116 Chiang Mai J. Sci.2011; 38(1) Chiang Mai J. Sci. 2011; 38(1) : 116-125 www.science.cmu.ac.th/journal-science/josci.html Contributed Paper Effects of Varieties, Heat Pretreatment and UHT Conditions on the Sugarcane Juice Quality Weerachet Jittanit*, Somsak Wiriyaputtipong, Hathainid Charoenpornworanam, and Sirichai Songsermpong Department of Food Science and Technology, Faculty of Agro-Industry, Kasetsart University, Bangkok 10900, Thailand. *Author for correspondence; e-mail:
[email protected] Received: 6 November 2009 Accepted: 7 May 2010 ABSTRACT In this work, the effects of sugarcane varieties, heat pretreatment methods and UHT conditions on the quality of sugarcane juice were investigated. The aim was to attain the background information that is useful for the production of high quality UHT sugarcane juice. The experimental results indicated that the sugarcane Suphan Buri 50 variety is more suitable for juice production than Singapore variety in aspects of total solid and consumer preference. Furthermore, it appeared that both the microwave heating for 5 minutes by frequency 2,450 MHz at 850 W and the blanching sugarcane in hot water at 80oC for 5 minutes could inactivate the peroxidase enzyme at the comparable level. Nevertheless, the blanching was preferred due to its ease of control, lower energy and equipment cost. In addition, if F0 > 4 is demanded, the UHT sterilization at 140oC and holding for 4 seconds could maintain the sugarcane flavors and provide the more favorable juice than those of o 135 C for 10 seconds. Keywords: sugarcane juice, blanching, microwave, UHT, sterilization. 1. INTRODUCTION Sugarcane (Saccharum officinarum L.) is one is limited because of its rapid quality of the most important crops in the world deterioration [2-4]. especially for the tropical countries. Most of The Ultra-High Temperature (UHT) them are used for the sugar and alcohol processing is an attractive technique to extend production. Fresh sugarcane juice is a popular the shelf-life and raise the consumer safety beverage in many countries such as China, while maintaining the fresh quality of Malaysia and Thailand due to its taste and sugarcane juice. In the UHT juice production, cheap price. Apart from that in the Indian the selections of sugarcane variety and the systems of medicine, it has been used to cure pretreatment are vital. Tangpremsri et al. [5] jaundice and liver-related disorders [1]. pointed out that the sugarcane variety Suphan Nevertheless, the marketing of sugarcane juice Buri 50 provided the mean juice yield 1.3 Chiang Mai J. Sci. 2011; 38(1) 117 times higher than the widely grown variety, varieties grown in the central region of Singapore. Besides, the juice from Suphan Buri Thailand were used in this study. The samples 50 was fine color (green yellow), tasty and were weighed, manually peeled, cut, cleaned o 10% higher oBrix than those of Singapore and then blanched in hot water at 80 C for 5 variety. To stabilize the fruit juice quality during minutes. After that, the samples were squeezed processing and storage, the pretreatments like by the “NHY” rolling squeezer motor 0.25 HP blanching in hot water and/or addition of 220 V 50 Hz and screened the solid particles antioxidant agents are commonly applied by the filter bag. The juices from both varieties [6,7]. These pretreatments aim to inactivate were compared in terms of total solid, the enzymes that cause the color, sensorial and pH, color and consumer acceptance. The nutritional changes in the fruit and vegetable descriptions of the juice quality determination products during processing and storage and the evaluation of consumer acceptance [8-13]. Qudsieh et al. [14] pointed out that the are presented in Section 2.4. The result of key enzyme related to the browning of varieties comparison would justify the sugarcane juice was the polyphenol oxidase sugarcane variety used in the following steps. that reacted with phenolic compounds. Mao et al. [4] showed that the blanching of 2.2 Heat Pretreatments sugarcane stems in boiling water for 5 minutes After the variety determination, the before squeezing and addition of 0.1% chosen sugarcane variety was exposed to the ascorbic acid could effectively prevent the comparison between the two heat pretreat- browning and reduce the enzyme activities in ment options, (1) blanching in hot water at o the fresh sugarcane