EFFECT OF DIFFERENT STORAGE CONDITIONS ON THE LIPID FRACTION OF A VEGETABLE CREAM

Fatty acids (free and esterified), diglycerides, peroxides and total sterols were determined in a vegetable cream. Cream samples were analyzed when fresh and after storage for 3 and 6 months at 4, 15, 30C and room temperature (10–25C). The product showed a higher amount of unsaturated fatty acids ( ≈ 50% of total fatty acids) with respect to milk fat and a low level of cholesterol ( < 0.01%). The phytosterol content ( ≈ 14 mg/100 g of cream) was not high enough to contribute to a decrease in cholesterolemia. Lipid oxidation remained low during storage (peroxides: 2.0–3.0 meq O₂/kg of fat), but a small increase was observed at room temperature after 6 months (about 6.0 meq O₂/kg of fat). Free fatty acids never exceeded 0.3% of fat. Storage at 4C and 15C delayed lipolysis in comparison to storage at 30C and room temperature.

PRACTICAL APPLICATIONS

The analysis of a vegetable cream demonstrated that it was a shelf-stable product, showing a high stability toward lipid oxidation and lipolysis. Such a product might be employed as vehicle for healthy fat compounds like long-chain polyunsaturated fatty acids, phytosterols and fat-soluble vitamins.     

Effect of somatic cell counts on lipolysis,proteolysis and apparent viscosity of UHT milk during storage

In this work, lipolysis, proteolysis and viscosity of ultra‐high temperature (UHT) milk containing different somatic cell counts (SCC) were investigated. UHT milks were analysed on days 8, 30, 60, 90 and 120 of storage. Lipolysis as measured by free fatty acids increase, casein degradation and viscosity of UHT milk were not affected by SCC but increased during storage. A negative relationship was observed between SCC and casein as a percentage of true protein on the 120th day of storage, hence indicating that high SCC increases the proteolysis of UHT milk by the end of its shelf life.     

Formation, Stability, and Properties of an Algae Oil Emulsion for Application in UHT Milk

This study aimed to develop a technology for producing ultrahigh temperature ultrahigh temperature-treated (UHT) milk enriched with docosahexaenoic acid. Starch hydrophobically modified with octenyl succinic anhydride (OSA starch) was used as an emulsifier to make algae oil emulsion in UHT milk. In this study, the stability of oil-in-water emulsions was examined. The emulsification of 10 % algae oil model emulsion with 10 % OSA starch and 40 % corn syrup had small droplets and was completely stable. Milk enriched with unsaturated fatty acids was heated using an indirect UHT treatment, and the milk was then stored at different temperatures. The oxidative stability of fish oil-enriched milk was investigated by measuring peroxide value, measuring volatile secondary oxidation products, and carrying out sensory analysis. All of the milk samples were stable. In summary, fish oil-enriched milk is resistant to oxidation. Algae oil-enriched drinking milk is a stable product during 11 weeks of storage. Application of high storage temperature (40 °C) does not significantly increase the oxidation process. The present study suggested that stable algae oil emulsion can be formed by OSA starches with corn syrup, and a food formulation test confirmed the successful application of algae oil emulsion to extend the shelf life of milk.     

Electrophoretic characterization of protein interactions suggesting limited feasibility of accelerated shelf-life testing of ultra-high temperature milk

Accelerated shelf-life testing is applied to a variety of products to estimate keeping quality over a short period of time. The industry has not been successful in applying this approach to ultra-high temperature (UHT) milk because of chemical and physical changes in the milk proteins that take place during processing and storage. We investigated these protein changes, applying accelerated shelf-life principles to UHT milk samples with different fat levels and using native- and sodium dodecyl sulfate-PAGE. Samples of UHT skim and whole milk were stored at 20, 30, 40, and 50°C for 28 d. Irrespective of fat content, UHT treatment had a similar effect on the electrophoretic patterns of milk proteins. At the start of testing, proteins were bonded mainly through disulfide and noncovalent interactions. However, storage at and above 30°C enhanced protein aggregation via covalent interactions. The extent of aggregation appeared to be influenced by fat content; whole milk contained more fat than skim milk, implying aggregation via melted or oxidized fat, or both. Based on reduction in loss in absolute quantity of individual proteins, covalent crosslinking in whole milk was facilitated mainly by products of lipid oxidation and increased access to caseins for crosslinking reactions. Maillard and dehydroalanine products were the main contributors involved in protein changes in skim milk. Protein crosslinking appeared to follow a different pathway at higher temperatures (≥40°C) than at lower temperatures, making it very difficult to extrapolate these changes to protein interactions at lower temperatures.     

