Optimization of ozone concentration and storage time in green asparagus (Asparagus officinalis L.) using response surface methodology

Background: Asparagus (Asparagus officinalis L.) green is a vegetable with a great demand worldwide, and likewise, it is highly perishable due to its high respiration rate that accelerates its senescence. Disinfection of vegetables after their harvest is an obligatory practice that can reduce losses by decomposition due to the attack of microorganisms. Therefore, it is vital to preserving its microbiological and sensory characteristics to reach the final consumer. Objective: To evaluate the effect of gaseous ozone (0 to 10 ppm) and storage time (0 to 30 days) on phenol content, overall appearance, count of molds, psychrophilic bacteria, and viable mesophilic aerobes. Methods: the response surface methodology was used, applying a rotatable central composite design. Results: The results indicated that there was a significant influence (p <0.05) of the independent variables on the characteristics studied, as well as an adequate lack of fit of the quadratic regression model (p> 0.05). By means of the contour superposition technique, it was determined that the optimal conditions for the highest retention of phenol content (16.99 mg/g) and overall appearance (7.61 points) and lower counts of viable aerobic mesophilic bacteria (5.3 x 103 CFU/g) they corresponded to 10 ppm of gaseous ozone up to 25.91 days of storage, with adequate quality characteristics in the shoots. Conclusion: the region of interest was determined for optimal retention of phenol content and overall appearance, and a lower count of viable aerobic mesophilic bacteria in green asparagus during postharvest, suggesting to use the initial application of ozone gas at 10 ppm allowing 25.9 days storage at 1 °C. The results indicate that this technology is a good alternative in the conservation of fresh vegetables.

Antifungal Effects of Cold Plasma, Coupled with Modified Atmosphere Packaging on Asparagus during Cold Storage

Asparagus spear is vulnerable to microbial groups which can cause deterioration and short shelf-life after harvesting. The effects of cold plasma, coupled with modified atmosphere (MA) packaging on microorganism development, and quality changes of green asparagus were investigated. The development of microorganisms was inhibited after sterilisation. After 21 days of storage, cold plasma for 6 h (P6h) and hot water combined with cold plasma for 3 h (HW+P3h) treatments obtained the lowest number of aerobic bacteria. Hot water (HW), P6h and HW+P3h treatments showed higher inhibition effect on yeast and mold, and also on E. coli. Visual quality and off-odour of P6h treatment were superior to and inferior to other treatments, respectively. Hot water and cold plasma treatments alone inhibited the firming. Cold plasma 1 (P1h) and 3 h (P3h) were better in retarding yellowing of asparagus. A difference in electrolyte leakage (EL) between control (43%) and sterilisation treatments (greater than 60%) was immediately observed on the sterilisation day. Treatments using HW and P1h decreased the EL after 21 days. The soluble solid content (SSC) decreased based on the initial content, and hot water treatment resulted in higher SSC. Increases in ethylene (C₂H₄) and carbon dioxide production and decrease in oxygen were observed during the first 3 days. The content of C₂H₄ under cold plasma treatments was higher than hot water and control on day 21. These results suggested that cold plasma 6 h treatment resulted in better sensory quality and less decay and softening for green asparagus.

Exogenous Melatonin Reduces Lignification and Retains Quality of Green Asparagus (Asparagus officinalis L.)

Asparagus (Asparagus officinalis L.) is highly perishable because of its high respiration rate, which continues after harvesting and leads to weight loss, increased hardness, color change, and limited shelf life. Melatonin is an indoleamine that plays an important role in abiotic stress. This study was designed to investigate the effects of melatonin on the quality attributes of green asparagus during cold storage. Green asparagus was soaked in a melatonin solution (50, 100, and 200 μM) for 30 min and then stored at 4 °C under 90% relative humidity for 25 days. The results indicated that melatonin treatment delayed the post-harvest senescence of asparagus and maintained high chlorophyll and vitamin C levels. Melatonin treatment hindered phenylalanine ammonia-lyase and peroxidase activities and reduced lignin content, thereby delaying the increase in firmness. Moreover, melatonin treatment enhanced catalase and superoxide dismutase activities, leading to reduced hydrogen peroxide content. These results indicate that melatonin treatment can be used to maintain the post-harvest quality and prolong the shelf life of green asparagus.

Effects of Furrow Height and Amount of Manure Compost on the Growth, Yield, and Quality of Organically Grown Green Asparagus

A two-season field trial was carried out in the Upland Crop Experiment Field of the Faculty of Agronomy, Vietnam National University of Agriculture (VNUA) to assess the effects of three furrow heights (20, 35, and 50cm) and three manure compost levels (15, 25, and 35 tons ha-1) on the growth, yield, and quality of green asparagus (Asparagus officinalis L.) grown organically. The experiments were arranged in a randomized completely block design (RCBD) with three replications. The results showed that the harvested yield was highest (11.3 and 25.1 quintals ha-1 in the 2019 autumn and 2020 spring season, respectively) in the treatment with a furrow height of 35cm and compost level of 35 tons ha-1 in both seasons, and explained by the increased spear diameters and number of spears per plant in this treatment when the furrow height and compost level were increased. Additionally, the chlorophyll content, water loss, and dry matter weight of the spears also increased when the furrow height and compost level increased. The obtained quality of the spears under organic management at the furrow height of 35 cm and compost level of 35 tons ha-1 was higher than the other treatments with higher reducing sugars, vitamin C, and Brix values, while the residue nitrate contents of all the treatments were lower than the allowed safety threshold.

Evaluation of Physiological and Quality Parameters of Green Asparagus Spears Subjected to Three Treatments against the Decline Syndrome

Green asparagus (Asparagus officinalis L.) is a widely grown and consumed crop which provides high-level nutritional interest. In recent years, the decline syndrome in asparagus plantations has been rapidly augmenting. This syndrome causes the early death of whole plants, also negatively affecting the new replanting. Decline causes notable economic losses in the sector. The objective of this work was to verify the effect of different treatments against asparagus decline syndrome on the physiological parameters and nutritional quality of the spears. To meet the objective, four different treatments were applied to asparagus plots strongly affected by decline syndrome: (T1) untreated control soil, (T2) biofumigation with Brassica pellets, (T3) biofumigation with chicken manure pellets, and (T4) disinfestation of the soil with Dazomet. The cumulative yield and physiological and quality parameters of green asparagus spears were studied. Thus, malondialdehyde (MDA), photosynthetic pigments, glutathione (GSH), ascorbate (AsA), total phenols, flavonoids, anthocyanin, antioxidant test, mineral nutrients, and the amino acid profile were measured on asparagus spears. The results showed that the Brassica pellets and Dazomet treatments were the most effective against the damage caused by the decline syndrome. However, it would be necessary to monitor the evolution in the following years.