1. Innovative Food Science and Emerging Technologies 80 (2022) 103097
Available online 29 July 2022
1466-8564/© 2022 Elsevier Ltd. All rights reserved.
Effect of UV-LED irradiation processing on pectolytic activity and quality in
tomato (Solanum lycopersicum) juice
Sebastián Pizarro-Oteíza, Fernando Salazar *
Laboratorio de Fermentaciones Industriales, Escuela de Alimentos, Pontificia Universidad Católica de Valparaíso, Av. Waddington 716, Valparaíso, Chile
A R T I C L E I N F O
Keywords:
UV-LED irradiation process
Pectolytic activities
Hot/cold break
Tomato (Solanum lycopersicum) juice
A B S T R A C T
The aim of this research was to analyze pectolytic activities (pectinmethylesterase “PME” and polygalacturonase
“PG”) and physical qualities in tomato juice treated by UV-LED, Hot Break (HB), and Cold Break (CB) processing.
Tomato juice treated by UV-LED (117 mJ/cm2
) obtained a residual PME activity similar to that of CB, and tomato
juice treated by UV-LED (351 mJ / cm2
) had a residual PME activity 28.3% lower than HB (p < 0.05). The effect
of UV-LED on PG activity was similar to HB and 49% lower than CB (p < 0.05). Furthermore, UV-LED processing
caused a decrease in pH and total acidity and a significant increase in total lycopene content. Antioxidant activity
and viscosity for UV-LED processing were similar to CB, total polyphenol content and ◦
Brix were similar to HB (p
> 0.05). Therefore, this study provides a promising application of UV-LED technology for controlling enzymatic
activity in tomato juice, and an alternative to heat treatment.
Industrial relevance: Nowadays, the tomato industry uses heat treatments to inactivate pectolytic enzymes. UV-
LED technology could have an industrial appreciation, as it was efficient in decrease the activity of these en­
zymes, in addition, preserved and increased some bioactive compounds. Therfore, it is proposed as an efficient
method for processing fruit and vegetable juices. Nevertheless, further studies are needed to clarify the effect of
this technology on pectolytic enzymes and quality parameters in liquid fruit and vegetable foods.
1. Introduction
Currently, world production of fresh tomatoes reaches 160 million
tons per year. Approximately 40 million of these tons are processed into
paste, sauces and ketchup, and smaller volumes are canned. The prin­
cipal producers and processors worldwide are: United States (Califor­
nia), China, Italy and Spain (Andreou, Dimopoulos, Dermesonlouoglou,
& Taoukis, 2020).
Tomato (Solanum lycopersicum) is the world's second most important
vegetable crop and an indispensable food for human nutrition (Briones-
Labarca, Giovagnoli-Vicuña and Cañas-Sarazúa, 2019). Among the nu­
trients that stand out for their composition are lycopene and poly­
phenols. Tomato lycopene boasts a high antioxidant activity and it
accounts for 80–90% of the total carotenoid content (Erge & Karadeniz,
2011). Flavonoids constitute the largest group of polyphenols: they are
anti-inflammatories for the intestines and help prevent gastric cancer
(Briones-Labarca et al., 2019) Accordingly, studies have reported that
the functional properties of tomatoes can be derived from lycopene,
vitamin C, provitamin A, carotenoid, β-carotene and vitamin E (Abadias,
Colás-Medà, Viñas, Bobo, & Aguiló-Aguayo, 2021; Esua, Chin, Yusof, &
Sukor, 2019; García-Closas et al., 2004). Hence, careful product pro­
cessing is important to maintain the functional and nutritional proper­
ties of this food.
The tomato processing industry faces significant challenges con­
cerning production yields, product losses and deterioration of product
quality (Andreou et al., 2020). Refrigeration and heat treatment are the
traditional methods of tomato preservation for products such as pastes,
sauces and ketchup (Bhat, 2016). Pilot scale processing of tomato
products includes various heat treatments such as heating, drying or
pasteurization, which are performed to extend shelf life, inactivate mi­
croorganisms and pectolytic enzymes (Bhat, 2016; Min, Jin, & Zhang,
2003). Pectolytic enzymes are found naturally bound to the cell wall in
most fruits, and are released at the time of juice extraction (Polydera,
Galanou, Stoforos, & Taoukis, 2004). There are two heat treatments
currently used to inactivate these pectolytic enzymes, where the election
of treatment is directly related to the final product viscosity, such as
tomato juices and sauces.
