009: Dairy Co-Products to Polyhydroxyalkanoates by Halophiles: Bioprocess Development and Mathematical Modeling

Introduction

Cheese is an essential product of the dairy industry. Cheesing making processes generate massive amounts of co-products such as whey sugar and delactosed permeate (DLP) with limited application and environmental concern. These feedstocks can be converted to polyhydroxyalkanoates (PHA), a type of biodegradable polyester that’s recognized as the most promising sustainable substitute for petroleum-based plastics. This study aimed at developing sustainable bioprocesses to convert cheese co-products into PHA by Haloferax mediterranei.

Methods

Factorial experiments were conducted with two substrate types, three substrate loadings (20, 40, and 60 g/L) and two aeration scenarios to study the effects on cell growth and PHA biosynthesis. A Monod-based kinetic model was established to simulate metabolic process in different aeration scenarios. Spent cell culture medium was reclaimed and recycled for 4 batch runs, the final PHA concentrations and compositions were measured.

Results

PHA had yields up to 0.40 ± 0.02 g/g substrate from whey sugar and up to 0.17 ± 0.12 g/g substrate from DLP. A higher log-phase dissolved oxygen (DO) led to faster biosynthesis, but a lower final PHA production (2.0 ± 0.3 g/L) compared to lower DO levels (3.0 ± 0.1 g/L), which was elucidated by distinctive profiles of kinetic parameters and metabolic reaction rates. The recycling of 90% salts and nutrients achieved consistent production and quality.

Significance

The biotechnology developed in this study helps upcycle low-value dairy co-products and improve the economics of PHA, with the potential scalability for industrial applications.

Authors: Ke Wang, Alex M. Hobby, Allan Chio, Hamed E. Elmashad, and Ruihong Zhang