Kareen Stanich

Antimicrobial activity of individual and mixed fractions of dill, cilantro, coriander and eucalyptus essential oils.

Essential oils from dill (Anethum graveolens L.), coriander (seeds of Coriandrum sativum L.), cilantro (leaves of immature C. sativum L.) and eucalyptus (Eucalyptus dives) were separated into heterogeneous mixtures of components by fractional distillation and were analyzed by gas chromatography-mass spectroscopy. Minimum inhibitory concentrations against gram-positive bacteria, gram-negative bacteria and Saccharomyces cerevisiae were determined for the crude oils and their fractions. Essential oil of cilantro was particularly effective against Listeria monocytogenes, likely due to the presence of long chain (C6-C10) alcohols and aldehydes. The strength and spectrum of inhibition for the fractions often exceeded those determined in the crude oils. Mixing of fractions resulted in additive, synergistic or antagonistic effects against individual test microorganisms.

Antilisterial activity of selected phenolic-acids

Phenolic acids are known to exhibit antimicrobial activity against a variety of micro-organisms. Their influence on the behavior of Listeria monocytogenes, particularly in foods derived from plants, is not well understood. Several phenolic acids including chlorogenic acid and the hydroxycinnamic acids, caffeic acid, p-coumaric acid and ferulic acid, were screened for activity against five strains of L. monocytogenes using a broth dilution method. Minimum inhibitory concentrations ranged between 0.20% and 0.27% (w/vol) for the hydroxycinnamic acids, but chlorogenic acid was ineffective at 1.0% (w/vol). Mixtures of the acids generally exhibited additive antilisterial effects in a checkerboard assay. Growth experiments performed at pH 4.5, 5.5 and 6.5 revealed a strong relationship between pH and activity. All the hydroxycinnamic acids were bactericidal at pH 4.5 and bacteriostatic at higher pH. In contrast, chlorogenic acid inhibited growth of L. monocytogenes only at pH 6.5. The implications of these finding for the ecology of the species in foods are discussed.

Disinfection of mung bean seed with gaseous acetic acid

Mung bean seed inoculated with Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes (3 to 5 log CFU/g) was exposed to gaseous acetic acid in an aluminum fumigation chamber. Salmonella Typhimurium and E. coli O157:H7 were not detected by enrichment of seeds treated with 242 microl of acetic acid per liter of air for 12 h at 45 degrees C. L. monocytogenes was recovered by enrichment from two of 10 25-g seed samples treated in this manner. Fumigation with gaseous acetic acid was also lethal to indigenous bacteria and fungi on mung bean seed. The treatment did not significantly reduce seed germination rates, and no differences in surface microstructure were observed between treated and untreated seed viewed by scanning electron microscopy.

Effect of pH on the inhibition of Listeria spp. by vanillin and vanillic acid.

The antimicrobial effects of vanillin and vanillic acid were verified against several species and strains of Listeria monocytogenes, Listeria innocua, Listeria grayi, and Listeria seeligeri in a laboratory medium adjusted to pH values ranging from 5.0 to 8.0. Medium pH had little influence on the MIC of vanillin as determined by a broth dilution assay, and growth of all test strains was inhibited by concentrations ranging from 23 to 33 mM. In contrast, none of the strains were inhibited by 100 mM vanillic acid at pH > 6.0, but complete inhibition was achieved at pH 5.0 with 10 mM. The effect of pH was further characterized by incubation of L. monocytogenes, L. innocua, and L. grayi in media containing 30 mM vanillin or 60 mM vanillic acid at pH 5.0, 6.0, and 7.0. Bactericidal effects increased with pH in media supplemented with vanillin. An inverse relationship was found for vanillic acid, and the lethality of the compound increased with declining pH. Mixtures of vanillin and vanillic acid exhibited additive inhibitory effects, particularly at lower pH. These natural antimicrobial compounds could prove useful either alone or in mixtures for the control of Listeria spp. in food products.

Evidence of an antilisterial factor induced by wounding of iceberg lettuce tissues

Aims:  To examine the influence of wound‐associated reactions in cut iceberg lettuce (Lactuca sativa L.) tissues on the fate of Listeria monocytogenes.

Destruction of Escherichia coli O157:H7 by vanillic acid in unpasteurized juice from six apple cultivars.

The behavior of Escherichia coli O157:H7 in Granny Smith, Gala, Empire, McIntosh, Red Delicious, and Golden Delicious apple juice with or without supplementation with 5 or 10 mM vanillic acid was examined over a storage period of 7 days at 4 and 15 degrees C. The consequences of supplementation on sensory difference and preference were also determined by triangle testing. Juices made from the six apple cultivars had pH values ranging between pH 3.13 and 3.92. Vanillic acid exerted a concentration, pH, and time-dependent lethal effect toward E. coli O157:H7 in unpasteurized apple juice. Supplementation with 10 mM vanillic acid led to a 5-logarithm reduction in populations after 7 days at both temperatures, but sensory analysis revealed significant differences from and preference for unsupplemented juices. Supplementation with 5 mM vanillic acid accelerated death of E. coli O157:H7, but population reductions ranged from 5 log CFU/ml in low pH juices to none in high pH juices, particularly at 4 degrees C. No sensory difference or preference was detected in two of the six juices at this level of supplementation.

