Acidification of food products

The United States Food and Drug Administration (FDA) has defined an “acidified food” as a low-acid food to which acid(s) or acid food(s) has been added to the product to produce a finished equilibrium pH of 4.6 or below and a water activity greater than 0.85.

In acidified foods, the addition of low-acid ingredients significantly alters the pH of the acid food ingredients in the product. The acidified food regulations apply to shelf-stable foods that are sold without refrigeration in sealed containers.

Certain dairy products, such as sour cream and fermented vegetables, such as sauerkraut are preserved through lactic acid produced by the growth of bacteria together with the holding of these products refrigerator temperatures above freezing.

When sauerkraut is canned, it is given a heat process sufficient to destroy all spoilage and disease microorganisms.

Acidified, low acid foods must be acidified to a pH of 4.6 or less. Preferably the pH should be less than 4.6 to allow a safety margin. Optimal flavor profiles for most products are reached at approximately pH 4.2. If the flavor is slightly acidic the flavor profile may be balanced with the addition of a small quantity of sugar.

The manufacturer of acidified foods must register their establishment and file a scheduled process established by a competent process authority. In addition, the operation must be under the supervision of an individual who has successfully completed an FDA approved course on processing acidified foods.
Acidification of food products

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