The Most Important Meal of the day must be the most well preserved

Ah, the breakfast cereal- a classic food that is probably the most common of pantry foods among households. Do you ever open a new box of cereal, pour it in with your milk, and take a bite, enjoying the sweet crunchiness? The cereal has gone through special treatment and preservation to make it to your morning bowl, and most of us don’t give it much thought because we tend to finish our boxes of cereal in a few days before we can ever see what “spoiled” cereal looks, tastes, and smells like- but it exists! Cereal can go bad, and that’s exactly why we’re here.

Cereal grains from which cereal is eventually produced are very susceptible to microbiological and environmental damages. Bacteria love to frequent cereal grains and contaminate them only to use them for proliferation. The perfect conditions for bacteria to grow in must be highly moist (have a high water activity) at equilibrium and must have a high humidity. The bacteria actually can do no damage until the grain is stored in aerobic conditions- until then, the bacteria are kept at bay by the plant’s cell walls. So naturally, a very important preservation method to consider is drying the cereal grains to a moisture level less than 14% and a temperature of less than 15 degrees Celsius. Yeasts also can carry on from the raw, unprocessed grain to the processed food and cause degradation there. But molds are the most damaging to the grain, causing more degradation than any bacteria living on the surface.

The two groups of fungi that can affect cereal grains are field fungi and storage fungi. Field fungi invade grain in the field when the grain is high in moisture (18 to 30%, i.e., at high aw) and at high relative humidities (90 to 100%). Storage fungi invade grain in storage at lower moisture contents (14 to 16%), lower aw and lower relative humidities (65 to 90%). To prevent spoilage by storage fungi, the moisture content of starchy cereal grains should be below 14.0%. As with any mold that grows on food, the most noticeable effects of deterioration are discoloration, development of visible mold growth, and musty or sour odors. But we must examine the possibility of the development of mycotoxins, and how they can be reduced.

A study in 2006 took 349 breakfast and infant cereal samples from 2002 to 2005 to test for aflatoxins (a form of mycotoxin). Chemically, aflatoxins look like this:


The results of the study showed that levels of aflatoxins in the surveyed cereals were almost significant, matching the exact maximum amount of toxins present in food as given by the European union.

Aflatoxins are classified in two broad groups according to their chemical structure; they display potency of toxicity, carcinogenicity, mutagenicity. Structurally the dihydrofuran moiety, containing double bond, and the constituents linked to the coumarin moiety are of importance in producing biological effects. 

The aflatoxins fluoresce strongly in ultraviolet light; B1 and B2 produce a blue fluorescence where as G1 and G2 produce green fluorescence.To test grains for mycotoxins (and subsequently aflatoxins, various detection methods, such as fluorescence, ultraviolet absorption, and others have been combined with chromatographic methods to be used. New methods based on the production of antibodies specific for individual mycotoxins have also been developed and include enzyme-linked immunosorbent assays and immunoaffinity columns. By detecting potential toxins before packaging and distributing, many future problems are spared.

Another very important method of assuring safe cereal grain and long preservation of cereal is mixing the grain with certain acids- in most cases, it is propionic acid. Propionic treatment will enable grain up to 30% moisture content to be safely stored. Without propionic acid, the grains depend on the reduction of lactic acid fermentation and lowering pH. Propionic acid works for the same purpose, but much more quickly- just 1% of propionic acid in high moisture grains completely inhibits aflatoxin development.

Although we don’t notice it because of its commonplace in our homes, cereal has to go through a very exact process of preservation, beginning from the grain, to ensure that it can safely travel to factories to be manufactured into the flavors and shapes we know today in our favorite cereal boxes. If it weren’t for these methods, we might still be eating cereal- but it would probably kill us.

Fermentation: Will it Happen?

The previous posts on the blog have dealt with some of the health benefits of foods preserved by fermentation. It’s no surprise the probiotic bacteria that culture fermenting food benefit the eater in addition to helping make delicious foods like kimchi or yogurt! The process behind fermentation seems relatively simple: put microbes and what you want to ferment together, seal it, and let it sit for a while. Well, why does this happen and what does it mean?

