UVA Induced Quality Deterioration of Ponkan Mandarin Juice

Guijie Li

1,2 a

, Yujiao Cheng

, Jun Wang

and Tenghui Zhang

Chongqing Collaborative Innovation Center for Functional Food, Chongqing University of Education, Xuefu Rd., Nan’an,

Chongqing, China

Citrus Research Institute, Southwest University, Xiema, Beibei, Chongqing, China

Chengdu Centre Testing International Group Co., Ltd., Xinsheng Rd., Wuhou, Chengdu, China

Keywords: UVA, Ponkan, Juice Quality, Volatile, Off-Flavor.

Abstract: Ponkan mandarin is a promising variety of citrus fruit for juice production. However, there is little knowledge

in shelf-stability of Ponkan juice under normal sun lighting. In this study, Ponkan juice was investigated for

the changes of quality under the most common powerful irradiation of sunlight, ultraviolet A (UVA).

Properties related to taste, color, nutritive values, characteristic mandarin aroma, and volatile sulfuric off-

flavor were analyzed to make a comprehensive evaluation. The results showed that after 50 days UVA

radiation through PET bottles at 25°C, juice acidity, total soluble solid content, chromaticity values, vitamin

C and B2 content decreased significantly, and the characteristic mandarin aroma weakened. In addition, 10

more volatile sulfur compounds introducing distinctly off-putting smell were detected than the fresh juice.

UVA is responsible for the accelerated deterioration of Ponkan juice quality and should be properly shielded.

1 INTRODUCTION

Mandarin (Citrus reticulata Blanco) is a verity of

citrus whose fruits are thin-skinned and easy-peeling.

The most popular cultivars include Ponkan, Satsuma,

Tangerine and Clementine. According to a report

from the United States department of agriculture, the

global production of mandarin will reach 30 million

tons per year (USDA 2019). Almost all mandarin

production is sold as fresh fruit. Due to the saturation

of the fresh fruit market and the changes in consumer

preferences, an increase in mandarin juice production

is to be anticipated.

Food products placed on outdoor market shelves

are exposed to sun light. It is known that light,

especially ultraviolet, can accelerate the oxidation of

fat, degradation of ascorbic acid, browning of color,

and formation of off-flavor

(Conrad 2005, Zhang

2015, Hashizume 2006). Riboflavin-promoted

formation of reactive oxygen species, such as

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superoxide anion, single oxygen, hydroxyl radical

and hydrogen peroxide, can result in the degradation

of amino acids, lipids, carbohydrates, and vitamin

(Grant 2017). In the presence of light and oxygen, off-

flavor can be formed in the orange juice due to the

lipid peroxidation (Fan 2004). Light also increases

the off-flavored volatiles in cloudy apple juice such

as 1-octen-3-one pentanal, 2-methyl-1-penten-3-one,

hexanal, (E)-2-heptenal, 6-methyl-5-hepten-2-one,

and (E)-2-octenal (Hashizume 2006).

Volatile sulfur compounds (VSCs) are known to

be responsible for heated juice off-flavor (Cheng

2020). They introduce a variety of odor

characteristics: rotten eggs, potato, cabbage, meat,

coffee, and onion (I-Min 2011). VSCs are

degradation products of amino acid precursors like

methionine, S-methyl methionine, cysteine and so on

(Gonda 2013, Lee 2014). In white wines, UV-visible

light can increase the amount of volatile methanethiol

and dimethyl disulfide, too, resulting in the sunlight

flavor (Grant 2017).

Juice quality is a comprehensive combination of

color, flavor, nutritive value, and other physical-

Li, G., Cheng, Y., Wang, J. and Zhang, T.

UVA Induced Quality Deterioration of Ponkan Mandarin Juice.

DOI: 10.5220/0011213600003443

In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 411-415

ISBN: 978-989-758-595-1

411

chemical properties. Mandarin juice had been less

studied for its quality. The objective of this study was

to investigate changes of several commercially

important properties of Ponkan mandarin juice such

as chromaticity, vitamin C and B2, volatile organic

and sulfur compounds after an ultraviolet-A (UVA)

radiated shelf-life, and evaluate the resulting

deteriorative effect on the juice quality.

2 MATERIALS AND METHODS

2.1 Sample Preparation

Fresh mature Ponakan fruits were purchased from a

local market in Chongqing, China. Fruits were hand-

squeezed and the released juice was pasteurized for

30s at 98℃ and hot-filled into sterile 200 mL

polyethylene terephthalate (PET) bottles. Bottles

were sealed and cooled immediately using an ice bath

to reach the ambient temperature. Bottles were

exposed separately in the dark (control) or under

UVA (360nm, 25μW/cm

) radiation at 25℃ for a 50-

day shelf-life study.

2.2 Vitamin C Determination

A 2,6-dichloro indophenol method was used to

determine the content of ascorbic acid (Harris 1942).