One of these methods is the “Hot Break” treatment, which occupies a
* Corresponding author.
E-mail address: fernando.salazar@pucv.cl (F. Salazar).
Contents lists available at ScienceDirect
Innovative Food Science and Emerging Technologies
journal homepage: www.elsevier.com/locate/ifset
https://doi.org/10.1016/j.ifset.2022.103097
Received 20 February 2022; Received in revised form 21 July 2022; Accepted 22 July 2022

2. Innovative Food Science and Emerging Technologies 80 (2022) 103097
2
temperature between 85 and 90 ◦
C and is used to completely inactivate
the pectolytic enzymes, ensuring aroma and high viscosity in the final
product (Goodman, Fawcett, & Barringer, 2002; Mirondo & Barringer,
2015). When pectinases are completely inactivated, tomato products
show higher viscosity and lower syneresis, i.e., there is low liquid/solid
phase separation (Verlent, Hendrickx, Rovere, & Moldenaers, 2003).
However, this procedure, followed by pasteurization or sterilization,
results in quality losses with respect to color, flavor and nutritional value
(Boulekou, Mallidis, Taoukis, & Stoforos, 2011). The other commonly
used process is called “Cold Break”, where tomatoes are crushed and
pre-heated to temperatures below 65 ◦
C and pectolytic enzymes such as
pectinmethylesterase (PME) and polygalacturonase (PG) are only
partially inactivated, while maintaining their pectinolytic activity and,
consequently, are still able to degrade pectin. Thus, the Cold Break
process causes quality defects, such as decreased viscosity and increased
syneresis. However, with this method the color and flavor of the fresh
tomato are conserved (Boulekou et al., 2011; Giner et al., 2000).
Hence, the control of pectolytic activity is a critical step for obtaining
products with stable rheological properties that are also acceptable to
the consumer. Both the loss of nutrients associated with conventional
processing and the increasing demand for minimally processed food
products have encouraged the search for alternative processing
methods, especially modern and non-thermal technologies (Aadil, Zeng,
Han, & Sun, 2013; Esua et al., 2019).
The use of ultraviolet (UV) light in food processing technology
continues to increase in popularity due to its non-thermal and non-
chemically invasive nature (Popović, Koutchma, & Pagan, 2020). This
technology is highly applicable in food processing and is effective
against most pathogens, easy to operate, requires no addition of chem­
icals, and does not form by-products (Song, Taghipour, & Mohseni,
2019). The successful implementation of UV-LED in disinfecting water,
air and smooth surfaces provided a gateway for this technology for the
industrial processing of various liquid and solid foods, including fresh
and whole products. Operation of this technology depends on the
wavelength ranges applied, for example; UV-C light operates from 200
to 280 nm, UV-B light from 280 to 320 nm and UV-A light from 320 to
400 nm (Koutchma, 2009).
Authors such as (Song et al., 2019) stated that the application of UV
has grown rapidly and the most commonly used ultraviolet light source
for disinfection is mercury lamps. Low-pressure mercury lamps emit
near monochromatic UV rays at 254 nm. Although they have high op­
tical power and good germicidal efficacy, they also have several disad­
vantages in food safety applications such as: mercury toxicity, fragility
of the material, short-lifetime, and the need to preheat before reaching
their maximum optical power (Popović et al., 2020).
Currently, UV-LED is a new source of ultraviolet light and has gained
interest as an alternative to conventional mercury lamps (Song et al.,
2019).Like the widely used visible light LEDs, UV-LED lights requires
little energy, have high longevity, and contain no mercury all advan­
tages over traditional UV lamps (Würtele et al., 2011). For this reason,
UV-LED has been implemented in food production processes and its
application has been found to promote plant growth, improve nutri­
tional value, and inhibit microbial growth in food, among others (Aba­
dias et al., 2021; D'Souza, Yuk, Khoo, & Zhou, 2015; Popović et al.,
2020). In contrast, UV-C exposure has been reported to delay senescence
and ripening in apples (Lu, Stevens, Khan, & Kabwe, 1991), tomatoes
(Maharaj, Arul, & Nadeau, 1999), oranges (D'hallewin, Schirra, Man­
ueddu, Piga, & Ben-Yehoshua, 1999), table grapes (Cantos, Garcia-
Viguera, De Pascual-Teresa, & Tomas-Barberan, 2000), peaches (Gon­
zalez-Aguilar, Wang, & Buta, 2004) and mangoes (González-Aguilar,
Zavaleta-Gatica, & Tiznado-Hernández, 2007). Research suggests that
one of the explanations for these delays could be the inactivation of
pectolytic enzymes that slow the degradation of the cell wall, decrease
the softening of plant tissues, and consequently slow ripening (Ait Barka,
Kalantari, Makhlouf and Arul, 2000; Jianwen, Yua and Guzhanuer
Aisikaera, 2013)
Therefore, the objective of the present study was to measure two
pectolytic activities (pectinmethylesterase “PME” and poly­
galacturonase “PG”) and quality features of tomato (Solanum lycopersi­
cum) juice treated by the UV-LED irradiation process.
