水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响

采用加速氧化的方法研究水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响。通过测定全脂羊奶粉的酸值、过氧化值、硫代巴比妥酸值(TBA)、颜色等指标评价全脂羊奶粉贮藏期间的氧化状况。结果表明,水分活度为0.32的全脂羊奶粉贮藏期间酸值、TBA值显著高于水分活度为0.11和0.23的全脂羊奶粉(p<0.05),且水分活度为0.32的全脂羊奶粉过氧化值变化速率较快(p<0.05),且褐变严重。因此,降低全脂羊奶粉的水分活度可以提高其贮藏稳定性。      

充氮包装对全脂羊奶粉贮藏期间脂肪氧化稳定性的影响

采用加速氧化的方法研究充氮包装对全脂羊奶粉贮藏期间脂肪氧化稳定性的影响。通过测定全脂羊奶粉的酸值、过氧化值、硫代巴比妥酸值(TBA)、色度值等指标评价全脂羊奶粉贮藏期间脂肪的分解氧化状况。结果表明:充氮包装的全脂羊奶粉贮藏期间酸值、TBA值和色度值变化趋势较慢,分别于第6周后、第3周后、第7周后显著低于普通包装的全脂羊奶粉(p<0.05);充氮包装的全脂羊奶粉的过氧化值于第7周达到最高值13.54mmol/kg脂肪,变化速率显著小于普通包装的全脂羊奶粉(p<0.01)。说明充氮包装可延缓酸值、过氧化值、TBA值和色度值的变化速率,显著提高全脂羊奶粉脂肪的氧化稳定性。      

贮藏温度对全脂羊奶粉品质稳定性的影响

本文主要研究了贮藏温度(5、25和35℃)对全脂羊奶粉品质稳定性的影响。通过测定全脂羊奶粉的酸值(AV)、过氧化值(POV值)、硫代巴比妥酸值(TBA值)、溶解度、色值等指标反应贮藏期间品质的变化。结果表明,贮藏在35℃的全脂羊奶粉贮藏期间酸值、过氧化值、TBA值变化速率较快,分别于第4个月后、第2个月后、第3个月后显著高于贮藏在5℃和25℃的全脂羊奶粉(p<0.05);所有样品的溶解度和色值变化规律相似,但差异不显著(p>0.05)。因此降低贮藏温度可提高全脂羊奶粉品质稳定性。      

水分活度对碧螺春绿茶贮存稳定性的影响

以碧螺春绿茶为实验材料,研究水分活度对绿茶贮存稳定性的影响.结果表明,水分活度对绿茶的贮存稳定性有很大的影响.不同水分活度下贮存4个月后,在高水分活度区域,绿茶的稳定性显著下降,各生化成分含量迅速降低.在低水分活度区域,碧螺春茶相对稳定,但脂质、咖啡碱、儿茶酚等成分含量的保留值小于A叫0.33处.碧螺春绿茶在Aw0.2～0.3范围内(单层水分含量对应范围)具有最佳稳定性.     

水分活度对贮藏脱水香葱的风味和菌群的影响

为研究水分活度(water activity,aw)对脱水香葱贮藏过程中风味和菌群的影响,本实验测定了脱水香葱在不同aw条件下贮藏50d后的挥发性成分和细菌群落组成,并探讨两者之间的相关性.结果 表明,在不同aw条件下贮藏50d后,脱水香葱的细菌多样性相比贮藏前显著升高(P＜0.05),脱水香葱样品的细菌群落结构与贮藏...     

等温水分活度及其对低水分食品中微生物抗热性的影响研究进展

水分活度（Water activity,a_w）是定义低水分食品（a_{w,25 ℃}<0.85）的关键指标,对低水分食品（LMFs）中微生物的抗热性起着决定性的作用。食品的水分活度受到食品组分、质构等的影响,并且与温度密切相关,在温度改变时呈现不同的变化趋势,是典型的温度依赖型指标。等温水分活度（a_w,T）反映了食品在高温灭菌过程中的实时水分活度,其准确测定或推算有助于学者量化低水分食品中微生物抗热性指标,进而设计、验证、完善相关热灭菌工艺。但商业化的水分活度仪只能测量低温区间（20~50 ℃）,人们对高温区间（>55 ℃）的水分活度还了解甚少。本文首先介绍了低水分食品微生物安全及其抗热性指标,然后对等温水分活度的定义、检测方法、模型预测、影响因素及其对微生物抗热性的影响研究进行综述。等温水分活度的认知与测定有利于食品企业降低低水分食品的微生物污染程度,保障消费者食品安全。     

