Basics of Fertilizers

There are several properties of fertilizers that a user should know. One important property is water solubility. Nearly all N fertilizers are completely water soluble. Because of their high water solubility, granule size and band placement are generally not important.

The two most common forms of N in fertilizers are ammonium (NH4+) and nitrate (NO3). Under conditions of good plant growth, NH4+ is rapidly converted to NO3by bacteria. Both forms can be taken up and utilized by plants. However, crops such as tobacco, potatoes and tomatoes prefer nitrate as their source of N. Because nitrate is much more mobile than ammonium, ammonium forms of N are recommended when the application is made prior to the time of greatest need. This practice minimizes potential loss by leaching.

Most phosphate fertilizers are highly water soluble. Phosphate water solubility is very important for early plant growth. Thus, it is important for banded starter fertilizers to contain highly soluble forms of P (less than 2 ppm in soil solution) but concentrations as high as 100,000 ppm have been measured in the fertilizer band. During cool and wet conditions when plant growth is slow and the root system is shallow, band placement of P fertilizers becomes extremely important.

Broadcast applications usually contact less than 2% of the total soil volume. Consequently, water solubility is of little importance where P fertilizers are broadcast.

Phosphorus availability in the band is generally improved by the addition of N to the P starter and by increasing the granule size. Large granules contact less soil per unit of P than small granules. Thus, initial P fixation is lower, and availability is improved.

Most potassium fertilizers are highly water soluble. Like NH4+, K+ is held in the soil by clay and organic matter. Unlike NH4+, however, K is not converted to a more mobile form. Potassium stays relatively close to the initial point of application. Leaching of K is not generally a problem, except on very sandy or gravelly soils, due to insufficient cation exchange bonds are much weaker. Because K is not subject to the same fixation reactions as P, water solubility is not considered important. Banding K is only important where soil tests for K are extremely low.

The following is a discussion of several of the more commonly used fertilizers. Table 1 contains the chemical analysis of these and other fertilizer materials.

Nitrogen Fertilizers

Anhydrous ammonia (82%N) is a liquid under high pressure and must be injected at least six inches deep into a moist soil because it becomes a gas once it is released from the tank. In soil, ammonia reacts with water to form the ammonium (NH4+) ion, which is held on clay and organic matter. Anhydrous ammonia is generally the cheapest source of N; however, the method of application is less convenient and requires more power to apply than most other liquid or dry materials.

Nitrogen solutions (28 to 32% N) are a mixture of urea and ammonium nitrate in water. The solution has no ammonia vapor pressure and is generally sprayed or dribbled on the soil surface. Under certain conditions, N loss due to ammonia volatilization may be serious. If the conversion of urea to ammonia in the liquid fertilizer takes place on the surface, some ammonia can be lost by volatilization. The remainder of the ammonia may react with water on the surface to produce an alkaline condition, which also promotes volatile ammonia loss.

The most favorable conditions for volatile N loss from surface-applied urea (solid or liquid) are alkaline soils, warm temperatures, intermediate relative humidity (50 to 90%) and sandy soils with low organic matter content and low cation exchange capacities.

One-inch of rain will normally move surface applied N solutions deep enough into the soil to prevent ammonia volatilization. Nitrogen solutions should not be applied in the fall, because one-fourth of the N is in nitrate form and is subject to loss by leaching or denitrification.

Surface application of N solutions to heavy residues, which occur in no-till systems, has been shown to reduce its effectiveness when compared to N that is incorporated or knifed-in. Nitrogen can be temporarily tied up in residues and unavailable to the crop until the residues decompose.

Aqua ammonia (21% N) is a liquid under low pressure and must be incorporated into the soil to prevent the loss of free ammonia to the atmosphere. It is possible to lose all of the free ammonia if it is not incorporated. Aqua ammonia has advantages over anhydrous ammonia: placement need not be as deep, and high-pressure applicators are not required.

Urea (46% N) is the most widely used dry N fertilizer. Once applied to the soil, urea is converted to ammonia which reacts with water to form ammonium within two to three days (faster under warm conditions). Some volatilization of ammonia can occur when urea is surface applied. However, avoid topdressing of urea under hot climate because of the potential for greater ammonia losses.

Ammonium nitrate (33% N) is decreasing in popularity because of storage problems associated with fire and explosive hazards. It is an excellent material for many purposes; however, one-half of the N is in nitrate form, which makes it immediately susceptible to potential leaching and denitrification losses after application. Calcium ammonium nitrate is a mixture of ammonium nitrate and crushed limestone.

