MILK TESTING AND CONTROL QUALITY OF LIQUID MILK
Objective
− Checking the quality of milk
− Use techniques to test and control milk quality
− Determine pH, the titratable acidity
Overview
− Milk, a nutrient-rich liquid sustenance, is secreted by the mammary glands of mammals It serves as the primary source of nourishment for young mammals, including human infants who are breastfed, until they transition to solid food Milk is obtained from lactating warm-blooded animals, encompassing species such as bovines, sheep, goats, horses, buffaloes, and others It offers vital elements like lipids and lactose for energy, proteins for amino acids and amino groups, essential fatty acids, vitamins, inorganic elements, and water.
− The composition and production of milk exhibit variations among different species, resulting in a range of health benefits Lipids present in goat and sheep milk possess anti-obesity and anti-atherogenic properties, with goat milk also acting as a prebiotic Goat milk boasts higher selenium levels, supporting the immune system, while camel milk is abundant in iron, aiding in oxygen transport Bovine milk is enriched with vitamins such as riboflavin, folic acid, B6, and vitamin A, contributing to hemoglobin synthesis Moreover, cattle milk supplies folate, and goat milk is rich in niacin, recognized for its anti-cancer properties.
Material and Procedure
− Unexpired sterilized TH True Milk
− Purely made with fresh milk from the TH Farm
− Closed and hygienic process from grass to glass
Table 1.1 Nutrition Information of TH true MILK UHT Pure Fresh Milk Per 100 ml
− Observe the appearance of the milk
− If still unable to make a clear judgment, taste the milk, but do not swallow it Spit the milk sample into a bucket provided for that purpose or into a drain basin, flush with water
− Look at the can lid and the milk can to check cleanliness
Table 1.2 Sensory evaluation of TH true milk
Purpose: The purity of milk is assessed using a lactometer test By dividing the density of milk by the density of water, it calculates the specific gravity of milk.
Color The color spans from ivory white to a gentle light cream.
Flavor The natural, inherent aroma and flavor of fresh milk, without any unusual or foreign smells or tastes.
Impurity for eyes No appearance
Procedure:Fill the 250 mL cylinder with TH genuine milk, then submerge the lactometer in the liquid
Table 1.3 The density of TH true milk
Three measurements indicate that milk has a density of 1024 kg/m 3
Purpose: To detect abnormal milk, such as colostrums or mastitis milk It is based on the instability of the proteins when the levels of acid and/or rennet are increased and acted upon by alcohol as a result of disturbances in the mineral balance of milk.
Procedure: For routine testing, 5 ml of milk is mixed with 5 ml of an ethanol solution If the tested milk is of good quality, there will be no coagulation, clotting, or precipitation The presence of flakes or clots indicates poor quality milk.
− After adding alcohol, there is no coagulation or precipitation occurrence for "TH true milk" that has been pasteurized This demonstrates that the acidity, calcium, and magnesium contents of the aforementioned milk are all within permissible bounds according to milk regulations.
− The Methylene Blue is based on the fact that the coloring matter known as methylene blue is blue in the presence of oxygen If the dye, methylene blue, be added to fresh milk, it will give to it a blue color This blue color will remain until all the oxygen is used up when the milk will almost immediately change back to white again.
− The larger the number of bacteria in milk, the sooner this change in the color will take place Hence the use of methylene blue becomes a valuable test for determining the relative number of bacteria present in a given number of milk samples
− Prepare: Methylene blue solution is prepared by dissolving 5 mg methylene blue into 100mL distilled water The solution is stored in the refrigerator, protected from sunlight, and used within 1 week.
Procedure: Conducted under sterile conditions Take 10 ml of milk and 1 ml of methylene blue solution into a sterile test tube Shake by turning it over and over again 2-3 times Incubate at 37 o C Shake every 1 hour and check the color change over time.
