2. 1. Introduction
Ketchup is defined as the concentrated product prepared from the liquid extracted from
sound, ripe, red or reddish tomatoes, and seasoned with characterizing ingredients such as
pepper, onions, vinegar and sweeteners in quantities that materially alter the flavour, aroma
and taste of the tomato component.1
The making of tomato ketchup consists essentially in
reducing tomatoes to pulp, removing the skins, seeds, hard parts and stems, adding salt,
sugar, condiments, and vinegar to suit the taste, and cooking to a proper consistency.2
2. Composition
The main ingredients of ketchup have been described in Table 2.1, in decreasing order of
predominance by weight in the finished food. Tomato Ketchup is a homogeneous condiment
sauce obtained from clean, sound, ripe tomatoes (Lycopersicum esculentum), along with
added vinegar, sugars, salt and aromatic ingredients and their extracts such as onions, spices
and the allowed additives. The tomato solid content should be over 12%.
INGREDIENTS
Water
Sugar
Tomato solids (Tomato paste (22.5%))
Salt
Vinegar/Acetic acid (0.8%)
Starch
Sodium benzoate (<0.1%)
Onion Powder, Garlic Powder
Spices and Condiments
Table 2.1: Typical ingredients found in a
ketchup manufactured by an Indian brand3
3. 3. Factors affecting Spoilage
Ketchup is a chemically complex matrix, and contains sufficient nutrients to support
microbial growth. Several factors encourage, prevent, or limit the growth of microorganisms
in foods. Table 3.1 lists and classifies these factors as as Intrinsic, Extrinsic, Implicit and
Processing factors.
Intrinsic Extrinsic Implicit Processing
o pH
o Water Activity
o Redox Potential
o Nutrient Content
o Antimicrobial
Constituents
o Temperature of
storage
o Relative humidity
o Presence and
concentration of
gases
o Synergism
o Antagonism
o Washing
o Pasteurization
o Packaging
Table 3.1: Factors affecting spoilage of ketchup
4. Intrinsic Factors
4.1 pH
Tomatoes inherently contain citric acid as the predominant acid and malic acid in low
concentration. Traces of acetic and lactic acid may also be present. The pH of tomatoes lies
within the range of 3.9 to 4.9.4
Ketchup contains approximately 20% natural tomato soluble
solids by weight. Consequently, pH of ketchup is normally between 3.89 and 3.92.The
microorganisms responsible for spoilage of ketchup are hence predominantly acidophiles.
Lower pH prevents bacterial growth. From Table 4.1, it is evident that spoilage is mainly
caused by yeasts, molds and lactic acid bacteria.
Minimum Optimum Maximum
Most Bacteria
Yeasts
Molds
4.5
1.5 - 3.5
1.5 - 3.5
6.5 - 7.5
4.0 - 6.5
4.5 - 6.8
9.0
4.0 - 6.5
8.0 - 11.0
Table 4.1: pH ranges of different microbial groups5
4. 4.2 Water Activity (aw)
Tomato is a ‘High Water Content Vegetable’, as 94% to 95% weight of tomato is water.
High sugar, salt and dry matter content in ketchup results in a reduction in water activity
levels to 0.93. The water activity requirement is greater for bacteria, as compared to yeasts
and molds, as evident from Table 4.2. In general, if a food has a water activity lower than
0.85, it is considered to be non-hazardous. Table 4.3 lists the microorganisms predominant
in the water activity range of ketchup.
Microbial group Minimum aw Examples
Most bacteria 0.91 Salmonella spp., Clostridium botulinum
Most yeasts 0.88 Torulopsis spp.
Most molds 0.80 Aspergillus flavus
Halophilic bacteria 0.75 Wallemia sebi
Xerophilic molds 0.65 Aspergillus echinulatas
Osmophilic yeasts 0.60 Saccharomyces bisporus
Table 4.2: Minimum water activity values of spoilage microorganisms5
Water activity (aw) Microorganisms growing at this water activity and above
0.95 – 0.91 Salmonella, Vibrio parahemolyticus, Clostridium botulinum,
Serratia, Lactobacillus, Pediociccus; some molds and yeasts
Table 4.3: Susceptibility to Spoilage based on aw
5
4.3 Redox Potential
Redox potential represents the sum of all compounds present that influence onidation-
reduction reactions. It also affects the solubility of nutrients, especially mineral ions.
