Did you find the soy sauce kept at your home spoiled? You made sure that it is kept in the desired storage conditions but still found the soy sauce without it's characteristic flavor. Have a look at this presentation to know the reason behind the spoilage of Soy Sauce & the various microbiological aspects responsible for the spoilage.

1. SOY SAUCE
MOKSHA CHIB
13FET1003

2. Introduction
 Soy sauce is a light brown to black liquid with a meaty-like, salty flavor
produced from soybeans with/without wheat by means of fermentation.
 It is a condiment made from a fermented paste of boiled soybeans,
roasted grain, brine, and Aspergillus oryzae or Aspergillus sojae molds.
 It is the chief savory seasoning agent in Oriental cookery, but it is becoming
increasingly popular in many other regions of the world.
 Chemical reactions between the original components and the fermentation
products create the color , consistency and aroma of soy sauce.

3. Factors Affecting Microbial Growth
 The following factors contribute to the growth of microorganisms.
Intrinsic Extrinsic Implicit Processing
pH Storage
temperature
Synergism Fermentation
Water activity Relative humidity Antagonism Refining
Redox potential Composition of
atmosphere
Commensalism Pressing
Nutrient content Packaging
Antimicrobial
constituents

4. Nutrient Content
Nutrition Value per 100 ml
Calories 60 kcal
Fat 0.1 g
Carbohydrates 5.57 g
Fiber 0.8 g
Protein 10.51 g
Sodium 6 g
Soy sauce contains:
Amino acids 25% (glutamic acid being the predominant.)
Carbohydrates 13% (glucose, arabinose, maltose, xylose & galactose.)
Polyalcohols 5% (glycerol, mannitol.)
Organic acids 3% (lactic, acetic, succinic, citric, formic, pyroglutamic acids.)
Soy sauce contains 1.5-1.65%
of Nitrogen.
40-50% of nitrogen is present in
amino acids,
Balance is contained in
peptides & peptones.

5. Intrinsic Factors
1. WATER ACTIVITY:
The aw of soy sauce is 0.803 at 25⁰C. Even though it contains 65% w/w of
water, the high salt content binds large amount of water in the product
reducing the free moisture content available for the microorganisms to
grow.
This amount of water activity will not suffice the growth of maximum microbes.
Still, many microbes can grow in deficit amount of water.
2. pH:
Generally, the pH ranges from 4.5-5.5 depending on different commercial
brands. Due to its slightly acidic nature, it is commonly used in alkaline
foods for e.g. in Chinese foods.
This slightly acidic pH favours growth of many microorganisms & hence
measures should be taken to arrest it.

6. …Intrinsic Factors
3 . Salt content:
The salt content of soy sauce is 14-18%. The fact that it does not feel as salty
as all that is because constituents such as amino acids and lactic acid
buffer the salty taste.
Salt content also protects the finished sauce from spoilage as it creates
osmotic pressure inside the cell which leaches out water from the cell and
leaves the organism dormant or lifeless, hence unable to reproduce.
4 . Sugar content:
The sugar content is 6% in soy sauce. The sweetness is due to glucose which
is produced by fermentation of starch in wheat.
Salts & sugars act as antimicrobial agents in soy sauce.
5. Ethanol: A little amount of ethanol is contained in soy sauce that reduces
the growth of various microorganisms.

7. Extrinsic Factors
 Storage Conditions:
If soy sauce is stored in warm temperatures, it may lead to growth of
microflora inside it, if the packaging is not efficient & not enough measures are
taken to eliminate the microorganisms from soy sauce. Also, cleanliness of
storage containers will affect the shelf life.
 Storage Atmosphere:
A sufficient amount of oxygen will promote the growth of microorganisms
as well as oxidation of components of soy sauce such as lipids or certain sugars.
Also higher relative humidity will increase the heat as well as the number of
organisms around the packaged product.

8. Implicit Factors
 Synergism:
Coagulase negative Staphylococcus spp. is one of major contaminant of
koji produced soy sauce. These microbes grow symbiotically with
the koji molds & their combination makes a problem when fermented
below 25°C.
 Antagonism:
B. Subtillis grows in competition with the koji molds at higher temperatures.
This will affect the quality of final soy sauce.

