Effects of a Combined Treatment of Hot Water with Green ...

ISSN 1226-8763

Kor. J. Hort. Sci. Technol. 33(3):364-374, 2015 http://dx.doi.org/10.7235/hort.2015.14042

Research Report

Effects of a Combined Treatment of Hot Water with Green Tea Extract and

NaCl on the Postharvest Quality of Fresh-cut Burdocks

Min-Sun Chang and Gun-Hee Kim*

Department of Food and Nutrition, Duksung Women’s University, Seoul 132-714, Korea

Abstract: This study investigated quality changes in fresh-cut burdocks treated with hot water and anti-browning agents. The

combined treatment using both heat treatment and anti-browning agents delayed the browning of burdocks, especially for those

dipped in hot water and a solution of green tea extract plus NaCl. This treatment reduced the respiration rate and inhibited

the growth of microorganisms more than heat treatment alone. The organoleptic quality of burdocks treated with the combined

method proved to be the best according to sensory evaluation. Hence, this combined treatment using heat and anti-browning

agents can enhance overall quality of processed fresh-cut root vegetables by browning inhibition and shelf-life extension.

Additional key words: antioxidant, browning, heat treatment, shelf life

*Corresponding author: [email protected]

※ Received 10 March 2014; Revised 26 August 2014; Accepted 5 September 2014. This work was carried out with the support of “Cooperative

Research Program for Agriculture Science and Technology Development (PJ0074812012)” Rural Development Administration, Republic of

Korea and in part from the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the

Ministry of Education Science and Technology (2009-0094017).

Ⓒ 2015 Korean Society for Horticultural Science

Introduction

The popularity of minimally-processed vegetables has

been increased due to not only their health benefits as

the fresh produce, but also the consumer demand as the

convenience fresh-cut products. Fruits and vegetables are living

organisms showing quick quality losses due to physiological

aging, biochemical changes, increase in respiration rate,

and the proliferation of microorganisms during processing

and distribution (Martin-Belloso et al., 2007). In particular,

the browning on the surface from cutting and peeling causes

the quality loss for fruits and vegetables (Lunadel et al.,

2011; Pristijono et al., 2006). It has been variously approached

to prevent the browning of fresh-cut fruits and vegetables,

such as citric acid, ascorbic acid (Sapers and Miller, 1998;

Dong et al., 2000), and oxalic acid (Son et al., 2001) as the

reducing agent, and calcium. In addition, sulfite-containing

additives have been extensively used as anti-browning

agents to keep vegetables and fruits looking fresh. However,

consumer awareness of the risks associated with sulfites

and increased regulatory scrutiny has created the urgent

need for substituting those chemical treatments (Iyengar

and McEvily, 1992).

Green tea (Camellia sinensis L.) is a popular beverage

exerting the beneficial effects on several diseases due to

their antioxidant, anticancer, and antimicrobial activities

(Si et al., 2006; Rietveld and Wiseman, 2003; Cooper et

al., 2005). Green tea is an excellent source of polyphenols,

natural antioxidants used as alternatives to synthetic anti-

oxidants (Martín-Diana et al., 2008). These antioxidants,

which inhibit the oxidation of organic molecules, are very

important for food preservation (Masuda et al., 2003).

Green tea has been used to extend the shelf-life of candy

jellies (Gramza-Michalowska and Regula, 2007) and cooked

pork patties (Nissen et al., 2004). However, only a few

studies can be found on the use of green tea in fresh-cut

fruits or vegetables. NaCl is a food preservative and commonly

used in most culinary habits. It binds water satisfactorily,

thus rendering it unavailable for microbial growth on food

products (Ehabe et al., 2006). In addition, it has been used

Min-Sun Chang and Gun-Hee Kim 365

to inhibit the browning of fruits and vegetables at home.

The heat treatment is able to inhibit the browning of

plants after harvest without using chemicals (Zuo et al.,

2004), and can be easily applied to fruits and vegetables

by using either hot water dips, vapor heat, or hot dry air.

