UHT灭菌乳贮存期间乳果糖的变化规律

商业UHT灭菌乳在室温(19±2)℃储存2个月,研究其乳果糖含量变化情况.结果表明,UHT灭菌乳中乳果糖含量在货架前期相对稳定.后期随储存时间的延长而增高,具体增高幅度与生产工艺有关.     

Composition and calcium status of acid whey from pasteurized,UHT‐treated and in‐bottle sterilized milks

Whey extracts were obtained from pasteurized, UHT‐treated and in‐bottle sterilized milks. After acidic precipitation of casein the concentration of protein, NPN, lactose, lipid, calcium, magnesium and potassium was determined. Among the parameters examined, protein content was significantly reduced in the whey extracts from UHT‐treated and in‐bottle sterilized milks compared with that from pasteurized milk, while lactose content was increased. Calcium extracted in whey was at least 80% of total calcium of the milk. The total calcium to protein ratio of whey was increased as a function of the thermal treatment of milk, while ionic calcium was about 50% of total calcium in all whey extracts. In vitro protein digestibility was found to be significantly lower in whey from UHT‐treated and in‐bottle sterilized milks than in that from pasteurized milk. Parallel estimation of the percentage of ionic calcium and of the solubility of proteins in the pH range 2–10 indicated that calcium was not involved in the pH‐dependent solubility of proteins extracted in the whey, the extent of solubility being essentially a function of the thermal treatment of milk. The results suggest that calcium was not responsible for the formation of soluble protein macroaggregates with impaired digestibility that are present in whey from milk subjected to heat treatment of increasing intensity.     

Heat-induced and other chemical changes in commercial UHT milks

The properties of commercial directly and indirectly heated UHT milks, both after heating and during storage at room temperature for 24 weeks, were studied. Thermally induced changes were examined by changes in lactulose, furosine and acid-soluble whey proteins. The results confirmed previous reports that directly heated UHT milks suffer less heat damage than indirectly heated milk. During storage, furosine increased and bovine serum albumin in directly heat-treated milks decreased significantly. The changes in lactulose, alpha-lactalbumin and beta-lactoglobulin were not statistically significant. The data suggest that heat treatment indicators should be measured as soon as possible after processing to avoid any misinterpretations of the intensity of the heat treatment.     

Lipolysis in cheddar cheese made from raw, thermized, and pasteurized milks

The evolution of free fatty acids (FFA) was monitored over 168 d of ripening in Cheddar cheeses manufactured from good quality raw milk (RM), thermized milk (TM; 65°C × 15 s), and pasteurized milk (PM; 72°C × 15 s). Heat treatment of the milk reduced the level and diversity of raw milk microflora and extensively or wholly inactivated lipoprotein lipase (LPL) activity. Indigenous milk enzymes or proteases from RM microflora influenced secondary proteolysis in TM and RM cheeses. Differences in FFA in the RM, TM, and PM influenced the levels of FFA in the subsequent cheeses at 1 d, despite significant losses of FFA to the whey during manufacture. Starter esterases appear to be the main contributors of lipolysis in all cheeses, with LPL contributing during production and ripening in RM and, to a lesser extent, in TM cheeses. Indigenous milk microflora and nonstarter lactic acid bacteria appear to have a minor contribution to lipolysis particularly in PM cheeses. Lipolytic activity of starter esterases, LPL, and indigenous raw milk microflora appeared to be limited by substrate accessibility or environmental conditions over ripening.     

UHT杀菌乳中耐热菌的分离与鉴定

采用2种不同的细菌富集方式对5种不同品牌UHT（Ultra High Temperature）杀菌牛乳中残留的细菌进行了分离，得到18株细菌，并对它们进行了耐热性和细菌学鉴定试验。结果表明，18株细菌全部耐热，初步将其归为3个属。其中，片球菌属10株，均为戊糖片球菌，肠球菌属3株，1株类鸟肠球菌，2株粪肠球菌；微球菌属5株，1株嗜冷微球菌，4株变异微球菌。虽然这些耐热菌均为非致病菌，但是遇到适宜条件，这些耐热菌会生长繁殖，导致乳产品在贮藏和流通过程中发生变质。     

