with the collaboration of Iranian Society of Mechanical Engineers (ISME)

Document Type : Research Article

Authors

Biosystems Engineering Department, Tarbiat Modares University, Tehran, Iran

Abstract

Introduction
One of the most important and sensitive steps after walnut harvesting is the separation of the kernel from its shell. Walnut rupture force is an appropriate criterion for design with high performance and better quality, which can be used as the basis for designing and adjusting the various parts of machines that are in contact with walnut. The lower rupture force caused the less energy requirement to separate the walnut kernel from the shell. The use of ultrasound in ambient fluids is well known to cause turbulence and biological cell rupture. These effects arise principally from the phenomenon known as cavitation which can scour surfaces and damage cellular material. Therefore the object of this study is to find the effect of ultrasound factors on the amount of walnut rupture force and quality of kernel extraction.
Materials and Methods
Walnut paper variety was selected from a Qazvin province orchard for this study. To determine the initial moisture content of the nuts, the samples were dried in an oven at 105°C for 24 h. Initial moisture content was found 5.5 (%w.b). The ultrasounds bath system (D-78224 Singen/htw, Elma, Germany) was used with a nominal frequency of 50 kHz and power of 1000 W. In this research, based on the pretest results and previous studies (Cao et al., 2010; Entezari et al., 2004) walnut samples were treated with three ultrasound time duration (5, 10 and 15 min) and three ultrasound bath temperature (20, 35, and 50ºC). Moisture content of the walnuts after ultrasound treatment was 8.8 (%w.b). After the walnut samples were treated by ultrasonic factors, a material testing machine (H50 K-S, Hounsfield, England) was used to determine the rupture force of the walnuts. The walnut was placed between two plates, and loaded at three loading speeds (0.5, 1.5, and 2.5 mm s-1) and pressed until the walnut ruptured. Rupture force was applied along with X and Y axes. The X-axis was in the longitudinal axis through the hilum to the tip (length) and the Y-axis was in the latitudinal axis (width) at right angles to the X-axis. Kernel extraction quality was classified into grades according to size and number of broken pieces of the kernel. Central composite design (CCD) of resound surface method was used to optimize the effect of ultrasonic factors on walnut kernel extraction.
Results and Discussion
The results indicated that the loading speed, ultrasound time duration, loading direction, and moisture content had a highly significant effect (P<0.01) and ultrasound bath temperature (P<0.05) on the rupture force and kernel extracting quality. Regarding the sum of squares of ANOVA results, the ultrasound time duration factor had the most effect on the rupture force and the loading direction factor had the most effect on kernel extraction quality. By increasing bath temperature and ultrasound time duration, walnut rupture force was decreased. The minimum walnut rupture force was obtained in 25 min ultrasound time duration, 50ºC bath temperature, 1.5 mm s-1 loading speed, and width loading direction for wet walnut. By increasing bath temperature, walnut kernel losses were increased. The best kernel extraction quality was obtained in 2.5 mm s-1 loading speed, 25 min ultrasound duration, 20ºC bath temperature, and longitudinal loading direction. The proposed optimal point was obtained at 64.4 N rupture force, and two half of the kernel at 1.3 mm s-1 loading speed,  25 min ultrasound duration, 50ºC bath temperature, and longitudinal loading direction for wet walnut.
Conclusion
The walnut ultrasound treated samples had minimum rupture force and the best quality kernel extraction. It was observed that by increasing the loading speed and ultrasound time duration, the percentage of whole kernels and the quality degree of broken kernels increased.

Keywords

Open Access

©2020 The author(s). This article is licensed under Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source.

