Measurement of ascorbic acid in Australian native plants

Ascorbic acid is one of the compounds found in a number of commercially important native plants fruits e.g. Kakadu plum, wild lime and bush tomato. High performance liquid chromatography (HPLC) was used to determine ascorbic acid in these native plant fruits. Ascorbic acid degradation of both standards and plant extracts was observed during HPLC sequence runs. These losses were considerable even though factors such as light, temperature and water activity, which accelerate the loss of ascorbic acid, were eliminated. Several concentrations of sodium metabisulphite were added to both standards and plant extracts to evaluate the effect on the rate of ascorbic acid degradation. A concentration of 500 μg/mL was the most effective but did not eliminate the problem. To correct for any loss still occurring, the rate constant k for ascorbic acid degradation was calculated and used to extrapolate back to the original ascorbic acid concentration. The k value was also found to vary for the different plants studied. For example the k value without added sodium metabisulphite for Kakadu plum, wild lime and Kakadu plum intermediate raw material were 0.00532, 0.02710 and 0.04429 respectively. With the addition of 500 μg/mL sodium metabisulphite the k value decreased to 0.00005, 0.00915 and 0.00586 respectively

A Critical Review of the \u3csup\u3e15\u3c/sup\u3eN\u3csub\u3e2\u3c/sub\u3e Tracer Method to Measure Diazotrophic Production in Pelagic Ecosystems

Dinitrogen (N2) fixation is an important source of biologically reactive nitrogen (N) to the global ocean. The magnitude of this flux, however, remains uncertain, in part because N2 fixation rates have been estimated following divergent protocols and because associated levels of uncertainty are seldom reported—confounding comparison and extrapolation of rate measurements. A growing number of reports of relatively low but potentially significant rates of N2 fixation in regions such as oxygen minimum zones, the mesopelagic water column of the tropical and subtropical oceans, and polar waters further highlights the need for standardized methodological protocols for measurements of N2 fixation rates and for calculations of detection limits and propagated error terms. To this end, we examine current protocols of the 15N2 tracer method used for estimating diazotrophic rates, present results of experiments testing the validity of specific practices, and describe established metrics for reporting detection limits. We put forth a set of recommendations for best practices to estimate N2 fixation rates using 15N2 tracer, with the goal of fostering transparency in reporting sources of uncertainty in estimates, and to render N2 fixation rate estimates intercomparable among studies

Drying of lemon myrtle (Backhousia citriodora) leaves: Retention of volatiles and color

Lemon myrtle plant (Backhousia citriodora) leaves were dried at three different drying temperature conditions (30, 40, and 50°C) in a fluidized bed dryer. The retention of the principal volatile compound, citral, was analyzed in dried products obtained at these three drying conditions. The changes in the color parameters L*, a*, b* of leaves were also analyzed. More than 90% of citral was retained at 50°C drying temperature, whereas the retention at 30 and 40°C was 81 and 85%, respectively, suggesting that higher temperature is beneficial to achieve higher retention of volatiles. However, in terms of the color, all the color parameters were changed maximum at 50°C drying temperature unfavorably, suggesting that the higher temperature drying causes more degradation of the pigment. Blanching of the leaves in hot water at 80°C for 1 min prior to drying did not result in any improvement in volatile retention or color

Effect of calcium infiltration on ripening of avocados of different maturities

Mature but unripe Fuerte and Hass avocados harvested at 3 stages of maturity were vacuum-infiltrated with 4 and 8% calcium chloride (CaCl) solutions and stored at 20°C. The fruit were assessed for ripening and injury development and analysed for Ca content. Postharvest application of Ca to fruit harvested 2 weeks before prime harvest elicited a greater delay in ripening and caused less fruit injury than application at prime harvest or 2 weeks after prime harvest. Fruit maturity did not have a significant effect on the amount of Ca taken up by fruit when infiltrated with each CaClsolution. Vacuum infiltration with 8% CaClsolution greatly enhanced the uptake of Ca by both Hass and Fuerte fruit but did not delay ripening further than 4% CaCltreatment

In vitro antibacterial activity of Australian native herb extracts against food-related bacteria

The antibacterial activities of water, ethanol and hexane extracts of five Australian herbs (Backhousia citriodora, Anetholea anisata, Eucalyptus staigerana, Eu. olida and Prostanthera incisa) against seven food-related bacteria (Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Enteritidis, Sal. Typhimurium and Staphylococcus aureus) were determined by the microtitre broth microdilution assay. The water extracts of all the herbs displayed no or low antimicrobial activity against all of the bacteria tested with the exception of S. aureus. Relatively high levels of activity (minimum inhibitory concentrations of 125-15.6 mu g ml(-1)) against this pathogen were present in water extracts from all herbs except P. incisa. The ethanol and hexane extracts of all herbs displayed some activity against a number of the bacteria tested, with no one particular herb displaying an obviously higher level or range of activity. Staphylococcus aureus proved to be the most sensitive of the bacteria tested against the solvent extracts with all extracts displaying activity ranging from 125 to 7.8 mu g ml(-1), while E. coli and L. monocytogenes, on the other hand, proved the least sensitive with only five of 15 herb/extract combinations displaying any activity against these pathogens. The extracts of the Australian native herbs examined in this study have potential for application in foods to increase shelf-life or promote safety. (c) 2005 Elsevier Ltd. All rights reserved

Phenolic compound profiles in selected Queensland red wines at all stages of the wine-making process

The phenolic profiles of Queensland red wines (two Cabernet Sauvignons and one Shiraz) from different stages of wine-making were studied. Samples were taken at crush, after the primary and malolactic fermentations, post-oaking, and post-bottling, and then extracted and separated into aqueous and organic fractions using liquid liquid extraction and solid-phase extraction, and analysed by HPLC-DAD-MS. About 75% of the phenolic compounds were extracted into the aqueous fraction, with malvidin-3-glucoside and derivatives as the main components. The major non-anthocyanin phenolic compounds (similar to 25%) included gallic acid, syringic acid, ethyl gallate, caftaric acid, coutaric acid, caffeic acid, coumaric acid, catechin, and quercetin. The polymerisation of anthocyanins was shown to occur progressively throughout the wine-making process. Most of the 25 identified phenolic compounds had highest concentrations during the fermentation stage, and stabilised or slowly decreased thereafter. There were weak and insignificant correlations (P > 0.05) between individual phenolic compounds and the total antioxidant activities (ORAC). Four groups of phenolic compounds (anthocyanins, hydroxybenzoic acids, flavanols and hydroxycinnamic acids) each showed some correlation with the total antioxidant activity, as did the total polyphenol content, suggesting that the antioxidant properties of red wine are due to a complex mixture of phenolic compounds that vary in composition throughout the wine-making process. (C) 2010 Elsevier Ltd. All rights reserved