Antioxidant activity of pasteurized and sterilized commercial red orange juices

Blood orange juice is a typical Italian product whose red color is primarily associated with anthocyanin pigments. Two orange-based products are present on the market: pasteurized pure juice with 40 days of shelf life, and sterilized beverage containing minimum 12% of concentrated fruit juice. The aim of the present paper is to verify the relationships between the antioxidant properties and the anthocyanins content in a sampling of pasteurized and sterilized commercial red orange juices. The anthocyanins composition was determined by HPLC-MS/MS, while the antioxidant activity was evaluated by the Briggs-Rauscher reaction, selected in order to acquire information at acid pH values, by three radical scavenging assays (DMPD, 2-2'-azinobis-(3-ethylenbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), DPPH), and by FRAP assay to monitor the ferric reducing power. Results showed that antioxidant activity, particularly when measured by ABTS method, is positively related to the content of anthocyanins and that the reduction of anthocyanins content, typical of commercial long-shelf life juices, leads to a remarkable loss of antioxidant power.     

Composition and calcium status of acid whey from pasteurized, UHT-treated and in-bottle sterilized milk

Whey extracts were obtained from pasteurized, UHT-treated and in-bottle sterilized milks. After acidic precipitation of casein the concentration of protein, NPN, lactose, lipid, calcium, magnesium and potassium was determined. Among the parameters examined, protein content was significantly reduced in the whey extracts from UHT-treated and in-bottle sterilized milks compared with that from pasteurized milk, while lactose content was increased. Calcium extracted in whey was at least 80% of total calcium of the milk. The total calcium to protein ratio of whey was increased as a function of the thermal treatment of milk, while ionic calcium was about 50% of total calcium in all whey extracts. In vitro protein digestibility was found to be significantly lower in whey from UHT-treated and in-bottle sterilized milks than in that from pasteurized milk. Parallel estimation of the percentage of ionic calcium and of the solubility of proteins in the pH range 2-10 indicated that calcium was not involved in the pH-dependent solubility of proteins extracted in the whey, the extent of solubility being essentially a function of the thermal treatment of milk. The results suggest that calcium was not responsible for the formation of soluble protein macroaggregates with impaired digestibility that are present in whey from milk subjected to heat treatment of increasing intensity.     

Variation in the lactulose content of UHT milk during the running of a pilot and a commercial indirectly heated plant

The lactulose content of UHT milk was measured during the running of a pilot and a commercial indirectly heated UHT plant. The lactulose content of milk processed in the pilot plant was found to decrease as the pressure drop across the heated sections rose. The lactulose content of the milk from the commercial plant varied little and showed no trend during an entire production shift. There was no evidence that deposit in the plants accelerated the formation of lactulose.     

Occurrence of aflatoxin M1 in raw, pasteurized and UHT milk commercialized in Esfahan and Shahr-e Kord, Iran

Between September 2006 and September 2007, 236 samples of raw (n = 140), pasteurized (n = 48) and UHT (n = 48) milk were collected from supermarkets and from bulk milk tanks of eight dairy plants in the cities of Esfahan and Shahr-e Kord, Iran. All samples were analyzed for aflatoxin M₁ (AFM₁) contamination by ELISA and 213 (90.3%) were positive with mean concentrations 65 ng.l⁻¹. These concentrations are lower than the standards of Codex Alimentarius and FDA (500 ng.l⁻¹), but 119 samples (55.9%) had higher concentrations than the maximum tolerance accepted by some European countries (50 ng.l⁻¹). Mean concentrations of AFM₁ in raw, pasteurized and UHT milk were 68, 56, and 65 ng.l⁻¹, respectively. Mean concentrations of AFM₁ in autumn and winter samples were significantly higher (P < 0.05) than those of spring and summer but differences between AFM₁ concentrations of spring and summer samples were not significantly different. Concentrations of AFM₁ in milk from Shahr-e Kord were significantly lower (P ≤ 0.05) than those from Esfahan.     

