunosorbent assay kit. AFM1 was detected in 62 of the 119 milk samples (52.10%). AFM1 contamination in pasteurized milk was higher than that in UHT milk samples (59.68% and 43.86%, respectively). Although the mean AFM1 concentration for the analyzed samples was 0.022 μg kg−1, the maximum AFM1 content of 0.217 μg kg−1 was found in milk samples collected in the autumn of 2019. Seven milk samples (5.88%) contained AFM1 at levels exceeding the European Union maximum residue permitted level. Overall, milk samples from 2019 had greater AFM1 contamination (81.36%) than those from 2020 (23.33%). The Human Exposure Assessment revealed that the Average Daily Dose (ADD) for adults was 0.082–0.096 ng kg−1 body weight (bw)/day. Also, the ADD was considerably higher in 2019 than in 2020 with no significant difference between the seasons.

The effects of packaging type and storage temperature on some of UHT milk quality indexes.

The objective of the present study was to illustrate the changes in physicochemical properties in ultra-high temperature (UHT) milk packed into a pouch and Tetra Brik during storage. UHT milk samples were kept at 5 and 25 °C for 3 months and regularly analyzed monthly. During storage, significant increases (p < 0.05) in titratable acidity (TA), water-soluble nitrogen (WSN), and non-protein nitrogen (NPN) when UHT milk was packed into pouch versus Tetra Brik and stored at 25 versus 5 °C. Neither type of packaging nor storage temperature affect pH values during storage. Spore-forming bacterial (SFB) count was always higher in UHT milk packed into pouch versus Tetra Brik. Refrigerated storage kept UHT milk without detectable SFB compared to UHT milk held at 25 °C. Pouch packages were responsible for the migration of phthalate derivatives [dimethyl phthalate "DMP", diethyl phthalate "DEP", dibutyl phthalate "DBP", and di-(2-Ethylhexyl) phthalate "DEHP"] into milk with significantly greater levels than milk filled into Tetra Brik. The total sensory scores were decreased significantly during storage, which was more pronounced in UHT milk filled into pouch versus Tetra Brik or stored at 25 °C versus 5 °C. It is concluded that UHT milk filled into Tetra Brik stored at 5 and 25 °C is better in terms of quality and safety indexes than such filled into a pouch.

A new and accessible instrumentation to determine urea in UHT milk using digital image analysis

This research demonstrates the development, optimization and application of a new low-cost detection system, based on digital image analysis, for the detection of urea in ultra-high-temperature (UHT) milk samples. The apparatus built in the laboratory, allows the capture of images through a simple system built by polyvinyl chloride (PVC) tubes, a digital microscope and a peristaltic mini-pump, after the colorimetric reaction between urea and diacetylmonoxime (butane-2,3-dionammonoxime). The red, green and blue (RGB) and hue, saturation and value (HSV) color systems were studied, with the saturation channel of the HSV color system selected as the analytical signal. Subsequently, the experimental chemical conditions were evaluated through multivariate experimental designs and the optimal conditions were defined. The proposed method was validated, and the detection and quantification limits presented by the method were 0.35 mg L−1 and 0.52 mg L−1, respectively; precision, ranged between 1.6 and 2.8 %. The results were compared with those obtained using the mid-infrared technique and no statistically significant differences were observed at a 95 % confidence level. The proposed method was applied to eight UHT milk samples that presented urea content ranging from 187 to 386 mg L−1. The mean values obtained are in agreement with values presented in other studies for the determination of urea in milk. The results indicated that the system described and validated here is promising and can be applied to assess the authenticity and quality of milk.

English

The aim of this study was to determine the level of aflatoxin M1 (AFM1) in pasteurized and UHT milk marketed in Dar es Salaam, Tanzania.&nbsp; AFM1 in pasteurized milk samples (75) and ultra-high temperature (UHT) milk (43) was determined by using immuno-affinity high performance liquid chromatography. AFM1 was detected in 97% (115/118) of samples that consisted of 96% (72/75) of pasteurized milk samples and 100% (43/43) of UHT milk samples. About 82% of the contaminated pasteurized and UHT had AFM1 levels above EU acceptable levels (0.05 &micro;g/L). However, none of the contaminated pasteurized and UHT milk sample had levels of AFM1 above the maximum recommended Codex limits (0.5 &micro;g/L). The results indicate that the contamination of the samples with AFM1 at such level could pose a serious public health problem. Thus, regular monitoring of AFM1 levels in milk is important in order to protect consumers.&nbsp; &nbsp; Key words: Aflatoxin M1, ultra-high temperature (UHT), milk, pasteurized milk, food safety.

