Glucosinolates, molecules found in vegetables like broccoli and are converted into compounds with significant nutritional benefits when they are hydrolyzed by enzymes called myrosinases, which are glycosyl hydrolases. The resulting compounds have been associated with several processes that protect from cancer.

However, myrosinases can be damaged during food preparation, especially when cooked, disabling them from producing the beneficial hydrolysis products. In broccoli, “boiling broccoli using a sous vide for 2, 6, and 8 min reduced myrosinase activity by 40%, 90%, and 100%, respectively,” meaning that normal cooking practices can completely eliminate these beneficial enzymes. They also tried adding myrosinase from other food sources in combination with heated broccoli and observed the production of sulforaphane, one of the hydrolysis products, which did not occur without the supplemented myrosinase. This showcases how myrosinases are impaired during the heating process, as the fresh myrosinase functioned as normal.

Myrosinases and glucosinolates are located in different cell types, which is why denaturation via cooking is a problem; the chewing process brings them together, which happens after preparation. If they had been together from the beginning, the myrosinases would be able to hydrolyze the glucosinolates before being denatured. As a result, researchers performed a mastication assay to mash the compounds together when they recorded the breakdown of glucosinolates.

In an attempt to find enzymes more resistant to heat than broccoli’s myrosinases, researchers tested glycosyl hydrolases from other sources for their persistence in high temperatures. The most heat-resilient one they found is called TGG4, which they edited into broccoli along with promoters to overexpress the gene. In one genetic sequence being edited into broccoli lines (construct A), the promoter added, pTGG1, is myrosinase-specific, so it would only operate in certain cells, emulating natural myrosinase activity. In another construct (construct C), they used p35S, a viral promoter from Cauliflower Mosaic Virus that drives expression in all tissues at all times, maximizing TGG4 myrosinase production regardless of location. The broccoli with the construct A did not exhibit resilience over high temperatures, despite the presence of the TGG4 myrosinase, which is expected to function up to 80 °C. This might be because the pTGG1 promoter isn’t strong enough, but no further studies have been conducted to test this possibility. However, broccoli with construct C were able to endure higher temperatures, with two lines maintaining glucosinolate hydrolysis at 20 °C higher than in wild type broccoli, up to 80 °C.

This stark improvement demonstrates the incredible potential of genetic engineering to elevate nutritional content in food. Although 80 °C is still below the boiling temperature of water, this edit involved only one myrosinase gene, picked from a screening of just 36 enzymes. Additionally, plants have not evolved for myrosinase heat tolerance at boiling temperatures, so the existing library does not represent the full possibilities of enzymes that could be unlocked through advancements in molecular biology. This research is early, but it showcases how much is possible through genetic engineering, and what the future of food might look like.

This week features another article from the Innovative Genomics Institute’s Plant Genomics and Transformation Facility! Figured I’d better get familiar with my future lab’s work before I arrive on set in a couple months. I don’t think this project is a big focal point for them, but I thought it was cool, and I’m sure to look at more later anyway.

Something I really loved from this paper was part of the conclusion; the authors assert that, like humans’ progression from learning to cook their food, the advancements of agricultural biotechnology will allow unforeseen progress in improving the human condition. I love that perspective on this technology, our role as scientists, and the future of humanity. As I said to Dr. Cho, the Principal Investigator of the lab, in my first email to him, it is about time that humans use our knowledge and technology to optimize our biological toolkit for the sake of our health, environment, and society.

This kind of innovation makes me wonder if we could genetically engineer food to maintain its nutrients when frozen. I know that access to fresh produce does not exist for everyone, especially those with lower incomes. Frozen food is often cheaper, easier to prepare, and lasts longer, which means less food waste. I will definitely have to investigate this topic for a future article! Stay tuned to learn with me!

https://pubs.acs.org/doi/10.1021/acssynbio.3c00676