PECTINOLYTIC LIQUEFACTION OF APRICOT, PLUM, AND MANGO PULPS FOR JUICE EXTRACTION

Abstract

The investigation envisaged to optimize the conditions of liquefaction of apricot, plum, and mango pulp with pectinase enzyme for juice extraction. Pectinase powder with pectinesterase and polygalacturonase activities of 1.15 and 6.68 units per gram, respectively, was used for liquefaction of pulps. An enzyme concentration of 0.5% was found optimum to liquefy apricot and plum pulps at 45°C in 5 h to obtain maximum juice yields of 78% and 82%, respectivly. An enzyme concentration of 0.9% and incubation at 45°C for 6 h gave maximum juice yield of 59% from mango pulp. Juices obtained after liquefaction of pulps had higher moisture, total soluble solids, total sugars, reducing sugars and acidity and lower crude fiber, vitamin C, and pH than pulps. The other constituents, namely fat, protein, ash, and β-carotene, remained nearly the same in juices as well as pulps.

INTRODUCTION

The tropical and temperate fruits are usually too pulpy and pectinaceous to yield juice by simple pressing or centrifugation. Such techniques involve excessive amounts of energy and result in meager juice yields (Joshi et al., 1991). Pectinases have been used for the clarification of wines since the beginning of 19th century. Pectinolytic enzymes hydrolyze pectic substances and aid in the flocculation of suspended particles and clarification of wines and juices. Enzymatic decomposition of pectin facilitates juice extraction and thereby results in high juice yield (Zetelaki, 1974).

The time required for pectinolytic liquefaction of fruit pulps depends on the type of fruits, type of enzyme, enzyme concentration, incubation temperature, and incubation time (Rajanala et al., 1996). In view of the above, the present investigation was undertaken to optimize the conditions for the pectinolytic liquefaction of apricot, plum, and mango pulps for obtaining maximum juice yield.

MATERIALS AND METHODS

Apricot (variety Charmagz), plum (variety Titrone) and mango (variety Amrapali) were procured from Horticultural Research Centre Patharchatta, G.B. Pant University of Agriculture and Technology, Pantnagar, UP, India. Pectinase enzyme was purchased from Triton Industries, Mysore, India.

Preparation of Fruit Pulps

Fully ripened fruits of apricot or plum were washed and cooked after adding 100 mL water per kg of fruits for 10 minutes at 5 psi as per the method described by Joshi et al. (1991). Softened fruits were then passed through a pulper. Pulp thus obtained was heated to boiling, cooled to room temperature, and preserved after adding 1500 ppm of potassium metabisulphite. Mango fruits were washed, peeled, destoned, and pulp was prepared as per the procedure of Chauhan et al. (1993). Pulp obtained from 1 kg of fruits was blended with 100 mL water and 150 ppm of sodium benzoate. The blended pulp was heated to 90°C for 2 minutes, hot filled in bottles aseptically, and pasteurized at 90°C for 25 minutes.

Liquefaction of Pulps for Juice Preparation

The procedure described by Rajanala et al. (1995) was followed for optimizing the conditions of liquefaction of fruit pulps. Trials were conducted to optimize the enzyme concentration (0.25, 0.5, 0.75, and 1%, respectively, for apricot and plum pulps and 0.3, 0.6, 0.9, and 1.2%, respectively, for mango pulp), incubation time (1, 2, 3, 4, 5, 6, and 7 hours, respectively) and incubation temperature (30, 35, 40, 45, and 50°C, respectively) for liquefaction of pulps. A 50-g sample of pulp was drawn into a 150-mL beaker and a specified amount of pectinase was added as 10% aqueous solution of enzyme powder. The samples were incubated after thorough mixing. The added enzyme was inactivated by heating the content to 80°C for 3 minutes at the end of incubation. Liquefied pulp was then cooled to 45°C and filtered through double-layered muslin cloth. The filtrate was centrifuged at 3000 rpm for 10 minutes to obtain clear juice. The conditions of liquefaction that gave maximum juice yield were taken as optimum for the preparation of juices. Percent juice yield was calculated by dividing grams of juice obtained by grams of pulp taken for liquefaction multiplied by 100.

