I had a chance to analyze hundreds of food items that had enough microbial growth to cause customer complaints. The most common occurrence was in various drinks and juices, which are relatively easy to analyze because most have negligible fat content. Most of the time these were merely spoilage microorganisms rather than pathogens that cause illness (and always in drinks with sufficiently low pH). Meat spoilage produces volatile fatty acids as well as nitrogen and sulfur compounds, and usually smells worse than fruits and grains. Vegetables containing polysulfides (onions. garlic) or isothiocyanates (crucifers and Brassica) are especially potent.
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Ketone odor (paint thinner, blue cheese) from slow mold growth – the molecules involved: Ketones are produced after lipolysis and oxidation of the fatty acids. The fatty acids in human food are mostly 16 and 18 carbon chains. The resulting ketones that cause the odor are assorted 4 to 11 carbon chains. The smallest possible ketone (the 3-carbon acetone) is not a major presence in these cases. Methyl ethyl ketone (MEK or 2-butanone) is a common solvent with a familiar odor that’s used in paint thinner and elsewhere.
https://danharring54.blogspot.com/2021/12/ketone-odor-paint-thinner-blue-cheese.html
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Fusel alcohols, congeners, Strecker degradation products: Found during exam of spoiled food products; amenable to GC-MS analysis. Produced from amino acids, especially leucine & isoleucine, phenylalanine, tryptophan, tyrosine, and methionine. Many microbes (especially Saccharomyces yeast) can de-aminate and then de-carboxylate these amino acids into relatively harmless alcohols (although some variant metabolites have strong physiological activity).
https://danharring54.blogspot.com/2022/09/fusel-alcohols-congeners-strecker.html
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Yeast spoilage in beverages: There’s often alcohol and CO2 production (but not always). Here is some additional information. I examined nearly a hundred incidents of beverage spoilage caused by yeast growth. It can originate at the food plant, or some packages can be damaged after leaving the plant, or it can happen after first opening. Compared to most bacteria, yeast are more tolerant of acidic pH conditions. With ordinary Saccharomyces cerevisia yeast, the chemicals produced are not toxic (unless you count ethanol) and the odors are not obnoxious.
https://danharring54.blogspot.com/2022/09/yeast-spoilage-in-beverages.html
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Mold spoilage in beverages: Mold spoilage has been seen mostly in sports drinks and flavored drinks, also in fruit juices, and rarely in carbonated beverages where some species can tolerate and break down the preservatives benzoic and sorbic acids.
https://danharring54.blogspot.com/2022/09/mold-spoilage-in-beverages.html
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Lactic acid bacteria spoilage in beverages
https://danharring54.blogspot.com/2022/09/lactic-acid-bacteria-spoilage-in.html
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Nail polish odor in sliced bread loaves: There have been instances where regular sliced bread loaves (with the standard preservatives and a shelf life up to 10 days) developed a solvent-y nail polish odor before the loaf got used up. The odor is also reminiscent of over-ripe bananas. One customer described it as the butyl acetate odor from the small tubes of glue used to assemble toys such as model cars and planes. The chemicals causing the odor were short-chain volatile esters produced by “wild yeast”. The esters ranged from ethyl acetate through the isoamyl acetates. The corresponding propionates were also present. I analyzed 3 cases about ten years apart. Previously I encountered it myself at home twice, so I realized this wasn’t someone making up a story. In my cases, I suspect that, a couple days before the odor became noticeable, I had reached into the bag with a wet hand right after rinsing something under the faucet. In some cases a whitish powder was present on the outer surface. The odor from the interior of the loaves was very strong. The lab did not have the capability to speciate the exact yeasts. The baking industry is very careful to minimize airborne microbial contaminants during the cooling off period after the production line exits in heating unit. The brewing industry has documented cases of “wild yeast” contamination causing spoilage. The solvents used in nail polish (and remover) at the time were primarily ethyl acetate along with acetone and toluene. The nail polish odor is easily recognizable whenever the vial is opened, even in the next room.
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Mold pellicles (ughh), the size & texture of a small mushroom (it could have been worse)
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Dan Harring (54) 