Info

Months

Low pH maintained by packaging

Bread

>4.5

>0.95

Days

Preserved by heat and low Aw in crust

Fruitcake

>4.5

<0.90

Weeks

Preserved by heat and low Aw

Milk

>4.5

>0.95

Days

Preserved by chilling

Yogurt

<4.5

<0.95

Weeks

Preserved by low pH and chilling

Dried milk

>4.5

<0.90

Months

Preserved by low Aw

treating individual particles so that they form free-flowing agglomerates of aggregates, in which there are relatively few points on contact (Fig. 12). The surface of each particle is easily wetted when the powder is rehydrated, and particles sink below the surface to disperse rapidly through the liquid. These characteristics are respectively termed wettability, sinkability, dispersibility, and solubility. For a powder to be considered instant, it should complete these four stages within a few seconds.

The convenience of instantized powders outweighs the additional expense of production, packaging, and transport for retail products. However, many powdered foods are used as ingredients in other processes, and these are required to possess a high bulk of density and a wider range of particle sizes. Small particles fill the spaces between larger ones and thus exclude air to promote a longer storage life. The characteristics of some powdered foods are described in Table 6.

Flavor and Aroma

Heat not only vaporizes water during drying but also causes loss of volatile components from the food. The extent of volatile loss depends on the temperature and solids concentration of the food and on the vapor pressure of the volatiles and their solubility in water vapor. Volatiles that have a high relative volatility and diffusivity are lost at an early stage in drying. Fewer volatile components are lost at later stages. Control of drying conditions during each stage of drying minimizes losses. Foods that have a high economic value due to their characteristic flavors (eg, herbs and spices) are dried at lower temperatures.

A second important cause of aroma loss is oxidation of pigments, vitamins, and lipids during storage. The open, porous structure of dried food allows access of oxygen. The

Particles

Figure 12. Agglomerated powder.

Table 6. Bulk Density and Moisture Content of Selected Powdered Foods

Food

Bulk density (kg m3)

Moisture content

(%)

Cocoa

Sleeping Sanctuary

Sleeping Sanctuary

Salvation For The Sleep Deprived The Ultimate Guide To Sleeping, Napping, Resting And  Restoring Your Energy. Of the many things that we do just instinctively and do not give much  of a thought to, sleep is probably the most prominent one. Most of us sleep only because we have to. We sleep because we cannot stay awake all 24 hours in the day.

Get My Free Ebook


Post a comment