Influence of temperature and ultrasound on drying kinetics and antioxidant properties of red pepper

Abstract

Red pepper samples (1 m/s) were dried at different temperatures (30, 50, 70ºC) without and with (20.5 kW/m 3 ; 21.7 kHz) ultrasound application. The antioxidant capacity (AC), the total phenolic content (TPC) and the ascorbic acid (AA) content of fresh and dried red pepper samples were used as indicators of the quality of the dried products. Ultrasound application significantly improved the kinetics in every case, influencing not only the effective diffusivity but also the mass transport coefficient thus implying a reduction in energy needs. Drying significantly reduced AC, TPC and AA, this reduction being significantly smaller at 70ºC due to the shorter drying time. Compared with conventional drying, ultrasound application reduced the loss of antioxidant properties at 50 ºC but produced greater degradation at 70 ºC, which points towards an optimal drying temperature when using ultrasound.

Fate of Residual Pesticides in Fruit and Vegetable Waste (FVW) Processing

“…In terms of the application of US to drying, high intensity ultrasound produces a series of effects that can enhance heat and mass transfer. In fact, US has been applied to intensify convection drying or atmospheric freeze-drying of different products and by-products [ 128 , 152 , 153 ], achieving important reductions in operation time and energy consumption [ 154 ]. In most cases, ultrasound-assisted processing was used as a method to improve appearance characteristics (color, tastes) of dried fruit products by modifying drying kinetics [ 133 ], or to preserve bioactive compounds such as polyphenols, anthocyanins and flavonoids [ 128 ].…”

Application of High-Power Ultrasound in the Food Industry

“…In the food industry, drying and dehydration of foods are important preserving processes where mass and energy transfer phenomena occur. They consist of removing a large part of the water from the food in order to improve the stability of the product, reducing its volume and weight and facilitating the handling and transport of the products [70,71]. Currently, one of the most widespread techniques in the food industry is air convection dehydration.…”

“…However, it is an energetically costly operation and, in some cases, requires long periods of time. In order to reduce drying times, some industrial strategies exist, such as increasing the temperature of the air, which can cause alterations in the composition and structure of foods, or increasing the air speed that might lead to the formation of a dry and impermeable layer that can inhibit the exit of humidity from the interior of the product [70].…”

“…More studies have been carried out with airborne ultrasound systems, reducing drying times by 20-30% when applied at low temperatures and low air velocities [70]. For example, García-Pérez et al [76] developed a convection drying equipment applying ultrasound to the air, in which the treatment chamber consisted of a vibratory aluminum cylinder coupled to a transducer (21.8 kHz,75 W).…”

Ultrasound Drying of Rose Hips: a Process Study

“…Перспективными направлениями в области создания ресурсосберегающих технологий в сушке растительного сырья являются инфракрасная сушка и сушка в поле действия ультразвука. Анализируя труды российских и зарубежных ученых в данной области, авторами статьи было решено использовать ультразвук для достижения цели исследования, а именно уменьшение потери витаминов за счет применения современных ультразвуковых технологий, позволяющих снизить температурный режим и сократить время сушки, а также улучшить качественные показатели высушенного продукта [4,11,[13][14][15][16][17][18][19][20].…”