Search

Modified atmosphere packaging (MAP) has been used to increase the shelf life of the green asparagus ( Asparagus officinalis , L.), meeting the market demand for fresh high quality products available annually and without the use of additives whenever possible. Green asparagus spears were stored under three different conditions until they were not fit for consumption: refrigeration at 2 °C, MAP at 2 °C, and MAP at 10 °C after 5 days at 2 °C. Gases (O 2 and CO 2 ), external appearance, weight loss, pH and acidity, vitamin C, texture and microbial quality, along with a microscopical analysis, were measured at regular intervals throughout the storage assays. Significant differences were found between packaged and non-packaged green asparagus in most of the parameters considered. Weight loss and hardening in the spears middle and basal sections increased markedly in refrigerated samples. Vitamin C contents decreased rapidly after storage in all treatments; however, this was more pronounced in refrigerated spears, while over the same time the ascorbic acid content was statistically higher in samples stored under MAP conditions. Also, MAP has a significant effect on the storage time, with the external appearance being the limiting factor for the shelf-life and reducing the microbial growth within the spears. Modified atmosphere, combined with refrigeration at 2 °C, showed the best results among the treatments in terms of retaining sensory and nutritional quality, increasing the safety and extending the shelf-life of green asparagus.

Asparagus is a highly perishable product owing to its high respiratory rate, a reason why modified atmosphere packaging (MAP) has been used in order to increase the shelf-life of fresh asparagus. Carotenoid and chlorophyll pigments are important compounds for the maintenance of both the nutritional and sensory quality of asparagus. In this study, green asparagus spears were stored under refrigeration at 2 °C for 14 days, under MAP at 2 °C for 26–33 days and under MAP at 10 °C for 20 days. Pigment profiles were determined using high-performance liquid chromatography (HPLC), with three classes of compounds being detected, namely oxygenated carotenoids (xanthophylls), hydrocarbonated carotenoids (carotenes) and chlorophylls. The xanthophylls identified were neoxanthin, violaxanthin, lutein and zeaxanthin. Only β-carotene was detected in the carotene fraction. In the chlorophyll pigments, three molecules were isolated, chlorophyll b, its epimer chlorophyll b′ and chlorophyll a. Also detected were the first degradation products of chlorophylls, pheophytins b and a respectively. Modified atmosphere packaging at 2 °C was found to be effective in extending the shelf-life for up to 4 weeks and in preserving the colour of fresh asparagus. Copyright © 2004 Society of Chemical Industry

Eighteen samples of soybean inoculants representative of the major manufacturing companies in Argentina were purchased from the market and evaluated using plate counts, most probable number (MPN) of Bradyrhizobium japonicum on plants and time of nodule appearance. One or two B. japonicum isolates per product were isolated and typed by analysis of their DNA patterns. The Log10 numbers of B. japonicum obtained were in the range of 0 to 6/soybean seed, with only two products above 1 × 106 bacteria/seed. Of 18 products, 17 were contaminated, and of these 14 contained more contaminants than B. japonicum. The time of nodule appearance varied between 8 and 16 days, indicating a great difference in microbial activity between products. The strains were found to be similar to USDA 138 (five isolates), E45-INTA Argentina (two isolates), USDA 142 (four isolates) and E4-INTA (one isolate). Thus, even if most of the typed strains are considered as good N2-fixing strains, the average quality of the analysed samples was low, and could not support efficient inoculation of soybean.

A survey of the changes in populations of heterotrophic bacteria, coliform microorganisms and S. meliloti was conducted in samples taken from the water irrigation channels of the Neuquén River (Argentina). Fifty-six water samples were collected during the spring-summer seasons of 1997-1999 years. Both the heterotrophic plate count bacterial and the number of coliforms oscillated between 110-5050 CFU/ml and 8-1400 CFU/100 ml, respectively, during the period this study was carried out. Fecal coliforms were detected in 91.1% of the water samples investigated. Moreover, the results showed that S. meliloti capable of nodulating alfalfa (Medicago sativa L.) Cuf 101 were present in 68% of the water samples and in effectiveness studies, no isolate out of 25 evaluated could be classified as superior N fixers. That is, they did not produce plants equal in weight to nitrate-grown plants (KNO3 0.05%). All the S. meliloti strains were resistant to novobiocin and bacitracin, while 72% of the microsymbionts demonstrated resistance to between seven and ten antibiotics. Results presented in this study showed that irrigation waters of the Neuquén river could act as dispersal agents of both ineffective S. meliloti strains and thermotolerant coliform bacteria.

Little is known about native populations of Bacillus thuringiensis (Bt) isolated from soils of Argentina. We undertook this study to determine the resistance to different pesticides of two commercial and fourteen native strains of Bt under in vitro conditions. An agar plate bioassay test conducted with ten pesticides and sixteen strains of Bt showed that Basagran, Scepter, Fungoxan and Decis were not toxic for the bioinsecticide bacteria at recommended application rates (RAR). In contrast, low concentrations (3.2% RAR) of Agil, Select and Isomero showed a deleterious effect on the bacteria investigated. Simultaneously, four of the pesticides were able to produce phenotypical changes on the Bt colonies grown on nutrient agar. Moreover, in a greenhouse experiment, seven pesticides applied at 1.6%, 12.5% and 100% RAR on soybean leaves were not as inhibitory as under in vitro conditions for two Bt strains (HD-1 and A61). However, survival of these strains in the phyllosphere of soybean differed significantly between untreated leaves and leaves treated with pesticides after 20 days of study (P0.05). Finally, and from an ecological point of view, these findings suggest that the addition of some pesticides to soybean leaves in lower concentrations than those recommended could be favourable for the persistence of Bt in this environment.