Light modulation of volatile organic compounds from petunia flowers and select fruits

Light intensity, duration, direction, and wavelength are informative to plants. The biochemical circuits that connect specific light wavelengths to expression of specific genes and the metabolic networks they govern have been well defined. However, little emphasis has been placed on how discrete wavelengths of light, alone or in combination, may be applied to manipulate postharvest qualities of high-value horticultural crops. Using narrow-bandwidth LED light we test the hypothesis that discrete light wavelengths can affect the accumulation of volatile compounds known to affect aroma or taste in select flower and fruit products. Volatile benzenoid/phenylpropanoid emission from petunia flowers could be altered with light application. Levels of a key floral volatile, 2-phenylethanol, increased with a red and far-red light treatment. Similar experiments demonstrated that fruit volatile profiles of tomato, strawberry, and blueberry can be manipulated with specific light treatments. These results suggest that compounds affecting sensory qualities of flowers and fruits can be modified by adjustment of ambient light conditions. These findings open new areas of inquiry about how the fragrance and flavor of flowers and fruits may be improved with simple changes in postharvest light conditions.     

Multivalent carboxylic acids to modify the properties of zein

Methods must be developed to improve both the processability and physical properties of zein-based articles. Typical plasticizing agents that improve processability have a negative impact on physical properties at elevated humidities. Continued efforts must be employed to discover improved plasticizers. Carboxylic acids having more than one carboxylic acid moiety have been evaluated in zein melt formulations produced in a torque rheometer. These reagents were effective plasticizers for zein, lowering zein viscosity, and delaying the onset of rapid viscosity increase. These reagents altered viscosity differently than the traditional plasticizers such as triethylene glycol. These additives also lowered the tensile strength (TS) of zein formulations at 50% RH. Surprisingly, TS at 70% RH was higher than that at 50% RH at elevated levels of these additives. NMR analysis of Soxhlet extracted samples showed that these multivalent carboxylic acids do not cross-link the zein under the reaction conditions employed.     

Bacterial community structure of nirK-bearing denitrifiers and the development of properties of soils in created mitigation wetlands

We investigated the abundance and genetic heterogeneity of bacterial nitrite reductase genes (nir) and soil structural properties in created and natural freshwater wetlands in the Virginia piedmont. Soil attributes included soil organic matter (SOM), total organic carbon (TOC), total nitrogen (TN), pH, gravimetric soil moisture (GSM), and bulk density (D_b). A subset of soil attributes were analyzed across the sites, using euclidean cluster analysis, resulting in three soil condition (SC) groups of increasing wetland soil development (i.e., SC1 < SC2 < SC3; less to more developed or matured) as measured by accumulation of TOC, TN, the increase of GSM, and the decrease of D_b. There were no difference found in the bacterial community diversity between the groups (p = 0.4). NirK gene copies detected ranged between 3.6 × 10⁴ and 3.4 × 10⁷ copies g⁻¹ soil and were significantly higher in the most developed soil group, SC3, than in the least developed soil group, SC1. However, the gene copies were lowest in SC2 that had a significantly higher soil pH (~6.6) than the other two SC groups (~5.3). The same pattern was found in denitrifying enzyme activity (DEA) on a companion study where DEA was found negatively correlated with soil pH. Gene fragments were amplified and products were screened by terminal restriction fragment length polymorphism (T-RFLP) analysis. Among 146 different T-RFs identified, fourteen were dominant and together made up more than 65% of all detected fragments. While SC groups did not relate to whole nirK communities, most soil properties that identified SC groups did significantly correlate to dominant members of the community.     

Proteolytic activity in soil: A review

The aim of this work is to review current knowledge on inputs, sources and regulation of protease activities in soils from different ecosystems, while exploring limitations to proteolysis and N mineralisation. Extracellular proteases enter the soil via microbial production and other sources, including plant root exudates, animal excrements, decomposition processes and leaching from agro-industrial fertilisers. The synthesis and activities of proteases in soil are regulated by many factors, including climate, soil properties and the presence of organic compounds of plant and microbial origin. Two particularly important areas for future research are the regulation of proteolysis by low-molecular-weight organic compounds, including amino acids, sugars, flavonoids, plant hormones and siderophores, as well as the identification and characterisation of proteinaceous protease inhibitors of plant and microbial origin in the soil. Despite all the work that has been performed on soil proteases, our understanding of the roles of extracellular plant root proteases in N nutrition is weak. Furthermore, the regulation of soil proteolytic activities of different ecosystems, especially in terms of pollutant inputs and the impact of climate change, requires investigation. Other areas that pose important questions for the future include assessments of protease inhibitor inputs to the soil, regulation of these inhibitors via naturally occurring soil organic compounds and the interactions between soil organisms.     