juice. Although the thermal 80 C for 5 minutes and (2) microwave heating resistance of polyphenol oxidase is dependent for 5 minutes using “SHARP” microwave on its origin or the product types, some oven model R-7A56 at frequency 2,450 MHz, researchers claimed that in most cases solely 850 W and setting convective air temperature o short exposures of fruit or vegetable at 250 C. These two pretreatments were products to the temperatures between 70 compared because the hot water blanching is o and 90 C were adequate for partial or a conventional method that has the advantages complete inactivation of the polyphenol in aspects of controllability, low energy and oxidase [10, 15]. equipment cost [16] while the microwave Owing to the lacking of research in the heating is a new approach that was proposed area of sugarcane juice processing, the effects to reduce enzyme activities in many studies of 3 parameters comprising with sugarcane due to its penetration depth and fast heating varieties, heat pretreatment methods and UHT rate [8, 13, 17]. The main function of the heat conditions on the quality of sugarcane juice pretreatments in this work was to diminish were investigated. The aim was to obtain some the enzyme activities that normally cause useful information for the UHT sugarcane quality deteriorations of sugarcane juice such juice production. as degreening and/or browning during processing and storage. The experiments for 2. MATERIALS AND METHODS each pretreatment were carried out at least 2 2.1 Comparison between Sugarcane replications. The juices squeezed from the Varieties samples pretreated by these two options were Samples of freshly harvested sugarcane exposed to the peroxidase activity test and of the “Suphan Buri 50” and “Singapore” sensory evaluation. Also, they were measured 118 Chiang Mai J. Sci. 2011; 38(1) the total solid, pH and color. Moreover, the conducted on the same day for each fresh juice squeezed from the non-pretreated experiment. As generally recognized, the sugarcane stems was exposed to the peroxidase process lethality (F0) is the most important activity test. However, the pH, color and total parameter that can indicate the level of the solids measurement and the sensory test were sterilization process and consequently not conducted for this sample because its the microbiological risk of sterilized food quality attributes were unstable and rapidly [18-22]. F0 is defined as the time (seconds) at o changed along the time due to the enzyme a reference temperature (121.1 C) to which activities and high microbial growth rate. the process is equivalent [19]. It was calculated from the temperature history of the sterili- 2.3 UHT Sterilization zation process by integration of the following After realizing the proper variety and heat equation over time (t) [20-22]: pretreatment for sugarcane juice preparation, the UHT sterilization was carried out using the lab-scale “MicroThermics” UHT/HTST Similar to the common sterilization of machine model “Lab 25 EHV Hybrid”. The food, the target microorganism of the UHT schematic diagram of the UHT process is sterilization in this work was Clostridium o illustrated in Figure 1. In the UHT machine, botulinum; hence, the z value of 10 C was there were Type-T thermocouples installed at applied in eq. (1) [21,22]. The F0 4 was various positions for measuring the juice specified for the UHT sterilization in this study temperatures. Prior to the UHT experiments, in order to slightly beyond a minimum the total solid of sugarcane juice was adjusted requirement (F0 3) for the low-acid food o to 12 Brix by adding the distilled water so that was recommended by Lewis [18]. There that the raw samples for all experimental runs were 4 conditions for the UHT experiments were in the same condition. The fresh juice as detailed in Table 1. The UHT experiments preparation and the UHT sterilization were were conducted without replication. Figure 1. A schematic diagram of the UHT process. Chiang Mai J. Sci. 2011; 38(1) 119 Table 1. The conditions of UHT experiments. UHT condition Run no. Raw sample Sterilization Holding time (s) temperature (oC) 1 Fresh sugarcane juice 140 4 2 Fresh sugarcane juice added with a sugar flavor 140 4 3 Fresh sugarcane juice 135 10 4 Fresh sugarcane juice added with a sugar flavor 135 10 The UHT processed juices were aseptically content, pH, color and peroxidase activity test filled in the clean fill hood and kept in the were done in three replications. The software sterilized glass containers for sensory package Statistica 5.5 StatSoftTM (supplied by evaluation and the determination of total StatSoft, Inc. Tulsa, OK 74104 USA) was used solid, pH and color. The sensory evaluation for the analysis of variance (ANOVA) and a and the quality determination were conducted Duncan’s multiple range test in the statistical within one week after the production of UHT analysis. samples. 