Food preservation has been used since ancient times by populations across the globe. Preservation vastly increases the variety of food options available. Rather than having access only to food items immediately available in the local environment, preservation techniques permit foods to be transported through time and space without spoilage.
Food spoilage is based on three main factors: water activity, acidity, and oxidation.
- Water activity refers to the amount of free water (uninhibited by ingredients such as sugar) within a food product. Salt is an example of a preservative that reduces water activity by pulling water out of a product.
- Acidity has to do with the concentration of hydrogen ions, or pH, of a product. Altering the pH with ingredients such as vinegar or other acids often makes the environment unsuitable for food spoilage organisms to survive and grow.
- Oxidation occurs when oxygen exposure causes molecular structure changes in a food, particularly in unsaturated fats, that result in rancidity. Antioxidant preservatives scavenge for free radicals and inhibit the oxidation process.
Foods are less likely to spoil if they have less water activity, greater acidity (lower pH), and protection from oxidation.
A variety of chemical ingredients may be used to help preserve foods. These include:
- Antimicrobial agents: sodium benzoate, nitrites, nitrates, and sorbates
Found in a variety of foods from juices to meats to yogurt to baked goods, antimicrobials help to prevent growth of food spoilage organisms by changing the acidity of the food product. Many antimicrobial agents are water-soluble and turn to acid when mixed with water, however, astringency and taste must be considered. For example, acetic acid (vinegar) is very commonly used to acidify foods, but the amount needed to effectively preserve the food may cause an excessively sour taste.
- Antioxidants: sulfites, Vitamin C (ascorbic acid), Vitamin E (alpha-tocopherol), BHA (butylated hydroxyanisole), and BHT (butylated hydroxytoluene)
Often used in fats, oils, and fruits, antioxidants help to bind free radicals to prevent them from oxidizing vulnerable molecules and causing rancidity. There is mixed research on antioxidants, showing that many are safe, yet others may be carcinogenic. However, in larger quantities, those same carcinogenic ingredients may actually provide a protective benefit in the body against cancer.
- Chelating agents: EDTA (Ethylenediaminetetraacetic Acid), polyphosphates, and citric acid
These bind metallic ions that cause oxidation in food products, and are often used in dressings, fruits and vegetables, and canned seafood.
Some particular preservative ingredients pose issues with regards to health and food product quality. Additionally, while some preservative ingredients (such as ascorbic acid and salt) are completely safe, others (such as BHT and some sulfites) may be questionable. While current evidence does not demonstrate danger related to consumption at reasonable levels, conclusions from the FDA Select Committee on GRAS Substances (SCOGS) indicate uncertainties as to whether the ingredient would be safe at greater levels or if consumed over longer periods of time.
- Antimicrobials – as antimicrobials typically work by acidifying foods, it is important to consider the taste of the food. For example, acetic acid (vinegar), a common acidifier that is safe to consume, may be used in a volume such that a food becomes too sour once preservation is achieved. A combination of salt plus an acidifier is often helpful to balance flavor and stability.
- Sodium benzoate – when combined with water, benzoic acid forms. In the presence of Vitamin C (ascorbic acid), benzoic acid becomes benzene, a known carcinogen. Adhere to guidelines for permissible quantities of sodium benzoate in a product (0.1%)
- Nitrates can react with secondary amines and create nitrosamines, which are known carcinogenic compounds. Adhere to guidelines for permissible quantities of allowable nitrates in foods (120ppm in cured meats).
- Sulfites destroy thiamin, therefore, are not allowable on products such as meats that are considered to be important sources of the vitamin.
- BHA and BHT – while research does not definitively show a danger, these antioxidants are also not certainly safe. Overall, the public is wary of BHA and BHT intake.
Alternative preservative ingredients
Researchers are currently exploring substitutes for typical food preservation ingredients. Many of these alternatives exist naturally rather than being produced synthetically.
- Glucono delta lactone (GDL) is an acidifying antimicrobial that offers a less astringent sourness. It is important to note that care must be taken when using GDL in a formulation, as it takes several hours to equilibrate and produce an accurate pH reading.
- Chitosin, found in the chitin of shellfish, has been found to be an effective antimicrobial agent in a study of shrimp mayonnaise salad.
- Nisin is a natural antimicrobial with applications in cheese, fruits, vegetables, meats, liquid egg products, sauces, and dressings.
- Natamycin inhibits yeast and mold formation in dried sausage, fruit juice, and cheeses. However, natamycin is water-insoluble, and is broken down by UV light.
- Antioxidant botanical extracts, including those from rosemary, oregano, cloves, sage, green tea, among many others, have been used as natural and flavorful antioxidant substitutes.
More and more, consumers are concerned about the ingredient lists of their foods. “Clean labels” are becoming increasingly important as a factor in buyer decisions. Thus, considering the perspectives of the target demographic is critical in making decisions about whether to include certain preservation ingredients, or whether to choose a different preservation method that may be considered more favorable by those expected to purchase the product. Assessing the drivers of food decisions made by the population in question, such as importance of “natural” ingredients, can help guide preservation choices.
When deciding which methods to use to increase shelf-life of a product, consider the following:
- Safety – the preservation method should meet legal safety standards set forth by regulating agencies such as the USDA.
- Cost to produce the food item – if the preservation method is more expensive, the cost of the product will increase, a necessary issue to address to meet needs of the target demographic.
- Intended use of the product – the preservation method should match the level of required preparation. For example, if the product is intended to be used as a quick, convenient food, the preservation method should allow for easy access by consumers.
- Consumer perception – whether the product and ingredients will be well-received by the target demographic is a critical consideration. Take care to use preservation methods that will be accepted by those intended to purchase the item.
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Food Preservation Methods, Purdue University Extension
Select Committee of GRAS Substances (SCOGS), U.S. FDA
National Center for Home Food Preservation, University of Georgia
Two Preservatives to Avoid? Berkeley Wellness
To Preserve and Protect, Natural Products Insider
Trend of the Year: Clean Label, Food Business News
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