Evaluation of Physicochemical Traits of Thorny and Thornless Blackberries at Ripening and During Storage

Blackberry (Rubus sp.) from Rosacea family is a fruit that has a high value due to its unique taste and high amounts of antioxidant compounds. Blackberries contain a wide range from completely thornless to thorny cultivars with highly dense spines of varying degrees of size and curvature. Blackberry fruits decay rapidly after harvest due to high respiration rate. Considering the nutritional value and increasing needs of the consumer market, in the present research physicochemical traits of thorny and thornless blackberries at ripening and during storage were evaluated.

Thorny and thornless blackberry fruits were harvested at commercial maturity and were compared in terms of physical characteristics in the form of a completely randomized design in three replications. In addition, a factorial experiment was conducted with two factors of blackberry type (thorny and thornless) and storage period (zero, four and eight days) in the form of a completely randomized design with three replications. For this purpose, about 100 grams of thorny and thornless blackberries were placed in porous polystyrene containers and kept at a temperature of 4±1 ˚C. The physicochemical characteristics of fruits were measured at the time of harvest (day zero) and on the fourth and eighth days of storage.

The results showed that at ripening stage, thorny blackberries had higher fruit length, diameter, vitamin C, soluble solids, pH, flavor index, anthocyanin, antioxidant activity and total phenol than thornless blackberries, while titratable acidity was higher in thornless blackberries. Increasing the number of thorns by expanding the photosynthetic surface, such as vegetative traits of leaflet width, diameter and number of branches, seems to increase carbohydrate production in thorny plants, which are also used to produce secondary metabolites and phytoalexins in the plant and provides reduction of damage from pests and diseases. With increasing the storage period, soluble solids, pH, flavor index, total phenol were increased significantly, but the antioxidant activity, vitamin C and titratable acidity were decreased. Also, the highest rate of fruit weight loss (9.54%) was recorded on the eighth day of storage in thornless blackberries. In both types of blackberries, the highest amount of anthocyanin was observed on the fourth day of storage, and the amount of anthocyanins in both thorny and thornless blackberries was decreased with increasing storage time, on the eighth day of storage as compared to the fourth day. In thorny and thornless blackberries, with the increase of storage period, at first days the amount of antioxidant activity was increased and then until the eighth day of storage, the amount of antioxidant activity was decreased, which was more in thornless blackberries than thorny blackberries. The amount of total phenol in thorny blackberries was decreased with increasing storage time until the fourth day of storage and then to the eighth day of storage the amount of total phenol was increased, however in thornless blackberries the situation was vice versa so that with increasing storage time to day fourth, the amount of total phenol was increased and then until the eighth day, the amount of total phenol was decreased.

Overall, thorny blackberries had a higher quality at the time of ripening and better shelf life during storage.