The process of fermentation is a spontaneous one; that is, it has a negative change in Gibbs free energy. Thermodynamically speaking, that just means that it is going to happen, and it will happen so that we get the delicious products of that chemical reaction. If you don’t believe me, look through this college chemistry lecture from the University of Massachusetts Amherst. Besides reviewing the concept of spontaneity, it shows some of the practical uses of knowing whether something is thermodynamically spontaneous and how it can further be analyzed thermodynamically in real world applications. For example, thermodynamic analysis of bioethanol production (essentially a modern biotech application of the ancient process of fermentation) can help find more efficient ways to produce biofuels or, perhaps more importantly to some, fine wines and other drinks of choice.

Fermentation process of beer.

For most of its history, beer was produced through spontaneous fermentation, or letting natural fermenting bacteria and yeast produce the alcoholic slurry that captured the hearts (and stomachs) of the people. Basics about fermentation have been explained in previous blog posts, but the important part to remember is that anaerobic respiration is similar to, but not quite the same as fermentation, with the latter using only substrate level phosphorylation to end up preserving the desired project with the production of alcohols, lactic acids, acetic acids, and fermentative alkaline solutions. As complex as they may seem, these processes have been happening naturally, though. The old proverb “let nature take its course” has been providing humans with a means of saving food for the long haul and introducing some beneficial bacteria into their natural flora: a real boost to their immune system.

Like a ball rolling down an incline or water down a stream, the process of fermentation is a favored one – it will be hard to stop it from happening. So what can you do now knowing that fermenting something is not that difficult, and science is behind your effort to make it happen? Well, those probiotic bacteria only work when inside your body, so follow these steps to get producing your own flavorful probiotics that will keep for months!

Kimchi: Fermented, Not Rotten, Cabbage

Kimchi is a traditional Korean delicacy that has been for hundreds of years.  This food is starting to get global recognition, and sometimes this global recognition isn’t just because of its taste- it is starting to be considered an odd eat, for people are claiming it to be “rotten cabbage.”  Now, with that logic, it is the same as saying that the scrumptious Chobani Greek Yogurt you had this morning was also rotten, not to mention that hot dog with saurkraut you bought from the 7 Eleven down the street (though that actually might be), or that Corona Sun that you downed when your parents weren’t home.

So, is kimchi still a “rotten” delicacy?

What causes some people to consider this food to be rotten is because it develops its taste from a process called lactic acid fermentation.

C6H12O6 (glucose) → 2 CH3CHOHCOOH (lactic acid)

This process occurs due to the presence of yeast as well as nearly 200 different kinds of bacteria in the kimchi.  That number of bacteria is more than the number of bacteria in yogurt.  Some of these bacteria break down complex sugars into simple carbohydrates, allowing others, such as Lactobacillus plantarum, to break down those simple sugars into  lactic acid.  This creates anaerobic conditions, inhibiting the growth of harmful bacteria.  Additionally, the lactic acid dissociates in the water found in the pickling spices in kimchi, causing the pH of the kimchi to drop.  Typically, kimchi is considered to be optimal when it is around a pH of 4.2, which hovers around the pH of grapes.

Eating kimchi may do more than just satisfy your hunger cravings though; a recent study has found that one species bacteria used in the fermentation process, Lactobacillus acidophilus, can suppress the growth of cancer cells.

Streptococcus faecalis is another bacterium utilized in the fermentation process, and it is rather interesting because it is responsible for causing meningitis and urinary infections.  But I assure you, the only condition you may get after eating kimchi is an insatiable desire for more.

Check out this video of Andrew Zimmern, host of “Bizarre Foods”, visiting a kimchi factory in Korea.

Feta and Brine

Feta is a traditional, hard, crumbly cheese made from sheep’s or goat’s milk and originating in Greece. It’s been growing in popularity since- today it is used in a number of salads and is widely eaten on it own throughout the Mediterranean. Feta is a very delicate dairy product and special steps must be taken to ensure that it remains fresh- and even then, it can only remain fresh for about 3 months! Freezing is not a good way to preserve feta, like many other foods, because it changes the texture of the cheese. So we turn to submerging the dairy in a brine solution and perhaps adding additional salts to see to its preservation.

