Comparison of free amino acids and volatile components in three fermented milks

Free amino acids (FAAs) and volatile components were analysed in commercial samples of yoghurt and Actimel^® drink as well as laboratory‐made kefir. The lysine and cysteine were the principal amino acids and accounted for about 70% of the total FAAs in all the samples. However, the amino acid profiles in the different fermented milk products differed: on the whole values for most of the amino acids were observed to be significantly higher in the Actimel^® samples. A total of 50 volatile components were identified. The largest number of volatiles were found in the kefir. Ethanol, 2,3‐ butanodione and 3‐hidroxybutan‐2‐one were the most prevalent volatile components, with ethanol significantly higher in the kefir samples.     

Adaptation of Escherichia coli O157:H7 to acid in traditional and commercial goat milk amasi

Acid resistance of Escherichia coli O157:H7 strains UT 10 and UT 15 were determined in traditional Amasi fermented for 3 days at ambient temperature (ca 30 °C) and commercial Amasi fermented at 30 °C for 24 h and stored at 7 °C for 2 days. Escherichia coli O157:H7 counts in commercial Amasi were detected at 2.7 log₁₀ cfu/ml after 3 days while those in traditional Amasi could not be detected after the same period. There was no significant difference (p ? 0.05) in the survival of acid adapted (AA) and non-adapted (NA) E. coli O157:H7 in traditional Amasi, while in commercial Amasi, the NA strain survived significantly (p ? 0.05) better than its AA counterpart. Regardless of prior adaptation to acid, E. coli O157:H7 can survive during fermentation and storage of fermented goat milk Amasi. Also, the fermentation time, pH and storage temperature affects the survival of E. coli O157:H7 in the fermented milk.     

共轭亚油酸强化型乳制品的稳定性研究

通过牛乳液中添加共轭亚油酸（CLA）,分析杀菌温度、均质压力、乳化剂类型、CLA添加量对牛乳稳定性的影响.实验结果表明：脱脂乳中添加0.17%的CLA稳定性较好,口感纯正;当灭菌温度超过100℃时,CLA含量明显降低;以单苷酯、三聚苷酯和蔗糖酯的混合乳化剂,按1∶1∶2混合的乳液稳定性好;35MPa以上的均质压力下,乳液中的脂肪球细小,分布均匀,口感细腻。     

牦牛α-乳白蛋白基因单核苷酸多态性分析

为明确牦牛乳中α-乳白蛋白遗传多样性,以α-乳白蛋白基因(LAA)的Ⅰ、Ⅱ、Ⅲ和IV外显子为研究对象,采用聚合酶链反应-单链构象多态性(PCR-SSCP)方法对麦洼牦牛的LAA进行分析,旨在从分子水平揭示LAA在牦牛乳中遗传多样性分布. 牛属不同来源的α-乳白蛋白基因的编码序列被用于构建系统发育树. 结果表明,牦牛乳中LAAⅠ外显子区域以杂合体形式存在,并发现了一个新变异体JN084189. 不同来源LAA的系统发育树分析表明,LAA在进化上存在一定的物种特异性.     

不同贮藏温度对UHT乳品质的影响

UHT乳作为一种经超高温瞬时灭菌、无菌灌装生产的长货架期液态乳,具有品质优良,饮用方便等优点.但是在贮藏过程中,UHT乳经常会因残留酶或微生物作用而产生蛋白质凝块、沉淀或脂肪上浮等缺陷,从而影响UHT乳的品质.本研究通过UHT中试生产线无菌灌装制备PET瓶装UHT乳,将其分别置于7,25,37℃下保温观察,定期测定色泽、酪蛋白胶体粒径、蛋白质水解度及理化指标等变化.结果表明,贮藏过程中UHT乳发生的主要反应为蛋白质水解、脂质氧化和美拉德反应,UHT乳的pH值、游离钙离子含量和酪蛋白胶体粒径呈下降趋势,b＊值、蛋白水解度、脂质氧化程度呈上升趋势.120 d保温试验结束后,除37℃贮藏下的UHT乳色泽从第90 d开始发生明显变化外,各UHT乳样品并未产生明显的脂肪上浮和蛋白沉淀等现象.     

