A New Rotary Dryer Assisted by Infrared Radiation for Drying of Acerola Residues
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ORIGINAL PAPER
A New Rotary Dryer Assisted by Infrared Radiation for Drying of Acerola Residues Priscila B. Silva1 · Geraldo D. R. Nogueira2 · Claudio R. Duarte2 · Marcos A. S. Barrozo2 Received: 26 February 2020 / Accepted: 3 September 2020 © Springer Nature B.V. 2020
Abstract Acerola is a tropical fruit whose residues from its processing contain amounts vitamin C, phenolic and other bioactive compounds at the same level of the fruit pulp and juice. In this work we used a novel system for acerola waste drying, which is composed by a new rotary dryer (developed by our research group), named roto-aerated dryer, equipped with a new pre-drying system using infrared radiation. In addition, a pretreatment with ethanol was performed to improve the process performance. The ascorbic acid content, total phenolic content, total flavonoid contents, and antioxidant activity were quantified before and after drying. The main phenolic acids and flavonoids were identified by high performance liquid chromatography. Operating conditions that promoted high moisture removal (91.2%) and that yield to a product with high antioxidant activity ( IC50 = 11.6 ± 0.3 µg/mL) and low water activity (0.374) were identified. The pretreatment with ethanol led to an increase of up to 72% of the moisture reduction. Therefore, the drying results revealed that this novel dryer system combined with the ethanol pre-treatment is a good alternative for dehydration, reducing the process time and maintaining a high antioxidant activity. Graphic Abstract
Keywords Acerola waste · Roto-aerated dryer · Infrared · Bioactive compounds
* Marcos A. S. Barrozo [email protected] Extended author information available on the last page of the article
Abbreviations AA Ascorbic acid content (mg/100 g of sample, dry matter) ACL Chlorogenic acid content (mg/100 g of sample, dry matter) APC P-coumaric acid content (mg/100 g of sample, dry matter) Awi Water activity after infrared dryer (–)
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Awr Water activity roto-aerated dryer (–) CAF Caffeic acid content (mg/100 g of sample, dry matter) CCD Central composite design CE Experiment with ethanol pretreatment CR Regression coefficient GAE Gallic acid (mg/100 g of sample, dry matter) HPLC High performance liquid chromatography IC50 Sample capable of reacting with 50% of the radical present in the DPPH• solution (μg of sample/ mL) Mir Moisture after infrared dryer (g H2O/100 g, dry matter) Mroto Moisture after roto-aerated dryer (g H2O/100 g, dry matter) MRi Moisture removed after infrared dryer (%) MRr Moisture removed roto-aerated dryer (%) MRtotal Total moisture removed (%) P Infrared lamp power (W) Rw Drying rate (percentage points per hour) SD Standard deviation SE Experiment without ethanol preteatment T Air temperature (°C) Τ Residence time (min) τtotal Total residence time (min) TFC Total flavonoids content (mg of rutin/100 g of sample, dry matter) TPC Total phenolic content (mg of gallic acid equivalent/100 g of sample, dry matter) V Air velocity (m/s
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