Effect of solution pH of cysteine-based pre-treatments to prevent browning of fresh-cut artichokes

Fresh-cut artichokes were treated with cysteine in the form of aqueous solutions of l-cysteine hydrochloride monohydrate at 0.5% (w/v) normal pH 2.2 adjusted to different pH values with NaOH (from 2 to 7). General appearance and colour measurements during storage at 5 °C showed different degrees of suppression of darkening on cut surfaces. Cysteine pre-treatments caused an increase in the yellow index (b* value) of fresh-cut artichokes compared to untreated samples, which was more pronounced at lower pH (47.9 versus the initial value of 28.3 after 1 day). Artichokes treated at lower pH values also had a lower appearance score and higher PPO activity than artichokes treated at higher values, closer to neutrality. Starting from 3 days of storage a negative correlation between solution pH and PPO activity was also observed, that for artichokes treated with cysteine at pH 7 was lower than for control samples. l-cysteine pre-treatments did not affect total phenolic content and antioxidant activity of fresh-cut artichokes, which showed an increasing pattern after 8 days. These data may represent an important step in prevention of browning in fresh-cut artichokes.     

Effect of alginate coating on physicochemical and sensory qualities of button mushrooms (Agaricus bisporus) under a high oxygen modified atmosphere

Button mushrooms (Agaricus bisporus) were dipped for 2 min in different concentrations (1%, 2% and 3%) of alginate, then placed in jars and ventilated continuously with 100% O₂ for up to 16 d at 4 °C. Mushroom respiration rate, weight loss, texture, color, percent open caps, chemical properties and activities of polyphenol oxidase (PPO), and peroxidase (POD) were measured. The results indicate that treatment with alginate coating (2%) + 100% O₂ maintained a high level of firmness, and delayed browning and cap opening. In addition, alginate coating (2%) + 100% O₂ also delayed changes in the soluble solids concentration, total sugars and ascorbic acid, and inhibited the activity of PPO and POD throughout storage. Our study suggests that the use of alginate coating under a high oxygen modified atmosphere has the potential to maintain button mushroom quality and extend its postharvest life to 16 d.     

Combination of electrolysed water,UV-C and superatmospheric O2 packaging for improving fresh-cut broccoli quality

The effects of neutral electrolysed water (NEW), ultraviolet light C (UV-C) and superatmospheric O₂ packaging (HO), single or combined, on the quality of fresh-cut kailan-hybrid broccoli for 19 days at 5 °C were studied. As controls, washing with water and sanitation with NaClO were both used. Electrolyte leakage, sensory, microbial and nutritional quality changes throughout shelf-life were studied. At day 15, the combined treatments achieved lower mesophilic and psychrophilic growth compared to the single ones. Single treatments produced higher ascorbate peroxidase (APX) reductions just after its application, while superoxide dismutase (SOD) showed the opposite behaviour. After 5 days at 5 °C, a great increase of APX and guaiacol peroxidase (GPX) activity was observed, NEW + UV-C + HO and HO-including treatments achieving the highest and the lowest APX increases, respectively. UV-C-including treatments produced the highest α-linolenic acid (ALA) decreases ranging 35–38% over control contents on the processing day. NEW-including treatments greatly reduced, throughout shelf-life, ALA and stearic acid (SA) content by 27–44% and 31–61%, respectively. Total phenolic content and antioxidant capacity (1415 mg ChAE kg⁻¹ fw and 287 mg AAE kg⁻¹ fw, respectively) remained quite constant during shelf-life. In general, the treatments and their possible combinations seem to be promising techniques to preserve, or even enhance, the quality of fresh-cut kailan-hybrid broccoli and, probably, other vegetables.     

Combined treatment of aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP) reduces melting-flesh peach fruit softening

The effects of postharvest application of aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP) on ethylene production and fruit quality, and thus on transportation and shelf-life, were evaluated in melting-flesh peaches. AVG (150 mg L⁻¹) significantly reduced ethylene production, and the effect was enhanced in combination with 1-MCP (1 μL L⁻¹). However, fruit treated with AVG alone softened to untreated control levels 2 d after harvest (DAH). Treatment with 1-MCP significantly reduced the rate of softening until 2 DAH, but the fruit rapidly softened thereafter, and reached untreated control levels by 4 DAH. A combination of AVG and 1-MCP significantly reduced fruit tissue softening throughout ripening. The effect of each chemical on flesh firmness indicated that 1-MCP affected fruit response in the early stages of ripening up to 4 DAH, and AVG significantly reduced softening in the latter stages from 4 to 9 DAH. Peaches treated with AVG and 1-MCP retained their ground color during ripening, but the effect of each chemical on color is unclear. The present study indicates that combined treatment with AVG and 1-MCP significantly delays the ripening of melting-flesh peaches.