Moreover, it costs less, and is easily able to be scaled-up

for commercialization (Silveira et al., 2011; Hofman et al.,

2002). The heat treatment can be positively applied for

fruits to improve the storability and marketability as it

can inhibit the ripening of fruits (Dea et al., 2010; Lurie

1998). They have been successfully used in the Amarillo

melon (Aguayo et al., 2008), mangoes (Djioua et al., 2009),

rocket leaves (Koukounaras et al., 2009) and shredded

carrots (Alegria et al., 2010). This method was also reported

to reduce growth phenomena, including sprout development

in potatoes (Ranganna et al., 1998), and has been considered

as an environmentally-friendly method for prolonging the

shelf life of minimally processed products (Hong et al.,

2000; Luna-Guzmán et al., 1999).

Burdock (Arctium lappa L.) is a root vegetable used as

a folk medicine, diuretic, and antipyretic (Kan, 1981; Chen

et al., 2004). Several studies have reported that the root

of burdock possesses various pharmaceutical activities,

including antibacterial activity (Chow et al., 1997), antioxidant

activity (Duh, 1998), and anti-inflammatory activity (Lin

et al., 1996). Hence, its demands have been increased, but

more considered processed ones due to its inconvenience

in handling. In addition, little is known about burdock

physiology and its shelf life when processed into fresh-cut

burdock slices in order to commercialize a high quality

product with an acceptable shelf life as the marketable

standard.

This study aimed to evaluate the effect of combined

treatment applying heat, green tea extract, and salt for

preventing browning and remaining the quality of fresh-cut

burdocks while storing at low temperature.

Materials and Methods

Plant Materials

Burdocks (Arctium lappa L.) were harvested from Bongwha-

gun, Gyeongsangbuk-do, Korea, transported to the laboratory,

and stored at 4°C overnight before processing. Burdocks

were selected based on their uniformity of size, color, and

defects-free.

Green Tea Extract Preparation

Dried green tea (Camellia sinensis) was purchased from

the medicine market in Seoul. Fifty-gram of the powdered

sample was then extracted three times with 80% ethanol

at 60°C for 6 h. After combining all extracts and evaporating

(Rotary Vacuum Evaporator, EYELA, Japan), the freeze-dried

powder was used in the experiment.

PPO Inhibitory Activity of Green Tea Extract

The assay was carried out by reacting 1.7 mL of phosphate

buffer (pH 6.5, 50 mM), 0.1 mL of substrate (1%) and 0.2

mL of polyphenol oxidase (PPO) (500 units/mg). The increase

in absorbance at 420 nm was monitored at 30 s intervals

for 5 min, using a microplate reader (M2, Molecular Device,

Canada) and the average change in absorbance per min was

calculated. One unit of enzymatic activity was defined as the

amount of enzyme causing a change of 0.1 in absorbance/min

(Dennis and Miller, 1998).

PPO inhibition activity (%) = (1-A/B) × 100

(A: absorbance of sample, B: absorbance of blank)

DPPH Radical Scavenging Activity of Green Tea Extract

1,1-diphenyl-2-picryhydrazyl (DPPH) radical scavenging

activity was analyzed by using a modification of the method

by Loizzo et al. (2010). Using 96-well microtitre plate,

reaction mixtures containing 50 µL of 0.1% sample and

150 µL of 0.3 mM DPPH were placed for 10 min at room

temperature. The reacted mixtures were recorded at 517

nm.

DPPH radical scavenging activity (%) = (1-A/B) × 100


Copper Chelating Activity of Green Tea Extract

The copper binding capacity of extracts was determined

according to the method of Wettasinghe and Shahidi (2002)

with a slight modification. Tetramethylmurexide (1 mM･L-1

)

and CuSO4 solutions (5 mM･L-1

) were prepared in 10 mM･L-1

hexamine-HCl buffer (pH 5.0) containing KCl (5 mM･L-1

).

Absorbance of the reaction mixtures was record at 460

and 530 nm and the ratio of A460 to A530 nm was calculated.