Many significant changes in the constituents and properties of feta cheese take place during its maturation which contribute to the development of feta’s physio-chemical properties. The first important factor is the type of milk used in feta production, with different milks having different fat contents that will later affect the taste of the finished product- but that is more biology than chemistry. After the milk has been carefully selected, a starter culture is added, which is usually a combination of lactic acid bacteria with a ratio 1:3 of lactococci to lactobacilli. The culture is added to a level of about 0.5 to 1% (volume of culture/volume of the milk) and incubated for 30 minutes. Afterwards, CaCl2 may be added up to 20g for every 100kg milk, but only to pasteurized milk. Its main purpose is to be able to keep the calcium balance in the milk, which was affected during pasteurization for pasteurized milk. Heat treatment of milk at high temperatures can bring about changes in the mineral constituents of the milk, principally the calcium, which can interfere with the secondary phase of gel formation during the ripening of the milk into cheese. Poor milk quality in terms of protein content, the pH of coagulation and the level of Ca 2+ in the milk will cause the coagulum to be soft resulting in heavy losses of caseins (a type of protein) and fat. In brief, heat treatment breaks down the calcium salts naturally found in milk by precipitating them. With the addition of Calcium chloride, the milk’s calcium levels are returned. It has also been noted that without the addition of CaCl2, milk’s pH levels were lower therefore creating a harsher taste. 

After the addition of a CaCl2 treatment to the milk, the milk must be coagulated. Coagulation was mentioned previously, but in short it is the curdling of the milk- the transition of the milk from liquid to a colloid where there are existing curds of fat and the whey running off as a liquid. Rennet is added to the milk to begin coagulation. After coagulation, the curds must be left to drain of whey- during this process, the pH of the cheese drops 2 levels, from roughly 6.59 to 4.91. During the next step, salting, it drops to about 4.8. Finally, the cheese must be left to ripen for another two days, allowing for the physio-chemical changes to be complete and the final flavor of the feta to develop. Proteolytic and lipolytic acitivty on the surface of the feta due to salting and low pH release many peptides, amino acids, and fatty acids essential to the taste.

But preserving and story feta is the most sensitive process, because one wrong or seemingly insignificant change in its setting can alter its taste and texture dramatically. Before feta cheese is packaged, it is submerged in a brine solution. If there is too much brine, many low-molecular weight compounds diffuse from the cheese into the brine (water-soluble nitrogen is one of these compounds). It is advised that fermentation gases be released periodically and to refill the containers of feta to appropriate levels once again. The barrels of feta are kept at about 14-18 degrees Celsius until their pH reaches 4.4-4.6. Any lower, and the cheese will be too acidic in taste and will lose its moisture. The temperature is most important and must be controlled. If depending on environmental temperatures, during the summer the cheese will ripen within 8-10 days as the higher temperature with enact fermentation faster, causing it to reach a desirable pH must sooner. In the winter, it would take a month to achieve the same result.

Jams and Jellies

ImageWhether you like Jellyfish Jam like SpongeBob or regular jam to put on your PB&J sandwich—here is the 411 on how jam and jelly are created and preserved.

They all consist of fruits preserved mostly by means of sugar and they are thickened or jellied to some extent. Fruit jelly is a semi-solid mixture of fruit juice and sugar that is clear and firm enough to hold its shape. Jam also will hold its shape, but it is less firm than jelly. Jam is made from crushed or chopped fruits and sugar. Jams made from a mixture of fruits are usually called conserves, especially when they include citrus fruits, nuts, raisins, or coconut.

The main factor preserving these foods is the acidity of the fruit.  The acidity will prevent the growth of the bacteria that causes botulism. Another preservative ingredient in jams and jam is sugar. Canning in boiling water will kill other microorganisms and seal the jars creating a vacuum. The problem with the acidity and sugar preservation factors is that molds can still grow and spoil your beloved jams and jellies. The mold that grows is no penicillin- some of the mold produces mycotoxins (mold poisons). For additional information about dangers of this read this.

Jam and jelly are made from fruit, fruit juice, sugar, and pectin.


Pectin is a carbohydrate found in fruits, and when sugar is added, pectin precipitates out of the fruit and forms insoluble fibers. The insoluble fibers create a mesh-like structure that traps the liquid in the fruit and this enables a gel to form. A catalyst in this process is acidic products, such as lemon juice. Some recipes that do not add pectin to the fruit simply use the natural pectin found in the fruit to form the gel. Also, under-ripe fruit contains more pectin than ripe fruit. For the best gel and flavor, a general technique is to use one part under-ripe fruit to two parts fully ripe fruit. The pectin in fruit becomes water soluble when it is heated, so for jelling to occur, the fruit must be heated. Acidity is also very important in the jelling process—gel will not set if there is too little acid and too much acid will cause the gel to lose liquid. Sugar also is crucial in the gelling process.

