Acetic acid, calcium gluconate and high molecular weight chitosan were purchased from Sigma Chemical Co (St. Louis, MO, USA). Coating solutions were prepared by dissolving 1% or 1.5% chitosan in 0.5% acetic acid solution. Chitosan coatings containing calcium gluconate were prepared by dissolving calcium salt at 0.5% or 0.75% in water prior to the incorporation of the acetic acid; chitosan was subsequently added to 1% or 1.5%, respectively.