Modelling the relation between bacterial growth and storage temperature in pasteurized milks of varying hygienic quality

The shelf-life of pasteurized milk was mainly determined by the level of contamination with Gram-negative psychrotrophic bacteria. The length of lag phase of the bacteria was also important, although the generation times of the naturally contaminating flora seemed to be of little relevance except for milks where the shelf-life exceeded 10 days at 6°C. The effect of temperature on growth of the contaminants could be accurately determined by the 'square root' plot but the conceptual minimum temperature for growth (T_o) varied. The variation was related to the quality of the pasteurized milk. Effects of temperature on generation time, length of lag phase and shelf-life were most marked at temperatures below 15°C.
The microflora of pasteurized milk varied significantly with storage temperature. At refrigeration temperatures, spoilage was mainly due to the growth of Pseudomonas spp. Enterobacteriaceae and Gram-positive bacteria assumed greater importance in the spoilage of milks stored at temperatures above 10°C. Milks of good quality also contained Bacillus spp and this group of bacteria were not detectable in milks with short shelf-lives.     

The effect of extended low-temperature storage of raw milk on the quality of pasteurized and UHT milk

The effect of storage of raw milk at 2 and 6°C on the quality of pasteurized and UHT milks produced from them has been investigated. There was no difference in shelf-lives of pasteurized milks produced from raw milks which had no obvious physical defects, odours and taints after storage at 2 and 6°C. This was true for pasteurized milks in the presence and absence of post-heat-treatment contamination. However, pasteurized milks of good quality could be produced from more than 80% of raw milk samples which had been stored for up to 5 days at 2°C, but this was only possible with raw milks which had been stored at 6°C for 2 days.Failure rates of experimentally-produced UHT milks were much higher in products manufactured from raw milks stored at 6°C for 4 days than those produced from raw milks stored at 2°C for 4 days. The main cause of failure was due to thermostable bacterial protease associated with high levels of bacterial growth in the raw milks. Other causes of failure included spore-forming bacteria, which may have survived UHT processing, and other organisms probably introduced as contaminants on filling.     

Mineral contents and distribution between the soluble and the micellar phases in calcium‐enriched UHT milks

A study concerning the content of mineral elements (calcium, magnesium, sodium, potassium and phosphorus) and the distribution between the soluble and the micellar phases has been carried out on mineral—mainly calcium—enriched UHT milks. Total calcium contents were 1371–1793 mg l^?1 in the 10 brands examined. Percentages of calcium in the soluble phase varied from 23.6 to 37.2%, whereas ionic calcium concentrations found were within a very wide range (44–91 mg l^?1). The different forms of phosphorus were studied by ³¹P‐NMR. Spectra indicated that the majority of the brands employed polyphosphates as stabilizers. Ingredients used to fortify these products consisted of dairy fractions and calcium salts. The modifications in salt balance as consequence of these practices are discussed. Copyright © 2004 Society of Chemical Industry     

Fatty acid profile and CLA isomers content of cow,ewe and goat milks processed by high pressure homogenization

High pressure homogenization (HPH) is a novel technology that promotes fat globule size reduction and microbial inactivation, but little research exists on the fate of milk fat lipids. This work studied the effect of HPH (0–350 MPa) of raw cow, goat and ewe milks on the fatty acid total content and profile to elucidate whether this technology has a major impact on the lipid fraction of milk and especially on CLA isomers. Fatty acids in processed milks were determined by GC-FID and CLA isomers by Ag+-HPLC.Our results indicate that the total amount of fat extracted from the milk samples decreased as the homogenization pressure increased, whereas no significant differences were found in the fatty acid composition, especially in the PUFA and CLA isomers profile of raw milk treated by HPH process up to 350 MPa.Industrial relevanceThe absent of significant modifications of the fatty acids content and CLA isomers profile in milk by using high-pressure homogenization is relevant in the development of nonthermal technologies able to pasteurize/sterilize foods, without the organoleptic, functional, and chemical alterations associated to thermal processing.     

The microbial content of raw and pasteurized cow milk as determined by molecular approaches

The microbial composition of raw and pasteurized milk is assessed on a daily basis. However, many such tests are culture-dependent, and, thus, bacteria that are present at subdominant levels, or that cannot be easily grown in the laboratory, may be overlooked. To address this potential bias, we have used several culture-independent techniques, including flow cytometry, real-time quantitative PCR, and high-throughput DNA sequencing, to assess the microbial population of milk from a selection of commercial milk producers, pre- and postpasteurization. The combination of techniques employed reveals the presence of a previously unrecognized and diverse bacterial population in unpasteurized cow milk. Most notably, the use of high-throughput DNA sequencing resulted in several bacterial genera being identified in milk samples for the first time. These included Bacteroides, Faecalibacterium, Prevotella, and Catenibacterium. Our culture-independent analyses also indicate that the bacterial population of pasteurized milk is more diverse than previously appreciated, and that nonthermoduric bacteria within these populations are likely to be in a damaged, nonculturable form. It is thus apparent that the application of state-of-the-art approaches can provide a detailed insight into the bacterial composition of milk and could potentially be employed in the future to investigate the factors that influence the composition of these populations.     

