Effect of supplemented brine concentration and amount and fermentation time on oyster mushroom (pleurotus spp.) sauce quality

AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> <br /> <br /> <br /> EFFECT OF SUPPLEMENTED BRINE CONCENTRATION AND AMOUNT<br /> AND FERMENTATION TIME ON OYSTER MUSHROOM (PLEUROTUS SPP.)<br /> SAUCE QUALITY<br /> <br /> Nguyen Thi Ngoc Giang1, Tran Van Khai1<br /> 1<br /> An Giang University, VNU - HCM<br /> <br /> Information: ABSTRACT<br /> Received: 09/10/2018<br /> Soy sauce has been widely used as one of the main seasoning agents in<br /> Accepted: 03/01/2019<br /> Asian countries. The chemical composition of sauce varies according to the<br /> Published: 11/2019<br /> ingredients, preparation attractive and the method of production. Sauce is<br /> Keywords: considered delicious when it has color, aroma and the sweetness of protein<br /> Oyster mushroom, soy sauce, and sugar. The study was investigated the effect of salt concentrations (10,<br /> salt concentration, water ratio. 15, 20, 25% w/v), the amount of water (100, 150, 200, 250, 300% compared<br /> with the raw material) and the fermentation time (0, 10, 20, 30, 40, 50, 60,<br /> 75, 90 days) to nutrient content as well as color of fermented oyster<br /> mushroom sauce.<br /> The results showed that when the salt concentration was 20%, the<br /> suplemented water was 200% (of the raw material) and the fermentation<br /> time was 60 days, the contents of amino acids, reducing sugars, total acid<br /> were the highest (11.73; 9.87; 8.71 g/100 g dry matter, respectively) and the<br /> color of fermented oyster mushroom sauce was the darkest.<br /> <br /> <br /> 1. INTRODUCTION Pleurotus spp., accounting for 46.6-84.8% of<br /> Pleurotus spp. can be called oyster, abalone or dry basis (compared to 60% of A.bisporus).<br /> tree mushrooms. Pleurotus mushrooms are According to Bano and Rajarthnam (1982),<br /> carbohydrates consist of 4.2% soluble<br /> developed in tropical and subtropical regions<br /> carbohydrate, 1.7% pentosan and 32.3%<br /> and easily artificially cultivated (Akindahunsi<br /> and Oyetayo, 2006). Oyster mushrooms have hexosan.<br /> aromatic and flavor properties (Herndndez et Fermentation is the process of using enzymes of<br /> al., (2003); Kalmis et al., (2008)). Their molds to hydrolyze proteins in raw materials<br /> nutritional value includes carbohydrates and into soy sauce. The difference between<br /> proteins, which are the main components, fermentation and rotting is that after<br /> accounting for 70 to 90% of dry matter). fermentation, the product does not produce a<br /> Besides, they have about 10% ash with many rotten smell (Bui Duc Chi Thien, 2014).<br /> kinds of minerals. Fat content is low (1-2%) (Le Fermentation is also an important stage. If the<br /> Xuan Tham, 2010). Proteins of Pleurotus raw materials are treated well and mold is<br /> mushrooms are present in all of essential amino grown properly, but the fermentation is not<br /> acids (Chang and Quimio, 1982). guaranteed, the soy sauce is still unsatisfactory<br /> Carbohydrates are the main component of and the efficiency is not high (Nguyen Duc<br /> <br /> <br /> <br /> 57<br /> AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> Luong, 2006). In soy sauce production, after study was to determine the brine<br /> raising the mold, the mold is mixed with salt supplementation and amount as well as the<br /> solution. In salt solution, the enzymes in the fermentation time on oyster mushroom sauce to<br /> mixture become active. The primary reach the best nutritional content and color.