Effect of Different Edible Coatings on Quality and Shelf Life of Pears Under Supermarket and Ordinary Market Conditions

Abstract

Pear fruits of the cultivar ‘Patharnakh’ were harvested at the physiological mature stage. The fruits were coated with different food grade coatings, such as citrashine, carnauba, terpenoidal oligomer, and Stay-fresh. After coating, the fruits were packed in corrugated fiber-board cartons and stored under two different conditions, i.e., under supermarket conditions (20–22°C and 80–85% RH) and under ordinary market conditions (30–32°C and 60–65% RH). The fruits were evaluated for various quality attributes periodically. The data revealed that citrashine or terpenoidal oligomer coatings proved quite effective in prolonging the shelf life and maintaining the quality of pear fruits under both of the marketing conditions.

Keywords:

• Pyrus
• pear fruit
• edible coatings
• storage conditions
• quality

INTRODUCTION

Fruit cultivation in India has received additional impetus in the form of various state governments realizing their functionary role in boosting a nationwide commerce. For increasing the fruit production in India, several efforts are being taken up by the government of India. Pear is an important fruit of India, growing primarily in the northern parts of the country. The important cultivars of pear grown here are ‘Patharnakh’, ‘Punjab Gold’, ‘Punjab Nectar’, ‘Punjab Beauty’, ‘Baggugosha’, and ‘LeConte’. Patharnakh is the leading cultivar and is widely accepted due to its hardy nature and wider adaptability to different climatic and soil conditions. The fruit of this cultivar are liked very much by the consumers due to its juicy pulp and crisp texture.

The harvesting of the ‘Patharnakh’ pear starts in the third week of July and continues up to the end of August. Generally, this period coincides with high rainfall and high temperatures, which interferes with postharvest quality and marketability of fruits. Therefore, the farmers are forced to sell their produce during this period at poor prices due to lack of knowledge about postharvest handling practices and this leads to a glut in the market, resulting in huge postharvest losses. The fruits have a natural wax coating, which develops during the maturation and ripening processes. However, during rough handling of fruits, the natural shield gets destroyed and, therefore, bruising occurs during the packing and transport operations. Thus, the application of commercial food grade waxes is important to replace this loss during the postharvest period. Coating or waxing reduces shriveling, wilting, and respiration rate of fruits and enhances the gloss and cosmetic appearance of fruits (El-Anany et al., 2009) The use of food grade wax coating on fruits is safe and is approved for application on fresh fruits and vegetables (PFA, 2008).

The fruits of the ‘Patharnakh’ pear after harvesting are mostly bulk packed in wooden boxes or jute bags and transported to wholesale markets for further distribution. Hence, there is a need to devise methods for maintaining quality and shelf life of pear fruits during marketing. The concept of the supermarket is appearing in our country and many leading corporate sectors have opened their outlets in various cities. These are marketing outlets where various types of fruits and vegetables are displayed in packaging after coatings have been applied and this can have an added advantage of maintaining freshness. Therefore, the present investigation was planned to study the effect of coating on the shelf life and quality of pear fruits under supermarket conditions (20–22°C and 80–85% RH) as well as under ordinary market conditions (30–32°C and 60–65% RH).

