It is a cyclic ester of D-gluconic acid. Pure GDL is a white, odorless crystalline powder. GDL is commonly found in honey, fruit juices, and wine. Because of its acidic nature, it adds a strong aromatic flavor to foods, although it has about one-third the sourness of citric acid. When dissolved in water, GDL rapidly enters dynamic equilibrium with gluconic acid, making the solution a mixture of this acid and GDL. The rate of hydrolysis of GDL increases at high temperatures and pH.
When tasted, GDL has a sweet taste that gradually turns sour. GDL hydrolyzes in water to form acid, forming a precipitate like lemon and vinegar but more slowly.
2.2. Technological process diagram
Additives
Clean
Clean
Chop
Boiled
Grind
Fat separator
The technological process of producing nem chua is presented in diagram 4.11.
Lean pork
Pigskin
Spice
Seasoning
Cut the thread
Mash
Dry
Shape
Packaging
Product
Ferment
Mix
Figure 4.11. Technological process of producing nem chua
2.3. Process description
Depending on the taste of each region, there will be many different recipes for making nem. Usually, the ratio between lean pork and pork skin is 4/1 or 3/1, with additional spices such as: salt, sugar, rice bran, MSG, garlic, pepper, chili and some additives: lactose, modified starch, phosphate salt, nitrate, colorants...
2.3.1. Raw material processing
Lean pork is washed with clean water, dried, tendons, fat, and meat are removed. Then the meat is cut into small pieces, ground, and marinated with necessary spices and additives, then ground (by machine or by hand). The pig skin is shaved, washed, boiled, cut into small pieces and dried before being mixed with pork. The skin should not be overcooked. Rice bran is made from washed, drained, roasted until golden brown, then crushed and sifted to get fine bran.
2.3.2. Mixing
Mix the minced pork with shredded pork skin, add rice powder and spices to the mixture and mix well.
2.3.3. Forming and packaging
Depending on the requirements, the mixed ingredients are formed into balls or blocks (round, square, long, depending on the size). The prepared meatballs are wrapped in 1 or 2 layers of vông leaves, then the banana leaves are tied very tightly and fermented at room temperature for 3 to 5 days. Some places use guava leaves or star fruit leaves instead of vông leaves. The requirement is to wrap tightly, do not leave any gaps, if exposed to the wind, the spring rolls will easily rot. You can also put the meat in a plastic bag and then wrap it with banana leaves.
2.3.4. Fermentation
Fresh meat is carefully packaged in anaerobic conditions, kept at a temperature of 27 30 o C, creating conditions for lactic acid bacteria to gradually become more active, converting sugar into lactic acid, making the meat fragrant and sour. The fermentation process is a transformation that occurs in the spring roll under the influence of lactic acid bacteria. The lactic acid produced reduces the pH of the meat, changes the structure of the meat, inhibits and prevents the growth of microorganisms that cause spoilage and creates the necessary sour taste for the product.
The fermentation process begins with the breakdown of glucides under the action of enzymes and microorganisms into glucose, glucose is converted into lactic acid under anaerobic conditions. The formation of this lactic acid causes the pH of the muscle to decrease from 5.6 6.2 to 4.5 5.0 to near the isoelectric point of the muscle, creating conditions for the coagulation and denaturation of proteins to promote the formation of protein gel to create a solid structure for the nem chua product.
Simultaneously with the fermentation process is the process of changing the color and creating the aroma of the nem chua product. The muscle component of the meat contains myoglobin, a complete protein with a deep red color, which determines the color of the meat. The structure of myoglobin includes proteins such as globin and the heme group in the heme component containing iron, the oxidation state of Fe (Fe 2+ , Fe 3+ ) in heme as well as the nature of the molecules bonded to Fe (O 2 , NO, CO) are the causes of the change in color of the meat. Because the red color of myoglobin is easily oxidized to brown due to the formation of metmyoglobin, in the process of producing nem chua, people often add a little nitrite, nitrate salt to provide NO combined with myoglobin to form a nitrozo-myoglobin compound with a relatively stable red color, so it maintains the color of the meat. In cases where these salts are not used, colorants such as ponceau 4R can be used to create color.
natural red, enhancing the sensory properties of the product.
