Effect of Pre-harvest Treatments on the Cellulase Activity and Quality of Ber Fruit Under Cold Storage Conditions

Studies were carried out to find out the effect of various pre-harvest treatments such as CaCl2 (0.5%, 1.0% and 2.0%), Ca(NO3)2 (0.5%, 1.0% and 2.0%), GA3 (20, 40 and 60 ppm) and Bavistin (0.1%) on the cellulase activity and quality of ‘Umran’ ber fruits during cold storage. Marked trees were sprayed at colour break stage with the test chemicals. Fruits were packed in CFB boxes and placed in cold storage (3-5 oC and 85-90 % RH) for 30 days. The fruits were evaluated after 10, 20 and 30 days interval for various parameters such as cellulase activity, phenolics content, palatability rating and rotting percentage. Cellulase activity registered a gradual increase upto 20 days of storage thereafter a decline was noted in all the treatments. The palatability rating increased up to 10 days of storage in all the treatments, except control but subsequently it decreased with an advancement in storage period. Among the various pre-harvest treatments CaCl2 (2%) recorded minimum cellulase activity and rotting percentage and have also registered high palatability rating and phenolics content during cold storage conditions. Studies showed that pre-harvest application of CaCl2 (2%) maintained very good fruit quality and prolonged shelf-life for 20 days under cold storage conditions.


Introduction
Ber (Zizyphus mauritiana Lamk) is a hardy fruit, which can thrive well under adverse edaphic and climatic conditions.It is nutrition -rich fruit, a tally of nutrititive worth of ber with apple reveals that it excels in calcium, phosphorus and vitamin C but has comparatively low market price and therefore, referred as poor man's apple.It is an ideal fruit for cultivation in the arid and semi arid zones of northern India, as it has the negligible irrigation requirement in the month of May-June.High yielding cultivar 'Umran' is commercially grown in Northern India.During its peak harvesting season there is usually a glut in the market with a crash in its market price and low returns to the growers.Like most of other fruits, ber is perishable in nature and after harvesting, it cannot be stored for longer period under ambient conditions (Salunkhe and Kadam, 1995).During storage the rotting of fruit depends upon the activity of cellulase enzyme.Higher activity of this enzyme results in fruit softening which subsequently leads to the decay of the fruits.Cellulase is considered to be responsible for the hydrolysis of cellulose fibrils of the cell wall (Babbita et al., 1973).Calcium compounds extends the shelf-life of several fruits by maintaining fruit firmness, minimizing rate of respiration, protein breakdown and disease incidence (Gupta et al., 1980).Calcium is important in the maintenance of cell wall integrity in plants.Heavy influx of external or internal calcium inhibits ripening process due to reduction in enzymatic activity.Similarly certain growth regulators like gibberellic acid are known to promote the shelf life of fruits.Mehta et al. (1986) reported that GA3 100 ppm significantly suppresses the succinate activities of malate-dehydrogenase during post-harvest ripening of papaya and thus retard ripening.The growers can be greatly benefited if storage health is maintained by application of these compounds.Therefore, the present studies were conducted to investigate the effect of per-harvest application of various chemicals on change in cellulase activity and fruit quality during cold storage.

