STORAGE LIFE

ASTM D1337-96 Standard test method for storage life of adhesives by consistency and bond strength. 

Dried fruit must be capable of being stored for up to 12 months to allow continuity of supply to the market. During this time, fruit can deteriorate in quality, so it is important to be able to predict the storage life of a dried apricot sample. The storage life prediction test is based on the condition in which fruit would be after 4 months storage at 25 °C and 65% relative humidity. 

Place lOOg of dried apricots in an open net bag. Then put sample in oven at 45 °C and 70% relative humidity for 7 days. The fruit is removed from the oven and the colour is detemined using the method described in Section 3.5 (Rettke 1993). If the reading is greater than 0.3, it is considered that the fruit will not store for more than 4 months (Dahlenberg, pers. comm. 1993). 

Acknowledgements. The authors wish to thank Mr. M. Rettke of the South Australian Department of Primary Industries for advice and encouragement during the preparation of this chapter, and the Dried Fruits Research and Develpment Council for financial support. 

Abbott JA, Watada AE, Massie DR (1976) Effi-gi, Magness-Taylor, and Instron Fruit Pressure Testing devices for apples, peaches, and nectarines. J Am Soc Hortic Sci 101 698-700 

AO AC (1990) Official methods of analysis of the association of official analytical chemists, 15th edn. Association of Official Analytical Chemists, Arlington, VA 

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Thorium, uranium, and plutonium are well known for their role as the basic fuels (or sources of fuel) for the release of nuclear energy (5). The importance of the remainder of the actinide group Hes at present, for the most part, in the realm of pure research, but a number of practical appHcations are also known (6). The actinides present a storage-life problem in nuclear waste disposal and consideration is being given to separation methods for their recovery prior to disposal (see Waste treati nt, hazardous waste Nuclear reactors, waste managet nt). 

The extension of the useful storage life of plant and animal products beyond a few days at room temperature presents a series of complex biochemical, physical, microbial, and economic challenges. Respiratory enzyme systems and other enzymes ia these foods continue to function. Their reaction products can cause off-davors, darkening, and softening. Microbes contaminating the surface of plants or animals can grow ia cell exudates produced by bmises, peeling, or size reduction. Fresh plant and animal tissue can be contaminated by odors, dust, iasects, rodents, and microbes. 

The pH of the chlorine dioxide reaction mixture must be maintained in the 2.8—3.2 pH range, otherwise decreased conversion yields of chlorite to chlorine dioxide are obtained with by-product formation of chlorate. Generator efficiencies of 93% and higher have been demonstrated. A disadvantage of this system is the limited storage life of the sodium hypochlorite oxidant solution. 

Many proprietary carries are available as soHds (flakes or pellets) or in preemulsified form. These present some difficulties in the dyehouse. The former require dispersion in water through steam injection and addition to a preheated dyebath. The latter suffer from short storage life owing to separation of the emultion. Currently the industry prefers clear products easily emulsified by premixing with water at the time of use. 

In dry air and in the presence of polymerisation inhibitors methyl and ethyl 2-cyanoacrylates have a storage life of many months. Whilst they may be polymerised by free-radical methods, anionic polymerisation is of greater significance. A very weak base, such as water, can bring about rapid polymerisation and in practice a trace of moisture on a substrate is enough to allow polymerisation to occur within a few seconds of closing the joint and excluding the air. (As with many acrylic monomers air can inhibit or severely retard polymerisation). 

Urea-formaldehyde moulding powders may be moulded without difficulty on conventional compression and transfer moulding equipment. The powders, however, have limited storage life. They should thus be stored in a cool place and, where possible, used within a few months of manufacture. 

Fillers. They are generally added to reinforce NBR adhesives. However, fillers can be added to promote tack, to increase the storage life, to improve heat resistance or to reduce cost. The most common fillers are carbon blacks. Precipitated silica can be used in applications where black colour is not acceptable, but excessive amounts tend to reduce adhesion. Titanium dioxide can be used to impart whiteness, improves tack and extend storage life. 

PVAc is another important type of adhesive, especially in furniture manufacturing and for carpentry. They form the bond line in a physical process by losing their water content to the two wooden adherends. PVAc adhesives are ready to use, have short setting time and give flexible and invisible joints. They are easy to clean and show long storage life. Limitations are their thermoplasticity and the creep behavior. 

Methods of arranging the product in the store will depend on the number of varieties and the storage life (see Figure 14.2). With short-term storage it may be necessary to get to any pallet, so access gangways will be required with only one row of pallets on each side. 

Some sacrifice of perfect accessibility is usually made in the interest of economy. Where storage life is long, pallets may be stacked as many as four rows deep, requiring one gangway for eight rows of pallets. In this case, a gangway of 3.7 m is required to shuffle pallets to get to those at the rear, and the usable floor space comes up to 68%. 

Fruits are seasonal in temperate climates, and a good harvest may be followed by a shortage if there is no method of preservation. The hard fruits, apples and pears, have traditionally been stored in cool places and may then last for several months, depending on the variety Refrigeration has extended the storage life, and made this more reliable. 

All fruits respire oxygen and, in doing so, start to decay. If the oxygen concentration can be reduced, the rate of respiration will be slowed and the storage life maybe extended. The maintenance of a low partial pressure of oxygen requires a gas-tight structure to prevent diffusion. Such controlled atmosphere stores are carefully constructed and sealed to achieve this, and are generally termed gas stores. 

The fruits are loaded and the store sealed. Within a few days they consume a proportion of the available oxygen and respire carbon dioxide. Considerable research over the past 60 years, mainlyin the UK [47], has determined the correct balance of gases to prolong the storage life of the different varieties of apples and pears, both home grown and imported. 

There is an increasing demand for ready-prepared foods for final re-heating or cooking in microwave ovens. Applications are for retail sale of take-away meals and factory/ office and institution catering. Such foods maybe frozen and will then have a longer storage life, but will require frozen storage. 

Of the numerous reasons for measuring and controlling the moisture content of dehydrated foods, one of the more important is the effect of moisture content on the stability of the food. The storage life of a food generally increases with decreasing amount of water and it is therefore customary to dehydrate the food to some safe moisture level which is determined empirically. 

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