<br /> biochemical nature in the production of soy 2. MATERIALS AND EXPERIMENTAL<br /> sauce is the hydrolysis of starches and proteins<br /> by the corresponding amylase and protease 2.1 Materials<br /> enzymes produced by microorganisms. The Pleurotus mushrooms purchased from<br /> scientific basis of the process is to use the Experimental – Practical Area of An Giang<br /> enzyme amylase, protease from University, Viet Nam. Fresh mushrooms were<br /> microorganisms to break down the starches into washed with water, drained, cut into small<br /> sugars with low molecular and proteolysis into spieces (0.5 x 1 cm) and used immediately.<br /> polypeptides, peptides, amino acids. There is Aspergillus oryzae molds were provide by the<br /> also the formation of alcohol, organic acids. All Institute of Biotechnology, Can Tho University,<br /> of these compounds create a unique flavor and Viet Nam.<br /> nutritional value for soy sauce (Nguyen Duc<br /> Luong, 2006). Meizan flour is roasted at 80oC for 15 minutes.<br /> <br /> Factors that affect moromi fermentation are: 2.2 Preparartion of Koji<br /> <br /> + The addition of salt with high concentration 200 g of oyster mushrooms were steamed until<br /> in the fermentation is a necessary condition to the mushrooms had just reached 90oC and<br /> hinder the development of undesirable mixed 10% wheat flour. The mixture was<br /> bioburden types. However, if the salt adjusted to pH6.0 (Jian Chen and Yang Zhu<br /> concentration is too high, it directly affects the (2013); Perrin (1974)) and added 0.03% mold.<br /> activities of the enzyme systems in the The koji was incubated at 30oC for 30 hours<br /> fermentation solution. (Nguyen Thi Ngoc Giang and Nguyen Minh<br /> Thuy, 2016; Nguyen Thi Ngoc Giang and Tran<br /> + The water supplemention has a strong<br /> Van Khai, 2018).<br /> influence on the end product quality. Lots of<br /> water addition leads to the concentration of 2.3 The experimental design<br /> nutrients decrease in fermentation sauce. If The experiment was designed with three factors<br /> water supplemention is little, the enzyme and three replicates, including (i): Salt<br /> activities in sauce mass decreases, leading to a concentration: 10, 15, 20, 25% w/v; (ii) Brine<br /> reduction in quality, and the cost of the product content: 100, 150, 200, 250, 300% compared to<br /> is increased due to low recovery efficiency the raw material; (iii) Fermentation time: from<br /> (Dang Hong Anh, 2011). Therefore, the choice 0 to 90 days.<br /> of supplemented brine concentration and<br /> 2.4 Determination of amino acids content<br /> amount is an important condition in soy sauce<br /> fermentation. Amino acids content was analysed by formol<br /> titration (Le Thanh Mai et al., 2005). Amino<br /> + Fermentation time: depending on the amount<br /> acids content (mg) is calculated by the formula:<br /> of water mixed and the fermention temperature,<br /> the fermentation time is long or short. The mgN = (A – B) x 1.4<br /> fermentation time can also be based on the Where, A- volume of NaOH 0.1N used for<br /> increase or decrease of formol protein. titration of the sample (mL)<br /> The hydrolytic capacity of enzyme system in B- volume of NaOH 0.1N used for<br /> mold is determined by the content of reducing titration of the blank (mL)<br /> sugar, amino acids and total acid. The present<br /> 2.5 Determination of reducing sugar content<br /> <br /> <br /> 58<br /> AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> Reducing sugar content was measured by DNS L* indicates lightness, a* is the red/green<br /> method (Le Thanh Mai et al., 2005). The coordinate and b* is the yellow/blue coordinate.<br /> concentration of reducing sugar was based on The difference is calculated:<br /> standard curve of glucose, y = 23885x + 0.126 , ∆L = L* - Lref (+ = lighter; - = darker)<br /> where R2 = 0.9923.<br /> ∆b = b* - bref (+ = yellower; - = bluer)<br /> 2.6 Determination of total acid content<br /> 3. RESULTS AND DISCUSSIONS<br /> Total acid content was determined by titration<br /> (Le Thanh Mai et al., 2005). 