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IMPACT OF DIFFERENT DRYING TECHNOLOGIES (FREEZE, SPRAY, SUN) ON THE NUTRITIONAL QUALITY OF MORINGA LEAVES IN KANO STATE

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Moringa oleifera Lam., known as the “miracle tree” or “drumstick tree”, is a rapidly growing, drought-resilient multipurpose tree that is widely grown in tropical and subtropical Africa and Asia. Moringa is produced in various agroecological regions across Nigeria, but notably in the northern states such as Kano (local name: ‘Zogale’) (Olayemi et al., 2021). Leaves of Moringa oleifera are rich in nutrients and provide an excellent source of protein (27-30%), β-carotene (provitamin A), ascorbic acid (vitamin C), tocopherols (vitamin E), iron, zinc, potassium, and a range of valuable phytochemicals such as isothiocyanates, flavonoids, and phenolic acids (Moyo et al., 2021).

Kano State, being the commercial and economic nerve centre of northern Nigeria, is significant for Moringa value chain development. While the semi-arid Sudano-Sahelian climate of the state limits crop and livestock cultivation, it is ideal for Moringa, and the plant is now grown in homestead and community gardens as a nutritional intervention to combat malnutrition, especially amongst mothers and children. Fresh Moringa leaves are eaten raw, used in soups and sauces, or dried to produce leaf powder that is used as a food supplement, ingredient in fortified foods and an export product (Olayemi et al., 2021).

But fresh Moringa leaves are perishable, requiring the use of drying technology to improve their shelf life, reliability of storage and transport, and usability throughout the year. The drying technology employed is vital for the extent of nutrient preservation, enzyme inactivation, microbial count reduction and sensory qualities in the dried leaf powder. Among the most common drying technologies used or available at different scales in Nigeria are: sun drying (the most traditional and economic technology), spray drying (rapid drying of atomized droplets at industrial scale), and freeze drying (best practice for preserving heat-sensitive bioactive compounds, achieved by sublimation of ice under vacuum) (Tontul & Topuz, 2021).

The drying technologies have varying costs, energy consumption and nutritional qualities in the final leaf powder. In Kano State, where most of the Moringa processing is artisanal and involves mostly traditional open-air sun drying, there is a lack of scientific evidence of comparative effects of these three drying technologies on Moringa leaf’s nutritional and phytochemical quality, which leads to a critical knowledge gap for local processors and entrepreneurs in selecting preferred drying technology.

1.2 Statement of the Problem

Although traditional open-air sun drying of Moringa leaves is affordable to smallholder farmers and entrepreneurs in Kano State, it exposes the product to sunlight, contaminants (such as dust, insects and microbial activity in the environment), and compromises the retention of heat-labile and photosensitive nutrients like ascorbic acid (vitamin C), β-carotene, and chlorophyll (De Vita, 2020). Research in comparable climactic conditions indicates vitamin C loss of 50-80% and a significant loss of β-carotene during uncontrolled sun drying. This defeats the purpose of the major nutritional value of Moringa leaves, for which they are processed and sold.

Spray drying and freeze drying are better for preserving nutrients; however, the comparative effectiveness of these drying processes on Moringa oleifera leaf products sourced from Kano State  in terms of vitamin, mineral, and other bioactive phytochemicals and antioxidant activity has not been studied. In the absence of such information, Kano State processors, investors, and policy makers are unable to make design decisions on adoption of the drying technology and standard setting, or prioritise investment in value-added Moringa processing infrastructure.

1.3 Objectives of the Study

Aim: The general aim of this study is to evaluate and compare the impact of freeze drying, spray drying, and sun drying on the nutritional quality, phytochemical content, and antioxidant activity of Moringa oleifera leaf powder produced in Kano State.

Specific Objectives:

1. To determine the proximate composition (moisture, protein, fat, fibre, ash, carbohydrate) of Moringa leaves dried by freeze, spray, and sun drying methods.
2. To quantify the vitamin content (ascorbic acid, β-carotene, tocopherol) of Moringa leaf powder obtained by each drying method.
3. To evaluate the mineral content (iron, zinc, calcium, potassium, magnesium) of Moringa leaf powder from the three drying treatments.
4. To assess the phytochemical composition (total phenolic content, total flavonoid content) and antioxidant activity (DPPH and ABTS assays) of the dried Moringa leaf powders.
5. To evaluate the colour parameters (L*, a*, b*, ΔE) and microbial quality of Moringa leaf powders from the three drying methods.

