Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2008
Publication Date: 4/1/2009
Citation: Montesinos-Herrero, C., Smilanick, J.L., Hurley, J.M., Lluis, P. 2009. Potassium sorbate residue levels and persistence in citrus fruit as detected by a simple colorimetric method. Journal of Agricultural Food & Chemistry. 57(9):3458-3463. Interpretive Summary: Potassium sorbate is a common food additive used to preserve the freshness of many food products, including fresh citrus fruit, where we and others showed it can be used in place of synthetic fungicides. However, nothing was known about how much potassium sorbate residue was present on citrus fruit treated with this material, and this is important to establish both methods to apply it to effectively control decay pathogens, and to estimate the amount of potassium sorbate reaching consumers for regulatory purposes. In this manuscript, the amount and persistence of potassium sorbate residues in citrus fruit is shown and the residues were low and relatively non-persistent, indicating the amount reaching consumers is small.
Technical Abstract: Postharvest applications of potassium sorbate (PS) to fresh citrus fruit control fungal decay pathogens, such as Penicillium digitatum, cause of green mold. Although PS effectiveness has been examined repeatedly, little is known about PS residues. A colorimetric method that employed extraction of the macerated fruit, followed by reaction with thiobarbituric acid, was used to quantify PS residues. A recovery of more than 90 % in oranges and lemons was obtained when fruit were spiked with 200 mg kg-1 PS before maceration. Residues of 20 mg kg-1 PS determined by this method and an HPLC method were similar. Immersion of fruit in PS at 2 % (w/v) for 1 min deposited residues of 37 mg kg-1 in lemons and 28 mg kg-1 in oranges, determined one day after treatment. Residues were proportionate to the PS concentration in the treatment solution. Immersion of oranges in PS at 0.5, 1.0, 2.0, or 3.0 % (w/v) for 1 min deposited residues of 8, 12, 26, or 43 mg kg1 determined the day of treatment. PS residues declined after treatment, initially rapidly and later more slowly, until residues stopped declining after 6 d when the oranges were stored at 15C. PS residues declined by one-half in about 5 d at 15C. Removal of the PS residue to minimize desiccation or visible residue deposits is sometimes needed, particularly when fruit are removed from storage for final processing. A brief double-dip rinse in tap water applied immediately after immersion of lemons in a 2 % (w/v) PS solution at 25C or heated to 40, 50, or 62C, removed more than 90 % of the PS residue. The influence of high pressure water washing (HPWW) on PS residues in PS-treated fruit was determined. PS residues were more effectively reduced by rinsing oranges than lemons. When oranges were HPWW rinsed one day after immersion for one minute in 2 % (w/v) PS, PS residues were reduced by 75 %. When similarly treated, stored 25 d at 15C, and rinsed, PS residues in oranges were reduced by 87 %. When lemons were HPWW rinsed one day after immersion for one minute in 2 % (w/v) PS, PS residues were reduced by 73 %. When similarly treated, stored 25 d at 15C, and rinsed, PS residues in lemons were reduced by 39 %.