Hitting the Marc

Environmental biotechnologist Dr Shan Yi saw a news article on grape marc in 2021, highlighting the lack of large-scale solutions to deal with increasing volumes of the pips and skins left in winery presses after juice has been extracted from grapes. “I found this challenge very intriguing and started mulling over the possible microbial biotechnology to help solve the problems mentioned in the article,” she says.

Now Shan is running a two-year grape marc project with the University of Auckland, thanks to funding through the New Zealand Wine Futures Fund (NZWFF), looking to transform marc into high-value, functional medium-chain organic acids, such as caproic acid, for goods such as stock feed.

“My research focuses on applying the fundamental understanding of microbial metabolism and interactions to improve the performance of engineering bioprocesses,” says Shan, who joined the chemical and materials engineering department at the University of Auckland in December 2019, to research the synergy between chemical and environmental engineering. “To align my research with New Zealand’s needs, I am specifically interested in developing low carbon-emission engineering bioprocesses to valorise biomass feedstock from New Zealand’s primary industries.”

At the time of reading the online article, Shan’s lab had just started a research project with a couple of chemical engineering undergraduate students in the university’s Part IV Project, which tasks participants with tackling a real-world problem “We were enriching the microbiomes for anaerobic chain elongation, a bioprocess that converts small organics, such as acetate and ethanol, into medium-chain organic acids with higher values,” says Shan. “The anaerobic chain elongation represents a sustainable low carbon-emission platform biotechnology that can be applied to different types of renewable feedstock. My instinct told me that this biotechnology could be an essential part of the picture to tackle the grape marc challenges.”

In a moment of “serendipity,” she received an invitation from Analeise Murahidy, the Director of Strategic Growth at UniServices, to join a workshop with Bragato Research Institute (BRI) at around the same time. Grape marc challenges came up in discussions, and Shan’s interest was further piqued.

Grape marc is packed with organic carbons that the grapevine has “worked really hard to fix from atmospheric carbon dioxide through photosynthesis”, says Shan. “These grape marc organic carbons represent a carbon-neutral and renewable feedstock if we can use them to produce chemicals and energy. However, grape marc organics are complex biomolecules that can be costly and energy-intensive to process.”

The research focuses on developing a novel anaerobic bioprocess to convert the bulk organics in grape marc to medium-chain organic acids by the catalytic abilities of microorganisms. “Compared with previous proposed alternative treatments, this new bioprocess produces higher-value products but does not require intense operation parameters such as heat or high-power consumption,” says Shan. “In addition, the products from our bioprocess can be used directly by wine (or another crop) growers to promote plant growth and fight against plant disease, creating a circular route for wine offerings and enhancing sustainability of the New Zealand wine industry,” she continues, noting “economic, environmental, and social benefits”.

Previous research on the alternative anaerobic bioprocess, such as biogas production from anaerobic digestion, revealed that biodegradation of grape seeds and other marc components is challenging. “Also, the price of biogas cannot offset the high cost of removal or processing the grape seeds, rendering the biogas production process economically unsound for commercialisation.”

However, the project’s production of higher-value products will likely justify the treatment cost, she says. “We will test the efficiency of a range of treatment methods in breaking down the recalcitrant organics. We will also identify the optimal treatment methods for future implementation and commercialisation by rigorously examining our bioprocess’s environmental and economic performance.”

Plenty of challenges remain, and not least the “swift and intensive process” of a grape harvest, with large quantities of marc generated within two months. The research will investigate a few process operation scenarios, “to balance the capacity of production and storage to develop an economically sound solution”, Shan says.

From left, Professor Brent Young, Dr Shan Yi, Dr Wei-Qin Zhand and PhD students Kai Xin Chin and Marc Rosenburg.

The project will rely on an understanding of the marc microbiology, including through genome sequencing. Shan compares bioprocess engineers to “loving pet owners”, who would want to know what their pet likes and dislikes to keep them in the best health. “Learning microorganisms’ traits is crucial for the successful performance of a bioprocess. However, it can be an impossible task in our bioprocess because there are too many microorganisms, most of which cannot be examined using other methods in laboratory conditions,” she says.

“Simply put, genome sequencing and analysis can reveal the critical metabolic traits and interactions of the key players in our bioprocess. We can use the information to create engineering conditions to encourage the growth and performance of microbes responsible for the conversion of grape marc to desired products, simultaneously limiting the microbes competing for the resources with the key players. By doing so, we can maximise production efficiency.”

The NZWFF is funded through New Zealand Winegrowers levies and project managed by BRI. BRI Project Manager Stephanie Flores says sustainably disposing of large quantities of grape marc has become one of the toughest challenges for a growing industry aiming to be zero-waste to landfill by 2050. “The research will not only contribute to existing knowledge relating to grape marc disposal, but also aims to provide a commercial opportunity for the industry as well.”

The grape marc project is one of two of NZWFF initiatives this year, along with a Plant & Food Research project led by Dr Jessica Vereijssen exploring ground wétá. To read more on that, check out the June/July 2022 edition of Winegrower Magazine.