A green strategy to transform pineapple peel into biobutanol includes microwave pretreatment and in-situ butanol recovery

Pineapple peel, a residue rich in free sugars, can be hydrolyzed under mild conditions. Here, direct enzymatic hydrolysis (EH) of pineapple peel in the presence of Cellic CTec 2 at only 5 FPU g−1 of pineapple peel dry mass yielded a hydrolysate containing 50.3 g L−1 total sugars, but which was poorly fermentable. Pretreating the pineapple peel with microwave (MW) at 130 °C in the presence of water provided a fermentable residue containing 43.7 g L−1 total sugars that generated 8.4 g L−1 butanol. Thus, thermal treatment helped to overcome fermentation hindrance. Treating the pineapple peel with MW at 130 °C followed by EH at enzyme loading of 5 FPU g−1 DM gave a fermentable hydrolysate containing 50.6 g L−1 total sugars. Fermenting this hydrolysate in a bioreactor with in-situ butanol recovery by gas stripping with a pulse of glucose/fructose solution increased the butanol concentration to 9.8 ± 0.4 g L−1. Overall, microwave pretreatment was essential to obtain a fermentable hydrolysate from pineapple peel, while gas stripping facilitated butanol removal during fermentation.