Pg. 23-27 The Refinement of the Promising Low pH ”Acid B” Post-Harvest Treatment

The promising results attained with the “Acid B” treatment during the 1999-2000-season, warranted further refinement of the application protocol, especially in terms of acid concentration and time exposure specifications. During the first trial conducted during the 2000/2001 season, “Acid B” was applied at different concentrations, ranging from 80 to 225 ml/l, for exposure times differing between 10 and 120s. Undesirable off-tastes were found to develop when dipped for longer than 10 seconds regardless of the concentration. Optimum product in terms of taste and colour was obtained between 166 – 170 ml/I for 10s. In terms of taste, the sensory panel found the 10s 170 ml/l treatment to be acceptable when compared to the SO₂ treated fruit. However, some panellists still recorded a slight burning sensation on the tongue. It was encouraging to note that the optimal “Acid B” treatments had lower fungal infection rates than the SO₂ treatment. The combination of the “Acid B” treatment with controlled and modified atmosphere was also investigated. Unfortunately, all the treatments developed unacceptable off-tastes and a high incidence of fungal infection occurred. The use of cocktail mixtures of “Acid B” and other food additives were also investigated. The combination of citric acid and “Acid B” showed promise, but requires further refinement. Semi-commercial trials are to be launched during the coming season.

Summary:

• The Acid B treatment showed promising post-harvest preservation results for litchi fruit during the 1999-2000 season, warranting refinement of application protocols focusing on acid concentration and exposure time.
• In the 2000-2001 trial, Acid B was tested at concentrations from 80 to 225 ml/l with exposure times between 10 and 120 seconds. Off-tastes developed when dipping exceeded 10 seconds regardless of concentration.
• Best taste and color retention was achieved at 166-170 ml/l Acid B with a 10-second dip, producing fruit with acceptable sensory qualities compared to SO₂-treated fruit, although some panelists noted a slight tongue burning sensation.
• Acid B treatment showed lower fungal infection rates than SO₂ treatment during shelf life, indicating good antifungal properties.
• Attempts to combine Acid B with controlled atmosphere (CA) and modified atmosphere (MA) storage led to unacceptable off-tastes and higher fungal infection, recommending Acid B only be used under regular atmosphere.
• Cocktail mixtures of Acid B with citric acid showed potential, especially improving flavor, but color retention and fungal infection rates require further research.
• Sensory analysis indicated the 170 ml/l Acid B 10-second dip fruit had higher acceptability and freshness ratings than SO₂-treated fruit, with most panelists willing to buy Acid B treated fruit.
• Residue analysis showed a slight increase in Acid B mineral residues in fruit flesh and skin during storage, but no major safety concerns.
• Recommendations include semi-commercial trials to assess practical application aspects like bath volume, bath solution change frequency, drying processes, and effects of fruit maturity on residues and quality.
• The study confirms Acid B as a promising SO₂ replacement for litchi post-harvest treatment, with ongoing development expected, especially on Acid B-citric acid mixtures and further refining commercial procedures.
• Controlled and modified atmospheres are better suited for use with SO₂ or disinfectants rather than Acid B.
• Acknowledgements and references for earlier related research are included.