Quality characteristics of dehydrated leafy vegetables influenced by packaging materials and storage temperature

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1 Journal of Scientific SINGH & Industrial & SAGAR Research : PACKAGING AND STORAGE OF DEHYDRATED LEAFY VEGETABLES Vol. 69, October 2010, pp Quality characteristics of dehydrated leafy vegetables influenced by packaging materials and storage temperature Uadal Singh and V R Sagar Division of Post Harvest Technology, Indian Agricultural Research Institute, New Delhi , India Received 05 April 2010; revised 28 July 2010; accepted 30 July 2010 Leafy vegetables (curry leaves and drumstick leaves) were dehydrated in cabinet drier at 58±2 C and packed in four packaging materials (200 gauge and 400 gauge LDPE, 200 gauge HDPE and 150 gauge PP) and stored at room temperature (RT) and low temperature (LT) for 3 months to evaluate best package and storage temperature for maximum retention of nutrients in leafy vegetables during storage. HDPE (200 gauge), followed by storage at LT (7±1 C), was found to be good for higher retention of β-carotene, ascorbic acid, chlorophyll content, rehydration ratio, sensory score and less moisture and non-enzymatic browning (NEB) in dehydrated vegetable leaves during 3 months of storage. Keywords: β-carotene, Chlorophyll, Curry leaves, Drumstick leaves, Drying, Storage Introduction India is second largest producer of vegetables in the world after China, accounting for 10% of world production. In India, different varieties of green leafy vegetables (LV) are available during winter season. LV 1,2 are relatively inexpensive, easily and quickly cookable and rich in several nutrients [â-carotene, riboflavin, folic acid, minerals like calcium (Ca), iron (Fe) and phosphorus (P) and fair source of protein (2-7%)]. Processing by dehydration makes LV light in weight and can be easily converted into fresh-like form throughout the year. This study presents suitable packaging material and storage condition for selected dehydrated LV. Experimental Section LV of curry leaves [CL, Murraya koenigii (Linn.) Spreng.] and drumstick leaves (DL, Moringa oleifera Lam.) were procured from experimental farm of Division of Vegetables Science and brought to Division of Post Harvest Technology, IARI, New Delhi to evaluate effect of packaging material and storage temperature on quality of dehydrated leaves. Both vegetables were washed in running tap water thoroughly; *Author for correspondence vidyaram_sagar@yahoo.com yellowish and unwanted leaves as well as hard stems were removed, and resultant leaves were trimmed manually. Standardization of Blanching Time and Dehydration of Leaves A known quantity of CL and DL were taken in a muslin cloth and dipped in boiling water containing 0.5% sodium metabisulphite (SMS) (1:5, leaves: water) for 15, 30, 45, 60, 90,120 and 150 s to inactivate enzymes 3. Blanching time was standardized by enzyme test in presence of guaicol and hydrogen peroxide. Pretreated leaves (CL and DL) were spread on an aluminium tray (1.05 m x kg/m 2 and dried in cross flow hot air (airflow rate of m/s) at 58±2 C (Kilburn make, model-0248) cabinet drier to a moisture content of 4-5% in finished product. Packaging and Storage Dehydrated CL and DL were packed in different packaging materials [200 gauge LDPE (low density polyethylene) pouches, 400 gauge LDPE pouches, 200 gauge HDPE (high density polyethylene) pouches and 150 gauge PP (poly propylene) pouches]. Packed samples were stored at room temperature (RT) (15-35 C) and low temperature (LT) (7±1 C) up to three months for storage study and product was drawn at one month interval for physico-chemical analysis.

2 786 J SCI IND RES VOL 69 OCTOBER 2010 Table 1 Equilibrium relative humidity (ERH) study of dehydrated vegetable leaves RH % Curry Leaves Drumstick Leaves Remarks EMC % Days to reach EMC % Days to reach equilibrium equilibrium Normal colour and texture, product crisp Normal colour and texture, product crisp Normal colour and texture, product crisp Normal colour, product slightly crisp Normal colour, product good in texture Colour fading, product slightly soft Colour fading, soft texture Product slightly, soft, mould growth Product soft, mould growth appeared Product soft, mould growth after 9 days Physico-chemical Analysis Moisture content (%) was determined by drying a known weight of sample in a hot air oven at 60±5 C to a constant weight. Chlorophyll, β-carotene, ascorbic acid and non enzymatic browning were determined according to reported procedure 3. Rehydration Ratio (RR) Dehydrated samples (5 g each) were put into a beaker and 50 ml of warm (60 C) water was added. After ½ h, drained weight of dehydrated material was taken 3. Sensory Analysis Overall acceptability (colour, flavour and texture), was evaluated by a panel of 7 semi trained members. Samples were presented after rehydration in tap water. Attributes were scored on 5 point hedonic scale 4 (excellent, 1; good, 2; fair, 3; poor, 4 and very poor, 5). Statistical Analysis Data was subjected to statistical analysis 5 [critical difference (CD) at 5% level of probability was compared for comparison among different treatments]. All treatments were replicated 3 times. Results and Discussion Relative Humidity (RH) Data are relationship between equilibrium moisture content (EMC) and number of days to reach equilibrium at particular RH (Table 1) and RH curve (Fig. 1). Product retained its quality of overall acceptability up to 60% RH and below in both dried EMC % EMC % C=Critical Point= 12.01% D=Danger Point= 11.12% a) Mould growth RH % a) C=Critical Point= 11.21% D=Danger Point= 9.15 % b) Mould growth D RH % b) Fig 1 - Equilibrium relative humidity curve for: a) Curry leaves; and b) Drumstick leaves (C, critical point; D, danger point) D C C

