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Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers, Original Paper Vol.33,No.3(2016),pp.267-272, doi: 10.11322/tjsrae.16-17NR_OA Received date: July 1, 2016; J-STAGE Advance publishied date: August 31, 2016 Effect of Freezing and Thawing on the Quality of Durian (Durio zibethinus Murray) Pulp

Jackie Lou TAGUBASE* Shigeaki UENO** Yumiko YOSHIE*** Tetsuya ARAKI*

*Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo (1-1-1 Yayoi, Bunkyo Ward, Tokyo, 113-8657) **Laboratory of Food Science, Faculty of Education, Saitama University (Shimo Okubo 255, Sakura Ward, Saitama, 338-8570) ***Department of Food Life Sciences, Toyo University (1-1-1 Izumino, Itakura-machi, Oragun, Gunma, 374- 0193)

Summary The effect of freezing, and iced and hot water thawing on the quality of durian pulp was investigated. Mature durian pulp was removed with seeds, vacuum-packed, and frozen at -20¡C. Thawing in iced water (~0¡C) and hot water (~90¡C) was then applied and the quality of the pulp was assessed based on physicochemical properties (pH, moisture content, soluble solids concentration (SSC), color, sugar content (sucrose, glucose, and fructose), and organic acid content (succinic acid and citric acid)), texture and smell profile. Overall, the freezing and thawing conditions, particularly the hot water thawing, posed an effect to the moisture content, color, and smell profile of the durian pulp. A significant increase in the moisture content, as well as a decrease in the color brightness was observed. Furthermore, the hot water-thawing process also induced slight variation to the smell attribute and strength of the entirety of smell. Although the sugar content significantly decreased after freezing and thawing, it was only affected by the freezing process but not by the thawing conditions. No significant variations were noted in the pH, SSC, organic acids and texture of the frozen durian pulp.

Keywords: Freezing, Thawing, Durian, Texture profile analysis, Smell analysis, E-nose

1. Introduction the Philippines, conventional freezing at -18 to - 20¡C using chest freezers is practiced by small-scale Durian (Durio zibethinus Murr.) is a native and entrepreneurs. While the vacuum packing and blast highly priced fruit in Southeast Asia due to its freezing at -40¡C and storage at -20¡C is applied by seasonality, unique smell, taste and texture. Its large-scale manufacturers. The current packaging of production and export are dominated by Thailand, frozen durian uses generic microwavable plastic and followed by Malaysia and Indonesia. On the wax paper to individually wrap durian pulp for average, the edible portion of the fruit is only 26% freezing. The frozen products are supplied in the of its weight and the composition of the rind and local market for direct consumption and for further 2) seeds are 60% and 14%, respectively. It is rich in processing of durian processors . carbohydrate, calcium, phosphorous, thiamin, Freezing is well known for keeping the quality of riboflavin, niacin, and ascorbic acid. Its unique smell foods at a longer period, however, there are still (volatiles) comes largely from thiols or thioethers, quality concerns associated with it depending on the 3) esters and sulphides. Ripe pulp is usually eaten raw, type and characteristics of the commodity . Studies right after opening the fruit or as a frozen have been reported for the quality changes related to commodity. It is also further processed to sweet the chemical and physicochemical properties, delicacies such as jams, candies, tarts, or used as a texture, color, and volatile profiles in frozen storage flavoring ingredient in ice cream and other of fruits such as apples, mango4), strawberry5), 6) 7) 8) products1). guava, passion fruit , peach , dates , and many Because of its seasonality, durian fruit processing others. On the other hand, thawing process is also is one of the means to absorb the excess supply important as it may further affect the food quality during peak season and also to widen its market. after freezing. Such in the study with strawberry Particularly, it is during this season of surplus yields frozen at -20¡C and thawed at 4¡C, which is a that producers look to the possibility of freezing the common practice, caused most pronounced pigment 9) durian pulp to preserve the excess supply and and ascorbic acid losses . provide durian during off-seasons. Moreover, In durian, researches are focused on the fresh and freezing contributes to the reduction of the bulk minimally processed fruit. Limited information is nature of the fruit and concealing its unique but provided for the quality changes in the frozen and strong and aroma during shipping and distribution1). thawed durian. Hence, this study aims to Frozen durian is achieved through individual quick investigate the effect of freezing and thawing freezing (IQF) technology and vacuum packing. In particularly on the physicochemical, textural and