Materials and methods
The present investigations were carried out in the department of Horticulture Punjab Agricultural University Ludhiana, during 2002-03 on Umran trees of uniform vigour.The chemicals viz; CaCl 2 (0.5, 1.0 and 2,0 %), Ca(NO 3 ) 2 (0.5, 1.0 and 2,0 %) and GA 3 (20, 40 and 60 ppm) were sprayed on the trees at the colour break stage.All the experimental trees, except control, were sprayed with Bavistin (0.1%) 15 days before harvesting.Eleven treatments including control were laid out in completely randomized design with three replications.
Fruits were harvested at optimum maturity from the representative trees.One kg fruit from each replication of respective treatment was packed in netlon carriers.Thereafter, the packed fruits were placed in corrugated fibre board (CFB) boxes (5% perforations) with paper lining and kept in cold storage (temperature 3-5°C and R.H-85-in CaCl 2 (2%) treated fruits because these fruits contained the higher substrate content for enzyme activity as compared to other treatments, as the same was decomposed to a greater extent in other treatments with in 20 days of storage.Similar results was reported by (Mahajan, 1994) in apple.
High phenolics content is linked with higher resistance of fruits towards various pathological rots.Total phenolics content decreased with the advancement of storage period regardless of pre-harvest treatment (Tab.2).Similar results were reported by Panwar (1981); Goel and Siddiqui (1999) in ber fruits.After 30 days of storage fruits treated with CaCl 2 (2%) exhibited maximum phenolics content (0.090 % and 0.093 %) while it was minimum in control.Similarly in avocadoes, calcium compound treatments resulted in suppression of respiration and high phenolic content of the fruits (Rensburg and Engelbrecht, 1986) At the time of harvesting the untreated fruits showed maximum palatability rating (Tab.3).The pre-harvest treatments might have retarded the ripening process of ber fruits which led to low palatability as compared to untreated fruits.But, after 10 days of storage the PR of fruits increased in all the treatments except control, where it decreased.However with the advancement of storage period, there was continuous reduction in PR in all the treatments.At the end of storage, the maximum PR (3.50 and 3.70) was recorded in Ca Cl 2 (2%) treated fruits which was followed by GA 3 60 ppm treatment.These preharvest treatments of Ca and GA 3 might have delayed senescence process which resulted in maintenance of fruit 90%).Fruit samples were analysed for physico-chemical characteristics after 10, 20 and 30 days of storage.Palatability rating (PR) was recorded on the basis of score card viz: 1-poor; 2-Fair; 3-Good; 4-Verygood and 5-Excellent.The per cent rotting of fruits (PRF) was calculated on the number basis by counting the number of rotten fruits (Fr) and total fruits (Ft) on each storage interval.The PRF was calculated as PRF = 100[Ft -Fr) (Ft) -1 ].Total phenolics were estimated as per method described in AOAC (1980).The cellulase activity was estimated according to the procedure of (Mahadevan and Sridhar, 1982).

Results and discussion
It is evident from Tab. 1 that the cellulase activity varied significantly among different treatments and on storage interval during both the years of study.All the treatments showed progressive increase in cellulase activity with the advancement of storage period up to 20 days of storage, but afterwards the enzyme activity decreased towards the end of storage (Tab.1).After 20 days of storage, the minimum cellulase activity was recorded in CaCl 2 (2%) treated fruits followed by GA 3 60 ppm treatment.Heavy influx of external calcium inhibits the ripening process due to reduction of enzyme activity.Presence of calcium ions limits the polyglacturonase activity in the cell wall of the fruit skin (Gleen and Pooviah, 1986).GA 3 may have lowered the cellulase activity due to anti-senescence effect.External application of Ca increased the rigidity of cell wall.At the end of storage the enzyme activity was highest  Kumar et al. (1994) in 'Banarasi Pawandi' fruits.
After 20 days of cold storage fruit rotting was noticed in some treatments (control > Bavistin 0.1% > Ca(NO 3 ) 2 0.5% > CaCl 2 0.5%) while fruits from remaining treatments maintained their normal health.At the end of cold storage, the percentage of rotten fruits were significantly higher in untreated fruits as compared to all other treatments (Tab.4).The fruit treated with CaCl 2 (2%) registered minimum rotting followed by GA 3 60 ppm treatment.An increase in calcium content of fruit has been associated with decreased incidence of physiological dis-  (Raese 1986;Conway and Sams 1994) as calcium is known to impart resistance against the attack of infectious pathogens (Bangreth et al., 1972).Calcium compounds, significantly thickened the middle lamella of fruit cells owing to increased deposition of calcium pectate and thereby maintained the cell wall rigidity which inhibits the penetration and spread of pathogens in fruits (Gupta et al., 1984)).The prolongation of fruit life due to growth regulators was probably due to effectiveness of these chemicals in retaining of green pigments, retardation of ripening and senescence (Huang, 1974).These results are in line with findings of Gupta et al. (1987) who suggested that the pre harvest sprays of calcium compounds (Chlorides, Nitrates, Sulphates and Phosphates) reduced the decay loss in ber fruits.
Tab. 1.Effect of different pre-harvest treatments on cellulase activity in ber fruit during cold storage.
health in storage.Similar results are obtained by Tab. 2. Effect of different pre-harvest treatments on total phenolics of ber fruit during cold storage Tab. 4. Effect of different pre-harvest treatments on per cent rotting of ber fruit during cold storage