The research team, led by Nour Elhouda Daoudi of Mohammed First University in Oujda, Morocco, together with collaborators at King Saud University and elsewhere, set out to answer a question that has lingered around this celebrated oil: does the heat of roasting destroy the very molecules that make argan oil medicinally interesting? Roasting is known to alter the chemical composition of vegetable oils, particularly their phenolic compounds, tocopherols, and antioxidant capacity. If heat-sensitive bioactives were the key to argan oil’s benefits, traditionally roasted oil might be nutritionally inferior to oil pressed from raw kernels. The new results suggest otherwise.

To test the question rigorously, the researchers harvested argan fruits from the Agadir region of Morocco in February 2019 and split the seeds into two batches. One batch was pressed raw to yield unroasted argan oil, with an extraction yield of 12.50 percent. The other was roasted at 100 degrees Celsius for roughly 20 minutes with continuous mixing to prevent localized overheating, then pressed to yield roasted oil at a much higher yield of 28.49 percent. Both oils were extracted mechanically, without solvents, using a cold-press expeller, then filtered and stored in opaque glass bottles at 4 degrees Celsius until use. Gas chromatography coupled with mass spectrometry, drawing on previously published characterization work, confirmed that both oils were dominated by unsaturated fatty acids, chiefly oleic and linoleic acids, alongside palmitic and stearic acids, with the unroasted oil showing a slightly higher ratio of unsaturated to saturated fats. One compound, the hydrocarbon heptadecane 2,6-dimethyl, appeared only in the roasted oil.

The biological test bed was a classic one: adult Wistar rats in which diabetes was induced by streptozotocin, a DNA-alkylating toxin originally isolated from the bacterium Streptomyces achromogenes that selectively destroys insulin-producing pancreatic beta cells. Thirty rats were divided into five groups of six: healthy controls, untreated diabetic controls, diabetic rats given the frontline drug metformin at 250 milligrams per kilogram of body weight per day, and two diabetic groups receiving either roasted or unroasted argan oil by daily oral gavage at 2 milliliters per kilogram of body weight. After six weeks of treatment, the researchers collected blood, liver, and heart tissue for a battery of biochemical assays and histopathological examination.

The metabolic results were striking. Untreated diabetic rats had blood glucose levels above 5 grams per liter, more than five times the normal value of roughly 0.94 grams per liter. Six weeks of treatment with either version of the oil drove glucose down to about 1.07 to 1.09 grams per liter, statistically indistinguishable from the metformin group and approaching normal. The oils also reversed the swelling of the liver that accompanies diabetic injury, restoring relative liver weight to near-normal values. In the lipid arena, both oils significantly lowered the elevated triglycerides, total cholesterol, LDL cholesterol, and VLDL cholesterol that streptozotocin had driven upward, while raising the depressed HDL cholesterol back toward healthy levels. Total cholesterol and HDL values in the treated animals were statistically comparable to those of the normal controls.

The liver, an organ that bears a heavy burden in diabetes, showed clear signs of recovery. Streptozotocin poisoning had sent the liver enzymes ALT, AST, and LDH surging into the bloodstream, a hallmark of hepatocyte damage, and had elevated both direct and total bilirubin, signaling impaired bile excretion. Treatment with either roasted or unroasted oil brought ALT and LDH back to normal and significantly reduced bilirubin, although AST remained somewhat elevated. Notably, metformin, for all its metabolic benefits, failed to significantly improve these liver markers in this model, and the authors caution that this may reflect the specific experimental conditions rather than an absence of hepatoprotective potential. The oils also restored hepatic glycogen, the stored form of glucose that insulin depletion drains from the liver, from a diabetic low of 0.64 milligrams per gram of tissue back to the normal value of about 1.01 milligrams per gram, likely by supporting the reactivation of glycogen synthesis.

Oxidative stress, the destructive accumulation of reactive oxygen species that underlies much diabetic tissue damage, was substantially tamed. Malondialdehyde, or MDA, the standard marker of lipid peroxidation, was sharply elevated in the livers and hearts of diabetic rats. Both oils cut MDA levels dramatically, and in the heart the values returned fully to normal, while in the liver they fell significantly though not completely. The antioxidant defenses themselves were replenished: reduced glutathione, depleted by diabetes, rebounded in both organs, and catalase, the enzyme that converts hydrogen peroxide into water and oxygen, recovered in the liver and improved in the heart. In a telling contrast, metformin did not significantly restore glutathione in this experiment, whereas both argan oils did.

Under the microscope, the protective story became vivid. Hematoxylin-eosin staining revealed that untreated diabetic livers were riddled with lipid droplets and patches of hepatocyte necrosis, while hearts showed disordered cardiac fibers and damaged cardiomyocyte nuclei. Masson’s trichrome staining, which dyes collagen blue, exposed extensive fibrosis, the scarring that stiffens organs and, in the heart, raises the risk of arrhythmias and heart failure. Treatment with either oil prevented the lipid droplets, limited collagen deposition in the portal triads of the liver and the myocardium of the heart, and preserved tissue architecture far better than untreated diabetes allowed. Metformin reduced collagen but did not fully normalize it. Quantification of collagen area confirmed that both oils significantly blunted fibrosis in both organs.

