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Why does vacuum sealing of foods prevent spoilage from anaerobic bacteria?

Why does vacuum sealing of foods prevent spoilage from anaerobic bacteria?


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I have noted that many purchased food items in containers only require refrigeration after they have been opened, thus eliminating the vacuum seal. Air contains bacteria and fungus spores that enter the food container and if not refrigerated, the aerobic micro-organisms will proliferate, thus altering and rotting the food. The air also allows any dormant micro-organisms that survived the factory sterilization process already in the food to come back to life and proliferate.

However I do not understand why anaerobic bacteria, that don't require and cannot survive in air, do not proliferate and thrive in the vacuum sealed food containers. That plus the fact that we can leave already opened food items such as honey, jams, and peanut butter out of the refrigerator for weeks but they do not spoil.


Just adding a little bit more info taking from the answer above.

You got two types of anaerobes:

  1. Facultative anaerobe that makes ATP by aerobic respiration if oxygen is present. It can switch to fermentation or anaerobic respiration if oxygen is absent. Most common example of a food pathogen in this category: E. coli

  2. Obligate anaerobe which are killed by normal atmospheric concentrations of oxygen. Example: C. botulinum, which is mentioned in the answer above.

I am using C. botulinum as the example here because it is widely used in making HACCP (Hazard Analysis Critical Control Point) plans. These are plans with certain steps which make sure that what you're producing is proven safe for consumption.

Now, C. botulinum vegetative cells die in the presence of oxygen. The spores allow the organism to survive when there's lack of nutrients and/or oxygen levels are too high. The spores are also heat-resistant. C. botulinum cannot grow below a pH of 4.6, so acidic foods, such as most fruits, tomatoes, and pickles, can be safely processed in a water bath canner.

If the pH is above 4.6 there's usually a CCP (Critical Control Point) in the HACCP plan to make sure the product is pasteurized. For C. botulinum that is a kill step at 85°C for 5min minimum to destroy the toxin.

Another product example would be cold brew coffee. You need a certain % of dissolved O2 so that C. botulinum doesn't proliferate since cold brew coffee has a high pH (>4.6 usually).

Another problem with Reduced Oxygen Packaging (ROP), not related to anaerobic bacteria, is mold growth. To mitigate this some products might have the air present in the bag replaced with nitrogen then flushed. Nitrogen Flushes in ROP can reduce the rate at which mold can grow.

TL;DR: They do grow but there's certain steps each company needs to take to prove safety of their product before sale. If your HACCP plan accounts for C. botulinum you're sure to knock out a wide majority of obligate anaerobes (if not all) that could grow in your product.


I do not understand why anaerobic bacteria, that don't require and cannot survive in air, do not proliferate and thrive in the vacuum sealed food containers

They do. Vacuum sealing can prevent aerobic bacterial growth but does not prevent anaerobic growth.

Botulism is a particularly dangerous consequence. If food containing C. botulinum spores is sealed without being properly treated (usually by heating) or otherwise by being inhospitable to bacterial growth (often due to acidity or salt), dangerous botulinum toxin can accumulate and be dangerous or fatal when the food is later eaten.


Why Do More and More Foods Use Vacuum Packaging

Of course, the above four points are inseparable from the role of air, which is the killer of food freshness! There are various microorganisms in the air, and the food materials are exposed in the air. In order to meet the needs of their own growth, these microorganisms will continuously decompose various nutrients in the food, which will accelerate the spoilage of the food and emit peculiar smells. It will accelerate the oxidation and moisture of nutrients, which will make food taste and deteriorate.

In daily life, there are many problems such as damp snacks, deterioration of seafood, bean borers, moldy tea, and refrigerator odor. The unscientific food preservation methods not only cause waste and pollution, but also endanger health after eat.