3. RESULTS AND DISCUSSION 2.4 Quality Determination The results of comparing the total solid, The total solid content, pH and color of pH, color and sensory evaluation (by 26 the sugarcane juice were measured by panelists) between Singapore and Suphan Buri “ATAGO” hand refractometer, “JENCO” 50 varieties in aspect of flavor are presented pH meter and “Minolta” color meter model in Table 2. It appeared that the mean total CM-3500d respectively. The sensory was solid of juice from Suphan Buri 50 was o evaluated using Hedonic scale test by at least 19.6 Brix, which was significantly higher than o 20 panelists who were the students in the that of the Singapore variety (12.1 Brix). department of Food Science and Technology, However, the average pH value of juices from Kasetsart University. The peroxidase activity both varieties were insignificant different test was conducted by putting the 5 drops of (average pH = 5.0 and 5.3 for Suphan Buri the juice sample into the enzyme test hole 50 and Singapore respectively). This went and then 2 drops of both the solutions of along with the result of Tangpremsri et al. [5] guaiacal 0.5% and hydrogen peroxide 0.3% who claimed that the total solid of juice from respectively [23]. After 30 s, the sample color Suphan Buri 50 was higher than Singapore. would change and be recorded. The Furthermore, the colors of the two varieties peroxidase enzyme is more heat stable than were significantly different. The color of juice polyphenol oxidase [11]. Therefore, if the from Suphan Buri 50 was darker (lower L*) peroxidase is inactivated, the polyphenol and more saturated (higher C*) than those of oxidase that is the key enzyme related to the Singapore. However, the juice from Singapore browning of sugarcane juice [14] would be variety was greener (higher h) than Suphan ceased as well. Buri 50. These results indicate the color The determination of the total solid features of juice from each sugarcane variety. 120 Chiang Mai J. Sci. 2011; 38(1) Importantly, the sensory test disclosed that Buri 50 variety was chosen for the following the flavor of juice from Suphan Buri 50 was experiments. significantly preferred. As a result, the Suphan After the varieties comparison, the results Table 2. The properties of sugarcane juice from Singapore and Suphan Buri 50 varieties. Color Sensory test Sugarcane variety Total solid result in o ( Brix) pH L* C* h aspect of flavor (7 = maximum) Singapore 12.1 0.4a 5.3 0.1a 55.8 0.02 a 9.1 0.11a 101.0 0.05 a 4.2 1.2a b a b b b b Suphan Buri 50 19.6 0.2 5.0 0.1 44.2 0.03 23.8 0.02 91.3 0.02 5.3 1.2 b Note: The color was measured in L* (lightness), C* (chroma) and h (hue). Total solid, pH, L*, C*, h and sensory test results are mean standard deviation. Means with the same superscript within same column are insignificant different (P < 0.05). of two pretreatment methods, blanching in L*, C* and h values could be observed among hot water and microwave heating are shown the samples pretreated by the steam blanching in Table 3. There were 30 panelists for this and microwave heating. The darker color of sensory evaluation. The peroxidase activity the juice from microwave-heated sugarcane test revealed that the color change happening can be explained by the fast heating rate inside in fresh juice from non-pretreated sugarcane the sugarcane stem occurring during the faster and more intense than those of microwave treatment. This heat expedited the pretreated samples. It means that the maillard reaction between the reducing sugar peroxidase activities in the sugarcane were and amino acid in the stem leading to the partially reduced by either blanching in hot browning or darker color [19]. For the juice water or microwave heating. Furthermore, preparation in the UHT experiments, the the color change for the peroxidase activity pretreatment by blanching sugarcane in hot