So the next time you open your delicious jar of jelly or jam, remember, there is more to it than its delicious taste.

Here is an informational video on how to make jams.


An Aspic Preparation

You may be thinking: “What does meat filled jell-o have to do with food preservation!?” Well, you’d be surprised to find out that gelatin has been used in food preservation dating back to at least 1375 with its publication in Le Viandier, a Medieval cookbook. Well, how is gelatin used for preserving food?

The proteins in gelatin form a protective gel at low to room temperatures that guards food from oxygen that allows spoilage bacteria to grow and flourish. Foods placed inside liquid gelatin before it cools will benefit from the protective gel, effectively preserving it for months at a time. The medieval population would have ben able to store meats like this during the colder months, when keeping live animals was economically unreasonable. Now you may be thinking, where did all that gelatin come from? By clarifying animal stock, naturally high in gelatin contained in animal bones, a base for these dishes was made. This, essentially cooled meat broth, was known as aspic. Aspic dishes have remained popular in many countries around the world, but why do they work?

The weak bonds between the collagen proteins in gelatin are broken when added to hot water. The swirling chains remain in the solution until it cools. The cooling gelatin solidifies when the polypeptide chains start returning to their original formation under the cooling conditions and form what are known as junction zones, or places where three polypeptide chains have reformed into helical structures. At this point, if there is enough gelatin in the solution, a three dimensional matrix will form from these junction zones to make the wiggling gelatin structure everyone knows and loves. A more detailed description of the process of the thermal dependent breakdown and reformation of gelatin can be found here at Scientific American and the detailed biochemistry of gelatin can be found here. As mentioned, the structural properties of gelatin are dependent on temperature. When energy is added to the jello, the weak bonds keeping it together, such as hydrogen-bonds, are broken with the extra energy and the structure falls apart. However, as the temperature cools, the polypeptide chains in gelatin attract one another and reform the three dimensional matrix.

Here’s an interesting slideshow summarizing some of the intricacies of gelatin:

Drying Without Heat

Freeze-drying has been around since the time of the Incas, yet so many people have no idea how this method of food preservation works.  In this process, foods are frozen, and their surrounding air pressure is lowered to cause the water to evaporate.  As a result of this, 100% of the water in the food is removed, leaving no water for harmful microorganisms and enzymes to flourish in.  The resulting freeze-dried food can have a shelf-life of up to 30 years!

Now, you may be thinking that drying foods under cold conditions is much harder than drying foods under hot conditions, and you are 100% right.  You’re thinking of a food preservation method called hot-air drying which we talked about in a previous post.  So go ahead, try to dry out the spaghetti that you want to save for next month by leaving it to dry in the sun.  After about a week or so, you’ll get you’re desired product: rotten spaghetti.

Okay, maybe it wasn’t what you wanted so let’s see why that happened.  Although hot-air drying removed moisture, it only removes 90-95% of the water, leaving some to allow microorganisms and enzymes to still flourish in the food, causing the spaghetti to rot away in the sun.

Oh, you want to try to dry the spaghetti in the oven?  Okay, so after 10 minutes at 200 degrees Celsius, you’ll get what you asked for: burnt spaghetti.  What happened there was that too much heat was added to the spaghetti, causing the spaghetti to burn as a result of a nice combustion reaction.

Freeze-drying may be more difficult than hot-air drying, but it is a much more effective method of food preservation.  It completely removes the water, and it adds minimal heat to the food to prevent the food’s texture and taste from changing.  This process can be explained through a phase chart of water:

This shows the different phases of water under specific conditions of pressure and temperature.  In freeze-drying, the food is first frozen, meaning that the water is in the solid phase.  Although we typically think of water turning into a vapor by first melting into the liquid phase, water can change from a solid to a vapor in a process called sublimation.  This can occur at 0 0C when the pressure is .006 atm (also known as the triple point of water) but also at any pressure less than that.  The temperature can be lowered as well, but then the pressure would have to be decreased too.

These conditions are induced in a freeze-drying machine, leaving us with our favorite freeze-dried foods such as instant coffee and freeze-dried ice cream.

Here is a cool video of a guy who made freeze-dried Jello.