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smell properties of durian pulp towards establishing Industries Co., Ltd, Tokyo) in L*, a* and b* mode. a thawing protocol for frozen durian. Preliminarily, The numerical values of a* and b* were converted the extreme thawing conditions are tested in this into hue angle (H¡ = tan-1 b*/a*). study. The iced water thawing (with temperature of approx. 0¡C), representing the slow process and hot 2.3.5 Sugar content water thawing (with temperature of approx. 92¡C) Ten g of durian pulp was blended with 100 ml of for the fast process. 85% methanol. In a steam bath, the mixture was heated for 30 min and filtered. The residue was re- 2. Materials and Methods extracted twice with 75 ml of 85% methanol. The collected supernatant was evaporated using a rotary 2.1 Durian samples and chemical reagents evaporator to remove the extraction solvent, and Durian fruits were procured from an online shop made up to 10 ml with deionized water. The that imports the fruit from Thailand, and stored in extracted sample was filtered through 0.22 µm filter cool (approx. 20~22¡C) area until the maturity is (FILSTAR Hydrophilic Nylon Syringe Filters, reached. The maturity was determined by the Starlab Scientific Co., Ltd, Shaanxi Province, China) appearance of crevices in the fruit rind. and 50 µL of the supernatant was injected to HPLC Pure grade chemical reagents such as the standards system with a refractive index detector (RID-10A, for sugar (sucrose, glucose, and fructose) and Shimadzu, Kyoto) at 1.0 ml min-1. The mobile phase organic acid (citric acid and succinic acid) analysis, was 5 mM aq H2SO4, and analytical column was methanol, and sulfuric acid were purchased from Shodex SUGAR SH-G (6 mm ID x 50 mm) (Showa Wako Pure Chemical Industries, Ltd., Osaka. Denko K.K., Tokyo) with column guard SH1821 (8.0 mm ID x 300 mm) (Showa Denko K.K., 2.2 Freezing and thawing Tokyo). Identification and quantification were The durian pulp was vacuum packed in a performed by comparison of sample peaks with polyamide nylon/polyethylene bag, and those of external standards' curve. conventionally frozen at -20¡C inside a home freezer (GS-3120HC, Freezer Co., Ltd., Tokyo) for one or 2.3.6 Organic acid content two weeks. The frozen samples were thawed using Five g of durian pulp was blended with 100 ml hot water (with temperature of approx. 92¡C) or iced deionized water and centrifuged (H-201FR, water (with temperature of approx. 0¡C) until the Kokusan Co. Ltd., Tokyo) at 4¡C, 12,000 g for 20 internal temperature reached around 10~15¡C (about min. The supernatant was filtered through 0.22 µm 3 min.) and -2~0¡C (about 30 min.), respectively. filter and 50 µL of the supernatant was injected to HPLC system attached with a UV-Vis detector 2.3 Physicochemical characteristics analysis (SPD-10A, Shimadzu, Kyoto) at 210 nm and 1.0 ml 2.3.1 Moisture content min-1 flow rate. The same mobile phase and columns Five g of durian pulp was dried in an oven set at with the sugar analysis were used. 105¡C for 3 h and equilibrated at room temperature inside a desiccator. The process was repeated until a 2.4 Texture analysis constant weight is obtained. The final weight was The Texture Profile Analysis of the durian pulp used to calculate the moisture content. was determined by a creep meter (Rheoner II, RE 2- 3305B, Yamaden Co. Ltd., Tokyo) under the texture 2.3.2 pH examination mode at 200 N load cell, 1 mm s-1 rate Ten g of durian pulp was homogenized (Poly Tron of measurement, 10 times amplitude and using 12 2100, Kinematica, Switzerland) with 100 ml mm (in diameter) plunger. The pulp was placed in a distilled water for 2-3 min and subjected to pH stainless container with 15 mm height and 40 mm determination using a compact pH meter diameter, and the hardness, cohesiveness and (LAQUAtwin, Horiba Ltd., Kyoto). adhesiveness were measured.

