Bioactive compounds conservation and energy-mass analysis in the solar greenhouse drying of blackberry pulps

Recently, the quality of food solar dried has been associated to solar irradiance, irradiation and UV-light. Different materials used as covering materials in direct solar dryers had different optical properties, thus, different quality should be expected in solar food drying. The objective of this study was to compare two direct solar dryers builder with different covering materials: Direct Solar Drying with Poly (methyl methacrylate) (DSD), and Greenhouse Solar Drying with polyethylene (SGD), based on their three aspects: chemical composition, heat-mass transference, economic-environmental effect. Chemical composition was evaluated as the total phenolic compounds (TPC), flavonoids (TF) anthocyanins (TA) and antioxidant activity (AA) of blackberry pulp (Rubus spp). Dehydrated blackberry pulp contains lower TA than raw samples because TA is sensitive to solar irradiation and UV solar irradiation. TPC, TF and AA averages do not show significant differences among all the drying processes. Evaluation of energy and heat transfer in the evaporative and diffusive periods of the drying technologies led to an assessment of the return of investment period for DSD and SGD technologies for different power sources. The results suggest payback periods between 39 and 121 months, considering only the 6 months of harvest duration without using the solar dryers the rest of the year.