1. Altuntas, E., and M. Erkol. 2009. The Effects of Moisture Content, Compression Speeds, and Axes on Mechanical Properties of Walnut Cultivars. Food and Bioprocess Technology 4: 1288-1295.
2. Bayazİt, S., C. Toplu, and O. Calıșkan. 2009. Yield and fruit characteristics of some walnut (Juglans regia L.) varieties in Yayladağı (Hatay) ecological conditions. Ziraat Fakultesi Dergisi, Mustafa Kemal Universitesi 14: 33-40.
3. Bezerra, M. A., R. E. Santelli, E. P. Oliveira, L. S. Villar, and L. A. Escaleira. 2008. Response surface methodology (RSM) as a tool for optimization in analytical chemistry. Talanta 76: 965-977.
4. Braga, G. C., S. M. Couto, T. Hara, and J. T. P. Almeida Neto. 1999. Mechanical Behaviour of Macadamia Nut under Compression Loading. Journal of Agricultural Engineering Research 72: 239-245.
5. Cao, S., Z. Hu, B. Pang, H. Wang, H. Xie, and F. Wu. 2010. Effect of ultrasound treatment on fruit decay and quality maintenance in strawberry after harvest. Food Control 21: 529-532.
6. Entezari, M. H., S. Hagh Nazary, and M. H. Haddad Khodaparast. 2004. The direct effect of ultrasound on the extraction of date syrup and its micro-organisms. Ultrason Sonochem 11: 379-384.
7. FAO. 2014. Statistical DatabaseFood and Agriculture Organization of the United Nations Statistics Division. http://faostat.fao.org/site/339/default.aspx.
8. Kabas, O., and V. Vladut. 2015. Determination of Some Engineering Properties of Pecan (Carya illinoinensis) for New Design of Cracking System. Erwerbs-Obstbau 58: 31-39.
9. Kacal, M., and M. A. Koyuncu. 2017. Cracking characteristics and kernel extraction quality of hazelnuts: Effects of compression speed and positions. International Journal of Food Properties: 1-11.
10. Kek, S. P., N. L. Chin, and Y. A. Yusof. 2013. Direct and indirect power ultrasound assisted pre-osmotic treatments in convective drying of guava slices. Food and Bioproducts Processing 91: 495-506.
11. Koyuncu, M. A., K. Ekinci, and E. Savran. 2004. Cracking Characteristics of Walnut. Biosystems Engineering 87: 305-311.
12. Mohammadi Ghermezgholi, K., H. R. Ghassemzadeh, H. Navid, M. Moghaddam, and H. Ghaffari. 2014. Evaluation of Walnut Kernel Quality (as Degree of Crushing) Obtained Under Impact Loading. Journal of Agricultural Machinery 4: 11-20. (In Farsi).
13. Mohapatra, D., and S. Bal. 2007. Effect of degree of milling on specific energy consumption, optical measurements and cooking quality of rice. Journal of Food Engineering 80: 119-125.
14. Mohsenin, N. N. 1986. Physical properties of plant and animal materials. Report no.
15. Özdemir, M., and M. Özilgen. 1997. Comparison of the quality of hazelnuts unshelled with different sizing and cracking systems. Journal of Agricultural Engineering Research 67: 219-227.
16. Povey, M. J., and T. J. Mason. 1998. Ultrasound in food processing. Springer Science & Business Media.
17. Sharifian, F., and M. H. Derafshi. 2008. Mechanical behavior of walnut under cracking conditions. Journal of Applied Sciences 8: 886-890.
18. Tang, G., T. Liang, and F. Munchmeyer. 1982. A variable deformation macadamia nut cracker. Transactions of the ASAE 25: 1506-1511.
19. Tibäck, E., M. Langton, J. Oliveira, and L. Ahrne. 2014. Mathematical modeling of the viscosity of tomato, broccoli and carrot purees under dynamic conditions. Journal of Food Engineering 124: 35-42.
20. Verhaagen, B., and D. Fernandez Rivas. 2016. Measuring cavitation and its cleaning effect. Ultrason Sonochem 29: 619-628.
21. Yaldagard, M., S. A. Mortazavi, and F. Tabatabaie. 2008. Application of ultrasonic waves as a priming technique for accelerating and enhancing the germination of barley seed: Optimization of method by the Taguchi approach. Journal of the Institute of Brewing 114: 14-21.
22. Zhang, L., C. Zhou, B. Wang, A. E. A. Yagoub, H. Ma, X. Zhang, and M. Wu. 2017. Study of ultrasonic cavitation during extraction of the peanut oil at varying frequencies. Ultrason Sonochem 37: 106-113.
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