The Presence of Aflatoxin M1 in Milk and Milk Products in Bangladesh.

As milk provides both micro- and macronutrients, it is an important component in the diet. However, the presence of aflatoxin B1 (AFB1) in the feed of dairy cattle results in contamination of milk and dairy products with aflatoxin M1 (AFM1), a toxic metabolite of the carcinogenic mycotoxin. With the aim to determine AFM1 concentrations in milk and milk products consumed in Bangladesh, in total, 145 samples were collected in four divisional regions (Sylhet, Dhaka, Chittagong, and Rajshahi). The samples comprised these categories: raw milk (n = 105), pasteurized milk (n = 15), ultra-high temperature (UHT)-treated milk (n = 15), fermented milk products such as yogurt (n = 5), and milk powder (n = 5). AFM1 levels in these samples were determined through competitive enzyme-linked immunosorbent assay (ELISA). Overall, AFM1 was present in 78.6% of milk and milk products in the range of 5.0 to 198.7 ng/L. AFM1 was detected in 71.4% of raw milk (mean 41.1, range 5.0–198.7 ng/L), and in all pasteurized milk (mean 106, range 17.2–187.7 ng/L) and UHT milk (mean 73, range 12.2–146.9 ng/L) samples. Lower AFM1 levels were found in yogurt (mean 16.9, range 8.3–41.1 ng/L) and milk powder samples (mean 6.6, range 5.9–7.0 ng/L). About one-third of the raw, pasteurized, and UHT milk samples exceeded the EU regulatory limit (50 ng/L) for AFM1 in milk, while AFM1 levels in yogurt and milk powder samples were well below this limit. Regarding regions, lower AFM1 contamination was observed in Chittagong (mean 6.6, max 10.6 ng/L), compared to Sylhet (mean 53.7, max 198.7 ng/L), Dhaka (mean 37.8, max 97.2 ng/L), and Rajshahi (mean 34.8, max 131.4 ng/L). Yet, no significant difference was observed in AFM1 levels between summer and winter season. In conclusion, the observed frequency and levels of aflatoxin contamination raise concern and must encourage further monitoring of AFM1 in milk and milk products in Bangladesh.

Aflatoxin M1 in pasteurized, ESL and UHT milk products from central China during summer and winter seasons: Prevalence and risk assessment of exposure in different age groups

This study aimed to investigate aflatoxin M1 (AFM1) contamination in pasteurized, extended shelf life (ESL) and ultra-high temperature (UHT) milk in central China in winter and summer, and to assess the risk of exposure to milk AFM1 in 10 different age groups. A total of 547 milk samples were collected in Henan, Hubei and Hunan provinces from 2019 to 2020, of which 142 pasteurized milk samples, 68 ESL milk samples and 69 UHT milk samples were collected in summer, and 161 pasteurized milk samples, 79 ESL milk samples and 28 UHT milk samples were collected in winter.The concentrations of AFM1 in these samples were determined by ELISA, with a recovery and relative standard deviation of 95.0–98.6% and 3.31–4.18%, respectively. AFM1 was detected in 431 samples (78.8%) with an average concentration of 19.6 ng/L in positive samples. The AFM1 concentrations in 29 samples (5.3%) were higher than the maximum residue level (MRL) of 50 ng/L set by the EU, but much lower than the value of 500 ng/L set by China. The average concentration of AFM1 (25.4 ng/L) in winter milk was 88.1% higher (p < 0.05) than that (13.5 ng/L) in summer. The concentration of AFM1 in UHT milk was lower (p < 0.05) than that in pasteurized and ESL milk in both winter and summer. Children aged 2–4 years had the highest risk of exposure to AFM1 in milk, with a mean estimated daily intake of 0.22 ng/kg bw/day. Therefore, it is necessary to strictly detect and prevent AFM1 contamination in milk, especially in winter, to reduce the risk of AFM1 exposure in humans.