These absorbance ratios were then converted to corresponding

free Cu2+

concentrations using a standard curve of free Cu2+

concentration vs absorbance ratio. The difference between

the total Cu2+

and the free Cu2+

concentrations indicated

the concentration of chelated Cu2+

. Copper chelating activity

was calculated using the following equation :

Chelating capacity activity (%) = (1-A/B) × 100


Kor. J. Hort. Sci. Technol. 33(3), June 2015366

Treatments

Burdocks were washed with running tap water to remove

the soil. Then they were peeled and cut into about 3 mm

thick slices using a sharp ceramic knife. Each burdocks

slice was dipped in the following solutions for 45 sec at

55°C (the selected heat treatment condition through the

preliminary experiment) : 0.5% green tea extract, 1% NaCl

(sodium chloride, > 99.5%, Sigma-Aldrich Corp., St. Louis,

Mo., USA), and 0.5% green tea extract + 1% NaCl. Dipping

in water (without browning inhibitors) at 55°C for 45 sec

was used as a control treatment. After dipping, each burdock

slice was kept over a plastic sieve and dried. 80 ± 5 g

of untreated and treated burdock slices were packaged

in polyethylene film bags (150 × 200 mm) of 30 µm and

sealed. The samples were stored at 4°C for 8 days and

weight loss, color, respiration rate, microorganisms, and

sensory characteristics were measured.

Weight Loss Rate

Bags were weighed at 0 day and each sampling day

during the storage period. Results were expressed as

percentage of weight loss relative to the initial weight at

0 day, and the weight loss rate (%) was calculated using

the following equation.

Weight loss rate (%) = [(W1 - W2) / W1] × 100

(W1: Initial weight, W2: Weight after storage)

Color

Color measurements were taken with a reflectance Chroma

Meter (CR-400, Minolta Co., Japan) on the cut surface of

burdock slices. There were ten measurements made per

treatment and color determined by measuring Hunter L,

a, and b values. The chromaticity difference of each treatment

was analyzed using color difference (△E) with the calculation

shown below. The Chroma Meter was calibrated on a

standard white tile (L = 97.40, a = -0.49 and b = 1.96)

before each series of measurements.

△E = (△L2 + △a

2 + △b

2)

1/2

Respiration Rate Measurement

Respiration rates of the burdocks were measured using

a closed system method (Hong et al., 2007). The 80 ±

5 g of burdock slices were taken at random from each

treatment, placed into airtight glass jars (1 L) with silicon

samplings ports and tightly sealed. Jars were stored at

4°C and a 1 mL gas sample from the headspace was taken

periodically through an airtight septum and analyzed by

an Oxygen Carbon Dioxide Headspace Analyzer (Model 6,600,

Illinois Instrument Inc., USA). The mean value was calculated

from the samples for each treatment.

Microbiological Analysis

To determine microbial load, a 10 g sample was mixed

with 90 mL saline solution in a sterile stomacher bag and

shaken for 1 min. Dilutions were made in 0.85% saline

solution as needed for plating. Plate count agar (PCA, Difco

Lab., USA) was used as the media for mesophilic aerobic

counts and Chromocult agar (CM, Merck Co., Germany)

was used as the media for coliform group counts. Prepared

dishes were incubated at 35°C for 48 h. The microbial

counts were expressed as log10 CFU/g. All measurements

were performed in three replicates.

Sensory Evaluation

A panel of ten people was trained to recognize and score

the quality attributes of the treated burdock slices. Appearance,

odor and texture were scored on a nine-point scale, where

1 = complete lacking or soft and 9 = fully characteristic of

fresh. On a similar scale for evaluating overall acceptability,

1 = inedible, 3 = poor, 5 = fair (limit of marketability),

7 = good and 9 = excellent.

Statistical Analysis

Statistical analysis of the data was performed using the

SPSS Win program (Version 12.0, SPSS Inc., Chicago, USA).

Analysis of variance (ANOVA) with Duncan’s multiple range

test was used to test the significance of differences among

means. Significance was accepted at p < 0.05. Three inde-

pendent trials were carried out.

Results and Discussion

Inhibition of Enzyme Activity and Antioxidant Activity of Green Tea Extract

Green tea extract showed high PPO inhibitory activity

(79.88%) (Table 1). The flavonoids present in green tea

is mainly catechins (flavan-3-ols) (Cabrera et al., 2006).

Catechin was probably acted as a competitive inhibitor

for PPO because of its structural similarity, which was able

to substrate for PPO (Nirmal and Benjakul, 2009). Green

tea extract, containing phenolic compound could be used

as the natural inhibitor against PPO.

DPPH is used as a free radical to evaluate antioxidant

activity of some natural sources, and the degree of its


Table 1. PPO inhibitory activity, DPPH radical scavenging activity, and copper chelating activity of green tea extract.

