Influence of Blanching and Drying Methods on the Retention of Nutritional Quality of Dried Moringa Leaves

INTRODUCTION

Moringa, Moringa oleifera Lam. belongs to the family, Moringaceae. It is also known as “Drumstick tree” and “Horse radish tree”. In India, it is cultivated in an area of 38,000 ha. Andhra Pradesh ranks first in cultivation in an area of 15, 655 hectares followed by Karnataka with 10,280 hectares and Tamil Nadu with 7,408 hectares. In Tamil Nadu, Theni, Madurai, Dindigul, Toothukudi, Ariyalur, Tiruppur and Karur districts have been declared as “Export zones of Moringa”. It is an important perennial leafy vegetables cultivated mainly for leaves, pods and seeds. Moringa leaves, pods, seeds and flowers are used in various food preparations as moringa leaves contain high nutritional and medicinal values [1]. Moringa leaves are  advocated as an outstanding indigenous source of good digestible protein, Vitamin A (378 µg/100g), calcium (440 mg/100g), iron (4 mg /100g), protein (6.7 g/100g) and folic acid. Iron is also present in high value, which can be a great dietary supplement for anaemic patients [2].

Moringa leaves are highly perishable posses very short shelf life due to leaf yellowing and senescence. Saponin content present in moringa leaves gives an unpleasant aroma and bitter taste which reduces the consumer acceptability. Extension of shelf life is need of the hour through the development of value added products of leaves with enhanced nutritional quality. Blanching prevents the enzyme activity and destroys microorganisms present on the vegetable surface reducing risk of food poisoning and reducing the saponin content in the moringa leaves [3] . Blanching influences the quality [4], nutritional content and digestibility [5]. Moringa has enormous potential uses but is very less explored. There is a great scope for moringa leaf based products such as soup, cookies, biscuits, bread, moringa panner, moringa chocolates, idli powder, dhal powder and halwa to make them available throughout the year. With increasing malnutrition, the need for nutrient rich value-added products is ever increasing. Ready-to-use moringa leaf powder has the potential of becoming an important product with changing lifestyles. Keeping these in view, the present study was conducted on the influence of blanching and drying methods on the retention of nutritional quality of dried Moringa leaves.

MATERIALS AND METHODS

The research work on “Studies on blanching and drying methods for the better retention of nutritional quality of dried Moringa (Moringa oleifera Lam.) leaves” was conducted at Horticultural College and Research Institute for Women, Tiruchirapalli, Tamil Nadu during 2018-19. The freshly harvested PKM 1 moringa leaves were procured from Thanjavur, Tamil Nadu. The cleaned, washed leaves were subjected to water blanching at 50^o, 60^o, 70^o and 80^oC for one, two and three minutes and then dried under a cabinet drier at 50^oC for standardizing the blanching treatment. The details are as follows.

T₀ : Without blanching

T₁ : Water blanching at 50^oC for one minute

T₂ : Water blanching at 50^oC for two minutes

T₃ : Water blanching at 50^oC for three minutes

T₄ : Water blanching at 60^oC for one minute

T₅ : Water blanching at 60^oC for two minutes

T₆ : Water blanching at 60^oC for three minutes

T₇ : Water blanching at 70^oC for one minute

T₈ : Water blanching at 70^oC for two minutes

T₉ : Water blanching at 70^oC for three minutes

T₁₀ : Water blanching at 80^oC for one minute

T₁₁ : Water blanching at 80^oC for two minutes

T₁₂: Water blanching at 80^oC for three minutes.

The drying ratio and rehydration ratio were calculated. Moisture content, total carotenoids, vitamin C, iron, calcium and non-enzymatic browning [6] were estimated to standardize the blanching method for better retention of nutritional quality in dehydrated leaves. Total carotenoids were measured at 452 nm using a spectrophotometer. Ascorbic acid was determined by titrating a known weight of the sample with 2, 6, dichloro phenol indo phenol dye using metaphosphoric acid as stabilizing agent [6]. The sensory evaluation for assessing the colour, flavour and texture of dried moringa leaves was conducted by a panel of seven judges and scoring was done using the nine-point hedonic scale [7] . A score of 5.5 and above were rated as acceptable. Based on biochemical analysis and sensory evaluation, the best blanching method was selected.

The unblanched and water-blanched (best blanching method 50^oC for three minutes) leaves were dried using different drying methods viz., sun drying, shade drying and cabinet drying.

