Quality Assurance and Shelf-Life Extension of Kinnow Mandarin Fruit Under Supermarket Conditions

ABSTRACT

Kinnow mandarin (Citrus nobilis × Citrus deliciosa) fruits were harvested at firm mature stage, packed in paper-molded trays, and tightly sealed in different packaging films commercially available in the market, viz. cryovac heat shrinkable RD-106 film (15 µ), low density polyethylene film (LDPE, 25 µ), and high density polyethylene film (HDPE, 10 µ). After packaging, the fruits were stored at supermarket conditions (18 to 20 °C; 80–85% RH). There were five storage intervals and for each storage interval three packs (six fruit in each pack) were prepared for each packaging film. In total, 60 packs were made for all packaging films including control to lay out this experiment. The fruits were evaluated for various quality attributes periodically. The shrink film helped in reducing the loss in weight and firmness and maintained the various quality attributes, such as total soluble solids, acidity, ascorbic acid, and carotene content of the fruit juice, during shelf life better than other packaging films and unwrapped control fruits. The in-package gaseous composition (O₂ and CO₂) in shrink film packed fruits was found to be at a desired level, which resulted in maintaining pleasant flavor of the fruits. On the other hand, LDPE and HDPE film accumulated a very high level of CO₂, which led to formation of a fermenting odor in the package. The data revealed that RD-106 film proved quite effective in prolonging the shelf life and maintaining the quality of Kinnow fruits for 25 days under supermarket conditions as opposed to 10 days only in the case of unpacked control fruits.

KEYWORDS:

• Kinnow mandarin
• packaging films
• shelf-life
• quality

Introduction

Kinnow mandarin (Citrus nobilis × Citrus deliciosa) is a predominant citrus fruit of Punjab state of India and ranks first with respect to area and production (Anonymous, 2012). Besides Punjab, it is also being commercially grown in parts of other states of India, such as Haryana, Rajasthan, and Himachal Pradesh. It has an attractive color, high juice content, pleasant taste, and good source of vitamin C. Due to these quality traits, it is in high demand in Indian and exotic markets. The commercial harvesting of Kinnow fruit falls between December to February and these months often witness a glut-like situation at major wholesale markets of India. Generally, in India, fruits and vegetables are sold at the prevailing ambient condition, which leads to huge qualitative and quantitative losses. The concept of supermarkets is fast gearing up in India and many companies like Walmart, Reliance, and Namdhari Fresh, etc. have opened up their retail outlets in big cities. Packing of fruits in polymeric films creates modified atmospheric conditions around the produce inside the package allowing a lower degree of control of gases and can interplay with physiological processes of commodity resulting in reduced rate of respiration, transpiration, and other metabolic processes of fruits (Lange, 2000), thereby allowing lower physiological weight loss, reducing decay incidence, and maintaining retention of color and texture of fruits during an extended shelf life (Sharma et al., 2010). With these viewpoints, the present investigation was conducted to study the effect of different packaging films on shelf life and quality of Kinnow fruits under supermarket conditions.

Materials and methods

Preparation of fruit samples

The Kinnow fruits were harvested with the help of scateur at the firm mature and full-color development stage from well-managed orchards located in Fazilka district in Punjab State in the first week of February. The fruits were packed in plastic crates and brought to the laboratory. The bruised and diseased fruits were sorted out and only healthy and uniform-sized fruits were selected. The fruits were washed with clean water, surface dried, and packed. The bruised and diseased fruits were sorted out, and only healthy and uniform-sized fruits were selected for the study.

Method of preparing fruit pack

The six-cell paper-molded tray (22 cm long × 14 cm wide and 0.3 cm thick) was used to hold the fruits in the orientation to make a nice pack. Three types of packaging films commercially available in the market viz cryovac heat shrinkable RD-106 film (15 µ), low density polyethylene film (low density polyethylene, 25 µ), and high density polyethylene film (high density polyethylene, 10 µ) were used for packaging of Kinnow fruits. Kinnow fruits were packed in trays and tightly sealed with different packaging films separately. However, the shrink-film-wrapped packs were passed through a shrink wrapping machine (Model BS-450, Samrath Engineers, New Delhi, India) preheated to 165 °C at a set speed for 10 s residence time. Thereafter, the packed fruits as well as the control (non-packed) fruits were stored at supermarket conditions (18 to 20 °C and 90–95% RH). There were five storage intervals and for each storage interval three packs (six fruit in each pack) were prepared for each packaging film. In total 60 packs were made for all packaging films including control to lay out this experiment.

