Climate Effects on Phytochemistry and Antioxidant Activity of Aloe Vera
Aloe vera (Aloe vera, Xanthorrhoeaceae), a perennial succulent native to South Africa, thrives in subtropical and tropical regions. It is drought-resistant and tolerates a wide range of climatic conditions. Aloe vera is a rich source of phytochemicals, some of which have been shown to have anti-inflammatory, antibacterial, antioxidant, immune-boosting, anticancer, anti-aging, and antidiabetic effects. Medicinally, it is used for burns, eczema, inflammation, and fever. Potent antioxidants such as barbendol, emodin, barbaloin A, and chrysene have been isolated from methanolic extracts of aloe vera as putative bioactive. However, its overall effects may be due to synergistic effects of these and other constituents.
To investigate effects of agro-climatic zones on phytochemical content of different populations of aloe vera in India, the authors harvested fresh leaves from 12 collection areas in six climatic zones, prepared methanolic extracts from them, and assayed their antioxidant capacity. Total phenolic content (TPC) of extracts was determined spectrometrically using the Folin-Ciocalteu method, with gallic acid as the standard and results expressed as mg gallic acid equivalent (GAE)/g of extract. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging, hydrogen peroxide (H2O2) scavenging, reducing power, metal chelating, and β-carotene-linoleic acid assays were performed on each extract in triplicate and mean values of results calculated. Preparation of extracts and each assay is described.
In qualitative phytochemical screening, aloe vera methanolic extracts showed the presence of alkaloids, glycosides, reducing sugars, phenolic compounds, steroids and terpenoids, flavonoids, tannins, and saponin glycosides. All antioxidant assays showed significant antioxidant activity ranging from 56-80%. Extracts from different agro-climatic zones differed significantly in antioxidant potential. For example, in the DPPH scavenging assay, Punjab (semi-arid), Himachal Pradesh (highland), and Haryana (semi-arid) accessions had the highest antioxidant capacity at 75.54-80.2%. Accessions from Telangana (tropical wet and dry), Gujarat (arid), and West Bengal (tropical wet and dry) had the least antioxidant capacity at 56.75-62.66%. By comparison, ascorbic acid had 96% radical scavenging ability. In the H2O2 scavenging assay, where ascorbic acid as the standard had reducing the activity of 97%, aloe vera extracts from Punjab, Telangana, and Himachal Pradesh had the highest activity, while that from West Bengal had the least. Strong correlations were observed between TPC and antioxidant activity.
Phytochemical composition of plants is influenced by environmental factors including geography, climate, soil type, sun exposure, grazing stress, seasonal changes, and more. Studies of plants in stressful situations show greater production of flavonoids, anthocyanins, and mucilaginous substances. An increase in unsaturated fatty acid production has been associated with cooler climates. In the case of aloe vera, previous findings on antibacterial activity on the same extracts as in the present study also support these statements. Aloe vera plants from hilly areas are traditionally more valued for nutritional use. In this study, accessions from colder regions in northern India had more antioxidant potential than those from hotter regions in southern India. Effects of soil conditions and other factors, including climate change effect, in these regions remain to be evaluated.
This study demonstrates that aloe vera is a promising source of bioactive phenolic compounds with good antioxidant capacity and that antioxidant capacity is higher in plants grown in northern India. However, without further identification of specific phytochemicals and biological testing, it is hard to suggest which combination of qualitatively determined phytochemicals is the most relevant for biological activity in humans. Further research should include in vivo studies of the extracts and individual constituents for inflammation and related conditions. The study may or may not guide some aloe vera cultivators to grow the plant in cooler areas for stronger antioxidant capacity; others may choose hotter climes to obtain more overall plant mass.
Regarding climate change, this must be seen as a baseline study. Plants were not subjected to documented climate change in this study but harvested one time from different climatic zones. While the authors state that India’s climate, largely controlled by an annual monsoon, “appears to be experiencing increasingly severe and erratic precipitation,” only an average rainfall is shown for each collection site, with no evidence of change. Nor is any effect of rainfall on TPC or antioxidant capacity discussed, only relative coolness and heat. If the study is repeated in five years and correlated with then-available evidence of climate change in India, it may or may not show divergence from the baseline data established by these authors. Caution is warranted regarding the study’s results as the information garnered is a very basic qualitative phytochemical screen and bioassays that have not been shown to have a direct biological correlation in vivo.
Kumar S, Yadav A, Yadav M, Yadav JP. Effect of climate change on phytochemical diversity, total phenolic content and in vitro antioxidant activity of Aloe vera (L.) Burm.f. BMC Res Notes. January 25, 2017;10(1):60. doi: 10.1186/s13104-017-2385-3.