The Anti-Listeria Activity of Pseudomonas fluorescens Isolated from the Horticultural Environment in New Zealand.

Beneficial bacteria with antibacterial properties are attractive alternatives to chemical-based antibacterial or bactericidal agents. Our study sourced such bacteria from horticultural produce and environments to explore the mechanisms of their antimicrobial properties. Five strains of Pseudomonas fluorescens were studied that possessed antibacterial activity against the pathogen Listeria monocytogenes. The vegetative culture of these strains (Pseudomonas fluorescens-PFR46I06, Pseudomonas fluorescens-PFR46H06, Pseudomonas fluorescens-PFR46H07, Pseudomonas fluorescens-PFR46H08 and Pseudomonas fluorescens-PFR46H09) were tested against Listeria monocytogenes (n = 31), Listeria seeligeri (n = 1) and Listeria innocua (n = 1) isolated from seafood and horticultural sources and from clinical cases (n = 2) using solid media coculture and liquid media coculture. All Listeria strains were inhibited by all strains of P. fluorescens; however, P. fluorescens-PFR46H07, P. fluorescens-PFR46H08 and P. fluorescens-PFR46H09 on solid media showed good inhibition, with average zones of inhibition of 14.8 mm, 15.1 mm and 18.2 mm, respectively, and the other two strains and P. fluorescens-PFR46H09 had a significantly greater zone of inhibition than the others (p < 0.05). There was no inhibition observed in liquid media coculture or in P. fluorescens culture supernatants against Listeria spp. by any of the P. fluorescens strains. Therefore, we hypothesized that the structural apparatus that causes cell-to-cell contact may play a role in the ejection of ant-listeria molecules on solid media to inhibit Listeria isolates, and we investigated the structural protein differences using whole-cell lysate proteomics. We paid special attention to the type VI secretion system (TSS-T6SS) for the transfer of effector proteins or bacteriocins. We found significant differences in the peptide profiles and protein summaries between these isolates' lysates, and PFR46H06 and PFR46H07 possessed the fewest secretion system structural proteins (12 and 11, respectively), while PFR46H08 and PFR46H09 had 18 each. P. fluorescens-PFR46H09, which showed the highest antimicrobial effect, had nine tss-T6SS structural proteins compared to only four in the other three strains.

Identifying Suitable Listeria innocua Strains as Surrogates for Listeria monocytogenes for Horticultural Products.

A laboratory-based study testing 9 Listeria innocua strains independently and a cocktail of 11 Listeria monocytogenes strains was carried out. The aim was to identify suitable L. innocua strain(s) to model L. monocytogenes in inactivation experiments. Three separate inactivation procedures and a hurdle combination of the three were employed: thermal inactivation (55°C), UV-C irradiation (245 nm), and chemical sanitizer (TsunamiTM 100, a mixture of acetic acid, peroxyacetic acid, and hydrogen peroxide). The responses were strain dependent in the case of L. innocua with different strains responding differently to different regimes and L. innocua isolates generally responded differently to the L. monocytogenes cocktail. In the thermal inactivation treatment, inactivation of all strains including the L. monocytogenes cocktail plateaued after 120 min. In the case of chemical sanitizer, inactivation could be achieved at concentrations of 10 and 20 ppm with inactivation increasing with contact time up to 8 min, beyond which there was no significant benefit. All L. innocua strains except PFR16D08 were more sensitive than the L. monocytogenes cocktail to the hurdle treatment. PFR16D08 almost matched the resistance of the L. monocytogenes cocktail but was much more resistant to the individual treatments. A cocktail of two L. innocua strains (PFR 05A07 and PFR 05A10) had the closest responses to the hurdle treatment to those of the L. monocytogenes cocktail and is therefore recommended for hurdle experiments.

The kiwifruit lycopene beta-cyclase plays a significant role in carotenoid accumulation in fruit.

The composition of carotenoids, along with anthocyanins and chlorophyll, accounts for the distinctive range of colour found in the Actinidia (kiwifruit) species. Lutein and beta-carotene are the most abundant carotenoids found during fruit development, with beta-carotene concentration increasing rapidly during fruit maturation and ripening. In addition, the accumulation of beta-carotene and lutein is influenced by the temperature at which harvested fruit are stored. Expression analysis of carotenoid biosynthetic genes among different genotypes and fruit developmental stages identified Actinidia lycopene beta-cyclase (LCY-beta) as the gene whose expression pattern appeared to be associated with both total carotenoid and beta-carotene accumulation. Phytoene desaturase (PDS) expression was the least variable among the different genotypes, while zeta carotene desaturase (ZDS), beta-carotene hydroxylase (CRH-beta), and epsilon carotene hydroxylase (CRH-epsilon) showed some variation in gene expression. The LCY-beta gene was functionally tested in bacteria and shown to convert lycopene and delta-carotene to beta-carotene and alpha-carotene respectively. This indicates that the accumulation of beta-carotene, the major carotenoid in these kiwifruit species, appears to be controlled by the level of expression of LCY-beta gene.