What explains this pharmacological breadth? The authors point to argan oil’s rich cargo of phytosterols, which compete with cholesterol for incorporation into intestinal micelles and thereby limit cholesterol absorption, and to its abundance of unsaturated fatty acids, which modulate hepatic lipid metabolism and oxidation. Its tocopherols and phenolics neutralize the free radicals that streptozotocin unleashes, easing the oxidative burden on liver and heart alike. Crucially, the comparison between roasted and unroasted oils showed no significant differences in glycemia, lipid profile, liver enzymes, bilirubin, glycogen, oxidative stress markers, or collagen deposition. The heat of traditional roasting, the study concludes, does not strip the oil of the molecules responsible for these effects, meaning that the aromatic, culinary-grade oil retains its medicinal character.

The findings come with caveats that the authors acknowledge candidly. Six animals per group is a small sample, the streptozotocin rat model cannot fully recapitulate human diabetes, and a single dose over six weeks says nothing about long-term outcomes or dose-response relationships. Clinical trials in humans remain the necessary next step, along with molecular studies to pin down the precise pathways involved. Still, with the International Diabetes Federation projecting 784 million people living with diabetes by 2040, and diabetic cardiomyopathy and liver disease among the most feared complications, the idea that a traditional food oil, roasted or not, could complement existing therapies is an appealing one. For the women of Morocco’s argan cooperatives who have roasted kernels by hand for centuries, science has now offered a measure of vindication: the heat that creates the flavor does not destroy the medicine.

Subject of Research: Hepatoprotective and cardioprotective effects of roasted versus unroasted argan oil in streptozotocin-induced diabetic rats

Article Title: Effects of Roasting on the Antioxidant and Lipid‐Modulating Activities of Argania spinosa Oil Under Diabetic Conditions

Article References: Daoudi, N. E., Aziz, M., Choukri, M., Younous, Y. A., Bouallegue, A., Elossaily, G. M., Gaafar, A.-R. Z., Said, M. A., Ali, H., & Bnouham, M. (2026). Effects of Roasting on the Antioxidant and Lipid‐Modulating Activities of Argania spinosa Oil Under Diabetic Conditions. Food Science & Nutrition, 14(10), Article e72441. https://doi.org/10.1002/fsn3.72441

Image Credits: AI Generated

DOI: 10.1002/fsn3.72441

Keywords: argan oil, Argania spinosa, diabetes, oxidative stress, hepatoprotection, cardioprotection, roasting, lipid profile, streptozotocin, antioxidants, fibrosis, Morocco

The research team, led by Chao Sun and Mengting Zhu, worked with fresh Zijuan leaves harvested in June 2025 from a plantation in Menghai County, in China’s Yunnan Province, picking the standard one bud with three leaves. The leaves were processed into oolong tea using a carefully standardized protocol: solar and static withering, two rounds of shaking with cooling intervals, piling, fixation at 280 degrees Celsius, rolling, and a two-stage drying sequence. After a three-day rest, the finished tea was divided into four batches. One batch was left unroasted as a control, while the others were roasted for two hours at 80, 110, or 150 degrees Celsius, representing light, medium, and high roasting intensities. All compositional data were expressed on a dry-weight basis to correct for the moisture that roasting drives off, which fell from just over 4 percent in the control to about 1.1 percent in the most heavily roasted sample.

Sensory evaluation followed the Chinese national standard GB/T 23776-2018, with a panel of seven trained assessors, each with more than five years of experience, scoring the teas on a 100-point system weighted toward taste and aroma. The results told a nuanced story. The lightly roasted tea earned the highest overall score of 91.7, praised for an elegant, sweet aroma and a thick, mellow taste with only slight astringency. The unroasted control scored 89.4, with a distinctly spicy aroma but noticeable astringency. Medium roasting produced a score of 89.5 and a return of the spicy, varietal character, while the high-roasted tea scored 90.8, distinguished by a pronounced roasted aroma and the highest taste score of all, a thick and robust mouthfeel with classic oolong character.

Instrumental color analysis of the tea liquors mirrored these impressions. The control tea, rich in anthocyanins, produced a light brownish-red liquor with a visible purple hue. Light and medium roasting shifted the liquor toward a brighter brownish-yellow, a color generally considered more desirable for oolong tea. But heavy roasting reversed the trend: the liquor darkened significantly, its brightness measured by the L* parameter dropping to 16.69 compared with 20.31 in the control, and the purple tone reappeared. The researchers attribute this to two converging processes, the complexation of anthocyanins with other polyphenols under thermal stress and the accumulation of brown melanoidins generated by advanced Maillard reactions, which together darken the infusion and reduce its visual clarity.

