CP6004 Food Chemistry AY2010/11 Semester 2 Group Formal Report

Experiment: Moisture in Foods I & IIClass: DFST/2A/21

Names: James Chan (0928199) & Sia Rui Ying (0928201)

Date Of Submission: 29th November 2010

AbstractMoisture content and Water Activity are two major aspects of food. They are very important in the preparation, preservation and storage of food. Using the open dish method, the infrared balance method and an Aw machine, we are able to determine the moisture content and water activity of our samples. <RESULTS>

Objectives

The objectives for the experiments were to observe the keeping quality of some food products, study the various simple methods of moisture determination using different drying methods and to determine the best drying conditions for a sample. Also, we were to determine the water activity of some food samples such as flour, bread and biscuits using a water activity measurement machine.

TheoryCalculating moisture content is to ensure the quality and required standards of food products and also help measure the foods mostly with respect to the texture, flavour and appearance to achieve better sensory evaluation. Essentially the shelf life is related to the moisture proportion present in foods.Microbiologically foods are susceptible to microbial load in presence of considerable amount of water.

Water activity (aw) can be defined moles of water in solution divide by the moles of water and solute in the solution.Water activity is the intensity with which water associates with no aqueous constituents. Water activity is affected by the moisture content in the air. At high humidity, food will have a higher water activity value. As humidity increases, more moisture would be absorbed into the food and the moisture content increases. As the moisture content increases, the aw increases. Water activity is the measure of unbound, free water in a system available to support the biological and chemical reactions. Water activity, is what bacteria, enzymes and chemical reactants will encounter which affects food materials at the micro ecological level. Moulds and yeast starts

One of the indirect distillation methods is the open dish method. This involves the measurements of the weight lost due to the evaporation of water.

Procedures

Determination of Moisture in an Open Dish

1. First, a clean metal dish together with a short glass rod was placed in an oven that was heated at 1300C for 10 minutes.

2. Next, the metal dish and glass rod were transferred to a dessicator for cooling.

3. After cooling, the metal dish and glass rod were weighed.4. 5g of accurately weighed flour were then, using the glass rod, evenly

distributed over the bottom of the metal dish.5. The dish was then returned to the oven for 1 hour.6. After heating for 1 hour, the dish was then transferred to a dessicator and

cooled for 10 minutes before weighing.7. The dish once again was returned to the oven and dried for an additional

30 minutes before cooling and reweighing.8. Then the moisture content was calculated from the % lost by the food

Determination of Moisture by the Infrared Balance Method

1. 10g of flour was dried under various conditions ranging from 1000C to 1250C for 10-15 minutes.

2. After each 1-minute interval, the % moisture content was recorded.

Determination of Water Activity Aw

1. The front door of the AW Chamber was pulled down2. The desired measuring head knob was lifted3. Measuring bowl was removed from measuring head with pincers4. Sample bowl was filled with sample (2/3 full)5. Sample bowl inserted into measuring bowl and repositioned in chamber

Results

Keeping qualitySample Types of spoilage occurring

during storage Suggestion to improve shelf-life

1 Bread Mould, Bacteria, yeast Store in cool and dry area or in a refrigerator

2 Flour Bacteria, Fungi, Non-Enzymatic Browning

Store in an air-tight container in a cool and dry area

3 Jam Yeast, Mould, Moisture Content Isotherm

Store in a container and placed in a refrigerator

4 Sugar Yeast, Mould, Moisture Content Isotherm

Store in an air-tight container

5 Salt Yeast, Mould, Moisture Content Isotherm

Store in an air-tight container

6 Ovaltine/Milo Lipid Oxidation, Non-Enzymatic Browning

Store in an air-tight container

7 Instant Coffee

Lipid Oxidation, Non-Enzymatic Browning

Store in an air-tight container

8 Lettuce Enzymatic Browning, Moisture Content Isotherm, Mould, Bacteria, yeast

Store in refrigerator

9 Apple Enzymatic Browning, Moisture Content Isotherm, Mould, Bacteria, yeast

Store in refrigerator

Determination of Moisture in an Open Dish1 2

Before Drying

Weight of dish + glass rod 37.8646 50.5280

Weight of dish + glass rod + flour

43.4668 55.5325

Weight of flour 5.5022 5.0045After Drying

Weight of dish + glass rod + dried flour

41.8313 55.0214

Weight of dried flour 3.9667 4.4934

Weight of water 1.5355 0.5111

Calculation Moisture Content of flour 38.7097 11.3745

s (%)

