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.     

IMPROVED SHELF LIFE ESTIMATION OF UHT MILK BY PREDICTION OF PROTEOLYSIS

ABSTRACT

During growth in raw milk, many psychrotrophic bacteria produce proteases that can retain activity following ultra‐high temperature (UHT) treatment. In this study, casein and skim milk powder assays for detecting very low levels of protease in UHT milk were optimized, and the suitability of azocasein and fluorescein isothiocyanate‐casein (FITC‐casein) as substrates was investigated. The strongest correlations of protease activity with proteolysis in stored UHT milk were observed when FITC‐casein was used as substrate in the assays. Assays using casein and FITC‐casein as substrates yielded the highest activities. To determine sensitivity, crude protease was added at low concentrations to UHT milk, and the milk was assayed for progress of proteolysis over 12 months and for protease activity using the casein and FITC‐casein assays. With long assay incubation times, the FITC‐casein assay was more sensitive than the casein assay and may be suitable for detecting very low levels of protease activity and predicting progress of proteolysis in stored UHT whole milk.

PRACTICAL APPLICATIONS

This study contributes to the development and evaluation of practical assays for the detection of protease activity in the industry to identify potential premature spoilage of contaminated UHT milk before it is distributed for sale. The developed assays are also useful for assessing the quality of milk powder as active protease can persist in milk powder to cause spoilage in reconstituted milk. Although the assays require up to 14 days to complete, this is not an excessive time, compared with the time required for microbiological clearance and total shelf life of the product. High protease activity can be identified with less incubation time. The cost of protease detection assays developed during this work is quite low and, although 20 min analysis time is required per sample, the tests can be very cost efficient when run in batches, as would be expected in a commercial testing facility.

     

WHEY PROTEIN DENATURATION OF UHT PROCESSED MILK AND ITS EFFECT ON RHEOLOGY OF YOGURT

The denaturation of whey proteins in whole milk during processing by the indirect UHT and vat systems was determined. Whey protein denaturation plateaued at about 88% following a UHT heat treatment of 149°C for 10 s. However, it reached about 88% with a vat heat treatment of 82°C for 5 min and reached 95 to nearly 100% after 10 to 15 min. Vat processing under pasteurizing conditions at 63°C for 30 min resulted in less than 10% denaturation. The yogurts prepared from the vat processed milk had considerably higher structural firmness than those prepared from the UHT milk, as confirmed by the lower value of curd firmness and the higher shear stress of these yogurts. It was also found that the structural or curd firmness of yogurts prepared from UHT milk was highest when the milk was processed for 3.3 s process holding time and was lower when the milk was processed for longer or shorter process holding times. The results suggest that the vat process at 63°C or 82°C brings about a specific change in the whey protein which leads to formation of a firm structure. This change apparently does not occur during the brief UHT treatment.     

INACTIVATION OF SELECTED MICROORGANISMS AND PROPERTIES OF PULSED ELECTRIC FIELD PROCESSED MILK

Raw skim milk and ultra-high-temperature (UHT) skim milk inoculated with Pseudomonas fluorescens, Lactococcus lactis and Bacillus cereus were processed by pulsed electric field (PEF) treatment. A continuous PEF bench scale system was set to deliver 35 kV/cm field strength with 64 pulses of bipolar square wave for 188 μs. The flow rate of milk was 1 mL/s. Milk temperature was raised to 52C and cooled to 22C during PEF treatment. Pasteurization at 73C for 30 s was used for comparison. Microbial inactivation and cell morphology were investigated. Analyses for protein, total solids, color, pH, particle size, density and electrical conductivity showed no significant effects (P > 0.05) in the PEF processed milk. PEF treatment accomplished a 0.3 to 3.0 log reduction of P. fluorescens, L. lactis and B. cereus in UHT milk and of total microorganisms in raw milk.     

耐热蛋白酶对UHT乳品质的影响及控制方法研究进展

从耐热蛋白酶对UHT乳品质的影响的角度出发．对近几年来国内外在牛乳中主要耐热蛋白酶的来源、检测方法、酶对UHT乳蛋白质水解和凝胶的影响、控制方法等方面的研究进展情况进行了综述，并提出今后深入研究应关注的方向和重点。     

ASEPTIC PROCESSING AND PACKAGING OF MILK

The commercial aspects of aseptic processing and packaging of milk showing only a slow rise in the market are assessed. The paper describes three types of process plant, the indirect plate heat exchanger, indirect tubular heat exchanger and direct steam injection plants and the various advantages are evaluated. Simplification of plants with the removal of de-gassers, flash cooling vessels etc. is emphasized in the modern indirect plant which will heat, cool and homogenize as simply as possible. Differences between operation of a UHT carton dairy and an average bottling dairy are described. ( Editor's summary )     

