Hot water treatments performed in the base of the broccoli stem reduce postharvest senescence of broccoli ( Brassica oleracea L. Var italic) heads stored at 20 °C

Effect of Aloe vera gel coating on organoleptic and nutritional quality of minimally processed carrot

Demand for fresh vegetables has led to development studies in postharvest area mainly focused on minimizing and look for alternatives to chemical additives for food preservation. The use of natural derived edible coatings emerges as a promising alternative for maintaining quality of vegetables. The objective of this study was to evaluate the effect of Aloe vera gel in minimally processed carrot during postharvest storage. Samples with different degrees of processing were immersed in Aloe vera gel, packaged polyolefin bags, and stored in refrigerated chambers at 5 °C for 12 days. Different organoleptic and quality parameters were evaluated. In general, the samples treated with Aloe vera gel showed less quality loss and a lower increment in the bleaching index. Moreover, sensory analysis allowed to establish that carrots processed in slices and shredded and coated with the gel had a more flavorful taste and higher moisture content. Aloe vera treatment did not influence the microbiological growth of bacteria and fungi during storage. Regarding nutritional quality, the treated samples showed a higher accumulation or lower degradation of phenols, flavonoids, and carotenoids, probably generating in this way, a higher antioxidant capacity in these samples. Finally, Aloe vera gel treatment did not influence sugar dynamics in any of the samples. It can be concluded that the treatment with Aloe vera gel allows maintaining a better organoleptic and nutritional quality of carrots with different degrees of processing during refrigerated storage.

Postharvest shelf life extension of minimally processed kale at ambient and refrigerated storage by use of modified atmosphere

Kale is becoming an important vegetable worldwide, mainly due to its nutritional properties. Kale leaves can be marketed whole, although minimal processing is also in demand. In this article, it was analyzed the effect of packaging in a modified atmosphere of fresh-cut kale leaves stored at 20 °C and 4 °C. Kale leaves were cut into 4 × 4 cm strips and stored in low-density polyethylene bags. Samples processed in the same way but stored in PVC were used as controls. Leaves kept in a modified atmosphere showed a delay in color change with Hue values from about 130 to 120 under PMA against 130 to 100 in control group (CTR) leaves. Chlorophyll degradation was also delayed in both storage temperatures. Samples stored under PMA showed about two times the levels of total chlorophylls with respect to CTR samples at the end of the storage. No changes in total sugar content were detected during storage and no differences were detected between control and modified atmospheres stored samples. Samples maintained in a modified atmosphere showed a lower decrement in soluble proteins and a lower rate of RUBISCO degradation at both temperatures. The relation of RUBISCO content PMA/CTR ranged from 1 to about 3 toward the end of storage No changes in phenols content were found when comparing control and treated samples. However, flavonoid and the antioxidant contents increased in samples stored in modified atmospheres with respect to their controls. We demonstrated that storage in modified atmospheres could be an adequate and simple methodology to extend postharvest life of this minimally processed product at both ambient and refrigerated storage.

Evidence of glucosinolates translocation from inflorescences to stems during postharvest storage of broccoli

Broccoli is a vegetable appreciated by consumers for its nutritional properties, particularly for its high glucosinolate (GLS) content. However, broccoli shows a high rate of senescence during postharvest and the GLS content in inflorescences decreases sharply. Usually, postharvest studies on broccoli focus on inflorescences, ignoring the other tissues harvested such as the stems and main stalk. In this work, GLS metabolism in whole heads of broccoli (including inflorescences, small stems and stalk) was analysed during postharvest senescence. The content of GLS content, expression of GLS metabolic genes, and expression of GLS transport-associated genes were measured in the three parts of harvested broccoli. A marked decrease in the content of all GLSs was detected in inflorescences, but an increase in the stems and stalk. Also, decreased expressions of GLS biosynthesis and degradation genes were detected in all tissues analysed. On the other hand, an increase in the expression of one of the genes involved in GLS transport was observed. These results suggest that GLSs would be transported from inflorescences to stems during postharvest senescence. From a commercial point of view, broccoli stems are usually discarded and not used as food. However, the accumulation of GLSs in the stems is an important factor to consider when contemplating potential commercial use of this part of the plant.

Phenylalanine ammonia lyase is more relevant than Chalcone synthase and Chalcone isomerase in the biosynthesis of flavonoids during postharvest senescence of broccoli

Broccoli contains a high content of nutraceutical compounds, such as glucosinolates and flavonoids. In this work, the effect of different treatments that modulate postharvest senescence of broccoli was evaluated and flavonoid metabolism during postharvest storage was analyzed at 20°C. A decrease in hue angle (HUE°) and chlorophylls and an increase in flavonoid content were detected during senescence. It observed that most of the treatments that delayed senescence also decreased flavonoid content, except visible light and UV-C treatments. In all cases, a direct correlation between those treatments that increased flavonoid biosynthesis and BoPAL gene expression was detected. This response was not detected in the expression of the other two flavonoid synthesis relevant genes BoCHS and BoCHI, suggesting that BoPAL has a greater influence on the regulation of the via, during broccoli senescence. PRACTICAL APPLICATIONS: Broccoli is a vegetable with valuable nutritional properties. Because it is in full development at the time of harvest, it has a short shelf life. In this work, it is showed that visible light and UV-C treatments not only delayed the senescence of broccoli, but also increased flavonoid content. Our results suggest that the most important enzyme in the phenylpropanoid biosynthesis pathway during broccoli postharvest is phenylalanine ammonia lyase, and that this may be a key point in regulating the biosynthesis of these nutritionally valuable compounds.

