Water activity in food

Water is an important constituent of all foods. In the middle of the twentieth century scientists began to realize that the active water could be much more important to the stability of a food than the total amount of water present.

Qualitatively, water activity or Aw is a measure of unbound, free water in a system available to support biological and chemical reactions.

Water activity, a thermodynamic property, also can be defined in still other terms in accordance with Raoult’s law. Thus, Aw of a solution is quantitatively equal to the vapor pressure of the solution divided by the vapor pressure of pure water.

Water activity affects the textural properties of food. Foods with high Aw have a texture that describe as moist, juicy, tender and chewy.

When the Aw of these products is lowered undesirable textural attributes such as hardness, dryness, staleness and toughness are observed.

Water activity is widely used to predict the stability of food with respect to the potential for growth of micro-organisms and also some for the physical, chemical and enzymatic changes that lead to deterioration. 

Critical water activities are found where the product becomes unacceptable from a sensory standpoint.

In packaged foods, the water-vapor permeability of the packaging material is a decisive factor in controlling changes in moisture content and thus the water activity of packaged foods.
Water activity in food

Pest Control of Fruits and Vegetables

Pest Control of Fruits and Vegetables
Insects, rodents, plant disease, and weeds can devastate food crops, and human history is filled with famines attributable to these scourges. Large scale agricultural production tends to increase the susceptibility of crops to these hazards. Pesticides are currently an integral component of an agricultural system that produces increased yields of fresh fruits and vegetables with good visual quality. Pesticides have become a major cost of production of fruit and vegetable farmers. The use of pesticides is associated with risks of increase pest resistance, environmental contamination, exposure to farm workers, and escalating costs. With mounting regulatory pressure on pesticides it is likely that fewer compounds will be available to the farmer and that these compounds will be available for only a few crops of high economic value.

Damage to fruits and vegetables by pests is not limited to loss of visual quality. Insects and rodents can inoculate plants in the field with microorganisms that can present a health hazard, particularly if the product is not properly washed and is eaten raw. These dangers are compounded if untreated animal wastes such as manure, a potent source of human pathogens, are used for fertilization, particularly with vegetables grown close to the ground. Mold, which can be held in check by fungicide, can infect fruits and vegetables products. Mycotoxins produced by molds, such as patulin in apple products and ochratoxin in citrus fruits, present additional concern. The potential danger of these naturally occurring mycotoxins has been documented but the practical implications of decreased fungicide use are not clear.
Pest Control of Fruits and Vegetables