Green tea extractzy

Ascorbic acidy

PPO inhibitory activity (%) 79.88 ± 1.73 19.35 ± 0.95

DPPH radical scavenging activity (%) 78.68 ± 0.89 95.12 ± 0.23

Copper chelating activity (%) 45.93 ± 2.25 90.64 ± 0.51zFifty-grams of dried green tea was extracted three times with 80% ethanol at 60°C for 6 h.yThe concentration was 0.1%.

Fig. 1. Weight loss rate of fresh-cut burdocks dipped in hot

water and browning inhibitors at 4°C (CT, control; HW, hot

water at 55°C; HW + GT, hot water at 55°C + 0.5% green

tea extract; HW + N, hot water at 55°C + 1% NaCl; HW

+ GT + N, hot water at 55°C + 0.5% green tea extract +

1% NaCl). Vertical bars represent ± SE of the means (n

= 5).

discoloration is attributed to hydrogen donating ability

of test compounds, indicating their scavenging potentials

(Shimada et al., 1992). DPPH radical scavenging activity

of green tea extract was 78.68% (Table 1). Green tea extract

was the potential free radical scavengers, as donating their

hydrogens and acted as primary antioxidants.

Green tea extract exhibited high copper chelating activity

(45.93%) (Table 1). Commercial catechin had the lowest

copper chelating activity. Due to copper chelating activity

of extracts, they could inhibit PPO by chelating Cu (II)

in the active site of PPO, thus leading to the lowered PPO

activity (Nirmal and Benjakul, 2011). The capacity of phenolic

compounds for chelating metals is strongly dependent on

the number of hydroxyl groups in ortho position (Maqsood

and Benjakul, 2010). PPO is one of the metalloproteins

with two copper atoms in the active site (Jang et al., 2003).

The copper chelating activity of extracts was in accordance

with PPO inhibitory activity.

Weight Loss Rate

The weight loss is a crucial quality parameter in the

economic stand point of view. In addition, the weight loss

strongly impacts appearance as it causes the shrinkage. The

weight loss of non-heat treated burdocks was compared

to burdock dipped in green tea extract and NaCl with heat

treatment during the storage period (Fig. 1). The use of heat

treatment with green tea extract and NaCl as anti-browning

agents induced to slow down the weight loss during the

storage period. For non-heat-treated samples, the weight

loss was 0.14% at 8 days of storage period in comparison

with the initial weight. Throughout storage, the weight

loss of non-heat-treated burdock slices was significantly

(p < 0.05) higher than heat-treated burdock slices (2-3.5

times higher). It was reported that the increased weight

loss is potentially associated with transpiration rate through

the microscopic cracking occurring on the fruit and vegetable

surface (Hong et al., 2007). If too much water is transported

from the fruit and vegetable turgidity is able to be reduced,

and even appeared slightly shriveled. The heat treatment

had a significant effect on reducing weight loss during

the storage period, compared to non-heat-treated samples.

Similar results have been reported for hot water treatments

applying to grapefruit (Porat et al., 2000) and minimally

processed leeks (Tsouvaltzis et al., 2006). In hot water

with the 0.5% green tea extract and 1% NaCl combination

solution, samples showed the lowest weight loss (0.04%)

at day 8 of storage period, whereas hot water with 0.5%

green tea extract or 1% NaCl reached 0.05%. The presence

of hydrophobic ingredients in the green tea extract and

NaCl as edible coating could be the potential reasons

decreasing the water vapor permeability of the surface,

thus restricting water transfer.

Color

Color is a critical quality of fresh-cut fruits and vegetables,

since cutting operations often lead to enzymatic browning

(Oms-Oliu et al., 2010). Color changes are also caused from

the wound-induced response due to the peeling and slicing

(Siomos et al., 2010). The L value, generally depending


A

B

C

Fig. 2. Changes in the Hunter L (a), a (b), and b (c) value

of fresh-cut burdocks dipped in hot water and browning

inhibitors at 4°C (CT, control; HW, hot water at 55°C; HW

+ GT, hot water at 55°C + 0.5% green tea extract; HW +

N, hot water at 55°C + 1% NaCl; HW + GT + N, hot water

at 55°C + 0.5% green tea extract + 1% NaCl). Vertical bars

represent ± SE of the means (n = 15).

on the surface reflectivity, is used to express the luminosity

of the sample surface, and the a and b values indicate

chromaticity on a green (-) to red (+) axis and blue (-)

to yellow (+) axis, respectively (Du et al., 2009).