2.3 Measurement of Chromaticity

L*, A* and B* were measured respectively by using

a Juice chromometer, where L* value indicates

whiteness, A* for red/green color, and B* for

yellow/blue color (Min 2002).

2.4 Extraction and HPLC Analysis of

Riboflavin

A C18 solid-phase extraction procedure was adopted

with modifications from Blanco-Gomis (Gomis

1994). Fifteen milliliters of juice were acidified with

2 mL of 1M H

at 100℃ for 30 min. It was cooled

down and adjusted to pH5-6. A 15 mL mixture was

centrifuged at 13362 g for 15 min. The supernatant

passed through a C18 cartridge that had been

previously conditioned by 5 mL methanol and

washed with 10 mL of water. Riboflavin was eluted

using 5 mL of methanol. Solvent was evaporated

under nitrogen at 35℃. The extract was then

redissolved in 0.4ml of aqueous methanol solution

(50/50, v/v) and membrane filtered before an HPLC

injection.

An Agilent C18 column (150×4.6 mm, 5μm)

connected to a 1260 LC system was used to analyze

riboflavin. Separation was based on an isocratic

method using methanol-water (35:65, v/v) as the

solvent. The flow rate was 0.7 mL/min, and the

injection volume was 5 μL. Fluorescence detection

was monitored at an emission wavelength of 522 nm.

2.5 Static Headspace Solid-phase

Micro-extraction

A 20 mL vial containing 5 mL of juice was

equilibrated at 40℃ for 20 min. A 2 cm-long fiber

coated with divinylbenzene/carboxen/polydimethyl-

siloxane (DVB/CAR/PDMS) was exposed in the

headspace for 30min. The extracted juice volatiles

were desorbed for 5 min at 200℃ in GC inlet port.

2.6 Gas Chromatography-Mass

Spectrometry/Pulsed Flame

Photometric Detection

(GC-MS/PFPD)

Volatiles were analyzed using an Agilent-7890B GC

equipped with a 5977B MS detector coupled to a

5380 PFPD (OI Analytical). Separation was on an

RTX-Wax column (60 m×0.25 mm id×0.25 μm). The

temperature program was set as the following

gradient: 35℃ for 6min; linearly elevated to 203℃ at

a rate of 7℃/min and held for 10 min. Electron impact

(EI) voltage was set at 70 ev, and the m/z range was

set between 44 and 300 amu. For VSCs detection, the

temperature of PFPD was set at 250℃. Identification

of compounds was confirmed by matching the TIC

spectra to the mass spectral library (W10N14),

comparing with authentic standards, and/or checking

their linear retention index (LRI). Quantitation of

characteristic volatiles was applied by using a

cyclohexanone internal standard method.

2.7 Sensory Evaluation

Ten well-trained assessors (6 females and 4 males,

ages between 22 and 40 years) participated in sensory

analysis of Ponkan juice. Sensory evaluation was

conducted at room temperature under clean air

conditions. Evaluation criteria are shown in Table 1

as below.

ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics

412

Table 1: Sensory evaluation criteria for Ponkan juice.

Item Score Criteria

Appearance

and Defects 20 No stratification, flocculation &

obvious defects, 20 points; a small

amount of flocculation,

stratification & impurities, 12-19

points; serious flocculation,

stratification & impurities, 0-11

points.

Flavor 50 Showing citrus characteristic

aroma, without any bitterness,

astringency, and off-flavor, 50

points; insufficient aroma, slightly

more sour or sweeter, no bitter,

astringent, but with a hint of

cooked smell, 35-49 points; poor

aroma, too sour or sweet, with a

slight bitterness and cooked smell,

18-34 points; no characteristic

aroma, very sour, bitter and

serious smelly, 0-17 points.

Color 30 Typical bright mandarin color,

stable and homogenous, 18-30

points; dim and uniform, 14-17

points; dark and less uniform, 10-

13 points; colorless and

nonuniform, 0-9 points.

2.8 Data Analysis

All analyses were performed in triplicate. Analysis of

variance were performed using SPSS 22.

3 RESULTS AND DISCUSSIONS

3.1 Changes in Physical and Chemical

Indices

After 50 days UVA radiation, results of the essential

physical and chemical properties relating to Ponkan

juice quality are shown in Figure 1. Juice stored in

dark condition is compared as a control. Data with

significant differences are labelled with different

letters. The figure shows that juice acidity, total

soluble solid content, color (including brightness L*,

redness a*, and yellow b*), vitamin C content, and

vitamin B2 content were all significantly lower in

UVA radiated juice than those in dark stored and

fresh juices. Particularly, over 98% of riboflavin

(VB2) had been lost. They were likely to participate

in the formation of reactive oxygen species and

responsible for the degradation of VC which

decreased by about 70%.

Figure 1: Comparison of major physical and chemical

properties among three juice samples.

Notes: TSS, total soluble solids; L*, a*, b*, three

dimensions of chromaticity; a-c, significant differences.

