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Plant Focus

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Dwarf cultivars can be ideal for a small garden. Here are three "mini oaks". 

Potential Applications of Acorns in the Food, Pharmaceutical, and Cosmetic Industries

Quercus incana
Quercus incana acorns reportedly have a high oil content © Ron Lance

Acorns can be a source of cheap plant material, in part due to underutilization, so from an economical perspective they have a high potential for the processing industry. Scientists have proposed the following applications for acorns: production of L(+)-lactic acid, bioethanol, biobutanol from acorn starch; biodiesel from acorn oil; fuel briquettes from acorn shells and cups; adsorbent for hexavalent chromium removal from acorn peel; natural coagulants for water turbidity removal from whole acorns; activated carbon from acorn shells; and extraction of bioactive compounds such as carotenoids, tocopherols, phytosterols, and phenolic compounds from acorn kernels. Out of all the proposed applications, the extraction of oil from acorns seems to have the highest potential of practical use on a small and medium scale, due to the popularization of the cold-pressed method for oil extraction from plant materials. 

Unfortunately, not all acorns are a good source of oil. The oil yield in acorns can range from about 1% to over 30% depending on the oak species. For plant material to be considered a viable source of oil, a yield of at least 10% is required. For instance, oil yields from Quercus rubra and Q. robur acorns ranged from 3.1–6.3% and 20.1–24.0%, respectively, so the acorns of Q. robur can be considered a good source of oil, while Q. rubra apparently are not. 

The acorns of some oak species have not yet been tested for oil content, or the data is outdated (mid-20th century), so it is worth testing as many different oak species as possible in order to find their potential utility value as a source of oil. Different concentrations of oil in acorns of the same oak species have been reported by different authors, mainly due to abiotic factors and oil extraction technique and its parameters (e.g., acorn moisture and fragmentation). The final expression of quantity also affects the oil yield, i.e., whether it is from acorn kernels or from whole acorns including the shell. The oak species with reported acorn oil yields of around 10% and higher are: Q. agrifolia (18.4–22.4%); Q. brantii (13.42–15.11%); Q. chrysolepis (9.5%); Q. douglasii (8.1–8.9%); Q. falcata (15.6–36.9%); Q. ilex (7.6–20.1%); Q. ilicifolia (19.4%); Q. incana (36.6%); Q. kelloggii (17.7–19.8%); Q. marilandica (10.7–18.2%); Q. nigra (20.9–31.8%); Q. texana (Syn. Q. nuttallii) (15.0%); Q. palustris (17.4–17.8%); Q. phellos (18.5–29.5%); Q. rotundifolia (7.3–12.1%); Q. montana (3.3–14.0%); Q. stellata (9.6%); Q. velutina (18.1–23.0%); Q. robur (6.7–24.0%);; Q. wislizeni (20.6%).

The oil is mainly a source of triacylglycerols, but also an important source of bioactive compounds such as carotenoids (provitamin A), tocopherols (vitamin E), and phytosterols. Phytosterols have been reported to reduce LDL cholesterol in some individuals, while carotenoids can inhibit the development of cardiovascular disease. The inclusion of tocopherols (vitamin E) in a daily diet is essential for the proper function of physiological human systems such as the reproductive, neural, vascular, and musculoskeletal systems. The composition and concentration of those bioactive compounds in acorn oil also depend on the oak species, but unfortunately only a few oak species have been investigated in this context. Over 90–95% of oak species with a high oil yield listed above were not analysed for bioactive compounds such as carotenoids, tocopherols, and phytosterols. 

It has been shown that the composition and concentration of tocopherols in different species can be diametrically different. For instance, Q. rubra acorn oil is rich in β-tocopherol (93% of total tocopherols), while Q. robur is rich in γ-tocopherol (96% of total tocopherols). On the other hand, the total content of tocopherols is nearly six-fold higher in acorn oil from Q. robur relative to Q. rubra. 

The high oil yield of some oak species and the low-cost availability of acorns make acorns an interesting source of plant material for industrial applications. There is limited information regarding the composition and concentration of bioactive compounds in the acorns of different oak species, especially those ones with the high oil content. It would therefore be important to investigate their chemical profile so as to enable a more targeted use of their biological potential in different industries.

Acorn Request

As he writes in his article above, Dr. Paweł Górnaś is looking for acorns of different oak species for his scientific project. He has appealed to the IOS for help. "Unfortunately, I cannot offer financial compensation,” he writes, “since this project does not have any financial support. However, I can offer co-authorship, including an institution's affiliation, and acknowledgments, if required, in future high-quality scientific articles reporting on the project. The species which are of most interest are those rich in oil (please see the name of species above).  Nevertheless, I would like to test species from the different sections of the genus,  therefore, I am hoping to collect the acorns of as many species as possible since many of them have not been tested yet. I will be very grateful for any species which can be provided. Thank you." 

Can you help? For more information email Dr. Górnaś: pawel.gornas@llu.lv 

To read more about Dr. Górnaś’s research, follow the links below: 

https://link.springer.com/article/10.1007/s00217-018-3150-0

https://www.sciencedirect.com/science/article/pii/S0957582019301156