食品中水份活度的测定

水份活度(Water Activhy)就是指放在一个密闭容器内的样品达到平衡时所产生的水蒸汽压与同一温度下纯水的蒸汽压之比,亦即平衡相对湿度(ESH): A_w=P/Po=ERH/100式中A:水份活度 P:样品平衡时所产生的水蒸汽压 Po:相同温度下纯水的蒸汽压 水份活度(Aw)决定了食品中不同存在状态的水的比例。它与食品的质构、色泽、营养、风味、流变特性及微生物的生长有着密切关系。因而它对食品的货架寿命有着重要的影响。根据样品的水份活度值可以选择     

植物精油蒸气与空气负离子在食品保藏中的应用研究进展

植物精油属于GRAS物质,具有较高的安全性,将其应用到食品的防腐保鲜中可以减少化学合成抗菌剂对人体产生的不良影响。精油的蒸气形式可以在不与食品直接接触的情况下对多种细菌、霉菌和酵母产生抑制作用,其主要抑菌成分为单萜烯和醛类,通过疏水性作用于细胞达到抗菌效果。植物精油蒸气与食品包装相结合,可以降低精油对于食品感官的影响并为食品提供抑菌保护。空气负离子能提高精油蒸气对微生物细胞的破坏作用,高浓度的空气负离子还能抑制微生物的活性,将精油与空气负离子结合使用,可以把对食品品质的影响降到最低,并提供更好的抑菌效果。     

谷物水活度的康卫氏皿测定方法分析

水活度是粮食储存安全的重要指标,利用传统测定食品水活度的康卫氏皿法测定了小麦、稻谷和玉米3种粮食籽粒的水活度,研究结果表明传统康卫氏皿测水活度方法也可以应用于粮食籽粒水活度的测定,结果能够基本反映粮食的当前水活度值,但是传统方法精确度不高,操作复杂,不适于储存粮食水活度准确便捷的测定。     

分析水活度用于食品质量与安全控制的研究进展

水活度作为食品质量与安全控制中的一项重要指标,其与水分含量之间存在密切联系,能够准确且高效的反映出食品品质,在食品安全中具有良好的应用价值。本文基于水活度与水分含量之间的关系出发,探究水活度研究的应用领域,分析水活度的测量方法及其相关标准,以促进水活度用于食品质量与安全控制相关研究的有效深入,仅供相关人员参考。     

氯化镁饱和乙醇溶液中溶剂活度的测定

在３４０－３６０Ｋ范围内分别测定了乙醇和氯化镁饱和乙醇浓液的蒸气压与温度对应关系数据;根据热力学原理推导出蒸气压法和沸点升高法精确计算乙醇活度的方程式,用本文中导出的方程式和教科收中常见的方程式处理实验数据,结果有所误别。     

水活度用于食品质量与安全控制的研究进展

与水分含量相比,水活度是更有效反映食品品质的热力学概念指标。国外多个组织如国际标准化组织(ISO)、美国公职分析化学师协会-食品药品管理局(AOAC-FDA),将水活度作为一项指标纳入多项有关食品质量与安全检验控制的标准。介绍水活度指标与水分含量指标的关系,并对水活度检测方法、相关规定以及其在食品质量与安全检验控制等方面的应用和研究进展进行了综述。我国水活度在食品安全相关应用和研究还存在标准制定、仪器研发等方面的严重不足。本文旨在引起相关重视,推动水活度在食品安全中应用的发展。     

天津开发出系列微波能设备

食品的灭菌和保鲜是食品加工行业的一个重要方面.传统加热、灭菌工艺主要依靠热力(热蒸气、红外线、热空气)通过热传导、热对流、热辐射三个途径对物料加热,这种由     

二 组分水溶液水活度简化预测法

本文介绍中等食品二组分水溶液有关浓度范围内的水活度(aw)简化预测法。水活度作为一些溶质(电解质和非电解质)重摩浓度的函数可用方程aw=1-Km描述,K为常数,m是重摩浓度。这里报导了15种非电解质和 8种电解质的K值。本法预测水活度的精确性可满足食品研究的实需。     

臭氧冰制备技术及其在食品保鲜中的应用研究进展

臭氧冰相较于臭氧气体和臭氧水具有易存储、半衰期长的优点，存储在冰中的臭氧可随冰的融化缓慢释放，应用于食品中可以达到较长时间持续杀菌保鲜的效果。文章从臭氧制备技术进展出发，介绍了臭氧的产生、臭氧水的制备，阐述了臭氧冰在食品保鲜中的应用，并展望了臭氧冰在食品中的应用前景。     