MATERIALS AND METHODS

The ‘Patharnakh’ pear fruits of uniform size, disease and bruise free were picked randomly from all the four directions of the tree at a physiological mature stage. The fruits were collected in plastic crates and transported to the laboratory. The fruits were sorted, graded, and washed with chlorine solution (100 ppm). Thereafter, fruits were divided into requisite lots for further handling. In the present studies, four types of edible coatings (citrashine, carnauba, Sta-fresh, and terpenoidal-oligomer coating) were used for application on pear fruits. The coatings were applied on the fruit surface manually with a piece of foam pad. The coated and control fruits were stored under two different conditions, i.e., under supermarket conditions (20–22°C and 80–85% RH) and under ordinary market conditions (30–32°C and 60–65% RH). The various physico-chemical parameters of fruits were recorded at weekly intervals for 4 weeks. The physiological loss in weight (PLW) was calculated on initial weight basis and expressed in percent. The fruit firmness was measured with the help of a penetrometer (Model FT-327, Italy) using an 8-mm stainless steel probe and expressed in terms of pounds force pressure. The overall organoleptic rating of the fruits was done by a panel of five judges on the basis of external appearance of fruits, texture, taste, and flavor, making use of a 9-point Hedonic scale (Amerine et al., 1965). The total soluble solids (TSS) of the fruit juice were determined using a hand refractometer and expressed as percent TSS after making the temperature correction at 20°C. The total sugars and titratable acidity were estimated as per standard procedure (AOAC, 1990).

RESULTS AND DISCUSSION

Physiological Loss in Weight (PLW)

The percent of PLW, in general, increased with the advancement of the storage period rather slowly in the beginning, but at a faster pace as the storage period advanced (Table 1). It was noticed that citrashine coated fruits registered the lowest average PLW (2.82%) followed by terpenoidal oligomer coated fruits (3.12%). The PLW in citrashine and terpenoidal oligomer coated fruits ranged between 0.45 to 7.10% and 0.58 to 7.93% from 3 to 24 days of storage as compared to the control, where PLW was found to be the highest and ranged between 1.69 to 13.70% from 3 to 24 days of storage. However, under ordinary market conditions, the lowest mean PLW (4.38%) was observed in fruits coated with citrashine closely followed by terpenoidal oligomer coated fruits (4.70%). On the other hand, the highest mean PLW (8.38%) was observed in the control fruits. This increase in PLW might be due to the detrimental effect of higher temperatures leading to increased respiration rates and moisture loss (Salisbury and Ross, 1992). In pear fruits, the permissible limit of weight loss is 6% to maintain the market acceptability (Singh et al., 2010). Keeping in mind this acceptable level of PLW, it can be seen from the data that under supermarket conditions (20–22°C), the citrashine and terpenoidal oligomer coated fruits can be stored for 21 days. On the other hand, under ordinary market conditions (30–32°C), the desirable weight loss was maintained up to 10 days in citrashine and terpenoidal oligomer coated fruits. The untreated control fruits maintained an acceptable weight loss for market acceptability only up to 12 days and 6 days under supermarket and ordinary market conditions, respectively. The citrashine and terpenoidal oligomer coating has been reported to play an important role in lowering the weight loss of kinnow (Mahajan et al., 2002, 2005) and sweet lime (Bishnoi et al., 2008).

TABLE 1 Effect of Different Coatings on Physiological Loss in Weight (% PLW) in Pear cv. Patharnakh under Supermarket Conditions (20–22°C and 80–85% RH) and Ordinary Market Conditions (30–32°C and 60–65% RH)

	Supermarket conditions									Ordinary market conditions
Treatments	3	6	9	12	15	18	21	24	Mean	2	4	6	8	10	12	Mean
Citrashine coating	0.45	0.83	1.33	2.01	2.62	3.34	4.86	7.10	2.82	1.38	2.29	3.37	4.87	5.64	8.75	4.38
Carnauba coating	0.77	1.13	2.23	3.33	5.57	7.20	8.52	10.67	4.93	1.62	2.60	4.20	5.53	7.90	11.80	5.61
Sta-fresh coating	0.96	1.75	2.89	3.58	5.90	7.86	9.50	11.39	5.48	1.70	2.76	4.52	6.21	8.32	12.23	5.96
Terpenoidal oligomer coating	0.58	0.95	1.65	2.26	2.89	3.71	5.01	7.93	3.12	1.49	2.47	3.68	5.08	6.10	9.38	4.70
Control	1.69	2.50	3.93	4.59	7.56	8.97	10.75	13.70	6.71	3.60	5.78	9.79	12.22	16.37	2.50	8.38
Mean	0.89	1.43	2.41	3.15	4.91	6.22	7.73	10.16		1.96	3.18	5.11	6.78	8.87	8.93	0.00
	CD at 5% level									CD at 5% level
	Treatment = 0.17									Treatment = 0.50
	Storage interval = 0.16									Storage interval = 0.40
	Treatment × Storage interval = 0.48									Treatment × Storage interval = 1.20