2.3.3 SSC 2.5 Smell analysis One part of durian pulp was blended with 3 parts of The smell/odor of the samples was analyzed using water and filtered using No.2 Whatman filter paper. e-nose (electronic nose) device (FF-2A Fragrance The soluble solids content (SSC) of the filtrate was and Flavor Analyzer, Shimadzu, Kyoto). Two point determined by a pocket refractometer (Atago, five g of durian pulp was contained in 20 ml Tokyo) and the reading was multiplied by 3 to give autosampler glass vial and crimp sealed. The vial SSC (%) at 20¡C. was then loaded in the tray and automatically transferred in the agitator or extraction control 2.3.4 Color apparatus (30¡C) attached to the sampling chamber The surface color of the durian pulp was measured of the e-nose. The headspace was extracted and through a ZE 2000 Color Meter (Nippon Denshoku pumped into the sensor chamber at injection volume

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of 2,500 µL and injector temperature of 110¡C. The types of food materials. It is either decreased or sample was measured in 3 trials. maintained after freezing and thawing. Such in the An e-nose is a device that evaluates and expresses case for apples and mangoes, wherein the water the quality and strength of the entirety of smell of content significantly decreased and did not vary, the samples. It works through a simulated respectively, after the freezing/thawing process4). organoleptic analysis, with its ability to detect and describe the similarities (by similarity index) of nine Table 1 Physicochemical properties of fresh and smell components (hydrogen sulfide, sulfurs, frozen-thawed (FT) durian pulp (N= 3-6) ammonia, amines, organic acids, aldehydes, esters, aromatics, and hydrocarbons) related to the smell of the samples (in absolute value). In this study, the Physicochemi Sample condition -cal property standard gases used were hydrogen sulfide (H2S), Fresh FT_Iced water FT_Hot water dimethyl disulfide (C H S ), ammonia (NH ), Moisture 2 6 2 3 64.83±0.89a* 62.62±1.34a** 67.67±1.05b trimethylamine (C3H9N), propionic acid (C3H6O2), content (%) butylaldehyde (C4H8O), butylacetate, C6H12O2), pH 6.61±0.16 6.83±0.06 6.88±0.20 toluene (C7H8), and heptane (C7H16). Meanwhile, the SSC (%) 24.42±1.35 21.70±6.01 19.70±0.61 strength of the smell is represented by an odor index means in row with different letters are significantly different at: equivalent value that is correlated to the *P < 0.05; ** P < 0.01 10,11) concentration of the smell . The device also measures this value. The moisture loss can be associated in the loss of Radar chart of the smell similarity index and the water holding capacity of the food material in analogue value of the odor index plot were effect to the disruption of the cell wall after the constructed to distinguish the similarity and strength formation of ice crystals during freezing. After of the smell of the fresh and frozen-thawed durian thawing, moisture can leak out of the cells resulting pulp. The analysis of the data was performed in drip loss. Different types of fruit have different through the ASmell2 software, built-in to the device. levels of drip loss such that apple and mango demonstrated the highest and lowest drip loss, 2.6 Statistical analysis respectively after freezing and thawing16). However, Mean values for the fresh and frozen thawed (iced the reverse was noted in the present study as shown and hot water) durian samples were statistically by the increase in moisture content following hot compared through ANOVA followed by Tukey water thawing. This variation might be due to the analysis for further test of significance. different levels of maturity of the samples upon processing, accounting to the inconsistency of the 3. Results and Discussion indicator for maturity (by the appearance of crevices in the fruit rind). On the other hand, the discordance 3.1 pH, moisture content, and SSC between the observed moisture contents of thawed The effect of freezing and different thawing durian pulp in iced water and in hot water can be conditions on the physicochemical properties of partly explained by their different thawing rates as durian pulp is presented in Table 1. The values the degree of thawing is directly correlated to the obtained are within the reported values in the increase in temperature. references for fresh durian, although variations can be attributed to the variety and maturity of the fruit. 3.2 Color Some Malaysian durian varieties have a pH range of 6.8-7.612,13). Meanwhile, Philippine durian varieties Table 2 Color measurements of fresh and frozen- have moisture content values of 62 - 84% depending thawed (FT) durian pulp (N = 6) on the period of harvest14). For Thailand varieties, 14% (immature) to 24% (mature) SSC values were Para- Sample condition reported15). meter Fresh FT_Iced water FT_Hot water As shown in Table 1, a significant change was only observed in the moisture content of the pulp L* 82.35±1.99a** 79.58±3.31ab 76.43±2.57b particularly after freezing and thawing using hot a* -1.04±0.47a* -0.27±0.73a** -2.34±0.80b water (FT_Hot water). In this condition, the b* 37.59±3.64a* 37.44±4.29a* 45.43±5.01b moisture content significantly increased after the ab a b** process. On the other hand, the moisture in iced H¡ 88.43±0.67 89.04±0.68 87.25±1.22 water thawed sample (FT_Iced water) did not means in row with different letters are significantly different at: significantly change with that of the fresh sample. * P < 0.05; ** P < 0.01 Previous studies revealed that the effect of freezing and thawing on the moisture content depends on the For the color of the durian pulp, as shown in Table 2, changes are prominent in hot water thawing

