Assessment of different drying methods with the stability of apocarotenoids and mucilage concentration in Saffron (Crocus sativus L.) stigmas based on mathematical modeling

Abstract

Saffron harbors invaluable apocarotenoids that are highly sensitive to environmental and storage influences. Consequently, post-harvest procedures are important in aligned with production stages and assume a pivotal role in ensuring the quality of the final product. This research investigated the repercussions of diverse drying methodologies on moisture ratio (MR) and alterations in secondary metabolites within saffron stigma. The employed drying techniques encompassed non-thermal methods (NTD) such as Shade Drying (SD) and Cold Air Drying (CD), thermal drying (TD) methods including Cabinet Dryer (CAD), and radiant drying methods, namely Infrared (IR) and Thermal Light (TL). The findings underscored that TL50 °C significantly expedites drying time, being 28.97 and 26.89 times faster than SD and CD, respectively. Notably, the preeminent apocarotenoids, Crocetin, and total Crocin were found to be sensitive to heat. Interestingly, mild heat at TL50 °C and IR50 °C resulted in a substantial augmentation of these two metabolites (P < 0.01). Elevated temperatures adversely impacted the crucial components of crocin (trans-4-GG) by increasing cis and trans isomers (R²=0.82). The mucilage characteristics of saffron stigmas remained unaffected by the diverse drying methods. However, there was a strong correlation between mucilage and crocin content (R²=0.98). According to the evaluation indices of drying models, the Demir and Midilli functions emerged as the most fitting across a majority of TD methods, boasting R²adj values ranging from 97 % to 98 %. In NTD methods, in addition to Demir and Midilli, the Wang and Singh function exhibited superior fits, attaining the minimum AICc and the highest R²adj values ranging from 0.985 to 0.999. These findings provide valuable insights into understanding the effects of temperature, drying methods, and the stability of secondary metabolites in saffron products, catering to both saffron research and the design of industrial saffron dryers.