不同水分活度降低剂对大菱鲆即食制品的影响

为了降低大菱鲆即食制品水分活度,延长制品保藏期,选择丙三醇、乳酸钠、麦芽糖醇3种水分活度降低剂,在单因素试验基础上,根据Box-Behnken原理设计三因素三水平响应面试验,建立二次多项数学模型,并进行保藏实验。以水分活度为指标,得到大菱鲆即食制品水分活度降低剂的最佳配比为丙三醇添加量4.1 mL/100 g、乳酸钠添加量1.5 mL/100 g、麦芽糖醇添加量4.0 g/100 g,在此配比下含水量40%的大菱鲆即食制品水分活度为0.781。将产品在37℃贮藏7 d后其菌落总数为4.04(lg(CFU/g))、TVB-N值为12.47 mg/100 g、TBA值为1.48 mg/100 g,均在国家标准限量范围内。说明利用水分活度降低剂能有效提高产品的保藏性能,延长产品的保藏期。     

发酵香肠的pH值、水分含量与水分活度(Aw)的关系及其对制品贮藏性的影响

对发酵香肠的 pH值、水分含量与水分活度 (Aw)的关系及其对制品贮藏性的影响作了初步的研究。结果表明 :水分活度的下降与 pH值及水分含量均是呈直线关系 ,随制品 pH和水分含量的降低 ,水分活度逐渐下降 ,但 pH值对水分活度的影响较小 ,水分含量影响较大。香肠的 pH值、水分含量和水分活度值越底其贮藏稳定性越高。     

高含水率脱水菜心降水分活度技术及贮藏稳定性研究

探讨了葡萄糖、乳糖、氯化钠、麦芽糊精复合使用对高含水率脱水菜心水分活度的降低作用，研究了不同包装条件、不同贮藏温度对高含水率脱水菜心贮藏稳定性的影响。结果表明，较佳的水分活度降低剂组合为：葡萄糖质量浓度8g／dL，乳耱质量浓度4g／dL，氯化钠质量浓度2g／dL，麦芽糊精质量浓度7．5g／dL。真空包装和避光包装可减小高含水率脱水菜心擘藏中叶绿素和抗坏血酸的损失，减缓褐变的产生；4℃贮藏可以较好地保持高含水率脱水菜心的品质。微生物实验表明，水分活度为0．69-0．70的高含水率脱水菜心可以安全贮藏。     

亲水性物质对低糖胡萝卜脯水分活度的影响

研究不同亲水性物质柠檬酸、酒石酸、乳酸钠和单甘酯对低糖胡萝卜脯水分活度(Aw)的影响。结果表明:水分含量在18%～20%时,其降低水分活度的能力不同,强弱依次为酒石酸>柠檬酸>乳酸钠>单甘酯,浓度越大降低水分活度的能力越强;亲水性物质在复合使用时,降低水分活度能力比其中任一种单一使用时强;通过回归方程分析,得出了柠檬酸+酒石酸的复合配比最好。     

Changes in free fatty acid composition during storage of whole milk powder

Changes in fat matter due to the microbial thermostable lipases are among the most significant deteriorations influencing the shelf life of whole milk powder. As a consequence, free fatty acids are produced, being the short-chain acids mainly responsible for the rancidity flavour. The aim of this work was to evaluate changes in different fatty acid concentrations during the storage of whole milk powder produced in two different seasons. Samples of whole milk powder produced in winter and summer and packed under inert atmosphere were used in the study. The samples were stored at 21°C and 40°C. Samples stored at 21°C were evaluated every 3 months, whereas samples stored at 40°C were evaluated monthly by free fatty acids profile and sensory analysis. Data were processed by principal component analysis and anova . Results showed that changes in the free fatty acids of milk powders were correlated with the season of manufacture. Temperature and storage time had little influence on that profile.     

