Good things don’t last, and neither does the bright green colour of your guacamole in the fridge.
After buying avocados and preparing a batch, it is incredibly frustrating to hesitate over a brown surface. Still, that hesitation is understandable, as it makes the avocado less visually appealing and may discourage consumption (Soliva-Fortuny et al. 2002). Throwing some away does not only waste a part of the money you spent, but also the resources used to grow, transport and store the fruit. Understanding the colour change, and how to slow it, can therefore help us examine when preservation is worth its environmental costs.
This colour change occurs via a process called enzymatic browning that relies on the catalytic activity of polyphenol oxidase (PPO) on its many phenolic substrates in the presence of oxygen (Peres et al. 2019). PPO and phenolic compounds are usually separated within cells; PPO is associated with plastids, while phenolics are stored in vacuoles (Peres et al. 2019). When you cut or mash an avocado, this natural compartmentalization is disrupted, allowing PPO to contact its substrates. PPO then catalyzes the oxidation of these phenolic compounds into quinones, which undergo further reactions to form the brown pigments that discolour your guacamole (Figure 1; Peres et al. 2019).
Keeping your guacamole green, then, means interfering with this process before brown pigments form. Pressing food wrap directly against the surface limits contact with oxygen, a reactant in the browning process (Schwarcz 2017). Refrigeration can also slow enzymatic browning by reducing PPO activity at lower temperatures (Soliva-Fortuny et al. 2002). A squeeze of lemon juice demonstrates another approach: its acidity can reduce PPO activity, while its vitamin C acts as a reducing agent, converting newly formed quinones back into phenolic compounds before brown pigments develop (Schwarcz 2017).
However, slowing down a reaction does not automatically reduce the environmental harm. Single-use plastic wrap adds disposable and often unrecyclable material, while refrigeration requires energy. Whether that investment is worthwhile depends on how much food it prevents us from wasting. A life-cycle assessment helps to compare impacts across a product’s life, including production and disposal. For avocados, those impacts begin long before they reach your fridge. Estimates from conventional orchards in Mexico put production emissions at 0.54 kg of CO2 equivalents per kilogram of fruit (Majumdar and McLaren 2024).
In a retail packaging study, Heller and Keoleian (2017) found that pre-packaged mushrooms and spinach had lower retail waste than those sold in bulk, yet only mushrooms showed a net reduction in emissions and energy demand. Mushroom production had a greater emissions burden than spinach relative to its packaging (6.9× vs. 0.27× packaging emissions, respectively), so avoiding mushroom waste had greater ability to offset the packaging’s impacts (Heller and Keoleian 2017). So although these findings do not apply directly to guacamole, the contrast shows why reducing food waste does not automatically lead to a net environmental benefit.
Looking back to the bowl in the fridge, preserving the colour is only environmentally worthwhile if enough food is saved to outweigh the added inputs and impacts. If the guacamole ends up in the bin anyway, what’s the point?
References
Heller, Martin, and Gregory Keoleian. 2017. “Optimizing the Environmental Performance of Food Product-Package Systems: A Life Cycle Assessment of the Tradeoffs between Packaging Design and Food Waste.” Center for Sustainable Systems, University of Michigan. https://doi.org/10.7302/21858.
Majumdar, Shreyasi, and Sarah J. McLaren. 2024. “Towards Use of Life Cycle–Based Indicators to Support Continuous Improvement in the Environmental Performance of Avocado Orchards in New Zealand.” The International Journal of Life Cycle Assessment 29:192–217. https://doi.org/10.1007/s11367-023-02238-x.
Peres, Shelby T., Kelsey A. Oonk, and Kasandra J. Riley. 2019. “The Avocado Lab: An Inquiry-Driven Exploration of an Enzymatic Browning Reaction.” CourseSource 6 https://doi.org/10.24918/cs.2019.38.
Schwarcz, Joe. 2017. “Can Placing an Avocado Seed in Guacamole Prevent Discolouration?” Office for Science and Society, McGill University. Accessed September 18, 2026. https://www.mcgill.ca/oss/article/you-asked/can-placing-avocado-seed-guacamole-prevent-discolouration.
Soliva-Fortuny, Robert C., Pedro Elez-Martı́nez, Mercè Sebastián-Calderó, and Olga Martı́n-Belloso. 2002. “Kinetics of Polyphenol Oxidase Activity Inhibition and Browning of Avocado Purée Preserved by Combined Methods.” Journal of Food Engineering 55 (2):131–37. https://doi.org/10.1016/S0260-8774(02)00027-4.
Tilley, Andrew, Mark P. McHenry, Julia Anwar McHenry, Vicky Solah, and Kirsty Bayliss. 2023. “Enzymatic Browning: The Role of Substrates in Polyphenol Oxidase Mediated Browning.” Current Research in Food Science 7:100623. https://doi.org/10.1016/j.crfs.2023.100623.
Comments
11 Responses to “Keeping Guacamole Green: At What Cost?”
This post is relevant to iSci as it demonstrates the intersection of biology and chemistry through enzymes and stoichiometry/limiting reactants. It also explores the concepts of sustainability and SDGs that we covered in last week’s green chemistry unit.