UHT乳贮藏期间理化特性和感官品质的变化

为探讨超高温瞬时杀菌(ultra-high temperature instantaneous sterilization,UHT)乳的营养价值随贮藏时间的变化,对不同贮藏期UHT乳的理化特性和感官品质进行监测。在6个月的贮藏期内,UHT乳中脂肪、蛋白质、乳糖以及固形物的总量并无明显变化,维生素C和泛酸的含量均损失了约25%,游离氨基酸和钙离子分别增加了5.35%和6.73%。不同贮藏期UHT乳的黏度变化不显著(P>0.05),但粒径大小强烈依赖于贮藏时间,乳脂肪球和酪蛋白胶束的尺寸在贮藏初期分别增加了约38 nm和14 nm,然后分别稳定在约173 nm和612 nm。贮藏1个月的UHT乳样品在风味和口感方面整体表现较好,贮藏6个月后,UHT乳的感官品质大幅下降,出现了许多不良风味。     

Proteolysis and storage stability of UHT milk produced in Turkey

The effect of raw milk quality (total and psychrotrophic bacterial and somatic cell counts, proteinase and plasmin activity) and UHT temperature (145 or 150 °C for 4 s) on proteolysis in UHT milk processed by a direct (steam-injection) system was investigated during storage at 25 °C for 180 d. High proteinase activity was measured in low-quality raw milk, which had high somatic cell count, bacterial count and plasmin activity. The levels of 12% trichloroacetic acid–soluble and pH 4.6-soluble nitrogen in all milk samples increased during storage, and samples produced from low-quality milk at the lower UHT temperature (145 °C) showed the highest values. Bitterness in UHT milk processed from low-quality milk at 145 °C increased during storage; gelation occurred in that milk after 150 d. The RP-HPLC profiles of pH 4.6-soluble fraction of the UHT milk samples produced at 150 °C showed quite small number of peaks after 180 d of storage. Sterilization at 150 °C extended the shelf-life of the UHT milk by reducing proteolysis, gelation and bitterness.     

Simultaneous lipolytic and oxidative changes in turkey meat stored at different temperatures

Samples from turkey breast and thigh muscle were taken from freshly slaughtered birds under sterile conditions and stored at 37, 4 or ?18°C for up to 24 months. Changes in lipid fractions, fatty acids compositions and oxidised products were determined at intervals. Lipolysis of phospholipids was observed at 37 and at 4°C and to a small extent at ?18°C, with little change in triglyceride levels. Free fatty acid levels in general increased as phospholipids decreased. Oxodienes and conjugable oxidation products increased with time of storage, the latter products being negatively correlated with phospholipid concentrations. Changes in the ratio of tetraene to triene conjugated oxidation products formed indicated that some preferential oxidation of fatty acids more unsaturated than linoleic acid was occurring initially and this was followed by an increase in the proportion of dienes being oxidised. Both lipolysis and oxidation were faster in thigh than in breast muscle (P < 0.01) in the stored meat and in in-vitro systems. It is concluded that lipolysis and oxidation interact in the degradation of lipids during storage of turkey meat.     

原生态与人工添加二十二碳六烯酸羊乳制品贮藏期脂肪酸稳定性比较

通过饲喂奶山羊富含二十二碳六烯酸（docosahexaenoic acid，DHA）的微藻粉，获得原生态DHA羊乳（DHA含量为30 mg/100 g原料乳），然后将其制作成超高温瞬时灭菌（ultra-high temperature instantaneous sterilization，UHT）乳及全脂乳粉，同时设立人工添加富含DHA微胶囊粉的UHT乳及全脂乳粉作为对照组，在常温（25 ℃）和高温（37 ℃）下进行为期28 d的贮藏实验，研究原生态与人工添加DHA羊乳制品贮藏期脂肪酸稳定性。结果表明，与人工添加组相比，贮藏期间原生态UHT乳及全脂乳粉的DHA含量下降速率明显减缓，在UHT乳中，人工添加组乳制品DHA含量降低率在37 ℃下最高达（40.92±3.52）%（贮藏第28天），此时原生态组DHA降低率为（36.70±4.84）%。贮藏期间，原生态与人工添加DHA的UHT乳及全脂乳粉中多不饱和脂肪酸相对含量总体均下降，且与人工添加DHA的乳制品相比，原生态组中多不饱和脂肪酸相对含量更高，更易氧化生成碳链更短的脂肪酸。此外，随着贮藏期的延长，原生态DHA乳制品组中的油脂氧化指标过氧化值和酸价上升速率明显低于人工添加DHA乳制品组。综上，本实验可为制备富含DHA的天然奶制品提供理论参考。     

