The Effect of Different Storage Conditions and Blending on Bioactive Compounds of Raspberries and Blueberries.
Background: Blueberries and raspberries are one of the richest dietary sources of health-promoting bioactive compounds, which have been shown to protect against degenerative diseases and certain cancers. Aims and Objectives: To determine the effect of different storage conditions such as refrigerating, refrigerating until overripe, freezing and blending, on the antioxidant capacity and total phenolic content of out of season red raspberries and highbush blueberries. To analyse the effect of refrigerating, refrigerating until overripe, freezing and blending on the pH, total anthocyanin content, chlorophyll A, chlorophyll B and carotenes contents of red raspberries and highbush blueberries. Materials and Methods: Fresh raspberries and blueberries were divided into six groups respectively as follow: fresh, fresh blended, frozen, frozen blended, overripe and overripe blended. Blending was achieved by homogenising the fruits using a hand blender to obtain a smoothie like consistency. All the frozen groups were stored in the freezer between -16 ºC and -20 ºC. All the overripe groups were stored at 2.7ºC in the refrigerator, until two days past their display by date. All the samples were freeze-dried prior to testing. The polyphenolic content was measured by using the Folin-Ciocalteu assay, and the absorbance was measured at 765nm using a UV-VIS spectrophotometer. The antioxidant capacity was measured by the FRAP assay, and the absorbance was measured at 600nm using a MPR-96 visible microplate reader. The chlorophyll content was determined by following the method described by Dere et al (1998). The total anthocyanin content was measured by using the method defined by Tashtoush et al (2016). The absorbance was read at 530 and 657mn using a UV-VIS spectrophotometer. Results: The polyphenolic content and the antioxidant capacity of blueberries were not affected by the different storage conditions and blending, as no statistical significant differences were observed between the various treatments. The polyphenolic content and the antioxidant capacity of red raspberries was significantly higher in the frozen blended (p<0.05), overripe (p<0.05) and overripe blended (p<0.05) samples, when compared to the fresh samples. The total anthocyanin content of blueberries was found significantly higher in the frozen samples (p<0.05), while total anthocyanin content in raspberries was found significantly lower in the frozen group (p<0.05). The chlorophyll A, chlorophyll B and carotene content in blueberries were found to be low; while the chlorophyll A and carotenes contents of raspberries were negligible. The pH in both berries was in the acidic range. Conclusion: Out of season highbush blueberries and red raspberries are still a great dietary source of essential bioactive compounds. Blueberries can be consumed as fresh, frozen, overripe and blended forms, without their antioxidant capacity and polyphenolic content being affected, except for their anthocyanin content. The antioxidant capacity and total polyphenolic content of red raspberries was higher in the overripe, overripe blended and frozen blended conditions. Key words: raspberry, blueberry, antioxidants, polyphenols, storage conditions, blending