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AROMA AND FLAVOR OF JAPANESE SOY SAUCE
BY TAMOTGU YOKOTSUKA No& Institute for Scientific Re.rcnrch, atld Research ltlstitirtc of
Noda Soy Sauce Company. Lfd., Nocla.shf. Chfba.ken. Japan
Page I . Introduction . . . . . . . . . . . . . 75 I1 . Composition . . . . . . . . . . . . . 77
A . Analysis . . . . . . . . . . . . . 77 B . Nitrogen-containing Compounds . . . . . . . . 78 C . Carbohydrates. Sugar. Alcohols. and Extractive . . . . . 82 D . Acids. Salts. and Related Compounds . . . . . . . &3 E . Color . . . . . . . . . . . . . . 87
I11 . Chemical Components of Flavor . . . . . . . . . 87 A . Fraction I . . . . . . . . . . . . . 96 B . Fraction I1 (b.p. < 78C.) . . . . . . . . . 97 C . Fraction I11 (b.p. >78C.) . . . . . . . . . 99 D . Fraction IV (The Aretal Fraction) . . . . . . . g9 E . Fraction VI . . . . . . . . . . . . 1 0
IV . Sources of Aroma and Flavor Development . . . . . . 104 A . Raw Materials . . . . . . . . . . . . 104 B.Processing . . . . . . . . . . . . . loFl C . Koji . . . . . . . . . . . . . . 108 D . Mash (Moromi) . . . . . . . . . . . 111 E . Pasteurization . . . . . . . . . . . . 115
V . Flavor Ingredients as Natural Preservatives . . . . . . 119 A . Natural Yeast-static and Bactericidal Compounds . . . . . 119 B . Artificial Preservatives for Soy Sauce . . . . . . . 121
VI . Summary . . . . . . . . . . . . . 121 Acknowledgments . . . . . . . . . . . . 123 References . . . . . . . . . . . . . 123
I . INTRODUCTION The four major characteristics of Japanese soy sauce. which differs
from other types produced in the Orient. are aroma. flavor. color. and stability . About 60 years ago. certain chemical procedures were intro- duced into the Japanese soy sauce industry. and since then the fermen- tation period has been shorter . Although these chemical procedures have come into general use. the basic method of manufacture is almost unchanged .
76 T A M OTSU Y OKOTSU K A
Oiir ancestors knew tlici tcwhnicliies of enzymatically hydrolyzing cer- tain protein foods into amino acids to make them more appealing. For example, since ancient times the people in the Orient have enriched the flavor of fish and meiit by fermenting it in the presence of high salt concentrations. These foods, formerly cidled fish soy or merely SOY, can still be seen today in nuoc-mam in Java, or shottsuru in Japan, and itre believed to be antecedents of the soy sniice now in use. Years ago several kinds of pulses and corn were used as raw materials; now, however, only soybeans and wheat are used.
The mold Aspergillrts soyne is the source of the proteolytic enzymes. The first soy sauce produced was cnlled soy, sho, or mislio, and was very different from soy sauce produced today. It resembled the present day miso ( Ilitrtl mitsh ) or moromi (miish ) and W B S consumed without further treatment. During the Muromachi period ( 1~28-1573), much research was done on the kinds and relative quantities of raw materials and on the fermentative process, with the result that the product was improved considerably.
Today three types of soy sauce are available in Japan: koikuchi, usukuchi, and tamari. About 90% of the Japanese soy sauce produc- tion is of the koikiichi type. In China, most of the soy sauces belong to the tamari type; that is, thcy are made of soybeans or with a greater amount of soybeans than wheat. High-quality Japanese fermented soy sauce is made from equitl amounts of soybeans and wheat. The product consists not only of amino acids, but also of many flavor inpedients derived from the alcoholic fermentation which is part of the manufac- turing process. Wheat bran also plays an importiint role in the develop- ment of flavor and aroma.
Chemical studies begitn to supplement sensory methods during the period from 1867 to 1912. In addition, autoclaves and hydraulic presses came into iise in its manufacture. At that time, the soy mash was usually fermented at ambient temperatures for 1 to 3 years. Next various lots of sauce (which had been fermented for different periods) were blended and sold. Several attempts were made to shorten the long fermentation period and hence lower the cost of production. Thus, dur- ing the last decade there hits been a growing tendency to make soy siiiice by acid hydrolysis, in order to increase the yield and reduce pro- duction time. A chemical method, announced by the Noda Soy Sauce Co., Ltd. (1955), is now being commonly used by soy sauce manu- factiircrs. Even where the fermentation method is still used, soybean Iiydrolyzates are added to the fermented soy sauce as a flavor booster.
The flavor siibstanccs of true Jiipancse soy saiice produced by the traditional fermentation method will be discussed in this review,
AROMA AND FLAVOR OF JAPANESE SOY SAUCE 77
A. ANALYSIS Most of the Japanese soy sauces are the koikuchi type, containing
5@% or more of i\ chemical hydrolyzatc of defatted soybeans. Only a few of the large manufacturers produce the bestquality product, which requires aging for more than a year. Good-quality fermented soy sauce contains 1.5 g. of total nitrogen, and 18 g. of sodium chloride per 100 ml., and appropriate proper amounts of amino acids, sugar, alcohol, glycerin, and organic acids. It should have a high buffer capacity, stability, and good aroma, flavor, and color. Typical composition of koikuchi soy sauce samples is shown in Table I and of a high-quality
TABLE I COMPOSITION OF KOIKUCHI SOY SAIJCI?'
