Bio-mechanical Behavior of Kiwifruit as Affected by Fruit Orientation and Storage Conditions

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1 Ref: C99 Bio-mechanical Behavior of Kiwifruit as Affected by Fruit Orientation and Storage Conditions Reza Tabatabaekoloor, Faculty of Agricultural Engineering, Sari Agricultural Sciences and Natural Resources University, Sari, Iran Abstract Bio-mechanical properties of fruits and vegetables are important for agricultural and food engineers, due to different causes. In this research, some engineering parameters such as bio-yield point, firmness, puncture force, cutting force and cutting energy were determined with respect to the fruit orientation and storage period under ambient and cold conditions. Also, water loss during storage period was investigated. Results indicated that fruit orientation had significant effect on the firmness and bio-yield point, while the effect of fruit orientation was not significant on the puncture force, cutting force and cutting energy. By increasing storage time, the firmness, cutting force and bio-yield point decreased with respect to storage time and the rate of reduction during last week of storage was higher than the rate of first week storage. Storage at ambient in comparison with cold storage decreased the fruit firmness and bio-yield point. At the end of 6 days storage, the fruit cumulative weight losses in cold and ambient conditions were 5. and.%, respectively. Keywords: Mechanical properties, Kiwifruit, Firmness, Storage. Introduction Many agricultural products are considered as biological materials. They are susceptible to mechanical damages during harvest and post harvesting process such as pick up, sorting, packaging and transporting. These damages are related to the external forces in the form of splits, punctures and bruises. Also, storage of fruits after harvesting can cause significant changes in physical and mechanical properties (Singh and Reddy, 6). The biomechanical characteristics of fruits are important in adoption and design of various postharvest systems. The fruit compression test simulates the condition of static loading that fruit can withstand in mechanical handling and storage (Gorji Chaksepari et al., ). Many researchers have investigated the mechanical properties of fruits and vegetables. Kheiralipor et al. (9) investigated some mechanical and nutritional properties of tow Iranian apple varieties. Oztork et al (9) studied some physico-mechanical properties of pear cultivars. Singh and Reddy (6) investigated physico-mechanical properties of orange peel and fruit. Effects of storage time and conditions on quality control are important aspects of food processing for acceptable nutritional value and providing food safety to consumers. The rate of kiwifruit softening is affected by storage period, temperature, ethylene levels and maturity of the fruit (Ritenour et al., 999). A study of respiratory and physico-chemical changes of four kiwifruit cultivars during cold storage indicated that physiological behavior of kiwifruit varieties is related to storage time (Manolopoulo and Padadopoulo, 998). The importance of water statues for fruit firmness also reveals itself through the reversible physical effect as seen for apple and kiwifruit (Jeffery and Banks, 99). With increasing and decreasing temperature, the water inside the fruits expands and contracts in volume (Chen, 99). Proceedings International Conference of Agricultural Engineering, Zurich, /8