Ketchup has an Eh of roughly around +400 mV.6
Antioxidants are also known as redox-
active compounds. Tomato contains lycopene. Processed foods like ketchup are a better
source of bioavailable lycopene than fresh tomatoes.7
Plant pigments are sensitive to redox
potential, and changes affect the colour. Strictly aerobic microorganisms can grow only in
positive Eh values. Redox potential is also influenced by the amount of undissociated acetic
acid present in ketchup.
5. 4.4 Nutrient Content
Ketchup is a chemically complex matrix, and contains sufficient nutrients to support
microbial growth, such as carbohydrates, minerals, vitamins and lycopene. Sugar or high-
fructose corn syrup form a major part (20% - 30%) of the total solids. Starch may also be
added to give the required consistency. Fruits tend to be lower in B vitamins than meats;
hence spoilage can be caused by molds, as they can synthesize most of their requirements.
Table 4.4 enlists the nutritional information of a standard ketchup finished product.
NUTRITIONAL INFORMATION (per 100 g)
Water (65 g)
Protein (traces)
Carbohydrates (33 g) – added Sugar (27 g)
Fat (0.5 g)
Minerals – Sodium (1070 mg)
Vitamin C (15 mg)
Lycopene (17 mg)
Table 4.4 Nutritional Information of Ketchup
4.5 Antimicrobial Constituents
Tomato inherently contains citric acid as the predominant acid, malic acid in low
concentrations, and traces of acetic and lactic acids may also be present. Ketchup also
contains spices like cinnamon (cinnamic aldehyde), cloves (eugenol), cayenne and garlic
(allicin) which contain naturally occurring substances possessing antimicrobial activity. 6
Ketchup preserved with benzoic acid or sorbic acid (< 0.1%). The amount of vinegar added
to ketchup typically results in 0.8% to 1% of acetic acid in the product.
5. Extrinsic Factors
5.1 Temperature of Storage
Ketchup is refrigerated after opening, which extends the shelf life. When stored at ambient
temperatures, mesophiles and certain thermophiles like Bacillus, Clostridium may grow.
Pantry Refrigerator
Ketchup, opened 1 month 8 – 12 months
Ketchup, unopened 1 year --
Table 4.5: Shelf life of ketchup at ambient and low temperature storage8
6. 5.2 Relative Humidity of the environment
Relative humidity and water activity are interrelated. When ketchup is stored in
environment of high humidity, water will transfer from the gas phase to the food and thus
increasing the aW , leading to spoilage by the viable flora. Foods that undergo surface
spoilage from molds, yeasts, and some bacteria should be stored in conditions of low
relative humidity to increase their shelf life. Ketchup, if not refrigerated, should be stored in
closed, air tight containers. Variations in storage temperature should be minimal to avoid
surface condensation.
5.3 Presence and Concentration of Gases
Oxygen is one of the most important gases which come in contact with food influence the
redox potential. Ketchup is oxygen-sensitive and should be stored in air-tight containers.
Packaging materials such as Ethylene vinyl alcohol (EVOH) are used, which possess gas
barrier properties.
The inhibitory effect of CO2 on the growth of microorganisms is applied in modified
atmosphere packaging of foods. With regards to the effect of CO2 on microorganisms,
molds and gram-negative bacteria are the most sensitive, while the gram-positive bacteria,
particularly the lactobacilli tend to be more resistant.
6. Implicit Factors
6.1 Synergism
When the pH of a food is 4.6 or below, spores of Clostridium botulinum will not germinate
and grow. When critical factors are not carefully controlled, the vegetative cells of some
microorganisms of non-health significance, such as some spoilage bacteria, yeasts, and
molds, can grow in an acid environment and, in so doing, cause the pH of the food to
increase. Bacillus coagulans strain could raise the pH to over 5.0 under aerobic conditions.
In addition, when critical factors are not properly controlled, spoilage microorganisms such
as Bacillus licheniformis produce heat-resistant, acid-tolerant spores that can germinate,
grow, and cause the pH to increase. Thermal processing may not be sufficient to destroy
their spores. 9
7. 6.2 Antagonism
Antagonism is the inhibition of growth of one species of microorganism by another, when
one organism adversely affects the environment of the other, or the interaction between two
or more chemical substances that reduces the effect that each substance has individually.
6.2.1 Combination of acid and osmolytes
The combination of acid and osmolytes (salts, sugars) is a common application of ‘hurdle
technology’. However, under certain conditions, osmolytes appear to protect Escherichia
coli and Salmonella enteric against acetic acid inactivation due to cell envelope changes that
accompany exposure to combined acetic acid and osmotic stress.10
6.2.2 Secondary metabolites produced by Lactic acid bacteria
Secondary metabolites produced by lactic acid bacteria have antagonistic activity. This
includes the compound reuterin and the antibiotic reuterocyclin, produced by strains of
Lactobacillus reuter. Reuterin has a broad spectrum of activity and inhibits fungi, protozoa
and a wide range of bacteria including both gram-positive and gram-negative bacteria.
