Investigation On The Fermentation Of Phaffia Rhodozyma And Development Of Astaxanthin Product

Astaxanthin has a long conjugated double bond and molecular terminal hydroxy ketone,which leads to the instability of astaxanthin.High temperature,low or high p H and light can result in the degradation of astaxanthin.The polyene chains are easy oxidized and isomerized,leading to the loss of color.The structure of astaxanthin also indicates its high oxidation resistance,contributing to its diverse protective properties against cancer,cardiovascular disease,and degenerative diseases such as macular degeneration and cataracts.In this study,Phaffia rhodozyma was cultivated with the mixed carbon source for the rapid accumulation of biomass at the first stage,and then carotenoids were synthesized by feeding additional peptone.The different methods of disrupting yeast cells were studied,and astaxanthin was partially released and emulsified using glass bead milling.And then yeast extract was prepared to improve the bioavailability of P.rhodozyma.Astaxanthin microencapsulation was prepared by composite materials.At first,effects of different carbon source ratio,C/N,feeding time of peptone and the amount of peptone supplementation on the growth of P.rhodozyma and the synthesis of carotenoids were studied.When sugar concentration was 30 g/L(glucose: total sugar in Jerusalem artichoke extract = 2: 1),yeast biomass could reach up to 13.54 ± 0.21 g/L at 36 h,while carotenoids production was only 37.76 ± 1.91 mg/L.When the optimum C/N ratio was 4,biomass reached the highest.The carotenoids production reached 83.34 ± 3.08 mg/L at 72 h by feeding peptone,leading to an increase by 10.62% compared with control.When feeding 0.75 g/L peptone in the medium,carotenoids production reached 82.35 mg/L at 60 h,which was 15.25% higher than the control.The yeast disruption was investigated by enzyme and glass bead milling.Two kind of cellulases could disrupt the yeast cells completely in spite of very high enzyme loading,leading to an extraction of carotenoids with 100%.While the highest extraction of carotenoids was only 64.96 ± 1.21% with angel complex enzyme(CE).The combination of cellulase and angel CE showed similar result to that of the single cellulase.When glass bead milling treated yeast cells for 6 h under mild conditions(150 rpm),extraction of carotenoids reached 98% and emulsified astaxanthin in aqueous phase was approximately 93.72 mg/L,which avoided the organic solvent extraction process.Two different processes were compared for preparing yeast extract from disrupted yeast cells by glass bead milling:(1)angel CE was added after yeast cell disruption;(2)glass beads and angel CE were added simultaneously.Loading of angel CE showed no significant effect on the recovery of amino-N(3.51-3.65%)for process(1),which were higher than that of process(2).The preparation of yeast extract by adding angel CE after yeast cell disruption achieved the recovery of solid of 52.73 ± 1.17% and the recovery of amino-N of 3.65 ± 0.07%.The emulsified astaxanthin was microencapsulated by gelatin and porous starch.The optimum microencapsulation conditions were obtained through orthogonal experiment design as follows: yeast extraction liquid(V,m L):porous starch(M,g):gelatin(M,g)= 400:15:6,where the encapsulation efficiency,loading astaxanthin and water solubility were 88.56%,1.55 mg/g and 81.5 ± 0.35%,respectively.Enhancing the intensity of yeast disruption,emulsified astaxanthin concentration in the water was significantly improved,leading to encapsulation efficiency of 75.62% and astaxanthin loading of 10.42 mg/g.Color and storage stability test showed that microcapsules with smaller particle size had vibrant color and those with bigger particle size possessed higher thermal stability.