A Survey of 61 Veterinary Drug Residues in Commercial Liquid Milk Products in China

To investigate the drug residue status in commercial liquid milk products in China, 190 samples, including ultrahigh temperature milk (n = 168) and pasteurized milk (n = 22) samples, were collected in 2019. Milk samples were analyzed for the presence of any of the 61 veterinary drugs in them by using a screening assay combined with an ultraperformance liquid chromatography-tandem mass spectrometry analysis. Ten (5.26%) samples were found positive for β-lactams, tetracyclines, and aminoglycosides, and six (3.16%) samples were confirmed residual for penicillin G (n = 6; 3.16%), tetracycline (n = 1; 0.53%), and oxytetracycline (n = 1; 0.53%), with the maximum concentration of 2.85, 40.64, and 12.35 μg kg-1, respectively. Drug residue detection rate in group II (4.55%; the local city domestic brands) was higher than that in group I (2.70%; the major brands of China) and group III (2.78%; the imported brands into China) and higher in domestic samples (3.39%) than that in imported samples (2.78%), and higher in pasteurized milk samples (9.09%) than in ultrahigh temperature milk samples (2.38%). All drug residue levels were far below the regulated maximum residue limits. However, based on some veterinary drug residues detected in the samples, there is a potential veterinary drug risk in liquid milk products in the Chinese market, and this situation deserves the attention of governments and consumers.

Trapping of Carbonyl Compounds by Epicatechin: Reaction Kinetics and Identification of Epicatechin Adducts in Stored UHT Milk.

The kinetics of the reaction between epicatechin and various carbonyl compounds typically formed in cooked and stored foods were evaluated in model systems at pH 7.4 and 37 °C, and the corresponding reaction products in stored ultrahigh temperature (UHT) milk-added epicatechin were identified by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The rate constants for the reactions of carbonyl compounds with epicatechin decreased in the following the order: methylglyoxal; 1.6 ± 0.2 M-1 s-1 > glyoxal; (5.9 ± 0.3) × 10-2 M-1 s-1 ≥ 5-(hydroxymethyl)furfural; (4.0 ± 0.2) × 10-2 M-1 s-1 ≥ acetaldehyde; (2.6 ± 0.3) × 10-2 M-1 s-1 ≥ phenylacetaldehyde; (2.1 ± 0.2) × 10-2 M-1 s-1 ≥ furfural; (4.3 ± 0.1) × 10-3 M-1 s-1 > 2-methylbutanal and 3-methylbutanal; ∼0 M-1 s-1. Reaction products generated by epicatechin and methylglyoxal, glyoxal, 5-(hydroxymethyl)furfural, and acetaldehyde were detected in UHT milk samples by incubating milk samples with epicatechin at 37 °C for 24 h. The lack of reaction between epicatechin and phenylacetaldehyde, furfural, 2-methylbutanal, and 3-methylbutanal in stored UHT milk may be due to their slow reaction rates or low concentration in stored UHT milk. It is demonstrated that epicatechin traps 5-(hydroxymethyl)furfural, acetaldehyde, glyoxal, and methylglyoxal and may thereby reduce off-flavor formation in UHT milk during storage both by trapping of precursors (methylglyoxal and glyoxal) for off-flavor formation and by direct trapping of off-flavors.

Prevalence of Milk Fraud in the Chinese Market and its Relationship with Fraud Vulnerabilities in the Chain.

This study aimed to assess the prevalence of ultra-high-temperature (UHT) processed milk samples suspected of being adulterated on the Chinese market and, subsequently, relate their geographical origin to the earlier determined fraud vulnerability. A total of 52 UHT milk samples purchased from the Chinese market were measured to detect possible anomalies. The milk compositional features were determined by standardized Fourier transform-infrared spectroscopy, and the detection limits for common milk adulterations were investigated. The results showed that twelve of the analysed milk samples (23%) were suspected of having quality or fraud-related issues, while one sample of these was highly suspected of being adulterated (diluted with water). Proportionally, more suspected samples were determined among milks produced in the Central-Northern and Eastern areas of China than in those from the North-Western and North-Eastern areas, while those from the South were in between. Combining the earlier collected results on fraud vulnerability in the Chinese milk chains, it appears that increased fraud prevalence relates to poorer business relationships and lack of adequate managerial controls. Since very few opportunities and motivations differ consistently across high and low-prevalence areas, primarily the improvement of control measures can help to mitigate food fraud in the Chinese milk supply chains.

