Relationship Between Water Supply and Sugar and Capsaicinoids Contents in Fruit of Chili Pepper (<i>Capsicum annuum</i> L.)

Abstract

Environmental factors influence the contents of taste components, such as capsaicinoid compounds, in the fruit of chili pepper (Capsicum annuum). The present research was conducted to evaluate the effect of water supply and harvesting date after flowering on sugar and capsaicinoid contents in fruit of the Japanese chili pepper cultivars 'Botankosho', 'Fushimiamanaga', 'Manganji', and 'Sapporo Oonaga Nanban'. The experiment was conducted in a greenhouse from April to October in 2016 and 2017. Three water supply treatments were applied: 260 mL (excess), 130 mL (standard), and 50 mL (drought) per application. Fruit were harvested at 20, 30, 40, and 50 days after flowering (DAF). Glucose, glutamic acid, and total sugar were measured using a portable spectrophotometer, and capsaicinoid content was measured by HPLC. Total sugar content and Brix tended to increase with later harvesting, whereas glucose content did not change significantly by DAF. Sugars in the fruit were dominated by fructose, and the ratio of fructose content to total sugar content increased as the fruit matured. Glutamic acid content in the fruit increased up to 40 DAF, and thereafter remained unchanged or decreased. The capsaicinoid content of the fruit increased with fruit maturation. Elevation in water supply induced an increase in the fruit glucose content and decrease in total sugar and glutamic acid contents. Previous studies of tomato (Solanum lycopersicum L.) found that total sugar and glucose contents decrease in response to increase in water supply. Therefore, it is suggested that sugar metabolism and accumulation differ in the fruits of tomato and chili pepper. The highest capsaicinoid content in chili pepper fruit was observed in response to the drought treatment.

Drought Stress Induced an Increase in the Pungency and Expression of Capsaicinoid Biosynthesis Genes in Chili Pepper (<i>Capsicum annuum</i> L.)

“…4). This result was in line with the authors' previous finding that capsaicinoid content in the placental septum increased under a drought stress condition in Japanese chili pepper varieties 'Botankosho' and 'Sapporo' (Rathnayaka et al, 2020). Estrada et al (1999) also reported that chili fruit was more pungent when grown under drought stress conditions.…”

“…Two kinds of stress treatment were used: drought stress treatment and excess water supply treatment. For the drought stress treatment, 150 mL of water was applied for each irrigation, and for the excess water supply treatment, 780 mL of water was applied for each irrigation based on pot size, as described by Rathnayaka et al (2020). In the excess water supply treatment, the excess water that overflowed from the pots was retained in a dish placed under the pot to allow absorption through the pot base.…”

“…In water-stressed plants of C. chinense Jacq., capsaicin concentration increases in some parts of the fruit (Ruiz-Lau et al, 2011). Our previous investigations found that taste components, including capsaicinoid content, were significantly increased in chili pepper fruits that were cultivated under a drought stress condition (Rathnayaka et al, 2020). We considered that the expression of capsaicinoid biosynthesis genes may be related to drought stress-dependent fluctuation in pungency, and were interested in elucidating the genetic mechanism by conducting a gene expression analysis.…”

Maturation and determination of the harvest point of Capsicum chinense Jacq. (‘biquinho’ pepper)

“…The content of soluble solids increased progressively in accordance with the stages of maturation, reaching a maximum value in the red-orange and red stages, with a significant difference for the green-orange and green stages (Table 4). Similarly, Rathnayaka et al (2020) also verified an increase in the soluble solids content in pepper cultivars as the fruits matured. Still, these results corroborate those obtained by Tsegay et al (2013) who evaluated the stages of maturation of sweet pepper fruits (Capsicum annuum L.) and found a progressive increase with fruit maturation, which may have occurred due to the dissociation of some structural organic molecules from soluble compounds.…”

Biosynthesis of capsaicinoids in pungent peppers under salinity stress

“…Furthermore, the pungency levels of the fruits change under environmental conditions such as soil salinity stress, drought stress, temperature, elevation, and light exposure. It was documented that the capsaicin content was raised in the fruits of C. chinense Jacq under drought stress (Rathnayaka, Kondo, et al, 2021; Rathnayaka, Minami, et al, 2021; Ruiz‐Lau et al, 2011). Also, Purnama et al (2022) found that salinity stress caused an increase in capsaicin content in the hot pepper type of Capsicum annuum .…”