A Rapid Immunoassay Method for Quantifying Mold in Harvested Wine Grapes

Abstract

A rapid immunoassay developed by the University of California, Davis, and E. I. Dupont de Nemours was compared to the visual inspection assay presently used by the California Department of Agriculture to determine the amount of mold in harvested wine grapes (<i>Vitis vinifera</i> L.). Over 1000 trucks were sampled with both assays during the 1991 and 1992 harvests from inspection stations in the Central Coast, Livingston, Woodbridge, Ripon, and North Coast wine grape production areas in California. The Pearson correlation coefficient (R) between the average of the visual assays and immunoassay was 0.99 and 0.97 for 1991 and 1992, respectively. Analysis of variance of the similarity of the two assays indicated that it was significantly affected by method of harvest (machine or hand) (<i>p</i> &lt; 0.01), but not significantly affected by color, site, variety, or time of harvest. In 1992, when enough data were obtained for analysis, the correlation between the two assays was significant (<i>p</i> &lt; 0.01) at all sites but North Coast (R = 0.23). This was probably due to the very low level of mold detected at the North Coast site with the visual assay (0.24%). At the other sites, R ranged from 0.66 to 0.76. The lowest correlation of the two assays was with machine-harvested black grapes (R = 0.23). The R for hand-harvested white and black grapes was 0.72 and 0.73, respectively, and 0.73 for machine harvested white grapes. This was concluded to be due to the difficulty of visually detecting diseased berries in machine harvested black grapes. Frequency distribution analyses indicated that the visual assay agreed closely with the immunoassay, usually resulting in a variance to mean ratio of less than one.