Patrick Silcock

Aboveground endophyte affects root volatile emission and host plant selection of a belowground insect

Plants emit specific blends of volatile organic compounds (VOCs) that serve as multitrophic, multifunctional signals. Fungi colonizing aboveground (AG) or belowground (BG) plant structures can modify VOC patterns, thereby altering the information content for AG insects. Whether AG microbes affect the emission of root volatiles and thus influence soil insect behaviour is unknown. The endophytic fungus Neotyphodium uncinatum colonizes the aerial parts of the grass hybrid Festuca pratensis × Lolium perenne and is responsible for the presence of insect-toxic loline alkaloids in shoots and roots. We investigated whether endophyte symbiosis had an effect on the volatile emission of grass roots and if the root herbivore Costelytra zealandica was able to recognize endophyte-infected plants by olfaction. In BG olfactometer assays, larvae of C. zealandica were more strongly attracted to roots of uninfected than endophyte-harbouring grasses. Combined gas chromatography–mass spectrometry and proton transfer reaction-mass spectrometry revealed that endophyte-infected roots emitted less VOCs and more CO2. Our results demonstrate that symbiotic fungi in plants may influence soil insect distribution by changing their behaviour towards root volatiles. The well-known defensive mutualism between grasses and Neotyphodium endophytes could thus go beyond bioactive alkaloids and also confer protection by being chemically less apparent for soil herbivores.

Fast Phenotyping of LFS-Silenced (Tearless) Onions by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS)

Fast MS techniques have been applied to the analysis of sulfur volatiles in Allium species and varieties to distinguish phenotypes. Headspace sampling by proton transfer reaction (PTR) MS and surface sampling by desorption electrospray ionization (DESI) MS were used to distinguish lachrymatory factor synthase (LFS)-silenced (tearless; LFS-) onions from normal, LFS-active (tear-inducing; LFS+), onions. PTR-MS showed lower concentrations of the lachrymatory factor (LF, 3) and dipropyl disulfide 12 from tearless onions. DESI-MS of the tearless onions confirmed the decreased LF 3 and revealed much higher concentrations of the sulfenic acid condensates. Using DESI-MS with MS(2) could distinguish zwiebelane ions from thiosulfinate ions. DESI-MS gave reliable fast phenotyping of LFS+ versus LFS- onions by simply scratching leaves and recording the extractable ions for <0.5 min. DESI-MS leaf compound profiles also allowed the rapid distinction of a variety of Allium cultivars to aid plant breeding selections.

Volatile release and structural stability of β-lactoglobulin primary and multilayer emulsions under simulated oral conditions.

The relationship between emulsion structure and the release of volatile organic compounds (VOCs) was investigated using a model mouth system under oral conditions (tongue mastication, artificial saliva, pH and salt). The VOCs were monitored on-line by proton transfer reaction mass spectrometry (PTR-MS). Two types of emulsion system were compared: primary and multilayer oil-in-water (P-O/W, M-O/W) emulsions consisting of soy oil coated by β-lactoglobulin and pectin layers. The P-O/W emulsions showed intensive flocculation at pH 5 and above 200 mM NaCl where the electrostatic repulsive charge was at a minimum. Bridging and depletion flocculation were mostly observed for P-O/W emulsions containing artificial saliva with 1 wt% mucin. The VOC release was found to increase when the emulsion droplets flocculated, thus changing the oil volume phase distribution. The adsorbed pectin layer stabilised the emulsion structure under conditions of short-time oral processing, and hindered the release of hydrophobic VOCs.

Effect of Season on the Sensory Quality of Sea Urchin (Evechinus chloroticus) Roe

The influence of season, gender, and reproductive maturity on the sensory properties (appearance, odor, taste, flavor, texture/mouth feel, and after taste) of roe from sea urchins (Evechinus chloroticus) was investigated. A trained sensory panel applied descriptive analysis, with a comprehensive sensory vocabulary of 35 descriptors to analyze sea urchin roe obtained from samples collected during the austral autumn, winter, summer, and spring, over a 2-y period. Sensory differences between genders were less pronounced in autumn (March to May) and winter (June to August) when more nutritive cells were present in the roe, and more pronounced over spring (September to November) and summer (December to February) months as the gametogenic cells matured. Roe from female sea urchins were commonly associated with sulfur odor, bitter taste, and metallic flavor, while roe from the male sea urchins were associated with sweet taste. During autumn, female roe were closest in sensory quality to male roe (least bitter and most sweet compared to other seasons), while there were little differences in sweetness and bitterness of male roe over the 4 seasons. Despite the relative size of the roe being lowest in autumn, it appeared to be the optimum season to harvest E. chloroticus sea urchins to obtain high-quality roe.