Nowadays, we advocated food safety, hygiene, and health. The continuous improvement of food preservation technology is to keep food fresh for a longer time. In addition to the commonly used refrigerator preservation and room-temperature storage, other common methods of food preservation are nitrogen filling, vacuuming, and adding preservatives. The most convenient and effective, natural, and additive-free method is the vacuum preservation method. At present, we can see all kinds of vacuum-packed foods, from whole grains, fruits, and vegetables, dried seafood to braised snacks. Vacuum preservation has become more and more common.

We all know that food decay and deterioration are mainly caused by the breeding of microorganisms, and most microorganisms (such as molds and yeasts) need oxygen for their survival. The most important feature of vacuum packing is the ability to extract oxygen from packing bag, so that the microorganisms lose their living environment, thereby prolonging the preservation time of food.

It is understood that when the oxygen concentration in the packing bag is less than or equal to 1%, the growth and breeding speed of microorganisms will drop sharply. If the oxygen concentration is less than or equal to 0.5%, most microorganisms will stop reproducing. However, the vacuum packing machine cannot inhibit the proliferation of anaerobic bacteria and the deterioration and discoloration of food caused by enzyme reactions. It needs to be combined with other auxiliary methods, such as refrigeration, quick freezing, dehydration, high-temperature sterilization, irradiation sterilization, microwave sterilization, and marinated. These combinations of food processing can make the food fresher and store longer.

In addition to the above-mentioned inhibiting the growth and reproduction of microorganisms, vacuum preservation has another important function to prevent food oxidation. Fatty foods contain a large amount of unsaturated fatty acids, which are easily oxidized by oxygen, so it can make food off-flavor and deteriorate. The oxidation can also cause the loss of vitamin A and vitamin C, and the unstable substances in food pigments will also be affected by oxygen to darken the color. Therefore, vacuum packing can effectively prevent food from discoloration and deterioration, and maintain its color, aroma, taste and nutritional value.

The food is isolated from the external environment after being vacuum packing, and there is no airflow. It can also effectively prevent odor, moisture, and insects, isolate bacteria and protect food from secondary pollution.

Based on the above, we advocate using the vacuum packing to keep food fresh to isolate air bacteria, solve the problems of moisture, rot, bacteria, odor, etc., and solve the problem of food preservation in a healthy and hygienic manner. At the same time, it also reduces waste and saves money and effort for everyone.


Vacuum-packing foods locks in goodness

Whether it's a can of coffee or a jar of roasted peanuts, the sudden rush of air when you open a vacuum-packed container tells you that the contents inside should be as fresh as the day they were packed.

That's why Elaine D'sa of Athens, Ga., uses a vacuum sealer at home.

"I have found that vacuum-packing spices extends the shelf life, and prevents their pungent odors from permeating other foods," D'Sa said. She vacuum-packs many of the items in her pantry, she said, because she likes to save money by buying in bulk repackaging her purchases keeps things fresh in her small household.

"It prevents freezer burn, if not [eliminating] it completely," she said. "If you buy meat [at a warehouse store], it lets you use it more efficiently."

D'sa, a research coordinator with the National Center for Home Food Preservation at the University of Georgia, has figured out what many consumers have learned as well: The vacuum sealers touted on television infomercials and elsewhere may cost a pretty penny, but they can save a bundle of dough.

Perhaps the most widely seen is Tilia's FoodSaver line. But other companies--Pump-N-Seal, Rival, Black & Decker, Hamilton Beach, Dazey and Deni, among others--have tested the home market too. (See sidebar on the one we liked best.)

Essentially, the machines do at home what food manufacturers do on their processing lines. By removing excess air (hence, oxygen) from a container, spoilage of the food inside is radically slowed. Vacuum-packed foods stay crisper, retain nutrients and last longer on the shelf or in the refrigerator. Meats and poultry that are vacuum-packed before freezing don't get freezer-burn, prolonging their useful life.

"You can portion-pack your foods," D'sa said. "Cook once, [portion them out], vacuum-seal them, then microwave them later in the week. If you do it in a bag, you can microwave or boil in the bag."

