Discovering The Impact of Different Cultivation Factors on The Phenolic Composition of Raspberries

Abstract

The red raspberry (Rubus idaeus L.) fruit is a rich source of health promoting phenolic compounds, such as anthocyanins, ellagitannins, ellagic acid derivatives as well as flavonols. Genotype, cultivation environment and developmental stage are factors that influence the accumulation of these compounds. However, the effect of cultivar genotype, cultivation system and harvest time on the phenolic composition of raspberry is still poorly understood under the Nordic growing conditions.

The phenolic profiles of four raspberry cultivars (Agat, Borgund, Glen Ample, and Ninni) were investigated with three different cultivation systems (open-field in-ground (A), open-field containerized (P) and tunnel containerized (T)), and at three ripeness stages (early, optimum and late ripeness). HPLC-DAD was used for analysis of phenolic compounds and LC-DAD-MS for phenolic compound identification. Principal component analysis (PCA) and three-way general linear model (GLM) analysis were performed to assess the effects of cultivar, cultivation system and harvest stage on the phenolic composition.

Thirty-three phenolic compounds were tentatively identified, including 10 anthocyanins, 3 ellagitannins, 11 ellagic acid derivatives, 7 quercetin derivatives and 2 kaempferol derivatives. Anthocyanins were the most abundant phenolics for all cultivars and treatments. The GLM analysis revealed that the cultivar identity was the prominent factor affecting each of the phenolic classes (p <0.001) with the model R2 values between 0.769 and 0.961. Agat had the highest total phenolic concentration (27.9 to 34.5 mg/100 g FW) while Borgund had the lowest overall accumulation (12.3 to 18.8 mg/100 g FW). Cultivation system significantly influenced all phenolic classes (p <0.001) with generally higher levels of anthocyanins being observed in open-field compared to tunnel grown systems. The significance of harvest time on flavonols, ellagic acid derivatives and total phenol sum was observed but not the significance of harvest time on anthocyanins as an independent main effect. PCA also reinforced that cultivar is the most important structuring factor for anthocyanin variation. Results in total indicate that the phenolic quality of the raspberries grown in Finland is mostly a result of the genotype but is also influenced by the cultivation system and harvest dates in a compound basis and cultivar-specific manner.