Analysis of the influence of different drying processes on the quality attributes of orange peel

Abstract

The present research aimed to assess the effect of different drying processes on kinetics, antioxidant content and activity, texture, colour, morphology, and β-carotene content of orange peel (OP). The utilization of microwave drying resulted in a notable increase in the rate of evaporation of water present in the orange peel. This process facilitated the release of bound polyphenols. The OP dried at 600 W exhibited the highest total phenolic compound (24.65 mg GAE/g) and total flavonoid compound (11.73 mg QE/g), as observed in the recorded data. The total antioxidant value exhibited a decrease at both elevated and reduced levels of microwave power compared to raw OP. The study found that the drying model proposed by the Weibull model exhibited the most optimal fit, as evidenced by a low SS_error (1.6 × 10⁻³-16.12 × 10⁻³), RMSE (0.02–0.05) and high R² (0.99–1.00). Among dried products, high hardness (30.92 ± 1.26 N), fracturability (28.31 ± 1.22 N), and lightness (74.01 ± 0.38) were observed in freeze-dried (FD) OP. The browning index was high in microwave drying at 180 W (MWD 180 W), and tray drying (TD) which also produced more vibrant colours, as observed in their high chroma value. The high performance liquid chromatography (HPLC) showed that the retention of β-carotene was observed highest in FD (0.057 ± 0.003 mg/g) and lowest in TD (0.032 ± 0.002 mg/g). The morphological study revealed small-sized particles in high-temperature drying methods (MWD 900 W and TD). Large pores and frequent cracking were observed in microwave drying compared to FD. Four clusters are formed in Principal component analysis (PCA) loading of Fourier transform infrared (FTIR) spectra based on their similar characteristics as found in FTIR. Antioxidant content and texture are closely related to the chemical moieties, as observed in PCA.