Ammonium sulfate (21% N) availability has increased in recent years primarily because it is a byproduct of some industries. All of the N is in the ammonium form. It is a good material for high pH soils (pH>7.0) and can be used where sulfur deficiency is suspected. If applied to alkaline or calcium soils, it should also be incorporated to eliminate potential ammonia volatilization losses. It has the disadvantage of being the most acidifying form of N fertilizer which requires more limestone to neutralize the acidity formed by the N fertilizer. The cost of ammonium sulfate is usually greater than urea because of its lower analysis and higher transportation costs.

Calcium nitrate (16% N) contains all of its N in the nitrate form, which is highly susceptible to leaching and denitrification losses as soon as it is applied. It is used most extensively in the fruit and vegetable industry where a readily available source of nitrate N may be desirable. It is also used as a soluble source of calcium.

Potassium nitrate (13% N) is used as both a K source and a N source. All of the N is in the nitrate form and is subject to leaching and denitrification as soon as it is added to soil. It is used primarily in the fruit and vegetable industry as readily available sources of N and K.

Sodium nitrate (16% N) contains all of its N in the nitrate form and is similar to potassium nitrate and calcium nitrate in its reaction in soils. It is used primarily in the vegetable industry when a readily available source of nitrate N is desired.

Phosphate Fertilizers

Rock phosphate has virtually disappeared from the market because of its very low water solubility and high transportation costs. Rock phosphate may, however, supply sufficient P for good crop growth where soils are moderately acid and where decomposing organic matter is abundant. Application of 1,000 to 2,000 pounds per acre may be necessary for good plant growth if soil test levels for P are low. On fields with high soil tests for P, broadcasting rock phosphate to replace crop removal may be acceptable, but rock phosphate is not acceptable for a starter fertilizer because of its low water solubility. Today, rock phosphate is generally processed before it is used as a fertilizer.

Normal superphosphate (20% P205), also referred to as ordinary superphosphate, is no longer used in large quantities. Because of its lower analysis and high transportation costs, it has been replaced by concentrated superphosphate (46% P2O5) and the ammonium phosphates. One of the advantages of normal superphosphate was its significant sulfur content. As consumption of this material has slowly decreased, concerns over the need for sulfur have come primarily from the fertilizer industry. Currently, sulfur from the atmosphere is keeping pace with crop removal.

Concentrated superphosphate (46% P2O5), also known as triple superphosphate, is being used in direct application as well as in granulated processes and in bulk blending with other materials. Consumption has decreased in recent years due to the competitiveness of diammonium phosphate (18-46-0) and monammonium phosphate (11-48-0). These materials have better storage properties and are more desirable for bulk blending, particularly where N is required in the final product.

Diammonium phosphate (18-46-0) is a dry material being used extensively for bulk blending and for direct application where soils do not need K or where K is broadcast. It has the advantage of being highly water soluble, having a high analysis and often a price advantage. Diammonium phosphate has an acid effect upon the soil similar to anhydrous ammonia. Because of the high ammonia content, this material can cause germination injury if used in direct contact with the seed.

Monoammonium phosphate (11-48-0) is a dry material being used for bulk blending or direct applications. Monoammonium phosphate has a lower ammonia content and may be less injurious to germinating seeds than diammonium phosphate. The general agronomic effects of diammonium and monoammonium phosphates are equal for most soils.

Polyphosphates differ slightly from the more common orthophosphate fertilizers. Nearly all of the liquid fertilizers containing P are of the polyphosphate type. Polyphosphates are composed of a series of orthophosphate molecules connected by the process of dehydration (removal of water). Commercial ammonium polyphosphates are usually a mixture of ortho- and polyphosphate. With prolonged storage, polyphosphates will hydrolyze to orthophosphates. Solutions of ammonium polyphosphate most commonly made are 10-34-0 and 11-37-0. The most common dry polyphosphate is 13-52-0.

In the soil, polyphosphate converts to orthophosphate by hydrolysis (adding on water). The time required for hydrolysis to occur varies with soil conditions. In come cases, 50% of the polyphosphate hydrolizes to orthophosphate within two weeks. Under cool, dry conditions, hydrolysis may take longer.

Some claims have been that polyphosphates will make certain unavailable micronutrients in the soil more available for plant uptake. Due to the rather rapid conversion of polyphosphates to orthophosphates in the soil, it is not likely that such complexes would be available for any significant length of time. The efficiency of polyphosphates is considered to be equal to, but not better than, the orthophosphates with more than 80 percent water solubility.