In pantry storage, D'sa said, "the important thing is always to keep air, moisture and insects away. Vacuum packing lets you do all of that. I use it for sugar, brown sugar, flour and dry milk. It's helpful for storing foods you buy in bulk, especially if you're single."

D'sa said she has found the vacuum-sealer handy for uses beyond the kitchen. She vacuum packs ice for camping, silver to prevent tarnishing and important papers for storing.

The "take-home message" is that vacuum-packing doesn't change the storage method, D'sa said. "If you would normally keep it in the fridge, then keep it in the fridge if it's vacuum-sealed," she said.

A few words about food safety

The very thing that keeps vacuum-sealed foods fresh longer can also create the perfect environment for botulism.

Botulism, produced by Clostridium botulinum bacteria, thrives in anaerobic, or oxygen-free, environments. Because vacuum sealing removes air, it sets up anaerobic conditions.

Botulism is so toxic that just a couple of nanograms of toxin can sicken or kill. The Centers for Disease Control in Atlanta report an average of 27 cases of food-borne botulism each year (the rest of the 110 cases each year are either infant or wound botulism). Symptoms of the disease, which usually manifests itself within 36 hours, include weakness, dizziness, double vision and progressive trouble in speaking and swallowing.

That's the bad news. The good news is it's easy to prevent botulism in vacuum-sealed foods.

First, remember that vacuum-sealing doesn't replace traditional food-preservation techniques. Shelf-stable dry foods, like crackers and cereal, pose no threat. But vacuum-sealed low-acid foods like fruits, vegetables and meats should still be refrigerated or frozen.

"It's critically important to protect the temperature--keep it under 40 degrees," said Michael Doyle of the Center for Food Safety in Griffin, Ga. "We still have to use good food-handling practices, so hot foods should be hot and cold foods should be cold. Keep the food under 40 degrees, or heat it to more than 140 degrees."

To be completely safe, heat foods to 180 degrees for 10 minutes or longer to be sure all botulism bacteria are killed.

Second, never thaw frozen vacuum-sealed foods at room temperature. "As long as you keep the temperature down, you'll prevent the germination and growth of spores," said Barry Swanson, a professor of food science and nutrition at Washington State University in Pullman, Wash. "You have to store in the freezer, and thaw in the refrigerator." Swanson said to cut the vacuum-sealed bag open before thawing to let in air, which prevents botulism from growing.

Vacuum sealer also a saver

Vacuum-sealers are widely available at warehouse stores such as Sam's Club and Costco, some retail stores such as Wal-Mart and from online outlets such as Amazon.com. Prices range from $50 to $300, and most require special bags (which aren't interchangeable among brands).

We've used a Tilia FoodSaver for nearly a decade, used a Rival Seal-a-Meal in the Tribune test kitchen, and tested a Pump-N-Seal for this story.

We fell in love with the less-expensive Pump-N-Seal, distributed by Pioneering Concepts of Cottage Grove, Wis. It works like a bicycle pump in reverse, takes only a few seconds to operate and uses no electricity. At $20 for the basic set-up and video instructions (optional accessories are available), the Pump-N-Seal represents an excellent value. Plus, it doesn't require special containers.

Instead of pricey specialty bags (we priced a box of 48 Tilia FoodSaver quart bags at $20 at Target recently, about 42 cents per bag) the Pump-N-Seal works with regular zip-top bags (we priced a box of 35 Hefty quart freezer bags at $4.19, or about 12 cents apiece). The procedure is easy enough, if a tad finicky. We sealed some graham crackers in a Glad bag the vacuum was still tight 10 days later and the crackers still crisp.

Items that can be packed into jars--coffee, fruits, vegetables, herbs--can be sealed in canning jars or any clean commercial jar that has a soft ring inside the lid. After using a thumbtack to make a hole in the lid, you place a small Band-Aid-like seal, called a Tab-Chek, over the hole. A few quick strokes with the Pump-N-Seal, and the jar is airtight. Tab-Cheks, which are reusable, cost about 7 cents apiece. We sealed a half-pound of dry beans in a pint Mason jar the process took less than two minutes. More than two weeks later, the lid was still snug.

