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The Science Behind Pickled Vegetables and Their Longevity

November 25, 2024

Pickled vegetables have a long shelf life, which is achieved through a combination of preservation techniques and science. Acidity, salinity, and microbial activity in the pickling process enable longevity in the product. Depending on the time, temperature, and quality of the pickling process, these can significantly affect the flavor, texture, and color of the final product. For instance, higher temperatures tend to fasten the process which may not allow much complex flavor development, unlike lower temperatures. 

How Pickling Works

Pickling typically involves submerging vegetables in a solution of vinegar (acetic acid) or saltwater brine. Sometimes salt can be used as a pretreatment in order to create safe lactic acid fermentation (Sawada 2021). A key factor in the pickling process is fermentation, particularly lactic acid fermentation which results in the tangy flavor of the product. Fermentation is a metabolic process where microorganisms, such as bacteria or yeast, convert sugars into acids, gases, or alcohol (Sato 2023). 

The acid or high-salt environment prevents the growth of spoilage-causing bacteria while encouraging the activity of beneficial microbes, particularly lactic acid bacteria. The vegetable is also placed into an airtight container because the presence of oxygen can encourage the growth of beneficial bacteria and promote undesirable microorganisms. The airtight container enables lactic acid bacteria to thrive due to lack of oxygen, thus allowing fermentation to occur. These microbes convert natural sugars into lactic acid, further lowering the pH and creating a hostile environment for pathogens. The result is a flavorful product that remains safe for consumption over extended periods.

Key Factors Contributing to Longevity

The low pH achieved during pickling is important for preservation. The optimal pH range is typically between 3.4 and 4.6 for pickling (Sato 2023). Fermentation-based pickling allows lactic acid bacteria to produce lactic acid over time. This method ensures the environment is inhospitable to harmful microorganisms. In fermentation-based pickling, salt concentrations between 2-5% are optimal for promoting the growth of lactic acid bacteria (Sawada 2021). This balance ensures both preservation and the development of the tangy flavors. Lastly, sealing the pickling container reduces oxygen levels, which is important for anaerobic microbes like lactic acid bacteria to grow. This prevents the growth of aerobic spoilage organisms and helps the fermentation process.

Example of Pickled Vegetable

When asked about what pickled foods there are, one might think cucumbers. However, there are many foods other than cucumbers that are pickled. A common example of pickled vegetables seen in Korean cuisine is kimchi. Some raw vegetables used for kimchi are cabbage, parsley, perilla leaf, green pepper leaf, garlic, and red pepper. This has many complex flavors and a crispy texture due to the numerous biochemical changes during kimchi fermentation. Kimchi not only tastes good but also brings nutritional value such as dietary fiber and vitamins from the B group, β-carotene, and ascorbic acid (Montaño 2016).

Why Pickled Foods Last

The longevity of pickled vegetables arises from a combination of microbial inhibition, acidification, and proper storage. When stored in cool, dark places, pickled foods can last for months or even years. This makes pickling a great technique for food preservation. Next time you visit the grocery store, take a moment to explore the variety of pickled products and you might just discover a new favorite!

 

Sources Cited

Encyclopedia of food and health. (n.d.). ScienceDirect. Retrieved November 25, 2024, from http://www.sciencedirect.com:5070/referencework/9780123849533/encyclopedia-of-food-and-health

Pickling—An overview | sciencedirect topics. (n.d.). ScienceDirect; Encyclopedia of Food and Health. Retrieved November 24, 2024, from https://www.sciencedirect.com/topics/food-science/pickling

Sato, T. (2023). The science behind food pickling: Understanding the fermentation process. 7(4), 190. https://www.alliedacademies.org/articles/the-science-behind-food-pickling-understanding-the-fermentation-process.pdf

Sawada, K., Koyano, H., Yamamoto, N., & Yamada, T. (2021). The effects of vegetable pickling conditions on the dynamics of microbiota and metabolites. PeerJ, 9, e11123. https://doi.org/10.7717/peerj.11123

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.