Estimation of quality attributes

The weight loss after each interval of storage was calculated by subtracting the final weight from the initial weight of the fruits and expressed in percent. The firmness of the fruit was measured with the help of Texture Analyzer (Model TA-HDi Make, Stable Microsystems, Godalming, Surrey, UK) using compression platen (75 mm in diameter) with a test speed of 1 mm/s and the total compression of the fruit was kept at 5 mm. The overall organoleptic rating of the fruits was done by a panel of 10 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 titratable acidity, ascorbic acid, and carotene content were estimated as per standard procedure (AOAC, 2005).

Gaseous composition (CO₂ and O₂ concentration)

The in-package gaseous composition (CO₂ and O₂ concentration) of a sealed package was monitored at periodic intervals with the help of a portable Head Space Gas Analyzer (Model GS 3/P, Systech Instruments, Thames, UK). Gases were analyzed with in-built sensors for CO₂ and O₂.

Statistical analysis

Data were analyzed for variance by using the SAS (V 9.3, SAS Institute Inc., Cary, NC, USA) package.

Results and discussion

Weight loss

Shrink film packed fruits registered the lowest mean physiological weight loss (1%) followed by LDPE and HDPE films (Table 1). The control fruits, on the other hand, recorded the highest PLW (12.2%). The acceptable level of weight loss for Kinnow fruit is <5.5% above which the fruits show symptoms of shriveling and wilting and are liable to fetch lower prices in the market (Mahajan et al., 2002). The data revealed that Kinnow fruits without wrapping can have less than 10 days shelf life, whereas fruits wrapped in heat shrink film recorded a significant reduction in weight loss even after 25 days of storage life (Plate 1). Although fruits packed in LDPE and HDPE film also recorded lower weight loss as compared to unpacked control fruits, these looked dull due to poor gloss characteristics of films, hence resulting in poor market acceptability. The highest weight loss in unpacked control fruit might be due to exposure of fruit surface to the open atmosphere resulting in a higher rate of transpiration and respiration thereby leading to a higher weight loss. Heat shrinkable films have been reported to reduce weight loss of pomegranate and papaya (Nanda et al., 2001; Singh and Rao, 2005) during storage.

Table 1. Effect of different packaging films on weight loss, firmness, and organoleptic quality of Kinnow fruit during storage^z.

Treatments	Days of storage
	5	10	15	20	25	Mean
PLW (%)
Shrink film	0.6	0.6	0.7	1.5	1.8	1.0
LDPE film	1.8	2.9	3.9	4.9	5.8	3.9
HDPE film	1.7	2.5	3.6	4.2	5.2	3.4
Control	4.0	6.9	12.1	15.6	22.3	12.2
Mean	2.0	3.2	5.1	6.6	8.8
LSD (p > 0.05)	Treatment (T) = 0.4, Storage days (S) = 0.3, T × S = 1.1
Firmness (g force)
Shrink film	1743.6	1699.1	1524.7	1427.5	1301.1	1539.2
LDPE film	1538.3	1212.4	1121.7	902.0	787.2	1112.3
HDPE film	1650.9	1361.5	1222.6	982.7	831.0	1209.7
Control	1130.2	1016.2	814.6	623.2	589.9	834.8
Mean	1515.8	1322.3	1170.9	983.9	877.3
LSD (p > 0.05)	Treatment (T) = 68.5, Storage days (S) = 49.4, T × S = 168.0
Organoleptic quality
Shrink film	7.6	7.9	8.0	8.7	7.6	8.0
LDPE film	7.3	7.4	7.5	6.4	5.3	6.8
HDPE film	7.5	7.7	7.6	6.8	6.1	7.1
Control	7.0	6.9	6.4	5.3	4.8	6.1
Mean	7.4	7.5	7.4	6.8	6.0
LSD (p > 0.05)	Treatment (T) = 0.1, Storage days (S) = 0.1, T × S = 0.2

^zInitial value at harvest: Firmness 1821.9 g; Organoleptic quality score 7.0.

