Document Type : Research Article
Authors
Shiraz University
Abstract
Introduction: Given that fruit drying is one of the best economical storing methods, in the present study attempt has been made to apply a commercial drying method, namely passing warm air through fruit in a cabinet drier, to pinpoint the change in textural properties of pear fruit during drying at different inlet air temperature and velocity levels. The outcomes of the study can be used for optimizing the drier operation during drying (intelligent driers) to keep suitable textural properties of final product for those who use sweet dried fruit as sweetener due to diabetic issues.
Materials and method: Pear fruits, Shah Miveh cultivar, were collected form a garden near Isfahan city and carried to the laboratory carefully. Experimental samples with 2×2.5×2.5 cubic centimeter dimension were prepared from upper part of pear fruits. A conventional cabinet drier was used for drying the pear cubes with adjustable inlet drying air temperature and velocity. Air temperature and velocity were adjusted at three levels of 40, 50 and 60 oC, and 0.5, 1 and 1.5 m/s, respectively. Initial moisture content was measured by gravimetric methods and samples weight loss measured during drying by an online system comprising hooked type balance with ±0.001 accuracy. Dried samples were then subjected to texture profile analysis (TPA) with Instron (Santam-STM 20). Two-bite test was performed with 20 mm diameter aluminum probe, at 1 mm/s speed rate for 5 mm deformation. Textural properties of samples such as hardness, cohesiveness, adhesiveness, springiness and chewiness were drawn from force-time curve. Textural properties were measured at five sample moisture contents of 82, 66, 51, 35 and 20 percent (w.b.). Data were analyzed according to the factorial experiments based on completely randomized design by SPSS software (version 16), and the means were compared by Duncan multiple range test at 5 percent of significance.
Results and Discussion: Mean comparison of drying time significantly affected by air temperature and velocity, and the effect of temperature was more than air velocity. Results revealed that textural properties of samples have changed during drying process and these changes were related to drying conditions. Hardness decreased exponentially and adhesiveness decreased linearly as fruits were being dried, whereas springiness and cohesiveness increased linearly. Chewiness followed a parabolic trend, reached to the peak in the range of 40 to 50 % moisture content levels (wet basis). ANOVA showed that drying air temperature had significant influence on hardness, springiness and chewiness, while its influence on adhesiveness and cohesiveness was not significant. Moreover, it was found that air drying velocity affected all aforementioned properties. Having considered the results of dried pear chewiness, the minimum chewiness (0.46 J) took place at air drying temperature of 40 ˚С and velocity of 1m/s, and therefore it is recommended as the best drying condition. Drying time period at this condition was measured nearly 33.5 hours, which was approximately 24 hours more than the shortest one in the drying condition of 60˚С and 1.5 m/s and 6.5 hours lower than the longest one in drying condition of 40˚С and 0.5 m/s.
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