title: Synergistic antimicrobial activity of caprylic acid in combination with citric acid against both Escherichia coli O157:H7 and indigenous microflora in carrot juice.
abstract: The identification of novel, effective, and non-thermal decontamination methods is imperative for the preservation of unpasteurized and fresh vegetable juices. The aim of this study was to examine the bactericidal effects of caprylic acid + citric acid against the virulent pathogen Escherichia coli O157:H7 and the endogenous microflora in unpasteurized fresh carrot juice. Carrot juice was treated with either caprylic acid, citric acid, or a combination of caprylic acid + citric acid at mild heating temperature (45 °C or 50 °C). The color of the treated carrot juice as well as microbial survival was examined over time. Combined treatment was more effective than individual treatment in terms of both color and microbial survival. Caprylic acid + citric acid treatment (each at 5.0 mM) at 50 °C for 5 min resulted in 7.46 and 3.07 log CFU/ml reductions in the E. coli O157:H7 and endogenous microflora populations, respectively. By contrast, there was no apparent reduction in either population following individual treatment. A validation assay using a low-density E. coli O157:H7 inoculum (3.31 log CFU/ml) showed that combined treatment with caprylic acid (5.0 mM) + citric acid (2.5 mM) at 50 °C for >5 min or with caprylic acid + citric acid (both at 5.0 mM) at either 45 °C or 50 °C for >5 min completely destroyed the bacteria. Combined treatment also increased the redness of the juice, which is a perceived indication of quality. Taken together, these results indicate that combined treatment with low concentrations of caprylic acid and citric acid, which are of biotic origin, can eliminate microorganisms from unpasteurized carrot juice.
authors.affiliation: Department of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: S A
authors.initials: SA
authors.lastname: Kim
authors.affiliation: Department of Food Bioscience and Technology, College of Life-Sciences and Biotechnology, Korea University, Seoul 136-713, Republic of Korea. Electronic address: rheems@korea.ac.kr.
authors.forename: M S
authors.initials: MS
authors.lastname: Rhee
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification; D001628:Beverages / Q000382:microbiology*; D002210:Caprylates / Q000494:pharmacology*; D019343:Citric Acid / Q000494:pharmacology*; D018552:Daucus carota / Q000737:chemistry / Q000382:microbiology*; D004357:Drug Synergism; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development; D005503:Food Additives / Q000494:pharmacology*; D064307:Microbiota / Q000187:drug effects*
chemical_list: D002210:Caprylates; D005503:Food Additives; D019343:Citric Acid; C031492:octanoic acid
keywords: Caprylic acid; Citric acid; Escherichia coli O157:H7; Indigenous microbial community; Natural food preservatives; Unpasteurized carrot juice