Assessment of proteolysis in ultra‐high temperature milk using attenuated total reflectance–Fourier transform infrared spectroscopy

This study investigated the suitability of attenuated total reflectance–Fourier transform infrared spectroscopy (ATR‐FTIR) as an alternative technique to assess proteolysis in ultra‐high temperature (UHT) milk. Commercial UHT milk samples were stored (5 and 30 °C) and analysed for four months. Milk samples were treated with acetic acid and trichloroacetic acid to obtain milk extracts containing peptides. The concentrated extracts were subjected to ATR‐FTIR, and the spectrum was obtained. Results were compared with techniques like high‐performance liquid chromatography, fluorescamine and 2,4,6‐trinitrobenzenesulphonic acid. The present study indicated that ATR‐FTIR‐based method can be used as an alternative method for assessing proteolysis in UHT milk.

The Occurrence and Risk Assessment of Exposure to Aflatoxin M1 in Ultra-High Temperature and Pasteurized Milk in Hamadan Province of Iran.

ObjectivesAflatoxins are a category of poisonous compounds found in most plants, milk and dairy products. The present research was carried out to detect the presence of aflatoxin M1 (AFM1) in samples of milk collected from Hamadan province, Iran.MethodsTwenty five samples of ultra-high temperature (UHT) and 63 samples of pasteurized milk were collected and the amount of AFM1 was measured by an Enzyme-Linked Immunosorbent Assay method. In addition, the estimated daily intake (EDI) and hazard index (HI) of AFM1 was determined by the following equations:(EDI= mean concentration of AFM1 × daily consumption of milk/body weight; HI= EDI/Tolerance Daily Intake).ResultsAFM1 was detected in 21 (84%) UHT milk samples and in 55 (87.30%) pasteurized milk samples. Seven (28%) samples of UHT and 21 (33.33%) pasteurized milk samples had higher AFM1 content than the limit allowed in the European Union and Iranian National Standard Limits (0.05 μg/kg). None of the samples exceeded the US Food and Drug Administration limit (0.5 μg/kg) for AFM1. EDI and HI for AM1 through milk were 0.107 ng/kg body weight/day, and 0.535, respectively.ConclusionA significant percentage of milk produced by different factories in Iran (84% of UHT and 87.3% of pasteurized milk) was contaminated with AFM1. Therefore, more control and monitoring of livestock feeding in dairy companies may help reduce milk contamination with AFM1. As the HI value was lower than 1, it can be assumed that there was no risk of developing liver cancer due to milk consumption.

Inhibitory effect of bacteriocins against Escherichia coli O157:H7.

The purpose of this study was to explore the activity of bacteriocin enterocin KP and lactococcin BZ against Escherichia coli O157:H7, a Gram-negative foodborne pathogen, in ultra-high temperature (UHT) milks with different fat ratios. Enterocin KP and lactococcin BZ were produced from two bacteriocinogenic strains, isolated in previous studies from White cheese and Boza. Full fat (3.0%), half fat (1.5%), and low fat (<0.1% fat) UHT milks inoculated with 102, 104, and 106 CFU/ml of E. coli O157:H7 were treated with different concentrations (400, 800, 1600, and 2500 AU/ml) of lactococcin BZ, enterocin KP, or a combination of both and stored at 4 or 20 ℃ for 20 days. The survival of E. coli O157:H7 was determined at both storage temperatures during the storage period of 20 days. Lactococcin BZ and enterocin KP had a bactericidal impact on E. coli O157:H7 in all UHT milk samples either separately or in combination. However, antibacterial activity of the bacteriocins decreased with increasing fat content of milk and inoculum levels of bacterium. The results of this study indicate that lactococcin BZ and enterocin KP may be useful candidates either separately or in combination as biopreservatives for use in the dairy industry to control the growth of pathogenic microorganisms.

Rapid detection of microbial contamination in UHT milk: practical application in dairy industry

Microbial quality of ultra-high temperature (UHT) milk is usually ascertained by a total bacterial count (TBC) cultivation. But this is time consuming, so there is a tendency to search for faster and simpler methods. We compared three instruments, focusing on shortening the detection time and their suitability for practical use in dairy plants. Two of them, RapiScreen Dairy 1000 and Promilite III, detect microbial contamination by measuring adenosine triphosphate bioluminescence; the third, GreenLight, is based on oxygen consumption analysis. In the laboratory experiments, samples of UHT milk, were spiked with low concentration of microorganisms and then the level of microbial contamination was evaluated using the above-mentioned instruments together with cultivation method as a control. The instruments were also applied in a dairy plant to test 182 real samples. All investigated methods determined microbial quality faster than the TBC, but in some cases false positive and false negative results were obtained. Therefore, precise testing including optimizing pre-incubation time for bacteria enrichment is needed prior to industrial use.

