Faculty of Engineering and Agro-Industry. Agro-Industry. Maejo University. Maejo University. Sansai, Chiang Mai 50290. Sansai, Chiang Mai 50290. Thailand.
Effect of Drying Methods on Color Quality of Sweet Basil (Ocimum basilicum Linn.) R. Assawarachan Drying and Dehydration Technology Research Unit Faculty of Engineering and Agro-Industry Maejo University Sansai, Chiang Mai 50290 Thailand
K. Kalayanamitra Faculty of Engineering and Agro-Industry Maejo University Sansai, Chiang Mai 50290 Thailand
Keywords: hot air drying, microwave drying, color difference Abstract The effect of drying methods on color quality of sweet basil (Ocimum basilicum Linn.) was investigated under the condition of hot air drying (HAD) at 55, 65 and 75°C and microwave drying (MWD) at 335, 400 and 545 W. These drying methods reduced the moisture content of sweet basil from 5.23 to 0.064 gwater/gdry matter. The dried samples were then analyzed in the CIE (L*-a*-b*) color system, the total color difference (ΔE) of rehydrated dried sweet basil and the Chroma values. The lightness (L*) values of dried sweet basil with HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W were 25.72, 27.25, 24.74 and 30.82, 28.47, and 29.35, respectively. a* values were 0.48, 0.53, 0.94 (red color) and -3.55, -3.54, -3.52 (green color), respectively. Total color difference (ΔE) of rehydrated dried sweet basil using HAD and MWD method gave average values of 6.62, 7.17, 7.53 and 6.53, 5.57, and 5.67, respectively. Chroma values were 4.48, 2.59, 2.56 and 8.48, 9.60, and 10.05, respectively. Fresh sweet basil and rehydrated dried sweet basil of MWD showed better quality than HAD. In addition, the specific energy consumption of MWD was 13.64-17.36 times lower than HAD. INTRODUCTION Sweet basil (Ocimum basilicum Linn.) is a member of the Labiatae family with square stem, opposite and decussate leaves with many gland dots (Paton et al., 2006). Hiltunen (2006) reported that sweet basil leaves contain 0.17% olean oli acid and small amount of ursolic acid. The dried leaves and flower tops of sweet basil contain essential oil (ca. 0.08%), protein (14%), carbohydrates (61%) and relatively high concentrations of vitamins A and C, rosmarinic acid and a flavone named xanthomicrol. Medicinal and aromatic plants contain a high level of moisture and microorganisms. Thus, drying is the most important operation in postharvest processing to avoid product losses (Müller et al., 1989). Previous studies have shown that microwave oven drying shortened the drying time, increased the phenolic content, and improved color (Arslan et al., 2010). Information on the effect of drying methods on color quality of Thai sweet basil is limited. The aim of this study was to evaluate the effects of hot air and microwave drying on color quality of sweet basil. MATERIALS AND METHODS Fresh sweet basil was procured from a local supplier in Chiang Mai, Thailand. Initial moisture content was measured by the standard AOAC (2000) method and was calculated to be 5.23±0.82 gwater/gdry matter. Two drying methods were tested. In the hot air drying (HAD), a sample of 30 g of sweet basil was placed in a perforated aluminum tray (20×20 cm) and dried at 65 and 75°C in a cross-flow type dryer with air flow rates of 1.0 m/s. Air was heated electrically before entering the heater. During air drying, weight and temperature of the samples were recorded at regular interval of times. In microwave drying (MWD), a programmable microwave oven (Panasonic Model NN-S235WF) with a maximum output of 750 W was used. Weight loss during drying process was recorded using a computer software data logger through a balance connected to a PC. The sample Proc. IInd Southeast Asia Symp. on Quality Management in Postharvest Systems Eds.: A.L. Acedo Jr. and S. Kanlayanarat Acta Hort. 1088, ISHS 2015
