Maintaining quality of fresh-cut mangoes using antibrowning agents and modified atmosphere packaging.

Treatments to inhibit browning and decay and prolong shelf life of fresh-cut mangoes were investigated. Combinations of antibrowning agents and modified atmosphere packaging (MAP) resulted in a reduction of browning and deterioration of fresh-cut mangoes stored at 10 degrees C. Combinations of several browning inhibitors were more effective than those applied individually. Among these treatments, solutions containing 4-hexylresorcinol (0.001 M) (HR) plus potassium sorbate (0.05 M) (KS) and HR plus KS plus D-isoascorbic acid (0.5 M) (ER) reduced changes in color (L, a, and b) and microbial growth and did not affect sensory characteristics of fresh-cut mangoes. In general, these treatments did not affect significantly the changes in organic acids and sugar content of slices during the 14 days of storage at 10 degrees C. High humidity created in the in-package atmosphere alleviated tissue dryness and was an important factor in the ability of the antibrowning solutions to prevent browning and decay. It appears that the maintenance of quality of fresh-cut mangoes is more related to particular combinations of the antibrowning agents used rather than the modified atmosphere created inside the package. HR + ER + KS treatment in combination with MAP could be used to inhibit browning, decay, and deterioration of fresh-cut mangoes.

Extending storage life of fresh-cut apples using natural products and their derivatives.

Prevention of browning of apples slices has been difficult to achieve because of the rapidity of the enzymatic oxidation of phenolic substrates even under reduced atmospheric pressure storage. Combinations of enzymatic inhibitors, reducing agents, and antimicrobial compounds containing calcium to extend storage life were tested to decrease the browning of Red Delicious apple slices stored at 5 and 10 degrees C under normal atmospheric conditions. Treatments were devised to prevent browning for up to 5 weeks at 5 degrees C with no apparent microbial growth using dipping solutions of compounds derived from natural products consisting of 4-hexylresorcinol, isoascorbic acid, a sulfur-containing amino acid (N-acetylcysteine), and calcium propionate. Analyses of organic acids and the major sugars revealed that the slices treated with the combinations of antibrowning compounds retained higher levels of malic acid and had no deterioration in sugar levels at 5 and 10 degrees C, indicating that higher quality was maintained during storage.

Growth of Listeria monocytogenes Restricted by Native Microorganisms and Other Properties of Fresh-Cut Spinach †.

A study was undertaken to investigate the cause of the bacteriostatic activity of fresh-cut spinach leaves against Listeria monocytogenes . L. monocytogenes was cultivated in pure tryptic soy broth for use as a monoculture, in tryptic soy broth containing 10 mg ml-1 of autoclaved or nonautoclaved freeze-dried spinach powder, and in tryptic soy broth in mixed cultures with various microorganisms isolated from fresh-cut spinach, including Pseudomonas fluorescens biovar I, P. fluorescens biovar III, Staphylococcus xylosus , and an undefined culture of mesophilic aerobic microorganisms (MAMs) isolated from freeze-dried spinach powder. These microorganisms were inoculated at 4.4 log CFU ml-1 and L. monocytogenes was inoculated at 2.4 and 4.4 log CFU ml-1 After 24 h of incubation at 30°C, the populations of the two inoculum levels L. monocytogenes increased to 9.0 and 9.6 log CFU ml-1 in the tryptic soy broth control, to 5.4 and 7.5 in nonautoclaved spinach powder cultures, and to 8.8 and 9.1 log CFU ml-1 in autoclaved spinach powder cultures; In mixed cultures with biovar I of P.fluorescens , L. monocytogenes increased to 7.4 and 8.6 log CFU ml-1; with biovar III to 7.7 and 9.1, with S. xylosus to 7.8 and 9.2, and with the MAMs to 7.1 and 8.0 CFU ml-1 in the low and high listerial inoculum cultures respectively. The LSD(0.05)of the means were 0.5 and 0.6, respectively. The freeze-dried spinach powder had an inhibitory effect on the growth of L. monocytogenes . The inhibitory effect was greatly decreased when the native microorganisms were almost eliminated by heating or irradiation. These results indicate that if L. monocytogenes is present as a contaminant on fresh-cut spinach, its growth probably will be restricted by native microorganisms.

Studies on the growth and indole-3-acetic acid and abscisic acid content of Zea mays seedlings grown in microgravity.