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condition than in iced water thawing. In general, the of the frozen durian, it is suggested to include the brightness (L*) has significantly reduced after drip during processing. freezing, regardless of the thawing method. Furthermore, the green (a*) and yellow (b*) hues Table 3 Organic acids content of fresh and frozen- were decreased following the hot water thawing. thawed (FT) durian pulp (N=5-6) Although no significant difference in the overall hue angle (H¡) was found between the hot water thawed Sample condition Organic acid and fresh samples, the difference in H¡ between the -1 FT_Iced FT_Hot (g kg ) Fresh iced and hot water thawed samples was statistically water water significant. These outcomes can be accounted to two Citric 4.12±2.03 2.82±0.26 4.08±0.70 possible reactions that must have taken place in the process: enzymatic activity and degradation of heat- Succinic 0.07±0.00 0.07±0.00 0.09±0.01 sensitive components of the fruit. Phytochemicals, such as carotenoid, polyphenol Table 4 Sugar content of fresh and frozen-thawed and anthocyanin, provide fruits and vegetables their (FT) durian pulp (N=5-6) 17) color . Polyphenols are known to be more sensitive to enzymatic browning reactions. After freezing, cell Sample condition decompartmentalized, permitting reactions between Sugar (g kg-1) FT_Iced FT_Hot enzyme activities and their corresponding substrates, Fresh water water such in the case for apple and mango freezing and a b b thawing wherein more pronounced color change (to Sucrose 46.34 ± 0.11 39.76 ± 1.31 37.90 ± 0.92 4) brown) was observed for apples than for mangoes . Glucose 12.00 ± 0.35a 8.57 ± 0.57b 9.08 ± 1.02b In frozen strawberries, polyphenoloxidases were a a a Fructose 9.01 ± 3.02 5.77 ± 0.33 6.95 ± 0.78 mainly made responsible for anthocyanin means in row with different letters are significantly different at P degradation in the fruit. With this assumption, < 0.01 considerable pigment losses were reported after freezing and thawing of strawberries18). It can be 3.4 Texture assumed that these reactions might have also In Table 5, it can be noted that freezing and occurred after freezing and thawing of durian pulp thawing did not significantly affect the texture of since it has been reported that the fruit contains the durian pulp based on the parameters tested. This substantial amount of phytochemicals, especially the result is in contrast to reports that generally, freezing polyphenols and anthocyanins19,20). and thawing caused reduction in the texture Meanwhile, the changes in the color can be also (firmness) of fruits due to the damaged cell structure associated with heat sensitive components in the and colloidal systems after the formation of ice fruit. Wherein the extent of effect depends on the crystals. The maturity of the durian sample can be heat sensitivity of the product component21). β- the reason for the slight variation in the texture carotene is the main contributor to the yellow color profile. It has been reported that variety and maturity of durian pulp22). In a study on the thermal of fruits minimized the effect of freezing in its processing of tomato, a significant decreased in its textural properties. A higher maturity reduced the β-carotene content after 2 min boiling was reported degradation observed on firmness following 23). freezing. Such in the frozen apple of the same variety, the ripe exhibited firmness degradation 3.3. Sugars and organic acids about two times lower than that of the unripe7). Table 3 and 4 present the changes in the organic acid and sugar content of the fresh and frozen- Table 5 Texture profile analysis for fresh and thawed durian pulp, respectively. In the data, frozen-thawed (FT) durian pulp (N=6) freezing and thawing did not affect the organic acids analyzed. However, the sugar content was generally Sample condition Parameters FT_Iced FT_Hot affected by freezing but not by the thawing method. Fresh After freezing, the sugars, particularly sucrose and water water glucose, were significantly reduced. These may Hardness (N) 0.89±0.33 0.92±0.30 0.78±0.26 have dissolved in the liquid that exuded from the Cohesiveness 0.24±0.26 0.38±0.22 0.28±0.24 Adhesiveness pulp (drip). As the cell wall is degraded due to ice 3 339.22±291.1 546.18±200.7 460.2±213.1 crystal formation after freezing, this facilitates (J/m ) extraction of soluble solid extraction (especially sugars) from cells 4). Moreover, freezing and high 3.5 Smell analysis temperature thawing caused the hydrolysis of To qualitatively assess the effect of freezing and sucrose 18). To avoid sugar loss in further processing different thawing conditions to the smell quality of the durian pulp, a radar chart on the similarity index

