Food waste as a sustainable source of astaxanthin through fermentation by phaffia rhodozyme

Astaxanthin is a carotenoid with remarkable antioxidant characteristics, traditionally obtained from chemical synthesis and natural acquisition. Both approaches are not capable of meeting the growing market demand in a lot of different fields. In this work, a fermentative approach was implemented for bioconversion of food waste (FW) into astaxanthin by Phaffia rhodozyme. In order to obtain an added value product through a sustainable and low cost process, leftover food rich in lipid, protein and minerals, was used as medium for direct fermentation (DF) by P. rhodozyme ATCC 74219. FW, used as carbon source and fermentation medium, was collected and pretreated by drying and grinding into a fine powder. A complete analytical characterization of FW consisting of proximate composition, elemental and fatty acids profiles was carried out; moreover, the reducing sugars composition was assessed. After the cultivation of P. rhodozyma, 2.5 mL of inoculum was directly introduced into a fermentation flask. The pretreated FW was sterilized and its pH was adjusted to 5.0. The fermentation conditions were 23 ℃ and 220 rpm, and the fermentation period was 115 hrs. The yield in astaxanthin obtained by DF was 132.6 mg· L-1. In order to improve the productivity of the DF process, four different substrate concentrations were tested and their effects on the accumulation of astaxanthin in P. rhodozyme were evaluated. The mass balance at the end of the fermentation approach at the optimal 20% substrate concentration of FW led to 0.25 % and 0.20 % of carotenoids and ethanol yields, respectively. The implementation of FW as direct and complete medium for fermentation is a green key to realize large-scale and low-cost commercial production of astaxanthin.