Effect of antioxidants and storage temperatures on browning and quality of custard apple (Annona squamosa L.) pulp

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1 Journal of Scientific & Industrial Research Vol. 73, September 2014, pp Effect of antioxidants and storage temperatures on browning and quality of custard apple (Annona squamosa L.) pulp D S Kumhar, S Pareek* and K D Ameta Department of Horticulture, Rajasthan College of Agriculture, Maharana Pratap University of Agriculture & Technology, Udaipur, Rajasthan India Received 23 September 2013; revised 22 January 2014; accepted 2 July 2014 Experiment consisted of 27 treatment combinations comprising 4 antioxidants (ascorbic acid, citric acid, cysteine and calcium chloride) with 2 concentrations (0.2% and 0.5%) and one control (without antioxidant) and 3 storage temperatures (ambient storage, 5ºC and 0ºC). These treatment combinations were evaluated under factorial completely randomized design with 3 replications. The stored pulp was examined for 120 days after storage at 30 days interval for biochemical and browning scores. Total soluble solids, acidity, ascorbic acid, sugars, phenols and colour were affected significantly up to 120 days of storage. The acidity and ascorbic acid decreased with the advancement of storage period whereas TSS, total sugars, and phenols increased. Browning of pulp also increased with the advancement of storage duration. Pulp treated with ascorbic acid 0.5% and stored under freezing temperature of 0ºC proved the most effective treatment for maintaining quality parameters up to 120 days of storage. Keywords: Custard apple, Pulp, Browning, Antioxidants, Storage temperatures, Ascorbic acid. Introduction Custard apple pulp is slightly granular, creamy yellow or white, sweet with a good flavor and low acidity. It is considered the sweetest of the Annona fruits. The edible portion is 28 37% of the total fruit weight and seeds correspond to 23 40%. 1 Carbohydrates present in the pulp include fructose (3.5%), sucrose (3.4%), glucose (5.1%) and oligosaccharides ( %). In India, custard apple is wildly grown fruit crop in Andhra Pradesh, Rajasthan, Karnataka and Maharashtra state. In the month of October December, there is glut in the market and growers forced to sell their product at thrown away prices. The fruit has an immense potential in processing industry but commonly susceptible to enzymatic browning catalyzed by polyphenol oxidase (PPO) affecting its sensory and nutritional qualities. In various fruit crops antioxidants and low storage temperatures are used to inactivate or reduce the activity of PPO. Oxygen removal or enzyme inhibition is necessary to prevent or decrease enzymatic browning 1 and antioxidants can be used to control enzymatic browning. 2 Ascorbic acid is probably the most widely used anti browning agent. 3 Thiol-containing compounds like cysteine are also *Author for correspondence sunil_ciah@yahoo.co.in reducing agents that control enzymatic browning. 4 Looking to this, an experiment was conducted to develop the technology for browning free pulp storage by using various antioxidants and storage temperatures. Materials and methods Experimental material Fresh, fully ripe and uniform sized fruits of custard apple were purchased from the fruit market of Udaipur, Rajasthan. Fruit were immediately brought to the Laboratory. Uniformly matured fruits were selected and washed by chlorinated water and then with tap water. After drying of fruits, pulp extracted by hand scooping and 10% water added to the pulp. Pulp with water was homogenized in emulsifier. This emulsified mixture then fed into the tomato pulper for separating seeds from pulp. The clear pulp was filled in the plastic jars of 500 ml capacity. Antioxidant treatment Experiment consisted of 27 treatment combinations comprising 4 antioxidants (ascorbic acid, citric acid, cysteine and calcium chloride) with 2 concentrations each (0.2% and 0.5%) and one control (without antioxidant) and 3 storage temperatures (ambient storage, 5ºC and 0ºC).

2 PAREEK et al.: EFFECT OF ANTIOXIDANTS AND STORAGE TEMPERATURE OF CUSTARD APPLE 623 Storage treatment The treated pulp was stored for 120 days at three different temperatures viz., ambient temperature (S 1 ), low temperature (5ºC) (S 2 ) and freezing temperature (0ºC) (S 3 ). Bio-chemical evaluation Total soluble solids, acidity, ascorbic acid, total sugars, and phenols were determined at 30 days interval for 120 days of storage duration. The total soluble solids, titratable acidity and ascorbic acid were determined by the method suggested by AOAC. 5 Total sugar content was determined by using Anthrone reagent. 6 Phenols of the fruit pulp was determined by Folin-Ciocalteau (FC) reagent. 7 Sensory evaluation The stored pulp at every 30 days interval was judged organoleptically by a test panel of five members. 9 point Hedonic scale was used for judging colour of stored pulp. Colour was judged from excellent to extremely poor (9 to 1). Statistical analysis: The experimental data were analyzed statistically according to analysis of variance as suggested by Cocharan and Cox. 8 Results and discussion All the characters studied were affected significantly with the application of antioxidants (Table 1 and Fig. 1). The highest per cent increase in TSS was recorded in ascorbic acid (0.5%) treatment, which was due to the contribution in TSS directly by the ascorbic acid whereas, it was lowest in control due to no contribution in TSS. It was observed that TSS of pulp increased with increase in storage temperature from 0+1ºC (S 3 ) to ambient temperature (S 1 ). The minimum increase in TSS under lower storage temperature might be due to low temperature and lower reduction in hydrolysis of polysaccharides and acids. Acidity per cent as citric acid affected significantly with the addition of different antioxidants (Table 1). It was due to the change in ph of pulp. Citric acid (0.5%) had also lowest ph and highest acidity, which also impart higher acidity to the pulp than rest of the treatments. Ascorbic acid (0.2%) contributed lowest in the acidity due the lower relative factor of ph. Whereas, cysteine is thiol containing amino acid which have very little action in acidity. The decrease in acidity observes during storage period of 15 to 120 days in all the different treatments applied. The acidity decreased with the decrease in the storage temperature from ambient storage (S 1 ) to 0±1 C storage temperature (S 3 ) (Table 1). Low temperature and high humidity declined the process of conversion of acid into sugars and salts by enzymes, particularly invertase. Similar results were reported by Jain et al. 9 in phalsa and Table 1 Effect of antioxidants and storage temperatures on TSS, acidity and total sugars of custard apple pulp during storage Treatments TSS (ºB) Acidity (%) Total sugars (%) Antioxidants Storage duration (days) Storage duration (days) Storage duration (days) T 1 (AA 0.2%) T 2 (AA 0.5%) T 3 (CA 0.2%) T 4 (CA 0.5%) T 5 (Cys 0.2%) T 6 (Cys 0.5%) T 7 (CaCl 2 0.2%) T 8 (CaCl 2 0.5%) T 9 (Control) SEm C.D. (P=0.05) Storage temperatures S 1 (Ambient) S 2 (5 + 1ºC) S 3 (0 + 1ºC) SEm C.D. (P=0.05) AA: Ascorbic acid; CA: Citric acid; Cys: Cysteine

