A message frequently conveyed by scientists involved in the human microbiome is that modern lifestyles have reduced our exposure to live microbes, exposure to microbes is likely good for us, and fermented foods are one way to get high levels of live microbes in our diet.
Most commercial foods are processed and stored in a way to reduce the levels of live microbes, to enhance both shelf stability and control any food pathogens that may happen to be there. But if our goal is to increase potentially beneficial microbes in our diet, it is not easy to know which foods contain cultures and which do not. Unfortunately, unlike the listing of micro- and macro-nutrients on food labels, there is usually no indication of how many live microbes are contained in commercial foods. The one exception is for probiotic foods, which might carry a statement of the quantity of probiotic present (at the end of shelf life). In the case of yogurt, the Live Active Culture seal is a voluntary mark that indicates live cultures are present. But some fermented foods are processed by heat or filtration after fermentation, leaving few if any live cultures. For your average aged cheese, bottle of wine, jar of sauerkraut, or loaf of sourdough bread, the number of microbes is not labeled.
The aim of a recent publication from Prof. Bob Hutkins and his group at the University of Nebraska, Lincoln, was to compile available information on the numbers of live microbes present in common fermented foods. Their open-access paper is titled “Fermented Foods as a Dietary Source of Live Organisms”. This paper reports their findings from scouring the scientific literature for published information on the number of live microbes that are present in fermented foods, including yogurt and other cultured dairy products, cheese, fermented meats, fermented vegetables, traditional fermented
Asian products, fermented cereals, craft beer, and fermented tea (Kombucha). Refer to the paper for tables on all these products, which stipulated the geographical region, the type of product, the source of the analyzed product, the microbes specifically assayed, the count (log cfu/ml or g) and the number of commercial products tested. Data from about 140 studies published over about a 50-year period were included. The review focused on papers testing fermented foods where live microbes would be expected at time of consumption.
The overall findings of levels of live microbes in different food categories are summarized nicely in the paper’s figure 1. Below are the data in text form.
- Yogurt: 104-109 cfu/g
- Cultured dairy products: 105-109 cfu/g
- Cheese: <103 cfu/g to 109 cfu/g (Cheeses aged 1 or more years showed fewer microbes)
- Fermented meats (sausages, made of pork and/or beef): <102 cfu/g to 1010 cfu/g (Sausages made in the USA in general had lower counts (107 or less)
- Fermented vegetables: <101 to 108 cfu/g
- Traditional Asian fermented products: 103 to 107 cfu/g
- Fermented cereals: 105 to 109 cfu/g
- Craft beer: 102 to 105 cfu/g
- Fermented tea: 106 to 107 cfu/mL
In general, “fresher” fermented products had higher numbers than aged ones. Also, not all olives or pickles are fermented – many commercial varieties are brined and then canned and heat-treated, or are kept refrigerated without heat processing. Some commercially available fermented vegetables such as sauerkraut are heat-treated to lengthen shelf life. Most “big beers” are heated or filtered, but some craft beers retain live microbes.
This paper demonstrates the many types of fermented foods that are likely to contain large numbers of live microbes. Most won’t be found on the shelves on the interior of your typical supermarket. Look in the refrigerated sections, look for labels indicating that the product is fermented or contains live microbes. Reach out to manufacturers of your favorite foods for information on what levels of live microbes are present. Or make your own fermented foods (see here, here).
Is it time for live cultures to be included in official dietary recommendations? (2017) Nature Café, London