Changes in surface color of non-heat-treated were compared

with heat-treated burdock slices, with and without treatments

of anti-browning agents, during the storage period. The

L and b values were decreased with extending the storage

period (Fig. 2a and 2c), which can be related to the appearance

of browning. The higher the L value of burdock slices,

the brighter the surface. The L value of the hot water

+ 1% NaCl sample and non-hot water-treated sample were

73.67 and 67.13, respectively, at 8 days of storage period (Fig.

2a). It is believed that the NaCl is interacted with the copper

at the active center of the enzyme (Iyengar and McEvily,

1992; Sapers, 1993). Several works have been reported

the effect of NaCl on PPO activity. Luh and Phithakpol

(1972) claimed that a 3% sodium chloride solution (0.51

M) is used as an inhibitor to hinder enzymatic browning

in cling peaches. Therefore, the combined treatment of hot

water with anti-browning agents was effective for inhibiting

the browning on the surface of burdock slices. In addition,

the darkening effect associated with decreased L values

may have been linked to fruit and vegetable dehydration

(Lydakis and Aked, 2003).

Generally the a value of burdock slices increased during

the storage period, and the a value of the controls was

highly increased in comparison with other treatments (Fig.

2b). The dipping hot water + adding 0.5% green tea extract

+ adding 1% NaCl treatment samples reported the slowest

trend during storage. As a result, the combined treatment

contributed to a slower accumulation of red color on the

burdock slices and delayed the browning of burdocks,

especially when slices were dipped in a hot water and 1%

NaCl combination solution. Polyphenol oxidase (PPO), a

key enzyme responsible for browning in fruits and vegetables

by catalyzing the oxidation of phenolic compounds, results

in this formation of colored melanins (Budu and Joyce,

2003). Green tea extract had a very high PPO inhibitory

activity and it seemed to help for the reduction of color

changes of burdocks.

The color difference (△E) was calculated with the collected

L, a, and b values. According to the measurement results,

the △E value was generally higher in the non-heat-treated

burdocks than the heat-treated burdocks (Fig. 3). In addition,

the △E value was 3.28 for the burdock slices that were

treated with combined heat, green tea extract, and NaCl,

showing the smallest change in color. The discoloration

was effectively prevented in the sample treated at 45 or

55°C optimally inhibiting PPO (Zuo et al., 2004). Moreover,

the combined effect of heat treatment and anti-browning

agents on the activities of PPO, POD, and pectin methylesterase

(PME) was better than control and thermal treatments

under the experiment conditions of this study. The burdock

slices that were heat-treated with browning inhibitors

showed the smallest change in color during the storage

period.


Fig. 3. Changes in the color difference (△E) of fresh-cut burdocks

dipped in hot water and browning inhibitors at 4°C (CT,

control; HW, hot water at 55°C; HW + GT, hot water at

55°C + 0.5% green tea extract; HW + N, hot water at 55°C

+ 1% NaCl; HW + GT + N, hot water at 55°C + 0.5% green

tea extract + 1% NaCl).

Fig. 4. Changes in the respiration rate of fresh-cut burdocks

dipped in hot water and browning inhibitors at 4°C (CT,

control; HW, hot water at 55°C; HW + GT, hot water at

55°C + 0.5% green tea extract; HW + N, hot water at 55°C

+ 1% NaCl; HW + GT + N, hot water at 55°C + 0.5% green

tea extract + 1% NaCl). Vertical bars represent ± SE of the

means (n = 5).

Respiration Rate

Fresh-cut fruits and vegetables are living tissues, even

after treatment. Damaged plant tissues exhibit an increase in

respiratory rate (Rico et al., 2007). The respiration rate of

slices untreated and treated with hot water + anti-browning

agents is shown in Fig. 4. It was shown that all treatments

were increased in relation to the microbial growth and

general tissue deterioration. Especially, the respiration rates

in the non-heat-treated burdock slices were significantly

higher than that in heat-treated burdock slices (5 times

higher). Fallik et al. (1999) observed that the respiration

rate on bell peppers dipped in hot water (55°C for 12 s)

was significantly lower than that in untreated ones during

15 days of storage period at 7°C followed by 4 days at

16-18°C. This effect could be a physiological response to

heat shock. The samples treated with the hot water and

NaCl combination solution showed the lowest respiration

rates (5.09 mL CO2/kg･hr) at day 8 days of storage period,

while hot water-treated samples reached values of 6.97

mL C02/kg･hr. Similarly, Lamikanra and Watson (2004)

and Luna-Guzmán and Barrett (2000) found a reduction

in respiratory rates in fresh-cut cantaloupe melon treated

with CaCl2 and lactate, in terms of ripening, which delayed

the senescence as a result of the combined additive effects of

hot water dipping and calcium salts. Hence, the combination

of heat and anti-browning agents were very effective in

markedly reducing the respiration rate of burdocks.