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of smell was constructed (Fig.1). The chart revealed 4. Conclusion the slight variations in the smell quality of the fresh and frozen-thawed samples. Particularly, in hot The effect of freezing and different thawing water thawing, the variations were observed in the conditions on the physicochemical, textural, and aldehyde, organic acid, and hydrocarbon aromatic attributes of durian was evident in this components of the pulp, although they were not study. Overall, the freeze-thawing conditions have a statistically significant. significant impact on the moisture content, color, Moreover, during sample preparation, stronger sugar content, and aroma profile of the durian pulp. smell was qualitatively observed after thawing the The moisture content of the pulp increased while the frozen samples compared to the fresh samples. In brightness of the pulp color decreased significantly this connection, it can be inferred in Fig.2 that the after hot water thawing. However, it is also smell strength of the durian pulp slightly increased necessary to consider the effect of maturity of the after hot water thawing. The difference can be fruit on the observed change in the moisture content attributed to the disruption of the cell structure of the of the samples. Meanwhile, for the organic acid and fruit during freezing causing the release of its sugar contents, generally, the sugar content was volatile components. The application of heat during affected by the freezing process but not by the thawing could also have contributed to the faster thawing conditions. The sugar content was diffusion of volatile compounds from the fruit. significantly decreased after freezing and thawing. In studies related to the analysis of the volatile Furthermore, the smell profile and strength of the components of durian, mostly esters, acids, and frozen and thawed durian pulp is generally affected sulfur containing compounds were detected24,25,26). It by hot water thawing according to the radar plot of is thus suggested to conduct the aroma profiling of smell similarity index and odor index plot, fresh and frozen-thawed durian by other analytical respectively. No significant variations were noted in methods such as gas chromatography-mass the pH, SSC, organic acids and texture of the durian spectrometry (GC-MS) to verify and identify the pulp after freezing and thawing. With these, the specific compounds that altered during processing. study is worthy of further investigation to provide relevant basic knowledge on the quality changes of durian after freezing and thawing. Other thawing conditions in between iced and hot water can be 8 explored to determine the condition under which the 6

4 quality variations occur. In addition, literatures reported that variety and maturity could cause 2

0 variation on the effect of freezing in the fruit, thus it would be also an interesting area for further study of durian. Lastly, correlation of the quality changes to consumer sensory evaluation would also be relevant to the frozen durian industry.

5. Acknowledgment

This work was partially supported by JSPS Fig. 1 The similarity index of the smell of the fresh KAKENHI 25350091. and frozen-thawed durian. 6. References

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