A couple of months ago, I bought some pesto alla genovese in one of my favorite (and trusted) grocery shop. What caught my attention, besides the essential and fancy packaging (well, marketing has a purpose, after all ;)), was the list of ingredients: brief and without additives. I put the bottle into my basket and I merrily proceeded towards the cashier’s desk.

On my way home, I thought what to make with that: a pasta with zucchini and pesto? Why not? Once home, I started to cook pasta and I simmered zucchini in a frying pan. I drained the pasta and I stirred fry it with the zucchini. And now, the final touch, the pesto. I opened it and...it was brownish...almost black...suspicious. I checked the expiration date, but nope, the pesto was not expired. I poured it in the pasta with some hesitation. I made two portions, sat down and, a bit anxious, I tried it…yuck. I thought asphalt tastes better. The conclusion? A ruined dinner that went directly to garbage. I took the pesto bottle and checked the list of ingredients. I so realized there was not ascorbic acid and I suddenly understood what happened to the poor pesto.

Let’s take a step back and try to rebuild the story. If you just check the labels of commercial pesto, very often, they contain ascorbic acid as additive (E300, in Europe). Why? Because basil, the main ingredient of pesto alla genovese, has the bad tendency to oxidize and brown, once sliced.  Maybe you noticed that, if you make your own pesto.

The browning process of certain foods is due to an enzyme called polyphenol oxidase (PPO). This enzyme is located in the vacuoles of plant cells and is liberated by actions as cutting, slicing, blending, which damage the plant cells. You probably noticed the browning of apples and pears, once peeled. PPO provokes the oxidation of phenolic compounds contained in plants, with the formation of molecules called quinones. These compounds can eventually condensate with each other, generating melanins, the pigments that cause the pulp to brown. The action of PPO is favored by the presence of oxygen.

If fruit browning might be desirable in certain cases (think about dehydrated prunes), more often causes troubles and commercial damages. Besides the poor appealing look, oxidized fruit and vegetables have a limited shelf life. For such a reason, the food industry has searched for solutions to prevent browning.

One of the most successful method is the addition of antioxidant. Sulphites have been widely employed for that purpose, but, following their banning, other antioxidants, as ascorbic acid, have been considered. Better known as vitamin C, ascorbic acid is now added to many strained fruits, sauces and other products. I have used it in the lab and I can confirm it is a powerful antioxidant. If the labels would report “vitamin C”, instead, I bet consumers might look at it less suspiciously :D

Back to my ruined dinner, if the manufacturer of the pesto would have added ascorbic acid, the poor thing would have not browned. Have you noticed how the pesto you buy is usually bright green? Read the label, you will find ascorbic acid or another antioxidant among the additives.

I know that many of you might twist their nose when they hear about additives, but, hey, let’s be honest here. If we want the convenience of ready-made food, we must accept the addition of additives in order to preserve the quality of the product.  The alternative is making everything from scratch. It’s your call :)  

Here, I just talked about antioxidant. But there are many additives with different functions. We will talk about additives again and, maybe, I will have another story to tell.

References

S.M. Son et al., Inhibitory effects of various antibrowning agents on apple slices, Food Chem., 73, 2001, 23-30

F. Taranto et al., Polyphenol Oxidases in Crops: Biochemical, Physiological and Genetic Aspects, Int. J. Mol. Sci., 18, 2017, 377