Table 7. Effects of pretreatments on the quality of onion shreds dried under different drying conditions.

	DR	RR	ΔE	b(pyruvic acid) µmol/g	w(ascorbic acid) mg/100 g
Hot air drying at 60 °C
Untreated	6.55±0.53	4.82±0.13	13.53±0.37	48.93±0.77	19.95±0.53
Salt-treated	6.13±0.59	4.56±0.25	12.76±0.49	45.28±0.78	17.23±0.58
Sulphited	7.43±0.37	5.01±0.39	9.80±0.38	46.52±0.69	18.45±0.75
Heat pump drying at 50 °C
Untreated	6.79±0.19	5.18±0.37	10.21±0.53	56.23±0.19	22.30±0.29
Salt-treated	6.20±0.27	4.86±0.22	9.77±0.35	53.98±0.37	21.18±0.23
Sulphited	7.54±0.23	5.25±0.38	8.93±0.37	54.66±0.49	21.65±0.33
Microwave-assisted drying at 240 W and 50 °C
Untreated	6.45±0.23	5.12±0.26	16.00±0.83	50.24±0.63	19.85±0.53
Salt-treated	6.34±0.28	4.98±0.22	13.70±0.72	48.45±0.72	19.81±0.55
Sulphited	6.62±0.31	5.20±0.37	11.73±0.68	48.82±0.86	19.99±0.61

DR=dehydration ratio, RR=rehydration ratio, ΔE=colour difference