Microbiological Analysis

The evolution of total microbial load during the storage

period of burdocks treated with green tea extract and NaCl

with hot water treatment is shown in Table 2. Initial

mesophilic aerobic count of 7.05 × 104 CFU/g was found

in the untreated control. When compared to non-treated

controls, the combination solution of hot water and anti-

browning agents detected mesophilic aerobic counts of 4.54

× 102

- 2.38 × 103 CFU/g. The decrease in the microbial load

produced by the heat treatment (by 3 logs) is in agreement

with Alegria et al. (2009) and Aguayo et al. (2008) where

total aerobic bacterial growth on fresh-cut Amarllo melon

pieces was reduced by dipping in hot water (60°C for 1

min). Heat treatment was effective for reducing microbial

count; furthermore, the heat treatment and anti-browning

agent combinations inhibited the growth of microorganisms

more effectively than heat treatment alone. In samples

from hot water supplemented with anti-browning agents,

there were low mesophilic aerobic counts (1.84-6.25 × 105

CFU/g) at 8 days of storage period, whereas samples with

hot water treatment alone were detected with 7.18 × 107

CFU/g. According to our results, heat treatment, followed

by adding green tea extract and NaCl, was successful for

controlling bacterial growth.

Similar results were observed in the reduction of coliform

group count on burdock slices (Table 3). Initial coliform

group count of 1.88 × 103 CFU/g was found in the untreated

control. When compared to non-treated controls, 4.79 ×

102 CFU/g were found in the hot water-treated sample,

and 1.13-2.57 × 101 CFU/g were found in samples that were

treated with hot water and anti-browning agents. Heat

treatment is an effective method for reducing microbial


Table 2. Changes in the mesophilic aerobic counts of fresh-cut burdocks dipped in hot water and browning inhibitors at 4°C.

Values are given in CFU/g

Treatmentz

Storage period (days)

0 2 4 6 8

CT 7.05 × 104 Aa

yx2.49 × 10

5 Bc 8.08 × 10

5 Ba 7.85 × 10

6 Bab 7.18 × 10

7 Cc

HW 5.16 × 103 Aa 2.19 × 10

4 Bbc 2.98 × 10

5 Ba 2.86 × 10

5 Cb 8.12 × 10

6 Cb

HW + GT 2.38 × 103 Aa 1.19 × 10

4 Ba 1.32 × 10

4 BCa 3.52 × 10

4 BCa 1.84 × 10

5 Cab

HW + N 8.10 × 102 Aa 1.31 × 10

3 Bb 2.68 × 10

3 BCa 7.31 × 10

4 Db 2.12 × 10

5 CDc

HW + GT + N 4.54 × 102 Aa 8.05 × 10

3 Bb 2.84 × 10

3 BCa 1.59 × 10

5 Cab 6.25 × 10

5 Da

zTreatment: CT, control; HW, hot water at 55°C; HW + GT, hot water at 55°C + 0.5% green tea extract; HW + N, hot water

at 55°C + 1% NaCl; HW + GT + N, hot water at 55°C + 0.5% green tea extract + 1% NaCl. Burdocks were harvested in September.yValues with different capital letters (A-D) among burdocks of the same treatment are significantly different at p < 0.05 based

on Duncan’s multiple range test.xValues with different small letters (a-c) among burdocks on the same storage day are significantly different at p < 0.05 based

on Duncan’s multiple range test.

Table 3. Changes in the coliform group counts of fresh-cut burdocks dipped in hot water and browning inhibitors at 4°C.