Expression of BoNOL and BoHCAR genes during postharvest senescence of broccoli heads

BACKGROUND

Chlorophyll is the most abundant pigment on Earth, essential for the capture of light energy during photosynthesis. During senescence, chlorophyll degradation is highly regulated in order to diminish toxicity of the free chlorophyll molecule due to its photoactivity. The first step in the chlorophyll degradation pathway is the conversion of chlorophyll b to chlorophyll a by means of two consecutive reactions catalyzed by enzymes coded by NYC1 (NON-YELLOW COLORING 1), NOL (NYC1-LIKE) and HCAR.

RESULTS

In this work, we studied the expression of NOL and HCAR genes during postharvest senescence of broccoli. We found that the expression of BoNOL increase during the first days of storage and then decrease. In the case of BoHCAR, its expression is maintained during the first days and then it also diminishes. Additionally, the effect of different postharvest treatments on the expression of these genes was also analyzed. It was observed that the expression of BoNOL is lower in the treatments performed with 1-methylcyclopropene (1-MCP), 6-benzylaminopurine (6-BAP) and modified atmospheres, while BoHCAR expression showed an increase in these same treatments, and a decrease in the treatment with ethylene. There were no variations in the expression of both genes in heat treatment, UV-C treatment and visible light treatment.

CONCLUSIONS

These results suggest that both BoHCAR and BoNOL show a lower regulation of their expression than other genes involved in chlorophyll degradation during senescence. © 2020 Society of Chemical Industry.

Exogenous application of phytosulfokine α (PSKα) delays yellowing and preserves nutritional quality of broccoli florets during cold storage

In this study, we tested the exogenous application of phytosulfokine α (PSKα) for delaying the yellowing of broccoli florets during cold storage. Our results showed that the lower yellowing in broccoli florets treated with 150 nM PSKα was probably due to the higher endogenous accumulation of PSKα, leading to the endogenous accumulation of guanosine 3', 5'-cyclic monophosphate (cGMP). Besides, broccoli florets treated with 150 nM PSKα exhibited a higher accumulation of phenols and flavonoids by triggering gene expression and activities of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS). Moreover, the higher expression of L-galactotno-1,4-lactone dehydrogenase (GLDH) gene and the lower expression of ascorbic acid oxidase (AAO) gene in broccoli florets treated with 150 nM PSKα may be the reasons for the higher accumulation of ascorbic acid. In conclusion, the exogenous application of PSKα is a promising strategy in delaying the yellowing and preserving the nutritional quality of broccoli florets during cold storage.

The time of the day to harvest affects the degreening, antioxidant compounds, and protein content during postharvest storage of broccoli

Harvesting of broccoli at several moments of the day affects the rate of senescence during storage. In this work, broccoli heads were harvested at several moments and then kept at 20°C in order to analyze protein metabolism and antioxidant compounds. Almost no differences were detected in the contents of total and soluble proteins, and free amino acids. Only an increment in free amino acids was detected by day 3 in samples obtained at 8:00 hr. With reference to antioxidants, the contents of ascorbic acid, carotenoids and xanthophylls, phenols, and flavonoids were similar in samples harvested at different moments. However, an increment was detected in carotenoids, phenols, and flavonoids during storage of samples collected at 18:00 hr on day 3 and samples collected at 13:00 hr on day 5. The combination of delay of senescence and increment in antioxidants suggest harvesting at 12:00 or 18:00 hr. PRACTICAL APPLICATION: Broccoli is a vegetable with an important level of nutrients. However, it is also highly perishable and suffers a high rate of senescence and loss of quality during postharvest. In this work, it is demonstrated that the simple practice of harvests in different moments of the day can affect the postharvest behavior of broccoli, and it is suggested to carry out the harvest toward the end of the day.

BrWRKY65, a WRKY Transcription Factor, Is Involved in Regulating Three Leaf Senescence-Associated Genes in Chinese Flowering Cabbage

Plant-specific WRKY transcription factors (TFs) have been implicated to function as regulators of leaf senescence, but their association with postharvest leaf senescence of economically important leafy vegetables, is poorly understood. In this work, the characterization of a Group IIe WRKY TF, BrWRKY65, from Chinese flowering cabbage (Brassica rapa var. parachinensis) is reported. The expression of BrWRKY65 was up-regulated following leaf chlorophyll degradation and yellowing during postharvest senescence. Subcellular localization and transcriptional activation assays showed that BrWRKY65 was localized in the nucleus and exhibited trans-activation ability. Further electrophoretic mobility shift assay (EMSA) and transient expression analysis clearly revealed that BrWRKY65 directly bound to the W-box motifs in the promoters of three senescence-associated genes (SAGs) such as BrNYC1 and BrSGR1 associated with chlorophyll degradation, and BrDIN1, and subsequently activated their expressions. These findings demonstrate that BrWRKY65 may be positively associated with postharvest leaf senescence, at least partially, by the direct activation of SAGs. Taken together, these findings provide new insights into the transcriptional regulatory mechanism of postharvest leaf senescence in Chinese flowering cabbage.