THE CHANGING ROLE OF MILK AND MILK PRODUCTS IN DIETS IN THE UNITED KINGDOM

The paper deals with: (1) The present contribution of milk in United Kingdom diets; (2) past changes in consumption; (3) factors affecting consumption; (4) how consumption can be changed; (5) likely future changes. One difficulty is that information on consumption refers to groups; little is known about individual consumption. This is even more true for past consumption patterns. Many factors affect consumption. A major part is played by government intervention, both in regulating prices and in distribution of welfare milk. Propaganda that milk fat is harmful has had little effect in this country. Future trends are difficult to forecast since they increasingly depend on government policy.     

SUBJECT: BITTY CREAM AND RELATED PROBLEMS:PROBLEMS ASSOCIATED WITH BACTERIAL SPORES IN HEAT-TREATED MILK AND DAIRY PRODUCTS

Spore spoilage in pasteurized milk and UHT and sterilized milk is reviewed with particular reference to cream. The problem of the incidence of bitty cream and the effectiveness of refrigeration in checking this is discussed. Results of studies on the bacterial quality of bulk raw milk and tanker reload milk using the thermoduric count are given in detail. Current methods for pasteurizing cream are described and studies on the effect of storage temperature on the shelf life of pasteurized cream are referred to in detail with particular reference to the lag in bacterial multiplication and the use of the Methylene Blue Test.     

浸入式和喷射式超高温瞬时灭菌对牛乳中活性蛋白和风味化合物的影响

超高温瞬时灭菌(ultra-high temperature treatment, UHT)是常用的牛乳杀菌技术,可分为直接式与间接式处理,其中直接式UHT技术由于成本高在乳品行业使用较少。近年来,随着消费者对牛乳营养物质和风味需求的升级,直接式UHT技术由于升温速度快、风味及营养成分损失少的优点,再次受到广泛关注。对比了浸入式和喷射式2种直接式处理技术对牛乳理化性质、活性乳清蛋白含量和挥发性化合物含量的影响。结果表明,浸入式UHT乳较喷射式UHT乳的平均粒径、失稳系数和黏度值均更小,但乳清蛋白变性率高。通过2种萃取方法——箭型固相微萃取法和溶剂辅助萃取法,结合气相色谱-质谱联用仪的分析结果,共在UHT乳中检测出59种挥发性化合物,其中,浸入式UHT乳中检测出50种,喷射式UHT乳中检测出52种。浸入式UHT乳中的酮、醛和脂肪酸类化合物比喷射式UHT乳中占比低,而酯类和醇类化合物占比高。主成分分析结果表明,浸入式UHT乳和喷射式UHT乳可根据挥发性化合物进行区分,说明不同的直接式UHT工艺可能对UHT乳风味产生影响。研究结果表明：若生产奶味更重的UHT乳,可选择喷射式UHT;若生产蒸煮...     

Review of UHT processing methods

The flavour and nutritional quality of UHT processed milk is discussed and suggestions are made for ways of minimizing undesirable changes during heat treatment. UHT treatment of milk using an infusion heater is described, and it is concluded that whole milk processed in this way is a typical directly heated UHT milk.     

THE NUTRITIONAL IMPORTANCE OF MILK AND MILK PRODUCTS IN THE NATIONAL DIET

The average consumption of milk and milk products is related to their composition and to the recommended intakes for nutrients, and the nutritional importance of dairy products is considered. The major contribution to the average diet is in the protein, calcium, riboflavin and vitamin A contained in dairy products.     

UHT乳非商业无菌原因分析及质量控制

分析了UHT奶非商业无菌的原因。依据GB/T4789.26-2003和ATD细菌生化鉴定义对UHT奶进行检测及细菌鉴定。结果表明,同一品牌不同品种的6种UHT奶中,有5种为非商业无菌;分别检出蕈状芽孢杆菌短小芽孢杆菌。结论:UHT乳质量把关须从原料乳,生产工艺,生长环境控制。     

Milk and cream: a review of recent market trends

There have been substantial changes in the market for liquid milk in the past few years. Within an overall decline in consumption there has been a marked shift to lower fat milks. The market for UHT milks is still low but is increasing. The cream market has also changed considerably, UHT cream now accounting for 20% of total sales. The reason is its long keeping quality. Fresh cream is still perceived as a quality product for use on special occasions.     