In Vitro and In Vivo Flavor Release from Intact and Fresh-Cut Apple in Relation with Genetic, Textural, and Physicochemical Parameters

UNLABELLED Flavor release from 6 commercial apple cultivars (Fuji, Granny Smith, Golden Delicious, Jonagold, Morgen Dallago, and Red Delicious) under static conditions (intact or fresh-cut samples) and during consumption of fresh-cut samples (nosespace) was determined by proton transfer reaction mass spectrometry. Textural (firmness, fracturability, flesh elasticity, and rupture) and physicochemical (pH, acidity, and water content) properties of the apples were also measured. Static headspace analysis of intact fruits revealed Fuji and Granny Smith apples had the lowest concentration for all measured flavor compounds (esters, aldehydes, alcohols, and terpenes), whereas Red Delicious apples had the highest. Fresh-cut samples generally showed a significant increase in total volatile compounds with acetaldehyde being most abundant. However, compared to intact fruits, cut Golden and Red Delicious apples had a lower intensity for ester related peaks. Five parameters were extracted from the nosespace data of peaks related to esters (m/z 43, 61), acetaldehyde (m/z 45), and ethanol (m/z 47): 2 associated with mastication (duration of mastication-t(con); time required for first swallowing event-t(swal)), and 3 related with in-nose volatile compound concentration (area under the curve-AUC; maximum intensity-I(max); time for achieving I(max)-t(max)). Three different behaviors were identified in the nosespace data: a) firm samples with low AUC and t(swal) values (Granny Smith, Fuji), b) mealy samples with high AUC, I(max), t(swal) values, and low t(con) (Morgen Dallago, Golden Delicious), and c) firm samples with high AUC and I(max) values (Red Delicious). Strengths and limitations of the methodology are discussed. PRACTICAL APPLICATION Volatile compounds play a fundamental role in the perceived quality of food. Using apple cultivars, this research showed that in vivo proton transfer reaction mass spectrometry (PTR-MS) could be used to determine the relationship between the release of volatile flavor compounds and the physicochemical parameters of a real food matrix. This finding suggests that in vivo PTR-MS coupled with traditional physicochemical measurements could be used to yield information on flavor release from a wide range of food matrices and help in the development of strategies to enhance food flavor and quality.

Bacillus Spores in the Food Industry: A Review on Resistance and Response to Novel Inactivation Technologies

The importance and challenges presented by Bacillus spores in the food industry are briefly outlined with a focus on Bacillus cereus. The structure and the mechanism of resistance exhibited by Bacillus spores are described, and the steps involved in their germination are included. Novel technologies, using no or only mild heat treatments, to inactivate Bacillus spores are covered, including ultraviolet radiation, pulsed electric field, and high-pressure processing, both as stand-alone techniques or techniques as part of a hurdle approach.

Emulsifying Properties of Legume Proteins Compared to β‐Lactoglobulin and Tween 20 and the Volatile Release from Oil‐in‐Water Emulsions

The emulsifying properties of plant legume protein isolates (soy, pea, and lupin) were compared to a milk whey protein, β-lactoglobulin (β-lg), and a nonionic surfactant (Tween 20). The protein fractional composition was characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The following emulsion properties were measured: particle diameter, shear surface ζ-potential, interfacial tension (IT), and creaming velocity. The effect of protein preheat treatment (90 °C for 10 min) on the emulsifying behavior and the release of selected volatile organic compounds (VOCs) from emulsions under oral conditions was also investigated in real time using proton transfer reaction-mass spectrometry. The legume proteins showed comparable results to β-lg and Tween 20, forming stable, negatively charged emulsions with particle diameter d3,2 < 0.4 μm, and maintained stability over 50 d. The relatively lower stability of lupin emulsions was significantly correlated with the low protein surface hydrophobicity and IT of the emulsion. After heating the proteins, the droplet size of pea and lupin emulsions decreased. The VOC release profile was similar between the protein-stabilized emulsions, and greater retention was observed for Tween 20-stabilized emulsions. This study demonstrates the potential application of legume proteins as alternative emulsifiers to milk proteins in emulsion products.

