Antifungal activity of lactobacilli and its relationship with 3-phenyllactic acid production O. Cortés-Zavaleta a , A. López-Malo b, ⁎, A. Hernández-Mendoza c , H.S. García a a Unidad de Investigación y Desarrollo en Alimentos, Instituto Tecnológico de Veracruz, Av. M.A. de Quevedo 2779, C.P. 91860, Veracruz, Veracruz, Mexico b Departamento de Ingeniería Química, Alimentos, y Ambiental, Universidad de las Américas Puebla, Ex-Hda. Santa Catarina Mártir, C.P. 72820, Cholula, Puebla, Mexico c Centro de Investigación en Alimentación y Desarrollo, Carretera a la Victoria Km. 0.6. C.P. 83304, Hermosillo, Sonora, Mexico abstract article info Article history: Received 10 September 2013 Received in revised form 2 December 2013 Accepted 19 December 2013 Available online 26 December 2013 Keywords: Antifungal agents Lactic acid bacteria 3-Phenyllactic acid In this study, 13 lactic acid bacteria (LAB) strains (including 5 Lactobacillus casei,2 Lactobacillus rhamnosus,2 Lac- tobacillus fermentum,1 Lactobacillus acidophilus,1 Lactobacillus plantarum,1 Lactobacillus sakei, and 1 Lactobacillus reuteri species) were assessed for both their antifungal activity against four food spoilage molds (Colletotrichum gloeosporioides, Botrytis cinerea, Penicillium expansum, and Aspergillus flavus) and their capability to produce the novel antimicrobial compound 3-phenyllactic acid (PLA). Results demonstrated that all molds were sensitive to varying degrees to the cell-free supernatants (CFS) from LAB fermentations (p b 0.05), with growth inhibitions ranging from 2.65% to 66.82%. The inhibition ability of CFS was not affected by a heating treatment (121 °C, 20 min); however, it declined markedly when the pH of CFS was adjusted to 6.5. With the exception of L. plantarum NRRL B-4496 and L. acidophilus ATCC-4495, all other LAB strains produced PLA ranging from 0.021 to 0.275 mM. The high minimum inhibitory concentration for commercial PLA (3.01–36.10 mM) suggests that it cannot be considered the only compound related with the antifungal potential of studied LAB and that syner- gistic effects may exist among other metabolism products. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Molds are capable of growth on all kinds of foods, including cereals, meats, fruits, and vegetables (Gerez et al., 2013). Food spoilage by molds causes extensive economic losses to the industry and may involve health risks to consumers due to both the toxicity and pathogenicity of some species, causing infections or allergies in susceptible individuals (Gerez et al., 2010). Currently, the use of food-grade chemical antifungal agents has become increasingly unpopular with consumers, who look for foods that do not contain them. Also, some authors reported high mutation frequencies of target microorganisms when using common antifungal agents, resulting in increased resistance (Gerez et al., 2010; Wang et al., 2012). In recent years, biopreservation (the use of microor- ganisms and/or their metabolites to prevent spoilage and to extend the shelf life of foods) has attracted interest due to consumer demand for reducing potential negative effects, including direct or indirect impact of chemically-synthesized products on the environment (Ström et al., 2002; Schnürer and Magnusson, 2005; Mu et al., 2009; Prema et al., 2010; Wang et al., 2012). Lactic acid bacteria (LAB) represent a large group of microorganisms that have long been used as natural or selected starter cultures for food fermentations, not only because they significantly contribute to the acid- ification and flavor production but also because they have antagonistic properties which offer protection against food spoilage molds and bacte- ria (Messens and De Vuyst, 2002; Kim et al., 2009). Such antagonistic properties have been associated with a wide variety of active antimicro- bial compounds produced during bacterial fermentation—for instance, lactic, acetic and benzoic acids, carbon dioxide, ethanol, hydrogen peroxide, diacetyl, hydroxyl fatty acids, reuterine, and bacteriocins (Lavermicocca et al., 2000; Messens and De Vuyst, 2002; Ström et al., 2002; Lind et al., 2007; Hassan and Bullerman, 2008; Dalié et al., 2009; Kim et al., 2009). All these antimicrobial compounds might be used as an integral part of hurdle technology (Ananou et al., 2007). In this regard, 3-phenyllactic acid (PLA) has gained interest in recent years due to its ef- fective antimicrobial activity. PLA was first described as a LAB metabolite in the study by Lavermicocca et al. (2000), where it was related with the inhibition of the conidial germination of Penicillium expansum, Penicilli- um roqueforti, Aspergillus flavus, Aspergillus niger, Monilia sitophila, and Fusarium graminearum, among others. PLA is a by-product of phenylala- nine metabolism in LAB, where the first step involves its transamination by a non-specific aminotransferase. The α-amino group is then trans- ferred to a suitable acceptor such as α-ketoglutarate, yielding phenyl pyruvic acid (PPA) and the corresponding amino acid. Finally, PPA can then be reduced by hydroxyl acid dehydrogenases to PLA (Vermeulen et al., 2006; Mu et al., 2012b; Rodríguez et al., 2012). PLA is an antimicrobial compound with a wide activity spectrum against some yeast such as Candida pulcherrima and Rhodotorula mucilaginosa (Schwenninger et al., 2008) and molds including some mycotoxigenic species such as Aspergillus ochraceus, Penicillium International Journal of Food Microbiology 173 (2014) 30–35 ⁎ Corresponding author. Tel.: +52 222 229 2126; fax: +52 222 229 2727. E-mail address: aurelio.lopezm@udlap.mx (A. López-Malo). 0168-1605/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijfoodmicro.2013.12.016 Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro