Search

Zebrafish (Danio rerio) hold immense promise for the study of learning and memory. Several attractive properties characterize this vertebrate animal model. For instance, zebrafish possesses a relatively reduced neural circuitry, which facilitates the drawing of causal relationships between changes on the behavioral scale to changes on the cellular-molecular level. They can also be affected by and absorb pharmacological agents in bath, and undergo learning and memory paradigms as early as 5 days post-fertilization (dpf). In particular, following a brief introduction of a noxious stimulus, allyl isothiocyanate (mustard oil, MO), 5-6 dpf zebrafish exhibit short-term sensitization. This memory has been demonstrated behaviorally through increased thigmotaxis and locomotion. However, the neuromodulatory mechanisms behind this non-declarative, non-associative form of memory remains to be elucidated. Exploiting this animal model’s strengths, we placed zebrafish under high-throughput pharmacological dissections with dopamine-receptor antagonists SCH-23390, eticlopride hydrochloride, haloperidol, and L-745,870 trihydrochloride in order to determine the role of dopamine and delineate receptor subtype-specific influences. These blockades have not only confirmed the role of dopamine, but also have demonstrated a differential involvement of the receptor subtypes within the two behaviors. Nonetheless, further investigations are required in order to determine the influence of other neuromodulators in the establishment of MO-induced short-term sensitization.

Since 2006 there have been four Salmonella enterica and one Listeria monocytogenes foodborne outbreaks linked to whole cantaloupe fruit. No post-harvest intervention to reduce potential contamination on cantaloupe currently exists. The complex surface topography of netted cantaloupes aids bacterial attachment. This research evaluates the use of allyl isothiocyanate (AITC; a natural antimicrobial) to reduce populations of S. enterica Michigan and L. monocytogenes on the surface of cantaloupe. Fifty μl of S. Michigan or L. monocytogenes was inoculated onto whole ‗Athena‘ or ‗Hales Best Jumbo‘ (‗HBJ‘) cantaloupe fruit in 22 mm diameter circles and allowed to dry for 90 min. resulting in 6.60 log CFU/g. Cantaloupe received either AITC liquid or vapor, sterile deionized water, 200 ppm sodium hypochlorite per circle, or no treatment. All cantaloupes were stored in separate sealed glass desiccators for 1 or 24 h at 25°C or 35°C. To enumerate the bacteria following treatment, 22 mm sections of the rind were removed, homogenized and plated onto appropriate agar. Headspace analysis using Gas Chromatography-Mass Spectrometry (GC-MS) quantified the concentration of each AITC vapor treatment. The texture quality of the pericarp tissue of whole cantaloupes was evaluated after 24 h treatments, followed by two weeks of storage at 4°C. The concentration of vapor ranged from 3.4 to 19.6 μl AITC/L inside the desiccators. The liquid treatment reduced (P < 0.05) S. Michigan populations on ‗Athena‘ (3 log CFU/g) and L. monocytogenes on ‗HBJ‘ (2.6 log CFU/g). The longer exposure time to the AITC vapor (24 h versus 1 h) resulted in a greater reduction of both S. Michigan and L. monocytogenes on ‗Athena‘ and treatments at 35°C reduced microbial populations up to 4.5 times greater (P < 0.05). The highest vapor concentration reduced (P < 0.05) both pathogens at least 3.0 log CFU/g on ‗Athena‘ at 25°C. Generally, bacterial pathogens from the surface of ‗Athena‘ cantaloupe were reduced more than pathogens inoculated on the surface of ‗HBJ.‘ The application of AITC liquid or vapor is a natural alternative post-harvest treatment to 200 ppm free chlorine to reduce the level of bacterial contamination on cantaloupe surfaces for certified organic production.

Wasabi (Wasabia japonica (Miq.) Matsum) is an aromatic herb that adds a sharp hot taste and pungent smell to food and, therefore, is highly appreciated in Japanese cuisine. Recently wasabi has emerged as a new flavour in western cuisine. The unique flavour of wasabi comes from the isothiocyanate (ITC) content which is the key quality parameter of wasabi. This research was performed to investigate the factors which affect the ITC profile in wasabi, as a way to support the emerging wasabi industry in New Zealand. The present study highlighted the existence of a misconception concerning the flavour difference between wasabi and horseradish. Wasabi is known as Japanese horseradish, but differs in its ITC profile compared to European horseradish. The key indicator is 2-phenylethyl ITC, which is found only in European horseradish and gives it a radish like flavour. Thus, it is very important for processors to understand the differences in ITC profile between wasabi and horseradish to manufacture a product which has a unique wasabi flavour. Seven ITCs have been investigated in New Zealand grown wasabi and, among them, allyl ITC was the most abundant ITC, contributing 86-94% of the total ITC concentration. 3-butenyl ITC and 4-pentenyl ITC made up 3-8% of the total ITC while the other ITCs (iso-propyl ITC, isobutyl ITC, sec-butyl ITC, 5-hexenyl ITC) contribute very small amounts to the total ITC content. The two cultivation methods (soil and water) showed no variation in ITC yields of larger rhizomes (>45 g). In soil cultivated plants, ammonium sulphate fertiliser (containing 21 % N with 24% S) was very effective in significantly increasing ITC yields from 2316 mg/kg to 3366 mg/kg (a 45% increase of allyl ITC in the rhizomes compared to the control level) when applied at a rate of 200 kg N /ha. This treatment also highlighted the importance of N and S nutrients for ITC synthesis in wasabi, as both N and S are components of ITCs and the precursor glucosinolates (GSLs). A 61-77% increase of ITC yield was also observed in the rhizomes when the plants commenced flowering after 18 months of growth. Consequently, this result suggests that flowering is an important event in the crop management process. Among the four plant parts of wasabi, rhizomes yielded the highest level of all ITCs and traditionally this is the most important plant part. Other parts like petioles and leaves gave lower yields of ITCs, but could be used when lower concentration of ITCs are required in the final product. The larger rhizome, the outer layer and distal portion of the rhizome had a higher ITC yield than smaller rhizomes, the inner tissues and proximal portion of the rhizome respectively. Suitable storage conditions for rhizomes are very important to retain the quality of the raw materials and, therefore, products. This research showed that defrosting can potentially lead to large losses of ITCs from frozen rhizomes. For example, a 99.7% loss of allyl ITC was observed after 16 days when snap frozen rhizomes were defrosted slowly at 4°C. Storage at -10°C or lower temperatures (up to -80°C) for two months retained the original ITC levels in the rhizomes. The shelf life analysis of allyl ITC in mayonnaise-type sauces containing wasabi oil (4400 mg of total ITC/kg of oil) gave a life of 8-9 weeks (considering 5% loss of allyl ITC to be the end of satisfactory storage) when stored at between 4 to 30°C. Shelf life was reduced to less than 2 weeks for a tomato based sauce prepared with a lower amount of wasabi oil, higher water content and heat treated by pasteurisation at 90°C for 30 minutes under the same storage conditions. Overall the data obtained from this study will assist farmers and processors to produce high quality products using recently introduced wasabi crop in New Zealand.