Effects of fruit dipping in sodium metabisulfite acidified with hydrochloric acid on quality of fresh longans during cold storage
The objective of this study was to determine alternative treatment to sulfur dioxide (SO2) gas fumigation to prolong storage life of longan for export. The sodium metabisulfite (SMS) dip technique was improved to correct problems of fruit wetting during either rainy or winter seasons, which constrained SO2 fumigation and may cause high residue in fruit. The experiment was to compare the effectiveness between SMS 5% containing HCl, SO2 and HCl alone on residue in fruit including fruit quality during cold storage. The longan fruit with panicle attached were packed in 11.5-kg perforated plastic baskets and washed with clean water before dipping. The fruits were dipped in a solution of SMS 5% + HCl 1% (pH 0.93) for 5 min and compared with fruits fumigated with SO2 and dipped in HCl 6.4% + NaCl 1% + Tween 20 (wetting agent) 0.1% for 5 min, then air dried for 2 h and stored at 6°C for 42 days. The control was untreated fruit. Results indicated that dipping in SMS 5% + HCl 1% (pH 0.93) for 5 min as well as SO2 and HCl showed no sign of pericarp browning and retained the highest value of pericarp color; the lightness of fruit pericarp (L* value) and the yellowness of fruit pericarp (b* value) including fruit decaying control when stored at 6°C for 42 days. Dipping in SMS 5% + HCl 1% (pH 0.93) maintained a higher score of consumer acceptance in fruit pericarp than SO2 according to the highest greenness value (the lowest a* value). This treatment also maintained a high score of consumer acceptance in flesh fruit quality, both aroma and taste, for 28 days, whereas for SO2 it was for 21 days. Moreover, there were no significant changes in some parameters in any treatment; SMS+HCl and SO2 during storage, i.e., SO2 residue in fruit flesh (except for the first days of storage for SO2 treatment), flesh pH, total soluble solid (TSS), titratable acidity (TA) and weight loss percentage. In conclusion, dipping in SMS 5% + HCl 1% (pH 0.93) could be used for extending the shelf life of longan for export and for correcting wet fruit problems caused by rain or mist because it maintained superior fruit pericarp color, less SO2 residue in flesh and consumer acceptance compared with the conventional method.
Apai, W., Likhittragulrung, S., Jaroensuk, S., Rattanakam, S. and Amareok, S. (2018). Effects of fruit dipping in sodium metabisulfite acidified with hydrochloric acid on quality of fresh longans during cold storage. Acta Hortic. 1213, 201-206
sodium metabisulfite, sulphur dioxide, muriatic acid, commercial practice, consumer acceptance