Firmness

The fruit firmness followed a declining trend commensurate with advancement in the storage period (Table 2). The fruits coated with citrashine maintained the highest average firmness (13.84 lb force) followed by terpenoidal oligomer (13.11 lb force). The control fruits registered the lowest mean firmness (10.02 lb force). The firmness of fruits coated with citrashine and terpenoidal oligomer ranged between 16.30 to 10.84 lb force and 15.91 to 8.98 lb force, respectively, from 3 to 24 days of storage, whereas in case of control fruits the decline in firmness was found to be abrupt and sharp and ranged between 14.00 to 5.29 lb force, thereby leading to excessive softening and shriveling of fruits. However, under ordinary market conditions, the citrashine coated fruits recorded higher average firmness (13.54 lb force) and ranged between 15.92 to 9.45 lb force from 2 to 12 days of storage followed by terpenoidal oligomer coated fruits (12.91 lb force), which ranged between 15.37 to 9.09 lb force. In the case of the control, the mean fruit firmness was 9.62 lb force and fruits experienced a faster loss of firmness during storage and ranged between 14.20 to 4.95 lb force. The pear fruits attain best eating quality at 12 lb force firmness (Singh et al., 2010). Considering this value as the cutoff limit for firmness, it was observed that citrashine and terpenoidal oligomer coated fruits can be stored for 21 and 18 days, respectively, at 20–22°C while control fruits maintained acceptable firmness up to 12 days of storage. On the other hand, under ordinary market conditions the coated fruits maintained acceptable firmness up to 10 days as opposed to 6 days in the control. Softening of fruits is caused either by breakdown of insoluble protopectins into soluble pectin or by hydrolysis of starch (Mattoo et al., 1975). The loss of pectic substances in the middle lamella of the cell wall is perhaps the key step in the ripening process that leads to the loss of cell wall integrity that causes loss of firmness and softening (Solomos and Laties, 1973). The coating of fruits with citrashine and terpenoidal oligomer resulted in higher fruit firmness under both the storage conditions, which might be due to reduction in moisture loss and respiratory activity, and, thus, maintained the turgidity of the cells. Citrashine and terpenoidal oligomer coated soft pear, kinnow, and apple fruits have been reported to maintain higher fruit firmness (Sidhu et al., 2009, Mahajan et al., 2002; Bishnoi et al., 2009).

TABLE 2 Effect of Different Coatings on Firmness (lb Force) in Pear cv. Patharnakh under Supermarket Conditions (20–22°C and 80–85% RH) and Ordinary Market Conditions (30–32°C and 60–65% RH)

	Supermarket conditions									Ordinary market conditions
Treatments	3	6	9	12	15	18	21	24	Mean	2	4	6	8	10	12	Mean
Citrashine coating	16.30	15.55	14.83	14.28	13.34	13.05	12.49	10.84	13.84	15.92	15.21	14.28	13.46	12.89	9.45	13.54
Carnauba coating	15.45	14.27	13.35	12.56	12.15	9.49	8.68	6.89	11.61	14.79	14.28	12.80	12.31	10.91	8.29	12.23
Sta-fresh coating	14.23	13.50	12.69	12.18	11.67	9.08	7.28	6.10	10.84	14.26	13.66	12.33	11.70	10.27	7.45	11.61
Terpenoidal oligomer coating	15.91	14.86	14.37	13.48	12.93	12.44	11.93	8.98	13.11	15.37	14.79	13.29	12.95	11.98	9.09	12.91
Control	14.00	12.88	12.50	12.00	8.92	7.85	6.70	5.29	10.02	14.20	12.36	11.30	8.00	6.90	4.95	9.62
Mean	15.18	14.21	13.55	12.90	11.80	10.38	9.42	7.62		14.91	14.06	12.80	11.68	10.59	7.85	16.80
	CD at 5% level									CD at 5% level
	Treatment = 0.27									Treatment = 0.39
	Storage interval = 0.26									Storage interval = 0.31
	Treatment × Storage interval = 0.78									Treatment × Storage interval = 0.95

