Instrumental Textural Changes in Banana (Var. Pachbale) During Ripening Under Active and Passive Modified Atmosphere

Abstract

Textural properties of modified atmosphere packaged banana (var. Pachbale), stored at 13 ± 1°C, followed by ethrel induced ripening at 30 ± 1°C were studied. Modified atmosphere included active as well as passive types involving flushing of polyethylene pouches (100 gauge) with specific gas mixture (3% O₂ + 5% CO₂ + 92% N₂) at partial vacuum (52.63 kPa), respectively. The MAP applications resulted in varied response of various textural parameters including penetration, shear, force-relaxation, and instrumental texture profile analysis. All the parameters showed a decline except adhesiveness with the progress in ripening. Both the gas flushed, as well as passive MAP stored samples, followed a trend similar to that for control ones, however, the partial vacuum packaged bananas showed persistence of overall texture followed by normal ripening under ethrel induction. The ripened fruits from all the three types of MAP applications did not show any impediment to the instrumental textural quality. In the case of partial vacuum packaged samples, a threshold low temperature duration of 30 days was found to be optimal to avoid abnormal ripening in terms of texture. The instrumental textural kinetic for TPA parameters was found to follow linear model for a longer duration of the storage at low temperature (13 ± 1°C) with high correlation coefficients ranging from 0.845 to 0.989.

Keywords:

• Banana
• Texture
• Ripening
• Modified atmosphere
• Vacuum packaging
• Kinetics

INTRODUCTION

Banana is one of the major commercial fruits grown extensively in tropical and subtropical countries. The fruit is a rich source of sugars and minerals and as such preferred during the summers in the Western countries. Banana being highly perishable is susceptible to excessive softening, discoloration and microbial decay. The optimum low temperature for storage of banana is at 13 ± 1°C, without any incidence of chilling injury. The higher optimal storage temperature and susceptibility towards softening and decay make the fruit highly vulnerable to post harvest losses. Banana packaged in card board boxes under low temperature storage gives approximately 3 weeks shelf life and is not suitable for sea shipment from the South-east Asian countries to European destinations. Therefore, extensive studies have been carried out on advanced post harvest technologies, i.e., modified atmosphere and controlled atmosphere storage methods. Modified atmosphere packaging is preferred over control atmosphere one due to relative cost effectiveness. Several reports exist regarding the extension in shelf life of banana under modified atmosphere packaging. The modified atmosphere includes active[1] as well as passive systems.[2] Partial vacuum packaging as means of active modified atmosphere systems also received considerable attention.[3]

Banana being highly susceptible for textural losses, the changes in the visco-elastic properties of the fruit in response to the modified atmospheres needs closer attention. Studies on the textural changes in banana during ripening involve significant changes in the texture profile.[4] Fruit pulp derived from ripened banana possess specific rheological properties in terms of shear stress values and apparent viscosity highlighting the flow properties for industrial applications.[5] Mohsenin and Mittal[6] termed Young's modulus of elasticity as modulus of deformability of fresh produce considering recoverable and non-recoverable deformations when the samples were subjected to minute strain. Ramaswamy and Tung[7] measured the apparent modulus of elasticity of banana by compression test. Attempts have been made to furnish objective texture measurements for providing optimal texture for ripened banana.[8] Fruit maturity in banana is largely subjective and reports exist with regards to coining of objective textural parameters as constituent of maturity indices. Mustaffa et al[9] reported the texture profile of banana (cv. Montel) during development and maturation by means of penetrometric studies. As such the literature is scarce with regards to the textural changes in banana in response to modified atmospheres. Modified atmospheres which involve depletion in O₂ and elevation of CO₂ levels may cause irreversible hardening of tissue or sub-optimal softening upon ripening of the fruit. Partial vacuum packaging causes a physical stress apart from the physiological one which may impede the attainment of optimal rheological properties due to prolonged low temperature storage. Therefore, this article is aimed at comprehensive rheological studies on banana var. Pachbale with emphasis on optimal termination of low temperature storage for active as well as passive modified atmosphere stored bananas, as well as to derive kinetics of textural changes during modified atmosphere storage.

MATERIALS AND METHODS

Raw Material

Mature hard and green banana (var. Pachbale) fronts at an optimum maturity of 3/4 full stage were procured from the local market. The fronts were cut into hands comprising of 9–12 fruits each. Grading was carried out to sort out uniformly mature hands and the greenish color was marked as stage 1 as per the color ripening chart. The hands were sanitized with chlorinated (100 ppm) water and dipped in thiabendazole solution (200 ppm) containing 0.1% tween-100 as a surfactant for 10 minutes. The surface moisture was removed by passing chilled dehumidified air over the fruits. The cut ends of the hands were sealed with waxol solution (2%) containing potassium sorbate (0.1%).

