Deterioration of protein fraction by Maillard reaction in dietetic milks.

The development of the Maillard reaction in pasteurized, UHT and in-bottle sterilized dietetic milks was studied. In these products damage caused by heat treatments could increase as a result either of the addition of various ingredients or of manufacturing processes that alter their content of reducing carbohydrates. Protein damage was evaluated by measuring furosine by reversed-phase ion-paired HPLC. The levels of furosine detected made it possible to assess the amounts of biologically unavailable lysine. In all milks analysed blocked lysine values were < 340-350 mg/g total lysine, the level at which lysine becomes the limiting amino acid in milk. Pasteurized dietetic milks had levels of blocked lysine similar to that in ordinary pasteurized cows' milk. In some UHT and in-bottle sterilized dietetic milks their different composition resulted in an increase in the blocked lysine content. In some in-bottle sterilized milks, protein damage greatly reduces the beneficial effects of milk as a dietary supplement. Lactose-free milks, which are more susceptible to protein deterioration because of their higher content of reducing carbohydrates, were also analysed after storage at 20 degrees C and at < or = 4 degrees C. At the end of their recommended storage times, they contained limited amounts of blocked lysine only if they had been stored at < or = 4 degrees C.     

Evaluation of heat-induced changes in Spanish commercial milk: hydroxymethylfurfural and available lysine content

Hydroxymethyfurfural (HMF) content and loss of available lysine were measured as indices of heat damage in various Spanish commercial milks (pasteurized, UHT sterilized and in-bottle sterilized milks) with similar processing dates. HMF level was determined by the traditional colorimetric procedure and by the reversed-phase HPLC method. Available lysine was measured by an alternative method with o -phthaldialdehyde as fluorescent marker. A significative relationship has been found between the HMF content and loss of available lysine and both are suitable for use as heat-induced indices. When loss of lysine ( y ) was expressed as percentage and HMF ( x ) as μ m , the function of the correlation line was, y =0.47x−0.089 ( r =0.958, P <,0.005).     

Automating a 96-Well Microtiter Plate Assay for Quick Analysis of Chemically Available Lysine in Foods

A new method for quick analysis of available lysine content in different food products has been developed by automating a 96-well microtiter plate assay. Although manual fluorometric methods validated in order to determinate available lysine content already existed for this compound, the benefits of applying appropriate automation should provide continuous operation, increased precision, an affordable electronic audit trail, and significantly reduced time and reagent consumption. The objective of this work was to adapt the ortho-phthaldialdehyde (OPA) fluorometric method to an automated workstation. Considerable effort went into developing and validating an automated method. The analytical parameters of linearity (r?=?0.999), the precision of the method (relative standard deviations?=?2.8–3.0 % for the different samples), and the results of the comparison with the corresponding OPA manual fluorometric method show that the studied method is useful for the measurement of available lysine in several food products from different natural origins such as liquid foods (soy, oat, quinoa beverages, and ultra-high temperature/sterilized milk) and powdered samples (powdered adapted, powdered follow-up, and junior milk infant formulas) with reduced time and reagent consumption.     

Distinguishing pasteurized, UHT and sterilized milks by their lactulose content

Commercial pasteurized, UHT and sterilized milk samples, and laboratory autoclaved milks, were analysed for lactulose by an enzymatic method. No lactulose was detected in the pasteurized milk. On the basis of the measured lactulose concentrations, the UHT and sterilized milk samples fell into five groups according to the type of process that they had received.
The lactulose concentrations in the laboratory autoclaved milks rose on storage, but this was not observed in the other milks.
It appears that pasteurized, UHT and sterilized milks can be differentiated by their lactulose content.     

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.     

Determination of whey protein to total protein ratio in UHT milk using fourth derivative spectroscopy

A fourth derivative spectroscopy method was applied for the quantification of whey protein to total protein ratio in UHT milks. Some analytical features such as model compounds, selection of wavelength, linearity, repeatability and interference of milk fat were studied. The effect of refrigerated storage of raw milk, UHT treatment, and storage of UHT milk at room temperature on whey protein to total protein ratio was evaluated. No significant (p<0.05) differences among samples were found in any case. The ratio of whey protein to total protein was also determined in batches of whole (n=28) and skimmed (n=27) commercial UHT milks from different Spanish geographic areas processed by direct or indirect UHT systems in different periods of the year. The mean value was 18.1% for both whole and UHT skimmed milks. The analysis of laboratory-made mixtures of UHT milk with acid and rennet whey (2.5–15% of whey in milk expressed in protein) indicated that adulterations of UHT milk with whey up from 5% could be detected by the proposed method.     