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was dried with three different microwave power levels of 335, 400 and 545 W from initial moisture content until the final moisture content was about 0.064±0.005 gwater/gdry matter. The color of dried sweet basil was measured in the CIELAB color system using spectrophotometer (Hunter Lab Color Flex Version 1.72, USA) which three parameters, L*-value (lightness), a*-value (redness/greenness), and b*-value (yellowness/ blueness)”were measured with three replicates and the data was presented in an average. During drying, the total color difference (ΔE) was also calculated using the following equation: ∆E =
( L*t L*0 ) 2 (a*t a*0 ) 2 (b*t b*0 ) 2
(1)
where L*0, a*0, b*0 are the initial color measurements of fresh sweet basil and L*t, a*t, bt* are the color measurements at a pre-specified time. Chroma was calculated as the squareroot of the sum of squares of a* and b* values. Energy consumption of the dryer was measured by a multifunction energy meter (KM-07-A-2, Primus Company Limited, Thailand). The energy used during heating up was excluded. Thereafter, the specific energy consumption (SEC) was obtained from the input electrical energy and the quantity of water removed during drying. SEC =
Input eletrical energy ( MJ ) Weight of water removes ( kg water )
(2)
RESULTS AND DISCUSSION Effect of Drying Methods on Color Quality L* values of dried sweet basil with HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W were 25.72, 27.25, 24.74 and 30.82, 28.47, and 29.35, respectively (Fig. 1). L* value of sweet basil leaves decreased when HAD temperature increased while L* value of MWD was closer to the L* value of 28.57 of the fresh sample. Krokida and Maroulis (1999) reported that microwave drying prevented color damages during drying. Oven dried rosemary and peppermint leaves were significantly darker in color when compared to the microwave dried sample (Arslan and Özcan, 2008; Arslan et al., 2010). The a* values of dried sweet basil with HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W were 0.48, 0.53, 0.94 (red color) and -3.55, -3.54, -3.52 (green color), respectively. a* value of MWD samples was not significantly different compared with that of fresh samples, indicating that MWD retained green color of sweet basil leaves better than HAD. b* values of fresh samples were higher than the HAD samples while MWD samples showed closer to the b* value of 8.9 of the fresh samples. The a* values of dried sweet basil with HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W were 0.80, 0.53, 0.61 (red color) and -1.64, -3.41, -3.59 (green color), respectively (Fig. 2). The results indicate that MWD method retained green color of sweet basil leaves better than HAD method. Total color difference (ΔE) of rehydrated dried sweet basil using HAD and MWD method presented average values of 6.62, 7.17, 7.53 and 6.53, 5.57, and 5.67, respectively. These results showed that the total color difference or distance value of MWD samples were different from fresh sweet basil were more different than HAD samples. Chroma values of dried sweet basil with HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W were 4.48, 2.59, 2.56 and 8.48, 9.60, and 0.05, respectively. Chroma describes the vividness or dullness of a color. Colors in the center are gray (dull) and become more saturated (vivid) as they move toward the perimeter. Specific Energy Consumption for Drying Process The drying rate values of dried sweet basil with HAD at 55, 65 and 75°C were 0.056±0.003, 0.101±0.002 and 0.149±0.002 gwater/gdry matter min, respectively (Table 1). The specific energy consumption (SEC) shows a value of energy efficiency and energy 616
