The effect of temperature, moisture content and pH during solid-state fermentation (SSF) of MD2 pineapple peel with Rhizopus oryzae (MUCL 28168) was evaluated on the release of bioactive compounds with antioxidant capacity. Applying a central composite design, it was found that temperature had a significant effect (p < 0.05) on the total phenolic content and DPPH antioxidant activity while for the ABTS radical elimination activity, the factor that presented a significant effect was the pH (p < 0.05); as this factor increases, the antioxidant activity enhances. The optimal conditions for fermentation process were 80% of moisture content, pH 5.5, temperature 37.3 °C and 24 h of process to maximize phenolic content and antioxidant activity. Gallic acid, chlorogenic acid, caffeic acid and cinnamic acid were identified in the extracts by HPLC analysis. These results permit to conclude that SSF of pineapple peel is an effective bioprocess for the release of phenolic compounds with antioxidant activity. Graphical abstract

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Antioxidant phenolic compounds were extracted from fermented samples of Golden pineapple peels via an ultrasound method. The fermentation conditions to maximize the production of phenolic content and antioxidant activity were previously determined (pH: 5.5, T: 37.3 °C and 85% moisture content). A central composite design with 20 treatments was applied to evaluate the effect of the ethanol concentration, time, and temperature on the production of phenolic compounds and antioxidant activity of the extracts. The statistical analysis showed that the optimal conditions to produce extracts with high phenolic content and antioxidant activity were: 62 °C, 30 min and 58% ethanol. We obtained 866.26 mg gallic acid equivalents (GAE)/g d.m in total phenolic content and for antioxidant activity expressed as percentage inhibition, 80.06 ± 1.02% for ABTS and 63.53 ± 2.02% for DPPH, respectively. The bioactive compound profile in the extracts was identified and quantified using ultra-high performance liquid chromatography (UHPLC), this method showed the presence of rosmarinic acid, caffeic acid, vanillic acid, p-coumaric acid, ferulic acid, quercetin-3 glucoside, rutine, quercetin, kaempherol-3 glucoside and gallic acid, demonstrating the great potential of these by-products to obtain components that can benefit the consumer’s health.

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Las técnicas de secado de Ventana de Refractancia (VR) y Fritura con Aire Caliente (AF), permiten obtener snacks de frutas de alta calidad nutricional y fisicoquímica. El propósito de este trabajo fue evaluar las técnicas de secado de WR-AF para obtener “snacks” de piña deshidratada. Se emplearon trozos de piña de la variedad MD2 con geometría triangular (40 mm de lado y 4 mm de espesor). En el secado por WR se emplearon tres temperaturas (70, 80 y 90 °C). Para cada temperatura se modeló la cinética de secado mediante cuatro modelos matemáticos (Newton, Page; Wang & Singh, y Midilli). Se determinó: color, en términos de Luminosidad (L*) y cambio total de color (ΔΕ), actividad de agua (aw), coeficientes de difusión y energía de activación. Para las muestras secadas en la combinación de las técnicas VR-AF, se determinaron las curvas de secado, L*, ΔΕ, aw y vitamina C. En total se realizaron 4 tratamientos en el secado con AF a 100 °C; tres de las cuales fueron muestras tratadas (MT) previamente por WR, y el otro fue muestra no tratada (MNT). Los resultados mostraron que, a mayor temperatura de secado por WR mayor fue el coeficiente de difusión y menor fue el tiempo de secado. Para un contenido de humedad de 9 % (d.b), los tratamientos a 90, 80 y 70 °C requirieron 90, 110 y 130 min de secado, respectivamente. El modelo de Midilli fue el que mejor ajustó las cinéticas de secado. Se observó que las técnicas de VR-AF permitieron obtener menor tiempo de secado, mayor retención de vitamina C y de color respecto a las MNT. Estos resultados indican que la técnica WR-AF es una alternativa viable para producir “snacks” de piña en tiempos mas cortos y con mayor conservación de las características de calidad.

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Phenolic compounds that are present in pineapple by-products offer many health benefits to the consumer; however, they are unstable to many environmental factors. For this reason, encapsulation is ideal for preserving their beneficial effects. In this work, extracts were obtained by the combined method of solid-state fermentation with Rhizopus oryzae and ultrasound. After this process, the encapsulation process was performed by ionotropic gelation using corn starch, sodium alginate, and Weissella confusa exopolysaccharide as wall material. The encapsulates produced presented a moisture content between 7.10 and 10.45% (w.b), a solubility of 53.06 ± 0.54%, and a wettability of 31.46 ± 2.02 s. The total phenolic content (TPC), antioxidant capacity of DPPH, and ABTS of the encapsulates were also determined, finding 232.55 ± 2.07 mg GAE/g d.m for TPC, 45.64 ± 0.9 µm Trolox/mg GAE for DPPH, and 51.69 ± 1.08 µm Trolox/mg GAE for ABTS. Additionally, ultrahigh performance liquid chromatography (UHPLC) analysis allowed us to identify and quantify six bioactive compounds: rosmarinic acid, caffeic acid, p-coumaric acid, ferulic acid, gallic acid, and quercetin. According to the above, using ionotropic gelation, it was possible to obtain microencapsulates containing bioactive compounds from pineapple peel extracts, which may have applications in the development of functional foods.

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