Antilisterial Properties of Cilantro Essential Oil

Abstract The minimum inhibitory concentrations (MIC) of crude essential oil of cilantro (Coriandrum sativum L.) and four fractions recovered by fractional distillation of the crude oil were determined against strains of Listeria monocytogenes, Listeria grayi, Listeria innocua and Listeria seeligeri. Crude oil inhibited all the test strains at concentrations ≤ 0.01% (v/v) and the remaining fractions were effective at concentrations < 0.07% (v/v). One fraction comprising a complex mixture of alcohols, aldehydes, alkanes and terpenes, including high concentrations of (E)-2-decenal, exhibited slightly greater potency than the other fractions. Listericidal activity was demonstrated by a rapid loss in cell viability upon exposure to crude oil dissolved in Tryptic Soy Broth. Cilantro oil is a potent antilisterial plant extract with potential applications as a food preservative or in the formulation of disinfectants for the control of Listeria monocytogenes in the food processing environment.

Shelf-life and sensory assessments reveal the effects of storage treatments with 1-methylcyclopropene on new and established apples

Stanich, K., Cliff, M. A., Hampson, C. R. and Toivonen, P. M. A. 2014. Shelf-life and sensory assessments reveal the effects of storage treatments with 1-methylcyclopropene on new and established apples. Can. J. Plant Sci. 94: 1427-1439. This research used shelf-life and sensory assessments to explore the influence of 1-methylcyclopropene (1-MCP) on four apples (Aurora, Fuji, Nicola™, Salish™). Maturity (internal ethylene concentration, starch clearing index), quality (soluble solids, titratable acidity, firmness) and sensory determinations were conducted on fruit that had undergone air (AIR) or controlled atmosphere (CA) storage treatments with and without 1-MCP. Trained panelists evaluated apples, along with industry standards (Gala, McIntosh and either Fuji or Ambrosia), for eight attributes (crispness, hardness, juiciness, skin toughness, sweetness, tartness, sweet-tart balance and flavour). Data were analyzed using analysis of variance and principal component analyses (PCA) to compare the treatment and cultivar responses. Cultivars responded very differently to CA and 1-MCP. Fruit from AIR with 1-MCP were very similar to CA fruit without 1-MCP; further improvements were not observed when 1-MCP was applied to CA fruit. PCA bi-plots of the shelf-life and sensory assessments revealed that treated Salish™ fruits were more similar to one another than to cultivars from other treatments. This work successfully documented the unique changes associated with the use of 1-MCP on new and established apple cultivars. It will assist industry in applying appropriate storage practices for new and established apple cultivars.

The use of reflective tarps at harvest to improve postharvest quality of blueberries

Effects of covering blueberries with reflective tarps to protect the fruit from exposure to the sun after picking were assessed. Quality was evaluated after 7 d storage at 1%C as well as after two additional days holding at 13%C. Covering fruit with reflective tarps resulted in significant improvement in quality. Improved quality of the blueberries was attributed to the lower fruit pulp temperatures and higher humidity in the airspace surrounding the tarp-covered fruit. Key words: Postharvest handling, temperature, humidity, reflective (laminated Mylar) film, microbial populations

Evaluation of the Sensory, Physicochemical, and Visual Characteristics of a Sweet Cherry Cultivar Treated in a Commercial Orchard with a Cherry Cuticle Supplement when a Rainfall Event Does Not Occur

The splitting of sweet cherry (Prunus aviumL.) just before harvest can be a considerable problem in the Okanagan Valley (BC, Canada). In an attempt to minimize economic losses, growers apply a commercial cherry cuticle supplement in anticipation of a rainfall event.However, it is unknown if this product affects flavor, texture (crispness, firmness, and juiciness), or visual characteristics (stem browning, pitting, and pebbling) of sweet cherry. Therefore, this research was undertaken to evaluate the effects of a cherry cuticle supplement on the sensory, physicochemical, and visual characteristics of ‘Skeena’ sweet cherry. Firmness measurements were assessed with a fruit-firmness tester, whereas sensory determinations were assessed at first bite (whole-cherry crispness) and after multiple chews (flesh firmness) by a panel of 14 trained panelists. Fruit treated with the cherry cuticle supplement had lower instrumental firmness compared with the control, which was most pronounced after 28 days, with a reduction of 0.53 N. Treated fruit also had significantly lower sensory firmness and higher juiciness than the control fruit. Fruit treated with the cherry cuticle supplement had reduced water loss, less pitting, and lower stem-pull force, resulting in higher frequency of detachment of the stems. Further research would be necessary to evaluate the effects with other cultivars, and in years with rainfall events, as well as when hydrocooling is used.