D₁: Control (Without blanching) + Sun drying

D₂: Control (Without blanching) + Shade drying

D₃: Control (Without blanching) + Cabinet drying

D₄: Water blanching (50^oC for three minutes) + Sun drying

D₅: Water blanching (50^oC for three minutes) + Shade drying

 D₆: Water blanching (50^oC for three minutes) + Cabinet drying.

The leaves were spread in the food grade trays and dried under sunlight for drying with frequent turning. Shade drying was carried out in the insect, rodent, dust proof and well ventilated room. In cabinet drying, the leaves were spread in thin layer and dried at a temperature of 50^oC for eight hours. In all the drying methods, leaves were turned over frequently for uniform drying. The experiment was laid out in Completely Randomized Design and subjected statistical analysis [8].

RESULTS AND DISCUSSION

Moringa leaves were primarily processed and the loss during primary processing was recorded as 58 per cent, edible to non-edible ratio is 0.92:1. The fresh leaves contain 70 per cent  moisture, 440 mg/100g calcium, 7 mg/100mg iron, 220 mg /100g vitamin C and 4mg / 100g total carotenoids.

Among twelve treatments, T₉ (Water blanching 70^oC for three minutes) recorded better drying ratio (9.00) than other treatments (Table 1). The rehydration ratio was slightly higher (1.94) in T₃ (Water blanching 50^oC for three minutes). This might be due to better water absorption, the increased porousness of the cell wall in dehydrated leaves and difference in the number of imbibing materials. Similar report of enhanced rehydration due to blanching was observed in cabbage [9]. The blanched moringa leaves recorded higher moisture content compared to unblanched dried moringa leaves (4.95%) due to the gel formation on pectin substances of cell membrane which hindered the water removal from the cell. Similar findings were reported [10]. 

Water blanching at 50^oC for three minutes retained a higher amount of total carotenoids (124.65 mg/100 g) and vitamin C (467.25 mg/100 g) followed by water blanching at 60^oC for one minute (Fig.1). There was a noticeable difference in the retention of total carotenoids in the dried moringa leaves might be due to the concentration of total carotenoids during blanching. Though thermal degradation of ascorbic acid occurs, the remarkable stability could be probably due to the inactivation of the ascorbic acid oxidase enzyme during blanching. Water blanching increased cell damage and membrane permeability. The leaching loss of ascorbic acid increased rapidly as the cells die and cell membrane turned permeable. Loss of vitamin C occurs during the blanching of vegetables was reported [4]. The highest iron (21.50 mg/100g) and calcium content (1413.10 mg/100g) in T₃ (Water blanching at 50^oC for three minutes) recorded was due to the concentration of nutrients during blanching. Water blanching might have heavily ruptured the cells and high permeability of the membrane through which nutrients might have leached out.

Non-enzymatic browning was found to be least (1.00) in T₃ (Water blanching at 50^oC for three minutes) compared to other treatments. It is due to the fact that inversion of sugar and degradation of ascorbic acid might be the two reasons for the enhanced browning. Moisture in the dried moringa leaves would also have played a crucial role in the formation of browning compounds.

            Sensory evaluation showed that the treatments influenced the sensory quality of moringa leaves (Table 3). The overall sensory score is higher (8.7) in T₃ (Water blanching at 50^oC for three minutes) followed by T₂ (Water blanching at 50^oC for two minutes) due to the reduction in saponin content during blanching [3]. At 50^oC, the rate of biochemical reaction is slower and helped in maintaining better colour and texture of dried moringa leaves.

Table1. Effect of blanching methods on moisture content, drying ratio and rehydration ratio of dried moringa leaves

Treatments	Moisture content (%)	Drying ratio	Rehydration ratio
T0	4.95	11.50	1.91
T1	5.10	11.33	1.93
T2	5.14	11.33	1.93
T3	5.17	12.00	1.94
T4	5.20	10.67	1.92
T5	5.37	11.00	1.92
T6	5.47	10.67	1.92
T7	5.50	10.17	1.91
T8	5.52	10.33	1.91
T9	5.56	09.00	1.91
T10	5.56	09.83	1.91
T11	5.59	09.83	1.91
T12	5.60	09.83	1.90
Mean	5.36	10.58	1.92
CD(0.05)	0.65	0.44	0.03
SEd	0.32	0.22	0.01