9. Spoilage during Processing
 Most of the microflora in the sauce is eliminated during heat treatments.
 Contaminations may persist after processing due to unhygienic use of
processing implements.
 During fermentation of soybeans, only selected strains of Asp. Oryzae or
Asp. Sojae are used as fungal starters. So the risk of other contaminants is
greatly reduced.
 During processing, brine is used after fermentation which inhibits the growth
of most microorganisms excluding the halotolerant lactobacillus & yeasts
such as Ped. Halophilus, which can survive high concentrations of salts.
 When raw soy sauce is stored after separation by a hydraulic press from the
mash, white dry pellicles are formed on the surface which are caused by
the growth of film forming yeast such as Zygosaccharide salsus &
Zygosaccharide japonicus.

10. Microbes involved in Spoilage &
Principles
 The major microorganisms which are responsible for spoilage of soy sauce
include:
1. Salt tolerant(halo-tolerant) Lactobacillus grow in soy sauce & will produce
biogenic amines such as tyramine & histamine. Some of these bacteria will
also produce ornithine by decomposing arginine resulting in accumulation
of citrulline as an intermediate. Ethyl carbamate can be produced by
reaction between ethanol and citrulline. This all leads to degradation of soy
sauce.
2. A salt tolerant yeast Z. rouxii var. Halomembranis can grow in soy sauce,
which is harmless to health but forms a membranous film on the surface of
soy sauce causing deterioration of the soy sauce aroma & flavour.

11. Microbes involved in Spoilage &
Principles
 Fermented shoyu is found to have bactericidal activity for some
enteropathogenic bacteria including S.typhi-shikata, Shigella flexnerii &
vibrio-cholerae-inaba. But all of these can be eliminated during later
stages of processing i.e. Pasteurisation.
 The mycotoxins produced during fermentation have no ill-effects on health.
Asp.oryzae & Asp.soyae will not produce any aflatoxins.
 Mycotoxins such as cyclopiazonic acid, kojic acid, beta nitropropionic acid
or aspergillic acid are harmful & may be present in traditionally prepared
soy sauces.

12. Preservation methods.
 My preservation method would emphasise on good pasteurization
processes.
 A well pasteurized soy sauce will contain no effective contaminations, and
hence will extend its shelf life.
 After fermentation, the raw soy sauce contains the lactobacillus as well as
molds which need to be removed from final product. Also, contaminations
present in raw materials, or from the processing instruments, or from the
strains of the cultures used, have to be necessarily eliminated, otherwise, it
will harm human health as well as spoil the sauce too quickly.
 After pasteurization, the main microbial control factor is the high salt
content.
 In addition to these, use of little amounts of preservatives like sodium
benzoate(GRAS) can be incorporated at concentration of 0.5%.

13. Packaging Perspective
 A packaging system should be designed to provide optimal efficiency in
storage, economy, etc. It should make product more stable & protect it
from microbial attack.
 Shelf life is shortened when oxygen, carbon dioxide, water vapour, odours
and flavours move out of packages or into them due to which quality is lost.
Hence, permeability of the material is a very important factor that should
be considered for packaging.
 A very advisable system for packing soy sauce is in a good quality
food-grade glass or a High Density Polyethylene polymer plastic bottles
that are air-tight which will protect from outer atmosphere and also counter
the escape of components from inside the bottles.

14. Packaging
 The next step to be considered is the composition of atmosphere inside the
bottles.
 My packaging system will incorporate a Modified Atmosphere
Packaging(MAP), that would be suitable for a long term storage without
addition of preservatives.
 In some packaging systems, no head space is left during packaging so as
to eliminate oxygen from the system to inhibit growth of organisms.
 But absence of oxygen will lead to anaerobic microbial growth, which will
cause off odours & flavours. This can be pathogenic and even fatal in case
of clostridium botulinum which produces botulinum toxin in absence of
oxygen.
 A modified atmosphere suggesting elevated levels of carbon dioxide and
lowered oxygen levels (most commonly both oxygen & carbon dioxide at
5% )

15. Storage & Transportation
 Storage Conditions:
It should be stored in dark and cool place in order to prevent any oxidation
after it is opened. Such storage prevents the growth of yeast. It is advisable
to refrigerate it even though it is stable at room temperatures. Before it is
open, it is not prone to any spoilage. But gradually the color darkens &
flavor fades.
 Transportation:
The packaged bottles should be kept in a carton which is cushioned with
material like bubble wrap during transporting.
This would prevent bumping of bottles into each other and hence will
arrest the leakage which would in turn cause microbial growth as well as
harm to other packaged bottles.
This helps in minimising the transportation losses.

16. THANK YOU !