Although many spices have antimicrobial properties, the idea they were used as a preservative is a myth. Just look at leftovers: My extra spicy kung pao goes ba

Although many spices have antimicrobial properties, the idea they were used as a preservative is a myth. Just look at leftovers: My extra spicy kung pao goes bad just as fast as my roomate's sweet and sour. Salt, acidity, and fermentation are both much more effective and well known in ancient times. Source: A Taste of Conquest by Michael Krondl discusses the historic uses of spices in great deal.