Reuterocyclin, the antibiotic produced by lactic acid bacteria, has a spectrum of inhibition
confined to gram-positive bacteria including Lactobacillus spp., Bacillus subtilis, Bacillus
cereus, Enterococcus faecalis, Staphylococcus aureus and Listeria innocua.11
6.2.3 Inhibitory Effect of CO2 produced by Lactic acid bacteria
Certain lactic acid bacteria like Lactobacillus fructivoras hydrolyze sucrose products to
produce carbon dioxide. C. pasteurianum also produces carbon dioxide. CO2 has an
inhibitory effect. Molds and Gram-negative bacteria are the most sensitive, while the gram-
positive bacteria, particularly the lactobacilli are tend to be more resistant.12
7. Processing Factors
Tomatoes are harvested, washed, graded, chopped, precooked in kettles, pulped and filtered,
heated to boiling. The ingredients are added and it is cooked again for 30 to 45 minutes,
passed through a finishing machine to remove fibre, deaerated, hot filled into containers at
over 700
C, cooled rapidly to prevent breakdown, stored and shipped.
8. The initial microflora of ketchup depends largely on the raw materials used; hence the
tomatoes should be washed thoroughly. Hot-filling into bottles usually eliminates
contamination from raw materials or the manufacturing process, thus ketchup is free of
vegetative spoilage organisms.
On a vastly large scale, the lack of adequate cleaning and sanitation procedures for
processing equipment can lead to product contamination during packaging and subsequent
spoilage for most types of acidified speciality products.
8. Spoilage Principle
Since the pH is less than 4.0, spoilage microbes are usually restricted to non-spore forming
bacteria like lactic acid bacteria, yeasts (Saccharomyces spp., Candida spp.) or molds
(Byssochlamus fulva).13
Bacillus coagulans can also cause spoilage at pH 3.8 - 4.0, but
growth is inhibited even by low concentrations of acetic acid. 4
Heterofermentative
lactobacilli cause gas formation in ketchup. Due to absence of liquid egg and dairy
ingredients in ketchup, there is no direct association of pathogens. Spices may introduce
Salmonella, but these are killed by the cooking process or inactivated by acetic acid.
9. Spoilage Microorganisms
9.1 Lactobacilli
Ketchup is often sensitive to spoilage by lactobacilli; L. brevis, L. mannitopeum, and L.
plantarum as spoilage organisms identified in studies of tomato ketchup. The lactobacilli are
controlled by cooking and hot filling at temperatures above 700
C. In products filled at lower
temperatures, lactobacilli are the predominant spoilage organisms. Lactobacilli can be
present in spoiled products in the form of large white spots or as small, hard, white dots,
which may easily be mistaken for undissolved ingredients or clumps of starch. The
lactobacilli can grow with or without gas formation. In the former case, swelling of plastic
containers will be seen. Lactobacillus brevis commonly causes fermentation of tomato
ketchup.14
Other lactobacilli and leuconostocs occasionally cause spoilage of ketchup. These
lactic acid bacteria produce gas as well as acid from the sugar so that spoilage is
accompanied by can distension; other end products include acetic acid and ethyl alcohol so
that with these diverse products such as lactic acid bacteria are termed 'heterofermentative'.
Lactobacilli are also known to grow under conditions of vacuum and modified atmosphere.
9. 9.2 Yeasts and Molds
Yeasts are extremely heat-sensitive and therefore rarely cause spoilage. Zygosaccharomyces
bailii and Pichia membranaefaciens, can both multiply in the presence of 3% acetic acid,
but require the presence of oxygen, therefore spoilage only occurs at the surface. Other
species found are Zygosaccharomyces rouxii, Saccharomyces cerevisiae and Candida
magnolia.14
Ketchup containing 0.8% acetic acid can be spoiled by Saccharomyces spp. as
these are resistant to acetic acid due to an inducible energy-requiring transport system that
removes acetic acid ions from the cells.15
Yeasts may cause spoilage by gas formation or by
growing as brownish colonies, which appear as small oil-like droplets. Explosion of glass
bottles with ketchup is a hazard. Fungal spoilage may be characterised by highly visible,
often pigmented growth, slime, fermentation of sugars to form acid, gas or alcohol, off-
odours and off-flavours. Molds, like yeasts, rarely cause spoilage, but two notable
exceptions are Byssochlamys fulva and B. nivea , the ascospores of which are unusually
heat-resistant tolerating 85o
C for 30 minutes.