Many of us first year iSci’s are buying/cooking/storing food for the first time this year, and I’ve found out the hard way that you can’t just toss leftovers into your fridge and forget about them. This made guacamole browning a relatable way to apply some course concepts to everyday decisions.
Hi Aarav,
Amazing first blog post! I really loved your discussion of the trade-off between reducing waste versus producing more waste in an effort to reduce waste. Very well researched.
Minor suggestion: I suggest you choose an image with better resolution for your figure. You can also make your own using ChemDraw (probably the preferred method).
Cheers,
Vani 🙂
Hi Vani,
Thank you for your kind words! I had no clue ChemDraw existed as a software, and I appreciate you for pointing me in its direction. I’ve gone ahead and updated my figure for better resolution.
For any first years that read this comment, McMaster gives us a free ChemDraw license that you can access using this link (you need to download it though): https://library.mcmaster.ca/databases/chemdraw
Thank you,
Aarav
Hi Aaarav,
First of all, incredible post! I really appreciated how you included the retail packaging study. It really helps readers consider why retail doesn’t just pack food better, and also allows the consideration of environmental impacts. Very well done.
A small suggestion is to include some numerical metrics to support your writing. You explained your writing with many strong sources, though your arguments would be much more powerful if you added the metrics from the studies you cited (e.g. additional packing vs greenhouse emissions in the Heller and Keoleian study).
Best,
Berk
Hi Berk,
Thank you for your suggestions! I definitely agree that quantitative statistics would support my writing, and better define the impact I’m trying to make. I added some numbers on the food to packaging emission ratios for mushrooms and spinach to support the comparison. I also added some numbers regarding carbon dioxide production as a result of avocado cultivation as I received similar advice from Gurleen.
Best regards,
Aarav Goel
Hi Aaarav,
I really enjoyed reading your post, and found interesting how you included connections to chemistry when discussing how avocados begin to break down!
Feedback: When discussing LCA, and referencing the Heller and Keoleian study, it would be impactful to touch on the “production” stage of the Life Cycle Assessment. For example, you could include stats about the carbon footprint or energy/water consumption of cultivating this fruit, and how that impacts the “green score” of avocados (thus connecting back to Green Chemistry principles).
*Note: “Green Score” is a grading system from A+ to E that measures the environmental impact of food products.
Regards,
Gurleen H.
Hi Gurleen,
Thank you for your thoughtful feedback! I’ve added a numerical estimate of emissions from avocado production to provide a more complete picture of the environmental impact it has prior to entering our kitchens. I didn’t add a green-score because after reading on it, I discovered that it combines several environmental indicators that seem to exit the scope of what I’m writing about. The carbon-footprint data it relies on alone wouldn’t support assigning it a reliable grade. I tried to instead use the production figures to strengthen the connection between preventing food waste and the resources invested in growing avocados.
Best regards,
Aarav Goel
Hey Aarav!
I really liked your post, and I’m super intrigued by your approach on analysing the impacts of waste reduction.
Although this is a minor complaint, I would avoid using casual terms like “guac,” as it doesn’t really feel like it matches the serious tone of the post. In addition, I feel like you could’ve spent a little bit longer reflecting on the results of the studies you talked about near the end. I feel like if you shortened the part where you talked about the chemical process behind avocado browning to make room for data reflection, your blog would have more of an impact on the reader. While interesting, it doesn’t seem to be as important to the point you’re trying to convey to the reader. Otherwise, fantastic blog post, and a very interesting read!
Cheers,
Daniel
Hi Daniel,
Thank you for your feedback! I’ve gone ahead and replaced “guac” with “guacamole”. After spending some time editing my draft, I found that I was able to elaborate more on the study regarding spinach/mushroom waste without needing to cut words from the background science section. I also revised the ending to connect those findings more clearly to whether preserving guacamole actually prevents waste.
I appreciate your suggestions, they helped me strengthen my post’s main takeaway!
Best regards,
Aarav Goel
Hi Aarav,
Great post! Your analysis and overview of the guacamole browning phenomenon was overall engaging and a pleasant read. That said, I have a couple of suggestions that I hope you will consider implementing for improvement.
In terms of academic flow and formality, I’d recommend replacing the informal/casual abbreviation “guac” with its full form guacamole throughout the text. Moreover, when discussing the environmental harm of “wrapping”, explicitly specifying the single-use nature of food wrapping can help emphasize the exact nature of food waste and help strengthen your life-cycle assessment. This can be easily done by simply specifying “plastic” before wrapping within your paragraph.
It may also be helpful to clarify why brown guacamole is a nuisance in the first place. Expanding on whether avocado browning alters its taste and nutrition profile or consumer perception can provide context for the root cause of this specific food waste. Overall, this is very much an interesting topic that I am certainly glad you explored over.
Regards,
Brand
Hi Brand,
Thanks for your thoughtful feedback! I’ve gone ahead and replaced all my instances of “guac”, with “guacamole”, and I’ve also added a sentence connecting avocado browning directly to food waste within the first paragraph.
Your suggestion about specifying “single-use plastic wrap” instead of “food wrap” was also great. I’ve been using saran wrap all my life, so the idea that people use other products to protect their food went right over my head.
Thank you once again!
Best regards,
Aarav Goel