By Susan Elrod, PhD
You might have heard the amount of polyphenols change based on whether you’re consuming the whole fruit, juice, or some other processed product. In some ways this change is positive; since a lot of fruit goes into juice, there may be a higher phenolic concentration in a serving of juice than in a serving of fruit. Furthermore, heating or other processing techniques makes some polyphenols more bioavailable (that is, usable by the body); lycopene from tomatoes and beta-carotene from carrots are two famous examples of this phenomenon.1Agarwal A, Shen H, Agarwal S, Rao A. Lycopene content of tomato products: its stability, bioavailability and in vivo antioxidant properties. Journal of medicinal food 2001;4(1):9-15. 2Kamiloglu S, Demirci M, Selen S, Toydemir G, Boyacioglu D, Capanoglu E. Home processing of tomatoes (Solanum lycopersicum): effects on in vitro bioaccessibility of total lycopene, phenolics, flavonoids, and antioxidant 3Livny O, Reifen R, Levy I, Madar Z, Faulks R, Southon S, et al. Beta-carotene bioavailability from differently processed carrot meals in human ileostomy volunteers. Eur J Clin Nutr 2003;42(6):338-345. But what about elderberries and other dark berries? Will those wonderful anthocyanins still be available to you in the form of juice or other processed products? If, like me, you enjoy a mug of mulled wine in the winter, are you destroying the beneficial polyphenols by heating?
Like a lot of topics related to diet and nutrition, the answer to those questions is quite complicated. First, it’s important to distinguish between simply heating the fruit and cooking the fruit. Heat itself may destroy certain polyphenols, but the incorporation of other ingredients (particularly yeast when baking) may actually stabilize and thus preserve certain compounds during the baking process. One study found the process of using heat to dry blueberries resulted in the loss of up to 55% of the initial polyphenols, and up to 95% loss of the initial anthocyanins.4Zielinska M, Michalska A. Microwave-assisted drying of blueberry (Vaccinium corymbosum L.) fruits: Drying kinetics, polyphenols, anthocyanins, antioxidant capacity, colour and texture. Food Chemistry 2016 1 December 2016;212(Supplement C):671-680. However, another study found that baking blueberries with yeast and other leavening agents acted to preserve or even increase polyphenolic compounds.5Rodriguez-Mateos A, Cifuentes-Gomez T, George TW, Spencer JP. Impact of cooking, proving, and baking on the (poly) phenol content of wild blueberry. J Agric Food Chem 2013;62(18):3979-3986. The difference here is that it’s not just heat that can affect polyphenols; pH and other factors affected by yeast can also affect the stability of such compounds.
So if a fruit product is simply heated, not incorporated into a baked food, it appears that may decrease the amount of anthocyanins and related products. However, the impact on total polyphenolic content may not be as significant; a study on Dwarf elderberry found up to 40% reduction in cyandin-3-glucoside, but only up to 5% decrease in total polyphenols and antioxidants.6Jimenez P, Cabrero P, Basterrechea JE, Tejero J, Cordoba-Diaz D, Cordoba-Diaz M, et al. Effects of short-term heating on total polyphenols, anthocyanins, antioxidant activity and lectins of different parts of Additionally, a study on grape juice found the pasteurization process increased anthocyanins and antioxidants.7Genova G, Tosetti R, Tonutti P. Berry ripening, pre‐processing and thermal treatments affect the phenolic composition and antioxidant capacity of grape (Vitis vinifera L.) juice. J Sci Food Agric 2016;96(2):664-671. It appears, then, that while you may not get the absolute best concentration of anthocyanins by heating dark berry products, there are ways to overcome that. Additionally, you may not have to worry quite as much about the total phenolic or antioxidant content decreasing due to heat. The best course of action may be to avoid heating if possible, but don’t worry too much about it if you have a warm fruit beverage on occasion.
We mentioned the issue of juicing above. As a larger amount of fruit goes into a single serving of juice, that may be an easy and quick way to get your fruit and/or vegetable servings. Studies on the juicing process in blueberries found that smaller polyphenolic compounds tend to be retained during this process, whereas larger polyphenols tend to be degraded. Blanching the fruit before juicing may also prevent polyphenolic loss.5Rodriguez-Mateos A, Cifuentes-Gomez T, George TW, Spencer JP. Impact of cooking, proving, and baking on the (poly) phenol content of wild blueberry. J Agric Food Chem 2013;62(18):3979-3986. Additionally, several studies conducted on elderberry and other fruits used juice rather than whole fruit, typically because experiments conducted during such studies require the fruit to be in a liquid form.8Fal AM, Conrad F, Schonknecht K, Sievers H, Pawinska A. Antiviral activity of the "Virus Blocking Factor" (VBF) derived i.a. from Pelargonium extract and Sambucus juice against different human-pathogenic cold 9Effects of Elderberry Juice from Different Genotypes on Oxidative and Inflammatory Responses in Microglial Cells. I International Symposium on Elderberry 1061; 2013. In the case of human studies, juices may be used due to ease of dosing and other experimental controls.10Frank T, Sonntag S, Strass G, Bitsch I, Bitsch R, Netzel M. Urinary pharmacokinetics of cyanidin glycosides in healthy young men following consumption of elderberry juice. Int J Clin Pharmacol 11Murkovic M, Abuja P, Bergmann A, Zirngast A, Adam U, Winklhofer-Roob B, et al. Effects of elderberry juice on fasting and postprandial serum lipids and low-density lipoprotein oxidation in healthy As such, while the polyphenolic profile may change due to juicing, the total polyphenols and benefits associated with such fruits may not be strongly impacted.
Related article: How Should I Think About Polyphenol Loss During Processing