Pump-N-Seal says its vacuum saver pulls a stronger vacuum (28.9 inches of mercury, or Hg, the standard U.S. vacuum measure) than its competitors. (The closest rival, according to Pump-N-Seal, is the Tilia FoodSaver at 24.2 inches Hg.)

For more information about Pump-N-Seal, visit pump-n-seal.com or call 888-839-8911.

What is `sous vide' cooking?

Cooking sous vide (soo VEED), the French phrase for "vacuum-sealed," has been the rage for the last several years among chefs, including Chicago's Grant Achatz and Charlie Trotter. Food writer Paula Wolfert credits French chef George Pralus with inventing the process in the 1970s, and includes three sous vide recipes in her revised "The Cooking of Southwest France."

The idea is that vacuum-packing literally pulls flavors through foods, and the low temperatures allow foods to retain their nutrients and flavors. The process usually involves vacuum-sealing meat, poultry or fish, then poaching the package in water heated to a simmer, not a boil. Directions might say, as one of Wolfert's recipes does, "Seal the salmon steaks in their special packaging and drop them directly into simmering water to cook for 7 to 8 minutes."

Health inspectors hate the idea, because vacuum-packed foods can provide environments for botulism to grow. City health inspectors in New York last spring began to fine chefs using the process, even though it had not been outlawed, The New York Times has reported.

Chefs use carefully calibrated equipment to maintain consistent, even temperatures when they cook sous vide. At the moment, such equipment is not available to home cooks. Until it is, food safety experts such as Washington State University's Barry Swanson suggest that home cooks limit vacuum-sealed cookery to boiling frozen foods in the bag.

"Sous vide is an interesting thing to do, but if you don't know what you're doing, you can get in a lot of trouble," Swanson said. "Fish, meat, poultry, even soy products are just too low in pH [acids] to be safe."

`Vacuuming' to marinate foods

Vacuum-sealing advocates say that the process can make marinating foods lightning-fast. We wondered if that was true, so we tested the idea.

The Tribune's test kitchen set up the experiment. Four boneless, skinless chicken breasts were cooked on a grill pan at the same time. One was not marinated. One was marinated in 1/2 cup bottled Italian dressing in a zip-top bag overnight. One was marinated in 1/2 cup bottled Italian dressing in a zip-top bag for 30 minutes. The last one was marinated in 1/2 cup bottled Italian dressing in a Rival Seal-a-Meal Minute Marinating Canister, also for 30 minutes.

Five tasters found the most marinated flavor in the breast that had marinated overnight in the zip-top bag. Tasters said it was "pungent," had "nice flavor and best penetration," and called it "very moist," and "very, very flavorful." Comments for the vacuum-marinated breast ranged from "very moist, not very flavorful" to "no marinade flavor" to "not very tasty." Tasters said the chicken breast marinated in a zip-top bag for 30 minutes was "moist with medium flavor."


What is Vacuum Sealing and why is it Essential in Food Industry

Vacuum sealing is one of the recent technological innovations that have taken the food processing industry by storm. This sealing technique is currently considered to be one of the most beneficial ways to store or preserve any food item. Vacuum sealers are available in the market in many different varieties. However, most of them are portable or built-in. The latest machines come with highly useful functions such as air return, sealing, vacuum marinating, etc. These sealers are easy to use, and can be installed seamlessly into any modern day industrial kitchen.

From keeping our catch fresh to storing off-season fruits, vacuum sealing is the perfect solution for the preservation of precious edibles. Before discussing its benefits, it is interesting to understand why this is the most effective way to extend the shelf life of any type of food.