2 Ayman et al. () investigated mechanical properties of pears during storage under variable conditions. They found that change of temperature significantly affected the mechanical properties of pears. Firmness as one of the fruit qualities has been determined by various researchers for different fruits (Donna et al., 8; Marina et al., 6; Jha et al., 6; Charles, 8; Qin et al., 6). Firmness is a critical attribute determining postharvest quality of fruits and vegetables (Hertog et al., ). Firmness is a key criterion by which the remaining storage potential of kiwifruit is assessed. At harvest, the flesh firmness of kiwifruit is generally in the range of 6- N but they are not eating- ripe until the firmness is in the range of about 8 N (McRae et al., 989). Therefore, a large decrease in firmness occurs after harvest before the fruit is ready to eat. McGlone and Jordan () measured kiwifruit firmness using a laser air-puff method. Results indicated that firmness at the beginning of storage was about N and it decreased to 5 N at the end of storage. There is a dearth of information on bio-mechanical properties of kiwifruit which are helpful in modifying and designing post-harvest systems. Therefore, the objectives of this study were to investigate the effect of kiwifruit storage conditions and fruit orientation at horizontal and vertical positions on bio-mechanical properties such as bio-yield point, firmness, cutting force, cutting energy and puncture force during 6 days of storage period.. Materials and methods.. Material Kiwifruits, cultivar 'Hayward,' were harvested at fully mature stage from different trees of a commercial orchard located in Amol, Mazandaran province of Iran in autumn. Random samples were drawn from a freshly harvested lot of kiwifruits at the time of harvest. Fruit were divided into two groups; one group of fruits was taken into refrigerator for cold storage at 6ºC and 6% RH. Another lot of fruits were kept in ambient at a temperature of ºC and 8% RH. Post harvest bio-mechanical properties of kiwifruits were determined with respect to orientation and the storage period in both ambient and cold conditions... Water loss For determining weight loss in kiwifruit during storage, ten fruits in each experimental lot were numbered and kept in ambient and cold conditions. Weight of the fruit was measured with respect to storage period with electronic balance having least count of. g. The loss in weight was expressed as percentage of original fresh weight of the fruit. The cumulative losses in weight were calculated as percent of initial weight lost... Firmness, bio-yield point and puncture force Compression force was applied using a flat base plate of Texture Analyzer (Model FG- 5A, Lutron Ltd, Taiwan). Probe carrier was fixed with an 8 mm diameter flat plate and brought in contact with the fruit. The firmness expressed as the force required to compress to fruit to mm distance. The firmness tests were carried out every four day on five fruit samples after being taken out of ambient and cold storage. Fruit compression test were performed in horizontal and vertical orientation (Figure ). The average values of five replications are reported for 6 days storage in both ambient and cols conditions. The bioyield point was considered as the force required causing permanent deformation indicated by the peak force before a sudden drop as shown in force-displacement curve (Figure ). Puncture force readings were taken by recording the maximum force required to compress the fruit using a 5 mm cylindrical probe to the probe carrier in vertical and horizontal directions. The fruit was positioned vertically, with the major axis of fruit parallel to the direction of loading. For horizontal loading, the major axis of the fruit was normal to the direction of loading, or lengthwise. At each sampling, ten fruit were randomly selected from each storage condition and five fruit were used for loading at each direction. The maximum Proceedings International Conference of Agricultural Engineering, Zurich, /8

3 force required to make the puncture on the fruit surface was taken from the forcedeformation curve (Figure )... Cutting force and cutting energy For measurement of cutting force a blade was attached to the probe carrier of the Texture Analyzer. Kiwifruit was positioned separately in horizontal and vertical positions. Cutting speed of mm.s- was used with a kn load cell. Peak cutting force was taken as the maximum peak force while the fruit separate two sections. The cutting energy was considered as the area under the force deformation curve (Figure ). The reported values are average of five replications in each storage conditions for 6 days. Figure : Kiwifruit orientation under compression Figure : Force-deformation curve (A) bio-yield point, (B) rupture point and (C) puncture force Figure : Force-displacement curve for fruit cutting (A) maximum cutting force and (B) cutting energy. Results and discussions Some physical characteristics of kiwifruit cv. Hayward used in the experiments are presented in the Table. As it is seen, based on the standard deviation there are uniformity among the samples. Data on physical properties of fruits and vegetable are usually useful in analysis of many postharvest processes. Proceedings International Conference of Agricultural Engineering, Zurich, /8