Oxidative stability of UHT milk as influenced by fatty acid composition and packaging

Control milk and milk enriched with unsaturated fatty acids (3.3% fat) were heated using an indirect ultra-high temperature treatment, then stored at 20 °C in containers from different packaging materials: glass (no exposure to light), high density polyethylene (HDPE) packaging with light barrier (3-HDPE; no exposure to light) and monolayer HDPE (1-HDPE; 1000 lx). The decrease in antioxidant content and the formation of oxidation products were monitored over three months. For milk stored in 1-HDPE packaging, the available antioxidants were consumed at the same rate for both milk types, suggesting that oxidation is initiated in the serum phase. After depletion of these antioxidants, oxidation products were formed according to the fatty acid profile. When using a light barrier in the packaging, no oxidation products could be detected over three months.     

Effect of calcium on fatty acid bioaccessibility during in vitro digestion of Cheddar-type cheeses prepared with different milk fat fractions

Calcium plays an important role in intestinal lipid digestion by increasing the lipolysis rate, but also limits fatty acid bioaccessibility by producing insoluble Ca soaps with long-chain fatty acids at intestinal pH conditions. The aim of this study was to better understand the effect of Ca on the bioaccessibility of milk fat from Cheddar-type cheeses. Three anhydrous milk fats (AMF) with different fatty acid profiles (olein, stearin, or control AMF) were used to prepare Cheddar-type cheeses, which were then enriched or not with Ca using CaCl₂ during the salting step. The cheeses were digested in vitro, and their disintegration and lipolysis rates were monitored during the process. At the end of digestion, lipids were extracted under neutral and acidic pH conditions to compare free fatty acids under intestinal conditions in relation to total fatty acids released during the digestion process. The cheeses prepared with the stearin (the AMF with the highest ratio of long-chain fatty acids) were more resistant to disintegration than the other cheeses, owing to the high melting temperature of that AMF. The Ca-enriched cheeses had faster lipolysis rates than the regular Ca cheeses. Chromatographic analysis of the digestion products showed that Ca interacted with long-chain fatty acids, producing Ca soaps, whereas no interaction with shorter fatty acids was detected. Although higher Ca levels resulted in faster lipolysis rates, driven by the depletion of reaction products as Ca soaps, such insoluble compounds are expected to reduce the bioavailability of fatty acids by hindering their absorption. These effects on lipid digestion and absorption are of interest for the design of food matrices for the controlled release of fat-soluble nutrients or bioactive molecules.     

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。     

Effect of green tea catechins on physical stability and sensory quality of lactose-reduced UHT milk during storage for one year

Ultra-high temperature (UHT) processed lactose-reduced milk containing added green tea extract (GTE) at two concentrations (0.1% and 0.25%) was stored at 22 ± 2 °C for one year. The effect of GTE addition on physical stability, protein binding, and sensory quality was evaluated. Sedimentation in skim milk and creaming of full fat milk were inhibited by addition of GTE. The formation of Maillard-related flavour compounds was inhibited during storage as determined by dynamic headspace GC–MS. Using Western blot analysis, milk proteins were found to be highly conjugated to polyphenols. Addition of GTE before UHT treatment resulted in increased bitterness and astringency in UHT milk and this remained during storage. Even though GTE addition improved the physical stability and inhibited Maillard reactions in the milk, the taste and flavour contribution from GTE was dominating throughout storage, and alternative sources of polyphenols should be explored for increasing shelf-life stability of long-life milk.     

Stability of fatty acid composition after thermal,high pressure,and microwave processing of cow milk as affected by polyunsaturated fatty acid concentration

Interest has been increasing to enhance the contents of healthy polyunsaturated fatty acid (PUFA) in milk. However, trans fatty acids and conjugated linoleic acid (CLA) can be altered after thermal processing and high pressures disrupt the milk fat globule membrane, exposing the lipid core and helping its oxidation. The objective of the present research was to study whether processing can alter the fatty acid composition of milk and if these changes are affected by PUFA concentration as previous studies suggest. Two cow milk batches (500 L each), one naturally enriched in PUFA, were processed to obtain pasteurized; high temperature, short time; UHT; high pressure; and microwave pasteurized samples. The detailed fatty acid composition was analyzed with special attention to trans fatty acids and CLA isomers. Results showed that after high temperature, short time processing, total CLA content increased in both milk batches, whereas sterilization resulted in a sigmatropic rearrangement of C18:2 cis-9,trans-11 to C18:2 trans-9,trans-11. The extent of these effects was greater in milks naturally enriched in PUFA.     