analysis. SEC of HAD at 55, 65 and 75°C were 1.466±0.033, 1.193±0.023 and 1.115± 0.028 MJ/kgwater. The drying rate values of dried sweet basil with MWD at 335, 400 and 545 W were 0.697±0.011, 0.951±0.044 and 1.299±0.006 gwater/gdry matter min, respectively. SEC of MWD at 335, 400 and 545 W were 0.097±0.003, 0.086±0.002 and 0.084±0.003 J/kgwater. These results showed that the specific energy consumption of MWD was 13.6417.36 times lower than HAD. The microwave energy can penetrate directly into materials and induce volumetric heating inside the materials, and therefore, the drying period and energy consumption were lowered while the overall quality of product was significantly improved (Assawarachan et al., 2013). CONCLUSIONS Color of fresh sweet basil and rehydrated dried sweet basil of microwave drying method showed better quality than hot air drying method. The specific energy of consumption of microwave drying gave lower value than hot air drying method of 13.6417.36 times. Microwave drying had faster drying rate than hot air drying method while consuming less drying energy. Therefore, microwave drying method may be utilized for optimizing the drying process of sweet basil. Literature Cited Arslan, D. and Özcan, M.M. 2008. Evaluation of drying methods with respect to drying kinetics, mineral content and colour characteristics of rosemary leaves. Energy Convers. Manage. 49:1258-1264. Arslan, D., Özcan, M.M. and Menges, H.O. 2010. Evaluation of drying methods with respect to drying parameters, some nutritional and colour characteristics of peppermint (Mentra × piperita L.). Energy Convers. Manage. 51:2769-2775. Assawarachan, R., Nookong, M., Chailungka, N and Amornlerdpison, D. 2013. Effect of microwave power on the drying characteristics, color and phenolic content of spirogyra sp. Int. J. Food, Agri. and Environ. 11(1):1-4. Hiltunen, R. 2006. Chemical composition of Ocimum species. p.67-74. In: R. Hiltunen and Y. Holm (eds.), Basil The Genus Ocimum. Taylor & Francis e-Library. Krodida, M.K. and Maroulis, Z.B. 1999. Effect of microwave drying on some quality properties of dehydrated products. Drying Technol. 17:449-466. Müller, J., Reisinger, G. and Mühlbauer, W. 1989. Drying of medicinal and aromatic plants in a greenhouse solar dryer. Landtech. 2:58-65. Paton, A., Harley, M.R. and Harley, M.M. 2006. Ocimum: an overview of classification and relationships. p.1-38. In: R. Hiltunen and Y. Holm (eds.), Basil The Genus Ocimum. Taylor & Francis e-Library. Tables Table 1. Drying rate and specific energy consumption of dried sweet basil during HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W of microwave power levels. Drying method Fresh HAD 55°C HAD 65°C HAD 75°C MWD 335 W MWD 400 W MWD 545 W
Drying rate (gwater/gdry matter min) 0.056 ± 0.003 0.101 ± 0.002 0.149 ± 0.002 0.697 ± 0.011 0.951 ± 0.044 1.299 ± 0.006
SEC (MJ/kgwater) 1.466 ± 0.033 1.193 ± 0.023 1.115 ± 0.028 0.097 ± 0.003 0.086 ± 0.002 0.084 ± 0.003
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-10
10 0
L*-values a*-values b*-values Color quality of dried sweet basil
-10
green
red 335 W Frash 400 W purple 545 W
8,90 9,60 9,69 9,16
20
yellow
-4,64 -3,55 -4,51 -3,62
-4,64 -0,43 1,21 0,98
0
30 Color-values
28,57 27,33 27,30 24,79
10
8,90 6,25 7,35 6,68
20
green
yellow red green purple
Color-values
30
Frash red 55 C 65 C purple 75 C
yellow
yellow red green purple
40
40
28,57 31,00 28,50 29,45
Figures
L*-values a*-values b*-values Color quality of dried sweet basil
-2 -4 -6
a*-values
∆E blue green
Chroma Frash red 55 C 65 C purple 75 C
Color quality of rehydrated dried sweet basil
2 0 -2 -4 -6
red green purple
-4,64 -1,64 -3,41 -3,59
4
red green purple
6
blue red green purple
8
4,48 2,59 2,56
6,53 5,57 5,67
0
10
Color-values
2
12
red green purple
4
-4,64 0,80 0,53 0,61
Color-values
6
blue red green purple
8
red green purple
6,62 7,17 7,53
10
8,48 9,60 10,05
Fig. 1. The CIELAB color parameters of dried sweet basil during HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W of microwave power levels.
a*-values
blue green
∆E Chroma Frash red 335 W 400 W purple 545 W
Color quality of rehydrated dried sweet basil
Fig. 2. The CIELAB color parameters, the total color difference (ΔE) and the Chroma values of rehydrated dried sweet basil during HAD at 55, 65 and 75°C and MWD at 335, 400 and 545 W of microwave power levels.
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