Organic preservatives for cereal grain storage: Mechanisms, nanoencapsulation advances, challenges, and future prospects – an update

Abstract

Post-harvest grain loss by fungi, bacteria, insects and oxidative rancidity remains a major threat to world food security. The use of synthetic preservatives (propionates, benzoates, sorbates, sulphites) to preserve stored foods is longstanding; but evidence of some of these compounds' carcinogenicity, allergenicity and persistent environmental residues has recently stimulated interest in organic alternatives. This review provides an integrated appraisal of the literature on organic preservatives (mainly essential oils) used in the storage of cereal grains over the past 25 years with regard to their antibacterial, antifungal, antioxidant and repellent properties, and recent advances in their nanoencapsulation and other formulating techniques. Some organic preservatives such as thyme, clove, cinnamon, oregano oils target microbial cells membranes, inhibit the biosynthesis of mycotoxins, and repel storage pests; for instance, microencapsulated thyme oil retained >80% of its antifungal activity after six months of storage (versus <30% of unencapsulated oil), while clove oil vapours suppressed maize weevil emergence by >70% in some trials. Nanoencapsulation with carriers such as chitosan and alginate may improve the stability and efficacy of natural preservatives with minimal impact on grain quality; but high production costs, scalability, complex compositional variation, impact of food matrices and lack of harmonized international regulation threaten to limit adoption of natural preservatives, so sustained investment in R&D and harmonization of regulations will be essential to realize their potential.