Production of D-tagatose and bioethanol from onion waste by an intergrating bioprocess

•Conversion yields of PPAI for D-tagatose and L-ribulose were 46.94% and 12.09%.•PPAI can produce the 0.99 g of D-tagatose from 10 g of onion juicing residues (OJR).•Bioconversion process can produce 1.56 g of bioethanol from 10 g of OJR.•OJR is major resource for the production of valuable maerials.

The rapid increase of agricultural waste is becoming a burgeoning problem and considerable efforts are being made by numerous researchers to convert it into a high-value resource material. Onion waste is one of the biggest issues in a world of dwindling resource. In this study, the potential of onion juice residue (OJR) for producing valuable rare sugar or bioethanol was evaluated. Purified Paenibacillus polymyxa L-arabinose isomerase (PPAI) has a molecular weight of approximately 53 kDa, and exhibits maximal activity at 30 °C and pH 7.5 in the presence of 0.8 mM Mn2+. PPAI can produce 0.99 g D-tagatose from 10 g OJR. In order to present another application for OJR, we produced 1.56 g bioethanol from 10 g OJR through a bioconversion and fermentation process. These results indicate that PPAI can be used for producing rare sugars in an industrial setting, and OJR can be converted to D-tagatose and bioethanol.