Potassium Fertilizers

Potassium Chloride (60 to 62% K2O), also referred to as muriate of potash, is one of the major source of K used. Nearly two-thirds is used for direct application, and the remainder is used in granulating processes or bulk blending of mixed fertilizers. It is available in four particle sizes: fine, standard, coarse and granular. The fine-size material is used primarily for liquid suspensions. Standard, coarse and granular sizes are used for granulating processes, bulk blending and direct application. Potash varies in color from pink or red to white depending on the mining and recovery process used. White potash, sometimes referred to as soluble potash, is usually higher in analysis and is used primarily for making liquid starter fertilizers.

Potassium sulfate (50% K2O), also referred to as sulfate of potash, is used to a limited extent on crops such as tobacco, potatoes and a few vegetable crops where chloride from potassium chloride might be undesirable. Potassium sulfate in some research studies has improved specific gravity of potato tubers. Potassium sulfate may also be source of sulfur when sulfur is required.

Potassium magnesium sulfate (22% K2O), also known as sulfate of potash magnesia, is used for both direct application and in bulk blending, particularly where magnesium is needed. If may also be used as a source of sulfur.

Potassium hydroxide, also known as caustic potash, is used to a limited extent in the production of liquid mixed fertilizers. The present cost of producing potassium hydroxide has limited its use in the fertilizer industry, even though it is a very desirable product due to high solubility and low salt index.

Potassium nitrate (44% K2O), also known as nitrate of potash, is being used primarily on high value crops such as celery, tomatoes, potatoes, leafy vegetables and a few fruit crops. It has a low salt index and provides nitrate N which may be desirable for these specialty crops. Production costs have limited general use for most agronomic field crops.

Table 1—Primary and Secondary Nutrient Composition of Some Selected Fertilizer Materials1
Fertilizer Materials Percent Nutrient composition
Nitrogen N N P2O5 K2O Ca Mg S
Ammonia, anhydrous 100 82
Ammonia, aqua 100 16-25
Ammonium nitrate 100 33.5
Ammonium nitrate-limestone 100 20.5 7.3 4.4
Ammonium sulfate 100 21 23.7
Ammonium sulfate-nitrate 100 26 15.1
Calcium cyanamide 100 21 38.5
Calcium nitrate 100 15 19.4 1.5
Nitrogen solutions 100 21-49
Sodium nitrate 100 16
Sulfur-coated urea Variable 35 21
Urea 100 46
Ureaform Variable 38
Phosphate P
Ammoniated super-phosphate 35 03-Jun 18-20 17.2 12
Ammoniated phosphate nitrate 100 27 15
Ammonium phosphate sulfate 90+ 13-16 20-39 15.4
Ammonium polyphosphate 100 Oct-15 34-62
Bone meal 2-4.5 22-28 20-25
Diammonium polyphosphate 95+ 16-21 48-53
Monoammonium phosphate 90+ 11 48 1.1 2.2
Nitric phosphates 40 14-22 Oct-22 08-Oct 1-3.6
Phosphoric acid 100 52-60
Rock phosphate <1 30-36*
Superphosphate, normal 85 18-20 20.4 11.9
Superphosphate, concentrated 87 42-50 13.6 1.4
Superphosphoric acid 100 69-75
Potash K
Nitrate of soda-potash 100 15 14
Potassium chloride (muriate) 100 60-62
Potassium magnesium sulfate 100 22 11 22.7
Potassium nitrate 100 13 44
Potassium sulfate 100 50 1.2 17.6
*Relatively unavailable to plants in most soils1From Fertilizer Handbook, The Fertilizer Institute

Reference : N-P-K FERTILIZERS. M.L. Vitosh, Extension Specialist, Crop & Soil Science,Agricultural Extension Bulletin, Michigan State University Extension.

Fertilizer Calculations for Greenhouse Crops


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Dragon Fruits – Fertilization Recommendations

Fertilization Regimen

Dragon Fruit requires judicious application of fertilizer for better yields. The recommendations for fertilizer rates varies considerably. However, it is generally found that the crop requires frequent fertilization at the early stage of growth. The recommended fertilization application in Taiwan is 4kg of organic manure per pillar every 4 months, supplemented with 100g per plant of NPK 13:13:1. In Hawaiian plantations, NPK 16:16:16 is applied at 180 – 230g per pillar every 4 – 6 months. Calcium and micronutrients are also applied to enhance fruit growth and firmness. Low nitrogen fertilizers mixtures of NPK 0:10:10 & 2:10:10 has also been recommended for Dragon Fruits.