Figure 1. Effect of drying methods on the retention of total carotenoids, vitamin C and

                  calcium content of dried moringa leaves

Table 3. Sensory evaluation moringa soup made from dried moringa leaves

Treatments	Colour	Flavour	Taste	Overall Sensory score
T0	7.3	6.9	7.5	7.2
T1	7.0	7.5	7.0	7.2
T2	8.0	8.0	8.5	8.2
T3	8.5	8.5	9.0	8.7
T4	7.0	7.5	7.1	7.2
T5	7.3	7.5	7.4	7.4
T6	7.3	7.6	7.5	7.5
T7	7.5	7.6	6.0	7.0
T8	7.7	7.7	6.3	7.2
T9	7.8	7.7	6.5	7.3
T10	7.8	7.8	6.3	7.3
T11	7.8	7.8	6.6	7.4
T12	7.8	7.8	6.7	7.4
Mean	7.6	7.7	7.1	7.5

Water blanching at 50^oC for three minutes (T₃) was adjudged as the best blanching treatment. The water blanched (50^oC for 3 minutes) and unblanched moringa leaves were dried under different conditions viz. cabinet drying, shade drying and sun drying. Treatment, T₁ recorded the lowest drying ratio (10.50) compared to other treatments (Table 4). The highest drying ratio in blanched, dried moringa leaves might be due to the leakage of water from cells during blanching and removal of water directly to the atmosphere which resulted in better drying. Rehydration ratio was found to be higher in T₃ (1.93) as compared to other treatments and moisture content was found to be lower in T₁ (4.52) as compared to blanching treatments (Table 4).

There was significant difference among the drying methods in the retention of total carotenoids. Total carotenoids content was found to be significantly higher in T₅ (133.61 mg/100g) followed by T₂ (124.65 mg/100g). High retention of total carotenoids observed in blanched, cabinet dried moringa leaves. This might be due to the concentration of total carotenoids during blanching and uniform temperature during drying. Sulphiting in addition to blanching was also more effective in the retention of beta-carotene in the dehydrated moringa leaves [11]. The retention of vitamin C was found to be significantly higher in T₅ (477.50 mg/100g) followed by T₆ (467.25 mg/100g). Thermal degradation is the main reason for decrease in ascorbic acid content. The loss of vitamin C varies with the drying technique employed [12]. Cabinet tray drying was found to be superior in respect of retention of vitamin C, total iron in selected vegetables as compared to sun drying and shade drying [13].

There was no significant difference on the retention of iron content in the dried moringa leaves dried under different drying methods. Studies conducted by various scientists from different parts of the world showed that different drying conditions did not bring significant change in the mineral content of vegetables [14]. Iron content was found to be higher in T₆ (21.50 mg/100g) followed by T₃ (21.08 mg/100g). Blanched, cabinet dried moringa leaves showed high iron content due to the concentration of iron during blanching. The retention of calcium content was found to be higher in T₅ (1498.08 mg/100g) followed by T₆ (1413.10 mg/100g). Higher calcium content was observed in blanched, cabinet dried moringa leaves due to concentration of nutrients during blanching. Blanched and shade-dried moringa leaves recorded higher nutrients content and were used for standardizing moringa leaf versatile food mix [15]. The dehydrated green leafy vegetable powder retained a good amount of calcium and iron [16].

Non-enzymatic browning was found to be significantly lower in T₆ (1.03 O.D.) followed by T₅ (1.72 O.D.).Sensory evaluation showed that the treatments influenced the sensory quality of moringa leaves (Table 5). The sensory score was higher in T₆ (8.8) followed by T₃ (8.3).

Table 4. Effect of drying methods on moisture content, drying ratio and rehydration ratio of dried moringa leaves

Treatments	Moisture content	Drying ratio	Rehydration ratio
D1	4.52	10.50	1.89
D2	4.62	11.12	1.92
D3	4.75	11.50	1.93
D4	4.65	11.37	1.88
D5	4.75	11.25	1.90
D6	5.12	12.00	1.92
Mean	4.74	11.29	1.91
CD (0.05)	0.59	0.23	0.04
Sed	0.24	0.11	0.002