3.1 Amino acids content (g/100 g dry matter)<br /> during fermentation time<br /> 2.7 Determination of color differences using<br /> L*a*b* (Ngo Anh Tuan, 2006) The effect of salt concentration and brine<br /> supplementation on the amino acids content<br /> during fermentation time are shown in Table 1.<br /> Table 1. Amino acids content (g/100 g dry matter) during fermentation time<br /> <br /> Amino acids content (g/100 g dry matter)<br /> Salt Brine<br /> concentration content Fermentation time (days)<br /> (%) (%)<br /> 0 10 20 30 40 50 60 75 90<br /> 10 100 3,26 3,41 3,61 6,53 8,55 10,73 8,47 4,38 4,60<br /> 10 150 2,94 3,39 4,58 7,20 8,53 10,39 10,28 2,58 1,54<br /> 10 200 3,84 1,42 1,24 6,00 8,08 8,81 10,34 7,68 4,27<br /> 10 250 2,47 5,27 6,54 8,84 9,05 10,49 11,30 2,47 1,86<br /> 10 300 3,02 2,97 4,09 4,90 8,61 10,32 15,37 2,01 1,98<br /> 15 100 2,44 3,47 4,75 7,75 7,51 7,91 10,47 2,42 1,55<br /> 15 150 3,36 3,69 5,74 6,29 11,00 12,64 8,69 4,91 3,76<br /> 15 200 4,00 3,31 7,12 9,48 10,29 11,81 12,09 7,35 5,09<br /> 15 250 1,95 3,88 3,73 4,73 7,08 7,83 10,23 4,00 2,21<br /> 15 300 2,23 2,73 4,52 4,33 5,70 6,52 10,37 2,46 1,57<br /> 20 100 2,65 1,92 4,91 6,12 7,37 8,50 10,29 7,92 3,34<br /> 20 150 1,59 3,13 4,23 6,29 7,31 10,14 11,13 11,22 4,32<br /> 20 200 3,61 3,68 5,93 6,99 9,16 10,26 11,73 9,18 6,03<br /> 20 250 2,71 1,56 4,97 5,89 6,19 10,24 9,31 5,37 3,69<br /> 20 300 2,31 1,83 3,10 4,40 5,30 9,25 10,74 5,17 1,05<br /> 25 100 2,31 2,17 2,26 2,07 2,98 3,86 7,63 2,45 0,83<br /> 25 150 2,45 1,51 2,29 2,86 7,43 8,29 6,59 3,26 2,09<br /> 25 200 2,84 3,81 4,87 5,92 8,30 9,96 9,55 6,65 2,15<br /> 25 250 1,88 2,33 2,25 2,05 7,21 3,27 5,29 0,89 0,37<br /> 25 300 1,93 2,24 2,09 1,87 2,31 7,28 4,20 2,24 0,48<br /> <br /> <br /> <br /> 59<br /> AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> The experimental data in Table 1 shows that the content increased with fermentation time and<br /> amino protein content was high at 10, 15 and reached the highest value at day of 60; and then<br /> 20% salt concentrations (the difference is not the amount of amino acids gradually decreased.<br /> statistically significant at 5%) and the lowest at Reduction of amino acids value was dued to<br /> 25% salt concentration. According to Le Van Maillard reaction. The highest amino protein<br /> Viet Man and Tran Thi Anh Tuyet (2006), the production (11.73 g/100 g dry matter) at 20%<br /> high salt concentration in the sauce (25% by salt concentration, 200% brine addition<br /> weight) reduced the catalytic activity of (compared to the weight of raw materials) was<br /> protease enzyme. In addition, the amount of on the 60th day of fermentation.<br /> amino acids was low at high levels of brine 3.2 Reducing sugar content (g/100 g dry<br /> supplementation (250 and 300%) or low (100 matter) during fermentation time<br /> and 150%). This is also proved similarly in the<br /> The effect of salt concentration and brine<br /> research of Dang Hong Anh (2011) that solid or<br /> supplementation on the reducing sugar content<br /> dilute masses all affected to the hydrolytic<br /> during fermentation time are shown in Table 2.<br /> capacity of protease enzymes. Amino acids<br /> <br /> Table 2. Reducing sugar content (g/100 g dry matter) during fermentation time<br /> <br /> Salt Brine Reducing sugar content (g/100 g dry matter)<br /> concentration content Fermentation time (days)<br /> (%) (%) 0 10 20 30 40 50 60 75 90<br /> 10 100 0,03 0,27 0,40 0,49 0,51 1,34 1,93 0,00 0,00<br /> 10 150 0,19 0,79 0,63 1,13 1,42 1,24 3,09 1,49 0,14<br /> 10 200 0,05 0,59 1,46 1,65 2,09 2,82 6,37 5,13 0,31<br /> 10 250 0,00 0,39 0,57 0,23 0,36 0,52 1,27 0,00 0,00<br /> 10 300 0,00 0,18 0,51 0,46 0,64 5,49 5,41 0,46 0,00<br /> 15 100 0,05 0,29 0,40 4,03 1,28 1,40 0,37 0,00 0,00<br /> 15 150 0,22 0,77 0,76 0,79 1,62 2,34 5,79 0,78 0,41<br /> 15 200 0,11 0,37 0,62 2,08 4,22 