Food and nutrition.pdf

242 Dried Fruits and Vegetablesarehygroscbpic, which absorb mOisture easilY' and'non .. h'ygroscopic,which-do' not absorb moisture. ThedCissic,exatnple is salt -and pepper, wheresalt is very hygroscopic and pepper is non-hygr.oscopic;-but similarexatnp1esexlst for fruit and veg~table products. This',difference determinE:sthe packaging requirement for different fruit and, vegetable products. Themoisture content at which ,a food is stable 'is known as the Equt'Iibrium'Moisture,CiJntentand examples of ' this for- different fruits and vegetab1esare shown ,in, Table 8;- together with the packaging requirement for differentgroups of foods. ..'Dried fruits and vegetables are usually packaged in one of the manydifferent types of plastic filn'h The 'selection of the correct type of packagingmaterial~depends on a complex mix of considerations 'which include:, • The temperature and humidityoHhe air in which the productis stored-. Thecapacity'ofthe productto pickup moistur~ fromthe air', • - Reactions within the' product caused by air or' sunlight duringstorage• The expected shelf life• Marketing considerations• Cost and availability of different packaging materials:-"lrt 'general~ altho'ttgh thin polythene fihn is usually the' cheapest and'mosfWidely a.'vailable' marerial, it is only"suitable for storing dried fruits. and vegetables' for a short time before they pick up moisWre,"soften,and· go InQulcfy:' " ''PolypropYrene' has' better barrier- prop~rtiesandtherefure gives. alonger shelf life, but ins 'usually more' expensive and it may not be· 'ava-lIable in many countries.' Other ·more complex films, .such as laminated· 'films made ft6mpolythene: and aluminium foil, offer much ·better"pr'otection to dried. foods, but'are considerably more expenSive and moredifficult to find in developing couhtries.· , ' .,'Moisture Contents;at wmen Selected Foods are Stable'. 'and Packaging Requirements'FoodMoisture content (%) Degree of protection requiredFresh fruit and 78-85 Package to prevent moist:ure lOss:35v~getables, .;!, . ,-7.Fruit sweets 3 . H)'groscopic:- Package to prevent.moisture uptake_ :' Most dried foods also ne~d a sturdy box or, carton 'to both preY~ntcrushing and: to exclude light which causes loss of colour and development