Table 5. Sensory evaluation of moringa soup made from dried moringa leaves

Treatments	Colour	Flavour	Taste	Consistency	Overall Sensory score
S1	7.0	7.0	7.0	7.0	7.0
S2	8.0	7.5	7.5	7.5	7.6
S3	8.0	8.0	8.0	8.0	8.2
S4	8.0	7.0	8.0	8.0	7.7
S5	8.5	8.1	8.5	8.5	8.4
S6	9.0	8.5	9.0	9.0	8.8
Mean	8.1	7.7	8.0	8.0	8.0

CONCLUSION

            The present study shows that water blanching at 50^oC for three minutes retained more nutrients and colour in dehydrated moringa leaves and recorded the highest rehydration ratio and other parameters and concluded that the nutrient contents of the dried moringa leaves were not significantly affected by the blanching and drying methods. Blanching before drying improved the water absorption efficiency of the dried moringa leaves. Among the treatments, total carotenoid content in the dried moringa leaves ranged from 90.30 to 133.61 mg/100g. Moringa leaves dried in cabinet drier after water blanching (50^oC for three minutes) retained the higher amount of total carotenoids, vitamin C, iron and calcium. The drying temperature caused decrease in colour parameter. Cabinet drying of moringa leaves after water blanching showed least non enzymatic browning. The sensory quality was found to be higher in cabinet dried moringa leaves.

REFERENCES

1. Farooq F, Meenu Rai, Avinash Tiwari, Abdul Arif Khan and Shaila Farooq (2012) Medicinal properties of Moringa oleifera: An overview of promising healer.  J Med Plants Res.6: 4368-4374.
2. Chandramouli P, Divya VS, Bharathi, Sivakami A, Bharathiraja B, Jayamuthunagai J (2012) Standardisation and nutritional analysis of soup powder prepared from Moringa oleifera, Solanum trilobatum and Centella asiatica. Int J Future Biotechnology. 1: 1–16.
3. Indriasari Y, Wignyanto W, Sri Kumalaningsih (2016) Effect of blanching on saponins and nutritional content of moringa leaves extract. J Food Res.5: 55-60.
4. Neelavathi R, Pal RK, Sangita Sen, Kumar P (2013) Effect of blanching on the quality of dehydrated cauliflower. Indian J Hort. 70: 313-315.
5. Mutiara K T, Harijono, Estiasih T, Endang S (2013) Effect of Blanching Treatments against Protein Content and Amino Acid Drumstick Leaves (Moringa oleifera). J Food Res.2: 101-108.
6. Ranganna S (2014)Handbook of analysis and quality control for fruits and vegetable products, Mc Graw Hill Education (India) Ltd, New Delhi.
7. Amerine MA, Pangborn RM, Roessler EB (1965) Principles of sensory evaluation of food. In: Food Science and Technology Monographs. Academic Press, New York. pp. 338-39.
8. Panse VG, Sukhatme PV (1985) Statistical methods for Agricultural workers. Fourth Enlarged Edition, ICAR publications, New Delhi.
9. Mulay SV, Pawar VN, Thorat SS, Ghatge UM Ingle UM (1994) Effect of pre-treatments on quality of dehydrated cabbage. Indian Food Packer. 48: 11-13.
10. Bakshi R, Arora S,. Kaur S (1995) Evaluation of cauliflower drying methods. J Res Punjab Agric Univ. 32: 442-446.
11. Subadra S, Monica J, Dhabhai D (1997) Retention and storage stability of beta-carotene in dehydrated drumstick leaves (Moringa oleifera). Int J Food Sci Nutr.48: 373-379.
12. Negi PS, Roy SK (2001) Effect of drying conditions on quality of green leaves during long term storage. Food Res Int. 34: 283-287.
13. Bharati B, Asha A (2010) Effect of drying on iron and vitamin C content of selected vegetables. Food Science Research Journal. 1: 157-161. 
14. Gothwal PP, Setty GR, Mookerji KK (1998) Effect of processing steps for dehydration of mango, pineapple, carrot and drumsticks on the retention of nutrients. Beverage and Food World.25: 23-24.
15. Parvathi S, Nithya M, Devi priya J, Yogeshwari R (2015) Effects of different drying methods and value addition of versatile food mix with moringa dry leaves. Internat J Home Sci Extn Comm Manage. 2: 8-12.
16. Lakshmi B, Vimala V (2000) Nutritive value of dehydrated green leafy vegetable powders. J Food Sci Technol. 37(5): 465-479.