Fruit firmness

A gradual decline in fruit firmness with advancement of storage period irrespective of different packaging films was noticed, whereas in the control package the decline in fruit firmness was found to be abrupt and fast (Table 1). The maximum average fruit firmness (1539.2 g force) was observed with shrink film packaging. The control fruits recorded the minimum average fruit firmness (834.8 g force). Fruit firmness is one of the most important attributes in determining the postharvest quality (Maude and Bouageois, 2013). Softening of fruits is caused by loss of pectic substances in the middle lamella of the cell wall that leads to the loss of cell wall integrity, thus causing loss of firmness leading to shriveling and softening (Solomos and Laties, 1973). The reduction in softening in packed fruits might be due to the effect of the films in lowering the rate of respiration, delaying the ripening process, and reduction in moisture loss (Zagory and Kader, 1988). The maintenance of higher firmness in shrink-film-packed peach fruits has been reported by Pongener et al. (2011).

Organoleptic quality

The film packed Kinnow fruits showed a gradual and steady increase in the organoleptic quality attributes up to 20 days, after which a gradual decline was observed; whereas in control fruits, the sensory score increased up to 5 days of storage and thereafter declined at a faster pace (Table 1). The highest mean organoleptic rating (8) was recorded in shrink-film-wrapped fruits. The control fruits displayed the lowest mean value in sensory rating (6.1). The recording of higher sensory score in shrink-wrapped fruit might be due to the ability of heat-shrinkable film to retain the desirable gaseous atmosphere inside the package, which is responsible for maintaining the texture and flavor of the fruit (Nanda et al., 2001). Wrapping of banana and kiwi fruits in heat-shrinkable film have been reported to maintain an acceptable appearance, flavor, and overall eating quality (Kudachikar et al., 2007; Sharma et al., 2012).

Total soluble solids

The shrink-wrapped Kinnow fruits maintained TSS (9.6%) after 5 days of storage, which reached to peak value of 12.6% after 20 days of storage, then declined (Table 2). The control fruit registered TSS (10%) after 5 days of storage, which reached to peak value at 10 days of storage (11.2%) and then declined faster afterward. The increase in TSS of fruits during storage may possibly be due to a breakdown of complex organic metabolites into simple molecules (Wills et al., 1980). The delayed increase in TSS over a longer period of time in film-wrapped Kinnow fruits might be attributed to delayed ripening and senescence processes. The present results confirmed the findings of Sharma et al. (2012) and Mahajan et al. (2013) who have reported a delayed and sustained increase in the total soluble solids and sugars in shrink-film-packed kiwi and pear fruits.

Table 2. Effect of different packaging films on TSS, acidity, and vitamin C content of Kinnow fruit during storage^z.

Treatments	Days of storage
	5	10	15	20	25	Mean
TSS (%)
Shrink film	9.6	10.6	11.0	12.6	11.8	11.1
LDPE film	9.1	10.2	10.5	11.2	11.0	10.4
HDPE film	9.3	10.4	10.7	12.0	11.2	10.7
Control	10.0	11.2	10.8	10.8	9.5	10.5
Mean	9.5	10.6	10.8	11.7	10.9
LSD (p > 0.05)	Treatment (T) = NS, Storage days (S) = 0.3, T × S = NS
Acidity (%)
Shrink film	0.60	0.57	0.54	0.50	0.47	0.54
LDPE film	0.56	0.53	0.52	0.49	0.48	0.52
HDPE film	0.58	0.54	0.53	0.50	0.42	0.51
Control	0.52	0.50	0.47	0.38	0.35	0.44
Mean	0.57	0.54	0.52	0.47	0.43
LSD (p > 0.05)	Treatment (T) = 0.03, Storage days (S) = 0.03, T × S = NS
Vitamin C (mg/100 g F.W.)
Shrink film	23.1	21.8	19.4	15.5	13.1	18.6
LDPE film	22.2	19.8	17.6	14.6	12.0	17.2
HDPE film	22.4	20.3	18.7	14.9	12.3	17.7
Control	21.1	17.7	15.8	13.2	11.0	15.8
Mean	22.2	19.9	17.9	14.6	12.1
LSD (p > 0.05)	Treatment (T) = 0.03, Storage days (S) = 0.03, T × S = 0.06
Carotene (mg%)
Shrink film	0.53	0.58	0.67	0.56	0.51	0.57
LDPE film	0.50	0.53	0.59	0.51	0.45	0.52
HDPE film	0.51	0.54	0.60	0.52	0.45	0.52
Control	0.51	0.54	0.52	0.44	0.41	0.48
Mean	0.51	0.55	0.60	0.51	0.46
LSD (p > 0.05) Treatment (T) = 0.03, Storage days (S) = 0.03, T × S = 0.06