10. Hurdles to the growth of microorganisms
Acidity provided from tomatoes and added vinegar (pH 3.9)
Multiple boiling steps
Concentration and lowering aw value from added salt and sugars
Pasteurization, hot filling and cooling of bottles
Refrigeration after opening
Newer processing techniques – UV treatment (1–5 MHz), Irradiation (1 – 10 kGy)
11. Alternative Packaging Techniques
11.1 Trends in the Existing Packaging Techniques
The past few years have witnessed an extension from packing ketchup in glass bottles to
squeezable co-extruded multi-layer plastic bottles with oxygen barrier material (EVOH) for
shelf life of 12-18 months. Recently launched stand up pouches for tomato ketchup are eye-
catching, economic alternatives to PET bottles for consumers. Heinz has recently launched
"Dip and Squeeze” packets which are far less messy than the traditional sachets. Figure 11.1
illustrates some of the newer trends in the packaging of ketchup. MIT has also created
superhydrophobic coating for condiment bottles, called LiquiGlide, which is FDA approved
and does not let ketchup stick to the surface of bottles.16
10. Fig 11.1 Newer trends in the packaging of ketchup
11.2 Proposed Alternatives
A proposed alternative is the replacement of the existing retort sachets that need to be torn
or cut to be opened, with zip-lock pouches, as shown in Fig 11.2, to minimize exposure to
the atmosphere after being opened. This idea for packaging of ketchup is derived from the
packaging of toothpaste, since their viscosity is comparable.
Fig 11.2 Replacement of retort sachets to be cut, with Zip-lock pouches
11.3 Use of AIP Technologies
The combined use of active packaging and intelligent packaging systems (AIP
technologies), where active packaging describes mainly food packaging that interacts
chemically or biologically with its contents or head space to extend shelf-life. Oxygen
scavengers, such as reduced iron-based or ascorbic acid-based oxygen scavenger sachets can
be incorporated into the core layers of polyester in ketchup bottles or sachets. Antimicrobial
agents may also be incorporated into packaging materials. A glass bottle of tomato ketchup
with a self-assembly Time-Temeprature Indicator (TTI) closure will inform the consumer of
the freshness status of product and remind the consumer to keep this product in the fridge
for longer shelf life. In TTI, the observable colour change correlates with the negative
influence of the microbiological process. 17
11. References
1) Kenya Standard, Tomato products - Specification, Part 3: Sauce and Ketchup, KEBS, 39,
3, 2005
2) Bitting. A. W., Experiments on the Spoilage of Tomato Ketchup
3) Kissan Fresh Tomato Kethcup, 1 kg pack, Hindustan Unilever Limited
4) Gould W. A., Tomato production, processing and technology, Third edition, 1992
5) Dilbaghi N., Sharma S., Food and Industrial Microbiology, 2007
6) Adams M.R., Moss M.O., Food Microbiology, Third Edition
7) Ramesh C. Ray, Aly F. El Sheikha, Smita H. Panda and Didier Montet, Anti-oxidant
properties and other functional attributes of tomato: An overview, Intl. Jrnl. of Food and
Fermentation Tech, 1, 2, 2011
8) www.shelflifeadvice.com/condiments-herbs-spices-spreads/condiments/ketchup-and-
mustard
9) Rees J.A.G., Bettison J., Processing and Packaging Heat Preserved Foods
10) Belinda Chapman, Osmolyte protection of Escherichia coli and Salmonella enterica
against inactivation by acetic acid
11) Rattanachaikunsopon P., Phumkhachorn P., Lactic acid bacteria: their antimicrobial
compounds and their uses in food production, Annals of Biological Research, 1, 4, 2010
12) Ray Bibek, Bhunia Arun, Fundamental Food Microbiology, Fifth Edition
13) Bjorkroth K. J., Korkeala H.J., Lactobacillus fructivorans Spoilage of Tomato Ketchup,
Jrnl of Food Protection, 60, 5, 1997
14) Hayes P.R., Hayes Richard, Food Microbiology and Hygiene, Second Edition
15) Doyle M.P., Sperbe W.H., Compendium of the Microbiological Spoilage of Foods and
Beverages
16) www.liquiglide.com
17) Satish H.S., Emerging Technologies in Packaging, CommodityIndia.com