The Science behind Vacuum Sealing:

Many of you may not be aware of the fact that air is one of the greatest enemies for almost all types of food. Vacuum sealing is most useful for foods that need to remain moist. As a result of an airtight environment, the food can no longer come in contact and be negatively impacted by air. This preservation technique is also good for solid foods such as flour, sugar, etc. By preventing the absorption of air, it restricts the food from getting hard.

Vacuum sealing is also an effective solution to freezer burn. As the food materials are not directly in contact to the freezer’s harsh environment, the time taken to suffer the effects of burn is much longer compared to when exposed to too much air or poorly stored.

The process of vacuum sealing seals a plastic bag’s contents through vacuum. Once the food is placed in a sealable bag, the air is removed by the vacuum sealer and the item remains intact for a long time. While storing a juicy food item, it must be freezed for a few hours before it is sealed for long-term storage.

All types of compounds are prevented from permeating into the bag, thanks to the vacuum created by the sealing machine. This may include spilled liquid, oxygen, and even insects.

When it comes to long term preservation, vacuum sealing is more preferred compared to other alternatives. Techniques such as drying, salting, and canning do have specific benefits depending on the type of food stored. However, vacuum sealing is extremely useful for a large majority of items. Vacuum sealed items stored in a freezer must be thawed properly before using them.

Benefits of Vacuum Sealing:

Vacuum sealing technique is widely used in food packaging because of its several benefits.

  • Preservation: From cheese to soup to meet, vacuum sealing extends the life of many different types of food. For example, meat lasts for no longer than six months using traditional methods in the freezer. However, it is possible to store vacuum sealed meat for 2-3 years in a freezer.
  • Savings: The ability to preserve food longer allows us to reduce food spoilage and waste. Also, vacuum sealing technology allows food businesses to buy in bulk for a lower price and store them effectively.
  • Protection: Vacuum sealing protects the food from external elements such as mold and bacteria. It also helps prevent the risk of dehydration as well as freezer burns.
  • Taste: As the food items are stored in the absence of air, their moisture, texture, and flavour gets retained. The nutritional value of the food also remains intact.
  • No Additive: Many traditional preservation techniques require harsh chemicals or additives. Unlike them, however, vacuum sealing doesn’t involve the use of any harmful external element.
  • Marination: Vacuum sealing is also an excellent alternative for meat marination or adding extra flavours or spices to food. Owing to the packaging, all the moisture and delicious flavours get sealed and marinate the meat directly.

Safety Guidelines for Vacuum Sealed Food:

Vacuum sealing of Reduced Oxygen Packaging (ROP) inhibits the process of food spoilage by eliminating atmospheric oxygen and limiting the growth of fungi or aerobic bacteria by creating an anaerobic environment. It also prevents the volatile components from getting evaporated.

Mentioned below are some guidelines for proper vacuum sealing of food items.

  • All counters, utensils, and cutting boards must be clean.
  • Employees handling the vacuum sealing process must keep their hands clean.
  • As far as possible, the food should not be touched with hands.
  • Ensure proper labelling with packaging date and the type of food.
  • Please remember that a low-acid vacuum packaged food should never be heated.

At Lumix, we are dedicated to providing state-of-the-art service solutions to the Industrial food industry. If you want to know more about efficient packaging solution for you food processing unit, please contact our experts immediately.


Open your vacuum packed fish before thawing

Vacuum packed fish is an excellent way to purchase fish in the grocery store. Vacuum packaging keeps the fish from drying out by preventing water loss. Vacuum packaging, also called Reduced Oxygen Packaging (ROP) is used because it allows for an extended shelf life in the freezer by reducing off odors and texture changes which may result in spoilage. When food is vacuum packed, air is sucked out of the packaging and then the packaging is hermetically sealed. Fish packaged this way are very popular in grocery stores, it&rsquos important to handle the fish correctly.

What&rsquos the concern? Clostridium botulinum and Listeria monocytogenes are the bacteria of primary concern when thawing vacuum packed fish.

