Drying kinetics of apple pomace cake

J Food Sci Technol 2009, 46(5), 477-479 Drying kinetics of apple pomace cake Shalini R, Gupta DK, Singh A* Department of Post-harvest Process and Food Engineering, GB Pant University of Agriculture and Technology, Pantnagar-263 145, India *Email:asingh3@gmail.com Pomace from apples of ‘Red delicious’ variety was dried at 50, 60 and 70oC with layer thickness of 2, 4 and 6 mm and air velocity of 1.5 meter/sec. The effect of air velocity 1.5, 2 and 2.5 meter/sec at 70oC and thickness 2 mm was observed. Drying from initial moisture content of 424.8-496.7% (db) to final moisture content of 2.3-6.6% (db) took 90 to 620 min. Air velocity had insignificant effect on drying rate of pomace. The sensory score for overall acceptability of apple pomace dried powder at 60oC and 4 mm thickness was maximum. It was concluded that apple pomace should be dried at 60oC with 4 mm layer thickness and with air velocity of 1.5 meter/sec. Keywords: Apple pomace, Thin layer drying, Drying kinetics, Sensory quality Apple (Malus domestica Borkh.), a rich source of carbohydrate, pectin, crude fiber and minerals is the most favoured fruit of millions of people and widely grown fruit in temperate regions of the globe. On global basis, 71% of fruit is consumed as fresh apple while about 20% is processed into value added products (Anon 2004). A conventional process removes 75% of fresh weight of apple as juice and the rest 25% is the pomace (Sargent et al 1986, Wang and Thomas 1989, Shah and Masoodi 1994, Kaushal et al 2002). Since, apple pomace is a part of the fruit, it has a potential for conversion into edible products (Kaushal and Joshi 1995). It is biodegradable in nature with high biochemical oxygen demand and disposal of apple pomace into the environment causes pollution, necessitating to find appropriate solution. Traditionally only a fraction of apple pomace is used as cattle feed due to its rapid spoilage (Bates and Roberts 2001). Drying is a step in the processing of high moisture products, like apple pomace. The present study was undertaken to study the drying behaviour of wet apple pomace under thin layer drying conditions in relation to drying air temperature, air velocity and layer thickness. Sensory evaluation of the dried apple pomace powder at different conditions of temperature and layer thickness was done to optimize the drying air temperature and layer thickness. Materials and methods Culled apples of ‘Red Delicious’ variety were procured from local market and thoroughly cleaned with 0.2 % of potassium permanganate solution (Agrahari and Khurdiya 2003) to remove any kind of infections and then washed with tap water to remove soil and dust particles. Washed apples were sliced into 4 equal parts and coring was done. After slicing the apple slices were blanched with potassium metabisulphite solution for 15 min at the rate of 100 mg/l of solution/kg of apple (Ranganna 1986). After blanching, the sliced apples were crushed in a fruit crusher and apple juice was separated through muslin cloth manually before further processing. The juice expression of crushed apple was done in a cylinder with a laboratory hydraulic press (Mode M-25, Fred S. Carver Inc. USA). The pressing of crushed apple was carried out at 59.7 kg/cm 2 pressing load for 1 h and 45 min. Apple pomace was recovered in the form of cake from the hydraulic cylinder. The apple pomace samples of 50, 90, 130 g corresponding to 2, 4, 6 mm thickness, respectively were spread uniformly as thin layer drying in the dryer. The initial mass of the sample along with the tray wire mesh was measured before placing in the dryer. Weight of the sample was recorded at an interval of 3 min for first 30 min of drying and then at 5, 10, 20 min intervals. The drying time interval was not fixed but varied with thickness and the drying was carried out till there was insignificant relative error (<0.1%) in weight of sample. The drying air temperatures were 50, 60 and 70oC and the air velocity was kept at 1.5 meter/sec. The drying was carried out on SATAKE 477 dryer (TDR Satake Mark, 0.746 Watt, rpm 2500, Tokyo). The drying experiments were replicated thrice. The initial moisture content of the sample was determined by drying the samples at 70±1oC for 18 h until 2 to 3 consecutive weights did not vary more than 0.3-0.5% (Ranganna 1986). The dried samples were then packed in polythene bag (40 µ gauge) to avoid moisture migration from atmosphere. The dried apple pomace was ground and milled in a Willey Mill (Arthur H. Thomas Co., Philadelphia, PA) to form dried apple pomace powder with a 1.5 mm sieve. Sensory evaluation of dried apple pomace powder was carried out by a 25-member panel of different age groups and different food habits for colour, texture, odour and overall acceptability. The sensory evaluation was done on 9point Hedonic scale as recommended by BIS (1971) and Kaushal and Joshi (1995). The average score of all the 25 panelists was computed to optimize the drying air temperature and layer thickness. Analysis of drying data: The experimental drying data was graphically analyzed in terms of reduction in moisture content and moisture ratio with drying time using the spread sheet in Microsoft Excel (XP) software on PC. The effect of temperature on the overall drying rate was studied using the analysis of variance technique. The regression was carried out using software CURVE EXPERT 3.0 on a PC. The overall rate of drying was calculated as ratio of difference of initial and final moisture content and total drying time. The data for the overall J Food Sci Technol 2009, 46(5), 477-479 drying rate was fitted in various equations with air