毛细管电泳法对乳及乳制品中真蛋白的测定

利用毛细管电泳法对市售乳清蛋白粉、采自当地奶牛场的牛初乳及原料奶、同一品牌不同阶段或同一阶段内不同厂家、不同国别的婴儿配方奶粉、不同保质期的液态奶、不同国别的超高温灭菌(UHT)奶和酸奶、国产复原乳中α- 乳白蛋白(α-Lac)、β- 乳球蛋白A (β-LgA)及β- 乳球蛋白B (β-LgB)的质量分数进行测定。结果表明：α-Lac、β-LgA 及β-LgB 的质量分数在乳清蛋白粉、牛初乳及原料奶中依次降低。液态奶中上述3 种蛋白的质量分数与保质期有关,一般保质期越久的产品,上述3 种蛋白的质量分数越低。大多数酸奶中α-Lac 的质量分数均高于UHT 奶。婴儿配方奶粉中α-Lac 质量分数随着阶段数的增加而增加,而且同一阶段内不同厂家不同国别配方奶粉中α-Lac 质量分数差异也较大,并非进口奶粉中α-Lac 质量分数均比国产奶粉高。     

Additive milks*

Over the last 10 years the range of ‘milks’ which dairy companies market has increased enormously. In addition to true low fat milks (ie, skimmed milk and semi-skimmed milk), various additive ‘milks’ are now available. These include low fat ‘milks’ with the taste of whole milk, ‘milks’ with added vitamins, ‘milks’ enriched with calcium and ‘milks’ low in lactose. There are even high fat ‘milks’, and of course flavoured milks. Many of these products are available fresh (ie, pasteurized) rather than long-life (ie, UHT). Improved technology and chilled distribution give the fresh products additional shelf-life. The equipment for making these products is outlined, as well as the quality control requirement. The relevant legislation is also considered.     

Evolution of available lysine and furosine contents in milk‐based infant formulas throughout the shelf‐life storage period

The evolution of the Maillard reaction (MR) by measuring the available lysine and furosine (FUR) contents in adapted and follow‐up powdered milk‐based infant formulas over the shelf‐life storage period, at 20 and 37 °C, was studied. Available lysine and FUR contents were determined by fluorimetry and high‐performance liquid chromatography respectively. Statistically significant differences were found between adapted and follow‐up infant formulas with respect to the available lysine and FUR contents. Available lysine contents decreased significantly throughout the storage time, and the contents at 37 °C were lower than at 20 °C. A statistically significant increase in FUR contents was observed during the storage period, with the contents being high at 37 °C than at 20 °C. A simple regression analysis between the available lysine and FUR contents during (a) the first year (b) the second year and (c) the two storage years was applied. The best correlations were obtained during the first year of storage. The results obtained show a clear MR evolution during the storage of infant formulas. Copyright © 2003 Society of Chemical Industry     

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.     

Application of Time-Temperature Indicators in Monitoring Changes in Quality Attributes of Perishable and Semiperishable Foods

The response of full-history time-temperature indicators attached to different packages containing five perishable and semiperishable foods (tomatoes, naked and wrapped lettuce, canned fruitcake, and UHT sterilized milk) was studied. The products were stored at constant and variable temperature treatments simulating commercial storage and handling practices. Changes in specific quality attributes were periodically evaluated by means of sensory analysis, and the monitored attributes were correlated with indicator response. Statistical analysis showed significant correlations (p < 0.05) between the indicators studied and quality changes in tomatoes and UHT sterilized milk.     

Effect of Processing and Storage Conditions on the Fate of Vitamins B1, B2, and C and on the Shelf-Life of Goat's Milk

Goat's milk was heat-processed under different time-temperature conditions of pasteurization and sterilization. Losses of thiamin, riboflavin, and total vitamin C in HTST, Flash, and UHT were less than that by LTLT and Autoclave. Also residual oxygen in the milk affected the loss of total vitamin C during storage. A longer shelf-life of pasteurized milk was obtained with HTST, HTST overpasteurization, and Flash process; however, there was no significant difference between UHT and Autoclave sterilized products. From the above results, HTST pasteurization was considered the best process to preserve milk quality.     