Measurements were made of the fresh weight, dry weight, dry weight-fresh weight ratio, free and conjugated indole-3-acetic acid, and free and conjugated abscisic acid in seedlings of Zea mays grown in darkness in microgravity and on earth. Imbibition of the dry kernels was 17 h prior to launch. Growth was for 5 d at ambient orbiter temperature and at a chronic accelerational force of the order of 3 x 10(-5) times earth gravity. Weights and hormone content of the microgravity seedlings were, with minor exceptions, not statistically different from seedlings grown in normal gravity. The tissues of the shuttle-grown plants appeared normal and the seedlings differed only in the lack of orientation of roots and shoots. These findings, based upon 5 d of growth in microgravity, cannot be extrapolated to growth in microgravity for weeks, months, and years, as might occur on a space station. Nonetheless, it is encouraging, for prospects of bioregeneration of the atmosphere and food production in a space station, that no pronounced differences in the parameters measured were apparent during the 5 d of plant seedling growth in microgravity.

Mechanism of aluminum tolerance in snapbeans : root exudation of citric Acid.

One proposed mechanism of aluminum (Al) tolerance in plants is the release of an Al-chelating compound into the rhizosphere. In this experiment, two cultivars of snapbeans (Phaseolus vulgaris L. "Romano" and "Dade") that differ in Al tolerance were grown hydroponically with and without Al under aseptic conditions. After growth in nutrient solutions for 8 days, aliphatic and phenolic organic acids were analyzed in the culture solutions with an ion chromatograph and a high pressure liquid chromatograph. The tolerant snapbean, "Dade", when exposed to Al, exuded citric acid into the rhizosphere in a concentration that was 70 times as great as that of "Dade" grown without Al, and 10 times as great as that of "Romano" grown with or without Al. The sensitive cultivar, "Romano", exuded only slightly more citric acid into the growing medium under Al-stress, compared to nonstressed conditions. Citric acid is known to chelate Al strongly and to reverse its phytotoxic effects. Also, citric acid has been shown previously to enhance the availability of phosphorus (P) from insoluble Al phosphates. Thus, one mechanism of Al-tolerance in snapbeans appears to be the exudation of citric acid into the rhizosphere, induced either by toxic levels of Al or by low P due to the precipitation of insoluble Al phosphates. Our experiment was not able to distinguish between these two factors; however, tolerance to both primary and secondary Al-stress injuries are important for plants growing in Al-toxic soils.

Allelochemicals in tall fescue-abscisic and phenolic acids.

Growth inhibitors that can be leached from excised leaves of tall fescue grass (Festuca arundinacea) were investigated as allelochemicals. Leachates of desiccated Rebel and Kentucky 31 grass cultivars contained three principal inhibitory compounds, abscisic acid (ABA), caffeic acid, andp-coumaric acid. After quantitative analysis, abscisic acid was determined to be the predominant inhibitor. A 10-fold increase in ABA levels in leachates occurred after one day of desiccation. The concentration of ABA was 40% greater in Kentucky 31 leachate than in Rebel. This difference was also found in subsequent analyses of leachates of grasses that had been allowed to dry up to 30 days; however, the ABA concentration was reduced by 60% from the 10-fold increased levels.

Comparison of a commercial ELISA assay for indole-3-acetic Acid at several stages of purification and analysis by gas chromatography-selected ion monitoring-mass spectrometry using a c(6)-labeled internal standard.

Quantitative analysis of indole-3-acetic acid (IAA) using selected ion monitoring gas chromatography-mass spectrometry (GC-MS) with (13)C(6)[benzene ring]-IAA as the internal standard was used to compare the quantitative accuracy of commercial enzyme-linked immunoabsorbent assay (ELISA) kits. Plant materials differed in the amount of purification required prior to use of ELISA for reliable estimates to be made. Purification similar to that obtained by at least one high performance liquid chromatographic (HPLC) step was generally necessary prior to ELISA analysis of plant materials. Additional levels of purification appeared to be required for some plant materials prior to HPLC in order to obtain an accurate estimate by ELISA techniques. In no case was it possible to obtain reasonable estimates of IAA from crude extracts or even from acidic fractions of extracts of plant tissues. GC-MS techniques provide a rapid and simple method for checking the validity of ELISA techniques. Quantitative GC-MS, or a similar technique that provides an independent quantitative validation, should, whenever possible, be applied to each new plant material under study if use of the ELISA is planned.