Green tea extract: A natural antimicrobial with great potential for controlling native microbiota, Listeria innocua and Escherichia coli in fresh‐cut beet leaves

Abstract

Antimicrobial effect of green tea (GTE), nisin (Ni), natamycin (Na), and their combinations on native mesophilic bacteria (MAB), Enterobacteriaceae (EB), and molds and yeast (M&Y) of fresh-cut beet leaves and on inoculated Listeria innocua (LI) and Escherichia coli (EC) were determined during storage at 15 8C. Individual treatments with Ni and Na were not effective in reducing nor controlling native microbiota. Conversely, treatments containing GTE 5% reduced MAB and EB initial counts to values below detection limit (DL 5 1 log UFC/g) for 24 hr. The most effective treatment for M&Y was the combination of GTE with Na, which maintained the counts in undetectable values (<DL) for 48 hr. Ni and GTE were very effective in controlling LI and their combination presented a significant improvement, it reduced by 4.4 log the initial count and maintained them around 4 log below control samples along storage. For EC control, only GTE treatments were effective presenting a concentration dependent behavior. Practical applicationsConsumers' demand for healthy, nutritious, minimally processed, free of additives and environmentally friendly products has markedly increased in recent years. In response to these demands, the application of green tea extract, nisin, natamycin, and their combinations, as natural antimicrobials against beet leaves native microbiota and inoculated L. innocua and E. coli, was evaluated in fresh-cut beet leaves; an underutilized by-product with high nutritional value. The results of this study showed that nisin, widely applied in dairy products, could be also highly effective against Listeria spp. on leafy vegetables. Moreover, green tea extract, either alone or combined, is a highly promising option with potential for reducing or preventing the growth of pathogenic and spoilage microorganisms (gram-negatives included) present in leafy vegetables, specifically in fresh-cut beet leaves. | I NTR OD U CTI ONIt is well known that fresh horticultural products, especially minimally processed ones, provide a good substrate for the growth of microorganisms (spoilage or pathogenic) during production, commercialization, and storage. Moreover, in the last two decades a marked increase in | M AT ER I AL S A N D M E TH ODS | Culture preparationIn this study, L. innocua (CIP 8011, CCMA 29, Facultad de Farmacia y Bioquímica, UBA, Argentina) and E. coli (ATCC 25922) were employed.These strains have been widely considered as surrogates of L. monocytogenes and E. coli 0157:H7, respectively, since they have shown similar behavior and resistance as pathogenic strains (Kamat & Nair, 1996;Kim & Harrison, 2009;Omac, Moreira, Castillo, & Castell-Perez, 2015).In both cases, fresh cultures were obtained by inoculating 150 ml of fresh sterile trypticase soy broth enriched with 0.6% yeast extract (TSBYE, Biokar Diagnostics, Allonne, France), and incubating them in a continuously agitated temperature-controlled shaker at 28 8C overnight. Then, 3 ml of this culture were inoculated in 150 ml of fresh TSBYE, agitated until obt...

Physicochemical Properties, Oxidative Stability, and Sensory Quality of Lamb Sausage Added with Green Tea Leaves (Camelia sinensis) Powder

“…It was very rational for using green tea extract or in the form of powder as a natural antibacterial to inhibit gram-negative bacteria involved in sausage deterioration due to its multipurpose power. Green tea extract had been largely reported to exhibit antimicrobial, antiviral, and anticarcinogenic activities (Alirezalu et al, 2019;Fernández et al, 2018;Aminzare et al, 2018). Epigallocatechin gallate (EGCG) and (−)-epicatechin gallate (ECG) are identified as the major bioactive antimicrobial compounds that are present in green tea powder (Schilling et al, 2018).…”

Application of a combined treatment using natural antimicrobials and modified atmosphere packaging to enhance safety, quality, and shelf‐life of fresh‐cut beet leaves

“…Changes in E. coli counts along storage (Figure c) and their response to treatments were very similar to that observed for mesophilic aerobic bacteria. This may be related with the fact that native microbiota in this type of product is conformed mainly by enterobacteria (Fernández et al, ). For E. coli control, again, the combined treatment T2.5N + MIA achieved significant improvements compared to its equivalent without MIA, implying a synergistic effect between preservation technologies.…”

“…A mixed culture of L. innocua and E. coli was used, for which each of the microorganisms was cultivated separately in its corresponding trypticase soy broth enriched with 0.6% yeast extract (TSBYE, Biokar Diagnostics, France) as detailed by Fernández et al (). An aliquot of each broth was mixed together to obtain the mixed broth containing 10 8 cfu/ml of L. innocua and 10 8 cfu/ml of E. coli .…”

“…In a previous study (Fernández, Agüero, & Jagus, ), it has been demonstrated that green tea extract (GTE) is a very promising option for reducing and preventing the growth of pathogenic and spoilage microorganism of leafy vegetables, specifically beet leaves. Moreover, their combination with nisin, a bacteriocin with GRAS degree, presented an increased effect for Listeria innocua and native mesophilic aerobic bacteria.…”

“…In a previous study (Fernández, Agüero, & Jagus, 2017a), it has been demonstrated that green tea extract (GTE) is a very promising option for reducing and preventing the growth of pathogenic and spoilage microorganism of leafy vegetables, specifically beet leaves.…”