Preharvest salicylic acid treatments improve phenolic compounds and biogenic amines in ‘Niagara Rosada’ table grape

Highlights

• 1 and 2 mmol L⁻¹ salicylic acid increase the shelf life of 'Niagara Rosada' in six days.

• 1 mmol L⁻¹ salicylic acid reduces berry drop and decay during storage.

• 1 mmol L⁻¹ salicylic acid induced the synthesis of delphinidin 3-O-glycoside.

• 1 and 2 mmol L⁻¹ salicylic acid increased the serotonin and melatonin content.

Abstract

The ‘Niagara Rosada’ (Vitis labrusca) grape is widely consumed for its nutritional qualities and flavor, in addition to presenting a great diversity of phytochemical compounds, mainly polyphenols. ‘Niagara Rosada’ has a limited shelf life, especially when kept at room temperature, a common form used by markets in Brazil. Salicylic acid (SA) is a low-cost alternative postharvest technique, due to its accessibility (low cost) and potential to mitigate postharvest losses, in addition to maintaining quality. Exogenous application of salicylic acid in the pre-harvest period was studied to improve the postharvest quality of ‘Niagara Rosada’ grapes with the aim of increasing its shelf life. SA was applied in different doses, in two stages during the pre-harvest, in the season of berry growth and during veraison. The results show that 1 and 2 mmol L⁻¹ were efficient in reducing the incidence of berry drop and decay of berries. Treatments with SA provided an increase in phenolic compounds. Among the phenolic acids, there was an increase in chlorogenic acid and gallic acid, related to antifungal action. Regarding polyphenols, rutin, cyanidin-3,5-diglucoside and 3-O-glycosidic delphinidin were the major compounds found in all treatments. Salicylic acid induced an increase in serotonin and melatonin content, as well as in the aminoacids (tryptophan and 5-hydroxytryptophan). During the storage, there was a decrease in histamine and dopamine levels. These alterations may be used as a tool to induce fruit resistance during storage, leading to an increase of crop yields. Thus, exogenous treatment using 1 and 2 mmol L⁻¹ SA increases postharvest life, improves biochemical quality of the musts and induces increased antioxidant compounds.

Introduction

Grapes are one of the most important fruit commodities, and the consumption of the in natura fruit or of their derivatives, such as juices, wines, raisins, and flour has increased due to the presence of compounds beneficial to human health. In Brazil, the cultivar ‘Niagara Rosada’ grape (Vitis labrusca) is widely produced, mainly for fresh consumption, due to its sweet taste, attractive color, and pleasing aroma and is known to be resistant to pests and diseases (Maia and Camargo, 2012). With these characteristics, combined with good acceptance in the domestic market, cv. Niagara Rosada has been replacing European table grapes in areas where diseases cause serious damage to vineyards (Maia and Camargo, 2012).

The grape is a fragile fruit, highly sensitive, and highly perishable due to high softening, weight loss, and fungal decay, which consequently leads to low storability (Mirdehghan and Rahimi, 2016). These changes cause a reduction in the quality of the fruit, reducing its acceptance in the market and limiting postharvest shelf life. Products that prolong and maintain quality after the harvest should be applied to reduce losses. According to Sonker et al. (2016), during the postharvest an estimated 30–40 % losses of tables grapes occur in developed countries, reaching 50 % in developing countries. In this context, several techniques have been used in the pre- and postharvest of table grapes, aiming to reduce the incidence of rotting and decay to maintain quality during storage, with an emphasis on the use of growth regulators.

Salicylic acid (SA), or orthohydroxylbenzoic acid, is a growth regulator of a phenolic nature present in grape berries, and its action is related to the characteristics of color, flavor, bitterness, and astringency (Chamkha et al., 2003). Studies suggest that the exogenous application of SA in the pre-harvest of fruit, e.g., grapes, improves the characteristics related to postharvest quality and leads to a higher content of bioactive compounds, such as polyphenols (Champa et al., 2015). These compounds reinforce the antioxidant capacity of the fruit and increase its shelf life contributing to the storage time, and grapes have been described for showing significant levels ​​of phenolic compounds, which are related to quality (Gomez et al., 2020). Quantitative and qualitative determinations of phenolic compounds are important for quality of table grapes and by-products (Gomez-Gomez et al., 2018; Monteiro et al., 2021). Among the phenolic compounds, flavonoids are important molecules with anti-inflammatory, antiallergenic, and anti-aging properties, as are anthocyanins, which contribute to the colorful appearance of grapes, and 3-glucoside is the most active anthocyanin antioxidant (Orak, 2007). These secondary metabolites act as antioxidants and are related to the plant's resistance against biotic and abiotic factors (Gomez-Gomez et al., 2018).

Other molecules have also been analyzed in response to SA, such as biogenic amines. They are involved in several physiological processes in fruits and vegetables and can act as an antioxidant, in the synthesis of protein, RNA, and DNA (Larqué et al., 2007), besides being considered a second messenger, thereby mediating the action of all growth factors (Champa, 2015). Few studies have demonstrated the action of salicylic acid and polyamines on fruits, including grapes. Cherry tomato fruit treated with methyl salicylate showed increased activity of enzymes involved in the synthesis of polyamines, such as ornithine decarboxylase (ODC) and arginine decarboxylase (ADC), as well as increased levels of some amines; in addition, higher levels of these amines were related to increased resistance to chilling (Zhang et al., 2011). Thus, it appears that SA increases the synthesis of some amines, such as putrescine, spermidine, and spermine, via ODC or ADC. However, the action of SA on others amines, such as histamine and tyramine, considered allergenic (Kovacova-Hanuskova et al., 2015; Ruiz-Capillas and Herrero, 2019) and serotonin, described in vegetables as an antioxidant (Borges et al., 2019), are poorly studied, which highlights this study as one of the pioneers in the field.

Furthermore, in addition to antioxidant compounds and signaling molecules, SA can affect the postharvest quality of fruits and vegetables and appears as a low-cost and easily accessible alternative to reduce losses. The exogenous application of salicylic acid in pre-harvest is well described in the literature, aiming to increase aspects of berry quality, such as color, flavor, astringency, bitterness (Chamkha et al., 2003), among others. Besides these effects, the application of SA in the pre-harvest period reduces the decay and softening of the fruit during storage, promoting an increase in shelf life (Champa et al., 2015). This metabolite may sometimes influence quality aspects, such as soluble solids and titratable acidity in grapes (Champa et al., 2015). Thus, SA plays an essential role in extending the postharvest life of the fruit; however, its action on 'Niagara Rosada' grapes and the responses in relation to shelf life have not yet been described. Therefore, considering the positive effects of SA in some table grape cultivars, the aim of this research was to evaluate the influence of exogenous salicylic acid application in the postharvest period of 'Niagara Rosada' grapes. We verified the physical-chemical properties of grapes treated with SA and evaluated the profile of phenolic compounds and biogenic amines and the antioxidant activity and their relationship with the maintenance of the quality of bunches during the postharvest storage.