Clostridium botulinum (C. botulinum) is an anaerobic bacteria (meaning they live and grow in low oxygen conditions) that forms spores which allow it to survive in unfavorable conditions. When the right conditions are present, the spore will develop into a vegetative cell which can produce a deadly toxin. The toxin causes a life threatening disease call botulism.

In order to prevent the production of the toxin, Michigan State University Extension advises it is important to keep food such as fish that is vacuum packaged (no oxygen) at the proper temperature. C. botulinum forms toxin more rapidly at higher temperatures than at lower temperatures. As storage increase above 38 degrees Fahrenheit, the time required for toxin formation is significantly shortened. Many home refrigerators have temperatures above 38 degrees Fahrenheit. Additionally, if thawing the fish in cold water, the temperature may also be above 38 degrees Fahrenheit.

Labeling on frozen fish products in ROP packaging will state: The fish should be kept frozen until time of use and prior to the fish being thawed under refrigeration or prior to or immediately upon completion of thawing, the fish should be removed from the packaging. By opening the packaging when thawing the vacuum packaged fish, oxygen is present and the spores will not produce the vegetative cells that produce the toxin.

Listeria monocytogenes is a bacterium that can contaminate food. If present, it can cause a serious illness primarily for high risk individuals such as older adults, pregnant women, newborns and adults with weakened immune systems. Unlike many bacteria, Listeria can grow and multiply in some foods in the refrigerator. Vacuum packed fish is not commercially stable or shelf-stable and must be refrigerated. Even while thawing, it is very important to following thawing guidelines provided by the processor.

Vacuum packaged fish results in a tasty and superior product when it is prepared. It is important to follow thawing recommendations when preparing the product at home.


2 Answers 2

Airtight packaging doesn't slow down bacteria growth. There are a few myths about them which don't apply in practice:

  • Bacteria are not kept out, despite popular belief – the air within the container has as many bacteria as the air outside. The food in the container also has bacteria – cooking doesn't sterilize food! – so you cannot keep the bacteria out that way.
  • The container is still full of oxygen. You don't get the effect of lowered-oxygen atmosphere that is sometimes used in packaging from industrial food producers.

These two hold whether your food is in the fridge or not – so storing the food in an airtight container outside of the fridge doesn't change anything about its safety either. *

The one way it helps with food safety is an edge case: if you forget something until it molds or spoils, the now-high levels of pathogens won't contaminate something else, exposing it to more than the normal "background" level.

The airtight container doesn't help with food safety, but it is quite good for food quality and has other convenience aspects:

  • if you put fresh fruit or vegetables in it, or cheese, you get a nice level of humidity, and vegetables stay crisp longer/cheese and other stuff doesn't dry out
  • many foods either emit or soak up smells. The airtight container prevents it.
  • if you have a mishap and drop something in the fridge, or a fermenting bottle of something spills over, it won't land in an open bowl of something else
  • modern containers have an almost-rectangular shape, which uses up the space in the fridge very efficiently, and allows stacking.
  • modern containers, as well as humble jars, are mostly transparent – so if you store the food in them as opposed to the pot in which you prepared it, it is easier to see what is where without opening lids
  • if you prepared food in a reactive pan (or even something not-very-reactive like seasoned cast iron) and store the leftovers in it, you are giving the pan time to react with the food and corrode and/or change the taste of the food. Food storage containers are nonreactive.

So the airtight containers are best practice for quality reasons. And non-air-tight containers, which have a loosely fitting lid (no visible holes, but also no gasket, such as a stock pot or a skillet covered with a lid) will give you about 80-90% of the desired effect.

* to be pedantic, it can interfere in one way: if you intend to store hot non-shelf-stable food outside for a short time, and are afraid it will enter the danger zone, a closed lid will slow down the time it cools down. But I suppose not many people keep a wireless temperature probe in their airtight container, so the point is quite moot in practice.