换气保鲜技术

<正>换气保鲜技术是国际80年代新技术,它是根据食品的不同变质原因和保鲜要求而配制的,产品装袋后抽完再充入无毒保鲜气体,经密封而成,不需再加热杀菌。它适用性广,应用灵活保鲜效果好,成本低,保鲜期是真空包装的1～3倍。采用换气包装的食品不受压、不变形、不走油、不走汁、不腐、不虫、不哈败,可以保香、护色,使食品在常期常温下贮存后色     

Water sorption isotherm of solution containing hydrogels at high water activity

Summary The water vapour sorption isotherm, in the water activity range of 0.9–1.0, was determined for hydrogels containing glucose or sodium chloride solutions, as a model of food systems. Due to their high osmotic pressure, these solutes play the major role in determining the osmotic pressure of the gel, thus its driving force for moisture uptake. As long as the gel's network pressure is relatively low, the sorption isotherm of the gel is similar to that of the solutions. At high water activity, the swollen gel develops a relatively large network pressure that not only counteracts the osmotic pressure and reduces moisture uptake, but also may induce syneresis. That is likely to take place if the network pressure exceeds the osmotic pressure of the polymeric matrix in the gel's internal solution. The onset of syneresis, which changes the gel composition, marks the end point of the sorption isotherm for the original gel.     

Ethanol in food: liquid–vapour partition in model systems containing Maillard reaction products

The effect of Maillard reaction products (MRPs) with different browning degree on the liquid–vapour partition of ethanol was studied in model systems. In particular, glucose–glycine aqueous solutions subjected to different heat treatments, which consequentely had different water activity values, were added to increasing amounts of ethanol and analysed for ethanol vapour pressure. In order to study the effects of the water activity change and of melanoidins' formation on the ethanol partition, experiments were also carried out on samples equilibrated at the same water activity. Ethanol vapour pressure decreased as the Maillard reaction proceeded. This result was attributed to the increase in water activity rather than to binding effects of melanoidins towards ethanol. Changes in water activity were mainly due to reagent consumption, water molecule formation and melanoidin production.     

Characterization of fish protein films incorporated with essential oils of clove,garlic and origanum: Physical,antioxidant and antibacterial properties

Consumers are demanding high quality foods using environmental-friendly packaging systems and natural preservatives, like edible/biodegradable films or coatings with bioactive properties. In this context, films prepared with Cape hake by-products proteins were combined with three essential oils (garlic, clove, and origanum) and characterized in terms of physical, mechanical, antioxidant, and antibacterial properties. Control films, without essential oils, were homogeneous, transparent, slightly yellow, and mechanically resistant. The incorporation of garlic, clove, and origanum essential oils in this film significantly decreased thickness, water solubility, breaking force and elongation, whereas increased the free radical scavenging activity of films. Particularly, clove films showed lower water vapour permeability than control films, and the highest antibacterial activity (against Shewanella putrefaciens). Garlic films were the most yellowish and had the highest antioxidant activity. Finally, origanum films were rather similar to the control, particularly in colour, transparency and reducing power. In conclusion, proteins recovered from Cape hake by-products combined with essential oils have adequate properties with applicability in new preservation food packaging systems.     

Effects of high pressure processing on antioxidant activity, and total carotenoid content and availability, in vegetables

High pressure processing (HPP) is a relatively new food preservation processing technology that enhances food safety and shelf-life without compromising organoleptic qualities. There has been little research on the impact of HPP on the nutritional and health-promoting properties of foods to date and most of it has focused on juices and purees of fruit such as oranges and tomatoes. The objective of this study was to determine the effects of HPP treatment at two pressure levels (400 MPa; 600 MPa) on antioxidant activity, total carotenoid content and carotenoid availability in vitro, of three commonly consumed vegetables. Antioxidant capacity and total carotenoid content differed between vegetables but were unaffected by HPP treatment. In vitro availability of specific carotenoids also varied greatly between vegetables (3–35%). HPP altered availability of carotenoids according to the type of vegetable treated and processing pressure applied, however the magnitude of the responses was minor.

Industrial relevance

This study provides further scientific evidence of the benefits of high pressure processing in retaining the nutritional attributes of fresh foods. Antioxidant activity and levels of carotenoids before and after exposure to high pressures (up to 600 MPa for 2 min) were essentially no different. Also, the data suggest that micronutrients and phytochemicals in certain vegetables may be made more bioavailable by high pressure treatment. From a nutritional perspective, high pressure processing is an attractive food preservation technology and clearly offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products.     

超高压作用下的食品包装问题

超高压技术是当前备受关注,且各国广泛开展研究的一项食品高新技术.超高压食品包装材料将伴随各类食品经受高压的作用和后续的储运过程.然而目前尚未形成与HPP技术配套的包装理论与技术.本研究拟对该领域的研究现状与局限性进行探讨,进而提出其未来的研究重点和发展方向.     