Comparative study on the characteristics and oxidation stability of commercial milk powder during storage

The quality of milk powder can decrease during storage. In this study, the characteristics of 12 kinds of commercial milk powder from China were investigated. Changes in various indicators were tracked to comprehensively estimate the oxidation stability of different commercial milk powders. The components of the commercial milk powder were different. The percentages of milk fat, protein, and carbohydrates ranged from 9.8 to 28.5 g/100 g, 15.0 to 24.0 g/100 g, and 32.0 to 67.5 g/100 g, respectively. The water activities ranged from 0.2394 to 0.5286. The diameters of the milk fat globules in different commercial milk powder ranged from 13.99 to 41.09 nm. At the same time, the peroxide value of the control sample was low (≤0.14 mEq/kg). After 3 mo of storage, the peroxide values of some of the commercial milk powder increased significantly. The changes in the thiobarbituric acid values during storage did not follow a common trend. The contents of free fat in the different control samples were 0.21 to 1.67 g/100 g, and these values did not increase during storage. After 3 mo of storage, the hydroxymethyl furfural values and b color values of the different commercial milk powder reached their highest levels. The concentrations of typical oxidized flavor compounds in different commercial milk powder increased greatly with prolonged storage time. The level of hexanal was the highest, and the contents in all the samples ranged from 28.56 to 4,071.28 μg/kg after 6 mo of storage and from 5.91 to 6,281.37 μg/kg after 12 mo of storage. Free radicals were found in some of the stored milk powder, and these were shown as single peaks or multiple peaks. The ratios of the peak areas and masses reached 12.42 × 10⁶ to 14.26 × 10⁸. However, the presence of free radicals in the commercial milk powder was not consistent. The water activities and diameters of the fat globules in the commercial milk powder were highly correlated with their oxidation stabilities during storage.     

全脂羊乳粉中塑化剂的暴露量调查及安全评估

目的调查国内有代表性的羊乳粉加工企业生产的乳粉中塑化剂的种类和含量,并评估羊乳粉中塑化剂的暴露量情况,为安全性评价提供参考。方法通过Monte Carlo模拟对不同年龄段的婴幼儿通过乳基粉对塑化剂的膳食暴露情况进行非参数概率评估,按照美国环境保护署(EPA)提出的经口摄入参考剂量(reference dose,RfD),对塑化剂膳食暴露引发的健康风险进行评价。结果Ⅰ、Ⅱ、Ⅲ段龄3组婴幼儿对邻苯二甲酸二(2-乙基)己酯(DEHP)摄入量的平均值(90%Confidence Interval)的致癌风险分别为1.56×10-5、2.16×10-5、1.33×10-5a-1,均在EPA推荐的最大可接受值1.0×10-4 a-1范围之内。以高百分位(P99)计算来看,3组婴幼儿的邻苯二甲酸二异丁酯(DIBP)、DEHP、邻苯二甲酸二环己酯(DCHP)、邻苯二甲酸二丁酯(DBP)的健康风险值均小于1,在风险控制标准之下。结论以羊乳粉作为生产婴幼儿配方乳粉的基料是安全的。     

Evaluation of test conditions during the measurement of coffee stability of instant whole milk powder

Coffee provides a harsh environment for the reconstitution of milk powder with undissolved powder being manifested as undesirable 'floaters' or 'sinkers'. A coffee test method was adapted to explore the behaviour of a range of industrial samples of coffee stable and coffee unstable instant whole milk powders, under varying pH, temperature and water hardness. The development and application of a simulation test suggests evidence of some stabilizing contribution by the coffee itself. High surface fat coverage, as determined by electron spectroscopy for chemical analysis, and high ionic calcium levels were associated with instances of poor coffee stability. The effects of the physicochemical characteristics of the powders on coffee stability appear to predominate when various measures were implemented, such as prior reconstitution of the powder before addition to coffee, increased agitation and use of surface active agents, which succeeded in reducing coffee sediment.