Impact of different drying methods on antioxidant properties of Moringa oleifera leaves

Introduction

A challenge facing small-scale processors across the tropics is simple: fresh Moringa oleifera leaves wilt within 24-48 h of harvest, but consumers want access to this nutritional powerhouse year-round [1] . Drying is the oldest and cheapest preservation technique, yet every drying method involves trade-offs-higher temperatures speed moisture removal but accelerate oxidation of phenolics, degradation of ascorbic acid, and isomerisation of carotenoids [2] . Moringa leaves are exceptionally rich in polyphenols (gallic acid, chlorogenic acid, quercetin), β-carotene, vitamin C, and minerals, and much of their health value is attributed to these heat-labile compounds [3] . Shade drying preserves bioactives well but takes 5-7 days and risks microbial spoilage in humid climates. Tray drying at controlled temperatures is faster but demands electricity. Sun drying is free and fast but exposes leaves to UV radiation and unpredictable temperature swings [4] . Comparative data under identical analytical conditions for these three methods are surprisingly scarce for the West African savannah setting, where ambient humidity (55-80% RH) during the rainy and post-rainy seasons alters drying kinetics [5] . This research therefore compared shade, tray (40-80 °C), and sun drying for their effects on antioxidant properties, vitamin content, and colour of Moringa leaf powder.

Material and Methods

Material

Fresh Moringa oleifera leaves (PKM-1 variety) were harvested from a 3-year-old plantation at the college farm, Tamale, Northern Region (9°24′N, 0°50′W), during September-October 2023. Leaves were washed, de-stalked, and divided into five batches. Analytical chemicals were from Merck (Germany) and Sigma-Aldrich (USA) [6] .

Methods

Drying treatments: (a) shade drying-single layer on mesh trays in a ventilated room (32 ± 3 °C, 55-70% RH, 5 days); (b) tray drying-forced-air oven at 40, 50, 60, 70, and 80 °C until moisture < 10%; (c) sun drying-single layer on black polythene sheets, turned twice daily, 2 days.

Dried leaves were milled, sieved (250 µm), and stored in aluminium foil pouches at -18 °C until analysis. Total phenolic content was determined by Folin-Ciocalteu (GAE), antioxidant activity by DPPH and FRAP assays, vitamin C by DCPIP titration, β-carotene by spectrophotometry (450 nm after hexane extraction), and colour by HunterLab (L*, a*, b*) [7] . All analyses in triplicate; ANOVA and Duncan's test (p<0.05) in SPSS v. 26.

Results

Comprehensive Interpretation

Shade drying preserved the most antioxidant activity and vitamins but required 5 days. Tray drying at 50 °C retained 72-89% of shade-dried values while completing in 6-8 h, making it the most practical choice for small processors.

Temperatures above 60 °C caused steep losses in all bioactives. Sun drying was fast but suffered from UVinduced oxidation and uncontrolled temperature spikes.

Discussion

Shade drying's superiority is consistent with earlier findings by Satwase et al. [4] , who reported 15-25% greater TPC retention in shade-dried vs sun-dried Moringa from Maharashtra. The present research extends this comparison to tray drying at five temperatures, filling a gap in the literature for humid eastern Ghana. The steep decline above 60 °C aligns with the thermal degradation kinetics of chlorogenic acid and quercetin reported by Sultana et al. [8] , who identified 55-60 °C as the critical threshold for polyphenol stability in leafy vegetables.

Vitamin C was the most sensitive marker: sun drying destroyed 70.4% of the fresh-leaf value, whereas shade drying retained 58.7%. This mirrors the oxidation-driven degradation pathway of ascorbic acid, which is accelerated by UV exposure and metal-catalysed reactions on sundrying surfaces [9] . The practical implication is clear: where electricity is available, tray drying at 50 °C should replace sun drying. Where it is not, shade drying under improved airflow (mesh trays, ventilated sheds) remains the best option, provided drying time can be tolerated [10] .

Conclusion

This research set out to identify the drying method that best preserves the antioxidant and vitamin profile of Moringa oleifera leaves for use as a functional food ingredient. Shade drying retained the highest bioactive levels (DPPH 81.2%, vitamin C 128.4 mg/100 g), followed by tray drying at 50 °C (72.1%, 98.3 mg/100 g). Sun drying and hightemperature tray drying (70-80 °C) caused severe losses. For small-scale processors in humid regions, tray drying at 50 °C offers the best trade-off between quality and processing time. Open questions include the long-term storage stability of powders from each method, the effect of blanching pre-treatment on colour and nutrient retention, and the consumer acceptability of Moringa powder in fortified food products.

