Novel non-destructive quality assessment techniques of onion bulbs: a comparative study.

This study was designed to compare the performances of four different non-destructive methods of assessing onion quality, one of which was based on near-infrared spectroscopy, and three of which were based on spectral imaging. These methods involve a combination of wavelengths from visible to near-infrared with different acquisition systems that were applied to discriminate between pre-sorted onions by in situ measurements of the onion surface. Compared with the partial least squares discriminant analysis classification models associated with different methods, hyperspectral imaging (HSI) with both static horizontal and rotating orientation obtained a higher level of sensitivity and specificity with a lower classification error than did other methods. Moreover, models built with the reduced variables did not lower the model performances. Overall, these results demonstrate that HSI with selected wavelengths would be useful for further developing an improved real-time system for sorting onion bulbs.

Artemisinin production and precursor ratio in full grown Artemisia annua L. plants subjected to external stress.

The concentration of the lifesaving antimalarial compound artemisinin (AN) in cultivated Artemisia annua (A. annua) plants is relatively low, and thus research in improving the content is important. In the present study, external stress was applied to adult plants of A. annua and the effect was examined on the concentrations of AN and its immediate precursors in leaves, and these concentrations were related to densities and sizes of the glandular trichomes (GT). Plants were stress treated weekly five times by sandblasting or spraying with salicylic acid, chitosan oligosaccharide, H2O2, and NaCl solutions. Contents of AN-related compounds (AN-c) were analysed in leaf samples from an upper and a lower position of the plants, and GT were quantified and measured. In lower leaves, several stress treatments had significant negative effects on concentrations of AN-c, whereas the ratios between compounds showed an increased conversion to AN. In the upper leaves, no changes were observed compared to controls. Linear relations were found between the concentrations of metabolites and the density of GT in both upper and lower leaves, and size of GT in lower leaves. Results suggested that older and younger leaves may respond differently to applied stress. A part of the plants were infected by powdery mildew, and this caused significantly different compositions of the AN-c, compared to uninfected plants. In conclusion, changes in concentrations of AN-c seemed largely to be related to changes in GT densities and sizes.

Noninvasive Determination of Firmness and Dry Matter Content of Stored Onion Bulbs Using Shortwave Infrared Imaging with Whole Spectra and Selected Wavelengths.

A firm texture of dry onions is important for consumer acceptance. Both the texture and dry matter content decline during storage, influencing the market value of onions. The main goal of this study was to develop predictive models that in future might form the basis for automated sorting of onions for firmness and dry matter content in the industry. Hyperspectral scanning was conducted in reflectance mode for six commercial batches of onions that were monitored three times during storage. Mean spectra from the region of interest were extracted and partial least squares regression (PLSR) models were constructed. Feature wavelengths were identified using variable selection techniques resulting from interval partial least squares and recursive partial least squares analyses. The PLSR model for firmness gave a root mean square error of cross-validation (RMSECV) of 0.84 N, and a root mean square error of prediction (RMSEP) of 0.73 N, with coefficients of determination ( R2) of 0.72 and 0.83, respectively. The RMSECV and RMSEP of the PLSR model for dry matter content were 0.10% and 0.08%, respectively, with a R2 of 0.58 and 0.79, respectively. The whole wavelength range and selected wavelengths showed nearly similar results for both dry matter content and firmness. The results obtained from this study clearly reveal that hyperspectral imaging of onion bulbs with selected wavelengths, coupled with chemometric modeling, can be used for the noninvasive determination of the firmness and dry matter content of stored onion bulbs.

Volatile organic compounds as markers of quality changes during the storage of wild rocket.

The quality of leafy green vegetables changes during storage. Leaves become yellow or disintegrate, and an off-odor may develop. In addition, small amounts of volatile organic compounds (VOCs) are released. In this study, the release of acetone, carbon disulfide, dimethyl sulfide, nitromethane, pentane, 3-methylfuran, 2-ethylfuran, and dimethyl disulfide from wild rocket with different initial qualities was monitored during 8d storage at 10°C and correlated to aerobic bacteria counts, yeast and mold counts, and degree of tissue disintegration. The release of VOCs, except for 3-methylfuran, was influenced by the initial quality of the leaves. The release of pentane and 2-ethylfuran was related to the degree of tissue disintegration, and the release of dimethyl sulfide and dimethyl disulfide was related to the total aerobic bacteria count. The results demonstrated that VOCs can be used as markers for monitoring the complex quality changes taking place in packaged fresh produce during storage.

Bioassay-Guided Chromatographic Isolation and Identification of Antibacterial Compounds from Artemisia annua L. That Inhibit Clostridium perfringens Growth.

