The E number known as E631 (or sodium inosinate) is an additive that is used in many products to act as a flavour enhancer and make foods taste good. As well as enhancing other flavours, it’s used frequently in products such as potato crisps as it also helps to reduce the amount of salt needed (and reducing salt intake has become quite a big health concern in recent years, with manufacturers vying to get their levels of salt in products down).
Sodium inosinate comes from inosinic acid, an acid that is naturally found in a variety of animals, such as pigs or fish, such as sardines. In some cases it can also be produced from bacterially fermenting some sugars.
As far as commercial use goes, most manufacturers do source their E631 from animals and fish, whilst a few may use the fermentation method. The tricky bit is if you want to specifically avoid E631 that comes from pork, as most products will not say on their ingredients list exactly where it comes from.
You could try writing to manufacturers to ask exactly where it comes from. There’s no guarantee that you’ll get a definitive answer, but it’s always worth a try and, you never know, some might be receptive and willing to give you the facts. However, if it’s an issue that really concerns you and you don’t want to find yourself unknowingly consuming food with E631 sourced from pigs, probably the best move is to avoid the products completely.
It’s hard work sometimes trying to avoid these pesky E numbers, especially with so many hidden in the foods and drinks we enjoy, but if you really do need or want to avoid certain numbers, scouring the ingredients lists before you buy products is the best way of ensuring you’re not getting more than you bargained for.