Experiment Set Up

Unit packages containing 1 kg of fruits as hands were pre-packed in polyethylene (100 gauge) pouches in to the following experimental blocks using MAP MIX 9000 (PBI, Denmark) a preset and programmed vacuumizing gas flushing and sealing schedule; A: packed in PE pouches with ethylene absorbent, CO₂scrubber and moisture traps (passive MAP), B: gas mixture flushing of PE pouches (3% O₂ and 5% CO₂) containg ethylene absorbent, CO₂ scrubber and moisture traps (active MAP); C: partial vacuum packaging (400 mm Hg) with ethylene absorbent, CO₂ scrubber and moisture traps (active MAP); and control kept as such without packaging. The head space gas composition in case of gas flushed samples was insured to be 3% O₂ and 5% CO₂ by using a gas analyzer (Dansensor, Checkmate 9900, Prg. Ver. 1.7, PBI, Denmark) calibrated with pure O₂ and CO₂ at room temperature. The samples were drawn by auto sampling device through a Teflon septum. The resultant three experiments consisted of sixteen 1 kg unit packages in each block. The experiment was replicated three times and sampling was carried out using a completely randomized block design. The results of each analysis were reported as mean of values for six sample replications.

Ethylene, Carbon Dioxide and Moisture Absorbent

Ethylene scrubber in granulated form was made by impregnating potassium permanganate into an inert matrix consisting of white cement and limestone powder.[10] The ethylene absorbing granules were packed in 5 g HDPE woven fabric sachets. Soda lime (3 g) and silica gel (2 g) were taken in porous cellulose based sachets. Each unit package of banana contained one sachet each of ethylene scrubber, CO₂, and moisture absorbent.

Storage and Sampling

All the samples were kept at 13 ± 1°C in a storage chamber maintained at a relative humidity of 90 ± 2%. Sampling for instrumental texture analysis was carried out at regular interval of 2 days. Samples were withdrawn from the low temperature storage for ethrel (200 ppm) induced ripening at 30°C at an interval of 4 days after the termination of the control experimental block. The periodic sampling of low temperature stored banana under MAP conditions for ripening was aimed at optimization of threshold low temperature holding under different MAP conditions. The low temperature duration for shifting of samples to ethrel induced ripening at 30°C was standardized as threshold storage duration, depending on the optimal ripening with out impeding the sensory attributes. Passive MAP stored samples, gas mixture flushed samples (3% O₂ + 5% CO₂ + 93% N₂) and partial vacuum packaged samples were held for 15, 25, and 30 days; respectively at low temperature prior to ethrel induced ripening.

Instrumental Texture Evaluation

Sampling for texture analysis was carried out through random samples of six different fruits from the central and peripheral portions on both sides of the hands for measurement of penetration force, shear force, force relaxation parameter, and texture profile analysis. Mean values of six observations were considered for computing of data. Texture analyses were performed by determining fruit firmness, shear force, force relaxation, and texture profile analysis (TPA) using a texture analyzer (TAHDi, Stable Microsystems, UK) equipped with a 5 kg load cell. The analyzer was linked to a computer that recorded data via a software program called Texture Expert (version 1.22, Stable Micro Systems, UK). Firmness evaluation was carried out by taking whole fruit with and without skin and penetrating it with a 2 mm diameter cylindrical rod at a speed of 0.5 mm/s with automatic return. The downward distance was set at 10 mm and pre-test speed and post-test speed were 1 mm/s and 10 mm/s; respectively. Samples were positioned so that the rod penetrated their geometric center at the middle of the fruit in longitudinal axis.