References

1. Gopalakrishnan L, Doriya K, Kumar DS. Moringa oleifera: a review on nutritive importance and its medicinal application. Food Science and Human Wellness. 2016;5(2):49-56.
2. Vega-Gálvez A, Ah-Hen K, Chacón M. Effect of temperature and air velocity on moisture sorption isotherms and drying kinetics. Food and Bioprocess Technology. 2012;5(7):2557-2567.
3. Sreelatha S, Padma PR. Antioxidant activity and total phenolic content of Moringa oleifera leaves in two stages of maturity. Plant Foods for Human Nutrition. 2009;64(4):303-311.
4. Satwase AN, Pandhre GR, Sirsat PG, Wade YR. Studies on drying characteristic and nutritional composition of drumstick leaves. Journal of Pharmacognosy and Phytochemistry. 2013;2(1):122126.
5. Ali MA, Yusof YA, Chin NL, Ibrahim MN. Effect of different drying treatments on colour quality and ascorbic acid concentration of guava fruit. International Food Research Journal. 2016;23(Suppl):S53-S60.
6. AOAC. Official methods of analysis. 20th ed. AOAC International, Rockville, MD. 2016.
7. Brand-Williams W, Cuvelier ME, Berset C. Use of a free radical method to evaluate antioxidant activity. LWT-Food Science and Technology. 1995;28(1):2530.
8. Sultana B, Anwar F, Ashraf M. Effect of extraction solvent/technique on the antioxidant activity of selected medicinal plant extracts. Molecules. 2009;14(6):21672180.
9. Davey MW, Van Montagu M, Inzé D. Plant L-ascorbic acid: chemistry, function, metabolism, bioavailability and effects of processing. Journal of the Science of Food and Agriculture. 2000;80(7):825-860.
10. Joshi P, Mehta D. Effect of dehydration on the nutritive value of drumstick leaves. Journal of Metabolomics and Systems Biology. 2010;1(1):5-9.
11. Potisate Y, Phoungchandang S. Drying of Moringa oleifera leaves in a modified domestic microwave oven. International Journal of Agriculture and Food Science https://www.agriculturaljournals.com Journal of Food Science and Technology. 2015;52(3):1767-1773.
12. Siddhuraju P, Becker K. Antioxidant properties of various solvent extracts of total phenolic constituents from three different agroclimatic origins of drumstick tree leaves. Journal of Agricultural and Food Chemistry. 2003;51(8):2144-2155.
13. Moyo B, Masika PJ, Hugo A, Muchenje V. Nutritional characterization of Moringa oleifera leaves. African Journal of Biotechnology. 2011;10(60):12925-12933.
14. Fuglie LJ. The miracle tree: Moringa oleifera. CTA/CWS, Dakar. 2001.
15. Nouman W, Basra SMA, Siddiqui MT, Yasmeen A. Moringa oleifera leaf extract: an innovative priming tool. Turkish Journal of Agriculture and Forestry. 2014;38(1):104-115.
16. Dillard CJ, German JB. Phytochemicals: nutraceuticals and human health. Journal of the Science of Food and Agriculture. 2000;80(12):1744-1756.
17. Nambiar VS, Parnami S. Standardization and organoleptic evaluation of drumstick leaf incorporated recipes. The Ghanan Journal of Nutrition and Dietetics. 2008;45(1):32-39.
18. Olabode Z, Akanbi CT, Olunlade B, Adeola AA. Effects of drying temperature on the nutrients of Moringa leaves. Direct Research Journal of Agriculture and Food Science. 2015;3(5):117-122.
19. Sagar VR, Suresh Kumar P. Recent advances in drying and dehydration of fruits and vegetables. Journal of Food Science and Technology. 2010;47(1):15-26.
20. Fitriani V, Amanto BS, Anam C. Influence of drying method on nutritional value of Moringa oleifera flour. IOP Conference Series: Materials Science and Engineering. 2017;193:012021.
21. Isitua CC, Ibeh IN, Olayinka JN. Proximate composition of Moringa oleifera leaves. Journal of Nutritional Ecology and Food Research. 2015;2(3):214218.