Predicting sediment formation in ultra high temperature-treated whole and skim milk using attenuated total reflectance-Fourier transform infrared spectroscopy

Establishing accelerated shelf-life testing using Fourier transform infrared spectroscopy (FTIR) as a tool for prediction of stability requires pre-assessment of correlations between spectral changes and instability development during storage at room temperature. Comparison of results with those at elevated temperatures would establish appropriateness of accelerated shelf-life testing. UHT skim milk (SM) and UHT whole milk (WM) were stored at 20 °C for 9 months to investigate the feasibility of identifying spectral markers to predict sedimentation (a measure of instability). Marker variables corresponding to changes in structure and interactions of lipids, proteins and carbohydrates successfully predicted sedimentation in SM (R² = 0.92) and WM (R² = 0.60). Low predictability in WM may be due to influence of fat. These markers were similar to those observed during accelerated shelf-life testing, hence affirming its application with further work required to develop a model able to forecast sedimentation and other instabilities in 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.     

Influence of pre-cure freezing of Iberian hams on lipolytic changes and lipid oxidation

The purpose of this work was to study the influence of pre-cure freezing of Iberian hams on lipolysis and lipid oxidation during the ripening of the product. At the green stage, the levels of fatty acids (FA) in the free fatty acids fraction were higher in pre-cure frozen (F) than in refrigerated (R) hams, whereas in the polar lipid fraction, FA and dimethyl acetals (DMA) values were higher in R than in F Iberian hams. These results point out the existence of lipolysis phenomena during the freezing storage. At the end of post-salting and at the final stage, both R and F hams showed similar FA and DMA profiles. The effect of pre-cure freezing of hams influenced lipolysis evolution throughout the processing. The development of lipid oxidation was similar in R and F hams, but Thiobarbituric acid-reactive substances (TBAR) values were significantly higher in F hams at the initial stage and at the end of post-salting and drying steps. Despite all these differences, at final stage the FA and DMA composition as well as TBAR levels were quite similar in R and F hams.     

On the influence of non‐enzymatic crosslinking of caseins on the gel strength of yoghurt

After storage of UHT milk at 37°C resp. 50°C, yoghurt was prepared. For a storage temperature of 37°C, breaking strength of the yoghurt samples increased from 2.7 to 5.8 N with increasing storage duration of the UHT milk. A plateau is reached after 17 days of storage. This increase in breaking strength correlates with a significant increase in non‐reducible casein oligomerization from 14% for fresh UHT milk to 25% measured using size exclusion chromatography under reducing and denaturing conditions and calculated as sum of predominantly formed dimers and trimers at the total casein fraction. At a storage temperature of 50°C, a less increase in breaking strength from 2.7 to 4.6 N with a plateau after 17 days was observed while casein oligomerization increased to 63%. After acid hydrolysis, only lysinoalanine and histidinoalanine were detected in the caseinate samples via amino acid analysis. The quantified concentration of lysinoalanine and histidinoalanine could not explain the observed casein oligomerization. Thus, unknown crosslinked amino acids must have been formed during storage, inducing significant changes in the functional properties of milk proteins.     

Ex vivo digestion of raw,pasteurised and homogenised milk – Effects on lipolysis and proteolysis

This study investigated the impact of pasteurisation and homogenisation on ex vivo gastrointestinal digestion of proteins and fat in bovine milk. Milk that was homogenised at 150 bar showed the highest degree of lipolysis (78%) after 120 min duodenal digestion. In comparison, milk homogenised at 50 bar showed 56% release of fatty acids whereas raw and pasteurised milk showed 49% and 44% hydrolysis, respectively. Pasteurisation had very much less effect upon lipolysis and proteolysis. Homogenisation increased the gastric proteolysis of specifically β-lactoglobulin, and also of α-lactalbumin. However, after 5 min duodenal digestion all the proteins were degraded in all milks tested. Thus, both lipolysis and proteolysis were increased by homogenisation of the milk, making fatty acids from lipids and peptides from β-lactoglobulin more readily available to the human body.     

Milk lipase and off-flavour development

The origins of milk lipases and free fatty acids are discussed, together with properties of the principal enzyme responsible for lipolysis in raw milk. Variations in milk free fairy acid levels are shown to result from the net effect of several factors which influence overall enzyme activity and the nature of the fat globule surface. Possible forms of damaged fat are described with evidence suggesting that gross damage such as clumping or coalescence does not necessari 1.v give rise to high free fatty acid values. The risks of lipolysis both with types of milking installation and during the handling. storage and processing of milk are assessed. Levels of free fatty acids likely lo produce detectable rancid flavour are given with typical values for milk and cream in the UK     

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...