Shear force was measured by cutting the fruit perpendicularly without skin in the middle with a Warner Bratzler Blade at a test speed of 0.5 mm/s. The pre-test and post-test speeds were set at 1 mm/s and 5 mm/s respectively. Force-relaxation and TPA test were carried out by compression test that generate plot of force (N) versus time (s). A 75 mm diameter cylindrical plate was used to measure both the properties. Cylindrical samples (16 mm dia and 10 mm height) were taken out from the pulp along the longitudinal axis using a cork borer and compressed up to 75% of their original height at a speed of 0.5 mm/s with pre-test and post-test speed of 1 mm/s and 5 mm/s; respectively. The duration of compression was 60 seconds for force relaxation and 3 seconds for TPA. The data obtained from the force relaxation curve were used to calculate maximum and residual force,[11] while the data obtained from TPA curve were used for the calculation of textural parameters.[12] Amongst the TPA parameters, hardness is expressed as maximum force for the first compression whereas adhesiveness is expressed as negative force area for the first bite or the work necessary to pull the compressing plunger away from the sample. Cohesiveness and springiness have been reported as ratios between areas under second and first compression and the height that the sample recovers during the time that elapses between the end of first bite and initiation of the second one respectively. Gumminess and chewiness have been reported as products of hardness, cohesiveness, gumminess, and chewiness, respectively. Experimental data were fitted to linear (Eq. 1), first-order (Eq. 2) models and a fractional conversion first order model (Eq. 3), to investigate the effect of test parameters on the kinetics of textural changes:[13]

Where TP is the textural property at a given time t, TP₀ is the initial textural property at time zero, TP_∞ is the non-zero equilibrium textural property after prolonged storage and k is the kinetic rate constant (day⁻¹).

Sensory Evaluation

The sensory attributes of ripened fruits in each experimental block were evaluated in terms of color, aroma, taste, texture, and overall acceptability by a trained panel consisting of 10 members from the scientific staff of the laboratory with knowledge of consumer preferences using a nine point hedonic scale having a score of 9 for extreme liking and 1 for extreme disliking.[14] One kg unit samples were randomly drawn from each experimental block and subjected for sensory evaluation. The samples were served at 11 a.m. each time to the judges after coding with three digits randomly selected numbers in a sensory lab illuminated with white light and maintained at 20°C.

Statistical Analysis

The data obtained for the physico-chemical as well as sensory parameters were analyzed statistically for analysis of variance amongst different experimental blocks vis-à-vis control samples and also amongst different modified atmosphere based experimental blocks.[15]

RESULTS AND DISCUSSION

This study explains the instrumental texture profile of banana stored under modified atmosphere at 13 ± 1°C as well as during ethrel induced ripening at 30°C. The control samples were shifted for ethrel induced ripening after 8 days of storage at low temperature. The samples with passive as well as active modes of MAP by means of specific gas mixture flushing and partial vacuum packaging showed extended periods of shelf life while the textural data showed varied response towards different MAP applications. Due to periodic sampling from low temperature storage followed by subsequent ethrel induced ripening, conclusive periods of shelf life could be drawn and as such the shelf life under the three different modified atmospheres, i.e., passive MAP (packaged in PE), gas mixture flushed samples in PE pouches, and partial vacuum packed samples in PE pouches was found to be 18, 28, and 36 days, respectively, inclusive of the periods of ethrel induced ripening at 30°C. The texture profile depicting firmness, shear force, force-relaxation and texture profile analysis inclusive of adhesiveness, springiness, cohesiveness, gumminess, and chewiness gave a comprehensive understanding regarding the textural changes in response to MAP application.

Penetration Force

The penetration data for banana stored under MAP conditions (Table 1) showed varied response. The partial vacuum packaged samples showed the maximum penetration force with and without peel on the day of control termination and a significant (p ≤ 0.01) variation vis-à-vis control samples. Firmness measures of fruit hardness, depicting the maximum force required to penetrate the fruit. The peel contributed more to the firmness of the fruit as the data showed significantly (p ≤ 0.01) lower values of penetration force for the pulp portion devoid of peel. The decrease in penetration force has been reported to be steady during the low temperature storage followed by an abrupt fall during the ripening. Laylieam[16] also reported a short fall in the penetration force of banana upon ripening. The penetration force of the ripened fruits with and without peel showed that the vacuum packaged samples were harder as compared to passive as well as gas mixture flushed samples. However, it was observed that the sensory perception of hardened pulp was within the tolerable limits till threshold low temperature storage of 30 days followed by ethrel induced ripening at 30°C. It was also observed that the vacuum packaged samples needed longer duration for ripening at elevated temperature compared to other modes of modified atmosphere. The penetration force values can be used as an objective test parameter for optimizing the low temperature holding of vacuum packaged banana without impeding the sensory quality.

Table 1 Effect of different types of modified atmospheres on firmness of banana during storage at 13 ± 1°C and ethrel induced ripening at 30°C (n = 6).

