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

Authors: Wang, Shiow; CHEN, CHITSUN - HUALIN DARES, TAIWAN; Wang, Chien

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2008
Publication Date: 2/1/2009
Citation: Wang, S.Y., Chen, C., Wang, C.Y. 2009. The influence of light and maturity on fruit quality and flavonoid content of red raspberries. Food Chemistry. 112:676-684.

Interpretive Summary: Fully matured berry fruits bruise easily during harvesting, transportation, and packing. Ripe berries also deteriorate rapidly after harvest because they are soft and vulnerable to attack by plant pathogens. Fruits harvested at a slightly immature stage are more firm and could withstand handling better with less mechanical injuries. However, there are concerns that immature fruits may not attain as good quality as mature fruits after harvest. In our study, we harvested red raspberry fruit at various maturities and compared their quality after 4 days at room temperature. We found that while very immature berries never developed the levels of sugars and acids as those of ripe berries, fruit harvested at 50% or more advanced maturity had the capacity of attaining comparable quality as those harvested at full maturity. In addition, the nutritional quality and antioxidant activities of fruit harvested at 50% or more maturity were comparable to those of full mature fruit after holding for 4 days at ambient temperatures. These results indicate that it may be feasible to harvest berry fruits at slightly immature stages to reduce mechanical injury and spoilage without compromising market quality. This information is useful to consumers, growers, and the berry industry.

Technical Abstract: The effects of fruit maturity (5%, 20%, 50%, 80% and 100% of full maturity) and different light intensities [56 ' 0.5 'mol m-2s-1 (H), 31' 0.2 'mol m-2 s-1 (L) and dark (D)] on fruit quality, antioxidant capacity and phytonutrient content 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 dark condition. Ripe raspberries (100%) had stronger antioxidant activities and higher total anthocyanin content when compared with the pink stage (50% maturity) which had the lowest antioxidant activities. Fruit harvested at greener stages (5 and 20%) consistently showed higher antioxidant activities and total phenolics than those harvested at 50% or higher degree of maturity. 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 dark condition. 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.