Beneath the sensory shifts lay systematic changes in the tea’s non-volatile chemistry. Anthocyanins, the signature compounds of Zijuan, declined steadily with roasting intensity, falling from 2.62 milligrams per gram in the control to 2.11 milligrams per gram after high roasting, a loss of roughly 19.5 percent. Under intense heat, anthocyanins are prone to structural cleavage, including chalcone ring-opening, and can degrade into phenolic acids and aldehydes or participate in co-pigmentation and polymerization with oxidized polyphenols. This pigment breakdown helps explain the visual migration from a purple-tinged liquor to a brownish-red one, and may also contribute to the softening of astringency that panelists noticed in the roasted samples.

The catechins, the bitter and astringent polyphenols central to tea taste, displayed their own choreography. Epi-type catechins, which made up nearly 88 percent of the total, remained stable under light and medium roasting but dropped significantly under high roasting, with epigallocatechin falling by almost 11 percent and epicatechin by more than 12 percent. Meanwhile, the non-epi-type catechin gallocatechin surged by 51.63 percent, a hallmark of thermal epimerization in which epi-forms convert to their non-epi counterparts under heat. Gallic acid rose from 0.51 to 0.80 milligrams per gram, likely released by thermal hydrolysis of galloylated catechins such as EGCG and ECG. The net effect was a 6.33 percent decline in total catechins under high roasting, a shift that weakens the interactions between polyphenols and salivary proteins and helps explain why heavily roasted tea tastes smoother and more full-bodied despite its darker character.

Sugars and amino acids, the fuel for flavor-generating thermal reactions, followed a rise-and-fall pattern. Soluble sugars initially increased from 7.85 to 8.21 milligrams per gram under light roasting, possibly through partial hydrolysis of polysaccharides, then fell to 6.57 milligrams per gram under high roasting as they were consumed in Maillard-type pathways. L-theanine, the predominant amino acid in tea and a key contributor to umami and mellowness, declined relentlessly across the roasting gradient, from 1.19 milligrams per gram in the control to just 0.53 after high roasting. Caffeine, by contrast, stayed essentially flat across all treatments, which means the reduced bitterness of roasted tea owes more to catechin changes than to any loss of this alkaloid.

The volatile chemistry revealed the most spectacular changes of all. Using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry, the team identified 64 volatile compounds across the treatments. The unroasted control contained only 29 volatiles, dominated by floral oxygenated terpenes such as hotrienol and linalool. Light roasting actually reduced total volatile content, yet improved perceived aroma, likely because diminishing green and sulfurous notes stopped masking the remaining floral and sweet compounds. Medium roasting exploded the volatile inventory to 55 compounds and more than doubled total abundance, introducing 22 new substances including terpenes, pyrroles, and the Strecker aldehydes 3-methylbutanal and 2-methylbutanal, direct chemical evidence of Maillard and Strecker reactions consuming sugars and amino acids. High roasting pushed further, generating roast-aroma pyrazines and furfuryl pyrroles while degrading many fresh, green volatiles, restructuring the profile toward nutty and roasted notes.

Multivariate statistics sharpened the picture. A partial least squares-discriminant analysis model, validated with a 200-permutation test to rule out overfitting, cleanly separated the samples by roasting intensity and identified ten key discriminant volatiles, led by the pyranoid and furanoid oxides of linalool, followed by linalool itself, alpha-farnesene, and 2-pentylfuran. Many of these compounds are associated with floral and fruity aromas, marking them as the chemical fulcrum on which the sensory character of Zijuan oolong turns. The researchers are careful to note that these statistical discriminants are not necessarily the aroma-active compounds themselves, but they provide a powerful fingerprint of how far the roasting process has progressed.

The practical implications reach beyond one purple cultivar. The study demonstrates that roasting is not a simple dial from raw to burnt but a staged chemical program: light roasting polishes and balances, medium roasting builds complexity and varietal intensity, and high roasting delivers the roasted depth that some oolong drinkers prize. Because consumer preferences vary, the authors emphasize that no single roasting level is universally optimal; instead, producers can select intensity according to the flavor profile and market position they want. For a cultivar as chemically distinctive as Zijuan, whose anthocyanin-rich matrix responds to heat in ways conventional green-leaf teas do not, that kind of compositional roadmap could help transform an ancient craft into a precision process, one carefully controlled degree at a time.

Subject of Research: Effects of roasting intensity on the sensory quality and chemical composition of anthocyanin-rich Zijuan oolong tea

Article Title: Effect of roasting intensity on sensory quality and chemical composition of Zijuan oolong tea

Article References: Sun, C., Song, T., Hu, J., Wang, M., Chen, C., Tian, Y., Yang, Y., Luo, Q., Li, Y., Shen, S., Liu, B., & Zhu, M. (2026). Effect of roasting intensity on sensory quality and chemical composition of Zijuan oolong tea. Food Chemistry: X, 39, Article 104462. https://doi.org/10.1016/j.fochx.2026.104462

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104462

Keywords: Zijuan tea, oolong tea, roasting, anthocyanins, catechins, L-theanine, Maillard reaction, volatile compounds, flavor chemistry, tea sensory evaluation, purple tea, Food Chemistry