Analysis of moisture contents of food

Moisture determination is one of the most important and most widely used measurements in the processing and testing of foods. It is an important factor in food quality preservation and resistance to deterioration.

The amount of moisture in food products is a measure of yield and quantity and as such is of economic importance.

Moisture content must be known for optimum processing of foods, for example, in the milling of cereals, mixing of dough to optimum consistency, and production of bread with the best grain.

Moisture removal or dehydration has long been used as a technique for improving food storage stability. Small increases in the moisture content of low and intermediate moisture foods can significantly reduce their shelf life.

Determination of moisture content is necessary to calculate the content of other food constituents on uniform basis. The dry matter that remains after moisture analysis is commonly referred to as total solids.

Of the oven methods, microwave drying, infrared drying and the moisture analyzer technique are fastest. 

Some force draft oven procedures require less than 1 hour drying, but most forced draft oven and vacuum oven procedures a much longer time.

Hygroscopic foods with low moisture contents may require the use of more sophisticated techniques, such as the Karl-Fischer procedure.

Oven drying procedures are official methods for a variety of food products. Reflux distillation is an AOAC method for chocolate, dried vegetables, dried milk and oils and fats.
Analysis of moisture contents of food

Determination of protein content

Protein content in food varies widely. Foods of animal origin and legumes are excellent sources of proteins. 

Determination of total protein can accomplished by a number of different techniques. Some of these include gravimetric, nitrogen determination, amino acid analysis, colorimetric, methods, spectrophotometric and fluorometric methods.

A nitrogen determination is the most commonly used protein assay. It is generally assumed that a mixture of pure proteins will contain 16% nitrogen.

Determination of protein concentration by micro-Kjehdahl method gives accurate and reliable results, providing that a correlation is made for non-protein nitrogen in the sample.

Various modifications have been devised to improve its accuracy and speed.

This method is very suitable for most commercial food proteins and feed proteins, since low amounts of lipid and even high amounts of carbohydrate and other contaminants do not interfere with the procedure.

The Kjehdahl procedure can be basically divided into three parts:
*Digestion
*Distillation
*Titration

In the Kjeldahl procedure, proteins and other organic food components in a sample are digested with sulfuric acid in the presence of catalysts. The total organic nitrogen is converted to ammonium sulfate.

The result of the analysis represents the crude protein content of the food since nitrogen also comes from non-protein component.

While the Kjeldahl method has been used widely, the availability of automated instrumentation for the Dumas method in many cases is replacing used the Kjeldahl method. Both methods are official for the purposes of nutrition labeling of foods.
Determination of protein content

Proteins

Proteins
Proteins are the chief organic constituents of muscles and other tissues. Proteins are the major components of the enzymes that regulate and carry out the general metabolism and functional process of living things.

Proteins are parts of the intracellular and intercellular structure of animals; they make up the structure and composition of many hormones and antibodies (disease related components)), and are concerned with many other factors to involved with body functions.

Proteins contain nitrogen, hydrogen, oxygen, and sometimes sulfur and phosphorus. All proteins contain nitrogen at a level of about 16%. The analysis of proteins is determined indirectly by analyzing for protein nitrogen, then multiplying the result by 6.25 to determine the actual amount of protein analyzed.

Because proteins contain carbon, they can be used as fuel since part of the molecule can be oxidized, sometimes involving deamination, to supply energy.

Proteins are required by humans for growth (protein synthesis) and for repair and maintenance of cells. Since mature adults have, in essence, ceased to grow, their protein requirement is less, per unit weight, than that of those who are still growing.
Proteins