Lipid compositional changes and oxidation status of ultra-high temperature treated Milk

BackgroundMilk fat is one of the complex fat and most sensitive biochemical compounds towards auto-oxidation. To enhance the shelf life, milk is subjected to Ultra-high Temperature (UHT) treatment followed by aseptic packaging. During the storage, several chemical and biochemical changes take place in lipid fraction of UHT milk. In current investigation, the effect of UHT treatment and storage was determined by making a comparison in fatty acid profile, triglyceride composition, organic acids and lipid oxidation of the thermally treated and stored milk with raw milk, which was not reported in earlier investigations.MethodsRaw milk samples were collected from the bulk storage facility of a dairy industry. The same milk was routed to UHT treatment and aseptically packaged samples were collected. The fatty acid profile, triglyceride composition, organic acids and lipid oxidation was determined in raw and UHT treated milk at 0, 30, 60 and 90 days. Fatty acid and triglyceride profile was determined on GC-MS while organic acids were determined by HPLC. For the measurement of induction period, professional Rancimat was used. Lipid oxidation was characterized through free fatty acids, peroxide value, anisidine value and conjugated dienes.ResultsCompositional attributes of milk remain unchanged during the entire length of storage. Concentrations of short-chain fatty acids in raw and UHT milk were 10.49% and 9.62%. UHT treatment resulted in 8.3% loss of short-chain fatty acids. Up to 30 days, storage did not have any significant effect on fatty acid profile of UHT milk. Concentration of medium-chain fatty acids in raw and UHT treated milk was 54.98% and 51.87%. After 30, 60 and 90 days of storage, concentration of medium chain fatty acids was found 51.23%, 47.23% and 42.82%, respectively. Concentration of C18:1 and C18:2 in raw and UHT milk was 26.86% and 25.43%, respectively. The loss of C18:1 and C18:2 in UHT treatment was 5.32%. After 30, 60 and 90 days of storage, the concentrations of C18:1 and C18:2 were 24.6%, 21.06% and 18.66%, respectively. Storage period of 30 days was found non-significant, while noticeable variations were found in triglyceride profile of 60 and 90 days old samples of UHT milk. UHT treatment and storage period significantly affected the concentration of organic acids in milk. After UHT treatment, concentration of lactic acid, acetic acid, citric acid, pyruvic acid, formic acid, succinic acid and oxalic acid increased by 3.45, 0.66, 3.57, 0.68, 2.24, 2.16 and 1.63 mg/100 g. Effect of storage period on the production of organic acids in UHT milk was non-significant up to 30 days. After 60 days of storage period, the increase in concentration of lactic acid, acetic acid, citric acid, pyruvic acid, formic acid, succinic acid and oxalic acid was 3.79, 0.75, 4.69, 0.78, 2.83, 3.03 and 2.38 mg/100 g. After 90 days of storage period, the increase in concentration of lactic acid, acetic acid, citric acid, pyruvic acid, formic acid, succinic acid and oxalic acid was 7.3, 2.18, 9.96, 3.58, 11.37, 5.22 and 5.96%. Free fatty acids content of raw, UHT treated and 90 days old milk were 0.08%, 0.11% and 0.19%. UHT treated version of milk showed similar peroxide value. While, the storage remarkably affected the peroxide value. After 30, 60 and 90 days, peroxide value was 0.42, 0.62 and 1.18 (MeqO2/kg). Induction period of raw, UHT and stored milk was strongly correlated with peroxide value and fatty acid profile. Mean value of lipase activity in raw milk was 0.73 ± 0.06 μmoles/ml. UHT treatment significantly decreased the lipase activity. The lipase activity of milk immediately after the UHT treatment was 0.18 ± 0.02 μmoles/ml. Lipase activity of UHT milk after 30, 60 and 90 days of room temperature storage was 0.44 ± 0.03, 0.95 ± 0.07 and 1.14 ± 0.09 μmoles/ml. Color, flavor and smell score decreased through the storage of UHT milk for 90 days.ConclusionThe results of this investigation revealed that fatty acid and triglyceride profile changed after 60 and 90 days of storage. Production of organic acids led to the drop of pH and sensory characteristics in UHT milk during the long-term storage. Induction period can be successfully used for the determination of anticipatory shelf life of UHT milk.