Effect of blanching and drying temperatures on the

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International Journal of Food Sciences and Nutrition, November 2010; 61(7): 702–712

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Effect of blanching and drying temperatures on the physicochemical characteristics, dietary fiber composition and antioxidant-related parameters of dried persimmons peel powder

MST. SORIFA AKTER, MARUF AHMED & JONG-BANG EUN Department of Food Science and Technology and Institute of Biotechnology, Chonnam National University, Gwangju, South Korea

Abstract The effects of blanching with hot water at 90 C for 2 min and hot-air drying temperatures (50 C, 60 C and 70 C) on the physicochemical properties, dietary fiber compositions, antioxidant activity and hydration properties of ripe, soft persimmon peels were investigated. Blanching and drying significantly reduced the retention of antioxidant-related parameters. Although there were no significant differences in total phenolics and b-carotene content at different drying temperatures for both dried unblanched and blanched peels, dried blanched peels had higher dietary fiber compositions and swelling capacity than those of dried unblanched peels at all drying conditions. In addition, blanched peels dried at 50 C had the highest dietary fiber compositions, swelling capacity and antioxidant activity compared with those at high drying temperatures (60 C and 70 C). Therefore, blanched peels dried at 50 C is suggested to obtain better quality dietary fiber powder from persimmon peel for use in food applications or in fiber-fortified foods for health promotion.

Keywords: Persimmon peel, blanching, hot-air drying, dietary fiber, water retention capacity, swelling capacity

Introduction Persimmon is a good source of nutritional antioxidative vitamins, polyphenols, and dietary fiber; these components are probably involved in the reduction of degenerative human diseases due to their antioxidative and free radical scavenging properties (Kim et al. 2006). The contents of these important components are higher in the peel than in the pulp (Gorinstein et al. 1998). In Korea, persimmon has been traditionally used for many medicinal purposes to treat ailments such as paralysis, frostbite, and burns, and to stop bleeding (Kim et al. 2005). Persimmon peel is discarded during the manufacture of dried persimmon product, even though it contains high levels of antioxidants and bioactive compounds (Yokozawa et al. 2007). Several antioxidants and dietary fiber have already been isolated from the peel of a wide variety of fruits including banana, rambutan, passion fruit, dragon fruit, mangosteen, coconut, long-gong

Correspondence: Jong-Bang Eun, Department of Food Science and Technology, Chonnam National University, 77 Yongbong-ro Buk-gu, Gwangju, 500-757, South Korea. Tel: +82 62 530 0255. Fax: +82 62 530 2149. E-mail: [email protected] ISSN 0963-7486 print/ISSN 1465-3478 online  2010 Informa UK, Ltd. DOI: 10.3109/09637481003757852

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(Okonogi et al. 2007), orange (Fernandez-Lopez et al. 2009), mango (Ajila et al. 2007), apple (Wolfe et al. 2003), and grape (Llobera and Canellas 2008). Peels are the major by-products obtained during the processing of various fruits and are good sources of polyphenols, carotenoids, and other bioactive compounds that have various beneficial effects on human health (Yokozawa et al. 2007). Persimmon peel dietary supplements showed hypocholesterolemic and antioxidative effects in rats (Gorinstein et al. 1998). Persimmon peel polyphenol contributes to the prevention of oxidative stress-related diseases including diabetes, and suggests the potential use of persimmon peel as a functional food (Yokozawa et al. 2007). Previously, many studies have shown that the processed fruit by-products are rich in dietary fibers (Larrauri 1999; Figuerola et al. 2005; Garau et al. 2007; Wachirasiri et al. 2009; Marin et al. 2007; Happiemaga et al. 2008). Blanching and drying are the common steps to obtain high dietary fiber powder from fruit by-products. During processing, blanching is usually performed before drying to inactivate enzymatic reactions (Larrauri 1999). In order to obtain a nonperishable product that is easy to use, the persimmon peels can be dried and ground into powder. Indeed, persimmon peel powder could be used to enhance food products through its nutrients, dietary fibers and natural antioxidants. Therefore, the objective of the present study was to investigate the effects of blanching and drying temperatures on the physicochemical properties and dietary fiber components of ripe soft persimmon peel and to evaluate the influence of drying temperatures on the functional properties. Materials and methods Sample preparation Persimmons (Diospyros kaki L. cv. Daebong) were purchased from a local farm in South Korea and selected on the basis of skin color, uniformity and size. The fruits were then kept to ripen at room temperature (20 C). After harvesting persimmon, it takes 3 weeks to use as a sample. The peels were removed and collected whereas the pulps were sieved to make puree. The peels were then chopped into small pieces using a stainless steel knife. The peels were subsequently blanched and dried with hot air as follows. A portion of the peels was blanched in water at 90 C for 2 min with the ratio of peels to water of 1:2 in the water bath; the other portion was not blanched. Excess water was subsequently drained off the blanched peels, which were allowed to cool at room temperature. Both blanched and unblanched peels were dried in a hot-air drier (Dasol Scientific Co. Ltd, Seoul, Korea) . The drying conditions were temperatures of 50 C, 60 C and 70 C, air flow rate of 5–6 ft/sec, dimensions of 195  195  80 mm3 (length  width  height), and a tray load of 0.7–1.0 kg/m2. The peels were dried until reaching a final moisture content of 3–4%, then ground with a blender (FM-681C; Hanil, Gwangju, Korea) and sieved through a 60-mesh (Chung-gye sang-gongsa, Seoul, Korea) screen to obtain peel powder.

