How ethanol can be obtained from apple pomace

Destillation
In Germany, residues from apple juice production are mostly processed into animal feed. However, higher-quality products can also be obtained from apple peel and seeds - in addition to ethanol, acetic and citric acid can also be obtained.

The further use of the apple pomace through hydrolysis and fermentation offers great potential for operators of juice presses in Germany, report chemists from TU Bergakademie Freiberg in the journal "Chemie Ingenieur Technik".
Bioethanol, which can be used as a basic chemical in disinfectants or biofuels, has so far mainly been made from sugar beet and grain. In the future, however, this universal substance could also be obtained from the residue of apple juice production. Particularly suitable for this is apple pomace, the solid components of stems, seeds, pulp and peel that remain after the apples have been pressed. In addition to sugar, it also contains starch, the thickening agent pectin and cellulose. These substances can be converted into higher-quality products such as ethanol, as well as acetic and citric acid, through hydrolysis and subsequent fermentation. The problem: So far, only low ethanol concentrations could be obtained from apple pomace.

A team led by chemistry professor Martin Bertau from TU Bergakademie Freiberg has now presented an optimized process by which ethanol with an alcohol content of up to 6 percent can be produced. "Previous methods achieve an ethanol content of up to 4.7 percent in apple pomace," explains Dr. Doreen Kaiser, who developed and tested the new process in laboratory experiments.

Better fermentation process thanks to the powerful enzyme complex

To produce purer ethanol from apple pomace, the team of scientists used an alternative enzyme complex obtained from the microorganism Penicillium verruculosum. Like other enzyme complexes, the cellulase complex used for the first time in this process has the ability to split the long-chain sugar molecules into simple sugars. If the simple sugars are fermented with the help of yeast and the aqueous solution is distilled, the chemists receive the ethanol in the desired concentration. “Compared to the biocatalysts used previously, the cellulase complex from Penicillium verruculosum has proven to be particularly robust against disruptive factors in the reaction. For this reason, a larger amount of apple pomace can be used than in conventional fermentation processes and, as a result, higher ethanol concentrations can be obtained, ”explains Dr. Doreen Kaiser.

Potential for bio-based industry in fruit production

Up to 650 million liters of apple juice are produced in Germany every year. As a by-product, up to 300,000 tonnes of apple pomace arise annually (source: Statista) – too good to end up as a feed in the pigsty. Disinfectants and even biofuel could be made from the solution.

Background: Biorefinery research at TU Bergakademie Freiberg

The sustainable use of biomass is the focus of the Federal Government's National Research Strategy Bioeconomy 2030. New processes for converting residues from agricultural production into high-quality basic chemicals are an important key to efficient utilization in a biorefinery on an industrial scale. At the Institute of Chemical Technology at TU Bergakademie Freiberg, processes for the production of flavorings from lignin are currently being developed in addition to the utilization of apple pomace.

Original publication: Doreen Kaiser, Martin Bertau: „Enzymatic hydrolysis and fermentation of apple pomace”. Chemie Ingenieur Technik 92.

Fragen beantwortet / Contact: 
Dr. Doreen Kaiser, Phone: 03731 39-3879, E-Mail: doreen.kaiser@chemie.tu-freiberg.de