4,58 0,73 0,00 0,00<br /> 15 250 0,00 0,45 1,26 1,44 1,74 7,78 0,34 0,00 0,00<br /> 15 300 0,01 0,40 0,31 2,07 2,63 1,23 0,76 0,66 0,00<br /> 20 100 0,05 1,69 1,95 2,99 4,17 6,37 7,43 5,90 0,56<br /> 20 150 0,58 2,20 2,70 3,22 5,34 5,19 8,,52 5,51 5,93<br /> 20 200 0,14 0,65 4,96 4,02 5,47 6,83 9,87 7,67 6,44<br /> 20 250 0,03 0,92 1,34 1,41 4,06 5,90 7,78 6,39 0,27<br /> 20 300 0,04 0,34 1,45 1,16 1,31 1,73 5,55 3,89 0,37<br /> 25 100 0,22 0,29 2,39 2,99 3,62 3,90 9,27 1,07 0,75<br /> 25 150 0,19 0,60 1,23 1,88 3,36 4,10 1,48 0,87 0,30<br /> 25 200 0,16 0,33 2,49 3,04 5,68 7,08 9,28 5,52 1,96<br /> 25 250 0,02 0,42 2,74 4,97 5,26 8,04 0,64 0,31 0,38<br /> 25 300 0,00 0,40 2,31 2,70 3,53 4,84 5,14 5,03 2,28<br /> <br /> <br /> <br /> 60<br /> AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> The analytical results in Table 2 show that the was 2 times the volume of koji produced. The<br /> reducing sugar content did not differ content of reducing sugars increases with<br /> significantly between the two salt fermentation time to an optimal value, then<br /> concentrations of 10 and 15%. In addition, the decreases. The rapid increase of reducing<br /> high content of reducing sugars was at the 20% sugars during fermentation is due to the<br /> salt concentration and the lowest reducing sugar involvement of the amylase enzyme. However,<br /> content was at salt concentration of 25%. This due to the aging process, the enzyme activity of<br /> result was also consistent with the study of Su the enzyme amylase is denatured in the salt<br /> et al. (2005), Dang Hong Anh (2011) that the solution and reduced in activity (Chou and<br /> content of salt from 10-15% did not affect to Ling, 1998). The reducing sugars content<br /> the activity of the amylase enzyme in the during aging was decreased by the Maillard<br /> fermentation sauce. At high salt concentration, reaction. The highest reducing sugars (9.87<br /> amylase enzyme activity was inhibited and g/100 g of dry matter) at 20% salt<br /> hydrolysis speed in fermentation solution concentration, the added salt water content (%<br /> decreased. On the other hand, the brine content compared to raw materials) is 200% at day 60<br /> of 200% (compared to the raw material) gave of the fermentation process.<br /> the highest content of reducing sugar. The 3.3 Total acid content (g/100 g dry matter)<br /> research of Dang Hong Anh (2011) also during fermentation time<br /> determined that the amount of water addition<br /> Table 3. Total acid content (g/100 g dry matter) during fermentation time<br /> <br /> Reducing sugar content (g/100 g dry matter)<br /> Salt Brine<br /> concentration content Fermentation time (days)<br /> (%) (%) 0 10 20 30 40 50 60 75 90<br /> 10 100 2,63 4,35 5,03 2,72 1,92 1,72 1,93 1,58 1,70<br /> 10 150 2,81 3,11 3,75 4,44 4,50 4,84 6,06 3,03 2,66<br /> 10 200 2,91 3,39 3,28 3,65 4,15 5,08 6,63 2,09 0,83<br /> 10 250 2,26 2,22 2,66 3,74 4,08 1,95 1,52 1,03 0,92<br /> 10 300 1,26 1,45 1,91 2,51 2,40 3,95 3,38 1,70 1,59<br /> 15 100 2,25 2,50 2,33 2,11 3,88 4,78 5,49 1,93 0,92<br /> 15 150 3,18 2,70 3,21 3,85 4,02 6,37 6,27 3,51 1,82<br /> 15 200 2,28 2,62 3,81 4,07 5,16 6,58 8,06 5,58 4,46<br /> 15 250 1,91 2,23 2,88 3,54 3,91 4,84 2,81 2,06 1,11<br /> 15 300 2,00 3,30 3,48 1,97 2,44 2,48 2,16 1,95 2,08<br /> 20 100 1,85 2,34 2,90 2,91 3,14 6,10 7,52 3,11 0,95<br /> 20 150 1,60 2,76 2,76 3,76 6,81 6,76 7,64 5,67 1,50<br /> 20 200 4,39 7,10 7,60 8,15 4,51 5,66 8,71 3,08 1,43<br /> 20 250 2,51 2,06 2,71 3,36 4,96 4,68 5,00 4,78 4,12<br /> 20 300 2,08 3,43 3,51 4,16 5,44 5,10 4,85 5,45 3,88<br /> 25 100 1,77 2,44 2,85 1,65 2,08 2,99 1,83 1,18 1,40<br /> 25 150 2,04 2,99 3,58 1,73 1,56 2,92 2,37 2,11 1,93<br /> 25 200 2,44 2,73 3,16 4,12 4,32 4,79 3,81 3,16 0,87<br /> 25 250 1,32 1,74 2,43 2,05 1,29 1,34 1,22 0,74 0,98<br /> 25 300 1,50 1,63 1,73 1,26 1,23 1,49 1,33 1,27 1,09<br /> <br /> <br /> <br /> <br /> 61<br /> AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> The analytical results in Table 3 show that the affects the darkening of soy sauce (Choi et al.,<br /> total acid content increases with the addition of 1990).