3 SINGH & SAGAR : PACKAGING AND STORAGE OF DEHYDRATED LEAFY VEGETABLES 787 Table 2 Effect of packaging and storage on quality characteristics of dehydrated curry leaves during storage (dry wt basis) Parameters Storage Storage Packaging material and storage temperature period, Initial Temp. 200 g 400 g 150 g 200 g Package Months value CD LDPE LDPE PP HDPE CD P=0.05 RT LT RT LT RT LT RT LT P=0.05 Moisture, % NS ß-carotene, µg/100g Chlorophyl, mg/100g Ascorbic acid, mg/100g NEB (O.D NS nm) NS Rehydration 1 1:3.62 NS 1:3.56 1:3.59 1:3.57 1:3.60 1:3.57 1:3.62 1:3.58 1:3.62 ratio 2 1:3.49 1:3.56 1:3.52 1:3.58 1:3.56 1:3.59 1:3.56 1:3.59 NS 3 1:3.59 1:3.52 1:3.50 1:4.22 1:3.52 1:3.57 1:3.55 1:3.59 Sensory Score NS vegetables. At higher levels of RH, products absorbed moisture and turned dark and fungal growth (Aspergillus sp. and Penicillium sp.) was observed at 80% RH and above. Optimum RH for dehydrated CL and DL was 60% or below for safe storage and shelf life. Critical and danger point in terms of moisture level for CL (12.01%, 11.12%) and DL (11.21%, 9.15%), were observed when initial moisture content in dehydrated CL and DL was 2.5% and 5.50% respectively. A similar trend is reported 6 in onion powder. Physico-chemical Analysis Moisture content increased during storage in both CL and DL irrespective of packaging material and storage period. Compared to other packaging materials for CL and DL, when samples were stored at LT for 3 months, gain in moisture content was low in 200 gauge HDPE, attributed to greater protection against water vapour infusion in HDPE. However, changes in moisture content within packaging material were non-significant. A similar finding was also reported 6 in onion powder. With regard to storage condition, moisture content was less in samples stored at LT compared to RT. Difference in moisture content was found statistically significant, might be due to more permeability of LDPE film to water vapor compared to HDPE films. Sagar & Khurdiya 7 also reported that moisture content increased very slightly during storage in dehydrated mango slices and powder. With increase in storage period, β-carotene, chlorophyll and ascorbic acid content decreased gradually during 3 months of storage of CL (Table 2) and DL (Table 3). β-carotene retention was better in dehydrated CL (4788 µg/100g) and DL (4658 µg/100g) when product was packed in 200 gauge HDPE and stored at LT (7±1 C). However, loss in β-carotene was significantly less among different packaging material. With regard to storage temperature, samples stored at LT retain more β-carotene as compared to RT. However, difference in β-carotene due to storage temperature was found statistically significant. Similar trend is reported 8 in green leaves. Chlorophyll was higher in CL ( mg/100g) and DL (65.25 mg/100g) when samples packed in 200 gauge HDPE and it was least in samples packed in 200 gauge LDPE pouches in CL and DL during 3 months of storage. In the same period, decrease in chlorophyll in CL and DL respectively was less at LT (112.0 mg/100g and mg/100g) compared to RT ( mg/100g and mg/100g). Difference among packaging was statistically significant, might be due to prevention of