− Methylene blue does not change color with TH true milk because TH true milk is heat-sterilized The heat-sterilization process kills all bacteria in the milk, so there are no bacteria to use methylene blue to create blue intermediate products
− In addition, TH true milk is also processed using ultraviolet (UV) light sterilization technology This technology also has the effect of killing bacteria in milk, so TH true milk also does not change color when methylene blue is added.
− Therefore, it can be concluded that methylene blue does not change color with TH true milk because TH true milk is heat-sterilized and processed using UV light sterilization technology.
− The pH of TH true milk is 6.64 (about 6.6 to 6.8) This is a neutral pH, which is within the safe pH range for human health TH true milk is produced from fresh cow's milk from TH farms, which are naturally grazing on pastures The milk is heat-sterilized and processed using ultraviolet (UV) light sterilization technology Therefore, TH true milk has a neutral pH, which is within the safe pH range for human health
Procedure: 10 ml of the milk measured into the erlen, add the water follow by ratio 1:2 and
3 drops Phenolphthalein is added Slowly drip down the NaOH 0.1N from the burette until the mixture appear pink, then stop The number of mL of Sodium hydroxide solution divided by 10 expresses the percentage of lactic acid.
Figure 1.0.11 The formula of titration
Table 1.4 The result of titration
Volume of NaOH titrated (mL)
Figure 1.12 The result of titration
− Based on the table above, the acidity of milk is 0.137 (range 0.14±0.01) The milk quality is good and not contaminated.
Conclusion
− Results are presented of the relationship of the formation of lactic acid in milk with (a) the production of acid-associated flavors, (b) the microscopic clump count, (c) the methylene blue reduction, and (d) titratable acidity
− A general relationship was noted in the lactic acid increases obtained by the colorimetric lactic acid method and by titration However, the titration results may vary appreciably from the true lactic acid changes in individual milks
− A discussion is given of the limitations and application of certain of these quality tests in a lactic acid grading program.
1 P Walstra, T J Geurts, A Noomen, A Jellema, M A J S van Boekel, 1999, DAIRY TECHNOLOGY principles of milk properties and processes, Department of 16 Food
Figure 1.13 The criteria of titratable acidity
Science, Wageningen Agricultural University, Wageningen, Netherlands, Marcel Dekker Inc
2 A H A Al-Shamary and N I Abdulali, 2011, Detection of microbial load in Imported UHT milk in Baghdad Markets, Al-Anbar J Vet Sci., Vol.: 4 No (2) Accessed: 02/28/2023, https://www.iasj.net/iasj/download/1deae599d1330089
3 Food Engineering Progress, 2013, Changes of Proteins and Physicochemical Properties of Cow's Milk by High Voltage Pulsed Electric Field Treatment, Sulhee Lee and Young-Seo Park, https://s.net.vn/QHtQ
YOGURT PRODUCTION
Objective
− Describe and explain the yoghurt manufacturing procedure
− Determine the technical parameters of yogurt processing
− Applying knowledge to real-world products
− Examining the factors that affect yogurt quality during production and storage
− Using ordinary laboratory equipment with mastery
− Determine pH, the titratable acidity, during fermentation
− Checking the quality of yogurt.