<br /> 10 - 20% salt and 100 - 200% water content. At The correlations between the salt concentration<br /> 25% salt concentration and 250-300% water and brine supplementation (% compared to the<br /> supplementation, the total acid content raw material) to color of soy sauce are<br /> increased slowly because of decreasing enzyme presented in Figure 1 and Figure 2. As shown in<br /> activity. The increase in total acidity was due to these figures, both of salt concentration and<br /> the action of enzymes that breaked down brine supplementation affected to color of the<br /> proteins into amino acids, peptides (containing solution at the 60th day of fermentation. The<br /> carbolylic chains), reducing sugars (Shieh et al., darkening of the sauce increased with<br /> 1982). The highest total acidity produced (8.71 increasing salt concentration and additional<br /> g/100 g dry matter) at a salt concentration of water content. Meanwhile, the yellow color of<br /> 20% and 200% water addition (compared to the the solution decreased with decreasing salt<br /> material) on the 60th day of fermentation. concentration and brine supplementation.<br /> 3.4 The change in color of soy sauce during Maillard reaction affected to the nutrients<br /> fermentation (reducing sugars content and amino acids),<br /> Color is one of the important parameters to affected to the color and flavor of the product.<br /> evaluate the effectiveness of the fermentation The browning rate depends on the water content<br /> process. The color of soy sauce is formed (Le Ngoc Tu, 2002). At the 20% salt<br /> through two stages: fermentation and concentration, the salt brine content is 200%,<br /> pasteurization (Miyagi et al ., 2013). This is all the solution has the darkest yellow color (and<br /> due to browning, known as a Maillard reaction the highest content of amino acids, reducing<br /> between amines and reducing sugars sugars). The change in color of soy sauce<br /> (Yokotsuka, 1986). Melanoidin from the during fermentation time is shown in Figure 3.<br /> Maillard reaction is the main ingredient that<br /> <br /> <br /> <br /> <br /> Figure 1. Correlation of color ∆L with salt Figure 2. Correlation of color ∆b with salt<br /> concentration and brine supplementation (% concentration and brine supplementation (%<br /> compared to raw material) compared to raw material)<br /> <br /> <br /> <br /> <br /> 62<br /> AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> <br /> <br /> <br /> Figure 3. The change in color of soy sauce during fermentation time<br /> <br /> 4. CONCLUSION mushrooms – Biological nature and<br /> Soy sauce produced by fermentation method cultivation methods. Chinese University<br /> almost retains all the amino acids in the Press, Hong Kong, pp 363 – 380.<br /> material. Fermented sauces also contain quite a Bui Duc Chi Thien (2014). Technology for<br /> lot of sugars because of the effect of the fermentation of soy sauce. HUTECH<br /> enzyme amylase on starch. The fermentation of Unversity, Viet Nam.<br /> oyster mushroom sauce under the effect of Chang. S.T. and Quimio, T.H. (1982). Tropical<br /> Aspergillus oryzae is carried out in 60 days mushrooms – Biological nature and<br /> with an additional salt concentration of 20% cultivation methods. Chinese University<br /> and brine content of 200% (compared to the Press, Hong Kong, pp 493.<br /> raw material) that will give a high nutrient<br /> Choi H.S., Lee J.S., Moon G.S and Park G.Y<br /> content of sauce (11,73; 9,87; 8,71 g/100 g dry<br /> (1990). Antioxidative characteristic of<br /> matter, respectively) and the darkest-yellow.