Sensory Quality

The maximum sensory score was shown by fruits coated with citrashine (7.62) followed by terpenoidal oligomer (7.48) coated fruits under supermarket conditions (Table 3). However, control fruits registered the minimum sensory score (5.69). The sensory score of coated fruits increased gradually up to 21 days in the case of citrashine and terpenoidal oligomer (8.17 and 8.02) and, thereafter, decreased. In control fruits, the sensory score increased up to 12 days of storage (7.85) and, thereafter, declined at a faster pace. Under ordinary market conditions, the data revealed that the mean sensory score was the highest (7.21) in citrashine coated fruits followed by terpenoidal oligomer (7.06). The sensory quality gradually increased in citrashine coated fruits up to 10 days (7.78%) and then declined followed by terpenoidal oligomer (7.55). Thereafter, a fast decline in the organoleptic score was noticed. However, the control fruits recorded the highest sensory score of 7.51 after 6 days of storage, but thereafter a sudden decline in sensory quality was noticed and fruits registered a score of 4.75 after 12 days of storage. It has been reported that the ethylene biosynthetic pathway functions better at 20–25°C (Yang, 1985), which may result in synthesis or formation of flavoring compounds. In the present investigation, it was noticed that pear fruits coated with citrashine and terpenoidal oligomer coatings followed by storage at 20–22°C developed better sensory quality, which may be due to the role of coatings in partial modifications of internal atmosphere of fruits resulting in development of the acceptable flavor. Mahajan et al. (2005) noticed that citrashine coating was most effective in improving the organoleptic quality of kinnow fruits without development of off-flavor.

TABLE 3 Effect of Different Coatings on the Sensory Quality (1–9) of Pear cv. Patharnakh under Supermarket Conditions (20–22°C and 80–85% RH) and Ordinary Market Conditions (30–32°C and 60–65% RH)

	Supermarket conditions									Ordinary market conditions
Treatments	3	6	9	12	15	18	21	24	Mean	2	4	6	8	10	12	Mean
Citrashine coating	7.16	7.35	7.50	7.69	7.83	8.05	8.17	7.20	7.62	7.11	7.23	7.38	7.60	7.78	6.17	7.21
Carnauba coating	7.09	7.18	7.26	7.40	7.51	6.68	5.83	5.15	6.76	7.07	7.16	7.25	7.28	5.95	5.49	6.70
Sta-fresh coating	7.06	7.14	7.18	7.32	7.36	6.12	4.72	3.50	6.30	7.05	7.12	7.20	7.19	5.68	5.15	6.57
Terpenoidal oligomer coating	7.13	7.25	7.38	7.51	7.69	7.85	8.02	6.98	7.48	7.09	7.20	7.31	7.42	7.55	5.80	7.06
Control	7.25	7.43	7.60	7.85	5.44	3.80	3.47	2.70	5.69	7.30	7.45	7.51	6.55	5.56	4.75	6.52
Mean	7.14	7.27	7.38	7.55	7.17	6.50	6.04	5.11		7.12	7.23	7.33	7.21	6.50	5.47	7.00
	CD at 5% level									CD at 5% level
	Treatment = 0.12									Treatment = 0.14
	Storage interval = 0.10									Storage interval = 0.09
	Treatment × Storage interval = 0.25									Treatment × Storage interval = 0.30

