Letters in Applied Microbiology zyxwvutsrq I99 1, zyxwvut 12, 65-68 ADONIS 026682549 zy 10002 1 J zy Bactericidal action of oleuropein extracted from green olives against zyxwvu Lactobacillus piantarum J.L. RUIZ-BARBA, A. GARRIDO-FERNANDEZ & R. JIMENEZ-DIAZ* Unidad Estructural de Biotecnologia de Alimentos, Instituto de la Grasa y zyxw sus Derivados (CSZC), Avda. Padre Garcia Tejero, zyxwvuts 4, Apdo. 1078,41012 Sevilla, Spain Received 25 October 1990 and accepted 27 October 1990 Paper number: GWGI114 RUIZ-BARBA, J.L., GARRIDO-FERNANDEZ, A. & JIMENEZ-DIAZ, R. 1991. Bactericidal action of oleuropein from green olives against Lactobacillus plantarum. Letters in Applied Microbiology 12. 65-68, The phenolic compound oleuropein extracted from green olives was shown to be bactericidal against nine strains of Lactobacillus plantarum isolated from green olive fermentation brines. Heat-treated oleuropein also demonstrated a strong bacteri- cidal effect but not alkali-treated oleuropein, which allowed survival of most of the strains tested. The bactericidal effect was accompanied by changes in the typical bacillary structure and Gram-positive stain of L. plantarum. Production of fermented green olives is an eco- nomically important industry in all the mediter- ranean countries. The fermentative process is mainly due to the growth of Lactobacillus plan- tarum in brines, which produces the high quan- tities of lactic acid necessary for olive preservation (Vaughn et al. 1943; Etchells et al. 1966; Borbolla y Alcala et al. 1971). Many factors are known to limit this complex fermen- tation but it is well established that certain phe- nolic compounds present in the olives are the major ones (Etchells et al. 1966; Fleming & Etchells 1967; Juven et al. 1968b; Fleming et al. 1969; Juven & Henis 1970; Fleming et al. 1973; Ruiz-Barba & Jimenez-Diaz 1989; Ruiz-Barba et al. 1990). They affect the normal development of L. plantarum in brines, which leads to an inadequately fermented product. Nevertheless, controversy exists about the antibacterial properties of oleuropein, a bitter glucoside present in significant amounts in the pulp of olive fruits (Vazquez-Roncero et al. 1974). After it was described by Juven et al. * Corresponding author (1968b) as inhibiting the growth of various bac- teria, including L. plantarum, no such activity for the glucoside was recorded by Fleming et al. (1973) or Federici & Bongi (1983). Garrido- Fernandez & Vaughn (1978) even reported uti- lization of oleuropein by micro-organisms associated with olive fermentations. One of the reasons for the controversy could be the use of rich assay media to carry out the tests. In fact, it has been demonstrated that the presence of organic nitrogenous compounds (amino acids or proteins) in the assay medium can mask the antibacterial properties of certain phenolic com- pounds present in the green olive fermentation brines (Ruiz-Barba & Jimenez-Diaz 1989). In order to improve the fermentation of olives, an increasing knowledge about the role of phenolic compounds in this fermentative process is necessary. So, the aim of this work was to establish whether oleuropein has any antimicrobial activity against L. plantarum when tested in an assay medium which avoids the above-described interferences. Activity was also determined following treatments known to enhance the fermentation of olives (heat and