A preservative is a substance that prolongs the shelf-life of food by protecting it against deterioration caused by micro-organisms, or against the growth of pathogenic micro-organisms. Makers add it so the food keeps for longer.
Vietnam regulates additives through a list of permitted additives (Circular 24/2019/TT-BYT, referencing international Codex standards); a substance not on the list is not permitted in Vietnam, and that is the first tier of the Yenzo Scale — see how levels are set.
High risk on Yenzo's scale. The cases at this level: it is not permitted in Vietnam (Circular 24/2019); neither JECFA nor EFSA has an ADI for it; a regulator withdrew it for safety reasons and no evaluator kept an ADI; nitrites and nitrates (EFSA 2023). How we score →
Very low risk: no concern at the levels used in food. How we score →
Fun fact. In 1902 the US Congress funded studies of chemical preservatives in food, led by Harvey Wiley, chief chemist of the Agriculture Department's Bureau of Chemistry. He recruited volunteers, who ate foods containing measured amounts of borax, salicylic acid, formaldehyde and other chemical preservatives. Wiley preferred to call these experiments the “hygienic table studies”. In the end he advocated that chemical preservatives should be used in food only when necessary, that the onus of safety should be on the producer, and that consumers should be informed about ingredients on food labels. An FDA historian describes the studies as a crucial prelude to the Food and Drugs Act of 1906. Source: A Century of Ensuring Safe Foods and Cosmetics (FDA Consumer, Jan-Feb 2006), FDA History: Food & Cosmetics Regulation
According to Yenzo pages, preservatives appear in many kinds of product: E211 in fizzy drinks, soy sauce, chilli sauce and pickles; E202 in bread, cheese, jams and sauces; E250 in processed meats such as sausages and ham. Each code has its own page listing the products where it is usually found.
Labels usually write the group name followed by the INS number in brackets, for example “preservative (211)”, or the code E211, or the name of the substance (sodium benzoate). A substance may be written in any of these ways.
Yenzo does not rank additives. Some codes of this group that have a page on Yenzo: E202 (potassium sorbate), E211 (sodium benzoate), E234 (nisin), E250 (sodium nitrite), E260 (acetic acid). All of them are named in Appendix 1 of Circular 24/2019/TT-BYT.
Updated 28 October 2026
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