Dry Weight Basis (DWB): Weight of water * 100/ Weight of dried flour

Wet Weight Basis (WWB): Weight of water * 100/Weight of flour

27.907 10.2128

Determination of Moisture Content Using the Infrared BalanceDrying Conditions

% Moisture

Time(mins)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1000C10 mins

0 0.15 0.81 2.76 4.81 6.28

7.59 8.74 9.61 10.29

10.85

1000C12 mins

0 0.22 1.26 3.1 4.68 5.96

7.21 8.11 8.88 9.54 10.08 10.55 10.93

1000C15 mins

0 0.15 1.05 2.93 4.52 5.77

6.86 7.96 8.81 9.53 10.09 10.57 10.94

11.23 11.46 11.65

1100C10 mins

0 0.81 1.88 3.03 4.14 5.55

6.07 6.88 7.6 8.23 8.79

1100C12 mins

0 0.76 1.70 2.69 3.64 4.55

5.39 6.16 6.86 7.5 8.06 8.58 9.03

1100C15 mins

0.01 0.77 1.69 2.65 3.61 4.52

5.37 6.15 6.87 7.52 8.09 8.6 9.07 9.5 9.88 10.19

1150C10 mins

0 1.24 2.77 4.21 5.51 6.60

7.74 8.68 9.48 10.17

10.76

1150C12 mins

0 0.98 1.98 2.98 3.91 4.78

5.59 6.35 7.05 7.68 8.27 8.81 9.29

1150C15 mins

0 1.26 2.98 4.63 6.12 7.38

8.48 9.43 10.22

10.88

11.34 11.8 12.14

12.33 12.58 12.73

1200C10 mins

0 0.07 0.8 3.30 6.83 10.2

11.98

13.11

13.63

13.83

13.92

1200C12 mins

0 0.13 0.52 2.26 5.06 8.48

10.43

11.86

12.75

13.24

13.49 13.62 13.69

1200C15 mins

0 0.36 1.73 4.38 7.27 9.27

10.66

11.8 12.47

12.88

13.1 13.23 13.32

13.55 13.57 13.39

1250C10 mins

0 0.95 2.33 3.79 5.16 6.38

7.47 8.36 9.18 9.82 10.38

1250C12 mins

0.03 0.88 2.07 3.43 4.65 5.8 6.85 7.8 8.6 9.31 9.91 10.44 10.88

1250C15 mins

0.08 0.81 1.98 3.29 4.56 5.76

6.85 7.8 8.63 9.36 9.98 10.55 10.96

11.33 11.64 11.91

Water Activity

Aw(Flour)

Aw(Bread)

Aw(Biscuits)

Aw(Instant Noodles)

0.652 0.956 0.124 0.465

0.644 0.927 0.120 0.4380.632 0.937 0.135 0.456

Discussions

All foods are prone to spoilage. Most of the foods are prone to bacteria, yeast and moulds spoilage as the water activity of most food is range from 0.7 – 1.0. To prevent this spoilage, dehydration, adding

In the experiment of the determination of moisture in an open dish, the moisture content of the flour should be about 12%. Yet from the result, it shows that it is above 12%. This means that there is product loss. This might be due to accidental spillage of the flour during weighing or after drying. In the water activity experiment, there is a difference even though it’s from the same sample. This is because different amount is put into the sample bowl and it uses different parts of the sample. This is because it gives approximate measurement, which is to fill 2/3 of the sample bowl. There should be a more specific measurement like the weight required and which part of the sample to used for this experiment. For example, for bread, we should not take the crust of the bread to measure as the crust of the bread’s water activity will be lower.

1) What is the difference between moisture and water activity of foods? What is the relationship between the two?

Moisture content is about quantity of water which means the amount of water. It is express in percentage by weight of water in the mass. WATER ACTIVITY (aw) is

about quality and refers to the unbound water which is not bound to food molecules which can support the growth of bacteria, yeasts and moulds. Aw also represents the ratio of water vapour pressure of the food to the water vapour pressure of pure water under the same conditions. Water activity is not the same as moisture content. In a variety of foods, they may have the same moisture as water activity but yet, have difference water activities.

The relationship between water activity and moisture content at certain temperature is called moisture sorption isotherm. This is complex and unique due to different interactions between the water and the components at different moisture contents.

2) From the results obtained in experiment 1(C), plot the curve of % moisture content versus drying time (min). Determine the best drying

condition. The best results will be obtained by a heat setting just low enough to prevent scorching and a timer setting just slightly beyond the point where the drying curve levels off. Explain your choice.

References:

3. http://ezinearticles.com/?Moisture-in-Food-Products&id=3834719

4. http://www.wateractivity.org/theory.html

5. http://www.crcnetbase.com.ezp1.lib.sp.edu.sg/doi/pdfplus/10.1201/9781420045338.ch3

6. http://www.cscscientific.com/application-library/articles-and-testimonials/articles/measuring-moisture-contents-in-the-snack-food-and-baking-industries/

http://www.aznco.com/UploadArticles/AW%20Water.pdfhttp://drinc.ucdavis.edu/dairychem4.htmhttp://www.rotronic-usa.com/Ref/Aw/aw_define.htmhttp://class.fst.ohio-state.edu/fst605/Laboratories/Lab%201_Water%20Activity.pdfhttp://www.aqualab.com/education/moisture-sorption-isotherms/