4 Table. Physical attributes of kiwifruit Properties No. of observations Max. Min. Mean ± SD Dimensions (mm) Length ±.9 Width ±.6 Thickness ±.8 Weight (g) ±5. Volume - (mm ) ±9.9 GMD (mm) ±.6 Sphericity (%) ±. Data are mean values of 5 replications.. Firmness, bio-yield point and puncture force Table shows the fruit firmness and bio-yield point of kiwifruit at ambient and cold storage conditions for two directions of loading. The fruit firmness varied from.6 N to. N at ambient and from. N to 8. N at cold conditions after 6 days of storage when it compressed at horizontal direction. For compression at vertical direction the changes of firmness were from. to 8. N at ambient and from 9.8 to. N at cold storage. The firmness in vertical orientation was significantly higher than horizontal direction under both ambient and cold storage (Columns C, C, C5 and C6 in Table ). The changes of firmness with respect to the storage period were significant for both conditions and orientations. No significant difference was observed between firmness of two storage conditions for horizontal and vertical orientations. It is also clear from Table that in ambient storage there is a more rapid decrease in firmness of fruit whereas in cold storage, this process occurred with a slow rate. Similar trends were also observed by Hertog et al. () for tomato, Qin et al. (6) for mango and by Katsiferis et al. (8) for orange. Generally, fruit softening accelerates over the first period of storage. Subsequently, the rate of softening slows. It can be concluded that fruits at vertical direction have more resistance against loads and it is better to put them inside the packs in vertical direction. The bio-yield point for ambient and cold storage had no significant difference (Columns C, C and C, C8) but it was slightly higher in cold storage. The reason can be due to less water loss of fruit at cold storage. In vertical orientation bio-yield point was significantly higher than horizontal direction under both ambient and cold storage (Table ). After 6 days of storage bio-yield point significantly decreased at both storage conditions. In horizontal direction, bio-yield point decreased from.6 to.5 N and 9.8 to 5. and in vertical direction it decreased from 8.6 to 8. N and. to. N at both ambient and cold storage, respectively. The puncture force of kiwifruit stored at ambient and cold conditions had no significant difference at horizontal and vertical direction until 8th day of storage and after that the puncture force for horizontal direction at ambient had significant difference with other situations (Table ). Increasing the storage period significantly decreased the puncture force. Puncture force in horizontal orientation decreased from.6 to. N and from. to. N with respect to storage period under ambient and cold conditions, respectively. In vertical orientation the puncture force decreased from.9 to 6.8 N and from.6 to.6 N with respect to storage period under ambient and cold conditions, respectively. As these results show, the effect of storage conditions on puncture force was not significant. Proceedings International Conference of Agricultural Engineering, Zurich, /8

5 Table. Firmness and bio-yield point of kiwifruit at two fruit orientation and storage conditions Storage Ambient storage Cold storage Firmness (N) Bio-yield point Firmness (N) Bio-yield point period (N) (N) Horizon- Verti- Hori- Vertical Hori- Verti- Hori- Vertical (days ) tal C cal C zontal C C zontal C5 cal C6 zontal C C8.6±.8.±8..6± 9 8.6±..± ± ±..±. 5.±5..±6. 8.9±.±.6 9.±. 6.±. 8.±8..±. 8.5±..±5. 6.5±8..6±9. 5.±..9±6..5±6. 8.±8. 6.9±..±. 9 9.±5. 9.±5..5±. 8.± ±..±9. 6.±. 8.±5..5±. 8.±6.5 8.±..±5. 5.±..±. The ±values are standard deviation. The values in each column show that storage period had significant effect (p<.5), on firmness and bio-yield point at all conditions and orientation. The values shown in columns Cand C5, and also, C and C6 had significant difference (p<.5). The values shown in columns C and C, and also, C and C8 had significant difference (p<.5). Table. Puncture force of kiwifruit at two fruit orientation and storage conditions Storage Ambient storage Cold storage period Horizontal vertical Horizontal vertical (days).6 ±. aa.9±. a A.±. aa.6±. aa 9.±. ba.±. ba.6±.9 ba.9±.5 aa 8 8.±5. ba 9.±9. ba 9.±. ba.±. aa 5.5±.8 ca 8.±9. bb 8.5±. bb 8.±. bb 6.±. ca 6.8±6. cb.±.5 bb.6±.5 bb The ±values are standard deviation. The values within a column (small letters) followed by the same letter are not significantly different (p<.5). The values within a row (capital letters) followed by the same letter are not significantly different (p<.5)... Cutting force and cutting energy Table shows the cutting force and cutting energy for kiwifruit at two directions when stored at ambient and cold conditions. No significant difference was observed between cutting force of horizontal and vertical directions of cutting. Also, similar result was observed for cutting energy. By increasing the storage period cutting force and energy significantly decreased at both direction of loading. Singh and Reddy (6) found that cutting force and energy for citrus decreased with the storage period. Cutting force for cold storage was higher than those obtained for ambient conditions but for cutting energy no significant difference was observed between two storage conditions. Proceedings International Conference of Agricultural Engineering, Zurich, /8

