The paradox of oleuropein increase in harvested olives (Olea europea L.)

Influence of 1-Methylcyclopropene (1-MCP) on the Processing and Microbial Communities of Spanish-Style and Directly Brined Green Table Olive Fermentations

This work evaluates the effect of 1-methylcyclopropene (1-MCP) on postharvest and fermentation of Manzanilla cultivar, processed as Spanish-style or directly brined table olives. During postharvest handling, 1-MCP (2.85 µL/L) reduced the number of colour-turning olives by 18.42% over the untreated fruits. In Spanish-style and directly brined fermentation, the 1-MCP treatment led to lower pH levels, higher titratable acidities, improved firmness and colour olives than untreated fruits. A panel of expert testers also gave higher scores, and overall acceptability to the 1-MCP treated fruits, especially in the case of Spanish-style fermented olives. Metagenomic analysis of olive biofilms at the end of the fermentation process (176 days) revealed that Lactiplantibacillus was the most abundant bacterial genus in both Spanish-style and directly brined olives (>72%). However, fungal biodiversity was higher than bacterial in all treatments. Saccharomyces was the predominant yeast genus associated with directly brined olives (>97%), whilst Wickerhamomyces (>37%) and Zygoascus (>18%) were with Spanish-style fermentations. The 1-MCP treatment doubled the presence of Wickerhamomyces in Spanish-style fruits (74%) whilst reducing the presence of Zygoascus and allowing the growth of Enterobacter (15%) in directly brined olives. Thus, the postharvesting treatment of table olives with 1-MCP could help reduce the maturation progress of olives and improve the organoleptic and quality characteristics of the products without affecting the microbiological evolution of the fermentations.

Effect of Magnetic and Electrical Fields on Yield, Shelf Life and Quality of Fruits

The presented article is a review of the literature reports on the influence of magnetic and electric fields on the growth, yield, ripening, and durability of fruits and their quality. The article shows the potential application of MF and EF in agricultural production. Magnetic and electrical fields increase the shelf life of the fruit and improve its quality. Alternating magnetic fields (AMF) with a value of 0.1–200 mT and a power frequency of 50 Hz or 60 Hz improve plant growth parameters. MF cause an increase in firmness, the rate of maturation, the content of beta-carotene, lycopene, and fructose, sugar concentration, and a reduction in acidity and respiration. The most common is a high-voltage electric field (HVEF) of 2–3.61 kV/cm. These fields extend the shelf life and improve the quality of fruit by decreasing respiration rate and ethylene production. The presented methods seem to be a promising way to increase the quantity and quality of crops in agricultural and fruit production. They are suitable for extending the shelf life of fruit and vegetables during their storage. Further research is needed to develop an accessible and uncomplicated way of applying MF and AEF in agricultural and fruit production.

Changes in volatile organic composition of olive oil extracted from cv. 'Leccino' fruit subjected to ethylene treatments at different ripening stages

BACKGROUND

Olive, as a non-climacteric fruit, is presumed to be ethylene independent with regard to ripening triggering/coordination. Nevertheless, studies have demonstrated that postharvest ethylene treatments induce changes in composition and properties also of non-climacteric fruits, including aroma profiles, a key quality parameter of extra virgin olive oils. Olive fruit of cv. 'Leccino' harvested at two distinct ripening stages (less advanced ripening, LAR; and more advanced ripening, MAR, with Jaén index of 4.58 and 5.10, respectively) were subjected to ethylene (1000 ppm in air) treatment for 24 h before oil extraction.

RESULTS

Based on multivariate analysis of volatile organic compound (VOCs), the effect of ethylene treatment appeared to be more pronounced in MAR samples. However, differences in organoleptic analysis were also detected in ethylene-treated LAR olive oils. Ethylene seems to selectively affect linolenic/linoleic acid metabolism, particularly concerning the C5 pathway, and reduce specific defect-associated compounds.

CONCLUSION

Exogenous ethylene applied to cv. 'Leccino' olives before processing was effective in inducing specific changes in the VOC profiles of the resulting oil. The effect was different depending on the ripening stage of the harvested olives. The lipoxygenase pathway (including the production of C5 compounds) and fermentative-related compounds appeared to be affected by the treatment. © 2020 Society of Chemical Industry.

Increased firmness and modified cell wall composition by ethylene were reversed by the ethylene inhibitor 1-methylcyclopropene (1-MCP) in the non-climacteric olives harvested at dark green stage - Possible implementation of ethylene for olive quality

This study aimed to investigate the firmness retention by ethylene treatment in olive fruit, as observed earlier. Ethylene concentrations up to 1000 μL L^-1 were applied to dark green 'Konservolia' olives harvested shortly before the green maturation and exposed to 20 °C for up to 9 d. Surprisingly, the results indicated a tendency to fruit firmness increases in concentration-dependent manner in a non-climacteric fruit. The highest concentration increased the firmness within 12 h by approximately 1.35-fold, but transiently for approximately up to 5 d; all ethylene inhibitors tested, either of synthesis (ethoxyvinyl glycine or AVG), or perception (1 -methyl-cyclopropene or 1-MCP, and silver nitrate) prevented the firmness increase. Texture was evaluated by firmness and changes in lignin, cellulose (CL), total pectins (TPC), water soluble pectins (WSP) and total non-cellulosic sugars (total sugars) concentrations, and in pectin esterification degree (DE) in the alcohol insoluble residue (AIR) of 'Konservolia' fruit pericarp during 1.5-d, 5-d and 10-d treatments with 1000 μL L^-1 ethylene at 20 °C. Pectins in AIR were also extracted sequentially with cyclohexane-trans-1,2-diaminetetra-acetate (CDTA), Na₂CO₃, 1 M and 4 M KOH. The results showed that on day 1.5, the increased firmness was consistent with increased CL (crystalline formation, as observed by microscopy), total sugars and DE levels, but reduced WSP, whereas softening reversed the changes and lowered TPC and CDTA-soluble pectins in all fruit on day 10. However, on day 5 ethylene-treated olives exhibited a transitional phase during softening, characterized by retention of high TPC concentration and energy demand, as indicated by elevated respiration rates. The inhibitor 1-MCP, applied before ethylene, did inhibit the responses to ethylene treatment. Ethylene firming effect and the respective cell wall changes in olives are demonstrated for first time. The experiments could be used for research on perception and transcription responses to ethylene in olive, a non-climacteric fruit. In practice, high ethylene concentrations could also be beneficial for firmness increase and/or short storage of dark green olives.