天然全脂超高温灭菌(UHT)乳生产中关键控制点的选择

基于牛乳的营养价值和当前的消费趋势，结合高速成长的乳业市场和极具发展潜力UHT乳，依据ISO9002质量保证体系、HACCP（危害分析和关键控制点）、GMP（良好生产规范）和SSOP（卫生标准操作规程）的思想，对创新性运用闪蒸工艺的天然全脂超高温灭菌（UHT）乳生产过程中影响产品品质及安全性因素进行了分析，确定了CCP（关键控制点），探索了生产“天然、绿色、安全、营养”全脂UHT乳的必要条件。     

Effect of addition of CO₂ to raw milk on quality of UHT-treated milk

The objective of this study was to evaluate the effect of addition of CO(2) to raw milk on UHT milk quality during storage. Control milk (without CO(2) addition) and treated milk (with CO(2) addition up to pH 6.2) were stored in bulk tanks at 4°C for 6d. After storage, both samples were UHT processed using indirect heating (140°C for 5s). Samples were aseptically packed in low-density polyethylene pouches and stored in the dark at room temperature. Raw milk was evaluated upon receipt for physicochemical composition, proteolysis, lipolysis, standard plate count, psychrotrophic bacteria, and Pseudomonas spp. counts, and after 6d of storage for proteolysis, lipolysis, and microbial counts. After processing, UHT milk samples were evaluated for physicochemical composition, proteolysis, and lipolysis. Samples were evaluated for proteolysis and lipolysis twice a month until 120d. Peptides from pH 4.6-soluble N filtrates were performed by reversed-phase HPLC after 1 and 120d of storage. A split-plot design was used and the complete experiment was carried out in triplicate. The results were evaluated by ANOVA and Tukey's test. After 6d of storage, CO(2)-treated raw milk kept its physicochemical and microbiological quality, whereas the untreated milk showed significant quality losses. A significant increase in proteolysis occurred during 120d of storage in both treatments, but the increase occurred 1.4 times faster in untreated UHT milk than in CO(2)-treated UHT milk. In both UHT milks, the proteolysis was a consequence of the action of plasmin and microbial proteases. However, the untreated UHT milk showed higher microbial protease activity than the treated UHT milk. The addition of CO(2) to the raw milk maintained the quality during storage, resulting in UHT milk with less proteolysis and possibly longer shelf life, which is usually limited by age gelation of UHT milk.     

乳中蛋白酶与UHT乳贮存中的胶凝现象

乳中的蛋白酶有2个主要的来源途径，乳中天然存在的蛋白酶和由某些微生物产生的蛋白酶，其中纤维蛋白溶酶和嗜冷菌产生的耐热性蛋白酶是存在于UHT乳中的主要蛋白酶，这些蛋白酶非常耐热，经UHT灭菌处理仍可存活。耐热性蛋白酶在UHT乳贮存中水解乳蛋白质从而导致了UHT乳的胶凝．简要介绍了纤维蛋白溶酶、嗜冷菌耐热性蛋白酶的性质、活性测定方法，论述了这些酶引起的UHT乳的胶凝性质、形成原因及影响因素，并提出了一些防止措施。     

超高温灭菌乳的主要质量问题及控制措施

本文对影响超高温灭菌乳质量的主要问题进行了阐述，其主要影响因素是原料乳的质量和超高温灭菌过程的几个重要方面。对超高温生产过程中的杀菌温度和保温时间，脱气和均质，无菌输送，无菌包装和无菌灌装阶段工艺设备进行分析，参照应用设备结构工艺特点，找出各阶段中影响超高温灭菌乳质量的主要因素，并提出控制措施。另一方面，对影响超高温灭菌乳质量的另一重要因素原料乳质量，根据乳的特性及采用的加工方法，提出控制措施，保证产品质量的稳定。     

苦味UHT乳原因分析

通过对发生苦味的UHT乳进行分析，将引起UHT乳贮存中出现苦味的原因分为两大类：一是受残留的微生物污染导致UHT乳产生苦味和其它异味，这类微生物包括耐热性强的解淀粉芽孢杆菌和青霉菌等；二是由于牛乳中存在的水解酶分解蛋白质和脂肪．生成肽、氨基酸和脂肪酸类，导致苦味的出现。针对这些影响因素，可以通过提高原料乳的卫生质量、严格控制生产加工过程和环境卫生，以避免UHTSL出现苦味的质量问题。     

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。     

UHT乳质量异常问题的分析及控制

为了提高UHT乳的乳质量，减少因质量问题给企业带来的不必要的经济损失，从超高温杀菌乳可能产生的质量问题出发．分析了影响乳成分稳定性的因素，并通过感官评定的方法及过滤、微生物检验的操作方法分析了超高温杀菌乳在生产及贮存中可能产生质量问题的原因，同时提出控制措施。结果表明，UHT乳质量与加工、贮存及原料乳的新鲜度密切相关，优质的原料乳和良好的生产规范生产出优质的UHT乳。