The characteristic aroma of nem chua depends on the spices and acids produced during the nem production process as well as some aromatic substances created during the metabolism of carbohydrates, proteins and fats.
Depending on the taste of each region, the sourness and flavor of the nem can be adjusted appropriately. The longer the fermentation time, the stronger the sour taste of the nem.
2.3.5. Product standards
A quality nem chua product when eaten has the toughness of the meat, the sourness of lactic acid, the spiciness of pepper, chili, the sweetness of sugar, MSG, the aroma is the blend of fermented cooked meat with spices. The surface of the nem must be dry, not slimy, the nem color is dark red, fresh and no mold growth. Microbiological indicators of nem chua are presented in table 4.4.
Table 4.4. Microbiological indicators of nem chua
TT
Indicator name | Maximum allowed level | |
1 | Total aerobic microorganisms (number of colonies/1ml) | 3.10 5 |
2 | Escherichia Coli, (SKL/1ml) | 3 |
3 | Coliforms , (SKL/1ml) | 50 |
4 | Clostridium perfringens , (SKL/1ml) | 10 |
5 | Salmonella | Do not have |
6 | Staphylococcus aureus (SKL/1ml) | 10 |
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2.4. Some common damages to nem chua
The spring rolls are dark in color, less chewy and elastic. When eaten, they feel a bit crumbly due to the low freshness of the meat and poor elasticity.
Nem quickly becomes sour, moldy, has a strange smell, strange color, and spoils quickly due to poor packaging, failure to create anaerobic fermentation, and unclean packaging.
REVIEW QUESTIONS
1. How does the process of fish meat hydrolysis in fish sauce production take place? How to enhance the hydrolysis of fish meat in fish sauce production?
2. How do temperature and pH factors affect the fish sauce production process? What needs to be done to create conditions for these factors to have a positive effect on the fish sauce production process?
3. What is the role of salt in making fish sauce? Why is it necessary to ensure the salt content and quality in making fish sauce?
4. State the process of producing fish sauce using the stirring method and explain what the phenomena of "fish demanding salt", "fish standing", "fish standing on its head" are?
5. Describe the process of producing fish sauce using the pressing method and what is a lù? Why is it necessary to press a lù during the process of producing fish sauce?
6. What is the purpose of the pressing step in fish sauce production? List the steps for pressing the batch.
7. How to determine if the fish sauce is ripe to proceed with extracting it?
8. What is the purpose of the fish sauce extraction process? Why is it necessary to add tanning water, dewatering water, and salt water during the fish sauce extraction process?
9. During the fish sauce production process, what phenomena often occur that damage the fish sauce and finished fish sauce? Explain why?
10. Problem: Calculate the ratio to mix 3 types of fish sauce with the following nitrogen levels: Fish sauce A: 30 o N, fish sauce B: 25 o N, fish sauce C: 15 o N to form fish sauce X: 20 o N.
11. What is the basis for making Nem chua? Explain the fermentation process of Nem chua.
12. Present the technology of producing nem chua, requirements of raw materials and hygiene in producing nem chua.
REFERENCES
[1]. Dr. Nguyen Trong Can, Do Minh Phung (1990), Aquatic food processing technology (volume 2), Agricultural Publishing House, Hanoi.
[2]. Le Hai Dang, Le Ba Thanh (2005), Fish sauce craft village in Phan Thiet,
http://vn.360plus.yahoo.com/bathanhhs/article?mid=581 , accessed August 28, 2010.
[3]. Associate Professor, Dr. Nguyen Thi Hien (2004), Technology for producing MSG and traditional fermented products, Science and Technology Publishing House, Hanoi.
[4]. Nguyen Duc Luong (2006), Microbiological technology volume 3 - Traditional fermented foods, Ho Chi Minh City National University Publishing House.
[5]. MSc. Phan Thi Thanh Que (2005), Textbook of seafood processing technology,
Can Tho University.
[6]. Nguyen Van Vinh (2008), Production techniques of fermented pork roll and fermented fish sauce, http://www.dostbentre.gov.vn/index.php?option=com_content&task=view&id=136 5&Itemid=138 , accessed December 1, 2009.
[7]. Phu Quoc fish sauce production process , http://www.thanhhaco.com.vn/tiengviet/vietnampage.htm, accessed December 1, 2007.