Influence of salicylic acid and edible wax coating on chilling injury -

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Influence of salicylic acid and edible wax coating on chilling injury

In the present investigation, the effect of bilayer coating was evaluated on the chilling injury and quality of guava fruits. The fruits of white fleshed guava cv. Allahabad Safeda and pink fleshed cv. Lalit were subjected to treatment with 5-sulfosalicylic acid (2 mM) followed by vegetable wax (1:4 v/v). The treated fruits were stored under two temperatures, namely, 5 and 10°C for 15 days. Post cold storage, fruits were transferred to supermarket conditions (20 ± 2°C) for a 2-day shelf life simulation period. The results revealed that treated fruits showed significantly lower weight loss and chilling injury compared to control fruits. The bilayer coating was effective in delaying yellowing of fruit skin and respiration peak with greater retention of total antioxidant capacity compared to control fruits. The treated fruits maintained the shelf life up to 12 + 2 days and 9 + 2 days under 5 and 10°C, respectively.  Guava fruit softening and color change are important indicators of fruit ripening. In this study observed retarded rate of fruit softening and color change in both guava cultivars, Allahabad Safeda and Lalit upon bilayer coating with sulpho salicylic acid (SSA) and vegetable wax (VW).

Mature green guava fruits of two cultivars, namely, Allahabad Safeda (white fleshed) and Lalit (pink fleshed), were harvested from the Indian Agricultural Research Institute orchard. Fruits of uniform size and maturity without wounds or rots were selected for the study. The fruits of the two guava cultivars were divided into 4 lots comprising of 210 fruits each. Two lots were dipped in distilled water for 5 min and served as control. The other two lots were immersed in 5-sulfosalicylic acid (5-SSA) solution (2 mM) for 5 min, drained, and air dried. Air dried fruits treated with 5-SSA solution were dipped into a second coating of edible vegetable wax formulation (1:4 v/v). The control and treated fruits were divided into two; one set was stored under 5°C while the other set of fruits was kept at 10°C under a relative humidity of 80 – 90%. After every 3 days of low temperature storage, fruits were transferred to 20 ± 2°C and kept for 2 days for simulation studies under supermarket conditions after which they were analyzed for different quality attributes.

Lower storage temperature (5°C) was found to be conducive for retarding weight loss due to suppressed metabolic activity. The wax coating applied helps in lowering the moisture loss due to its hydrophobic nature while, salicylic acid helps in reduction of respiration rate and imparts chilling injury tolerance to the fruits. Membrane disintegration at low temperature is the major cause for chilling injury of fruits that results due to oxidative lipid peroxidation with a simultaneous increase in MDA content. Treated fruits stored at 5 or 10°C showed CI symptoms on 15 + 2 days of storage. It was also observed that untreated fruits stored at 5°C are more prone to chilling injury compared to fruits stored at 10°C because of loss of cell membrane permeability at lower temperatures. During ripening of guava fruits, the color of peel changes from green to yellow hue. Treatment with 5-SSA + VW delayed the development of yellow color in both guava cultivars signifying a delay in the respiratory processes. Under storage conditions of 5°C, fruits coated with bilayer turned completely yellow after 15 + 2 days of storage in contrast to untreated fruits that turned yellow after 9 + 2 days. Storage at 10°C resulted in control fruits turning completely yellow after 6 + 2 days whereas change of hue to yellow was delayed up to 12 + 2 days in coated fruits. The delay in ripening process was mainly due to the inhibitory effect of salicylic acid on ethylene synthesis and the barrier properties of vegetable wax formulation on gaseous exchange further resulting in suppressed activities of enzymes such as ACC synthase and ACC oxidase. Treated fruits of both cultivars showed suppressed and delayed respiration peak compared to control fruits in both the cultivars under all the storage conditions. This might be due to the synergistic effect of salicylic acid and wax coating wherein SSA helped to lower the chilling injury and wax coating helped to act as barrier to gases. It was also observed that fruits stored at lower temperature recorded higher antioxidant activity compared to fruits stored at slightly higher temperature that may be attributed to delay in ripening process. The higher PAL activity in SSA + VW treated fruits helped in retention of phenolic compounds during the storage which further led to reduced incidence of chilling injury of these fruits. Low levels of MDA in treated fruits might be ascribed to the inhibitory effects of the coatings and salicylic acid on ripening process by curbing the ethylene evolution and senescence further resulting in lower chilling injury of the fruits and less production of free radicals.

This study conclude that this technique is a user friendly can be successfully applied on-farm or before storage to supply better quality fruits in the marketing value chain. Further, submicron dispersions of the wax biopolymer maybe tried to improve its efficacy and barrier properties.

Reference:

Madhav, J.V., Sethi, S., Sharma, R.R., Nagaraja, A., Arora, A. and Varghese, E., 2021. Influence of bilayer coating of salicylic acid and edible wax on chilling injury and functional attributes of guava. Journal of Food Processing and Preservation, 45(7):15601.