X-Ray Micro-Computer Tomographic Method to Visualize the Microstructure of Different Apple Cultivars

Apples are appreciated for their texture with firmness acting as an indicator of quality. During prolonged storage, apples can soften and their texture can become undesirably mealy. Using an X-ray microcomputer tomography (μ-CT) scanner, the porosity (ratio of intercellular space [IS] to total volume) and the structural arrangement of the parenchyma tissue of 4 apple cultivars (Braeburn, Fuji, Golden Delicious, Jazz) stored under similar conditions for 100 d were visualized via the development of 2D and 3D images. The texture of the apples was also measured using a puncture test. The morphometric and textural measurements revealed that firm Jazz apples (flesh firmness: 29.84N) had a lower porosity (17%) compared to soft Golden Delicious apples (flesh firmness: 14.16N; porosity: 29.8%). In general, firm apples had a higher dry matter (%) and a lower porosity (%), while the reverse was true for softer apples. However, this was not an absolute trend as cultivar specific differences in the microstructural organization and consequent mechanical strength of the parenchyma tissue also influenced firmness. For example, although Fuji apples were firm (28.42N), they had a high porosity (29.3%) due to the presence of numerous small and compact IS. In comparison, soft Golden Delicious apples had a high porosity (29.8%) due to the presence of large, interconnected IS. Imaging technologies have the potential to provide a pictorial or graphical database showing the size range distribution of IS corresponding to different parenchyma tissue types and how they relate to apple texture and eating quality.

Tongue Pressure and Oral Conditions Affect Volatile Release from Liquid Systems in a Model Mouth

The release of volatile organic compounds (VOCs) into the mouth cavity is an integral part of the way flavor is perceived. An in vitro model mouth with an artificial tongue was developed to measure the dynamic release of VOCs from liquid model systems [e.g., aqueous solution, oil, and oil-in-water (O/W) emulsions] under oral conditions. The release of seven selected VOCs was affected by the different polarity and vapor pressure of the compounds and their affinity to the liquid system media. Different tongue pressure patterns were applied to the liquid systems, and the release of VOCs was monitored in real time using proton transfer reaction-mass spectrometry. The release was significantly more intense for longer tongue pressure duration and was influenced by the tongue altering the sample surface area and the distribution of the VOCs. The role of saliva (artificial versus human) and the sample temperature had a significant effect on VOC release. Saliva containing mucin and a higher sample temperature enhanced the release.

Effects of pH, temperature and pulsed electric fields on the turbidity and protein aggregation of ovomucin-depleted egg white

The effect of either pulsed electric fields (PEF) or thermal processing on protein aggregation of ovomucin-depleted egg white (OdEW) solutions at different pH was assessed by solution turbidity and SDS-PAGE. Heating to 60°C for 10min caused marked protein aggregation of OdEW at pH5, 7, and 9. At constant electric field strength (E=1.4-1.8kV/cm), PEF processing under high specific energy input (Wspec=260-700kJ/kg) induced some protein aggregation at pH5 and 7, but not at either pH4 or 9. Similar effects of pH on protein aggregation were observed upon PEF processing at varied E (from 0.7 to 1.7kV/cm) but with constant Wspec (713kJ/kg). Analysis by SDS-PAGE revealed that proteins in the OdEW solution at pH5 were most susceptible to both PEF- and heat-induced protein aggregation and lysozyme was only involved in the formation of insoluble aggregates under PEF. The present study shows that PEF treatment has considerable potential for minimizing protein aggregation in the processing of heat-labile egg white proteins. Retaining the OdEW proteins in solution during processing has potential industry application, for example, protein fortification of drinks with OdEW, where minimizing solution turbidity would be advantageous.