Lecture # 3

MOISTURE

Moisture Analysis• Introduction • Importance of moisture analysis• Forms of water in foods• Moisture content of foods • Oven drying methods• Temperature control • Types of oven• Distillation Procedures• Chemical Method• Physical Methods

Introduction

• Moisture assays can be one of the most important analyses performed on a food product and safety.

• It is one of the most difficult analytical forms to obtain accurate and precise data.

Importance of Moisture Analysis

• The assay of the amount of moisture is one of the most fundamental and important analytical procedures. dry matter that remains after moisture removal is commonly referred to as total solids. This analytical value is of great economic importance to a food manufacturer because water is an inexpensive filler.

• The following listing gives some examples in which moisture content is important to the food processor.

Importance of Moisture Analysis

1- Moisture is a quality factor in the preservation of some products and affects stability in

a. dehydrated vegetables and fruitsb. dried milksc. powdered eggs d. dehydrated potatoes e. spices and herbs2- Moisture is used as a quality factor fora. jams and jellies, to prevent sugar crystallizationb. sugar syrupsc. prepared cereals conventional,4-8%; puffed, 7-8%

Reduced moisture is used for convenience in packaging or shipping of

a. concentrated milksb. liquid cane sugar (67% solids) and liquid corn sweetener

(80% solids)c. dehydrated productsd. concentrated fruit juices4- Moisture (or solids) content is often specified in

compositional standards (i.e., Standards of Identity)

a. Cheddar cheese must be ≤ 39% moisture.b. Enriched flour must be ≤ 5% moisture.c. Pineapple juice must have soluble solids of ≤10.5° Brix

(conditions specified).d. Glucose syrup must have ≥ 70% total solids.e. The percentage of add water in processed meats.

5- Computations of the nutritional value of foods require that you know the moisture content.

6- Moisture data are used to express results of other analytical determinations on a uniform basis (i.e., dry weight basis).

Forms of Water in Foods

• The ease of water removal from foods depends on how it exists in the food product. The three states of water in food products are:

• Free water: This water retains its physicalproperties and thus acts as the dispersing agentfor colloids and the solvent for salts.

• Adsorbed water: This water is held tightly oris occluded in cell walls or protoplasm and isheld tightly to proteins.

• Water of hydration: This water is bound chemically, for example, lactose monohydrate.

Moisture Content of Selected Foods

Food Item % of MoistureWhite bread, enriched 13.4

Corn flakes cereal 3.0

Milk, whole, fluid, 3.3% fat 88.0

Ice cream, vanilla 61.0

Margarine, regular, hard, corn 16.7

Oil 0

Oranges, raw 86.8

Apples, raw, with skin 83.9

Beef, ground, extra lean, raw 63.2

Egg, whole, raw, fresh 75.3

Peanuts, all types, dry roasted with salt 1.6

Sugar, granulated 0

Sugar, brown 1.6

Cucumbers, with peel, raw 96.0

Methods Used to Measure Moisture

1)-Dry oven method there are many types of oven:

• Forced draft oven.• Vacuum oven. • Microwave oven. • Infrared drying.• Rapid Moisture Analyzer Technology• Nuclear Magnetic Resonance Analysis 2)-Distillation Procedures.3)-Chemical methods.4)-Physical methods.

OVEN DRYING METHODS

• In oven drying methods, the sample is heated under specified conditions, and the loss of weight is used to calculate the moisture content of the sample.

• The moisture content value obtained is

highly dependent on The type of oven used. Conditions within the oven. The time and temperature of drying.

Oven Drying Methods

• Various oven methods are AOAC approved for determining the moisture in many food products.

• The methods are simple, and many ovens allow for simultaneous analysis of large numbers of samples.

• The time required may be from a few minutes to over 24 hr.

• AOAC (Association of Official Analytical Chemists)

Removal of Moisture

• Any oven method used to evaporate moisture has as its

foundation the fact that the boiling point of water is 100°C;

however, this considers only pure water at sea level.

• However, if 1 gram molecular weight (1 mole) of a solute is

dissolved in 1.0 liter of water, the boiling point would be

raised by 0.512°C. This boiling point elevation continues

throughout the moisture removal process as more and more

concentration occurs.

Moisture removal is sometimes best achieved in a two - stage process.

1- Liquid products (e.g., juices, milk) are commonly prettied over a steam bath before drying in an oven.

2- Products such as bread and field dried grain are often air dried, then ground and oven dried, with the moisture content calculated from moisture loss at both air and oven drying steps.

Factors influence of the rate and efficiency of moisture removal

1- Particle size

2- Particle size distribution

3- Sample sizes

4- Surface area during drying

Temperature Control

• Drying methods utilize specified drying temperatures and times, which must be carefully controlled. Moreover, there may be considerable variability of temperature, depending on the type of oven used for moisture analysis.

Types Of Ovens• Forced draft oven.

Usually used with liquid dairy products, nuts.

Should not be used with high carbohydrates sample

Drying time 0.75-24 hr

• Vacuum oven. draying under reduced pressure

used with high carbohydrates sample

• Microwave oven.

Fast, accurate method of analysis

• Infrared drying.Forced ventilation to remove moisture

Drying time 10-25 min

• Rapid Moisture Analyzer TechnologyUsed widely from the food industries because it is fast, accurate, and easy.

Other Methods

• Distillation ProceduresCodistilling the moisture in a food sample with a high boiling point (direct & reflux)

• Chemical Method• Used with sample low in moisture

• Physical Methods• Hydrometer (gravity & density)• Refractometer (liquid moisture)