<Superscript>1</Superscript>H NMR characterization of milk lipids: A comparison between cow and buffalo milk

Characterization of the lipid fraction of raw cow and buffalo milk samples, collected in different breeding areas in Apulia, a region of southern Italy, were performed by means of ¹H NMR. The aim of this work was to establish whether FA composition data obtained by ¹H NMR can be used in the differentiation of buffalo and cow milk samples according to species. A complete assignment of the signals present in the spectrum was attempted by COSY, heteronuclear coherence spectra. Quantification of FA was carried out by inserting the integrals of particular peaks in suitable calculations. Multivariate statistical analysis, conducted on the results of the quantification, permitted buffalo and cow milks to be distinguished.     

Thermal behavior of fat droplets as related to adsorbed milk proteins in complex food emulsions. A DSC study

The thermal behavior of hydrogenated palm kernel oil-in-water emulsions, which differed in their milk-protein composition, was studied in parallel with other characteristic parameters such as the aggregation/coalescence of fat droplets, and the proportion of adsorbed proteins at the oil/water interface. DSC was applied to monitor the crystallization and melting behavior of nonemulsified and emulsified fat samples. Comparison between nonemulsified and emulsified fat samples showed that in emulsified samples the initial temperature of fat crystallization and the temperature of the completion of melting were invariably lower and slightly higher, respectively. Furthermore, in complex food emulsions the supercooling temperature needed to initiate fat crystallization and the variation in its growth rate in the cooling experiment were dependent on the amount and nature of the adsorbed proteins. Our results indicate that the total replacement of milk proteins by whey proteins affected the fat crystallization behavior of emulsified fat droplets, in parallel with changes in their protein surface coverage and in their physical stability against fat droplet agglomeration.     

Phase equilibrium and crystallization behavior of mixed lipid systems

As complex lipid systems, the phase and crystallization behavior of mixtures of a high-melting milk fat fraction with a low-melting milk fat fraction or canola oil was studied. A turbidity technique was developed to estimate solubility and metastability conditions of these lipid mixtures. Both solubility and metastability of the high-melting milk fat fraction in liquid lipids increased exponentially with temperature. At a given equilibration temperature, liquid phases and solid fractions with nearly identical melting profiles and TAG compositions were obtained regardless of the original concentration of the lipid mixture. The maximum melting temperature (MMT), as measured by DSC, of the liquid phase increased dramatically in the equilibrium temperature range of 27.5–35.0°C but did not change at temperatures below and above this range (down to 25.0°C and up to 40°C in this study). The content of long-chain TAG (C₄₆−C₅₂) increased and short-chain TAG (C₃₆−C₄₀) decreased in the liquid phases as the equilibrium temperature increased. A plot of the TAG group ratio (i.e, long-short-chain TAG) vs. equilibrium temperature was generated to illustrate the phase behavior of the complex lipid system and to represent a solubility curve, from which the supersaturation level for crystallization kinetics was determined. Higher supersaturation and lower temperature resulted in higher nucleation and crystallization rates. Compared to the system with a low-melting milk fat fraction, mixtures of the high-melting milk fat fraction with canola oil had higher nucleation and crystallization rates due to the lower solubility found for this system.     

Oxidative stability of milk drinks containing structured lipids produced from sunflower oil and caprylic acid

Milk drinks containing 5% traditional sunflower oil (SO), randomized lipid (RL) or specific structured lipid (SL) (both produced from SO and tricaprylin/caprylic acid) were compared with respect to their particle size, viscosity and oxidative stability during storage. Furthermore, the effect of adding potential antioxidants EDTA or gallic acid to the milk drink based on SL was investigated. The lipid type significantly affected the oxidative stability of the milk drinks: Milk drink based on SL oxidized faster than milk drink based on RL or SO. The reduced oxidative stability in the SL milk drink could not be ascribed to a single factor, but was most likely influenced by the structure of the lipid and differences in the process applied to produce and purify the lipids. EDTA was a strong antioxidant, while gallic acid did not exert a distinct antioxidative effect in the milk drink based on SL.     

MODELING WATER SORPTION IN OKARA SOY MILK

ABSTRACT

Moisture sorption isotherms of okara soy milk were determined using the gravimetric method in the range 20 - 50 °C. The sorption isotherms exhibited hysteresis along all the water activity range (0·1 - 0·9). The amount of sorbed water increased as the temperature was decreased. The GAB and Halsey models gave a good fit for okara isotherms over the range of water activity 0·1 - 0·9. As temperature increased, GAB k-values increased towards unity where the GAB equation reduces to the BET equation. The influence of temperature on the constants of GAB and Halsey models was evaluated through Arrhenius-type equations. The Clausius Clapeyron equation was used to estimate the isosteric heats of sorption.