Analysis

Fruits pulps and juices were analyzed for moisture, protein, fat, ash, titratable acidity (as percent citric acid), pectin, and crude fiber by the methods described in AOAC (1990). Total soluble solids, sugars, pectin esterase activity, and polygalacturonase activity were determined using methods described by Ranganna (1991). The pH of pulps and juices was determined by a digital pH meter (Model 316, Electronic Corporation of India).

RESULTS AND DISCUSSION

Chemical Composition of Pulp

Chemical composition of apricot, plum, and mango pulps and juices are given in Table 1. The values of chemical composition of apricot pulp were similar to the values reported by Sharma et al. (1990), Joshi et al. (1991), Chauhan et al. (1993), and Singh (1995). The values obtained for the chemical composition of plum pulp were in consonance with the earlier findings of Wani and Saini (1990), Joshi et al. (1991), Sharma and Joshan (1993), and Prakash et al. (1994). The composition of mango pulp resembles the findings of Gosh et al. (1975) and Prasad (1984).

Table 1. Chemical Composition ^a of Fruit Pulps and Juices

	Apricot		Plum		Mango
Characteristics	Pulp	Juice	Pulp	Juice	Pulp	Juice
Moisture contents (%)	83.25 ^b	84.5	87.75	86.20	83.75	84.56
T.S.S (°Brix)	15.20	15.50	14.00	14.50	17.00	17.40
Protine (%)	1.06	1.06	0.82	0.80	0.72	0.72
Fat (%)	0.41	0.41	0.44	0.44	0.43	0.42
Ash (%)	0.76	0.76	0.51	0.50	0.47	0.46
Total suger (%)	9.36	9.90	7.37	7.96	15.02	15.88
Reducing suger (%)	5.87	7.28	6.86	7.02	10.20	10.78
Crude fiber (%)	1.10	0.94	1.25	1.02	1.04	0.94
Pectin (%)	0.32	nil	0.46	nil	0.79	nil
Vitamin C (mg/100 g)	6.38	6.32	5.78	5.68	19.20	19.00
Acidity (% citric acid)	1.94	2.25	2.14	2.19	0.670	0.69
pH	3.37	3.27	3.34	3.24	4.96	4.78
Carbohydrates (%)	14.62	14.86	14.60	14.90	16.25	16.46

^a Wet basis.

^b Values are an average of triplicate determination.

Optimization of Conditions of Liquefaction

Enzyme Concentration

At different intervals of incubation, juices were extracted from the liquefied pulps. Maximum juice yield were obtained by liquefaction of apricot (78%) and plum (82%) with an enzyme concentration of 0.5%. Further increase in enzyme concentration had no appreciable effect on juice yield (Tables 2 and 3). These findings are in agreement with the observations made by Wani and Saini (1990) and Joshi et al. (1991). However, in the case of mango pulp, the maximum juice yield (59%) was obtained at an enzyme concentration of 0.9% (Table 4). No juice could be extracted without adding pectinolytic enzyme. Similar observations were also made by Sreekantiah et al. (1963) and Gupta and Girish (1988).

Table 2. Effect of Conditions of Liquefaction by Pectinolytic Enzyme on the Juice Yield (%) from Apricot Pulp

		Incubation Time (Hours)
Enzyme Concentration (%)	Incubation Temperature (°C)	1	2	3	4	5	6	7
Control		6	9	11	17	17	17	17
0.25	30 ^a	20	24	30	45	55	60	60
	35	27	30	36	50	59	64	64
	40	29	33	44	56	64	66	66
	45	30	36	49	65	68	68	68
	50	30	35	49	64	68	64	64
0.50	30	22	28	34	50	62	70	74
	35	27	32	38	54	69	76	76
	40	30	32	44	60	73	60	60
	45	30	36	49	65	78	78	78
	50	32	40	50	60	75	78	70
0.75	30	26	32	38	45	60	68	72
	35	30	34	40	50	62	69	72
	40	32	36	49	59	68	74	74
	45	35	38	50	70	78	78	78
	50	37	40	55	68	74	73	70
1.00	30	20	24	30	49	62	74	76
	35	22	26	32	59	68	72	72
	40	30	38	50	70	70	75	75
	45	36	39	52	74	78	78	78
	50	38	39	55	70	68	68	67

^a Values are an average of triplicate determination.

