奶粉中水吸附研究检测方案(蒸汽吸附仪)

Page 1 of 1PN 59000-44 REV.AINSTRUMENTS POWDER"TECH NOTE44 Water Vapor Sorption by Milk Powders Material Category： Food Method Category： Water vapor sorption Instrument Category： Aquadyne DVS Milk powder is a valuable commodity for industrialized andthird world countries. It is widely used in industrializedcountries as the basis for powdered infant foods and bythe baking and confection industries as a raw ingredient.In developing countries， especially those hit by famines，milk powder isan important source of proteinandcalories. In both cases transportation charges for anequivalent nutritional value are significantly lower for milkpowder than for bulk whole milk， and milk powder hasgreater shelf life not requiring refrigeration. Free moisture promotes mold growth in foods； the higherthe relative humidity the greater the potential for molding，particularly over 65%RH. However， like most desiccatedfood stuffs， milk powder exhibits a tendency to absorbmoisture from the atmosphere.e.1In a closed container，therefore， it has self-desiccating qualities to some degree.Sugar and table salt are two examples of foods withstrong desiccating qualities and are therefore used as preservatives for other foods which are less desiccating.So， the moisture sorption quality of a foodstuff is essentialinformation when it comes to considering packaging andstorage conditions. Moisture sorption can also affecttexture， color and flowability of powders. The moisturesorption behavior of foods is quickly and convenientlymeasured by dynamic gravimetric water vapor sorption，often referred to simply as DVS. In the example below， two milk powders were dried andanalyzed at 22°C (72°F). Drying consisted of flowing drynitrogen over the sample for six hours in the samplechamber of the DVS analyzer. Measurement of the watersorption consisted of a number of RH steps， first increasing，then decreasing followed by a final increase.The kineticsof the sorption process can be evaluated from thesecurves..The corresponding isotherms reveal the curiousbehavior associated with the crystallization of amorphouslactose. Experimental Conditions：Sample mass： ~50mg In-situ drying time： 6hrs | In-situ drying temperature： 22°C| Analysis temperature： 22°C 七E工 Fig.1. Measurement results showing steps in relative humidityand response in sample mass to adsorption and desorption. Fig. 2. Measured isotherms demonstrating the difference between firstand second adsorption cycles due to the behavior of lactose.