Proximate composition analysis Moisture, crude protein, crude lipid and ash content were determined by the official AOAC methods (AOAC 2000).

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Hunter color values The color attributes (Hunter L*, a* and b* values) were measured with a spectrophotometer (CM-3500d; Minolta, Japan) . In addition, the total color difference (DE) and Hue angle (Ho) were calculated using the following equations:

DE = [(a ∗ − ao )2 + (b∗ − bo )2 + (L∗ − Lo )2 ]0.5 where Lo, ao and bo are the color values for fresh peel.

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H o = tan −1(b * / a * )

Determination of total phenolic content Total phenolic contents were determined with the Folin–Ciocalteau method (Swain and Hillis 1959). The sample (1 g) was extracted three times with 20 ml of 75% methanol and filtered through Whatman No. 2 filter paper. Extracts were combined and concentrated in a rotary vacuum evaporator (Rikakikai Co. Ltd, Tokyo, Japan) at 40 C; the volume was then adjusted to 20 ml with 75% methanol. One milliliter of extract, 5 ml distilled water and 2 ml of 10% Folin–Ciocalteau reagent were added into a falcon tube. After 3 min at room temperature, 2 ml of 7.5% Na2CO3 solution was added and the sample was diluted to 20 ml with distilled water. Each sample was allowed to stand for 1 h at room temperature and was measured at 760 nm (UV-1201; Shimadzu, Japan) . The total phenolic content was calculated on the basis of calibration curves of gallic acid and was expressed as milligrams of gallic acid per 100 g. Determination of total antioxidant activity The total antioxidant activity was measured according to the method described by Bhandari and Kawabata (2004). The sample (1 g) was extracted with ethanol and then filtered through Whatman No.1 filter paper. The reaction mixture contained peroxidase (4.4 units/ml; Sigma, St. Louis, MO, USA), H2O2 (50 mM; Merck, Merck Co., Darmstadt, Germany), and 2,2-azino-bis (3-ethyl-benz-thiazoline-6-sulfonic acid) (100 mM; Sigma) in a total volume of 1 ml. Persimmon peel ethanol extract (0.2 ml) was added to the reaction mixture and the decrease in absorbance was determined after reacting for 8 min at 730 nm (UV-1201; Shimadzu). The total antioxidant activity was calculated as follows:

Total antioxidant activity (%) = [1 − ( A730 nm , sample /A730 nm , control )] × 100

Determination of ascorbic acid content The ascorbic acid content was determined according to a slightly modified method described by Doner and Hickts (1981). The sample (2 g) was mixed with 10 ml of 5% metaphosphoric acid solution and extracted by vortexing at room temperature for 1 min. The mixture was centrifuged for 15 min at 3,000  g and the supernatant was filtered through a 0.45-mm PVDF syringe filter; 20 ml sample was then injected onto the liquid chromatograph. Ascorbic acid was separated on an ODS

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C18 column (4.6  250 mm2; YMC Inc., Kyoto, Japan) using a gradient mobile phase of acetronitrile:0.005 M KH2PO4 (60:40 v/v) (solvent A), and 100% high-performance liquid chromatography water (solvent B) was used according to the following program: linear increment starting with 5–22% solvent A in 6 min and the return to the initial conditions within next 9 min with a flow rate of 1 ml/min. The detection wavelength was 254 nm. The ascorbic acid content was calculated by comparing the peak area at 254 nm with those of standard solutions and expressed as milligrams per 100 g.