Table 3. Effect of Conditions of Liquefaction by Pectinolytic Enzyme on the Juice Yield (%) from Plum Pulp

		Incubation Time (Hours)
Enzyme Concentration (%)	Incubation Temperature (°C)	1	2	3	4	5	6	7
Control		9	10	10	10	10	10	10
0.25	30 ^a	18	20	43	53	60	62	63
	35	24	28	46	54	62	63	63
	40	22	24	51	60	66	68	69
	45	24	32	57	64	71	71	71
	50	26	36	54	67	71	70	69
0.50	30	20	24	46	57	64	64	65
	35	26	36	49	59	66	68	68
	40	28	38	54	66	70	72	72
	45	34	40	58	68	82	82	82
	50	35	41	59	72	79	76	66
0.75	30	21	26	49	58	68	70	70
	35	30	37	51	63	70	74	74
	40	33	39	57	70	74	79	79
	45	35	40	60	73	82	82	82
	50	37	42	61	76	80	76	76
1.00	30	22	30	50	50	72	74	74
	35	27	37	52	64	74	78	80
	40	30	40	59	74	82	80	80
	45	32	40	63	82	82	82	82
	50	36	46	65	81	80	75	75

^a Values are an average of triplicate determination.

Table 4. Effect of Conditions of Liquefaction by Pectinolytic Enzyme on the Juice Yield (%) from Mango Pulp

		Incubation Time (Hours)
Enzyme Concentration (%)	Incubation Temperature (°C)	1	2	3	4	5	6	7
Control		Juice could not be extracted
0.30	30 ^a	6	11	14	16	19	23	30
	35	8	14	16	18	24	31	32
	35	8	14	16	18	24	31	32
	40	9	18	19	26	30	35	36
	45	10	19	26	30	36	39	39
	50	12	18	27	30	36	38	38
0.60	30	10	16	15	18	23	27	32
	35	12	17	18	21	27	34	36
	40	14	19	22	30	33	41	42
	45	22	27	29	38	49	59	59
	50	22	26	30	36	40	43	43
0.90	30	11	25	16	19	26	40	42
	35	19	26	19	24	31	49	52
	40	21	26	24	36	38	55	57
	45	22	27	29	38	49	59	59
	50	23	27	37	48	56	59	57
1.20	30	13	25	18	23	30	45	47
	35	21	26	20	30	41	56	57
	40	22	27	29	40	47	57	58
	45	25	27	32	42	53	59	59
	50	27	30	37	44	49	57	57

^a Values are an average of triplicate determination.

Incubation Temperature

Incubation of pulp after adding pectinolytic enzyme at different temperatures revealed that a temperature of 45°C was found to be optimum for the liquefaction of apricot, plum, and mango pulps. Incubation of pulps above 45°C resulted in a reduced juice yield (Tables 2-3 and 4) that might be attributable to the evaporation of water and partial denaturation of enzyme. These findings are similar to the findings of Reymand and Bush (1972). They further reported that the enzyme was partially inactivated at 50°C.

Incubation Time

Incubation of apricot, plum, and mango pulps for 7 hours at different temperatures after adding varying concentration of enzyme revealed that the maximum juice yield could be obtained from apricot and plum pulps after 5 h of incubation (Tables 2 and 3). For mango pulp, the maximum juice yield was obtained after 6 h of incubation (Table 4).

Chemical Composition of Juice

The juices extracted under optimum conditions of liquefaction were analyzed for their physicochemical characteristics and the results obtained are presented in Table 1; These result are in consonance with the values obtained by Sreekantiah et al. (1963), Wani and Saini (1990), and Joshi et al. (1991). The moisture, total soluble solids, total sugars, reducing sugars, carbohydrates, and acidity increased in juices as compared with pulp while the crude fiber and vitamin C contents decreased. The pH of juices was also found lower than parent pulps. The other constituents, namely fat, protein, and ash contents, remained nearly the same in pulps and juices. However, no calcium pectate could be detected in juices because liquefaction by added pectinase caused a complete hydrolysis of pectin. Similar observations were made by Rajanala et al. (1995).

CONCLUSION

Maximum juice yields of 78% and 82% can be obtained by liquefaction of apricot and plum pulps, respectively, with 0.5% pectinase at 45°C for 5 h. Mango pulp should be incubated with 0.9% pectinase at 45°C for 6 h to obtain the maximum juice yield of 59%.

Acknowledgments