Specific Year and gravity Sodium Total Amino Total Alcohol
grade BC Extract" chlorideb nitrogenh nitrogcnb Sugarb acidsb (% vol. )
1937 23.84 20.50 18.46 1.52 0.65 5.19 0.63 1.63 1949 19.10 7.16 17.70 0.73 0.39 0.79 0.30 0.41 1957
Grade A 22.75 18.15 18.50 1.49 0.79 4A5 0.90 2.00 1957
Grade B 22.38 16.19 18.25 1.28 0.68 3.02 0.86 0.88
From Nuda Soy Sauce Company, 1,iniitcd ( 1958). Data cxprcsscd a'i g./lM nil.
fermented soy SilUCe in Table 11. The composition of tamari and usukuclii soy swces is shown in Tables I11 and IV.
Sodium chloride in soy sauce is usunlly determined by titration with silver nitrate, using potassium chromate as nn indicator. Accurate re-
TABLE 11 COMPOSITION OF A TYPICAL HIGH-QLMLITY FERMENTED SOY SAUCE"
Specific gravity, B6 24.00 Extract, g./100 ml. Total nitrogen, g./lOO ml. 1.51 Protein nitrogen. g./100 ml. Amino nitrogen, g./lOO ml. 0.70 Reducing sugar, g.1100 ml. Dextrin, g./lOO ml. 1.06 Viscosity Total acid as lactic, g./lOO ml. Alcohol, % 2.00 Glycerin, g./lOO ml. Inorganic substances, % 19.70 Sodium chloride, g./lOo ml. PH 4.02
0.48 Volatile arid, g./lOO ml.
From No& Soy Snwe Company, Limitrd (1957).
38.13 0.09 5.99 3.50 0.17 1.00
78 TAMOTSU YOKOTSUKA
specific gravity Sodium Total ( n o chlorideb nitrogen* Extracth
Sample 1 25.90 16.43 2.86 31.78 Sample 2 23.45 19.29 1.80 19.42
From Noda Soy Sauce Company, Limited ( 1957). b Data expressed as g./lOO ml.
sults are obtainable only when the sample is first ashed; otherwise, cer- tain corrections are necessary, depending on the nature of the sample. Sato (1955) proposed the use of bromophenol blue as an indioator for
TABLE IV cOhfPOSI1 ION OF LrSUKUCIXI SOY SAW
AROMA AND FLAVOR OF JAPANESE SOY SAUCE 79
These investigators reported also that almost 9& of the total nitrogen was easily converted by the ordinary Kjeldahl method, in which only cuproiis srilfate was used as the catalyst; however, the remaining 2% was very resistant to digestion. They attributed this resistance to the nitrogen-containing phenolic fraction, which increases when soy saiice is heated. Since the quality of a soy sauce may be relnted to its total nitro- gen content, this observation is important. Accordingly, faster and more accurate methods of analysis are needed.
The nitrogen compounds consist of about 40 to 50% amino acids, 10 to 15% ammonia, 40 to !50% peptides and peptones, and less than 1% proteins. Takada (1934) stated that 45% subpeptone and peptone, but no protein or metaprotein are present. Tsunoda and Ishizuka (1952) also claimed the absence of protein on the basis that no precipitate was obtained with sodium tungstate or trichloroacetic acid. These workers are believed to have studied commercially pasteurized soy sauce in which the proteins would have been precipitated by heat.
Sakasai and Yokotsuka (1957) divided the total nitrogen of unheated soy sauce into: ( 1) tannin-coagulatable, ( 2) phosphomolybdate-pre- cipitable, and (3) residual nitrogen. The quantity of each fraction was 0.2 to 1.5%, 45.9 to 46.88, and 52.6 to 53.3%, respectively. The ammonia content was 8.8 to 11.2%, the difference between formol nitrogen and ammonia nitrogen was 34.1 to 43.11, and the free glutamic nitrogen was 3.8 to 4.9% of the total nitrogen. These ratios varied depending on the extent to which the raw materials had been cooked.
The ratio of amino nitrogen to total nitrogen has been considered as a criterion for judging quality, with a high ratio indicating high quality. Usiially the amino nitrogen content has been reported to be 50 to 6oR, of the total; however, the imperfect formol titration method that has been used has caused erroneous results because of the ammonia present. Moreover, because of the intense color of soy sauce, it is difficult to obtain a sharp end point by formol titration. Ohara and Moriguchi (1954) tried to determine formol nitrogen by electrometric titration at pH 8.0 without adjusting the pH of the sample. Sakasai and Yokotsuka (1957) also reported a method of determining the formol nitrogen in soy sauce by electrometric titration; the ammonia nitrogen con- tent was d