In Vietnam, young (less than 3 years old) plants are fertilized with 10 – 15kg of farmyard manure and 100 g of super phosphate/plant at the time of planting. During the first two years, 300 g of urea and 200 g of NPK (16:16:8) is applied to each plant every year. The fertilizer is applied in three lots, at one month, six months and twelve months after planting, respectively (Ke, 1997). According to Tri et al (2000), mature plants (at least three years old) should be fertilized 4 times a year as follows :

No. Stage Type of fertilizer Application rate per pillar
1 Immediately after harvest N




216 g


2 Two months later N






3 Just before flowering N






4 When young fruits are developing N






For BINH THUAN Dragon Fruit, the fertilization regimen is as follows :

Stage Type of Fertilizers Application Rate per pillar Frequency
Year 1 NPK 20:20:15 50g Once a month
Year 2 onwards NPK 20:20:15




Once a month
Flower bud generating stage (about 25 days) Fertilizers for spraying on foliage e.g. GA3, Antonics NA Spray on the 7th, 14th & 21st day after flower buds appear
Bearing fruits stage (about 30 days) Fertilizers for spraying on foliage e.g. GA3, Antonics NA Spray on the 3rd and 14th day after flowering

The fertilization regimen reportedly practiced by some farmers in Vietnam  is as follows :

Stage Type of fertilizer Application rate per pillar Application Frequency
Year 1 Urea

Super Phosphate



Every 4 months
Fruit bearing stage Urea

Super Phosphate


Organic Fertilizer





Every 4 months
During fruits development Micro elements e.g. foliar fertilizer Once a week
10 days before harvest No fertilizer to be applied

The fertilization practice recommended by the Malaysian Department of Agriculture is as follows:

Stage Type of Fertilizer Application Rate per pillar Application Frequency
Young plant (Up to 6 mth) NPK 15:15:15 100g 2 months once
Young plant (7 mths and above) NPK 15:15:15 200g 2 months once
Fruit bearing stage NPK 13:13:21 300g Alternate 1 month fertilization for fruiting and 1 month fertilization for growth
After fruiting NPK 15:15:15 300g Alternate 1 month fertilization for fruiting and 1 month fertilization for growth

The fertilization practice recommended by Department of Agriculture Sarawak is as follows:

Stage Type of fertilizer Application Rate per pillar Application Frequency
Initial (after planting) Rock Phosphate







Note : Apply fertilizers at the root, body, branches before planting

Year 1 NPK 15:15:15 0.1kg Once every 2 months
Start flowering NPK 12:12:17.2+TE 0.1kg Once every 2 months
Year 2 and above NPK 12:12:17.2+TE

Organic fertilizer



Once every 2 months

Once every 4 months

References :

Ke, N.V. (1997). Dragon fruit. Agriculture Publisher, Ho Chi Minh City, Vietnam

Tri. T.M., Hong, B.T.M. and Chau, N.M. (2000). Effect of N, P and K on yield and quality of Dragon fruit. Annual Report of Fruits Research, 2000, Southern Fruit Research Institute. Agriculture Publisher, Ho Chi Minh City, Vietnam.

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Foodborne Listeria Monocytogenes in Seafood – Preventive Controls

Listeriosis, caused by Listeria monocytogenes, is a significant public-health concern as a result of its clinical severity and high mortality. Large foodborne outbreaks of listeriosis have occurred during the last two decades in Europe and the United States. L. monocytogenes has been associated with a wide variety of food especially seafood and poultry. As such it is highlyimportant that seafood manufacturers establish effective Listeria control plans in their factories.