贮藏温度及时间对不同类型商品乳酸度的影响

为研究不同贮藏温度及时间对不同类型商品乳酸度的影响情况。选取超高温(UHT)灭菌乳、巴氏灭菌乳、乳饮料、酸牛奶各10盒,将每种类型的商品乳分成2组,开封后进行贮藏。一组放入0~4℃的冰箱冷藏,另一组放在常温下贮藏。分别在0, 1, 2, 3, 4, 5和6 d测定各组商品乳的酸度。结果表明,酸牛奶、UHT灭菌乳和巴氏灭菌乳放在常温下贮藏时酸度分别在第1,第3和第3天出现显著性差异(p<0.05),在低温下贮藏时酸度均未出现显著性差异(p>0.05)。乳饮料在常温和低温下贮藏1 d后酸度均出现显著性差异(p<0.05)。4种类型的商品乳放在低温下贮藏时更能保持酸度的稳定。     

Digestible reactive lysine in selected milk-based products

Reactive lysine contents, true ileal reactive lysine digestibility, and true ileal digestible reactive lysine contents were determined in a wide range of processed milk products. A previously validated assay based on determining reactive lysine in both food and ileal digesta, after reaction of these materials with O-methylisourea, was applied. Semisynthetic diets containing milk products as the sole sources of protein and including chromic oxide as an indigestible marker were fed to growing rats. Digesta from the terminal ileum were collected posteuthanasia and, with samples of the diets, analyzed for reactive lysine (homoarginine) contents. True reactive lysine digestibility was determined after correcting for endogenous lysine loss at the terminal ileum of rats fed an enzyme hydrolyzed casein-based diet, followed by ultrafiltration (5000 Da) of the digesta. Digestible total lysine (determined using conventional methods) was also determined. The true ileal reactive lysine digestibility was high (>91%) in all the milk products tested, but was highest in the UHT milk (100%) and lowest in the infant formulas (91 to 93%). Total lysine digestibility (conventional measurement) significantly underestimated reactive lysine digestibility for all the products tested. The mean underestimation ranged from 1.3 to 7.1% units. The mean digestible total lysine content was significantly different from the available lysine content for most of the products examined. In some cases this difference was small (<3%), but for a number of the products (evaporated milk, whole milk protein, lactose hydrolyzed milk powder, and a sports formula) the difference was greater (6.5 to 14%). This would suggest firstly that total lysine and total lysine digestibility determined using conventional methods were inaccurate when applied to some milk-based foods, and secondly that some of the milk products have undergone lysine modification. In general, milk proteins are a highly digestible source of amino acids and lysine.     

PROGRESS AND DEVELOPMENT OF UHT MILK AND MILK PRODUCTS IN THE UK DAIRY INDUSTRY

The paper covers the history of UHT sales in the UK and explains reasons for the small sale of UHT milk. Sales are expected to rise significantly - more sterilized milk is being replaced by UHT, and skimmed milk and flavoured milks being promoted. UHT product sales are encouraging with cream, custards, desserts and ice-cream established. With continual price increases, caterers and shops would want to reduce waste and require non-perishable goods. UHT processing could be beneficial to dairies for doorstep delivery as well as shop sales. Particular mention is made of the success dairies have had with aseptically packed juice.     

保藏温度及时间对UHT 灭菌乳品质的影响

以复合塑料袋装UHT 灭菌乳为研究对象,考察保藏温度和时间对UHT 灭菌乳品质的影响。研究表明,保藏温度和时间对UHT 灭菌乳的蛋白质、乳脂肪、乳糖、滴定酸度及感官指标均有显著影响。具体而言,随保存时间延长,蛋白质、乳脂肪、乳糖含量及感官品质降低,而滴定酸度升高。保藏温度越高,以上变化明显加剧。4℃条件下,保藏时间范围内,样品的感官评分均保持在98 分以上,说明具有优良的感官品质;而保存在22℃和37℃条件下,感官品质下降,且保藏温度越高,感官品质降低越明显。     