o test in case of blanching the cane in hot water water at 80 C for 5 minutes was selected due was in the comparable rate and intense to the to its ease of control, lower energy and microwave heating. This result is similar to the equipment cost [16] but providing comparable Moreno et al. [13] who found that the enzyme enzyme inactivation level and juice quality to activities of strawberries after steam blanching the microwave pretreatment. and microwave heating were decreased to the The experimental results of the four similar levels. In terms of the total solid, pH UHT runs are presented in Table 4. The and sensory, there was insignificant difference sensory evaluation in this part was performed between juices squeezed from samples by 20 panelists. It was clear that the juice pretreated by these two methods. Nonetheless, sterilized at 140 C for 4 seconds was preferred the color of juice from microwave-heated to those of 135 oC for 10 seconds. Moreover, sugarcane was slightly darker (lower L*) and the juice without sugar flavor additive acquired greener (higher h) than those of hot-water the higher rating than the flavor-added juice. blanched sugarcane. Likewise, Moreno et al. In addition, the color of UHT processed juice [13] stated that merely small differences of significantly differed from the fresh Table 3. The properties of sugarcane juice from different heat pretreatments. Peroxidase activity test Total Color Sensory test result in aspect of flavor Pretreatment results solid (7 = maximum) (oBrix) pH Chiang Mai J. Sci. 2011; 38(1) The time Intensity level duration to of color L* C* h Color Flavor Taste Sweetness Overall change change (5 = liking color (s) maximum) Non- 10 5 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A pretreatment (1) Blanching in hot water 80 C 25 4 19.6 0.2a 5.0 0.1a 44.2 0.03a 23.8 0.02a 91.3 0.02a 5.2 1.1a 5.2 1.3a 5.3 1.3a 5.4 1.3a 5.4 1.2a for 5 minutes (2) Microwave heating for 5 25 4 18.9 0.6a 5.3 0.1a 39.5 0.09b 23.1 0.03b 94.0 0.12b 5.7 1.0a 5.1 1.2a 5.4 1.1a 5.7 1.1a 5.6 1.0a minutes Note: N/A = Not applicable The color was measured in L* (lightness), C* (chroma) and h (hue). Total solid, pH, L*, C*, h and sensory test results are mean standard deviation. Means with the same superscript within same column are insignificant different (P < 0.05). 121 122 Table 4. The properties of sugarcane juice from different UHT conditions. UHT condition Total Color Sensory test result (9 = maximum) Sample Sterilization Holding Adding solid pH Ap- Overall No. Temperature time flavor ( oBrix) L* a* b* pearance Aroma Color Taste Texture liking o ( C) (s) 1 140 4 No 12.1 0.4a 5.0 0.04 a 32.8 2.7 a,b 4.2 0.4a 19.2 0.5a 6.7 1.6a 6.9 1.7a 6.7 1.8a 6.9 1.7a 6.4 1.1a 7.1 1.4 a a b a,b a b,c a,b b a,b a,b a 2 140 4 Yes 11.9 0.5 4.5 0.01 32.1 0.8 4.5 0.1 18.2 0.1 5.9 1.8 5.4 1.8 5.9 1.8 5.9 2.1 6.3 1.3 6.1 1.4 b 3 135 10 No 11.0 1.1a 5.0 0.10 a 30.6 1.5a 4.2 0.2a 18.6 0.5a,c 4.9 1.3 b 4.9 2.1 b 5.0 1.6 b 4.5 2.2c 5.8 1.3a 4.9 1.5c 4 135 10 Yes 11.8 0.4a 4.5 0.01b 30.6 2.3a 4.4 0.3a 17.6 0.5 b 5.1 1.6 b 5.4 2.3 b 5.2 1.4 b 5.3 2.1 b,c 5.6 1.2a 5.0 1.5c a c b b c 5 Fresh juice No 11.8 0.5 5.2 0.05 34.6 0.3 2.9 0.1 18.4 0.1 N/A N/A N/A N/A N/A N/A Note: N/A = Not applicable The color was measured in L* (lightness), a* (redness) and b* (yellowness). Total solid, pH, L*, a*, b* and sensory test results are mean standard deviation. Means with the same superscript within same column are insignificant different (P < 0.05). Chiang Mai J. Sci. 2011; 38(1) Chiang Mai J. Sci. 2011; 38(1) 123 counterpart especially the redness (a*, +). Therefore, the flavor additive was deemed The redness of UHT processed juice was unnecessary in this case. higher than the fresh juice while the lightness (L*, +) was lower. The explanation was that ACKNOWLEDGEMENTS the heat during sterilization expedited the The authors would like to convey special maillard reaction between the reducing sugar thank to the Commercial Research and and amino acid in the juice leading to the Development Project Cooperated Between browning and degreening [19]. Moreover the Government and Private Sector, the Office degreening of UHT juice could be occurred of the Higher Education Commission, by the decrease in chlorophyll content [2] Thailand and the T.N. Sugar Industry Co.Ltd. during the sterilization. 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