Values are given in CFU/g

Treatmentz


0 2 4 6 8

CT 1.88 × 103 Aa

yx3.01 × 10

3 Ba 9.72 × 10

4 Ba 1.70 × 10

4 BCa 7.10 × 10

5 Ca

HW 4.79 × 102 Aa 3.85 × 10

2 Ba 6.59 × 10

3 Ba 7.74 × 10

3 Ca 1.40 × 10

3 Ca

HW + GT 2.57 × 101 Aa 4.41 × 10

2 ABa 1.17 × 10

3 BCa 1.83 × 10

3 CDa 1.00 × 10

3 Da

HW + N 2.19 × 101 Aa 1.31 × 10

1 ABa 1.87 × 10

2 Ba 1.44 × 10

3 Ca 1.42 × 10

3 Ca

HW + GT + N 1.13 × 101 Aa 1.07 × 10

2 Ba 3.66 × 10

2 BCa 1.89 × 10

3 BCa 6.56 × 10

3 Ca

zTreatment: CT, control; HW, hot water at 55°C; HW + GT, hot water at 55°C + 0.5% green tea extract; HW + N, hot water

at 55°C + 1% NaCl; HW + GT + N, hot water at 55°C + 0.5% green tea extract + 1% NaCl. Burdocks were harvested in September. yValues with different capital letters (A-D) among burdocks of the same treatment are significantly different at p < 0.05 based

on Duncan’s multiple range test.xValues with different small letters (a-c) among burdocks on the same storage day are significantly different at p < 0.05 based


counts and effectively inhibits the growth of microorganisms.

Heat treatment with green tea extract and NaCl seemed

to have a synergistic effect for controlling the microbial

growth of fresh-cut burdocks.

Sensory Evaluation

The overall quality and shelf life of fruits and vegetables

are reduced by several factors, including water loss, enzymatic

browning, texture deterioration, senescence processes, and

microbial growth (Rojas-Graü et al., 2008). Sensorial results

for appearance, odor, texture, and overall acceptability are

shown in Table 4. Ranking scores of all sensory attributes

were significantly different among samples (p < 0.05).

Untreated samples suffered from poor overall visual quality

and surface edge browning.

Appearance scores were decreased during the storage

period. At 8 days, burdock slices treated with hot water

+ green tea extract + NaCl scored the highest (5.5 score).

The odor of burdock slices was improved with heat treatment.

Moreover, heat treatment with green tea extract and NaCl

still was scored within the limit of marketability (5.0 score),

and they were no significant differences. Texture decreased

during the storage period, showing a similar trend with

appearance values. Texture also did not differ between

treatments at the beginning of the experiment, however,

other treatments had unacceptable scores for consumption

except of hot water + green tea extract + NaCl at 8 days

of storage period. The lowest texture score was scored (2.0)


Table 4. Sensory evaluation of fresh-cut burdocks dipped in hot water and browning inhibitors at 4°C.

