Light modulation through spectrally selective materials in solar dryers for the retention of bio-compounds

In this work, we explore the requirements for preserving natural pigments such as anthocyanins, carotenoids, and chlorophylls after solar drying. We focus primarily on how to modulate lighting conditions inside the drying chamber of solar dryers using spectrally selective glazing materials: Green material (<b>G</b>), red material (<b>R</b>), and a nonmetallic plasmon (Cu2-xSe coated polycarbonate, <b>C</b>). These materials modulated the solar irradiance intensity in the spectral range: 450–600, 600–1050, and 450–1050 nm, respectively. This affected to different extents the stability and consequent retention of bio-compounds contained in the food. The changes in the optical absorption spectrum during the drying process of strawberry and cilantro organic extracts (OE) were analyzed. Glycosylation ratio (GR) and acylation ratio (AR) were the chosen variables in the experiments with strawberry OE. Chlorophylls and total carotenoid concentration were the variables chosen in the experiments with cilantro OE. The maximum temperature, 66 °C, was reached using C material, which allows for light transmission in the green to the near-infrared (NIR) spectral interval. The absorption spectrum of the natural pigments evolved over time, influenced by each treatment: <b>G</b>, <b>R</b>, <b>C</b> and open sun drying <b>S</b>. GR and AR increased with the drying time in all the treatments. Better stability of the pigments was observed in strawberry OE in solar drying under G, R, and C covering materials compared with S. A greater retention of chlorophylls and carotenes in cilantro OE was obtained using G and C covering materials. Thus, modulation of light is desirable to improve the retention of bioactive compounds during food drying.

本研究探讨了太阳能干燥过程中花色苷、类胡萝卜素与叶绿素等天然色素的留存保护需求。本研究重点探讨如何通过光谱选择性窗用材料调控太阳能干燥箱干燥腔内的光照条件，所用材料包括绿色窗材（<b>G</b>）、红色窗材（<b>R</b>），以及非金属等离子体材料（Cu₂₋ₓSe包覆聚碳酸酯，<b>C</b>）。上述三种材料分别调控了450~600 nm、600~1050 nm以及450~1050 nm光谱区间内的太阳辐照强度，该调控对食品中含有的生物活性化合物的稳定性及最终留存率产生了不同程度的影响。本研究分析了草莓与芫荽有机提取物（OE）在干燥过程中的光吸收光谱变化：针对草莓有机提取物的实验，选取糖基化率（GR）与酰化率（AR）作为观测变量；针对芫荽有机提取物的实验，则以叶绿素与总类胡萝卜素浓度作为观测变量。采用<b>C</b>材料时可达到最高干燥温度66℃，该材料可透过绿光至近红外（NIR）区间的光线。天然色素的光吸收光谱随时间发生演化，其变化受四种干燥处理方式的影响：<b>G</b>、<b>R</b>、<b>C</b>窗材覆盖干燥，以及露天日晒干燥（<b>S</b>）。所有处理组中，糖基化率与酰化率均随干燥时长的增加而上升。相较于露天日晒干燥组<b>S</b>，采用<b>G</b>、<b>R</b>、<b>C</b>窗材覆盖的太阳能干燥方式下，草莓有机提取物中的色素稳定性更佳。采用<b>G</b>与<b>C</b>窗材覆盖的干燥方式，可使芫荽有机提取物中的叶绿素与类胡萝卜素获得更高的留存率。综上，通过调控光照条件，可有效提升食品干燥过程中生物活性化合物的留存率。