4 788 J SCI IND RES VOL 69 OCTOBER 2010 Table 3 Effect of packaging and storage on quality characteristics of dehydrated drumstick leaves during storage (dry weight basis) Parameters Storage Storage Packaging material and storage temperature period, Initial Temp. 200 g 400 g 150 g 200 g Package Months value CD LDPE LDPE PP HDPE CD P=0.05 RT LT RT LT RT LT RT LT P=0.05 Moisture, % NS ß-carotene, µg/100g Chlorophyll, mg/100g Ascorbic acid, mg/100g NEB (O.D nm) NS Rehydration 1 1:4.27 1:4.29 1:4.28 1:4.29 1:4.29 1:4.31 1:4.32 1:4.32 ratio 2 1:4.31 NS 1:4.23 1:3.92 1:4.26 1:4.26 1:4.26 1:4.29 1:4.28 1:4.30 NS 3 1:4.19 1:4.22 1:4.13 1:4.24 1:4.27 1:4.27 1:4.29 1:4.29 Sensory Score NS chlorophyhllase activity and conversion of chlorophyll to pheophytin. Chlorophyll content was slightly better at LT than RT. However, difference in chlorophyll content due to storage temperature was found statistically significant. Similar results were observed 9 in CL (Table 2) and DL (Table 3). Ascorbic acid was higher in CL ( mg/100g) and DL ( mg/100g) after 3 months of storage when samples were packed in 200 gauge HDPE and stored at LT, might be due to better protection by packages due to less permeability of film as compared to other packaging materials, wherein ascorbic acid was less but reduction in ascorbic acid was statistically significant. Similar trend is reported 6 in onion powder. Ascorbic acid content was higher in CL and DL stored under LT compared to RT (Tables 2 & 3), might be due to rapid degradation of ascorbic acid at higher temperature. Similar pattern has been reported 10 in other dehydrated vegetables. Ascorbic acid content also decreased with increase in moisture content during storage, might be due to rapid increase in activity of ascorbic acid oxidation and other relevant oxidizing enzymes in dried and dehydrated leaves at higher moisture content in samples compared to others. Similar work is reported 11 in dried onion flakes. However, difference in reduction on ascorbic acid was statistically significant. Non-Enzymatic Browning (NEB) NEB increased with increase in storage period at both temperatures in all packaging materials. NEB was less in dehydrated samples of CL and DL when products were packed in 200 gauge HDPE and stored at LT for 3 months, might be due to less moisture content in samples packed in 200 gauge HDPE pouches compared to others. Changes among packages were not found statistically significant. NEB was less in samples stored at LT as compare to RT, may be due to less moisture absorption at LT and reduced reaction between sugar and amide components of dried LV. Similar trend is reported 9 in LV. Changes due to storage temperature were statistically significant (Tables 1 & 2). Rehydration Ratio (RR) RR was higher in CL (1:2.59) and DL (1:4.29) when products were packed in 200 gauge HDPE and stored at LT for 3 months, might be due to less absorption of moisture in HDPE film during storage. Similar result is reported 12 in mango slices. Changes occurred due to packaging material and storage temperature were

5 SINGH & SAGAR : PACKAGING AND STORAGE OF DEHYDRATED LEAFY VEGETABLES 789 non-significant (Tables 2 & 3). RR was less at RT in all packages. However, decrease in RR was less when product was stored at LT compared with RT. Sensory Analysis Sensory score made based on 5 point hedonic scale increased, irrespective of packaging material and storage temperature. Increase in score was due to poor texture, loss of flavour and poor in colour with prolonged storage. Best score was obtained to the product packed in 200 gauge HDPE and stored under LT for 3 month (Tables 2 & 3), might be due to less gas permeability of packaging material and reduced physiological activity of product under LT. Higher score was obtained when product was packed in 200 gauge LDPE for CL (3.33) and for DL (4.33) at LT storage for 3 months. Increase in sensory score in respective of packaging material for DL was found statistically significant but for CL it was non-significant. However, changes in sensory score in respective of storage temperature were found statistically significant for CL and it was non-significant for DL. Conclusions Dehydrated LV have great potential to use throughout the year for preparation of several types of mix vegetables after rehydration even during off-season. Drying of LV and making them use for future open up new vistas in the field of food technology as curry mix and other condiments. Dehydrated LV are rich in antioxidants and could be added as natural antioxidants to develop new commercial products. Developing new packaging and storage techniques are essential to extend their shelf life without much deterioration. References 1 Singh Uadal, Sagar V R & Sureshkumar P, Effect of pre-treatment on the quality of dehydrated leafy vegetables rich in vitamin A. Indian J Agric Sci, 7 (2006) Narsinga Rao B S, Deosthale Y G & Pant K C, Nutritive Value of Indian Foods [National Institute of Nutrition (ICMR), Hyderabad] Ranganna S, Handbook of Analysis and Quality Control for Fruit and Vegetables Product, 2 nd edn (Tata McGraw Hill Publication Co. Ltd, New Delhi) 1986, Okoli E C, Nmorka O G & Unaegbu M E, Blanching and storage of some Nigerian vegetables, Int J Food Sci Technol, 23 (1988) Gomez A K & Gomez A A, Statistical Procedure for Agricultural Research, 2 nd edn (John Wiley and Sons, Singapore) 1984, Sagar V R & Maini S B, Studies on the packaging and storage of onion powder, Indian J Hort, 54 (1997) Sagar V R & Khurdiya D S, Studies on dehydration of Dashehari mango slices, Indian Food Pack, 53 (1999) Negi P S & Roy S K, Retention of quality characteristics of dehydrated green leaves during storage, Plant Foods Hum Nutr, 56 (2001) Negi P S & Roy S K, Effect of drying conditions on quality of green leaves during long term storage, Food Res Int, 34 (2001) Chauhan A S, Ramteke R S & Eipeson W E, Properties of ascorbic acid and its application in food processing: A critical appraisal, J Food Sci Technol, 35 (1998) Kumar P & Sreenarayanan V V, Studies on storage of dehydrated onion flakes, Indian Food Pack, 54 (2) (2000) Khedkar D N & Roy S K, Storage studies in dried and dehydrated raw mango slices, Acta Hort, 231 (1988)