Attributesz

Treatmenty


0 2 4 6 8

Appearance CT 8.3 Aaxw

5.0 Ba 3.7 Ba 2.0 Bb 1.0 Ba

HW 8.7 Aa 7.0 ABa 6.0 ABa 5.3 Bab 3.0 BCa

HW + GT 8.7 Aa 7.5 ABa 7.0 Ba 6.0 ABa 4.0 Ba

HW + N 8.7 Aa 8.5 Ba 7.3 Ba 8.0 Bab 5.5 Ba

HW + GT + N 8.7 Aa 9.0 Ba 8.3 ABa 6.0 Bab 4.0 Ba

Odor CT 8.3 Aa 6.5 Aa 6.3 Ba 3.0 Ba 3.5 Ba

HW 8.0 Aa 6.5 ABa 7.0 Ca 3.7 BCa 4.0 Ca

HW + GT 8.7 Aa 6.5 ABa 7.0 BCa 4.3 BCa 5.0 Ca

HW + N 8.7 Aa 6.5 Aa 7.0 Ba 4.7 Ba 5.0 Ba

HW + GT + N 8.7 Aa 6.5 Aa 7.0 Ba 4.7 Ba 5.0 Ba

Texture CT 9.0 Aa 6.5 ABa 5.0 BCa 4.3 Ca 2.0 Ca

HW 9.0 Aa 8.0 ABa 6.0 BCa 5.7 Ca 4.0 Ca

HW + GT 9.0 Aa 8.0 ABa 6.3 ABa 6.3 Ca 3.5 Ca

HW + N 9.0 Aa 8.5 ABa 6.7 ABa 7.3 BCa 5.0 BCa

HW + GT + N 9.0 Aa 8.5 ABa 7.0 ABa 7.3 BCa 4.5 CDa

Overall acceptability CT 9.0 Aa 3.5 Bb 4.0 BCa 1.7 Ca 1.0 Ca

HW 9.0 Aa 7.0 ABab 5.3 BCa 4.5 Ca 3.0 BCa

HW + GT 9.0 Aa 8.0 ABa 7.0 BCa 5.3 Ca 4.5 Ca

HW + N 9.0 Aa 8.5 Bb 7.3 Ba 7.7 Ba 6.0 BCa

HW + GT + N 9.0 Aa 9.0 ABab 8.0 Ba 5.3 Ba 4.5 BazAppearance, odor and texture were scored on a nine-point scale, where 1 = complete lacking or soft and 9 = fully characteristic

of fresh. On a similar scale for evaluating overall acceptability, 1 = inedible, 3 = poor, 5 = fair (limit of marketability), 7

= good and 9 = excellent.yTreatment: CT, control; HW, hot water at 55°C; HW + GT, hot water at 55°C + 0.5% green tea extract; HW + N, hot water

at 55°C + 1% NaCl; HW + GT + N, hot water at 55°C + 0.5% green tea extract + 1% NaCl. Burdocks were harvested in September. xValues with different capital letters (A-D) among burdocks of the same treatments are significantly different at p < 0.05 based

on Duncan’s multiple range test.w

Values with different small letters (a-c) among burdocks on the same storage day are significantly different at p < 0.05 based


for the non-heat-treated sample. Texture is a critical quality

for consumer acceptability of fresh vegetables. Weigh loss

has a key role in stem texture, since tissue dehydration is

accompanied by increasing elasticity and fibrous structure

(Serrano et al., 2006). At the end of storage, general accep-

tability scored similar values for samples treated with hot

water + 0.5% green tea extract and hot water + 1% NaCl

(4.5 score). The hot water + 0.5% green tea extract + 1%

NaCl treated samples generated high overall acceptability

values (> 6.0). Browning is one of the main factors causing

these changes during the storage period, and it strongly

affects the extension of shelf life and consumer purchase

decisions in fresh-cut fruit (Oms-Oliu et al., 2010). The

organoleptic quality of burdocks treated hot water + green

tea extract + NaCl were the best in sensory evaluations.

There was a significant difference in appearance score

between non heat-treated and heat-treated burdocks (Fig.

3 and 5). Sample treated with hot water showed less change

in appearance than the non-heat-treated burdocks. Changes

in color and browning were especially found on the surface

of the non-heat-treated burdocks. Browning was present

mainly in the control sample (without the heat treatment),

and reduced in samples with a previous heat treatment.

Enzymatic browning was mainly present in control samples


Fig. 5. Appearance after storage at 4°C of fresh-cut burdocks dipped in hot water and browning inhibitors (CT, control; HW,

hot water at 55°C; HW + GT, hot water at 55°C + 0.5% green tea extract; HW + N, hot water at 55°C + 1% NaCl; HW

+ GT + N, hot water at 55°C + 0.5% green tea extract + 1% NaCl).

without a thermal treatment. Thermal treatment at 50°C

probably inhibited the activity of phenylalanine ammonialyase

(PAL), the enzyme involved in the first step of the phenyl-

propanoid pathway leading to the production of the major

phenolic compounds and causing the browning (Pereyra

et al., 2005).

Conclusion

Hot water + 0.5% green extract + 1% NaCl treatment

could be used as natural postharvest treatments in fresh-cut

burdocks to delay postharvest browning and maintain quality.

Hot water treatment at 55°C lowered the increase in weight

loss rate of fresh-cut burdocks. The burdock slices with

heat treatment in green tea extract and NaCl also showed

a higher L value and lower △E value than the non-heat-

treated burdocks in storage. In addition, the heat-treated

burdocks had a lower respiration rate and showed a more

gradual speed of microorganism proliferation. The hot water

+ 0.5% green extract + 1% NaCl solution was effective

in reducing the browning of burdock slices. The use of

heat treatment and anti-browning agent combinations for

processing fresh-cut root vegetables may improve quality

through the inhibition of browning, extending the shelf

life for the products through an environmentally-friendly

technique.

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