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Determination of b-carotene content The b-carotene content was determined using the modified method of Park (1987). The sample (1 g) was extracted with a mixture of hexane and acetone (7:3, 25 ml). The extract was filtered through a Buchner funnel with Whatman No. 1 filter paper. The residue was re-extracted until it became colorless. The filtrates were combined in a separatory funnel and washed with 50 ml distilled water. The water phase was discarded and Na2SO4 was added as desiccant. The hexane phase was transferred to a volumetric flask. The concentration of carotene in the solution was determined from the absorbance at 450 nm (UV-1201; Shimadzu). The b-carotene content was determined from the standard curve prepared for b-carotene. Determination of dietary fiber compositions Dietary fiber compositions (soluble, insoluble and total fibers) were determined according to method 991.43 of the AOAC (2000). Determination of hydration properties The water retention capacity (WRC) and the swelling capacity (SWC) were determined according to the procedures recommended by Robertson et al. (2000). The sample (1 g) was hydrated in 30 ml distilled water at room temperature (30 C). After equilibration for 18 h, the sample was centrifuged at 3,000  g for 20 min. The supernatant was discarded and the residue was dried at 105 C until a constant weight was obtained. The WRC was calculated by the following equation:

WRC (g/g) = [residue fresh weight (g) − residue dry weight (g)]/residue dry weight (g) A sample (0.2 g) was hydrated in 10 ml distilled water in a calibrated cylinder (1.5 cm diameter) at room temperature (30C). After equilibration for 18 h, the bed volume was recorded. The SWC was calculated by the following equation:

SWC (ml/g) = volume occupied by sample (ml)/original sample dry weight (g)

Statistical analysis Results are expressed as mean values ± standard deviations. Data were statistically analyzed (SPSS for Windows version 14.0) by one-way analysis of variance. Mean comparisons for treatment effects at different drying temperatures were performed using Duncan’s multiple range tests for significant effect at P < 0.05.

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Results and discussion

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Proximate composition The proximate compositions of ripe soft persimmon peels treated under different process conditions are presented in Table I. The moisture, protein, lipid, ash and carbohydrate content in fresh peel were 86.28, 0.45, 0.24, 0.22 and 12.81 g/100 g fresh weight, respectively. An increase in protein, lipid and carbohydrate contents and a decrease in moisture and ash contents were observed after blanching. These results were similar to those of persimmon fruit as reported by Gorinstein et al. (2005). After drying, the moisture, protein, lipid, ash and carbohydrate contents of dried unblanched and blanched peel ranged from 3.43 to 8.29, from 2.08 to 3.28, from 2.76 to 3.18, from 0.96 to 1.39 and from 92.44 to 94.06 g/100 g dry weight, respectively. These results were consistent with the previous report of dried persimmon (D. kaki L. cv. Sangjudungsi) peel (Lee et al. 2006). Hunter color values Table II summarizes the Hunter color values (L*, Ho and DE) of ripe soft persimmon peels under different processing conditions. The L* and Ho values in fresh peel were 38.74 and 53.61, respectively. A higher L* value and the lower Ho value were observed after blanching. The increased L* value might be due to the inactivation of enzymes during blanching, and the reduced Ho value due to the leaching of reducing sugar and b-carotene content (Pedreschi et al. 2005). The L* and Ho values increased after drying as compared with their not-dried counterparts. In addition, dried peels had higher DE values compared with blanched peel. This might be due to the effect of drying temperatures on heat-sensitive compounds such as carbohydrates and vitamins (Vega-Galvez et al. 2009). There were no significant differences in L*, Ho and DE values at different drying temperatures for dried unblanched and blanched peels.