	Penetration force, N (with peel)		Penetration force, N (without peel)		Shear force (N)
Treatment	Control shifting day (8^th day)	Individual sample termination day	Control shifting day (8^th day)	Individual sample termination day	Control shifting day (8^th day)	Individual sample termination day
Initial	14.786 ± 0.74		4.658 ± 0.46		11.739 ± 0.83
Passive MAP	3.538 ± 0.32	3.597 ± 0.18	0.451 ± 0.02	0.353 ± 0.01	4.862 ± 0.15	3.268 ± 0.32
Gas mixture flushed	12.338 ± 0.24	3.773 ± 0.36	3.929 ± 0.94	0.499 ± 0.03	6.818 ± 0.61	3.180 ± 0.14
Vacuum Packed	13.279 ± 0.61	5.498 ± 0.41	4.370 ± 0.37	0.764 ± 0.06	10.245 ± 0.72	3.618 ± 0.25
Control	3.354 ± 0.15	3.154 ± 0.19	0.438 ± 0.04	0.421 ± 0.02	3.248 ± 0.43	3.048 ± 0.17
F value	**	**	**	**	**	**
CD (p ≤ 0.01)	0.237	0.191	0.139	0.024	0.194	0.193
SEM±	0.050	0.041	0.029	0.005	0.041	0.041

Shear Force

The effect of different types of modified atmosphere on the shear force of banana showed a declining trend (Table 1). Though, the trend was in compliance with the decrease in penetration force, the variance amongst the MAP stored ripened samples and the control samples upon ripening showed less variation as compared to the penetration force. With regards to vacuum packaging, the ripened samples showed less variation indicating normal texture profile vis-à-vis control samples. The definition of banana texture has been different in different reports. The shear force may be more applicable since banana is consumed without peel with a shear bite with the incisor teeth and therefore, may be more applicable as compared to penetration force. Soliva-Fortuny et al.[17] reported the texture profile of fresh cut pears kept under modified atmosphere conditions. Restricted textural losses were attributed to low O₂ concentration in the surrounding atmosphere. Similarly in the case of banana, the low O₂ concentration can be attributed to a role of restricting the textural losses with the active MAP stored samples ripening more or less similar to that in control as compared to the vacuum packaged samples in terms of texture upon ethrel induced ripening.

Force-Relaxation

Force-relaxation was measured with recording of maximum force under compression for 60 seconds followed by measurement of residual force (Table 2). Vacuum packaged samples showed maximum F_max (maximum force) and F_t (residual force) values followed by active Map (gas mixture flushed) and vacuum packaged samples in the descending order with significant (p ≤ 0.01) variance vis-à-vis control samples except the residual force of passive MAP stored samples which did not show any significant difference. In terms of percent decay, the control samples showed maximum decay force with significant (p ≤ 0.01) difference with the MAP stored samples and amongst the MAP stored samples, the passive MAP stored banana showed higher decay force compared to other MAP stored samples. On the day of termination of individual samples, the active MAP stored and vacuum packaged samples showed significantly (p ≤ 0.01) higher values as compared to those for control whereas the passive MAP did not show any significant effect. The difference in term of decay force was significantly (p ≤ 0.01) lower for the vacuum packaged samples suggesting persistence of tissue firmness upon ripening. Kojima[18] used stress relaxation technique involving a conical probe to measure softening of banana during ripening and suggested elasticity and viscosity changes as major physical factors involved in softening of banana fruits. In the force relaxation study on MAP stored banana fruits, it was found that the decay force could indicate the relatively higher firmness of vacuum packaged samples with more variation amongst the samples towards the end of shelf life under different MAP stored samples. However, the sensory data suggested that the variation in texture as well as overall sensory acceptability do not differ significantly from those for experimental control upon ethrel induced ripening. Ramaswamy and Tung[7] reported that the texture profile of banana during puncture test was similar to that during compression with the force increasing rapidly up to the maximum value, however during compression of intact bananas, after an initial lag, a smooth linear increase in force occurred until about half the original sample height. This trend renders importance to force relaxation as a unique tool in the understanding the textural changes during MAP storage of bananas and as such has been helpful in determining the threshold low temperature storage of banana with particular reference to persistence of firmness in case of partial vacuum packaged samples.

Table 2 Effect of different types of modified atmospheres on the decay force during force-relaxation test of banana during storage at 13 ± 1°C and ethrel induced ripening at 30°C (n = 6).