3 624 J SCI IND RES VOL 73 SEPTEMBER 2014 Fig. 1 Effect of antioxidants and storage temperatures on (A) ascorbic acid, (B) phenols and (C) colour of custard apple pulp during storage

4 PAREEK et al.: EFFECT OF ANTIOXIDANTS AND STORAGE TEMPERATURE OF CUSTARD APPLE 625 litchi juices.the highest vitamin C content was recorded in the treatment ascorbic acid (0.5%) (Fig. 1). As ascorbic acid is directly related with the vitamin C along with dehydroascorbic acid. Therefore, it seems logically that highest vitamin C was recorded with higher concentration of ascorbic acid (T 2 ). Further, ascorbic acid content was decreased with the increase in the storage duration. It was due to the oxidation of ascorbic acid to dehydroascorbic acid and then further degraded to 2,3-diketo-gluconic acid by the action of ascorbic acid oxidase enzyme. The retention of ascorbic acid was more at lower storage temperature of 0±1 C (S 3 ) as compared to storage temperature of 5±1 C (S 2 ) and ambient temperature (S 2 ). This might be attributed to low temperature and high relative humidity in storage, which inhibited the rate of oxidation and metholic activities. The decreases in ascorbic acid content of juices with increase in storage temperatures were also reported by Pareek et al. 10 in the stored mandarian juice. The maximum per cent increase in total sugar was recorded in the ascorbic acid (0.5%) treatment over initial period to 120 days storage period (Table 1). The trend in increase or decrease of sugars content directly correlated with the TSS content of the pulp. Citric acid and calcium chloride had acidulent effect therefore, they contributed minimum to the sugar content. The total sugar contents of the pulp were increased with the advancement of storage period in all the treatments. The increase in total sugars might be due to the hydrolysis of polysaccharide like pectin, cellulose, starch, etc. and its conversion into simple sugar. Pareek et al. 10 observed that total sugars increased during storage in mandarin juice. Phenols increased with the advancement of storage period in all the treatments. At the end of experiment, maximum phenol (0.872%) was observed under T 9 and minimum (0.136%) under T 2 treatment. Phenols increased under all the storage temperatures with the advancement of storage duration up to 120 days. Whereas, it showed decreasing trend with the decrease in storage temperatures from ambient (S 1 ) to freezing (S 3 ) treatment. Phenols are involved in one of the most important reaction that affects color of minimally processed fruits and vegetables. Antioxidants may have formed adduct products with phenolic compounds, which is the proposed mechanism for inhibition of enzymatic browning. 11 The phenol increased with the decrease in storage temperature from ambient storage (S 1 ) to 0 C storage temperature (S 3 ). Low temperature and high humidity declined the process of conversion of soluble tannins into insoluble tannins. 12 Colour score of pulp decreased in all the treatments with the advancement of storage period (1 to 120 days). However, maximum score 7.00 under T 2 treatment and minimum score 3.33 under T 9 treatment was recorded at the end of experiment. A further reference to data revealed that the colour score of pulp was decreased under all the storage temperatures with the advancement of storage duration up to 120 days. It showed an increasing trend with the decrease in storage temperatures from ambient (S 1 ) to freezing (S 3 ) treatment. At the end of storage period maximum score 5.72 under S 3 treatment and minimum score 4.82 under S 1 treatment was recorded. Citric acid used in the experiment lower down the browning reaction by lowering the ph and acidulent reaction. Ascorbic acid has reducing properties. Ascorbic acid reduces the O- benzoquinones back to O-diphenols, and it also have a direct effect on PPO. 13 Cysteine is a thiol containing compound, also behave as reducing agent that inhibit enzymatic browning. 14 Calcium chloride is also known to inhibit browning, its inhibition increased as ph decreases. Chloride is a week inhibitor. Chloride levels required for PPO inhibition are elevated, and may comprise product taste. 15 Conclusion Ascorbic acid 0.5% and storage temperature of 0+1ºC maintained better qualitative characteristics viz., TSS, acidity, ascorbic acid, sugars, phenols and colour during 120 days of storage. Therefore, it is recommend that custard apple pulp can be stored at 0ºC temperature and treated with 0.5% ascorbic acid up to 120 days. The stored pulp can be used in lean period for making various processed products from stored pulp. 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