Table I. Effects of blanching and drying temperatures on proximate composition of ripe soft persimmon peel. Composition (g/100 g) Persimmon peel

Moisture

Protein

Lipid

Ash

Carbohydratea

Freshb Blanchedc Unblanched and dried at 50 C Dried at 60 C Dried at 70 C Blanched and dried at 50 C Dried at 60 C Dried at 70 C

86.28 ± 0.05C 84.00 ± 0.68B 8.29 ± 0.05A

0.45 ± 0.02A 0.55 ± 0.02B 2.28 ± 0.09D

0.24 ± 0.14A 0.38 ± 0.06B 2.76 ± 0.03C

0.22 ± 0.03A 0.20 ± 0.03A 1.39 ± 0.24C

12.81 ± 0.54A 14.87 ± 0.30B 93.55 ± 0.31C

6.01 ± 0.01A 4.24 ± 0.03A 6.39 ± 0.04A

2.16 ± 0.02CD 2.08 ± 0.09C 3.28 ± 0.03E

2.77 ± 0.02C 2.80 ± 0.15C 3.18 ± 0.22D

1.02 ± 0.25B 1.02 ± 0.15B 1.08 ± 0.03BC

94.05 ± 0.17C 94.06 ± 0.20C 92.44 ± 0.70C

5.11 ± 0.05A 3.43 ± 0.08A

3.20 ± 0.09E 3.14 ± 0.10E

3.08 ± 0.34D 3.04 ± 0.04D

1.00 ± 0.03B 0.96 ± 0.04B

92.71 ± 0.18C 92.85 ± 0.51C

Data expressed on a dry weight basis, except fresh and blanched peel, as mean ± standard deviation of three determinations. Means followed by different uppercase superscript letters in each column are significantly different (P < 0.05). aDefined as the residue excluding moisture, protein, lipid and ash (= 100 – moisture – protein – lipid – ash). bFresh persimmon peel. cBlanched persimmon peel without drying.

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Ripe soft persimmon peel Table II. Effects of blanching and drying temperatures on color of ripe soft persimmon peel. Persimmon peel a

38.74 44.53 54.41 54.05 53.80 55.84 54.44 55.00

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Fresh Blanchedb Unblanched and dried at 50 C Dried at 60 C Dried at 70 C Blanched and dried at 50 C Dried at 60 C Dried at 70 C

± ± ± ± ± ± ± ±

DE

Ho

L* A

0.62 0.54B 0.35CD 0.14C 0.09C 0.27D 0.55CD 0.53CD

53.61 52.10 59.33 60.29 61.15 59.87 59.03 60.33

± ± ± ± ± ± ± ±

B

0.40 0.05A 0.23C 0.28CD 0.03D 0.14C 0.28C 0.47CD

7.05 16.74 16.58 16.52 18.01 17.43 17.34

– ± ± ± ± ± ± ±

0.15B 0.09C 0.14C 0.14C 0.37C 0.10C 0.37C

Data expressed as mean ± standard deviation of three determinations. Means followed by different uppercase superscript letters in each column are significantly different (P < 0.05). aFresh persimmon peel. bBlanched persimmon peel without drying.

Ascorbic acid, total phenol, b-carotene content and total antioxidant activity The ascorbic acid, total phenol, b-carotene content and total antioxidant activity in ripe soft persimmon peels under different processing conditions are presented in Table III. The ascorbic acid content in fresh peel was 210.00 mg/100 g dry weight. The 48.87% loss in ascorbic acid content was observed after blanching. This could be attributed to the fact that ascorbic acid is very soluble in water and, at the same time, it is not stable at high temperature (Negi and Roy 2000). The degradation of ascorbic acid also occurred during drying. After drying, the dried unblanched peels had higher ascorbic acid content than that of blanched peels. The ascorbic acid content in dried unblanched and blanched peel ranged from 14.86 to 21.59 and from 9.98 to 12.02 mg/100 g dry weight, respectively. The ascorbic acid content was lower at a higher drying temperature. The maximum loss of 95.25% ascorbic acid content was observed in blanched peel dried at 70 C. The drying temperature had a detrimental effect on the retention of ascorbic acid, since heated air inherently exposes the products to oxidation, reducing their ascorbic acid content. Vega-Galvez et al. (2009) observed 98.20% losses in ascorbic acid content during red pepper drying at 90 C. Table III. Effects of blanching and drying temperatures on ascorbic acid, total phenolics, b-carotene content and total antioxidant activity of ripe soft persimmon peel. Parameter

Persimmon peel Fresha Blanchedb Unblanched and dried at 50 C Dried at 60 C Dried at 70 C Blanched and dried at 50 C Dried at 60 C Dried at 70 C

Ascorbic acid (mg/100 g)

Total phenolics (mg/100 g)

b-carotene (mg/100 g)

Antioxidant activity (%)