	Control shifting day (8^th day)			Individual sample termination day
Treatment	Fmax	Ft (t = 60 sec)	Decay (%)	Fmax	Ft (t = 60 sec)	Decay (%)
Initial	73.607 ± 3.45	35.639 ± 1.26	51.58 ± 2.13	73.607 ± 3.12	35.639 ± 1.10	51.58 ± 2.13
Passive MAP	15.820 ± 0.98	6.629 ± 0.12	58.10 ± 1.95	8.245 ± 0.68	3.186 ± 0.36	61.35 ± 1.85
Gas mixture flushed	48.150 ± 1.46	22.226 ± 0.70	53.84 ± 2.01	9.862 ± 0.42	3.694 ± 0.15	62.54 ± 3.14
Vacuum Packed	70.284 ± 2.61	34.373 ± 1.04	51.09 ± 1.45	13.450 ± 0.33	6.153 ± 0.86	54.25 ± 2.16
Control	10.612 ± 0.64	4.102 ± 0.23	61.35 ± 1.76	8.132 ± 0.21	2.959 ± 0.11	63.69 ± 2.41
F value	**	**	**	**	**	**
CD (p ≤ 0.01)	3.351	5.640	5.806	1.388	0.139	7.488
SEM±	0.708	1.191	1.226	0.293	0.029	1.581

Instrumental Texture Profile Analysis

Hardness

Hardness, as a measure of force necessary to attain a given deformation, gave a different response to the various types of MAP application. It showed a consistent decline during the low temperature storage of MAP stored bananas (Fig. 1). The modified atmosphere conditions in the passive as well as active modes contributed significantly (p ≤ 0.01) towards the hardness of fruits. However, the vacuum packaged samples maintained the hardness throughout the storage period and showed relatively higher persistence (p ≤ 0.01) as compared to control as well as the gas mixture flushed and passive MAP stored samples (Table 3). The persistence of firmness continued during the ethrel induced ripening at 30°C. Termination of partially vacuum packaged samples after 30 days of low temperature storage at 13 ± 1°C is essential as prolonged low temperature storage was found to impede the sensory quality in terms of texture due to abnormal ripening. Optimal sensory data pertaining to texture and overall acceptability has been obtained till threshold low temperature duration of 30 days for the partially vacuum paced samples. Therefore, it may be appropriate to take TPA parameters also as indicators of optimal low temperature storage duration. The data pertaining to hardness is helpful in determining the threshold storage duration, especially in the case of vacuum packaged samples.

Figure 1 Changes in hardness of banana during modified atmosphere storage at 13 ± 1°C and ethrel induced ripening at 30°C.

Table 3 Effect of different types of modified atmospheres on instrumental texture profile of banana during storage at 13 ± 1°C and ethrel induced ripening at 30°C (n = 6).

Instrumental texture profile parameters	Storage time	Passive MAP	Gas mixture flushed	Vacuum packed	Control	CD (p ≤ 0.01)	SEM±
Hardness (N)	Initial		0.171 ± 0.003
	Control shifting day (8^th day)	0.151 ± 0.002	0.162 ± 0.002	0.174 ± 0.002	0.120 ± 0.006	0.006**	0.001
	Individual sample termination day	0.117 ± 0.001	0.120 ± 0.001	0.141 ± 0.001	0.120 ± 0.004	0.003**	0.002
Adhesiveness (Ns)	Initial		1.094 ± 0.004
	Control shifting day (8^th day)	1.211 ± 0.006	1.154 ± 0.007	1.109 ± 0.003	1.230 ± 0.007	0.015**	0.003
	Individual sample termination day	1.552 ± 0.005	1.610 ± 0.004	1.415 ± 0.006	1.667 ± 0.004	0.016**	0.003
Springiness	Initial		0.732 ± 0.005
	Control shifting day (8^th day)	0.721 ± 0.001	0.728 ± 0.003	0.731 ± 0.001	0.665 ± 0.002	0.003**	0.001
	Individual sample termination day	0.625 ± 0.004	0.631 ± 0.001	0.669 ± 0.002	0.621 ± 0.001	0.002**	0.001
Cohesiveness	Initial		0.335 ± 0.003
	Control shifting day (8^th day)	0.328 ± 0.001	0.331 ± 0.001	0.336 ± 0.001	0.331 ± 0.002	0.003**	0.001
	Individual sample termination day	0.312 ± 0.003	0.318 ± 0.001	0.316 ± 0.001	0.310 ± 0.001	0.009**	0.002
Gumminess	Initial		0.065 ± 0.001
	Control shifting day (8^th day)	0.051 ± 0.001	0.054 ± 0.001	0.056 ± 0.001	0.050 ± 0.001	0.002**	0.0004
	Individual sample termination day	0.032 ± 0.001	0.040 ± 0.001	0.051 ± 0.001	0.040 ± 0.001	0.001**	0.0003
Chewiness	Initial		0.041 ± 0.001
	Control shifting day (8^th day)	0.032 ± 0.001	0.035 ± 0.001	0.040 ± 0.001	0.031 ± 0.001	0.002**	0.0004
	Individual sample termination day	0.022 ± 0.001	0.024 ± 0.001	0.030 ± 0.002	0.023 ± 0.001	0.002**	0.0004