基于荧光法快速判定巴氏杀菌乳和超高温灭菌乳

目的 基于荧光法快速简便地鉴别巴氏杀菌乳和超高温(ultra high temperature,UHT)灭菌乳。方法 基于美拉德产物荧光值的不同,采用直接荧光法结合综合热损伤指数(fluorescence of advanced Maillard products and soluble tryptophan, FAST)快速鉴定巴氏杀菌乳和UHT灭菌乳。结果 巴氏杀菌乳和UHT灭菌乳由于热处理强度不同,二者的荧光值存在显著差异 (P<0.01),巴氏杀菌乳荧光值在13215±236~15359±156之间、UHT灭菌乳荧光值范围为15788±200~20440±270。与巴氏杀菌乳相比,UHT灭菌乳直接测定荧光强度和FAST指数明显升高且差异显著(P<0.01)。在商品巴氏杀菌乳和UHT灭菌乳结果的基础上,利用自制产品对荧光法进行了验证。结论 直接荧光测定法和FAST指数能够快速有效区分和识别巴氏杀菌乳和UHT灭菌乳,该技术对产品热处理强度评价及质量监管具有一定指导意义。     

Effect of feed supplementation based on extruded linseed meal and fish oil on composition and sensory properties of raw milk and ultra-high temperature treated milk

The objectives of this study were to test the influence of a recently developed rumen protected feed supplement containing extruded linseed meal and fish oil (LFO), which was fed to lactating Holstein-Friesian cows for 10 weeks at the rate of 800 g day⁻¹ per animal, on the chemical and fatty acid (FA) composition of raw and ultra-high temperature (UHT) treated milks and to evaluate changes in sensory properties of UHT milk by both instrumental analysis and a panel of human assessors. Inclusion of LFO in the diet did not affect milk yield or the protein and fat contents of raw and UHT milks; however, it improved the FA composition of the milk fat by increasing the concentrations of health-enhancing polyunsaturated FA and beneficially decreasing the n-6/n-3 FA ratio without adversely affecting the sensory properties of the final product (UHT milk).     

Survival analysis,consumer perception and physico-chemical analysis of low fat UHT milk stored for different time periods

Survival analysis based on consumers' acceptance or rejection of milk of different storage ages, was used to validate the shelf-life of low fat ultra-high temperature treated (UHT) milk in high density polyethylene bottles, as previously determined by a multivariate accelerated shelf-life test (MASLT). UHT milk between 120 and 290 d of storage were evaluated. Based on 50% of consumers rejecting the product, the shelf-life was estimated to be 214 d, validating the shelf-life of 211 d estimated by the MASLT. In addition, consumers completed check-all-that-apply attribute questions and rated the acceptability of the milk. The consumers noted positive sensory attributes more frequently in fresher milk samples with an increase in negative attributes with storage. Along with this, hedonic scores for the milk decreased and physicochemical and enzymatic reactions associated with the deterioration of UHT milk increased with storage.     

Mineral retention in three-week-old piglets fed goat and cow milk infant formulas

Goat milk and cow milk are commonly used in infant formula preparations and, as such, understanding the nutritional characteristics of infant formulas made from these milks is important. In this study, a goat milk infant formula was compared with an adapted (whey-enhanced) cow milk infant formula with respect to mineral absorption and deposition using the 3-wk-old piglet as a model for the 3-mo-old infant. Equal numbers of piglets (n = 8) were fed either the goat milk formula or the cow milk formula. The mineral composition of the prepared goat milk formula was higher than that of the prepared cow milk formula for most minerals, including calcium (75.1 vs. 56.7 mg/100 mL) but excluding iron, which was higher in the prepared cow milk formula (0.92 vs. 0.74 mg/100 mL). The amounts of calcium, phosphorus, and manganese absorbed by the piglets were significantly higher for the goat milk formula, whereas the amounts of zinc, iron, and magnesium absorbed were significantly higher for the cow milk formula. Apparent mineral absorption, relative to intake, was statistically higher in the cow milk formula for calcium and phosphorus, although the actual differences were very small (less than 1.3%). For copper, zinc, iron, and magnesium there was no significant difference between treatments in apparent mineral absorption, whereas for manganese, absorption was higher for the goat milk infant formula. The absolute mineral deposition was higher in piglets fed the goat milk formula for calcium, phosphorus, and manganese, whereas iron deposition was higher in the piglets fed cow milk formula. For all other minerals tested, there were no significant differences between treatments. The goat milk infant formula provided a pattern of mineral retention in the 3-wk-old piglet very similar to that of the adapted cow milk infant formula. The minor differences observed between the 2 appeared to be due to the different mineral contents of the 2 formulas.