Elements of a Complete Listeria Control Plan

  1. Sanitation and GMPs
  2. Training of Plant Personnel
  3. Plant Environmental Monitoring/Testing
  4. Raw Material Controls
  5. MinimizeGrowth in Finished Product

Various biocides and sanitation methods have been tried by the industry. Some of the sanitation methods currently being used include:

  • Liming – this is a cost effective method and is being used to treat raw whole Atlantic salmon. The salmon is soaked prior to raw processing. Chlorine dioxide is frequently used as a dip after liming and before splitting.
  • Sodium hypochlorite – this is added to the processwater and used on raw headed and gutted fish and raw fillets. This is the one of the most cost effective method.
  • Nisin-containing ingredientsystem (maltodextrin, cultured dextrose, sodium diacetate, egg white lysozyme, and nisin). This however, is a rather costly method.
  • Sodium/potassium lactate/sodium diacetate – these were tested on cold smoked salmon at brine/cure step. However, the treatment leaves a strong flavor giving a negative effect on the seafood quality
  • Citro bio – this has been tested oncold smoked fillets. Applied prior to drying and after fat line removal.
  • Lactobacillus extract spray – this proprietary chemicalhas also been tried
  • Lime or Ozone – washing raw headed andgutted fish in lime or with ozone. Somewhat effective.
  • Acidified Sodium Chlorite or Chlorine Dioxide – these has been used to wash headed and gutted fish prior to splitting. This is normally used as a fish wash dip after the liming process and before splitting the fish.

Acidified sodium chlorite solution is an FDA approved secondary direct food additives permitted in food for human consumption (21CFR173.325). The additive is allowed to be used as a single application in processing facilities as an antimicrobial agent to reduce pathogenic bacteria due to cross-contamination during the harvesting, handling, heading, evisceration, butchering, storing, holding, packing, or packaging of finfish and crustaceans; or following the filleting of finfish. The solution may be applied as a dip or spray. It is used at levels that result in a sodium chlorite concentration of 1,200 ppm, in combination with any GRAS acid at levels sufficient to achieve a pH of 2.3 to 2.9. Treated seafood shall be cooked prior to consumption.

Equipment Focussed in Sanitation Programme

  1. Slicers – Spray with chlorine dioxide at the end of the workshift. If environmental sampling shows any bacterial counts on equipment orproduct contact surfaces, the equipment is dismantled and heated at 300 F for 35min in the smoke oven. Larger pieces of equipment are shrouded andsteamed.
  2. Skinner
  3. Splitting machines
  4. Smoking racks
  5. Floor stress mats – soak inchlorine dioxide at 150 ppm without drying
  6. Drains and drain coverings – some manufacturers use iodine blocks in the drains and pluggingthe drains and soaking them with 200 ppm chlorine
  7. Tubs
  8. Food contact areas that involve complex equipment and parts that are not alwaysconstructed with sanitary parts, e.g., use of rubber or other absorbentmaterials that can be difficult or impossible to sanitize.
  9. Cart wheels, doors, smoke racks, pallet jacks, etc. – some manufacturers practice spraying these with chlorine dioxide solution during processing

Plant Environmental Monitoring

The frequency of conducting microbiological testing varies between the variousseafood manufacturing facilities. The frequency can range from 2 times per weekto 2 times per year, depending on the rate/size of operation, the level ofcontamination usually detected, the amount of historical data available, the effectiveness of the sanitation programme in place, etc. Some facilities even engage third party to verify routinely.

Minimize Growth in Finished Product

All seafood manufacturers have testing programmes in place for their finished product. However, the frequency of testing varies, ranging from every batch to 4 times per week to 4 times per year where some even engage third party testing routinely.

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Ready-to-eat Food – Prevention of Microbial Contamination at Home

The potential for microbial contamination from raw meat and poultry to ready-to-eat (RTE) fruit and vegetables at home is well recognised. It is important that all steps are taken during food storage and preparation to prevent such contamination from taking place. This includes ensuring that food handlers properly wash their hands before and after handling raw meat and poultry. Raw and RTE foods should be stored completely separated and the handler should decontaminate utensils like knifes, cutters, food processors and cutting boards between use (or have dedicated utensils and cutting boards for raw and RTE foods).

How to avoid cross-contamination in RTE fresh fruits or vegetables at home?

Tips that can help to prevent cross-contamination and minimize hazards to our food:

Good Practices During Shopping

  • Separate raw meat, poultry and seafood from RTE fresh fruits and vegetables in the shopping cart.
  • Keep the RTE fresh fruits or vegetables in different shopping bags to prevent the juices from the raw food from contaminating the RTE food.

Good Practices In Storage

  • Store raw food segregated from fresh fruits and vegetables.
  • Place packages containing raw meat, poultry or seafood in plates before refrigerating. Where possible, place raw meats that has potential to drip juices, at the bottom shelf of the refrigerator so that the juices would not drip onto other food. Do not use the same plate that is used to hold raw meat, poultry or fish to place cooked food unless thoroughly washed.
  • Store fresh fruits and vegetables in clean plastic bags when not in use.
  • Keep fresh fruits and vegetables covered and elevated from the floor during storage and handling.
  • Place food that is likely to spill in a suitable covered tray or container and place it in the lower part of the refrigerator.