Adhesiveness

The data pertaining to adhesiveness of MAP stored banana (Fig. 2) showed a consistently increasing trend with a maximum rise in adhesiveness in the case of control samples followed by passive, gas flushed, and partial vacuum packaged samples. It is interesting to note that the partial vacuum packaged samples recorded slower and steadier increment in the adhesiveness as compared to the other samples. Reports exist with regard to the effect of ethylene treatment on banana ripening in terms of cell rupture and cell debonding, resulting in alteration in texture profile analysis.[19] Ethrel induced ripening showed similar beneficial effect in rendering significantly different (p ≤ 0.01) viscoelastic properties in terms of TPA parameters such as adhesiveness in response to different MAP applications. The lower adhesiveness in vacuum packaged samples upon ripening can be attributed to slowing down of the senescence process due to low O₂ in the atmosphere or due to the presence of vacuumized head space within the pouches. The alteration in visco-elastic properties did not show any adverse effect on the sensory quality as long as the duration of low temperature storage was restricted to 30 days in case of partial vacuum packaged samples. The passive MAP as well as gas mixture flushed samples, though, significantly different (p ≤ 0.01) vis-à-vis control showed changes in adhesiveness similar to those in control samples. In this case, low temperature storage, the duration had effect on the changes in adhesiveness primarily due to the restriction in senescence and as such the threshold levels of low temperature storage were decided based on the ripening stage rather than the adverse effect of prolonged low temperature storage as in the case of partially vacuum packaged samples. The increment in adhesiveness during banana ripening has significance as the fruit pulp of banana has the tendency to be sticky due to its mucilaginous nature which increases during ripening with a simultaneous decrease in astringency associated with unripened banana pulp.

Figure 2 Changes in adhesiveness of banana during modified atmosphere at 13 ± 1°C and ethrel induced ripening at 30°C.

Springiness

Different types of modified atmosphere applied for the storage of banana also showed varied changes (p ≤ 0.01). The application of modified atmosphere is known to alter the viscoelastic properties of the whole as well as pre-cut fruits.[20] Springiness is an important TPA parameter and the data on springiness (Fig. 3) showed a sharp decline in the case of control samples, however, the MAP stored samples showed a steady decline during the initial period of low temperature storage followed by an abrupt fall during the ethrel induced ripening. The partial vacuum packaged samples could retain the springiness for longer duration vis-à-vis passive MAP and gas flushed samples. Soliva-Fortuny et al.[17] reported significant but steady decline in springiness of fresh cut pears in response to modified atmosphere application using films with low O₂ and high CO₂ compositions in the active mode. The retention of springiness for a longer duration and consistent springiness after ripening as compared to other samples as well as control denotes a different masticatory property without impeding the sensory attributes in terms of texture.

Figure 3 Changes in springiness of banana during modified atmosphere storage at 13 ± 1°C and ethrel induced ripening at 30°C.

Cohesiveness

Cohesiveness contributes to the comprehensive understanding of viscoelastic properties including tensile strength. The application of modified atmosphere to banana ripening showed a significant (p ≤ 0.01) effect on the cohesiveness. A consistent declining trend in cohesiveness was observed (Fig. 4), however, the differences in the magnitude of cohesiveness were not found to be conspicuous as in the case of adhesiveness and springiness. Based on the declining trend, it was noticed that the senescence manifesting tissue softening resulted in loss of cohesiveness. This phenomenon can be attributed to solubilization of pectinaceous material in the middle lamellae of adjacent cells which ultimately lead to improvement in juice yield. As far as mastication is concerned, cohesiveness plays an important role in the mouthfeel towards the end of mastication by the molar teeth. The partial vacuum packaged samples showed conspicuous deviation from the rest in terms of persistence of cohesiveness after ripening, which signifies a different masticatory property without impeding the sensory quality. Partial vacuum can cause undesirable textural changes as reported by Dong et al.[21] in pre-cut pear slices treated with calcium chloride after a threshold storage duration. The present study showed similar effects of partial vacuum packaging during banana ripening and the threshold low temperature duration of 30 days need to be followed for the specific variety of Pachbale to avoid undesirable losses in texture parameters in terms of springiness. The slight variation in the texture profile as a sensory attribute after ethrel induced ripening was more pronounced in the case of partial vacuum packed samples without causing drastic reduction in sensory score.

