The use of bacterial alkaline phosphatase assay for rapid monitoring of bacterial counts on spinach.

This study was undertaken to evaluate the applicability of bacterial alkaline phosphatase (ALP) activity for rapid monitoring of total mesophilic bacteria counts in spinach. A set of fresh and decayed spinach mixtures were tested to rapidly (10 min) monitor spinach bacterial counts. To assay ALP activity, Lumigen APS-5 was used as a substrate. Bovine ALP was reduced after heat treatment at 75 degrees C for 1 min; in contrast, bacterial ALP activity increased. To differentiate bacterial ALP from other ALP, heat treatment (75 degrees C, 1 min) was applied before measurement. As a result, a regression equation was established between the actual mesophilic aerobic bacteria count and ALP activity of spinach mixtures (r= 0.90). The predicted total mesophilic aerobic bacterial count calculated from the fitted regression line (predicted log(10) CFU/g = 0.00056 x ALP values + 1.4002) showed a high correlation with the actual observed total bacterial count (r= 0.93). The ALP assay is a simple and rapid method to utilize for estimation of existing or contaminating microorganism levels on spinach.