Total Soluble Solids (TSS) and Total Sugars

The fruits coated with citrashine registered maximum average TSS and total sugars concentrations (12.37 and 8.90%) followed by terpenoidal oligomer coated fruits (12.14 and 8.68%) under supermarket conditions (Tables 4 and 5). The control fruits recorded the lowest average TSS and total sugar concentration (10.71 and 7.48%). It was further observed that in citrashine and terpenoidal oligomer coated fruits the TSS and total sugar concentration increased slowly and steadily up to 21 days and thereafter declined after 24 days storage. On the other hand, the control fruits recorded a rise in TSS and total sugar concentration up to 12 days and thereafter declined at a faster rate. Under ordinary market conditions, citrashine coated fruits registered an increase in TSS (12.66%) and total sugar (9.25%) concentration up to 10 days. In control fruits, the TSS (12%) and total sugar (8.90%) concentration increased up to 6 days and thereafter a decline was noticed. The increase in TSS and total sugars during storage may possibly be due to the breakdown of complex organic metabolites into simple molecules or due to hydrolysis of starch into sugars (Wills et al., 1980). The delayed increase in TSS and total sugar over a longer period of time in coated pear fruits at 20–22°C might be attributed to the fact that the coating retards ripening and senescence processes and simultaneously delayed the conversion of starch into sugars. The results of the present study on TSS and total sugars as influenced by edible coatings are in agreement with the findings of Sidhu et al. (2009) and Bishnoi et al. (2008) in soft pear and apple.

TABLE 4 Effect of Different Coatings on the Total Soluble Solids (%) of Pear cv. Patharnakh under Supermarket Conditions (20–22°C and 80–85% RH) and Ordinary Market Conditions (30–32°C and 60–65% RH)

	Supermarket conditions									Ordinary market conditions
Treatments	3	6	9	12	15	18	21	24	Mean	2	4	6	8	10	12	Mean
Citrashine coating	11.48	11.86	12.30	12.58	12.89	13.30	13.46	11.05	12.37	11.46	11.76	12.18	12.49	12.66	10.58	11.76
Carnauba coating	11.32	11.49	11.69	11.95	12.22	11.45	10.14	9.50	11.22	11.28	11.48	11.67	11.82	10.05	9.74	11.03
Sta-fresh coating	11.28	11.43	11.60	11.79	12.00	11.05	9.71	9.32	11.02	11.24	11.39	11.52	11.64	9.74	9.46	10.88
Terpenoidal oligomer coating	11.39	11.73	12.07	12.32	12.64	13.08	13.14	10.71	12.14	11.39	11.60	11.92	12.20	12.37	10.20	11.55
Control	11.55	11.95	12.41	12.70	9.61	9.30	9.14	9.00	10.71	11.66	11.88	12.00	10.86	10.55	10.30	11.21
Mean	11.40	11.69	12.01	12.27	11.87	11.64	11.12	9.92		11.41	11.62	11.86	11.80	11.07	10.06
	CD at 5% level									CD at 5% level
	Treatment = 0.16									Treatment = 0.10
	Storage interval = 0.12									Storage interval = 0.08
	Treatment × Storage interval = 0.30									Treatment × Storage interval = 0.17

TABLE 5 Effect of Different Coatings on the Total Sugars (%) of Pear cv. Patharnakh under Supermarket Conditions (20–22°C and 80–85% RH) and Ordinary Market Conditions (30–32°C and 60–65% RH)

