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

ABSTRACT:  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 °C for 1 min; in contrast, bacterial ALP activity increased. To differentiate bacterial ALP from other ALP, heat treatment (75 °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 log₁₀ CFU/g = 0.00056 × 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.