Moisture Content vs Water Activity

Moisture Content vs Water Activity

In this article, we will discuss the moisture content vs water activity of food products. Also, we will focus on the importance, types of moisture present in food and method of calculation.

Moisture content of food products

Moisture content of a food plays a vital role in the characteristics, perishability, mode of spoilage (fungi or bacteria) as moisture is favoured by many spoilage causatives.

Apart from that analyzing moisture in food is important for,

• Economic feasibility to the processor and consumer.

• Compositional analysis

• Assessing the quality and stability of the food product is dependent on the moisture

content of the food.

• And also for analyzing the moisture content is important in designing the packaging

material as well as extending the shelf life.

• Moisture is inversely proportional to the amount of nutritional value.

Moisture present in food systems is of 2 types.

1.     Free moisture

The moisture available for microbial growth, enzymatic reactions and other chemical reactions is

free moisture and referred to as water activity (aw).

Water Activity (aw) =           Partial vapour pressure of food at a certain temperature

                                   Partial vapour pressure of the atmosphere at the same temperature

Free moisture can be analyzed by evaporating the moisture present in the food at 100-105°C. So free

moisture is what we are concerned about.

 

2.     Bound moisture

Bound moisture is within the food lattice due to which it cannot be evaporated at 105°C and requires

higher temperatures.

Greater amount of moisture in food does not necessarily mean the food is high in its water activity.

The moisture content can be high in the food product, but the water activity can still be low if the

moisture is present in bound form (Intermediate Moisture Food). 

Intermediate moisture foods such as cheese, jams and jellies have water activities in the range 0.6 to 0.9

and are generally shelf-stable without refrigeration or heat processing, although they may still be

susceptible to other deteriorative reactions such as enzymatic browning or the Maillard reaction.

Moisture content on dry basis turns out to be more accurate when compared with the moisture content

on wet basis. Both accuracy and magnitude are higher in dry basis compared to wet basis.

                     Moisture content on wet basis % = w – d * 100

                                                                          w

                     Moisture content on dry basis % = w – d * 100

                                                                      d

w – weight of the sample

d – dry weight