Spoilage of Canned Foods (With Diagram) | Microbiology

If a canned food contains viable micro-organisms capable of growing in the product at ambient temperatures, then it will spoil. Organisms may be present as a result of an inadequate heat process, under processing, or of post process contamination through container leakage. Spoilage by a single spore former is often diagnostic of under processing since rarely would such a failure be so severe that vegetative organisms would survive.

A normal sound can will either be under vacuum with slightly concave ends or have flat ends in those cases where the container is brimful. Spoilage often manifests itself through microbial gas production which causes the ends to distend and a number of different terms are used to describe the extent to which this has occurred (Table 4.6).

The spore-forming anaerobes Clostridium can be either predominantly proteolytic or saccharolytic but both activities are normally accompanied by gas production causing the can to swell. Cans may sometimes swell as a result of chemical action. Defects in the protective lacquer on the inside of the can may allow the contents to attack the metal releasing hydrogen. These hydrogen swells can often be distinguished from microbiological spoilage since the appearance of swelling occurs after long periods of storage and the rate at which the can swells is usually very slow.

In cases where microbial growth occurs without gas production, spoilage will only be apparent once the pack has been opened. Bacillus species, with the exceptions of B. macerans and B. polymyxa, usually break down carbohydrates to produce acid but no gas giving a type of spoilage known as a ‘flat sour’, which describes the characteristics of both the can and the food.

The heat process a product receives is determined largely by its acidity: the more acidic a product is, the milder the heat process applied. Although more complex schemes have been described, the essential classification of canned foods is into low acid (pH > 4.5, or 4.6 in the United States) and acid foods (pH < 4.5 or 4.6).

We have already seen how this is applied to assure safety with the requirement that products with a pH > 4.5 must undergo a botulinum cook to ensure 12 decimal reductions of C. botulinum spores. This is not a concern in acid foods and the F0 applied to products with a pH in the range 4.0-4.5 such as canned tomatoes and sopie canned fruits is generally 0.5-3.0. In higher acidity products such as canned citrus fruits (pH < 3.7) the heat process is equivalent only to a pasteurization.

A product’s acidity also determines the type of spoilage that may result from under-processing since it can prevent the growth of some spoilage organisms. At normal ambient temperatures (< 38 °C) only mesophilic species will grow. Typical examples would be C. botulinum, C. sporogenes and B. subtilis in low acid products and C. butyricum and C. pasteurianum in products with a pH below 4.5.

Cans are cooled rapidly after processing to prevent spoilage by thermophiles. Thermophilic spores are more likely to survive the normal heat process but would not normally pose a problem. If however a large assemblage of cans is allowed to cool down naturally after retorting, the process will be slow and the cans will spend some time passing through the thermophilic growth range.

Under these conditions surviving thermophilic spores may be able to germinate and grow, spoiling the product before it cools. This may also occur if cans are stored at abnormally high ambient temperatures (>40 °C) and canned foods destined for very hot climates may receive a more stringent process to reduce thermophilic spoilage.

Thermophilic organisms commonly associated with spoilage of low acid canned foods are the saccharolytic organism C. thermosaccharolyticum, B. stearothermophilus and Desulfotomaculumnigrificans. The last of these causes a type of spoilage known as ‘sulfur stinker’. It produces hydrogen sulfide which does not usually distend the can but does give the product an objectionable smell and reacts with iron from the can to cause blackening.

Leakage is the most common cause of microbiological spoilage in canned foods. Cans are the most common containers used for retorted products, although glass jars, rigid plastic containers and soft pouches are also sometimes used. Cans are usually made of two or three parts: the three-part can consists of a base, body and lid while in two part cans the body and base are made from a single piece of metal.

In a three-part can the body seam is electrically welded but the lid on all cans is held in place by a double seam (Figure 4.7). The correct formation and integrity of this seam are crucial to preventing leakage and monitoring seam integrity is an important aspect of quality control procedures in canning.

