Báo cáo thực hành sản phẩm sữa

Experiment 1: Freshness/ raw milk quality 1.1 Measurement of density a.. Objective The purpose of the first experiment are measure the density and identify 3 samples: normal raw milk, sk

University of Agriculture and Forestry Faculty of Food Science and Technology

MILK AND DAIRY PRODUCTS LABORATORY REPORT

Name: Nguyễn Thị Thanh Hằng

Experiment 1: Freshness/ raw milk quality 1.1 Measurement of density

a Objective

The purpose of the first experiment are measure the density and identify 3 samples: normal raw milk, skimmed milk and water-added milk

b Materials and Methods

 Apparatus and reagents

- Milk: normal milk, skimmed milk and water-added milk

- Lactometer used for measuring the density

 Method: Put the lactometer into the flask, which contain milk inside, to measure

the density Part of lactometer rises on the surface Record the value

c Results

Table 1 The density value of 3 milk samples Sample Density (Kg/ m 3 ) Conclusion

d Discussion

- The density of milk depends on temperature The higher the temperature is, the more liquid expenses, the lower the density is

- Density also depends on composition of milk:

 Fat content decrease density

 Solubilized components increase density, so Dskimmed milk > Dwhole milk

 Addition of water leads to the decreasing of milk density

e Conclusion

- The identification of various types of milk can be considered based on its density value

- The density of milk can be measured by using a lactometer The standard temperature for the measurement is normally 20 C However, this experiment⁰C However, this experiment was conducted at room temperature and because of some human mistake during value recording step, the results maybe not entirely accurate

1.2 Acidity

a Objective

This experiment was conducted to measure the acid value of milk as well as to evaluate milk quality based on this value

b Materials and Methods

 Apparatus and reagents

- pH meter

- Burret

- Pipet 10 mL

- Beaker 25 mL

- Bottle of distilled water

- Erlen 50 or 100 mL

- NaOH 0.1 N solution

- Phenolphthalein sulution

 Method

1.2.1 Procedure for pH reading

- Put several mL of the sample into the beaker

- Calibrate the pH meter before use Read pH with the pH meter (pay attention to the sample temperature)

1.2.2 Procedure for titration

- Pipet 10 mL of the sample into the Erlen, add 10 mL of distilled water and

2 drops of phenolphthalein solution (indicator)

- Titrate the content with NaOH 0.1 N to the appearance of pink color which remains for about 10 seconds

- Calculate into Dornic degree using the following conversion

1° Dornic is equal to 0.1ml of NaOH 1/9N necessary to neutralize 10 mL of sample

c Results

Table 2 pH result, volume of titrated NaOH (mL) and Dornic degree of milk samples

NaOH (mL)

Dornic degree

1 6.1 2.6 23.4

2 6.28 2.3 20.7

3 6.25 2.3 20.7

4 6.29 2.3 20.7

5 6.43 2.2 19.8

6 6.4 2.2 19.8

d Discussion

- Acidity is an important parameter to indicate the quality of milk as well as fermentation process Normal milk often has pH of 6.6 to 6.8 and is the result

of dry matter, not lactic acid

e Conclusion

- In conclusion, this is a quantitative method used to evaluate the quality of milk

- The result cannot be exactly due to mistake from equipment (burret for titration) as well as human during conducting the experiment

1.3 Alcohol test

a Objective

This experiment was conducted to evaluate the freshness of milk by observing its coagulation when adding alcohol

b Materials and Methods

 Apparatus and reagents

- Test tubes (e.g, 150 mm length x 16 mm diameter)

- Test tube rack

- 68% alcohol solution (68% of 96% alcohol + 28% of distilled water)

 Method

Single test

1 Bring equal volumes of milk and 68% alcohol (2 mL each) into a test tube

2 Invert the test tube several times which the thumb held tightly over the open end of the tube

3 Examine the tube to determine whether the milk has coagulated If it has, fine particles of curd will be visible

Double test

1 Bring 1 volume of milk and 2 volumes of 68% alcohol into a test tube

2 Proceed and examine similarity

c Results

Table 3 Phenomenon results of Alcohol test Sample Single test Double test

1 Precipitation occurs

2 Precipitation occurs

3 No Precipitation Precipitation appear but less

than single test experiment

4 No Precipitation Precipitation appear but less

than single test experiment

6 No Precipitation Precipitation occurs

d Discussion

- Milk that contains more than 0.21% lactic acid, or calcium and magnesium compounds in greater than normal amounts, will precipitate when alcohol is added

- In case of this experiment, when alcohol was added, the two samples (1 and 2), did not coagulate when alcohol is added It shows negative alcohol test or both

of samples had good quality

e Conclusion

- Milk quality can be tested by using alcohol test, especially for determining the sour milk

- When using this test, the observer should differentiate the bubbles and curd particle so that the result in this test can be obtained exactly

