Avocado seed waste bioconversion into poly(3-hydroxybutyrate) by using Cobetia amphilecti and ethyl levulinate as a green extractant

Abstract

The avocado processing industry produces up to 1.3M tons of agro-waste annually. Chemical analysis of avocado seed waste (ASW) revealed that it is rich in carbohydrates (464.7 ± 21.4 g kg−1) and proteins (37.2 ± 1.5 g kg−1). Optimized microbial cultivation of Cobetia amphilecti using an acid hydrolysate of ASW, generated poly(3-hydroxybutyrate) (PHB) in a 2.1 ± 0.1 g L−1 concentration. The PHB productivity of C. amphilecti cultivated on ASW extract was 17.5 mg L−1 h−1. The process in which a novel ASW substrate was utilized has been further augmented by using ethyl levulinate as a sustainable extractant. This process achieved 97.4 ± 1.9 % recovery yield and 100 ± 1 % purity (measured by TGA, NMR, and FTIR) of the target PHB biopolymer, along with a high and relatively uniform PHB molecular weight (Mw = 1831 kDa, Mn = 1481 kDa, Mw/Mn = 1.24) (measured by gel permeation chromatography), compared to PHB polymer extracted by chloroform (Mw = 389 kDa, Mn = 297 kDa, Mw/Mn = 1.31). This is the first example of ASW utilization as a sustainable and inexpensive substrate for PHB biosynthesis and ethyl levulinate as an efficient and green extractant of PHB from a single bacterial biomass.