	Supermarket conditions									Ordinary market conditions
Treatments	3	6	9	12	15	18	21	24	Mean	2	4	6	8	10	12	Mean
Citrashine coating	8.05	8.35	8.73	9.05	9.35	9.62	9.78	8.29	8.90	8.10	8.39	8.75	9.05	9.25	8.00	8.59
Carnauba coating	7.78	7.97	8.28	8.66	8.80	7.57	7.19	6.85	7.89	7.91	8.10	8.39	8.54	7.25	7.02	7.87
Sta-fresh coating	7.75	7.90	8.12	8.39	8.58	7.34	6.92	6.63	7.70	7.82	8.01	8.21	8.35	7.05	6.65	7.68
Terpenoidal oligomer coating	7.92	8.18	8.53	8.82	9.10	9.35	9.52	8.00	8.68	8.02	8.22	8.49	8.82	9.02	7.71	8.38
Control	7.90	8.50	8.95	9.16	6.85	6.42	6.20	5.85	7.48	8.36	8.78	8.90	7.86	7.59	6.77	8.04
Mean	7.88	8.18	8.52	8.82	8.54	8.06	7.92	7.12		8.04	8.30	8.55	8.52	8.03	7.23
	CD at 5% level									CD at 5% level
	Treatment = 0.13									Treatment = 0.15
	Storage interval = 0.12									Storage interval = 0.13
	Treatment × Storage interval = 0.28									Treatment × Storage interval = 0.24

Acidity

The acidity of pear fruits experienced a linear decline as the storage period advanced (Table 6). It was noticed that citrashine coated fruits showed significantly higher acidity over the other treatments throughout the storage period and recorded mean acidity (0.34%) followed by terpenoidal oligomer coated fruits (0.31%). The control fruits showed the lowest mean acidity (0.18%). The acidity content in citrashine and terpenoidal oligomer coated fruits ranged between 0.44 to 0.22% and 0.42 to 0.20%, respectively, from 3 to 24 days of storage as compared to the control where acidity was found to be the lowest and ranged between 0.34 to 0.10%. Under ordinary market conditions, the highest mean acidity content (0.36%) was observed in fruits coated with citrashine, which was found to be statistically significant as compared to other treatments and it was closely followed by terpenoidal oligomer coated fruits (0.33%). On the other hand, the lowest mean acidity (0.19%) was observed in control fruits. During different storage intervals, citrashine coated fruits registered the highest acidity content ranging between 0.44 to 0.28% from 2 to 12 days of ambient storage, respectively, as compared to the control where acidity ranged from 0.30 to 0.10% during the same storage intervals. The decrease in titratable acids during storage may be attributed to utilization of organic acid in pyruvate decarboxylation reaction occurring during the ripening process of fruits (Pool et al., 1972).

TABLE 6 Effect of Different Coatings on the Titratable Acidity (%) of Pear cv. Patharnakh under Supermarket Conditions (20–22°C and 80–85% RH) and Ordinary Market Conditions (30–32°C and 60–65% RH)

	Supermarket conditions									Ordinary market conditions
Treatments	3	6	9	12	15	18	21	24	Mean	2	4	6	8	10	12	Mean
Citrashine coating	0.44	0.42	0.39	0.35	0.33	0.30	0.26	0.22	0.34	0.44	0.41	0.39	0.35	0.31	0.28	0.36
Carnauba coating	0.38	0.34	0.30	0.26	0.22	0.18	0.16	0.14	0.25	0.35	0.31	0.27	0.24	0.21	0.17	0.26
Sta-fresh coating	0.35	0.31	0.27	0.23	0.19	0.15	0.14	0.12	0.22	0.33	0.28	0.24	0.21	0.17	0.15	0.23
Terpenoidal oligomer coating	0.42	0.39	0.36	0.33	0.28	0.25	0.22	0.20	0.31	0.40	0.38	0.36	0.32	0.28	0.25	0.33
Control	0.34	0.29	0.20	0.17	0.14	0.12	0.11	0.10	0.18	0.30	0.24	0.20	0.15	0.12	0.10	0.19
Mean	0.39	0.35	0.30	0.27	0.23	0.20	0.18	0.16		0.36	0.32	0.29	0.25	0.22	0.19
	CD at 5% level									CD at 5% level
	Treatment = 0.01									Treatment = 0.02
	Storage interval = 0.01									Storage interval = 0.01
	Treatment × Storage interval = NS									Treatment × Storage interval = NS