6 Table.Cutting force and cutting energy of kiwifruit at two fruit orientation and storage conditions Storage Ambient storage Cold storage Cutting force Cutting energy Cutting force Cutting energy period (N) (kj) (N) (kj) (days Horizontal Vertical Horizontal Vertical Horizontal Vertical Horizontal Vertical ) C C C C C5 C6 C C8 5. ±8. 5.9±..±.6.98±. 5 6.±. 65.±9..5±.8.±. 6 8.± 5.±..±..±. 6.±. 6.±.±.5.8± ±8. 9.±9..±..56±. 58.±. 6.±8..±.6.5±. 5.± ±9..8±..±. 55.±9. 5.±.6±..±. 6.±6..±6..±..±. 6 5.±6.5 5.±..9±..±. The ±values are standard deviation. No significant difference was observed for horizontal and vertical orientation. The values shown in columns Cand C5, and also, C and C had no significant difference. The values shown in columns Cand C6 had significant difference (p<.5), while C and C8 had no significant difference.. Water loss Figure shows the weight loss of kiwifruit with storage period at ambient and cold storage conditions. The results show that the rate of water loss at ambient due to higher temperature is much more than cold condition. After 6 days of storage at ambient, the fruit lost about % of weight, while in cold storage the water loss was about.5%. The kiwifruits stored under ambient lost the weight about three times more than fruits stored in cold condition. The weight loss followed second order regression equations (Equations and ). Similar trends for oranges were reported by Singh and Reddy (6) and Katsiferis et al. (8). Water loss from the fruit is driven by the water gradient between the internal fruit space and the surrounding air. At the constant relative humidity, temperature is the main factor affected water loss. Nanda et al. () found that storage temperature is the main reason of weight loss for pomegranate. The rate of water loss at the first eight day was gradual but after 8th day of storage, the fruit exhibited a rapid increase in water loss especially in ambient. The relationship between weight loss and storage days of kiwifruit for two conditions can be expressed mathematically as follows: WL (ambient) =.8 D +.8 D +. (R =.98) () WL (cold) =. D +.8 D +.56 (R =.9) () Where WL is the cumulative weight loss during storage, %, D is the storage days and R is the correlation coefficient. Proceedings International Conference of Agricultural Engineering, Zurich, /8

7 Weight loss (%) Cold storage Ambient storage Storage time (days) Figure : Weight loss of kiwifruit during storage under ambient (ºC and 8%RH) and cold (6ºC and 6%RH) conditions. Conclusions Bio-mechanical properties of kiwifruit such as bio-yield point, firmness, puncture force, cutting force and cutting energy were investigated when stored at ambient and cold conditions with respect to the fruit orientation. Kiwifruit orientation had significant effect on the firmness and bio-yield point, while the effect of fruit orientation was not significant on the puncture force, cutting force and cutting energy. By increasing storage time, the firmness, cutting force and bio-yield point decreased with respect to storage time and the rate of reduction during last week of storage was higher than the rate of first week storage. Storage at ambient in comparison with cold storage decreased the fruit firmness and bio-yield point. At the end of 6 days storage, the fruit cumulative weight losses in cold and ambient conditions were 5. and.%, respectively. 5. Acknowledgements The authors would like to thank engineers; Atena gholampor and Sehre Ebrahimi for their assistance to perform experiments and measurements. Further thanks to the manager of Postharvest Laboratory of Sari University of Agricultural Sciences and Natural Resources. 6. References Ayman, H., Amer, E., Alghanam, A. O., & Azam, M. M. (). Mathematical evaluation changes in rheological and mechanical properties of pears during storage under variable conditions. Journal of Food science and Engineering,, Charles, F. F. (8). Optimizing the storage temperature and humidity for fresh cranberries: a reassessment of chilling sensitivity. Hortscienc, 9-6 Chen, H. (99). Analysis on the acoustic impulse resonance of apples for non destructive estimation of fruit quality. Thesis No. 6, Faculty of Agricultural and Applied Biological Science, K.U. Leuven, p. 65 Donna, A. M., James, M. S., & Stephen, J. S. (8). Blueberry splitting tendencies as predicted by fruit firmness. Hortscience,, 56-5 Gorji Chaksepari, A., Rajabipor, A., & Mobli, H. (). Strength behaviour study of apples under compression loading. Modern Applied Science, (), -8 Proceedings International Conference of Agricultural Engineering, Zurich, /8

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