Figure 4 Changes in cohesiveness of banana during modified atmosphere storage at 13 ± 1°C and ethrel induced ripening at 30°C storage.

Gumminess

The MAP stored banana showed gumminess pattern similar to other TPA parameters with compliance to drop in hardness (Fig. 5). Different MAP applications showed significant (p ≤ 0.01) variation amongst various applications vis-à-vis control samples. The persistence in gumminess during the ripening of partially vacuum packaged banana can be attributed to the coalescence of cells due to greater physiological and physical stress caused by lowered O₂ as well as vacuumized conditions. Therefore, unlike the passive MAP or gas mixture flushed samples, following threshold low temperature storage protocol prior to ethrel induced ripening is mandatory for bananas stored under partial vacuum to restrict undesirable textural changes in terms of gumminess. It is also pertinent that sensory perception of banana differs substantially depending on the end use of the product. In the case of salads, it is desirable to have better tissue integrity similar to vacuum packaged samples.

Figure 5 Changes in gumminess of banana during modified atmosphere storage at 13 ± 1°C and ethrel induced ripening at 30°C storage.

Chewiness

Chewiness is the energy required to masticate a solid food product to a state ready for swallowing. Therefore, it is considered as an important parameter since the final phase of mouthfeel and the ease in swallowing depends on the chewiness of the banana. During the texture profile analysis, it was observed that the drop in chewiness is sharper compared to the gumminess of the tissues. Banana, being a smoothening fruit, the mouthfeel at the time of swallowing need to be appropriate. The passive MAP stored, as well as gas flushed samples, showed a sharp decline in the chewiness as compared to the partial vacuum packaged ones, however, the decline in the chewiness of the partial vacuum packaged samples is sharper as compared to the other TPA parameters (Fig. 6). A declining trend was observed, suggesting an easy swallowing nature of vacuum packaged banana stored up to a specific period without impeding sensory properties (Fig. 7), under low temperature followed by ripening at elevated temperature under ethrel induction.

Figure 6 Changes in chewiness of banana during modified atmosphere storage at 13 ± 1°C and ethrel induced ripening at 30°C storage.

Figure 7 Sensory Scores of banana packed in different types of modified atmospheres after etherel induced ripening.

Many reports exist regarding the relationship between the changes in the cellular structures and contents such as starch during ripening. Raffo et al[22] described NMR measurements in relation with the cytoplasmic and vascular water, and the turn over of starch during ripening of banana. Instrumental techniques such as NMR were used as a powerful tool for the analysis of microscopic tissue changes. A number of enzymes which are cellulolytic or of pectin degrading nature are responsible for the structural changes affecting the texture of the fruit ultimately leading towards softening.[23] Ripening of banana was subjected for extensive studies with reference to texture aspects and the appearance of peel and the pulp in terms of instrumental texture analysis. The use of 1-methyl cyclopropene (1-MCP) was extensively reported since use of 1-MCP beyond certain threshold level was found to result in adverse textural and sensory changes which could be attributed to undesirable structural changes.[24] In the case of partial vacuum packaging, excessive vacuum was found to lead towards toughening of tissues, impeding the sensory attributes. Changes in instrumental measurement of texture parameters inclusive of hardness, adhesiveness, cohesiveness, springiness, gumminess, and chewiness can be attributed to the structural changes in banana with emphasis on solubilization of pectinaceous material binding the tissue system and maintaining the integrity. As such except adhesiveness, all other texture profile parameters showed a decline due to the disintegration of tissue integrity and increased solubilization. The increased adhesiveness can be due to the enhanced solubilization and it holds good in establishing the relationship between structural changes and ripening stages. Certain post harvest applications such as infusion of calcium were targeted at maintaining the tissue integrity due to formation of calcium pectate.[25] Ripening of banana is also closely associated with certain specific ultrastructural changes responsible for tissue metabolism such as in the case of peroxysomes.[26] Instrumental techniques such as chlorophyll fluorescence measurement was also used as a non-destructive method to detect tissue damages ultimately leading towards textural as well as physiological changes.[27] The structural changes have a role in the changes in physical characteristics of tissues, i.e. thermal conductivity, which ultimately could be correlated with instrumental measurements of texture during banana ripening.[28] The varietal differences in banana could also be attributed to the physico-chemical as well as functional quality of reserve starch, which ultimately determine the viscoelastic properties of the fruits.[29] Electro-physiological models of intact banana tissue could also highlight on membrane integrity and permeability associated with plant tissues.[30] These aspects indicate the proximity of structural changes with the changes in texture and associated instrumental parameters and the structural aspects also deal with the ultrastructure at cell orgenelle level depicting the changes in cell physiology.

