But enough of the sarcasm for today. A recent study from the Faculty of Agriculture at the South Valley University does in fact confirm that adding sage, thyme or rosemary to a commercially (canola based) frying oil can more than double its induction period, i.e. the time it takes until the oil is literally inedible ... and profoundly unhealthy.
|Figure 1: Oxidation stability (y-axis) of refined rapeseed oil treated w/ different herbs during frying for 0-32h (Taha. 2014).|
Accordingly, both, the rosemary and sage enhanced oils retained a significant albeit highly reduced alpha- and gamma-tocopherol content even after 32h of frying, while the control oil and the thyme-enhanced oil lost all its vitamin E after only ~14h and ~29h of frying, respectively.
There's one "on the other hand": You will probably know by now, that there no SuppVersity article with a simplified bottom line that does not at least mention the "other hands", i.e. things you should keep in mind, when reading the bottom line. For the study at hand this is the increase in free fatty acids with frying time. This is another, albeit very unspecific marker of the deterioration of a given oil during the frying process. In view of the superior outcome for both the oxidative stability, as well as the reduced depletion of tocopherols (vitamins E) I will still whole-heartedly conclude that adding sage and especially rosemary to your oils is a good idea.Although both will work, there are a couple of things that speak in favor of rosemary, which are not directly related to the results Taha et al. (2014) present in their latest study. If you look at the results of a recent study from the University of Madras, for example you will see that rosmarinic acid, one of the major active ingredients in rosemary will also have protective effect on your glucose and lipid metabolism (Jayanthy. 2014).
In said study, the provision of 100mg/kg of rosmarinic acid (human equivalent: 8mg/kg) reverted almost all of the detrimental changes in liver and glucose metabolism in a rodent model of diet-induced diabetes. And as the authors point out, the obtained results were almost comprable to those of the anti-diabetes drug, metformin (see Figure 2).
Rosemarinic acid is on par with metformin!
Noot bad, given the fact that the same compound from the fragrant, evergreen, needle-like leaves and white, pink, purple, or blue flowers of the perennial shrub from the Mediterranean has a whole host of additional benefits. It...
|Figure 2: Effect of Rosmarinic acid (100mg/kg | human equivalent: 16mg/kg) and metformin (200mg/kg | human equ.: 32mg/kg) on the insulin sensitivity in a rodent model of experimental diabetes (Jayanthy. 2014)|
- inhibits seasonal allergic rhinoconjunctivitis in humans (Takano. 2004) and the immune over-reaction to mite allergens (Sanbongi. 2004).
- has potent (in-vitro) anti-Parkinson's effects (Wang. 2012)
- ameliorates diabetic nephropathy in a rodent model of diabetes (Tavafi. 2011).
- appears to help with arthritis and rheumatoid joint degeneration (Youn. 2003; Khanna. 2007)
- induces apoptosis (cell death) in various cancers, including human colorectal cells (Xavier. 2009)
- has anti-hypertensive and pro-metabolic (glucose + fat metabolism) effects in rodents on high fructose diets (Karthik. 2001)
- Jayanthy, G., and S. Subramanian. "Rosmarinic acid, a polyphenol, ameliorates hyperglycemia by regulating the key enzymes of carbohydrate metabolism in high fat diet–STZ induced experimental diabetes mellitus." Biomedicine & Preventive Nutrition (2014).
- Khanna, Dinesh, et al. "Natural products as a gold mine for arthritis treatment." Current Opinion in Pharmacology 7.3 (2007): 344-351.
- Sanbongi, C., et al. "Rosmarinic acid in perilla extract inhibits allergic inflammation induced by mite allergen, in a mouse model." Clinical & Experimental Allergy 34.6 (2004): 971-977.
- Taha, Eman, et al. "Stabilization of refined rapeseed oil during deep‐fat frying by selected herbs." European Journal of Lipid Science and Technology (2014).
- Takano, Hirohisa, et al. "Extract of Perilla frutescens enriched for rosmarinic acid, a polyphenolic phytochemical, inhibits seasonal allergic rhinoconjunctivitis in humans." Experimental Biology and Medicine 229.3 (2004): 247-254.
- Tavafi, Majid, et al. "Rosmarinic Acid Ameliorates Diabetic Nephropathy in Uninephrectomized Diabetic Rats." Iranian Journal of Basic Medical Sciences 14.3 (2011).
- Wang, Jieyu, et al. "Neurorescue effect of rosmarinic acid on 6-hydroxydopamine-lesioned nigral dopamine neurons in rat model of Parkinson's disease." Journal of molecular Neuroscience 47.1 (2012): 113-119.
- Youn, Jeehee, et al. "Beneficial effects of rosmarinic acid on suppression of collagen induced arthritis." The Journal of rheumatology 30.6 (2003): 1203-1207.
- Xavier, Cristina PR, et al. "Salvia fruticosa, Salvia officinalis, and rosmarinic acid induce apoptosis and inhibit proliferation of human colorectal cell lines: the role in MAPK/ERK pathway." Nutrition and cancer 61.4 (2009): 564-571.
- Zheng, Wei, and Shiow Y. Wang. "Antioxidant activity and phenolic compounds in selected herbs." Journal of Agricultural and Food chemistry 49.11 (2001): 5165-5170.