Application of Ultrafine Bubble Technology for Reducing Sodium Metabisulfite Concentration in Preserving Trimmed Coconuts

The export of trimmed coconuts necessitates controlling microbial growth and browning, often achieved through the use of sodium metabisulfite (SMS). However, SMS can elicit allergic reactions in operators. To address this concern, ultrafine bubble (UFBs) technology was applied to reduce the SMS concentration. Trimmed coconuts were dipped in either a 1.5% SMS solution or a combination of 1.5% SMS with UFBs (1.5% SMS-UFBs) and compared to coconuts dipped or not dipped in a 3% SMS solution. All treated coconuts were then wrapped with polyvinyl chloride (PVC) film and stored at 2–4 °C for 2 months, followed by transfer to storage at 8–10 °C for an additional 14 days. The results indicated that halving the SMS concentration, with or without UFB application, effectively controlled microbial growth and browning, comparable to using 3% SMS. No contamination of E. coli or Salmonella spp. was detected. The mesocarp whiteness, browning index, polyphenol oxidase (PPO) activity, and total phenolic content of coconuts treated with 1.5% SMS or 1.5% SMS-UFBs did not differ significantly from those dipped in 3% SMS solution (p > 0.05). Similarly, the quality of coconut water and coconut meat in SMS or SMS-UFB treatments did not show significant differences. In dry seasons, using 1.5% SMS with or without UFBs yielded comparable results to those obtained using 3% SMS. However, in wet seasons, the synergistic effects of UFBs on reducing microbial growth incidence were observed, similar to the impact achieved with 3% SMS, whereas 1.5% SMS alone did not inhibit microbial growth. Overall, UFB technology shows promise in reducing SMS concentration by 50% for trimmed young coconuts throughout the year.