3.2 Characteristic Volatile Flavor

Components

In addition to taste, color and nutritional properties,

characteristic mandarin aroma is another important

trait of Ponkan juice. The characteristic aroma

compounds in fresh juice and juices that had been

stored for 50 days in dark condition and under UVA

lighting were analyzed using GC-MS. The odor

activity value (OAV), which is a quotient of the

sample concentration divided by the threshold

concentration, were calculated to describe the

aroma/flavor intensity of each compound. The results

of compound identification, odor description and

OAVs of the three samples are shown in Table 2.

There were significant differences of the intensities of

various aroma attributes among samples. For

example, OAVs of off-flavor compounds such as α-

pinene (piny), β-myrcene (moldy), perillaldehyde

(solvency), terpinen-4-ol (woody), thymol

(medicinal), and carvone (caraway) have greatly

increased after 50 d UVA irradiation. Accumulation

of these compounds would destruct the aroma balance

of the Ponkan juice. Only slight increases were

detected in the juice sample stored in dark. In

addition, some typically good aroma attributes such

as citrusy, green, lemony, floral, mint, and fruity have

decreased considering their total aroma intensity.

UVA Induced Quality Deterioration of Ponkan Mandarin Juice

413

Table 2: Characteristic aroma identification and flavor intensity among three Ponkan juice samples.

No. Compounds Odor

OAV

0 d

50 d

dar

50 d

1 α-pinene piny 59 100 124

2 camphene camphor 16 2 2

3 β-myrcene moldy 45 63 82

4 d-limonene citrusy 1430 860 1060

5 p-cymene citrusy 51 71 173

6 γ-terpinene citrusy 43 34 23

7 terpinolene piny 26 21 17

8 hexanal green 16 7 6

9 nonanal lemony 6 4 2

10 perillaldehyde solvency 4 5 7

11 1-octanol citrusy 1 1 -

12 linalool floral 860 370 330

cis-p-2-

menthen-1-ol

mint 16 2 2

14 fenchol unpleasant - - 2

15 terpinen-4-ol woody 2 5 5

16 α-terpineol floral 4 15 23

17 citronellol fruity 9 19 24

18 carveol caraway 0 0 1

19 thymol medicinal 2 2 8

20 carvone caraway 2 4 120

ethyl 2-methyl

ropanoate

fruity 30 36 43

butanoic acid,

ehtyl este

fruity 8 2 2

ethyl 2-methyl

utanoate

fruity 1720 1790 340

Notes: OAV, odor activity value.

3.3 Volatile Sulfur Compounds

Volatile sulfur compounds (VSCs) are known to be

responsible for a variety of bad smell characteristics.

In this study we found both the number of compounds

and their concentrations were increased after 50 d

storage. As shown in Figure 2, fresh Ponkan juice

only contain small amount of hydrogen sulfide (H

S),

methanethiol (MeSH), dimethyl sulfide (DMS), and

ethyl (methylthio)acetate (EMA). Additional VSCs

were found in the 50 days stored juice, such as S-

Methyl thioacetate, (MTA), dimethyl disulfide,

(DMDS), 2-methylthiophene (2-MT), 3-

methylthiophene (3-MT), dimethyl trisulfide

(DMTS), and methional. The content of DMS

increased, too. After 50 days storage under UVA

radiation, more amount of DMS, DMDS, 2-MT, 3-

MT, DMTS and methional were observed. Carbon

disulfide (CS

) and three unknown VSCs were newly

detected. The odors of DMS, DMDS, DMTS,

methional, and CS

have been described as cabbage,

onion, garlic, cooked potato, and solvency,

respectively. Increases of these specific sulfur off-

flavors in addition with other unknown VSCs would

definitely undermine the comprehensive flavor of

Ponkan juice.

3.4 Deterioration of Juice Overall

Quality

The overall apparent sensory quality scoring by

assessors showed a consent to above analytical

results. In the item of Appearance and Defects, scores

for fresh juice, 50 days in dark and 50 days under UV

were 18, 17 and 15. Scores of Flavor were 40, 37 and

30, respectively. Color scores were 18, 18 and 17,

respectively. The total scores were 76 (fresh), 72

(dark) and 62 (UVA).

ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics

414

4 CONCLUSIONS

In this study we have shown that the overall quality

of Ponkan mandarin juice deteriorated after being

placed on shelf under UVA radiation at an ambient

temperature (25°C) for 50 days. The control, same

juice placed in dark, showed a much better quality

close to the fresh juice. These results demonstrate that

UVA, the major UV irradiation in our everyday life,

should be screened so that to protect juices from

quality deterioration.

Figure 2: VSCs chromatogram detected using PFPD.

ACKNOWLEDGEMENTS

This work was financially supported by the Scientific

and Technological Research Program of Chongqing

Municipal Education Commission (KJQN201801613

and KJQN202100209).

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