210.00 ± 0.72H 107.37 ± 0.13G 21.65 ± 0.07F

228.32 ± 0.85D 175.87 ± 0.29C 21.56 ± 0.35B

2101.53 ± 5.60B 1779.18 ± 3.83A 322.36 ± 1.98C

67.80 ± 0.24H 65.42 ± 0.33G 58.02 ± 0.37F

19.86 14.86 12.02 10.86 9.98

± ± ± ± ±

0.11E 0.14D 0.18C 0.23B 0.26A

20.18 20.35 15.86 15.03 15.44

± ± ± ± ±

0.28B 0.39B 0.24A 0.38A 0.11A

309.20 304.73 309.60 304.14 302.02

± ± ± ± ±

2.29C 2.18C 1.47C 1.97C 1.04C

50.06 45.29 56.09 42.00 40.04

± ± ± ± ±

0.27D 0.44C 0.21E 0.30B 0.23A

Data expressed, on a dry weight basis, as mean ± standard deviation of three determinations. Means followed by different uppercase superscript letters in each column are significantly different (P < 0.05). aFresh persimmon peel. bBlanched persimmon peel without drying.

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The total phenolic content in fresh peel was 228.32 mg/100 g dry weight, which was much higher than in Maekawa-jiro (18.4 mg/100 g dry weight) and Matsumoto-wasefuyu (14.8 mg/100 g dry weight) persimmon fruit (Suzuki et al. 2005). A significant (22.97%) decreased of total phenolic content was observed after blanching. Similar results were obtained from other authors for carrot peel and cabbage during blanching with hot water (Chantaro et al. 2008). This was probably due to leaching into the water or to chemical oxidation (Garau et al. 2007). The results showed that total phenolic content decreased after drying. However, there were no significant differences in total phenolic content at different drying temperatures for both dried unblanched and blanched peels. It was found that dried unblanched peel had higher total phenolic content than the dried blanched peel. This could be due to the changes in the phenolic compositions and contents that might occur during blanching and drying (Guan et al. 2005). b-Carotene contents in fresh peel were 2101.53 mg/100 g dry weight or 288.33 mg/ 100 g fresh weight, which was higher than that in Fuyu persimmon fruit (158 mg/100 g fresh weight) as reported by Wright and Kader (1997). The b-carotene content was significantly decreased after blanching. The 15.33% loss of b-carotene content was observed during blanching. This might be due to leaching of b-carotene (Negi and Roy 2000). A significant loss of b-carotene content was observed in both dried unblanched and blanched peels as compared with their not-dried counterparts. A maximum loss of 85.62% b-carotene content was observed during blanching and drying at 70 C. The b-carotene contents of dried unblanched peels were 304.73–322.36 mg/100 g dry weight whereas dried blanched peels were 303.79–309.60 mg/100 g dry weight. However, the values were not significantly different. These values were lower than that found in dried persimmon peel (340.60 mg/100 g dry weight) as reported by Lee et al. (2006). This might be explained due to the different variety of persimmon and operating conditions were used. In the present study, the total antioxidant activity in fresh peel was 67.80%. The degradation of total antioxidant activity was observed after blanching and drying. The total antioxidant activity was higher at a lower drying temperature in both dried unblanched and blanched peel. The blanching process reduced the total antioxidant activity of 3.5%, whereas a maximum loss of 40.94% was observed in dried blanched peel (at 70 C). The decrease in the antioxidant activity was attributed to the loss of the total phenolic and ascorbic acid contents. Dietary fiber compositions Table IV presents the effects of blanching and drying temperatures on the dietary fiber composition of ripe soft persimmon peel. Total dietary fiber (TDF) in fresh persimmon peel was 16.77 g/100 g dry weight. A significant (16.27%) increase of TDF was observed after blanching. Low-molecular-weight components such as minerals, vitamins and sugars might be lost from the plant cells into the blanching water, leading to a relative increase in the dietary fiber contents (Wenberg et al. 2006). The TDF in dried unblanched and blanched peel ranged from 70.85 to 71.02 and from 81.01 to 81.15 g/ 100 g dry weight, respectively. This value was higher than that of Ruby grape and Fino lemon peel (62.6 and 68.3 g/100 g dry weight, respectively) as reported by Figuerola et al. (2005). However, it was lower than that of apple pomace (89.8 g/100g dry weight) and banana peel (83.0 to 89.35 g/100g dry weight) as observed by Figuerola et al.

