Improvement of Bacterial Separation from Leafy Vegetables by Enzymatic Digestion

Introduction:  An accurate and effective method to separate bacteria from food matrices is essential to the rapid bacteria detection for food safety; however, there remain significant challenges for the improvement of bacterial separation. Bacteria, such as Salmonella, can strongly attach to the surface of food or internalize within the food matrices, making their separation extremely difficult. Traditional methods of separating bacteria from food, such as blending, shaking, and stomaching, may not be efficient at removing all the bacteria.

Purpose:  The purpose of this study was to develop a rapid and effective method to improve the separation of Salmonella from spinach and lettuce by enzymatic digestion.

Methods:  Enzymatic digestion by pectinase and cellulase was used to break down the structure of the leafy green vegetables. After digestion, immunomagnetic separation of Salmonella from the liquefied samples was conducted to achieve a pure sample without leaf debris. The optimal combination of pectinase and cellulase was investigated and the effectiveness of enzymatic digestion was compared with other methods (stomaching and manually shaking) on bacterial separation.

Results:  The optimal combination of pectinase and cellulase provided an effective digestion for lettuce and spinach, resulting in the detachment and release of Salmonella from the leaves. The change in physical appearance and structure of the leaves demonstrated that the whole leaves were digested and became liquefied after enzymatic digestion. The recovery of the Salmonella from the spinach and lettuce after enzymatic digestion was significantly (P<0.05) higher (about twice) than the recovery when using traditional sample preparation methods (stomaching and manually shaking).

Significance: The results demonstrated the potential for use of enzymatic digestion prior to separation as a means to improve the efficiency of bacterial separation and increase the likelihood of pathogen detection in the final detection assay.