Good Practices In Food Preparation

Caution : Pay attention to personal hygiene during food preparation.

  • Keep hands clean by washing hands thoroughly with soap including fingertips before, during and after food preparation, and when changing tasks.
  • It is essential that jewellery worn on hands and fingers such as rings be removed before handling fresh fruits and vegetables as they may harbour pathogenic microorganisms.
  • Avoid touching your face, skin and hair or wiping your hands on cleaning cloth.
  • Cover any open wounds or cuts with waterproof bandages before preparing food.
  • Avoid preparing food for others if you are sick or has a skin infection.
  • Use separate utensils for preparing raw food and fresh fruits or vegetables, unless you thoroughly wash them prior to using them for RTE food.
  • Use different serving plates for raw food and fresh fruits or vegetables.
  • Ideally, use separate cutting boards and knives for cutting raw meat/seafood products and for cutting fruits and vegetables. Alternatively, wash cutting boards thoroughly between usage of raw food and RTE food. Replace cutting boards that become excessively worn out or which has developed difficult-to-clean grooves.

Wash and sanitize all equipment and utensils that came into contact with food with water and detergent between tasks and handling raw and RTE food. Some people prefer to use chemical sanitizers such as the common household bleach (like Clorox) or the more environmental friendly stabilized chlorine dioxide solutions (like Klorsafe-H).

  • After preparing raw food in a food processor, clean the equipment components thoroughly.
  • Keep all work surfaces clean between each task to remove all food residues, crumbs or spillage that serve as potential reservoir of bacteria.
  • Discard food that has dropped on the floor or the work table.
  • Regularly change, wash and sanitize cloths used for wiping tables or equipment. Do not use cloths for cleaning dirty areas to clean anything that may come into contact with food.
  • Do not recycle used food packaging and paper bags for storage of food.

Good Practices In Serving Food

  • Always use a clean plate.
  • Never place cooked food on cutting board or a plate that wa previously used to hold raw meat, seafood or poultry.
  • Wash fresh fruits and vegetables thoroughly to remove soil prior to serving. Trim any bruised areas before eating to reduce the risk of consuming harmful pathogenic microorganisms which may be present in the food (there are no effective means of removing pathogens from cuts and bruises on fruits and vegetables (whether physically or chemically) unless you thoroughly cook them.

Good Practices In Storage of Leftovers

  • Refrigerate or freeze leftovers within two hours in clean, covered containers to prevent harmful bacteria from multiplying.
  • When in doubt, discard the leftovers. Don’t take the risk.


Avoiding Cross-Contamination, Agri-Food & Veterinary Authority of Singapore.

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Fresh Produce – Prevention of Microbial Contamination

Most people believe that if fruit and vegetables were properly washed, then there is little health risk. It is a common believe that freshness of fruit and vegetables could be easily detected via look, smell, texture, colour, best before date on packaging and many deduced that one would be unlikely to eat a fruit or vegetable if it has gone “bad”. Most consumers are not aware of the risks of Salmonella, E.coli, etc. when it came to the fruit and vegetables category. These risks are normally linked with poultry and meat products only.

There are many points during production of fruits and vegetables at which microbiological contamination can occur. These include:

  • Growing (seeds, soil, water, manure, insects, animals)
  • Harvesting (faeces, handling, equipment, transport)
  • Post-harvest handling (washing, packing, vehicles, cross-contamination)

Fruit and vegetables (also termed ‘fresh produce’) are increasingly being recognised as an emerging vehicle for foodborne illness in humans. Traditionally meat, milk and egg products were the ‘usual suspects’. The consumption of fresh produce has now been linked, both epidemiologically and microbiologically to infectious intestinal disease.

Fresh produce foods typically have fewer barriers to microbial growth such as preservatives; therefore, simple errors can make the food unsafe. Cross-contamination is understandably a major contributing factor in outbreaks involving fresh produce as these foods are usually eaten raw.

