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Fat cells bring the flavor to lab-grown meat

Engineers juggle flavor compounds in a tricky metabolic balancing act

Tissue Engineering

Fat cells bring the flavor to lab-grown meat

Engineers juggle flavor compounds in a tricky metabolic balancing act

by Laurel Oldach
October 13, 2024 | A version of this story appeared in Volume 102, Issue 32
An illustration of a grilled burger patty.

Credit: C&EN/Shutterstock | Getting the right flavor compounds into lab-grown meat products takes some metabolic engineering.

 

Tissue Engineering
by Laurel Oldach
October 14, 2024 | A version of this story appeared in Volume 102, Issue 32

As a teenager, Nanette Boyle competed in national meat-judging competitions with the National FFA Organization, once known as the Future Farmers of America. Now a chemical engineer at the Colorado School of Mines, she never thought she’d use those meat-judging skills again. But her laboratory recently branched into cultivated meat, reminding her of a lesson she learned from her extracurriculars: fat is flavor.

“Most of the flavor profile of the meat is due to the fat and the marbling,” Boyle says. That’s why she—and many others working to improve lab-grown meat—consider growing superlative fat cells to be key to the final product.

The phrase “lab-grown meat” suggests that scientists are growing a slab of tissue in a dish. But no one has figured out a way to do that economically. “It’s not going to be straightforward to get 100% cultivated meat products on the market at price parity with conventional meat,” says Claire Bomkamp, a scientist at the Good Food Institute, a think tank for alternative proteins. The cultivated meat products currently sold in Singapore and California, the only areas that have yet approved lab-grown meat products, are instead hybrids combining less-expensive textured plant proteins with a small percentage of animal cells called fibroblasts. But many companies would prefer to use fat cells, or adipocytes.

It’s not going to be straightforward to get 100% cultivated meat products on the market at price parity with conventional meat.
Claire Bomkamp, scientist, Good Food Institute

David Kaplan, director of the Tufts University Center for Cellular Agriculture, says that “adipocytes are the holy grail, as most people would put it, for taste.” Although protein-packed muscle cells contribute texture and nutrients to meat, many signature flavor compounds come from oxidation of lipids during cooking. To deliver volatile flavorants, including aldehydes, alcohols, esters, furans, and ketones, researchers grow adipocyte progenitor cells on 3D scaffolds and feed them culture media and growth factors designed to promote the formation of lipid droplets (J. Agric. Food Chem. 2023, DOI: 10.1021/acs.jafc.2c08004).

Sensory studies show that hybrid products still can’t match animal foods on flavor, but they are getting closer. Last year, volunteer taste testers concluded that a soy-and-cultured-fat nugget was almost as tasty as a traditional chicken nugget (Nat. Food 2023, DOI: 10.1038/s43016-022-00658-w). Soon after, scientists in Kaplan’s lab offered volunteers a whiff of cooked cultured fat or genuine pork belly. The volunteers could tell the samples apart but did not have a preference between their scents (Sci. Rep. 2024, DOI: 10.1038/s41598-024-68247-4). Ironically, the panelists reported more of a barnyard aroma from the cultured fat; when the scientists later identified the top volatile organic compounds in both samples, they blamed certain medium-chain fatty acids that are more abundant in the cultured fat.

Sometimes, Bomkamp says, flavor shortcomings can happen because producers start by growing as much tissue as they can and then tweak the taste later. It’s a practical strategy: you need to be able to produce tens or hundreds of grams of a product to test it with a human sensory panel. But it can lead researchers to inadvertently leave out ingredients that are more important for flavor than they are for cell growth.

“Your cells might be fine without compound A,” Bomkamp says. But suppose that cells metabolize compound A into compound B. “If you get your media formulation wrong, maybe you’re not including compound A, and then your product tastes wrong because it doesn’t have compound B.”

A light micrograph of cultured cells that are clear and roughly boat shaped but filled with round droplets that scatter the light differently. These are lipid droplets.
Credit: David Kaplan
Cultured adipocytes accumulate fat in round lipid droplets. Researchers are working to make sure these droplets, and the cells, contain the right mix of molecules.

Metabolism is notoriously complex. A product development team might choose to add the precursor to the media, or they may add the metabolite to the final product instead. To track down the source of an unwanted flavor compound, such as the barnyard-scented medium-chain fatty acids, researchers might use isotope-labeled molecules to study metabolic flux, or they might analyze the chemistry of spent media.


How fibroblasts bring the flavor
Textured plant proteins and flavorful animal fat cells can be combined to make a hybrid cultured meat product. Researchers are working on optimizing their culture protocols for animal fat cells to reduce costs and unpleasant tastes.
A schematic shows the combination of cultured fat and textured protein to make cultured meat. The cultured fat is created from fibroblasts grown in a bioreactor with growth factors. The textured protein is created from the extrusion of soy protein.
Credit: Yang H. Ku/C&EN/Shutterstock/Adapted from Nat. Food

And that brings us back to Boyle, the former future farmer. To help researchers find their way across multidimensional metabolic landscapes, she and her team are building a genome-scale metabolic model of pig cells, using tools from systems biology (Compr. Rev. Food Sci. Food Saf. 2023, DOI: 10.1111/1541-4337.13193). They aim to represent all of a cell’s metabolic enzymes, their substrates, and their reaction products as a complex set of interdependent equations. Boyle says the model will help scientists design media that balance ingredient costs with biomass yields. It could also help predict how the chemical composition of media will influence the cells’ makeup, including their potential flavor compounds.

To introduce especially elusive flavor notes, food chemists might incorporate non-cell ingredients into a food product. In a recent paper, researchers at Kangwon National University developed an edible scaffold material for muscle cells to grow on. When the resulting mixture is cooked, heat-labile bonds in the scaffold break, releasing volatile flavorants for a boost of meaty and savory notes (Nat. Commun. 2023, DOI: 10.1038/s41467-024-49521-5).

Producers of cultured meat have plenty of challenges to address. They need to scale up production, bring down the cost of raw materials, and phase out animal-derived media ingredients. But none of those economic parameters is important if customers won’t bite. And for that, researchers say, flavor is key.

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