1.4 Clot-on-boiling and CaCl 2 20% test

a Objective

The clot-on-boiling test is used to determine whether milk is suitable for processing, as it indicates whether milk is likely to coagulate during processing (usually pasteurisation)

b Materials and Methods

 Apparatus

- One boiling water bath (a 60 mL beaker on a gas or electric heater is adequate)

- Test tubes

- Timer (a watch or clock is adequate)

 Method

- Place about 5 ml of milk in a test tube (the exact amount is not critical) and place the test tube in boiling water for 5 minutes

- Carefully remove the test tube and examine for precipitate The milk is rejected if any curd forms

- Place 2 drops of CaCl2 in each test tube

c Results

- All samples give precipitate

- Milk in sample 1 and 2 showed with visible fine particles of curd around the test tube when heating

- With milk in the three sample (3,4,5 and 6), there was a lot of precipitate when heating so it not suitable for processing due to poor quality

d Discussion

- The experiment is based on the acidity of milk

- When milk is stored for a long time at ambient temperature, the increased acidity will reduce the heat stability of milk caused by fermentation or growth

of bacteria Heating will precipitate protein if milk is sour Therefore, that milk cannot be used

e Conclusion

- Beside the other testing methods, clot-on-boiling test is one type of test that used to check the milk quality, especially the heat stability of milk during storing

in long time

- Results cannot be accurate due to human error and long execution time while conducting experiments

1.5 The methylene blue reduction test

a Objective

This experiment was carried out to determine the length of time milk takes to decolourise methylene blue is a good measure of its bacterial content and hence of its hygienic quality

b Materials and Methods

 Apparatus and reagents

- A water bath at 37 – 38 C⁰C However, this experiment

- Test tubes graduated at the 10 mL mark

- A supply of 1 mL pipettes (bacteriological type)

- A thermometer, 0 - 100 C graduated at 0.5 C intervals⁰C However, this experiment ⁰C However, this experiment

- A supply of sterilised rubber stoppers for closing the tubes when the samples have been put into them These can be conveniently sterilised before use by immersing in boiling water for 10 minutes

- A methylene blue solution made up from standard methylene blue milk testing tablets which are available commercially

- Test-tube racks

 Method

When the test is used to grade suppliers’ milk the samples are taken in the milk reception area

1 Mix the supplier’s milk thoroughly

2 Take the sample with a clean, sterile dipper and fill the test tube to the 10 mL mark

3 Stopper the test tube with a sterile rubber stopper and mark the milk supplier’s number on the tube

4 Place the test tube in the test tube rack

5 When sufficient samples to fill the test tube rack have been collected, add 1 ml

of the methylene blue solution to each test tube Replace the rubber stopper with aseptic precautions

6 Invert each tube twice, to mix the milk and solution thoroughly, and place the tubes in the water bath at a temperature of 37 - 38 C.⁰C However, this experiment

7 Make a note of the time at which the tubes are put into the water bath

8 Examine the samples after 30 minutes, note the numbers of decolourised samples and remove them from the bath Do not disturb partly decolourised tubes Invert all other tubes

9 At half-hourly intervals examine again for decolourised samples and repeat as above

Control tubes

Include two control tubes with each batch consisting of:

 10 mLof mixed milk plus 1 ml of methylene blue solution

 10 mL of mixed milk plus 1 ml of water

Immerse both tubes in boiling water for 3 minutes to destroy the natural reduction action of the milk

Table 4 Standard time for evaluating milk quailty Time taken to

decolorized milk Grade

< 30 min Very bad

c Results

Figure 1 & 2 Color changes during incubation time

d Discussion

- The time for blue color of methylene solution to disappear is related to amount

of microorganisms in milk

- In this experiment, milk takes more than 3 hours to decolorize blue color of methylene and this indicate the low amout of microorganism in milk

- The length of time milk takes to decolorize methylene blue is a good measure

of its bacterial content and hence of its hygienic quality The time is governed

by the activity of reducing bacterial present in milk and the oxygen content

When oxygen has been used the methylene blue is reduced, changing in color from blue to white

- The temperature of incubation tank can cause error to this experiment If the temperature is too high, it can destroy all the bacteria and then the milk will not decolorize methylene blue

e Conclusion

- This experiment can test the stability of milk but takes time

- Incubation tank should be check carefully to ensure the result of this experiment

- Results cannot be accurate due to human error and long execution time while conducting experiments

Experiment 2: Fermented milks: yogurt

a Objective

This experiment was conducted to know how to make two types of yogurt, namely set yogurt and stirred yogurt Yogurt products were made from different recipes and than were evaluated by sensory test

b Materials and methods

 Apparatus and reagents

- Raw milk

- UTH –full fat milk

- Skim milk powder

- Starter culture (thermophilic bacteria)