An accelerated method for adjustment of equilibrium moisture content of foods

The long equilibration period required to attain a desired water activity by traditional methods can lead to microbiological and physico-chemical changes in the food under study. To mitigate these difficulties, a system has been developed for adjusting the relative humidity of food samples to the desired levels in less than an hour. Food samples are exposed to either a saturated or a near zero water vapour pressure thereby greatly decreasing the time required for equilibration. This is mainly due to the increased mass transfer driving force. Evacuation, along with agitation of the head-space, is found to enhance the rate of moisture change. By using the sorption curves prepared using this technique, the time required for a particular food to reach a certain moisture (or a_w) level can then be predicted. The moisture and a_w levels predicted were found to be in good agreement with experiment.     

Scaling approach to water sorption isotherms of hydrogels and foods

Mechanisms affecting water sorption isotherms of foods, at high water activities, were evaluated by the processes of swelling and shrinking of model systems of uncharged and charged hydrogels. Their water activity was found to be determined by the combined effect of their osmotic pressure and the network pressure of the polymeric network. The scaling approach in polymer science indicates that in an uncharged network the osmotic pressure is affected by the mobility of the polymer segments and thus by the degree of cross-linking. However, in charged gels, which behave in a similar manner to many food systems, the counterions play the dominant role in determining the osmotic pressure. The network pressure may shift from a positive to a negative value during shrinking (dehydration), thus counteracting or co-operating with the osmotic pressure in decreasing the water activity. A scaling sorption isotherm, at high water activity, is formulated for a food system with physically significant parameters.     

Antibacterial Activity and Physical Properties of Edible Chitosan Films Exposed to Low-pressure Plasma

The challenge for food industry is developing gentle processes concept, which will prevent food spoilage and leave a food natural, minimally processed, fresh-like and safe. A new technique of food preservation could be usage of combined methods of green process, such as cold gas plasma with bioactive substances, and protective coatings. The aim of this study was to determine the antibacterial activity of chitosan films incorporated with lysozyme exposed to helium plasma treatment as well as evaluate their physical properties. The edible films have been prepared basing on low molecular weight chitosan by casting from lactic acid solution with water solution of lysozyme in three various concentrations (0, 0.5 and 1 %). Dried films were then modified by exposition on cold helium plasma treatment for 0, 5 and 10 min. Obtained films were tested against growth of Listeria monocytogenes, Yersinia enterocolitica and Pseudomonas fluorescens. In order to characterize chitosan-based films, their mechanical properties, theromogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), contact angle measurement, water vapour permeability (WVP) and scanning electron microscopy (SEM) were evaluated. The films with 1 % lysozyme incorporation enhanced the inhibition efficiency of chitosan-based films against gram-positive (L. monocytogenes) and gram-negative (P. fluorescens) bacteria, where reduction zones were 42.5 and 69.8 mm, respectively. Besides that, hydrolytic changes of chitosan chain caused by lysozyme activity were confirmed by TGA and DMTA. Contact angles and WVP of tested films were not significantly affected by helium plasma exposition, nor lysozyme dosage. Hydrophilic natures of chitosan-based films were confirmed by both tests. Microscopy image of cross-section structure was smooth and continuous due to lysozyme addition in film composition. Application of chitosan films incorporated with lysozyme and low-pressure plasma treatment could be used as innovative preservation method in a wide range of food products.     

水分活性对控制食品安全和质量的稳定作用

通过控制水分活性能防止食品腐败和保证食品质量。水分活性是同温度下食品中水蒸气的分压力与纯水蒸汽压力之比。食品的水分活性描述的是食品中的自由水，自由水是参与化学／生化反应和微生物生长的溶剂，因此水分活性是食品质量控制中的一个重要指标。本文介绍了水分活性的定义并对其检测方法、作用及研究现状进行综述。     

水蕨提取物的抗菌作用及其应用研究

为了探讨可食野生植物水蕨的消炎防腐性能,利用了水蕨植株和孢子的水溶性及醇溶性粗提取物作抑菌和食品保鲜实验。结果表明：两组提取物对革兰氏阳性和阴性细菌的生长都有一定的抑制作用,而对真菌无明显抑制现象;食品保鲜试验显示: 水蕨植株的水提取物和孢子的乙醇提取物能延长肉类熟食和新鲜海鲜的一级保鲜期12h以上,而水蕨植株的乙醇提取物和孢子的水提取物效果一般,说明水蕨植株中的抗菌成分与孢子中的成分可能有所区别。