temperature and layer thickness as variables using the software NLREG Version 4.1. The sensory data were statistically analyzed by the method of two-way analysis of variance for different process conditions. In built two-way ANOVA program was used in the analysis of quality data with the help of Microsoft Excel (XP) software on PC. Results and discussion Effect of drying conditions on drying of apple pomace: To get a final moisture content of 2.3 to 6.6 % (db), it took 90 to 620 min of drying time at different temperatures and thickness (Table 1). Typical drying curves between the moisture ratio and time are given in Fig. 1. Drying rate exhibited a nonlinear behaviour with time. Overall drying rate varied from 0.69 to 4.7%/min (db) for the total range of variables of the study. Normally, it can be expected that the overall drying rate should be higher at higher temperature, which is observed from the results presented in Table 1. The overall drying rate increased with increase in temperature and decreased with increase in layer thickness at all temperatures. The following regression equations were obtained for different layer thicknesses of apple pomace between overall drying rate versus temperature: y = 0.153x - 5.8533 (R2 = 0.9829) for 2 mm thickness y = 0.0885x - 3.3033 (R2 = 0.9856) for 4 mm thickness y = 0.078x - 3.2333 (R2 = 0.9973) for 6 mm thickness Drying rate decreased with decrease in moisture content and the drying took place in falling rate period. Effect of both temperature and thickness was significant at 5% level of significance. The increase of overall drying rate with increase in temperature and decrease of overall drying rate with increase of layer thickness was represented by equation on the basis of high coefficient of determination (R2 = 0.9406) in comparison to other equations fitted with the data, the following equation was chosen as the best fit. where, The other equations were = overall drying rate (%db/min), T is the temperature (oC), L = layer thickness (mm) and A, B, C = constants. The constants for the equation (1) are tabulated in Table 2. Sensory quality of dried apple pomace powder: The maximum scores for colour, odour, texture and overall acceptability were obtained for 60oC and 4 mm layer thickness of apple pomace (Table 1). Therefore, on the basis of Table 1. Overall drying rates, drying period of apple pomace at different drying conditions and sensory quality of dried powder Temp, Moisture content o C 50 60 70 Thickness, Initial, mm %db 2 424.8 4 429.9 6 429.9 2 431.4 4 431.3 6 427.1 2 431.5 4 455.7 6 496.6 Final, Drying %db time, min 250 400 620 120 200 300 90 160 220 5.4 4.7 4.9 3.8 5.6 6.7 4.7 2.3 2.4 Drying Sensory quality rate, Colour Texture Odour Overall %db/min accept. 1.68 6.6 7.0 6.3 6.6 1.06 6.0 6.2 6.7 6.2 0.69 6.2 6.3 6.7 6.4 3.56 7.0 6.9 6.8 7.1 2.13 7.9 7.8 7.2 8.0 1.40 7.1 7.3 7.0 7.4 4.74 7.7 7.0 6.8 7.1 2.83 8.0 7.9 7.2 7.8 2.25 7.4 7.3 6.9 7.2 (n=3) Time, Min Fig. 1. Interrelation between moisture ratio and time of drying of apple pomace cake of different thickness at different temperatures (n=3) 478 J Food Sci Technol 2009, 46(5), 477-479 Table 2. Calculated parameter values for the best fit equation P A B C FE 0.107 5.557 -5.828 SE 0.015 0.850 0.930 t 7.22 6.54 -6.27 Prob(t) 0.00036 0.00061 0.00077 P: Parameter, FE: Final estimate, SE: Standard error overall acceptability the process can be optimized to 60 oC and 4 mm layer thickness at air velocity of 1.5 meter/sec. Conclusion Drying of apple pomace takes place in falling rate period. The overall drying rate linearly increased with increase in temperature and decreased with increase in layer thickness. Apple pomace should be dried at 60oC with 4 mm of layer thickness at 1.5 meter/sec to get acceptable sensory quality of dried apple pomace powder. References Anon 2004. Comprehensive study on processing of apple. Status of apple processing industry in India. The Ministry of Food Processing Industries, Government of India Agrahari PR, Khurdiya DS 2003. Studies on preparation and storage of RTS beverage from pulp of culled apple pomace. Indian Food Packer 57(2):56-61 Bates AW, Roberts JS 2001. The utilization of apple pomace as a press aid in fruit juicing. In: IFT annual meeting – New Orleans, Louisiana: Session 88E, Fruit and Vegetable Products Processing BIS 1971. IS: 6273 I and II, Guide for sensory evaluation of foods. Bureau of Indian Standards, New Delhi Kaushal NK, Joshi VK 1995. Preparation and evaluation of apple pomace based cookies. Indian Food Packer 11(2):17-24 Kaushal NK, Joshi VK, Sharma RC 2002. Effect of stage of apple pomace collection and the treatment on the physical-chemical and sensory qualities of pomace papad. J Food Sci Technol 49:388-393 Ranganna S 1986. Handbook of analysis and quality control for fruit and vegetable products. Tata McGraw Hill Pub. New Delhi Sargent SA, Steffe JF, Pierson TR 1986. The economic feasibility of in-plant combustion of apple processing wastes. Agric Waste 15(2):85-96 Shah GH, Masoodi FA 1994. Studies on the utilization of wastes from apple processing plants. Indian Food Packer 48(5):47-52 Wang HJ, Thomas RL 1989. Direct use of apple pomace in bakery products. J Food Sci Technol 54:618-620, 639 Received 21 July 2008; revised 30 March 2009; accepted 1 April 2009 Forthcoming events IFT/EFFoST Nonthermal Food Processing Workshop and Short Course Date: October 12-15, 2009 Venue : Beijing, China For further information please visit : http://www.info@ift.org Food ingredients India Date: October 23-24, 2009 Venue : Mumbai, India For further information please information : http://www.Vincent.Brain@ubm.com http://www.fi-events.com 479 View publication stats