Tomato paste is a product made exclusively from fresh, ripe, healthy tomatoes of the Lycopersicum esculentum species. It is a widely consumed product that is highly vulnerable to fungal spoilage. Chemical products are the most widely used technique, because they are easy to apply. However, the intensive use of these products poses health risks, which is why we decided to replace them with natural preservatives. In this context, we evaluated the in vitro antifungal activity of the essential oil extracted from the zest of Citrus limon of two varieties by hydrodistillation and cold pressing, and applied it to tomato concentrate. From the results of the statistical analysis, we can conclude that the variety has no influence either on the yield or on the antifungal activity of the oils, unlike the extraction method, which does have an influence on these two parameters. On the basis of this study, we can conclude that lemon essential oil appears to be suitable as a preservative in tomato paste.