Pathogens transmitted via fruit and vegetables


  • Aeromonas
  • Bacillus cereus
  • Campylobacter
  • Clostridium botulinum
  • Clostridium perfringens
  • Escherichia coli O157
  • Listeria monocytogenes
  • Salmonella
  • Shigella
  • Staphylococcus aureus
  • Vibrio cholerae


  • Hepatitis A
  • Norovirus


  • Cryptosporidium parvum
  • Cyclospora cayetanesis
  • Giardia

Preventing Microbial Contamination along the Food Chain

There are a number of sources of contamination, all of which must be controlled in order to prevent or minimise microbial contamination of fresh produce. The key areas where microbial contamination can occur are in the field;during harvesting and processing; and in the home.

All efforts should be taken to harvest fresh produce that is of the highest microbiological quality possible. Preventing cross-contamination during harvesting can be achieved via thorough cleaning and decontamination of equipment, containers and transport vehicles. An effective decontamination stage is essential prior to packaging to help reduce the level of pathogenic and spoilage organisms in Ready-to-Eat produce.

Strategies used to control harmful bacteria:

  1. organic acid rinse: lactic, acetic & propionic
  2. ozonation
  3. chlorinated water wash
  4. hydrogen peroxide
  5. combinations of acid and hydrogen peroxide (peroxyacetic acid)‏
  6. acidified sodium chlorite (ASC)
  7. storage temperature after anti-microbial treatment

How effective are the decontamination strategies?

One study conducted in 2003 tested 13 disinfectants on strawberries. Of all the products tested, sodium chlorite acidified with citric acid (ASC) was the most effective. (Food Protection Trends, November 2003, pp. 882 – 886).

Acidified Sodium Chlorite (ASC) solutions is approved by FDA (21CFR173.325 (e)) to be used as an antimicrobial agent on raw agricultural commodities in the preparing, packing, or holding of the food for commercial purposes. It may be applied as a dip or a spray. Treatment of the raw agricultural commodities with acidified sodium chlorite solutions shall be followed by a potable water rinse, or by blanching, cooking, or canning.

Acidified Sodium Chlorite (ASC) solutions is also approved by FDA (21CFR173.325 (g)) to be used as an antimicrobial agent in the water applied to processed fruits and processed root, tuber, bulb, legume, fruiting (i.e., eggplant, groundcherry, pepino, pepper, tomatillo, and tomato), and cucurbit vegetables as a component of a spray or dip solution, provided that such application be followed by a potable water rinse and a 24-hour holding period prior to consumption. However, for processed leafy vegetables (i.e., vegetables other than root, tuber, bulb, legume, fruiting, and cucurbit vegetables) and vegetables in the Brassica [Cole] family, application must be by dip treatment only, and must be preceded by a potable water rinse and followed by a potable water rinse and a 24-hour holding period prior to consumption.

However, heating remains the most effective technique used to control pathogenic microbial growth. Heating of all fruits and vegetables is not possible due to the negative effects on some products. However, it is possible to use heat on some products. In one study, hot water treatment of Cantaloupe with 158 deg. F. water was able to achieve a 2-log reduction of Salmonella and treatment with 206 deg. F. water achieved 3.4-log reduction of Salmonella (Journal of Food Protection, Vol. 67, No. 3, 2004, pp. 432-437).

New technologies are continuously being explored to reduce foodborne pathogens in fresh produce. These include:

  • High pressure processing
  • Dense phase carbon dioxide processing
  • Ultra-violet irradiation processing
  • Electron-beam irradiation processing


Consumer Focused Review of the Fruit and Vegetable Food Chain, February 2007 (Safefood)

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Klorsafe500 – Disinfectant for Swine Industry

Klorsafe500 is a Broad Spectrum Oxidising Biocide disinfectant. Safe and effective use in husbandry industry for disinfection of equipment, barns and environment, and also deodorization of animal droplets. It is biodegradable, making it an environment friendly sanitizer.

Klorsafe500 is a two parts chemical system, when reacted producing a strong oxidant chlorous compound. The biocide system is approved by FDA and EPA as a safe sanitizer. It is extensively used in various industries such as food processing plant, animal farms, disinfecting meat and poultry, controlling odour, washing fruit and vegetables, as well as, treating municipal water.

It is more powerful as an oxidizing biocide than chlorine and chlorine-type disinfectants. Klorsafe500 is effective against a wide range of microorganisms including coliform, salmonella, listeria, E. coli and viruses.

Klorsafe500 Applications in Swine Industry

The importance of drinking water quality for the production and performance of pigs is often overlooked. Pigs consume 4 to 6 times as much water as feed. Sows consume as much as 10 gallons of water per day. Without an adequate supply of good quality water, pig growth and reproduction may suffer.

