Pg. 29-35 Semi-commercial Evaluation of the ‘Acid-B’ Litchi Postharvest Treatment and Laboratory Evaluation of Alternative ‘Acid-B’ Cocktails

The promising results attained with the “Acid B” treatment during the 2000-2001 season, warranted further semi-commercial air and sea-freight trials. Before the first sea freight trial was attempted, a number of refining experiments were conducted. “Acid B” treated fruit were dried directly or left for a period of 30 minutes before being dried. Additionally, the fruit were packed in an absolutely dry or “slightly damp” state. When packed absolutely dry, the fruit developed brown patches. There was a slight improvement when the fruit stood for 30 minutes before being dried. Best quality was obtained when the fruit was dried to a “slightly damp” stage and packed directly after treatment. During the semi-commercial export trial, ‘HLH Mauritius’ fruit that were treated according to the latter protocol were exported to Canada. The fruit arrived in a good condition with slight browning, mainly around the stems, while the skin was also found to be slightly brittle. Taking in consideration that the export trial was not conducted under optimum conditions, the results obtained were satisfactory. The export company subsequently ordered a container of similarly treated fruit for the coming season. It is doubtful whether this treatment is appropriate for air freight fruit due to the low humidity associated with ambient conditions. In addition to the above, a number of trials were conducted with “Acid B” cocktails. Certain of these showed considerable potential for further improvement of the procedure. A supposedly effective method recently developed in China, is also to be evaluated.

Summary:

• The promising “Acid B” low pH treatment for litchi fruit from the 2000-2001 season led to further semi-commercial air and sea freight trials and laboratory experiments during 2001-2002.
• Refining experiments tested drying protocols where “Acid B” treated fruit were dried directly or left 30 minutes before drying, and packed either completely dry or slightly damp.
  • Fruit packed completely dry developed brown patches.
  • Best visual quality was when fruit were dried directly to a slightly damp state and packed immediately.
• In a semi-commercial export trial to Canada, HLH Mauritius fruit treated with the optimized “Acid B” protocol arrived in good condition with only slight browning around stems and slightly brittle skin.
  • Despite suboptimal shipping conditions, results were satisfactory.
  • The import company reordered for the next season.
  • The treatment may not be suitable for air freight due to low humidity effects.
• Trials with various “Acid B” cocktail combinations showed potential for improved postharvest treatment.
  • Combinations of “Acid B” and citric acid were evaluated for color enhancement and fungal control.
  • The best combination for color, firmness, and taste was 30 g/l citric acid + 30 ml/l “Acid B” with a 30-second dip.
• The study tested “Acid B” as a replacement for post-fumigation hydrochloric acid (HCl) treatment, banned by UK authorities for food safety.
• Storage trials simulated sea freight conditions: 25 days at 1°C followed by 7 days at 13°C.
  • Measured criteria included mass loss, fungal infection, firmness, total soluble solids, titratable acid, and fruit appearance.
• “Acid B” treated fruit showed comparable mass loss and fungal infection rates to conventional SO₂ treatments during initial storage periods, but fungal infection increased after 7 days in some “Acid B” treatments.
• Fruit quality before treatment affected outcomes:
  • Sub-optimal or over-mature fruit showed browning and poor results with “Acid B”.
  • SO₂ treatments masked some blemishes that “Acid B” did not.
• Additional trials:
  • Sodium-acid-pyro-phosphate and N-Benzyladenine were tested for browning control but were ineffective.
  • Ozone-enriched atmosphere combined with SO₂ improved red color appearance but did not significantly affect mass loss or fungal infection rates.
• Recommendations for “Acid B” applications:
  • As sole treatment for sea freight and local market fruit: 170 ml/l “Acid B” or 100 ml/l “Acid B” + 500-550 g/l citric acid for 10-second dips, with immediate drying to a damp state.
  • As post-fumigation treatment for air freight and local markets: lower concentrations and longer dips (e.g., 30 ml/l “Acid B” + 30 g/l citric acid for 30 seconds) with immediate damp drying.
  • Not recommended as sole treatment for air freight due to low humidity.
  • Use only in top-quality fruit; avoid over-mature or corky pericarp fruit.
  • Due to corrosiveness, specialized packhouse equipment is recommended.