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Chemical methods for food preservation
Introduction
Our shopping baskets include various foods which, although not processed, have undergone treatment to extend their shelf life. With this article, I’d like to show you how different food preservation techniques are present in our daily lives, and how some of them can even be applied at home.
Vacuum Packaging
Vacuum packaging is a method where food is packaged in the absence of oxygen. This prevents aerobic contamination or microorganism growth. Its goals are to prolong shelf life and allow for food preparation in advance without losing product quality. It’s particularly useful for taking advantage of seasonal products when they are more affordable. Ideally, this technique is combined with pasteurisation or sterilisation and refrigeration.
Nowadays, this method is accessible to households, with vacuum packers available on the market that are affordable and easy to use at home.
Its downside is that with soft or bakery products, the vacuum application can cause irreversible deformation.
Another technique that uses chemical methods is modified atmosphere packaging. This method involves replacing air with a more suitable atmosphere during packaging to better preserve the product. It prevents the growth of microorganisms and undesirable chemical and enzymatic reactions. Variations include vacuum packaging and packaging with modified gases.
In gas-modified packaging, surface air is removed and replaced with another gas. This can be done either mechanically or passively (as with fruits and vegetables).
Applications include:
- Dry products like coffee and nuts: oxidation is prevented by replacing oxygen with nitrogen.
- Medium moisture foods like bread and pastries: oxygen is removed to avoid oxidation, and CO2 is added to prevent microbial growth.
- High moisture content products require more complex treatment.
| GASES USED IN MODIFIED ATMOSPHERES | |
| CO2 | – Bacteriostatic and fungistatic |
| – Soluble in water and fats (can cause package collapse) | |
| O2 | – Inhibits anaerobic microorganisms |
| – Preserves red meat colour (myoglobin oxidation) | |
| – Maintains respiratory metabolism in fruits/vegetables | |
| – Promotes aerobic microorganism growth | |
| – Causes oxidation of fats and oils | |
| N2 | – Replaces O2/CO2 and balances atmosphere |
| – Prevents fat oxidation | |
| – Inhibits aerobic microorganisms | |
| Examples of Modified Atmospheres | |||
| PRODUCT | %O2 | %CO2 | %N2 |
| Bakery products | – | 50 | 50 |
| Fresh red meats | 40–60 | 10–20 | Rest |
| Fresh poultry | – | 20–30 | 70–80 |
| Processed meats | – | 20–30 | 70–80 |
| Fresh oily fish | – | 40–60 | 40–60 |
| Fresh white fish | 10–20 | 30–40 | Rest |
| Fresh pasta | – | – | 100 |
| Fresh cheese | – | 30–40 | 60–70 |
| Apples | 1–3 | 1–5 | Rest |
| Avocados | 2–5 | 3–10 | 75–80 |
| Strawberries | 5–10 | 15–20 | 50–70 |
| Mixed vegetables | 2–4 | 2–4 | Rest |
Biopreservatives
Another method is the use of biopreservatives. This extends shelf life by using natural or controlled microflora and/or their antibacterial compounds, known as bacteriocins. A good example is lactic acid bacteria, which inhibit others through antimicrobial metabolites or by competing for nutrients. Examples include nisin, produced by Lactococcus lactis and used in cheese for anti-botulinic effects, and pediocin, from Pediococcus acidilactici, which helps prevent pathogen growth. There are many more.
Another chemical method involves active packaging, where packaging acts with the product and environment to improve safety and quality:
- O2 absorbers: often small sachets with iron powder.
- CO2 absorbers/emitters: used to regulate carbon dioxide levels.
- Generators: calcium bicarbonate
- Antioxidants: ascorbic acid
- Removers: calcium hydroxide
Ethanol vapour generators are also used for their antimicrobial properties. Food should be reheated before consumption, as ethanol may be absorbed. This applies to baked goods, grapes, etc. Ethanol barriers are created in packaging using zeolites infused with ethanol or combinations of ethanol, water, silica, and vanilla.
Lastly, there are ethylene absorbers. Ethylene is a ripening hormone—if it accumulates, respiration increases and shelf life shortens. Absorbers include graphite, zeolites, bentonite, silicates, clay, silica gel, and alumina.
More and more preservation techniques are being developed. Next time you go shopping, read the labels—you’ll spot many of the methods covered today.
Mi nombre es MªÁngeles Cano Villalba, pero llámame Geles. Soy Dietista-nutricionista y cocinera aficionada. En Natural Castelló voy a ayudarte a cuidar tu alimentación y tu salud.