非线性电化学指纹图谱技术鉴别羊奶和牛奶及其产地

以非线性电化学指纹图谱技术鉴别羊奶和牛奶及其产地。测定不同产地羊奶和牛奶的非线性电化学指纹图谱,通过指纹图谱直观特征鉴别羊奶和牛奶,利用系统相似度模式识别羊奶或牛奶的产地。结果显示:羊奶和牛奶非线性电化学指纹图谱均有很好的重现性和特征性,利用其直观特征就可准确鉴别羊奶和牛奶;不同产地的羊奶或牛奶可利用系统相似度模式识别。同一产地羊奶或牛奶的指纹图谱系统相似度在99.06%⁹9.86%,不同产地的系统相似度在90.42%99.86%,不同产地的系统相似度在90.42%⁹8.86%,不同种类奶品的系统相似度在76.25%98.86%,不同种类奶品的系统相似度在76.25%⁸2.43%。用系统相似度模式鉴别奶品产地的准确度≥91.9%,其平均准确度达到94.3%;鉴别奶品种类的准确度≥94.6%,其平均准确度达到98.5%。说明利用非线性电化学指纹图谱技术能准确鉴别羊奶和牛奶及其产地。     

Kinetics of hydroxymethylfurfural,lactulose and furosine formation in milk with different fat content

In the context of the general applicability of hydroxymethylfurfural (HMF), lactulose and furosine as time-temperature integrators (TTIs) for thermal processing of milk, the influence of milk fat content was studied. Formation kinetics were analysed for milk with fat content of 4.0 +/- <0.1%. In previous experiments, it was observed that, under isothermal and non-isothermal heating conditions, formation of the three chemical compounds could be described by pseudo-zero order kinetics. Since the kinetic model was known, the experimental design could be simplified. Data were analysed by a non-linear regression procedure and results were evaluated by construction of joint confidence regions and temperature time tolerance (TTT-) diagrams. Formation kinetics of HMF and lactulose was not affected by milk fat content. Regarding furosine, significant differences were observed between kinetic parameters in whole, semi-skimmed and skimmed milk. The observed differences however were negligible in the context of process impact evaluation.     

The use of the chromogenic Limulus amoebocyte lysate assay to distinguish between ultra high temperature and in-container sterilized milks

The chromogenic Limulus amoebocyte lysate (LAL) assay may be used to distinguish between ultra high temperature (UHT) and in-container sterilized (ICS) milks, when applied to samples which have received an additional heat treatment of 100°C for 10 minutes. This heat treatment resulted in a significant increase (p < 0.001) in the availability of lipopolysaccharides in ICS milks which did not occur in UHT milk samples. This method for distinguishing between these milk types is, however, limited to samples whose sera require extensive dilution prior to testing. This possibly reflects the calcium levels present.     

Distinction of different heat-treated bovine milks by native-PAGE fingerprinting of their whey proteins

Native-PAGE (polyacrylamide gel electrophoresis) was used for the simultaneous qualitative and quantitative analysis of whey proteins of raw, commercial and laboratory heat-treated bovine milks. Four whey protein bands, including β-lactoglobulin variants (β-LG A and B), could be distinctively separated in the gel. The results showed that levels of the major whey proteins were reduced by less than 23% in the pasteurized milks and by more than 85% in the UHT milks as compared with raw milk. The α-lactalbumin (α-LA) exhibited the strongest heat-tolerance: about 32% of it remained in its native state after the milk was heated at 100 °C for 10 min. About 42% of β-LG A and 53% of β-LG B were lost after the milk was heated at 75 °C for 30 min. Blood serum albumin (BSA) was lost almost completely when the milk at pH 5.0 was heated at a temperature of 75 °C or higher. The β-LGA and β-LGB were much more stable at low pH than in neutral conditions.