Chitin as a measure of mold contamination of agricultural commodities and foods

Chitin is a polysaccharide of beta-(1-->4)-linked 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine) that is found in the cell walls of fungi. In an effort to develop new methods to detect fungi in plant and animal tissues, chemical analyses based on fungal cell wall components have been evaluated. Chitin is not present in plant or most food animal tissues; therefore, the entire sample can be hydrolyzed and analyzed for fungal chitin. Acid, alkaline, and enzymatic hydrolysis have been used to cleave the beta-(1-->4)glycosidic bond to produce glucosamine, chitosan, or N-acetylglucosamine. The major methods used to analyze these degradation products have included colorimetry; chromatography (gas chromatography, high performance liquid chromatography, amino acid analysis); microscopy, using fluorescent, nonfluorescent or immunofluorescent dyes; near-infrared spectroscopy; and titrametric assays. Chitin has been used to estimate and quantify fungal growth in plants, wood, grains, hay, and foods. There was an increase in the chitin content as the mold increased; however, the chitin assay showed more variability than other assays for detecting fungal contamination. The future use of the chitin assay will depend upon improvements in sensitivity, assay time, simplified methodology and equipment, and development of reliable conversion factors for converting chitin to fungal dry weight.