Kiwifruit-based polyphenols and related antioxidants for functional foods: kiwifruit extract-enhanced gluten-free bread.

The present study investigates the production of gluten-free bread enhanced with polyphenols and related antioxidants derived from a natural aqueous extract from green-fleshed kiwifruit (Actinidia deliciosa). Puree and four aqueous extracts, produced from ripe green kiwifruit in the absence of artificial preservatives, were subjected to storage stability trials at 4 degrees C, 20 degrees C and 38 degrees C, and were chemically characterized (phenolic, vitamin C and pectic polysaccharide contents). The aqueous extract with good stability and high phenolic and vitamin C contents was used for gluten-free bread-making. The resultant kiwifruit extract-enhanced bread was acceptable to a taste panel, possessing softer and smoother texture than plain gluten-free bread. Thus, the aqueous extract of kiwifruit puree containing health-beneficial constituents can be considered a functional ingredient for gluten-free bread formulation.

Chemical composition and in vitro anti-inflammatory activity of apple phenolic extracts and of their sub-fractions.

Apple extract powders from three different manufacturers were investigated for their anti-inflammatory activity, their total phenolic content, and their chemical composition. The samples represented two production batches for two products and a single batch of a third. The samples showed similar, but clearly different, anti-inflammatory activities, and had substantially different total phenolic contents, and different chemical compositions. Differences in chemical composition for batches of the same product were significant, although not as great as differences between products. The samples were fractionated into chemical classes. The most active fractions were those that contained epicatechin, catechin with phloridzin and quercetin glycosides, or those that contained procyanidin polymers. It was not possible to link activity to the presence of individual components or combinations of these. If fruit extracts are to be reliably linked to validated health benefits, then the source materials, the extraction processes, and the final composition of such products need to be more clearly defined than at present.

Comparison of enzymically glucuronidated flavonoids with flavonoid aglycones in an in vitro cellular model of oxidative stress protection.

This study modeled, in vitro, the potential effect of conjugative (phase II) metabolism on the cytoprotective capacity of fruit flavonoids against oxidative stress. Flavonoid aglycones were compared with their corresponding isomeric mixtures of glucuronides for their ability to enhance the survival of cultured human Jurkat T and neuroblastoma cells stressed with hydrogen peroxide. Various polyphenolic compounds were tested as substrates in vitro for an ovine liver glucuronyl transferase preparation. Flavonoids and their glycoside derivatives were found to be good substrates, whereas phenolic acids were either poor or nonsubstrates. Five common flavonoids were glucuronidated to prepare mixtures for bioassay testing. Glucuronidation generally weakened the cytoprotective capacities of flavonoids (in the presence of H(2)O(2)), but some compounds were weakened much more than others. The concentration that halved cell death was well below 0.5 microM for most flavonoids tested, but glucuronidation increased median effective concentration values to a range of 1-16 microM. This compares with the generally accepted physiological range (0.1-10 microM) for circulating dietary polyphenolics detected in the body. Therefore, some flavonoids may retain a reduced cytoprotective capacity in vitro, after glucuronidation, whereas others may be effectively inactivated.

Comparison of the relative recovery of polyphenolics in two fruit extracts from a model of degradation during digestion and metabolism.

To simulate the effects of digestion and metabolism on the survival of different polyphenolic compounds, extracts of blueberry and apple were deglycosylated by acid hydrolysis, followed by enzymic glucuronidation under neutral conditions, yielding approximately 5% overall recovery of polyphenolics. The major polyphenolics before and after the treatment were compared, to estimate which species are likely to be present in the intestinal lumen, undegraded and available for absorption, after consumption of the fruit. Whereas blueberry extract consisted predominantly of anthocyanins, epicatechin and caffeoyl quinate esters, the major components of the treated extract were quercetin glucuronides and (unglucuronidated) caffeoyl quinates, with only traces of anthocyanidin derivatives. In apple extract, compositional changes were less marked, but caffeoyl quinates, procyanidins and quercetin were enriched at the expense of caffeic acid, epicatechin and catechin. Hydrophobic compounds like phloretin and quercetin were extensively glucuronidated, whereas caffeic acid and caffeoyl quinate were not. These results suggest that the major polyphenolic components of a fruit are not necessarily the most important contributors to any health benefits because the polyphenolic composition in the intestinal lumen and consequently, in the circulation, may be considerably different.