Postharvest Ripening and Fermentation of Noni Fruit (Morinda citrifolia) In Hawaii

Noni (Morinda citrifolia) is a tropical plant used traditionally in Polynesia, Southeast Asia and other regions for medicinal purposes. Noni fruit and juice extracts are reportedly therapeutic for diabetes, high blood pressure, and certain types of cancer. Research was conducted to determine the physiology of noni fruit ripening, as well as the chemical and microbial changes that occur during noni fermentation. Mature noni fruit at the firm yellow stage were harvested, measured for respiration and ethylene rates, and held in sealed glass jars for juice production up to 42 days at 22ºC. Noni juice exudates were analyzed weekly for pH, total soluble solids (TSS), titratable acidity (TA), and bacterial and fungal populations. Ripening noni fruit had a non-climacteric respiratory pattern with an average rate of 34 mg CO₂∙kg^-1h^-1 at 22ºC and no detectable ethylene production. The various profiles indicated differences among fresh and fermented samples and storage duration. Bacterial populations did not differ from 0 to 35 d, but increased significantly at 42 d. The only fungus consistently isolated (85%) from fermented juice was Mucor circinelloides f. sp. circinelloides, which had populations that peaked at 14 d. Head space analysis indicated that CO₂ was highest at 14 and 21 d (25 and 20 kPa, respectively), while O₂ was never lower than 8 kPa. TSS was 9.8% in fresh noni, and decreased to 5.7% after 14 d and 4.9% at 42 d. The greatest decline in TSS at 14 d coincided with the highest Mucor populations and CO₂ levels. The pH was greatest (3.8) in fresh noni juice and lowest (3.5) after 14 d storage. The volume of noni juice exudates followed a normal distribution pattern with storage time and peaked at 21 d. The significant changes observed at 14 d for Mucor population, CO₂, pH, and TSS levels preceded the highest juice yield that occurred at 21 d. Although the optimal duration for maximum juice production was 21 d, noni biological and chemical factors are dynamically changing over storage duration and can affect juice quality during the course of fermentation.