Clostridium perfringens is the causative agent of necrotic enteritis leading to significant losses in the poultry industry. Dichloromethane and n-hexane extracts of aerial parts of Artemisia annua (Asteraceae) exhibited activity against C. perfringens with minimum inhibitory concentrations (MIC) of 185 and 270 µg/mL, respectively. Bioassay-guided fractionation of the extracts gave several active fractions (MIC between 75 and 600 µg/mL). Investigations of the most active fractions resulted in the isolation and characterization of the polyacetylene ponticaepoxide (MIC between 100 and 200 µg/mL) and (+)-threo-(5E)-trideca-1,5-dien-7,9,11-triyne-3,4-diol (MIC between 400 and 800 µg/mL), the flavonols chrysosplenol D (MIC between 200 and 400 µg/mL) and casticin (slight inhibition at 800 µg/mL), and 2,4-dihydroxy-6-methoxyacetophenone (slight inhibition at 800 µg/mL). Also, the coumarin scopoletin and the sesquiterpene lactone artemisinin were isolated from active fractions but showed no inhibition of C. perfringens growth at 800 and 2000 µg/mL, respectively. Fractions containing essential oil components with camphor constituting >60% did not show inhibition of C. perfringens up to 1600 µg/mL. Extracts and some active fractions showed higher antibacterial effect than individual bioactive compounds, suggesting that synergistic effects may underlie the observed antibacterial effect. The present study adds new valuable information on the antibacterial effect of A. annua against C. perfringens.

Effect of external stress on density and size of glandular trichomes in full-grown Artemisia annua, the source of anti-malarial artemisinin.

BACKGROUND AND AIMS: Glandular trichomes (GT) of Artemisia annua produce valuable compounds for pharmaceutical and industrial uses, most notably the anti-malarial artemisinin. Our aim was to find out whether the density, number and size of GT can be manipulated to advantage by environmental stress. A range of external stress treatments, including stress response regulators, was therefore given to fully grown plants under field and greenhouse conditions. METHODOLOGY: In a field experiment (Ex1), seed-grown plants were subjected to chemical or physical stress and plants analysed after 5 weeks. In a greenhouse experiment (Ex2), three groups of clonally derived plants were stressed at weekly intervals for 5 weeks. Stress treatments included sandblasting, leaf cutting and spraying with jasmonic acid, salicylic acid, chitosan oligosaccharide (COS), H(2)O(2) (HP) and NaCl (SC)at different concentrations. Leaves from an upper and a lower position on the plants were analysed by fluorescence microscopy to determine the density and size of GT. PRINCIPAL RESULTS: Densities of GT on upper leaves of full-grown A. annua plants generally showed no response to external stress and only plants from one clone of Ex2 supported the hypothesis that increased density of GT was inducible in upper leaves by stress (significant for SC, HP and COS). The density of GT on lower leaves was not affected by stress in any experiment. Glandular trichomes were significantly smaller on the lower leaves in response to stress in Ex2, and a similar non-significant trend was observed in Ex1. CONCLUSIONS: The results indicate a dynamic system in which stress treatments of large A. annua plants had a minor promoting effect on the initiation of GT in developing leaves, and a maturing effect of GT later in the lifetime of the individual GT. The hypothesis that applying stress can induce larger GT or more numerous GT was rejected.

Investigation of genetic and morphological variation in the sago palm (Metroxylon sagu; Arecaceae) in Papua New Guinea.

BACKGROUND AND AIMS: The genetic and morphological variation in the sago palm (Metroxylon sagu, Arecaceae) in Papua New Guinea (PNG) was investigated. METHODS: Amplified fragment length polymorphism (AFLP) was used to investigate the genetic structure of 76 accessions of M. sagu, collected in seven wild and semi-wild stands in PNG. KEY RESULTS: An analysis of ten quantitative morphological variables revealed that most of these were mutually correlated. Principal component analyses of the same morphological variables showed that neither armature (presence or absence of spines) nor geographical separation was reflected clearly in the quantitative morphological variation. Similarity matrices of genetic, quantitative morphological, geographical and armature data were tested for pair-wise correlations, using Mantel's test. The results only showed a significant correlation between genetic and geographical distances. Visual inspection of principal component analyses plots and a neighbour-joining dendrogram based on genetic distances supported this trend, whereas armature showed no relation with genetic distances. CONCLUSIONS: Geographical distribution defines some weak patterns in the genetic variation, whereas the genetic variation does not reflect any patterns in the morphological variation, including armature. The present study supports the accepted taxonomy of M. sagu, recognizing only one species of M. sagu in PNG.