The influence of light and maturity on fruit quality and flavonoid content of red raspberries

The effects of various fruit maturities and different light intensities on berry fruit quality, antioxidant capacity and phytonutrient levels in red raspberries (Rubus ideaus L.) were determined. At harvest, immature berries contained significantly lower levels of sugars and acids than ripe berries. When berries were harvested at 5% or 20% maturity, they never developed the levels of soluble solids content (SSC) and titratable acid (TA) values observed in ripe berries at harvest. However, fruit harvested at 50% or more advanced maturity had the capacity of attaining comparable levels of SSC, TA and sugars as those harvested at 100% maturity. When 5% and 20% berries were stored under light, higher level of SSC and lower levels of TA values were observed than those kept in the dark. However, light condition showed little effect in 50% and 80% maturity fruit after 4 days at 24/16°C (day/night). Ripe raspberries (100%) had stronger antioxidant activities and higher total anthocyanin content when compared with the pink stage (50% maturity). Fruit harvested at greener stages (5% and 20%) also consistently showed higher antioxidant activities and total phenolics than those harvested at 50%. Cyanindin-based anthocyanins increased during postharvest period. On the other hand, other polyphenols such as ellagic acid, quercetin 3-glucoside, quercetin derivative, and kaempferol 3-glucuronide were initially present at high levels but decreased drastically during storage. Red raspberries harvested at different developmental stages continued their development during storage even under the dark conditions. The antioxidant activity of red raspberries was directly related to the total amount of phenolics and flavonoids. Results of this study indicate that red raspberries harvested at 50% or more advanced maturity could develop comparable quality and antioxidant levels as those harvested at full maturity.