Effect of modified atmosphere packaging on shelf life and quality of curry leaves and Moringa leaves

Introduction

Murraya koenigii commonly known as curry plant belongs to the family Rutaceae. The plant is a medicinal plant and native to India, Sri Lanka and other South Asian countries. Curry leaves or sweet neem leaves are used in a variety of Indian dishes. The plant is highly valued for its leaves which are used for flavouring and spicing of food. Leaves are rich in many bioactive compounds like polyphenols, alkaloids and flavonoids which showed multiple bioactive functions like antioxidant, anticancer, antimicrobial, antidiabetic and hepatoprotective. Higher concentration of the bioactive compounds seen in plants leaves showed higher antioxidant activities. Whereas, Moringa leaves also contains non-nutritive chemicals or phytochemicals involving self-defence mechanism. Those phytochemicals include catechol, tannins, steroids, triterpenoids, flavonoids, saponins, alkaloids and reducing sugars having medicinal properties. In India, vegetable production contributes nearly 59% of total horticultural output, with a steady increase in per capita availability (Kumar et al., 2017) [4] . Among leafy vegetables, Moringa (Moringa oleifera L.) and curry leaf (Murraya koenigii L.) are widely consumed owing to their exceptional nutritional, medicinal and culinary importance. Despite their importance, both leaves are highly perishable and undergo rapid postharvest deterioration due to high respiration rate, moisture loss, enzymatic activity and microbial spoilage, leading to severe quality losses. Low-temperature storage below 10 °C is effective in slowing senescence and preserving quality; however, such facilities are often unavailable during transportation and marketing in developing countries. Storage conditions significantly influence chlorophyll retention, ascorbic acid content, phenolics and antioxidant activity in leafy vegetables (Singh and Sagar, 2010; Serea et al., 2014) [8,7] . Modified atmosphere packaging (MAP) is an effective postharvest technology that alters the gaseous composition surrounding the produce, thereby reducing respiration rate, delaying senescence and suppressing microbial growth. The study indicates that Moringa leaves stored in refrigerated conditions exhibited the least reduction in shelf life compared to those at ambient temperatures. Notably, aluminum foil-wrapped leaves maintained a shelf life of twelve days, significantly longer than the four days of the control group. Among various packing materials, polyethylene covers of 400-gauge thickness without vent gave a shelf life of nine days, whereas HDPE with vent and LDPE without vent both had eight days. In contrast, LDPE with vent at ambient conditions had a substantially shorter shelf life of two days. These findings align with Panta and Kanal (2018) [6] , who observed similar results for coriander leaves stored without perforations in cold environments.

Materials and Methods

Modified atmosphere packaging (MAP) treatments

Curry and Moringa leaves were packaged using modified atmosphere packaging under different gas compositions, packaging materials and storage temperatures. Three gas combinations consisting of oxygen (O₂), carbon dioxide (CO₂) and nitrogen (N₂) were employed:  C₁: 2% O₂, 4% CO₂, 94% N₂  C₂: 4% O₂, 6% CO₂, 90% N₂  C₃: 6% O₂, 8% CO₂, 86% N₂ Three packaging films, namely low density polyethylene (LDPE), polypropylene (PP) and aluminium laminate (Al), were used. The packaged samples were stored under two temperature conditions: ambient temperature (38 ± 2 °C) and refrigerated storage (8 ± 1 °C).

Experimental design

The experiment was laid out in a completely randomized design (CRD) with a factorial arrangement. A total of 18 treatment combinations (3 gas compositions × 3 packaging materials × 2 storage temperatures) were employed for curry leaves, and the same set of treatments was applied to Moringa leaves. Each treatment was replicated three times. Gas composition, packaging material and storage temperature were considered as independent variables, while physico-chemical and microbial attributes were taken as dependent variables.

MAP system and packaging operation

The MAP system consisted of gas cylinders (O₂, CO₂ and N₂), a gas mixer (Dansensor MAP Mix 9001 ME), a stainless steel buffer tank and a vacuum-gas flushing packaging machine. Individual gas cylinders were fitted with pressure regulators and connected to the gas mixer through high-pressure flexible tubing. Gas mixing was carried out by adjusting the CO₂ concentration and gas mix ratio as per the manufacturer's guidelines. The mixed gas was temporarily stored in a buffer tank and subsequently flushed into the packaging pouches after vacuum creation. Packaging involved evacuation of air, injection of the desired gas mixture and heat sealing of the pouch.

Headspace gas analysis

The headspace concentrations of O₂, CO₂ and N₂ in the packaged samples were measured using an O₂/CO₂/N₂ gas analyzer (PBI Dansensor). Gas analysis was performed by inserting a hypodermic needle through a rubber septum attached to the package surface prior to opening the pouch.

Physico-chemical analysis 2.5.1 Weight loss

Weight loss was determined using an electronic balance (Essae, FB 200±0.01 g accuracy). The initial sample weight (10±0.5 g) was recorded before storage, and the final weight was recorded at the end of storage. Weight loss (%) was calculated.

Moisture content

Moisture content was determined by the oven-drying method following AOAC. 1990 [1] method. Approximately 5 g of sample was dried at 105 °C for 3 h, and moisture content was expressed on both wet and dry basis.