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Table IV. Effects of blanching and drying temperatures on IDF, SDF, and TDF content of ripe soft persimmon peel. Parameter (g/100 g dry weight) Persimmon peel

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a

Fresh Blanchedb Unblanched and dried at 50 C Dried at 60 C Dried at 70 C Blanched and dried at 50 C Dried at 60 C Dried at 70 C

IDF 15.37 17.63 66.80 66.74 66.94 75.55 75.67 75.47

± ± ± ± ± ± ± ±

SDF A

0.18 0.20B 0.34C 0.22C 0.31C 0.28D 0.66D 0.16D

1.40 1.87 4.10 4.11 4.08 5.60 5.47 5.53

± ± ± ± ± ± ± ±

TDF A

0.20 0.10B 0.18C 0.52C 0.46C 0.20D 0.24D 0.12D

16.77 19.50 70.90 70.85 71.02 81.15 81.14 81.01

± ± ± ± ± ± ± ±

0.13A 0.17B 0.58CD 0.31CD 0.22D 0.60E 0.51E 0.20E

Data expressed as mean ± standard deviation of three determinations. Means followed by different uppercase superscript letters in each column are significantly different (P < 0.05). aFresh persimmon peel. bBlanched persimmon peel without drying.

(2005) and Wachirasiri et al. (2009), respectively. The result showed that most of the dietary fiber in persimmon peel was in the form of insoluble dietary fiber (IDF). IDF constituted 90–94% of TDF. It was already reported that IDFs were found to be the major fiber fraction in the pomace and agricultural by-products of many other fruits and vegetables (Grigelmo-Miguel and Martin-Belloso, 1999). The increase in IDF could be due to breakdown of cell wall structure, or due to retrograde starch formation by the action of heat or dehydration during processing (Viswanathan et al. 2000). Both dried unblanched and blanched peel had more than 50% TDF. According to Larrauri (1999), it could be considered rich sources of dietary fiber. On the other hand, according to the recommendation of Spiller (1986), the IDF:soluble dietary fiber (SDF) ratio should be in the range of 1.0–2.3 in order to obtain the physiological effects associated with both the soluble and insoluble fractions. However, IDF was a larger fiber fraction than SDF and the ratio of IDF:SDF was much higher (9–16). Similar results were found in dried persimmon peel and other cereal by-products as reported by Lee et al. (2006). Hydration properties The effects of blanching and drying temperatures on the WRC and the SWC of ripe soft persimmon peel are shown in Figure 1. The WRC of dried unblanched and blanched peel ranged from 5.67 to 6.69 g/g dry weight. However, these values were not significantly different from each other. The SWC of dried unblanched and blanched peel ranged from 7.18 to 8.47 ml/g dry weight. This result was in agreement with the SWC of Ruby grape and Liberty apple fiber (Figuerola et al. 2005). The SWC of dried blanched peels was higher than that of unblanched peels at all drying temperatures. This could be due to the loss of some components during blanching with water, and the changes of structural tissues might enhance the water uptake. Conclusion In the present study, the effect of blanching and hot-air drying temperatures on the physicochemical characteristics, dietary fiber compositions and antioxidant-related

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A

b

b b

ab

ab

a

6 5

Unblanched

4

Blanched

3 2 1 0 50

60

70

Drying temperature ° C 9

B

f SWC mL/g dry weight

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WRC g/g dry weight

7

e

8.5 8

d c b

7.5

a Unblanched

7

Blanched

6.5 6 50

60 Drying temperature ° C

70

Figure 1. Effects of blanching and drying temperatures on hydration properties of ripe soft persimmon peel. (a) Water retention capacity (WRC) and (b) swelling capacity (SWC). Means followed by different superscript letters in each column are significantly different (P < 0.05).

parameters of ripe soft persimmon peels were evaluated. Both blanching and drying improved dietary fiber compositions, color values (L* and DE) and hydration properties. However, blanched and dried peels had lower amounts of antioxidant-related parameters such as ascorbic acid, total phenolic content, b-carotene content and antioxidant activity as compared with fresh peels. Although there were no significant differences in total phenolic and b-carotene contents at different drying temperatures for both dried unblanched and blanched peels, dried blanched peels had higher dietary fiber compositions and swelling capacity than those of dried unblanched peels at all drying conditions. In addition, dried blanched peels had higher antioxidant-related parameters and antioxidant activity at 50 C than those at high drying temperatures (60 C and 70 C). Therefore, blanched peels dried at 50 C are suggested to obtain better quality dietary fiber-rich powder from persimmon peels, which could be used as a fiber supplement in the food industries.

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Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

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