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Essay: The Production of Soy Sauce

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  • Published: 26 December 2019*
  • Last Modified: 11 September 2024
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Abstract
Soy sauce is an essential seasoning that is used in many Asian cuisines. It is commonly used to marinate, to cook or as a dipping sauce. Today, soy sauce is made using two methods: a traditional brewing fermentation method or a chemical acid hydrolysis method. With the fermentation method, it takes eight months to get an authentic taste. Whereas, the chemical hydrolyzation method is able to produce soy sauce in a few days but has a different flavour, aroma and texture. Since people are more attracted to the fermented soy sauce, the solution to a faster procedure using the traditional method is by adopting a bioreactor. By allowing the fermentation to be in a continuous culture in a bioreactor, it will shorten the production time to eight days while still maintaining an authentic taste. Thus, soy sauce production adopts a bioprocess method rather than a chemical method.
Introduction
Soy sauce is one of the oldest condiment and is used all around the world. In 1988, it was revealed by Japan Soy Sauce Brewers Association that the daily consumption of soy sauce in Japan by one person is around 30ml. Studies have shown that soy sauce contains taste and aroma compounds with certain bioactive compounds (Watson, Zibadi and Preedy, 2010). It would help in many biological functions including atioxidative activities. Thus, soy sauce is a traditional seasoning which people have come to use daily and its production is important. There are currently two methods that is used in the production of soy sauce: traditional fermentation and the chemical acid hydrolysis method. This paper will cover the two main methods for the production of soy sauce. On top of that, it will also indicate the advantages and the disadvantages of each method. Finally, the paper will end with addressing current technology and recent signs of progress in the soy sauce production which decreases production time.
Results and Discussion
Traditional Fermentation Method
Figure 1. Schematic Diagram of Fermentation Method
The traditional fermentation method is complex and time-consuming. It is considered as the biochemical method since it relies on enzymes for the development of the flavour and the production of soy sauce. Even though it is time-consuming, there are many opportunities that can help influence the flavours and the final concentration of the finished product. This process uses four ingredients including wheat, soybeans, water and salt. When it comes to the traditional brewing method, it consists of three distinct steps: Koji-making step, brine fermentation and refinement (Yokotsuka, 1986; O’Toole, 2004).
Koji is a mould from the combination of soybeans and wheats. This mould is a key aspect of developing the soy sauce flavour. Before the Koji-making step, the soybeans are picked carefully before getting soaked in water and later boiled until cooked. The wheats are also roasted and cracked. The step begins with the soybeans and wheats crushed and blended together in equal proportions while still warm. Water is added to the mixture, allowing the system to be boiled until the grains are soft and well cooked. This mixture will be incubated for 72 hours at 35 degrees Celsius (Luh, 1995). The mash is allowed to cool to about 27 degrees Celsius before it is inoculated with 0.1% of the Aspergillus oryzae mould. This Aspergillus oryzae mould is an enzyme that is added to help break down the proteins in the mash(HORITSU, MASEDA and KAWAI, 1990). This is left for three days to mature where the air is circulated. The resulting culture of soybeans, wheat and mould forms Koji.
The second step in making fermented soy sauce is the brine fermentation step. The Koji is transferred into fermentation tanks where it is mixed with water and salt to produce a mash called moromi. The amount of water and salt will vary the taste of the soy sauce. So, the deciding factor for the amount of water and salt to be added is dependent on the size of the tank. However, the recommended ratio of salt to water is usually 20g to 100mL (O’Toole, 2004). After this step, Lactic acid bacteria, Pediococcus halophilus, and yeast species, Zygosaccharomyces rouxii and Candida, are added to promote further fermentation (O’Toole, 2004). This will also help prevent the growth of any undesirable microorganisms. It will also allow the Aspergillus oryzae mold to release more enzymes which breaks down the grain and soy proteins into free amino acids and protein fragments. The starches are converted into simple monosaccharides. The moromi must be left to ferment for several months. The time it is left for will allow the soy and wheat paste to turn into a semi-liquid mature mash, filled with simple macromolecules. Since it is a long period of time, this will allow it to fully develop with rich flavour.
Refinement step is the final step in this procedure. This includes the pressing, filtration, pasteurisation and packaging of the soy sauce. After six months of moromi fermentation, the raw liquid is separated from the solid wheat and soybean residue by pressing it through layers of filtration cloth. It is possible to redevelop the cake residue so that more raw liquid can come out of it and thus this liquid can continue on to the pasteurisation step. The liquid that emerges from the cake residue is then pasteurized in a heat-exchanger at 70-80 degrees for a few minutes (Hamada et al., 1991). This will allow it to inactivate residual enzymes that was previously used to fermentation with any undesirable microorganisms. It also serves two other purposed: it is also able to have a longer shelf-life, as well as add additional aromatic and flavour compounds. Finally, the liquid is bottled up as soy sauce and placed on the shelves.
