Pre- and Post-Harvest Conditions Affect Polyphenol Content in Strawberry (Fragaria × ananassa)

Abstract

The strawberry fruit contains abundant polyphenols, such as anthocyanins, flavan-3-ol, and ellagitannin. Polyphenol enrichment improves the quality of strawberries and leads to a better understanding of the polyphenol induction process. We measured the total polyphenol content of strawberry fruits under different growth conditions, developmental stages, and treatment conditions during pre-harvest and post-harvest periods. High fruit polyphenol content was observed in cold treatment, which was selected for further analysis and optimization. A transcriptome analysis of cold-treated fruits suggested that the candidate components of polyphenols may exist in the phenylpropanoid pathway. Coverage with a porous film bag excluded the effects of drought stress and produced polyphenol-rich strawberry fruits without affecting quality or quantity. The degree of stress was assessed using known stress indicators. A rapid accumulation of abscisic acid was followed by an increase in superoxide dismutase and DPPH (2,2-Diphenyl-1-picrylhydrazyl) activity, suggesting that the strawberry fruits responded to cold stress immediately, reaching the climax at around 6 days, a trend consistent with that of polyphenol content. These findings enhance our understanding of the mechanism of post-harvest polyphenol accumulation and the value of strawberries as a functional food.

Storage of halved strawberry fruits affects aroma, phytochemical content and gene expression, and is affected by pre-harvest factors

“…Changes in genes associated with phenylpropanoid metabolism confirmed previous work where strawberry fruit were stored at a much colder temperature of 0°C ( Koyama et al., 2022 ) for a longer period of time (10 days). Genes encoding coniferyl-aldehyde dehydrogenase (EC:1.2.1.68), and beta-glucosidase (EC:3.2.1.21) were up-regulated in both studies while genes encoding cinnamyl alcohol dehydrogenase (EC:1.1.1.195) were down-regulated, and peroxidase (EC:1.11.1.7) genes were both up- and down-regulated during storage.…”

“…It is also of interest that ABA related genes were only up-regulated later, perhaps when storage dehydration is acting as a trigger. A peak in ABA content was noted on day 2 of storage at 0°C (Koyama et al, 2022) and would be consistent with the subsequent activation of ABA responsive genes. The down-regulation of abiotic stress related genes later in storage is perhaps surprising although it may reflect a general shutting down of metabolism linked to senescence.…”

“…The majority of the DEGs found here associated with starch and sugar metabolism increased in expression. Starch and sugar metabolism was also an enriched pathway when strawberry fruit were exposed to 0°C for 10 days ( Koyama et al., 2022 ). Most of the enzymes encoded catalyse the production of monosaccharides: glucose, maltose, and fructose or dextrin, a breakdown product of starch.…”

“…Genes encoding coniferyl-aldehyde dehydrogenase (EC:1.2.1.68), and beta-glucosidase (EC:3.2.1.21) were up-regulated in both studies while genes encoding cinnamyl alcohol dehydrogenase (EC:1.1.1.195) were down-regulated, and peroxidase (EC:1.11.1.7) genes were both up- and down-regulated during storage. However, genes for two further enzymes: shikimate O-hydroxycinnamoyl transferase (EC:2.3.1.133) and ferulate-5-hydroxylase (EC:1.14.-.-) were only up-regulated when fruit were exposed to 0°C for 10 days ( Koyama et al., 2022 ) and not here where storage was at 8°C suggesting that genes for these enzymes are only activated at a colder storage temperature or a longer period of time. Conversely genes encoding other enzymes in this pathway, including cinnamoyl-CoA reductase (EC 1.2.1.44) were only down-regulated, and others including coniferyl-aldehyde dehydrogenase (EC 1.2.1.68), were only up-regulated here.…”

“…Treatment with phytohormones postharvest ( Chen et al., 2016 ), oF fruit stored at ambient temperature for 2 days showed that auxin delayed postharvest ripening whereas ABA accelerated it. A study of changes in polyphenol content during fruit storage at 0°C over a 10 day period ( Koyama et al., 2022 ) identified changes in expression of genes for several key enzymes in the phenylpropanoid biosynthesis pathway which may be linked to changes in polyphenol content in response to cold storage.…”