Kinetic Model for Changes in TPA Parameters

The TPA parameters could be described with greater accuracy by linear model. Chen and Ramaswamy[31] reported on the kinetics of textural change during the ripening of banana, to highlight the changes in visco-elastic property. The model fitted with the experimental data with high determination coefficients. Although, TPA parameters tend to stabilize towards the end of the storage, the linear models were achieved consistently during a dominant portion of the storage at low temperature (13 ± 1°C) and therefore the consideration of first order kinetics patterns was discarded because of the good results achieved with linear model. The correlation coefficients were found satisfactory with consistent values (above 0.9 or with in close to it) underlying the dependability of the kinetics worked out based on a linear model (Table 4). The different parameters pertaining to texture profile are as such imitative to varying proportions depicting the mastication from incision to munching followed by swallowing. Therefore, the objective of deriving instrumental data on texture is to render objectivity for arriving at objective textural standards for different end use purposes. Since, the application of modified atmosphere results in considerable physiological stress in terms of lowered O₂ and elevated CO₂ levels, any adverse impact on the texture need to be envisaged to undertake precautionary measures as well as to prescribe suitable end uses for specific MAP applications. The study as such revealed the importance of following specific low temperature storage protocols to avoid deleterious texture losses as in the case of partially vacuum packed samples.

Table 4 Kinetic constants of the linear model used to describe the changes in TPA parameters in banana during storage at 13 ± 1°C and ethrel induced ripening at 30°C (n = 6).

Parameter	Packaging Method	TP0	TPt	CD (p ≤ 0.01)	K0 (day^−1)	R^2
Hardness (N)	Passive MAP	0.171 ± 0.048	0.115 ± 0.012	0.007	0.0204	0.963
	Gas mixture flushed		0.116 ± 0.026		0.0138	0.898
	Vacuum Packed		0.135 ± 0.039		0.0058	0.959
	Control		0.116 ± 0.019		0.0280	0.965
Adhesiveness (Ns)	Passive MAP	1.089 ± 0.101	1.552 ± 0.104	0.014	0.0304	0.963
	Gas mixture flushed		1.610 ± 0.075		0.0216	0.959
	Vacuum Packed		1.407 ± 0.088		0.0076	0.912
	Control		1.659 ± 0.047		0.0455	0.945
Springiness	Passive MAP	0.727 ± 0.043	0.665 ± 0.009	0.015	0.0067	0.845
	Gas mixture flushed		0.660 ± 0.018		0.0044	0.931
	Vacuum Packed		0.677 ± 0.048		0.0023	0.893
	Control		0.659 ± 0.031		0.0128	0.976
Cohesiveness	Passive MAP	0.332 ± 0.021	0.309 ± 0.004	0.005	0.0036	0.981
	Gas mixture flushed		0.308 ± 0.012		0.0029	0.984
	Vacuum Packed		0.312 ± 0.009		0.0019	0.982
	Control		0.313 ± 0.008		0.0048	0.971
Gumminess (N)	Passive MAP	0.055 ± 0.004	0.035 ± 0.002	0.004	0.0207	0.970
	Gas mixture flushed		0.035 ± 0.006		0.0123	0.967
	Vacuum Packed		0.046 ± 0.007		0.0036	0.939
	Control		0.035 ± 0.001		0.0304	0.984
Chewiness (N)	Passive MAP	0.040 ± 0.008	0.025 ± 0.002	0.004	0.0256	0.95
	Gas mixture flushed		0.025 ± 0.004		0.0148	0.896
	Vacuum Packed		0.030 ± 0.003		0.0082	0.881
	Control		0.025 ± 0.005		0.0366	0.989

CONCLUSIONS

The study showed that the response of banana towards MAP application was varied and the changes were conspicuous in a number of parameters including penetration, shear force, force relaxation, as well as TPA parameters. The partial vacuum packaged banana (Pachbale) showed conspicuous significant (p ≤ 0.01) deviation in terms of texture profile changes as compared to other two types of modified atmosphere stored as control samples. The texture profile data may be useful in the termination of storage threshold values, for partial vacuum which has become popular over the years due to its being simple and cost effective as compared to other modes of packaging. A significantly longer shelf life ranging up to 36 days attainable by partial vacuum of banana in polyethylene pouches at low temperature storage, can be optimized by using a textural profile data with out any detrimental effect on sensory quality, following appropriate low temperature storage and ripening protocols.

Notes

**significant.