Effect of vacuum and through flow drying technique on mathematical modelling, functional properties, color degradation kinetics, and essential oil components of fish mint (Houttuynia cordata Thunb)

Abstract

Fish mint (Houttuynia cordata Thunb) was dried using vacuum dryer (VDT) and through flow air dryer (TFDT) at 35 °C, 40 °C and 45 °C, respectively. Drying behaviour of the fish mint was performed using eight different mathematical models. The effective moisture diffusivity D_eff values were found as 1.02741 × 10⁻¹⁰, 1.17146 × 10⁻¹⁰ and 1.47784 × 10⁻¹⁰ m²/s at 35 °C, 40 °C, and 45 °C, respectively for through flow dried samples. Color degradation kinetics using three models were conducted that showed promising results of first order reaction for TFDT₂ samples. The essential oil of freshly harvested and dried fish mint, produced by different drying techniques, were found to be seven compounds namely 5-O-caffeoylquinic acid, 3- O-caffeoylquinic acid, 4- O-caffeoylquinic acid, rutin, hyperoside, isoquercitrin, and quercitrin. The ratios of the different components were significantly impacted by the drying techniques which was estimated by FTIR analysis. Further the dried fish mint was subjected to grinding process to obtain powder and its engineering properties and techno-functional were analysed. The powdered fish mint found significant difference in colour, techno-functional properties, and engineering properties. The fish mint dried at 40 °C and TFDT resulted in better properties with color, techno-functional properties and engineering properties, (L*- 7.41, a*-1.27, b*-4.36, hue-74.85, chroma- 4.57), Bulk Density - 114.4 kg/m³, Tap Density - 139.6 kg/m³, Carr Index - 12.40, Hausner Ratio - 1.171, Water Holding Capacity - 14.84 %, and Oil Holding Capacity - 33.24 %.