Enhancement of astaxanthin production from food waste by Phaffia rhodozyma screened by flow cytometry and feed application potential.

Astaxanthin is widely used in food, aquaculture, cosmetics, and pharmaceuticals due to its strong antioxidant activity and coloring ability, but its production from Phaffia rhodozyma remains the main challenge due to the high fermentation cost and low content of carotenoid. In this study, the production of carotenoids from food waste (FW) by a P. rhodozyma mutant was investigated. P. rhodozyma mutant screened by UV mutagenesis and flow cytometry could stably produce high carotenoids at 25°C, with carotenoid production (32.9 mg/L) and content (6.7 mg/g), respectively, increasing by 31.6% and 32.3% compared with 25 mg/L and 5.1 mg/g of wild strain. Interestingly, the carotenoid production reached 192.6 mg/L by feeding wet FW, which was 21% higher than batch culture. The 373 g vacuum freeze-dried products were obtained from the fermentation of 1 kg FW by P. rhodozyma, which contained 784 mg carotenoids and 111 mg astaxanthin. The protein, total amino acids, and essential amino acids content of the fermentation products were 36.6%, 40.5%, and 18.2% (w/w), respectively, and lysine-added fermentation products had the potential of high-quality protein feed source. This study provides insights for the high-throughput screening of mutants, astaxanthin production, and the development of the feed potential of FW.

Fluorescent enzyme-linked immunoassay based on silane-doped carbon dots for sensitive detection of microcystin-LR in water and crucian samples.

In this work, a fluorescent nanoparticles labeling-free fluorescence enzyme-linked immunoassay (FELISA) has been established for the ultrasensitive detection of microcystin-LR (MC-LR) in water and fish samples. Polyclonal antibody against MC-LR was labeled with horseradish peroxidase (HRP) and used as signal probe for binding with analyte in sample or for coating antigen. After washing of the unbound antibody, the substrate system (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS)/H2O2) was added. The oxidation product of ABTS (ox-ABTS) catalyzed by HRP effectively caused the fluorescence quenching of subsequently added silane-doped carbon dots (Si-CDs), and the change in fluorescence intensity of Si-CDs was used to realize the quantitative detection of MC-LR. Under the optimum conditions, the Si-CDs based FELISA method showed a good linear relationship from 0.001 to 3.20 µg L-1 (R2 = 0.994) and provided a low detection limit of 0.6 ng L-1, which was approximately 30-fold lower than that of traditional indirect competitive ELISA. Average recovery values from 79.9% to 109.2% was obtained from spiked water and crucian samples, suggesting its potential application on the monitoring of MR-LR at a trace level.