 Method

Yogurt was made by following the procedure below

Explanation of main steps

- Milk/ standardization

Each group starts with one litter of milk and proceeds accordingly with the table below

Table 5 Types of milk and incubation temperatures for making yogurt

Types of milk Incubation temperature

UHT full-fat milk 43⁰C However, this experimentC

UHT full-fat milk + 2% Skim milk powder 43⁰C However, this experimentC

UHT full-fat milk 37⁰C However, this experimentC

UHT full-fat milk + 2% Skim milk powder 37⁰C However, this experimentC

Milk

Standardize

Homogenize

15 - 35 MPa, 50⁰C

Heat

15 min at 90⁰C

Cool down

To 43⁰C Innoculate

Pour into pots

Incubate 43⁰C or 37⁰C Cool down e.g by ice water

Storage

4⁰C

- Inoculation

 Add appropriate amount of starter culture (0.25%) into milk

 Mix the content after addition and then incubation

- Incubation/ Fermentation

 For set type of yogurt: Leave a small amount of sample for determination of pH

and Dornic at the starting point Pour the rest into pots (e.g., 100 mL) and ⁰C However, this experiment incubate at 43 C until a pH of 4.6 (90-120 D) The fermentation time is about ⁰C However, this experiment ⁰C However, this experiment

4 - 5h, depending on the strength of the starter culture

 For stirred type of yogurt: Leave a small amount of sample for determination

of pH and Dornic at the starting point Incubate the rest directly at 37 C until a⁰C However, this experiment ⁰C However, this experiment

pH of 4.6 (14 - 16h) Cool down, stir and transfer into pots

c Results

Table 6 pH assessment during incubation time

Time pH

- pH of the final yogurt is 4.6

- The final product after incubation and cool storage had these

characteristics: white color,

smooth texture, and slightly sour

d Discussion

- Heating step in the procedure is carried out to destroy the undesirable

microorganism and inhibit the activity of enzyme

- The final product belongs to stir type group, this group is incubated at 37⁰C However, this experimentC so that

it has longer fermentation time (14 - 16 hours) compare to at 43⁰C However, this experimentC (4 - 5 hours)

e Conclusion

- Yogurt is a fermented product that can help preserve milk for a long time

- Each step in making process should be carried out carefully to obtain the final product

Experiment 3: Making ice cream

I Objective

- This experiment was carried out to show how to make ice cream product as well as factors affect to the processing

II Materials and methods

 Apparatus and reagents

- 2 chicken eggs

- 4 egg yolks

- 250gr of sugar

- 20 mL of vanilla

- 800 mL of fresh milk without sugar

- 300 mL of whipping cream

- 10gr of cornstarch

- 30gr of cocoa powder

- 34gr of instant coffee powder

- 8 passion fruits

 Method

- Making ice cream

 Beat eggs, egg yolk and sugar then adding milk  heat with a small flame (warm) and stir  boil the mixture at low temperature (warm), adding

cornstarch (which should be stirred first with a little water) Lifted out of the kitchen

 Whip the whipping cream and adding to the mixture

 Incubate in the fridge for 4 hours and then pour into the ice cream maker

 Get the final product.

- Making chocolate ice cream: Take the same steps as making vanilla ice cream but instead of adding vanilla, we adding cocoa powder and instant coffee powder

III Results

Table 7 Sensorial properties of the product Vanilla ice cream Chocolate ice cream Passion fruit ice cream

- Dark brown color

- Cocoa, coffee and milk

flavor

- Not fatty

- Sweet

- Light yellow color

- Smoother and fattier than chocolate ice cream

- Slightly sweet

- Yellow color

- Smoother

- Slightly sour taste

- Natural aroma of passion fruit

IV Discussion

- When making ice cream, milk is not heated to very high temperature, if not, when add egg yolk, it will not curdle

- Some stabilizers (CMC, xanthan gum, corn starch) can be used to increase the thickness and help the product melt slowly

V Conclusion

- Ice cream is one type of frozen dairy product that can be served as a dessert

- The quality of ice cream varies depends on how it made so that every step in process should be taken out carefully

Experiment 4: Tasting of milk and dairy products

Consumption milk

Table 8 Sensorial evaluation results of milk product Yakult Steurilized milk

- Light yellow color

- Sweet and sour taste

- Smell of fresh milk

- White color

- Fatty taste

Fermented milk products

Table 9 Sensorial evaluation results of fermented milk product

Fermented milk

Dink yogurt

- Odorous, sweet taste

- Opaque yellow color

- Liquid form

Yogurt 1 -- Sour tasteWhite with slightly yellowish color

- The structure is smooth

Yogurt 2 -- Slightly sour taste, sweetWhite color

- The structure is very smooth

Yogurt 3 -- Sour tasteWhite color

- Soft texture, smooth, no water separation

Yogurt 4 -- Slightly sour tasteWhiter color

- Soft texture, no smooth, water separation