Ascorbic acid content

Ascorbic acid content was estimated by the 2, 6dichlorophenol indophenol titrimetric method (AOAC 2005) [2] . Samples were extracted in 4% oxalic acid and titrated against standardized dye solution. Results were expressed as mg ascorbic acid per 100 g fresh weight.

Microbial analysis

Microbial quality was assessed by determining total viable count (TVC). After serial diluting the samples up to 10 5 , No. of colonies were counted on Plate Count Agar (PCA) using the pour plate method. Plates were incubated at 37 °C for 48 h, and microbial load was expressed as colonyforming units per gram (CFU/g), (Mohammadi et al. 2019) [5] .

Statistical analysis

The experimental data were analyzed statistically using analysis of variance (ANOVA) under a completely randomized design (CRD) with factorial arrangements. The effects of gas composition (A), packaging material (B), storage temperature (C) and their interactions were evaluated using OPSTAT software. Differences among treatment means were considered statistically significant at p<0.05.

Results and Discussion

Effect of MAP on Physico-Chemical Properties of Leaves

The Curry leaves and Moringa leaves were packed under two different conditions viz. refrigeration temperature and ambient temperature in three different packaging materials Low density Polyethylene (LDPE), Aluminium (Al) and Polypropylene (PP) in three different compositions of 2%, 4%, 94% (C1); 4%, 6%, 90% (C2) and 6%, 8%, 86% (C3) of O 2 , CO 2 and N 2 respectively. The storage temperatures were measured using a digital thermometer (Plate 1). Statistical analysis indicated significant differences in moisture content for both Moringa and Curry leaves based on composition and packaging materials under refrigeration (p<0.05). Overall, LDPE packaging was noted to effectively obstruct moisture infusion. The Curry leaves packed in LDPE had longer shelf life (15 days) followed by Al and PP (12 days). Spoilage was observed in Moringa leaves on 6th day in both Al and PP, whereas the LDPE had longer shelf life (20 days). Ascorbic acid content of stored produce generally decreases more rapidly at higher storage temperature since it was thermo labile. The reason for the decrease of ascorbic acid under ambient conditions due to the oxidation of ascorbic acid to de-hydro ascorbic acid by the enzyme, ascorbic-nase (Ambrose et al. 2017) [3] . The microbial load of curry and Moringa leaves was assessed at ambient and refrigeration temperatures, measured in log cfu/g. At ambient temperature, curry leaves packed in LDPE + C1 recorded the lowest microbial count of 5.60 log cfu/g, while the highest was in LDPE + C3 (5.69 log cfu/g). Moringa leaves followed a similar trend with counts of 5.62 log cfu/g in LDPE + C1 and 5.70 log cfu/g in LDPE + C3 after 15 days. Both types remained consumable for 15 days in LDPE. Refrigerated storage extended the shelf life to 20 days for both leaf types, with curry leaves in LDPE + C1 showing the lowest count of 5.45 log cfu/g and Moringa leaves in LDPE + C1 at 5.48 log cfu/g. Microbial growth was notably higher at ambient temperature due to elevated atmospheric gas effects, while refrigeration reduced growth due to lower temperatures and humidity, resulting in longer shelf life for the leave.

Conclusion

The study concluded that LDPE packaging material was found to be best for increasing shelf life of curry leaves and Moringa leaves at ambient and refrigerated temperature compared to Al and PP. Storage at refrigerated temperature maintained the quality of Moringa and curry leaves compared to storage at ambient temperature. The MAP gas composition of C1 (2%, 4%, 94%) was found to be the best for increasing shelf life compared to C2 (4%, 6%, 90%) and C3 (6%, 8%, 86%) at both ambient and refrigerated temperatures. MAP using LDPE with low O₂ and moderate CO₂ under refrigeration is a promising technique for extending the postharvest life of fresh curry and Moringa leaves.

References

1. AOAC International. Official methods of analysis of AOAC International. 15 th Ed. Washington (DC): Association of Official Analytical Chemists; 1990.
2. AOAC International. Official methods of analysis of AOAC International. 17 th ed. Washington (DC): Association of Official Analytical Chemists; 2005.
3. Ambrose DCP, Naik R, Daunty AL. Studies on fresh processing of Moringa oleifera leaves. Int J Food Ferment Technol. 2017;7(2):309-316.
4. Kumar R, Bhatia AK, Davinder S. Present status of vegetable production and their impact in human nutrition. Int J Agric Sci. 2017;9(55):4945-4949.
5. Mohammadi H, Kamkar A, Misaghi A, ZunabovicPichler M, Fatehi S. Nanocomposite films with CMC, okra mucilage, and ZnO nanoparticles: Extending the shelf-life of chicken breast meat. Food Packag Shelf Life. 2019;21:100330.
6. Panta R, Khanal S. Effect of modified atmospheric packaging on postharvest storage life of cilantro (Coriandrum sativum L.) stored under different conditions. J Hortic. 2018;5:243.
7. Serea C, Barna O, Manley M, Kidd M. Effect of storage temperature on the ascorbic acid content, total phenolic content and antioxidant activity in lettuce (Lactuca sativa L.). J Anim Plant Sci. 2014;24(4):1173-1177.
8. Singh U, Sagar VR. Quality characteristics of dehydrated leafy vegetables influenced by packaging materials and storage temperature. J Sci Ind Res. 2010;69:785-789.