Acid Hydrolysis Method
Figure 2. Schematic Diagram of Acid Hydrolysis
Another method that is also adopted is the acid hydrolysis method. This is the chemical way of the soy sauce production. This method takes only a few days where it artificially breaks down the soy proteins by a chemical process known as acid hydrolysis. The method utilises hydrochloric acid where it is boiled with soybeans for 15-20 hours to remove the amino acids (Liu, 2008). When the maximum amount has been removed, the mixture is left to cool to stop the hydrolytic reaction. The amino acid liquid is then neutralised with sodium carbonate. It is then pressed through a filter, mixed with active carbon and purified through filtration. This final solution can be referred as hydrolysed vegetable protein. Carmel colour, corn syrup and salt are added to this protein to obtain the appropriate colour and flavour. Finally, it will be refined and packaged as the final product.
Using the fermentation method, it is able to produce soy sauce that is rich in flavour and it helps enhance people’s cooking. In particular, when allowing the Koji to ferment, there have some by-products that are made during this process. These by-products help constitute the flavour and thus does not need an extra step to remove them. This allows time to be minimised while still allowing the rich flavour to come through. However, the amount of effort and time that needs to be put into this fermentation method is too long for its production. Since it takes almost eight months to allow it to “fully” ferment, this amount of waiting time is not suitable for commercial production in comparison to acid hydrolysis that takes a few days in production.
Undergoing the acid hydrolysis method, the soy sauce has an undesirable taste. The reason why the taste is not like the traditional soy sauce is due to the acid hydrolysis doing a complete job at the fermentation section. This means that the chemical methods remove almost all the proteins while the traditional methods still have many peptides left, giving it a different flavour. The brewed product’s fermentation step produces many by-products that are quite useful to the flavour compounds. This includes alcohols, esters which help contribute to the different aroma and flavour in the mouth. Meanwhile, the acid-hydrolysis by-products are undesirable and must be removed. Thus, separation methods are needed to remove the undesirable by-products.
To improve the method for the production of soy sauce, the combination of the two methods can be used. However, since both methods are so different in steps, it is difficult to combine the two methods. So, the best way is to have a blending of the two soy sauces production into one (Kim and Lee, 2007). This may enhance the taste of the acid hydrolysed soy sauce. However, it would not improve the production time for the traditional fermentation. So, this kind of method can only balance out the flavour.
Bioreactor Process
Figure 3. Schematic Diagram For Bioreactor Process
Thus, another method to help improve the production time of the traditional method is by adopting a continuous culture in a bioreactor (KOSEKO et al., 1993). To begin the bioreactor method, the preparation of the liquid Koji needs to be made. This is done by mixing cooked soybeans and roasted wheat with the broth of Aspergillus oryzae. It will be enzymatically hydrolysed in the presence of salt and at a temperature of 45 degrees Celsius for three days. It will be stirred evenly before it forms a mesh. Once it is at its right consistency, this mash will be filtered through a press cloth. This will allow the liquid to be separated from the mash. The raw liquid will be used during the continuous fermentation method.
Once the liquid is prepared, it is passed through a series of bioreactors that will help enhance its taste. It will pass through a glutaminase reactor which helps increase the quantity of glutamic acid. Glutamic acid is important since it is a natural constituent in fermented food, including soy sauce. Thus, it is able to enhance the flavours in soy sauce. Then it will pass through a Pediococcus Halophilus reactor which will carry out the lactic acid fermentation. This step is important in controlling the pH of the liquid, as well as preparing the appropriate conditions for the ethanol fermentation. Next, it will go through the Zygo-saccharomyces Rouxii reactor to allow the proceeding of the ethanol fermentation. This step is also an important step in allowing the stabilisation of the quality and flavour of the soy sauce. Finally, in parallel to the third reactor, it will be a Canadia Versatilis reactor, which will produce the final aroma compounds such as 4-ethyl-guaiacol (Hamada et al., 1991). These reactors allow continuous fermentation using the different types of immobilized cells. Once it has passed through all the reactors, it will undergo a refinement step. This will include the final filtration and pasteurisation of the raw liquid. The liquid will be pasteurized in a heat-exchanger. This step will allow it to eliminate undesirable microorganisms in the liquid. Finally, it is ready to be packaged and placed on the shelves. This procedure takes only a maximum of two weeks in comparison to the traditional method of eight months.
This kind of procedure was also run for 100 days and there was no problem with microbial contamination (KOSEKO et al., 1993). Data revealed that the contents of the major ingredients of soy sauce was kept at proper ratios. The only thing different was the total nitrogen and sodium contents. However, it was not significant enough to lower its flavour standards. Thus, by undergoing this procedure, the fermentation method has been shortened to eight days instead of the eight months. It also allowed true brewed flavours to be reproduced in a shorter amount of time. Thus, through this procedure, it is more convenient for the soy sauce industry to adopt the biochemical method in making soy sauce rather than the chemical method.
Conclusions
The production of soy sauce occurs using two kinds of methods: the traditional fermentation method or the chemical acid hydrolysis method. Using the traditional fermentation method takes almost 6 months to produce a well-flavoured soy sauce. However, although the acid hydrolysis method only takes a few days, the taste is different and less appealing than traditional soy sauce. It is found that by combining the two methods in different sections of the traditional fermentation method, it will allow a decrease in time, yet help develop a much richer soy sauce than the chemical soy sauce.
 

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