Overview
A fermented milk obtained by a simultaneous operation of L bulgaricus and S thermophilus in which the two specific cultures remain active (living) until consumption
Thermal treatment after fermentation is not allowed
On the market today, yogurt products are very diverse in terms of standard types, structures, and flavors of yogurt, which are always changed by manufacturers to suit the tastes and usage habits of customers in different countries Yogurt products can be classified as follows:
− Traditional yogurt (set type): the product has a smooth gel structure In the traditional yogurt production process, the raw milk is processed, inoculated, and then poured into the packaging Fermentation takes place in the packaging causing the appearance of a curd mass and a characteristic structure for the product
− Stirred type yogurt: the curd that appears in the product after fermentation is partially destroyed by mechanical damage During the production of stir-fried yogurt, raw milk is treated, inoculated, then fermented in specialized equipment,
13 then cooled and poured into packaging Yogurt will not have a smooth and uniform gel structure like traditional yogurt
− Drinking yogurt or liquid yogurt: the curd that appears in the product after the fermentation process is completely destroyed The product has a liquid form, when using the consumer does not need to use a spoon The difference is that after the fermentation process, people use stirring or homogenization to destroy the gel structure of the coagulant and reduce the viscosity of the product
− Frozen yogurt: the product is similar to ice cream The milk fermentation process is carried out in specialized equipment, then the mixture after fermentation will be treated and frozen to increase the hardness of the product and then packaged
− Concentrated yogurt: the production process includes important stages such as milk fermentation, concentration, cooling and product packaging During the concentration process, the milk serum is separated from the product Today, to diversify yogurt even 23 more on the market, people can add flavoring, food coloring or fruit purée to the product
− Yogurt cheese: is a fresh cheese created by draining and separating whey overnight The flavor is akin to sour cream and has the texture of soft cream cheese A liter of yogurt produces around 500 mL of cheese Yogurt cheese has a shelf life of 7-14 days when wrapped and refrigerated at 4°C or below
− Dried yogurt (Kurut in Turkey): Yogurt is sun dried for longer preservation Quality criteria
Based on the TCVN 7030:2002 standard for yogurt products:
Table 2.1 The TCVN 7030:2002 Sensory criteria
1 Color Milky white color or characteristic color of additional ingredients
2 Flavor, taste Features for each type of product
− Considering physical and chemical markers of yogurt
Table 2.2 The TCVN 7030:2002 Physical and chemical criteria
1 Fat-free dry matter, % mass fraction, not less than 8.2
− Considering heavy metal indicators in yogurt
Table 2.3 The TCVN 7030:2002 heavy metal criteria
Table 2.4 The TCVN 7030:2002 Bacteria criteria
1 Total number of aerobic microorganisms, number of colonies in 1 g of product
2 Coliform group, number of bacteria in 1 g of product
3 Staphylococcus aureus, number of bacteria in 1 g of product
4 E.Coli, number of bacteria in 1 g of product 0 0
5 Salmonella, number of bacteria in 25 g of product
6 Yeasts and molds, number of colonies in 1 g of product
Material and procedure
Figure 0.2.2 The power milk (left) and fresh milk (right)
In this experiment, we used both sterilized milk (11% TS) and milk powder (96%TS) to make a standardized milk with total solid content is 15%
Lactobacillus bulgaricus and Streptococcus thermophilus are the two major (starter) microorganisms found in yogurt The starter cultures' role is to ferment lactose (milk sugar) and create lactic acid The rise in lactic acid lowers pH and causes the milk to coagulate, resulting in the soft gel typical of yoghurt In this experiment, we utilise the starter from Vinamilk yogurt (no sugar added) We purchased the product with the most recent manufacturing date in order to maximise the amount and quality of the lactic acid bacteria present The starting concentration is 4.5%
For this experiment, we used two types of milk: sterilized fresh milk and reconstituted powdered milk As a result, we had to calculate the mass of each component in order to get the final result for a yogurt product with a 15% dry matter
{ a + b = 1000 0.11a + 0.96b = 0.15 × 1000 ↔ { a = 952.94 g b = 47.05 g Where: a: weight of sterilized fresh milk
Figure 2.0.3 The vinamilk yogurt non sugar
From whole cream milk powder with 4% moisture, preparing 1000 mL reconstituted milk with 15% dry matter by dissolving 47.05g whole milk powder into 952.94 g of fresh milk Reconstituting thoroughly by vigorous agitation and allow to stand for about 30 minutes
Purpose: adjust the fat concentration content for fermentation (0.5−3.5%) The dry matter content of milk for yogurt production is usually increased to about 16%, with 1−5% being fat and 11−14% being solids-not-fat (SNF) It also contributes to increased lactose, protein, mineral, and vitamin content
Purpose: reduces fat globules to