Optimizing insect repellence in open sun drying of fish through the combined influence of salt, turmeric, pepper and the bacteriocin nisin under tropical conditions

Background

Sun drying of fish in open air is an age-old traditional practice in Asia and some other parts of the world. This study aims to suggest optimal field doses of turmeric, pepper, salt and the bacteriocin nisin (food additive, E234) for open-sun-dried silver jewfish (Johnius argentatus) under a tropical environment. Investigations were carried out on the blowfly infestation, proximate composition, water reconstitution properties and organoleptic and microbial quality of open-air-dried fish samples.

Results

A direct relationship between moisture reduction and drying period was observed with salt-treated samples demonstrating accelerated moisture reduction, reaching as low as 14.1% after 34 h. Turmeric and pepper treatments provided some protection against weight loss but ultimately extended the drying time to 38 h. Botanical pesticides like turmeric or pepper exhibited significant efficacy against blowfly adult and larval infestation with similar efficacy observed in 15% and 25% salt-treated samples. Proximate composition analysis revealed that salt-treated samples had lower moisture ranging from 14.1% to 16.0% but higher protein of 58.2%–62.1%, while the lipid and ash content did not vary significantly (p > 0.05). The water reconstitution properties of salt-treated samples exhibited superior rehydration rates, with the highest in nisin (Niseen S) + 15% salt-treated samples at 60°C, while organoleptic evaluations revealed salt-treated samples to possess favourable attributes with minimal insect infestation and broken pieces. Finally, microbial analysis demonstrated the lowest aerobic plate count in dried fish samples treated with nisin (Niseen S) alone or in combination with 15% salt and/or 3% turmeric ranging from 3.97 ± 0.20 to 4.33 ± 0.07 log cfu/g.

Conclusion

It is concluded that 200 ppm nisin (Niseen S)-treated samples in combination with 3% turmeric and/or 15% salt are a viable option for producing high-quality dried fish in traditional open-air sun-drying practices.