Water can be a source of contamination if the microbiological load in the water is too high. This can affect digestion and absorption of nutrients from the feed, as well as additives like medications, vaccines and vitamins. Health problems caused by drinking contaminated water include diarrhea, salmonella, listeria, transmissible gastroenteritis, pneumonia, typhoid, cholera and hepatitis.

Routine drinking water additives, like vaccines and vitamins contribute to a polysaccharide layer (known as slime) inside the drinking lines. Waterborne bacteria flourish within this layer and are difficult to kill as they are encased within the slime. Unlike Klorsafe500, most water treatments and disinfectants, including chlorine, cannot penetrate and eliminate the slime.

Weaning pensWeaning pens 2

Prevention and control of disease in livestock husbandry can make a tremendous difference to overall performance of young stock.

Scours (diarrhea) is often a problem with baby pigs. Sanitation is extremely important to reduce the incidence of piglet scours. The use of untreated water in open water troughs may lead to the introduction of pathogens coming from the water supplies and faecal contamination.

The temperature and humidity of bedded pens,  will create a breeding ground for bacteria. Reacted Klorsafe500 can be effectively applied in these areas to remove this bacterial contamination.

Bedding straw sanitation is achieved using Klorsafe500 to reduce challenge as a result of reduced surface bacteria contamination.

Farrowing SowsFarrowing sows 3

Farrow crate sanitation is an important part of any good livestock husbandry bio-security programme. Klorsafe500 can be applied to provide excellent sanitation without causing distress to stock.

Where & when to use Klorsafe500

  • Well water and drinking water treatment
  • Potable water treatment with excellent slime control
  • Disinfectant in boots bathsDisinfect Farm Equipment
  • Facilities sanitation: walls, floors, ceiling, equipment, fogging
  • Disinfect footwear of workers and visitors before entering and on leaving animal housing area
  • Disinfect trucks for transportation of pigs

Klorsafe500 Application

Use site

Method of application

Application rate


Disinfection of swine pens Use commercial sprayer to saturate all surfaces 300-500 ppm Remove all animals and feed. Thoroughly clean all surfaces before spraying.
Control for odour and slime forming bacteria Use commercial sprayer to saturate all surfaces 1000 ppm Thoroughly clean all surfaces
Swine drinking water Add to water 5 ppm
To deodorize swin holding rooms, sick rooms, morgues and work rooms Spray on surfaces 200-500ppm Clean surfaces and rinse with water
Disinfection of equipment, footwear and vehicles. Spray on surfaces 200-500ppm Clean surfaces and rinse with water before applying disinfectant.

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Klorsafe – Chemistry & Mode of Action

Klorsafe contains Acidified Sodium Chlorite (ASC) which is approved by the FDA (21 CFR 173.325) as a ‘secondary direct food additive permitted in food for human consumption’ specifically as an antimicrobial intervention treatment for poultry carcasses, poultry carcass parts, red meat carcasses, red meat parts and organs, seafood, and raw agricultural commodities.

ASC is often confused with chlorine dioxide (ClO2), also approved by the FDA (21 CFR 173.300) as a secondary direct food additive largely because solutions of ASC can, under certain conditions, generate small quantities of chlorine dioxide. However, by judicious selection of reaction parameters (nature and concentration of activating acid, chlorite concentration, catalysts, total titratable acidity) chlorine dioxide formation is typically minimized in true ASC solutions. ASC is a highly effective, broad spectrum antimicrobial, which is produced by lowering the pH of a solution of sodium chlorite into the 2.5 to 3.2 range with any GRAS acid.

ASC chemistry is principally that of chlorous acid (HClO2), which is the metastable oxychlorine species, which forms on acidification of chlorite. Once formed, chlorous acid gradually decomposes to form chlorate ion, chlorine dioxide, and chloride ion. It is hypothesized that the mode of action of ASC derives from the uncharged chlorous acid, which is able to penetrate bacterial cell walls and disrupt protein synthesis by virtue of its reaction with sulfhydryl, sulfide, and disulfide containing amino acids and nucleotides. The undissociated acid is thought to facilitate proton leakage into cells and thereby increase energy output of the cells to maintain their normal internal pH thereby also adversely affecting amino acid transport.

Reference :

Session 91, Acidified sodium chlorite – an antimicrobial intervention for the food industry, 2001 IFT Annual Meeting – New Orleans, Louisiana.

Additional reading material :


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