<br /> fermented soybean sauce on the oxidation of<br /> REFERENCES fatty acid mixture. Korean Journal Food<br /> Akindahunsi AA, Oyetayo FL (2006). Nutrient Science Technology (22), 332-336.<br /> and antinutrient distribution of distribution Chou CC and Ling MY (1998). Biochemical<br /> of edible mushroom, Pleurotus tuber – changes in soy sauce prepared with<br /> regium (fires) singer. LWT Food Sci Tech extrucded and traditional raw material. Food<br /> 39, 548 – 53. Research institute (31), 487- 492.<br /> Bano, Z. and Rajarathnam. S. (1982). Pleurotus Dang Hong Anh (2011). Research to perfect<br /> mushroom as nutritious food. Tropical technonology and equipment for producing<br /> <br /> <br /> <br /> 63<br /> AGU International Journal of Sciences – 2019, Vol 7 (3), 57 – 64<br /> <br /> soy sauce with microbiology. Food Nan-Wei Su, Mei-Ling Wang, Kam-Fu Kwork<br /> Technology Institute, Hanoi, Viet Nam. & Min-Hsiung Lee (2005). Effects of<br /> Hernandez, D., J.E. Sanchez and K. Yamasaki temperature and sodium cloride<br /> (2003). A simple procedure for preparing concentration on the activities of proteases<br /> substrate for Pleurotus ostreatus cultivation. and amylases in soy sauce koji. Journal of<br /> Bioresource Technology 90: 145-150. Agriculture and Food chemistry (53),<br /> pp:1521-1525.<br /> Jian Chen & Yang Zhu (2013). Solid state<br /> fermentation for food and beverages. Ngo Anh Tuan (2006). Theoretical color and<br /> Jiangnan University, China. application. Ho Chi Minh National<br /> University Publishing House.<br /> Kalmis E, Nuri A, Hasan Y, Fatin K. (2008).<br /> Feasibility of using olive mill effluent Nguyen Duc Luong (2006). Traditional<br /> (OME) as a wetting agent during the fermented foods (3). Ho Chi Minh National<br /> cultivation of oyster mushroom, Pleurotus University Publishing House.<br /> ostreatus on wheat straw. Bioresour Nguyen Thi Ngoc Giang and Nguyen Minh<br /> Technology 99:164-169. Thuy (2016). Production of enzyme by<br /> Le Ngoc Tu (2002). Industrial biochemistry. Aspergillus Oryzae on Oyster mushroom<br /> Hanoi Science and Technology Publishing koji as affected by treatment conditions and<br /> House. wheat flour supplement. Science Journal of<br /> Can Tho University (1), pp: 147-155.<br /> Le Thanh Mai, Nguyen Thi Hien, Pham Thu<br /> Thuy, Nguyen Thanh Hang and Le Thi Lan Nguyen Thi Ngoc Giang and Tran Van Khai<br /> Chi (2005). Methods of fermentation (2018). The effect of pH, mold and<br /> technology analysis. Hanoi Science and incubation temperature on Oyster mushroom<br /> Technology Publishing House. koji in soy sauce production. Journal of<br /> Science and Technology of An Giang<br /> Le Van Viet Man and Tran Thi Anh Tuyet<br /> Province (1), pp: 32-34.<br /> (2006). Characterization of protease from<br /> Aspergillus oryzae surface culture and Perrin D.D. (1974). Buffers for pH and metal<br /> application in fish sauce processing. Journal ion control. John Curtin school of medical<br /> of Science and Technology Development (9), reseach, Australian National University, pp<br /> pp: 53 - 58. 94 – 108.<br /> <br /> Le Xuan Tham (2010). Oyster mushrooms Shieh YSC, Beuchat LR, Worthington RE &<br /> Pleurotus spp.. Scientific and technical Phillips RD (1982). Physical and chemical<br /> publishing House. changes in fermented peanut and soybean<br /> pastes containing koji prepared using<br /> Miyagi Atsushi (2012). Research on purchase<br /> Aspergillus oryzae and Rhizopus<br /> consciousness and color preference of<br /> oilgosporous. Journal of Food Science (47):<br /> Japanese soy sauce among general<br /> 523-529.<br /> consumers in Chiba prefecture. Journal<br /> Intergr. Stud. Diet. Hab. (22), 320-324. Yokotsuka T. (1986). Soy sauce biochemistry.<br /> Advances in Food Research (30), 195-329.<br /> <br /> <br /> <br /> <br /> 64<br />