During processing cans are subjected to extreme stress, particularly when the hot can is cooled down rapidly from processing temperatures. The negative pressure created in the can under these conditions could lead to micro-organisms on the container’s surface or in the cooling water being sucked inside through a small defect in the seam.

The defect in the hot can that allowed leakage to occur may seal up and be undetectable when the can is cool since leaker spoilage can cause cans to blow. Since the micro-organisms enter the can after processing there is no restriction on the type of organism capable of causing leaker spoilage, therefore the presence of a mixed culture or non-sporing organisms is almost certainly a result of can leakage.

To prevent leaker spoilage it is essential that the outside of cans is clean and uncontaminated and that chlorinated water is used to cool them. Failures in this respect have been the cause of a large typhoid outbreak in Aberdeen, Scotland where cans of corned beef made in the Argentine had been cooled with river water contaminated with Salmonella typhi and in an outbreak of botulism associated with canned salmon where the C. botulinum type E spores which were associated with the raw product contaminated the outside of the cans after processing and were sucked into one can during cooling.

There have been occasional reports of pre-process spoilage in canned foods where there was an unacceptable delay between preparing the product and heat processing. During this time spoilage may occur although the organisms responsible will have been killed by the heat process.


In the 17th century, Denis Papin carried out new research into preserving food. He began experimenting with vacuum pump technology and managed to keep an apple fresh for several months using vacuum packaging.

Following up on this work, he published his first essay, Les Nouvelles expériences sur le vide. At the time, there were few known physical procedures for preserving food and it was not until 1920 in the United States that the first pieces of vacuum-packed meat became available. The technique has evolved toward other uses over the last twenty years or so and is now associated with culinary techniques, such as modified atmosphere packaging and cooking food in a vacuum.

Vacuum sealing was originally used by food packing companies in the 1940’s as a way to save money. The technique prevented spoilage and prolong the shelf life of food products, especially ones transported over long distances. Not only it hindered the growth of bacteria and mold, but it also kept food fresh and prevented freezer burn. Vacuum sealing is still used for the exact same purpose today. It’s a convenient and economical way for households to preserve, protect, and store their food.


How to vacuum seal your food

Boneless meat should be washed, dried, and sealed while still fresh. Make sure there’s no bone that might tear up the bag.

Fruits should be peeled and cut into smaller pieces before vacuum sealing. Berries can be pre-frozen on a cookie sheet and vacuum sealed once hardened, to avoid crushing.

Freezing vegetables can be tricky. In order to make sure that they won’t get all mushy, and to extend their shelf life and health properties, it’s indicated to blanch all vegetables for maximum 4 minutes in boiling water and place them in ice-cold water immediately after. Drain the water and seal the blanched vegetables to keep their taste and texture for as long as possible.

Never store sealed cruciferous (broccoli, cabbage, cauliflower, kale, Brussels sprouts, etc.) without blanching. When kept in airtight packaging, these vegetables emit gasses that will make the plastic bags expand and the products will spoil faster.

Freezing vegetables in small portions is always a good idea. Don’t forget to write down the date and make sure to consume the products in the indicated time spawn.

Avoid vacuum packaging mushrooms, fresh tomatoes, soft cheese, and garlic. Also, while celery can be vacuum sealed, freezing them is not recommended. Instead, they may be stored in the refrigerator for up to six weeks.


Cancer: Epidemiology of Gastrointestinal Cancers Other than Colorectal Cancers

Prevention

Evidence points to the importance of improving diet and eradicating H. pylori infection. A diet rich in fresh fruits and vegetables without highly salted, preserved, or smoked food will theoretically offer benefits in primary prevention. In countries where the incidence of stomach cancer is high, screening for H. pylori may be effective for secondary prevention. To this end, programs of mass screening and eradication of H. pylori by antibiotics are being performed in Japan. However, because only a small proportion of individuals with H. pylori colonization develop stomach cancer, concerns have been raised regarding the possibility of antibiotic resistance by a mass H. pylori eradication program. Use of vaccines against H. pylori may be an alternative approach.