High levels of branched chain fatty acids in nātto and other Asian fermented foods
Introduction
Fermented foods play important roles in the diets and culture of Asian countries. Some varieties are as common as yogurt in the western world. For instance, fermented vegetables known as kimchi is a daily part of Korean diets, and fermented soy miso is a common food in Japan. Douchi is a fermented black soybean product considered an indispensable ingredient in Chinese kitchens across the country. Nātto is a traditional Japanese food made from fermented cooked soybeans, consumed by many Japanese weekly. Limited data on chronic disease prevention is available for some foods. For instance, nātto intake is associated with less bone loss in Japanese postmenopausal women (Ikeda et al., 2006). Non-vegetarian fermented foods are available in most parts of Asia, for example shrimp paste, employing Acetes as the fermentation organism, and fish sauce made from fermented anchovy. While dairy consumption in Asian countries is low, these fermented foods contribute protein, fat and vitamins in a traditional cereal based diet.
BCFA are mostly saturated fatty acids with a terminal propan-2-yl (isopropyl) group (iso) or butan-2-yl (sec-butyl) group (anteiso) (Favre & Powell, 2013). Food BCFA originate primarily from bacterial action. U.S. milkfat contains 2% BCFA derived from ruminal fermentation (Ran-Ressler et al., 2011), though milkfats of some animals such as yak and sheep contain >3% (Or-Rashid, Odongo, Subedi, Karki, & McBride, 2008) and 2.7%, respectively (Ran-Ressler, Bae, Lawrence, Wang, & Brenna, 2014). Together with beef, BCFA daily intake for an average American is about 500 mg (Ran-Ressler et al., 2014), greater than other bioactive fatty acids such as omega-3 EPA and DHA averaging 100 mg for Americans (Brenna and Lapillonne, 2009, Ervin et al., 2004). High BCFA intake from dairy and beef products may support gut health. Early evidence indicates that BCFA alter nascent microbiota and reduce the incidence of necrotizing enterocolitis in a neonatal rat study (Ran-Ressler et al., 2011), and reduce pro-inflammatory markers in a human intestinal cell line (Yan et al., 2017).
In Asian countries where dairy consumption is relatively low, intake of potential health-promoting BCFA might be expected to be low. However, a recent study found a comparable amount of BCFA in the breast milk from Chinese mothers and American mothers (Dingess et al., 2017). We speculate that fermentation may be a source of BCFA in Asian foods. The nātto organism Bacillus subtilis biosynthesizes BCFA to supply membranes to about 95%,w/w of total fatty acids (Kaneda, 1977). This observation suggests that nātto may be rich in BCFA. Kimchi is fermented by lactic acid bacteria (Lee, 1997) which are another group of BCFA producers (Kaneda, 1991). Fermented foods may also have other distinct fatty acid properties from the unfermented raw food, specifically a high concentration of fatty acid ethyl esters (FAEE) as are found in miso (Yamabe, Kaneko, Inoue, & Takita, 2004).
Numerous reports are available on the BCFA contents of ruminant milks and meat (Bravo-Lamas et al., 2018, DePooter et al., 1981, Dreiucker and Vetter, 2011, Klir et al., 2017, Ran-Ressler et al., 2011, Rawdah et al., 1994). Other than our previous work (Ran-Ressler et al., 2014), reports of fatty acid profiles of other foods, including fermented foods, rarely specify BCFA levels, and no studies have systematically considered the content of BCFA in fermented foods. The goal of this study is to determine the BCFA composition of popular fermented Asian foods that are fermented by BCFA producing microorganisms and/or high in fat content. Nātto and kimchi were chosen mainly because they are fermented by BCFA producing microorganisms while miso and douchi are high in fat that could contribute significant amount of BCFA even if the concentration is low. Although it is unclear if Acetes species are naturally rich in BCFA, as seen in some true krill such as Antarctic krill (Euphausia superba) (Fricke, Gercken, Schreiber, & Oehlenschlager, 1984), shrimp paste undergoes complex bacterial fermentation that could also contribute to BCFA content.
Section snippets
Sampling
A total of 9 different brands and/or preparations of nātto were purchased from Asian grocery stores for the study purposes. Nos.1–7 nātto brands/preparations were purchased in Austin, TX (Nos.1–3 are three preparations of Shirakiku brand, Japan; No.4 is Hime brand, Japan; No.5 is Azuma Brand, Japan; No.6 is Kazoku brand, Japan and No.7 is imported by JFC from Japan). Nātto No.8 and No.9 were two different preparations (Mizkan Co., Ltd., 2–6, Nakamura-cho, Handa-shi, Aichi-ken, Japan) purchased
Results and discussion
Nātto BCFA concentrations were 1.00 ± 0.64%, w/w of total fatty acids (mean ± SD). Fermented shrimp paste had the highest concentration of BCFA at 1.63 ± 0.72%, similar to the proportion of 2% BCFA in fluid milk in the USA (Ran-Ressler et al., 2011). BCFA were 0.62 ± 0.05, 0.73 ± 0.04, 0.37 ± 0.06%, 0.64 ± 0.08% and 0.08 ± 0.01% in fish sauce (liquid), fish sauce (paste), miso, homemade kimchi and douchi, respectively. iso-14:0, iso-15:0, anteiso-15:0, iso-16:0, iso-17:0, anteiso-17:0 and iso
Conclusion
Our data show that branched fats are more widely distributed in human diets than previously appreciated. Nātto is the first fermented food discovered that has comparable concentration of BCFA as milkfat, averaging 0.6 or 0.21–1.43 mg/g. We found that fermentation itself can dramatically increase BCFA compared to the known composition of the parent food. Fermented foods may provide significant BCFA in diets low in milk, beef, and other ruminant products. Our study supports further research into
Declaration of interests
None.
Acknowledgements
This work was supported by NIH grant R01 AT007003 from the National Center for Complementary and Alternative Medicine (NCCAM) and the Office of Dietary Supplements (ODS). Its contents are solely the responsibility of the author and do not necessarily represent the official views of the NCCAM, ODS, or the National Institutes of Health.
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