Comparative Evaluation of Physicochemical Properties of Pine Needle Powders Prepared by Different Drying Methods

Abstract

Systematic study of how different drying methods, namely hot-air drying, vacuum-drying, and freeze-drying, affect color, browning index, degree of rehydration, water solubility, and vitamin C content is critical for utilizing pine needle powders (PNP) as a novel ingredient in functional foods. Samples prepared by vacuum-drying showed a significantly higher L*-value, whereas higher a*- and b*-values were detected in the hot-air dried samples (P<0.05). The browning index was significantly higher in samples prepared by vacuum-drying compared to samples prepared by freeze-drying (P<0.05). Freeze-dried PNP exhibited a significantly higher degree of rehydration than hot-air dried samples (P<0.05). Water solubilities of freeze-dried and hot-air dried samples were significantly higher than that of vacuum-dried sample (P<0.05). Vitamin C was less destroyed during freeze-drying compared to hot-air or vacuum-drying (P<0.05). Freeze-dried samples displayed a clear porous structure and appeared to have a bigger space, whereas hot-air dried samples showed lower porosity than vacuum and freeze-dried samples.

Keywords: drying methods; physicochemical properties; pine needle; powder.

Fig. 1

Scanning electron microscope photographs (15.0 kV 500×, 15.0 kV 1,000×, and 15.0 kV 1,500×) of PNP prepared by (A) hot-air, (B) vacuum, and (C) freeze-drying methods, respectively.

Fig. 2

Vitamin C content as affected by different drying methods. Means with different letters (a,b) are significantly different according to Duncan’s multiple range test (P<0.05).