^zInitial value at harvest: TSS 9.1%; Acidity 0.63%; Vitamin C 24.3 mg%; Carotene 0.48 mg%.

Abbreviation: NS, nonsignificant.

Acidity

The acidity of Kinnow fruit showed a linear declining trend with advancement of storage period (Table 2). The highest average acidity (0.54%) was recorded in the fruit wrapped in shrink films and the lowest average acidity (0.44%) was recorded in control fruits. The progressive reduction in the acidity with advancement of storage period might be due to the increased catabolism of organic acids present in fruit through the process of respiration. 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 (Echeverria and Valich, 1989). The packaging films helped in better retention of acidity as compared to control. In wrapped fruits, the lowering of acidity was delayed, which might be due to the effect of packaging films in delaying the respiratory and ripening process. Nanda et al. (2001) and Sharma et al. (2012) observed higher acidity content in shrink-wrapped pomegranate and kiwi fruits.

Ascorbic acid

A continuous decline in vitamin C content in Kinnow fruits was noticed with advancement of storage period irrespective of different packaging films (Table 2). The maximum average vitamin C content (18.6 mg%) was observed with shrink film packaging. The control fruits recorded the minimum average vitamin C content (15.8 mg%). The decrease in ascorbic acid during storage may be due to the oxidation of L-ascorbic acid into dehydroascorbic acid (Mapson, 1970). The influence of heat-shrinkable films on maintaining higher ascorbic acid content in sweet orange had also been reported (Ladaniya and Singh, 2001).

Carotene

The film packed Kinnow fruits showed a gradual and steady increase in carotene content up to 15 days, after which a decline was observed; whereas in control fruits, the carotene content increased up to 10 days of storage and thereafter declined at a faster pace (Table 2). The highest average carotene content (0.57 mg%) was recorded in shrink-film-wrapped fruits, whereas the control fruits displayed the lowest value in carotene content (0.48 mg%). The occurrence of rise in carotene content of Kinnow juice during storage may be due to synthesis of carotene as a result of carotenogenesis reaction and afterwards the decline in carotene content may be due to oxidative changes leading to degradation in carotene (Meyer, 1987).

Gaseous composition

A decrease in O₂ and an increase in CO₂ levels were observed for passive modified atmospheric packaging (MAP) in all three films during 25 days of cold storage at supermarket conditions (Figure 1). However, gaseous composition inside the package was significantly different depending on the film used. The heat shrinkable packaging film registered a gradual increase and decrease in CO₂ and O₂ concentration within the package, whereas LDPE and HDPE film recorded a sharp increase and decrease in gaseous concentration. These findings are in accordance with Nanda et al. (2001) who observed reduced respiration rate in shrink-packed pomegranate fruit. Zagory and Kader (1988) confirmed modification of the atmosphere around the fresh produce in the package made of flexible plastic films. The shrink film is known to have better gas exchange properties and, therefore, maintains better gaseous environment within the package.

Figure 1. Effect of different packaging films on in-package CO₂ (a) and O₂ (b) concentration.

Conclusions

The present study envisaged that packaging of Kinnow fruits in consumer packages followed by wrapping with heat shrinkable packaging film can prolong the shelf life of Kinnow fruits up to 25 days with minimum weight loss, acceptable firmness, and desired quality in terms of sugar acid blend, vitamin C, and carotene content.