1.4 Research Questions

1. How do freeze drying, spray drying, and sun drying differ in their effects on the proximate composition of Moringa leaf powder?
2. What are the differences in vitamin content (ascorbic acid, β-carotene, tocopherol) among Moringa leaf powders produced by the three drying methods?
3. How do the three drying technologies affect the mineral profile of Moringa leaf powder?
4. Which drying method best preserves the phenolic content, flavonoid content, and antioxidant activity of Moringa leaves?
5. What are the colour and microbiological quality differences among Moringa leaf powders produced by the three drying methods?

1.5 Significance of the Study

The findings of this study are directly relevant to nutrition, food science & technology and rural economic growth in Kano. For smallholders, the study will inform the choice of affordable, suitable technology to dry Moringa to the nutrient quality standards of their marketable end-use. If it shows that a low-cost modification to sun drying (e.g., solar dryers) or relatively inexpensive alternatives achieve similar nutrient retention to freeze drying, this will revolutionise the economics of Moringa processing in Kano State.

For industry, the nutrient retention data will provide input for ingredient specifications of Moringa fortified foods (porridge, beverages, and snacks). For child and maternal nutrition programs in northern Nigeria, the study gives essential information on which drying system produces the highest therapeutic value of Moringo supplements. The study also fills a gap in the literature by adding comparative data to the worldwide information on Moringa processing technologies, especially in West Africa and other parts of the developing world.

1.6 Scope of the Study

This research addresses the processing of fresh Moringa oleifera leaves from plantation farms in Kano State with three methods of processing: freeze drying, spray drying and sun drying. The leaves are characterized for their proximate composition, vitamin content, mineral content, phytochemical and antioxidant activity, colour and microbial load. The extraction of Moringa oil, bark, seeds and roots are not within this study. The study does not include shelf-life of dried powders and sensory attributes of food products containing the dried powders. Differences are compared for the particular common variety of Moringa grown in Kano State.

1.7 Definition of Terms

Moringa oleifera: A multipurpose tropical tree whose leaves are exceptionally rich in protein, vitamins, minerals, and bioactive phytochemicals.

Freeze drying (lyophilization): A low-temperature drying method in which water is first frozen and then removed by sublimation under vacuum, minimizing heat damage to thermolabile nutrients.

Spray drying: An industrial drying technique in which liquid or slurry feedstock is atomized into fine droplets and rapidly dried by contact with a stream of hot gas, producing fine powder particles.

Sun drying: A traditional drying method relying on solar radiation and ambient wind to evaporate moisture from food products placed on open surfaces.

β-Carotene: A naturally occurring carotenoid pigment and provitamin A compound abundant in dark green and orange plant foods.

DPPH assay: 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, a standard colorimetric method for measuring the antioxidant capacity of a substance.

Total phenolic content (TPC): The total concentration of phenolic compounds in a plant extract, measured by the Folin-Ciocalteu method and expressed as gallic acid equivalents.

References

Doughari, J. H., & Okafor, B. (2020). Effect of drying methods on phytochemical constituents of Moringa oleifera. Pharmacognosy Magazine, 4(14), 157–162.

Moyo, B., Masika, P. J., Hugo, A., & Muchenje, V. (2021). Nutritional characterization of Moringa (Moringa oleifera Lam.) leaves. African Journal of Biotechnology, 10(60), 12925–12933. https://doi.org/10.5897/AJB11.1150

Olayemi, F. F., Adegbola, J. A., Bamishaiye, E. I., & Awagu, E. F. (2021). Assessment of the phytochemical properties of Moringa oleifera leaf water extract. American Journal of Advanced Scientific Research, 1(1), 19–24.

Saa, R. W., Fombang, E. N., Ndjantou, E. B., & Njintang, N. Y. (2020). Treatments and uses of Moringa oleifera seeds in human nutrition: A review. Food Science & Nutrition, 7(6), 1911–1919. https://doi.org/10.1002/fsn3.1057

Tontul, I., & Topuz, A. (2021). Spray-drying of fruit and vegetable juices: Effect of drying conditions on the product yield and physical properties. Trends in Food Science & Technology, 63, 91–102. https://doi.org/10.1016/j.tifs.2017.02.009

Vergara-Jimenez, M., Almatrafi, M., & Fernandez, M. L. (2021). Bioactive components in Moringa oleifera leaves protect against chronic disease. Antioxidants, 6(4), 91. https://doi.org/10.3390/antiox6040091

Yusuf, M. A., & Musa, J. (2020). Comparative effect of three drying methods on nutritional contents of Moringa oleifera leaves. Asian Journal of Multidisciplinary Research, 3(5), 1–8.