Optimization of a process for extracting astaxanthin from Phaffia rhodozyma by acidic method was investigated, regarding several extraction factors such as acids, organic solvents, temperature and time. Fractional factorial design, central composite design and response surface methodology were used to derive a statistically optimal model, which corresponded to the following optimal condition: concentration of lactic acid at 5.55 mol/L, ratio of ethanol to yeast dry weight at 20.25 ml/g, temperature for cell-disruption at 30 °C, and extraction time for 3 min. Under this condition, astaxanthin and the total carotenoids could be extracted in amounts of 1294.7 µg/g and 1516.0 µg/g, respectively. This acidic method has advantages such as high extraction efficiency, low chemical toxicity and no special requirement of instruments. Therefore, it might be a more feasible and practical method for industrial practice.

Fermentation of Phaffia rhodozyma is a major method for producing astaxanthin, an important pigment with industrial and pharmaceutical application. To improve astaxanthin productivity, single factor and mixture design experiments were used to investigate the effects of nitrogen source on Phaffia rhodozyma cultivation and astaxanthin production. Results of single factor experiments showed nitrogen source could significantly affect P. rhodozyma cultivation with respect to carbon source utilization, yeast growth and astaxanthin accumulation. Further studies of mixture design experiments using (NH(4))(2)SO(4), KNO(3) and beef extract as nitrogen sources indicated that the proportion of three nitrogen sources was very important to astaxanthin production. Validation experiments showed that the optimal nitrogen source was composed of 0.28 g/L (NH(4))(2)SO(4), 0.49 g/L KNO(3) and 1.19 g/L beef extract. The kinetic characteristics of batch cultivation were investigated in a 5-L pH-stat fermentor. The maximum amount of biomass and highest astaxanthin yield in terms of volume and in terms of biomass were 7.71 mg/L and 1.00 mg/g, respectively.

The role of nitric oxide (NO) during storage in wax apple through NO (10 μL/L) fumigate fruit was investigated. Wax apple fruit treated with NO had a significantly lower rate of weight loss, a softening index, and loss of firmness during storage. The transcriptional profile of 10 genes involved in lignin biosynthesis has been analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). The qRT-PCR analysis showed nine genes regulated in the wax apple (p < 0.05) upon NO fumigation, which coincided with the enzyme activity results (NO group lower than control group in peroxidase, phenylalanine ammonia-lyase, and 4-coumarate-CoA ligase), whose total lignin content decreased upon treatment with NO. These results indicate that NO treatment can effectively delay the softening and senescence of wax apple fruit and play an important regulatory role in lignin biosynthesis.

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