Mouldy half used tomato paste jars are thankfully a thing of the past at my place. I used to hate wasting this great stuff but could never use it fast enough. Now I avoid that problem entirely by freezing in easy to use small portions when fresh. I simply freeze it in ice cube trays, then store in a container in the freezer.
As I've said previously red tomatoes are a potent source of the carotenoid lycopene which is protective against prostate cancer. Cooked tomatoes liberate greater quantities of lycopene, and tomato paste is the most concentrated form. Eating tomatoes with a healthy oil source such as olive oil also improves its absorption. Conventionally grown tomatoes are frequently found to contain pesticide residues, so wherever possible choose organically grown tomatoes or grow and enjoy your own