2. Material and methods
2.1. Raw material
Organic tomato (Solanum lycopersicum) was obtained from farms in
the village of Romeral, Valparaíso, Chile. Samples weighing 100–120 g
and of medium size were taken to the School of Food Engineering of the
Pontificia Universidad Católica de Valparaíso, Chile. Samples were
washed and following, tomato juice was generated according to the
methodology of (Bhat, 2016) with some modifications, where a com­
mercial juicer (Panasonic MJ-70 M) was used to separate the skin and
seeds. Finally, the juice was stored in a freezing chamber (− 20 ± 2 ◦
C)
and then thawed (4 ± 2 ◦
C) overnight until analysis. All experiments
were performed in triplicate and the control was unprocessed tomato
juice.
2.2. Enzyme extractions from tomato juice
The extractions of two pectolytic enzymes: polygalacturonase (PG)
and pectinmethylesterase (PME) were obtained according to method­
ology reported by (Jianwen et al., 2013) with some modifications. To
extract PME, 1 mL of tomato juice was homogenized with 4 mL of 8.8%
NaCl containing 10 gL− 1
polyvinylpolypyrrolidone (PVPP). The
extraction solution was centrifuged for 20 min at 10143 ×g at 4 ◦
C. The
supernatant was removed and centrifuged for at 10143 ×g for 20 min at
4 ◦
C. The pH of the supernatant was adjusted to 7.5 with 1 M NaOH and
the resultant solution was used for the enzyme assay.
To extract PG enzyme, 1 mL of tomato juice was combined with 4 mL
of 40 mM sodium acetate buffer (pH 5.5) containing 1 M NaCl and 10
gL− 1
polyvinylpolypyrrolidone (PVPP) for 3 h. The extract solution was
centrifuged for 10,143 ×g for 20 min at 4 ◦
C. The resulting supernatant
was used to measure enzyme activity. All measurements were performed
in triplicate.
2.3. Pectolytic activity
Pectolytic activities for PME and PG enzymes were measured ac­
cording to the methodologies outlined by (Ezugwu et al., 2014; Jianwen
et al., 2013) with some modifications. The reaction mixture for PME
enzyme activity contained 2 mL of 0.05% Sigma® commercial citrus
pectin adjusted to pH 7.5 with 1 M NaOH, 0.15 mL of 0.01% (w/v)
bromothymol blue solution in 0.3 M potassium phosphate buffer (pH
7.5), 0.75 mL of distilled water and 0.1 mL of PME enzyme extract. After
addition of the enzyme sample, the Eppendorf tubes were shaken gently
and then incubated in a spectrophotometer at 40 ± 2 ◦
C for 60 min,
while recording the absorbance at 620 nm to measure the kinetic PME
activity (Spectronic Instruments, Spectronic 20 Genesys, NY, USA).
For PG enzyme activity, a solution consisting of 0.2 mL 40 mM so­
dium acetate buffer (pH 4.6), 0.3 mL 1% (w/v) polygalacturonic acid,
0.1 mL enzyme extract and 0.4 mL distilled water was used. The mixture
was incubated to activity condition and this was at 40 ± 2 ◦
C for 60 min.
After, the absorbance was measured at 540 nm using a spectropho­
tometer (Spectronic Instruments, Spectronic 20 Genesys, NY, USA). All
experiments were replicated thrice and average values were used for
analysis. In addition, protein content of the enzyme extracts (for both
PME and PG) was determined by the Bradford method with a calibration
curve of BSA 100–300 μg/ml.
Pectolytic activity is expressed as residual activity as proposed by
Rudra Shalini, Shivhare, and Basu (2008) and Akgün and Ünlütürk
(2017). Residual activity is defined as the ratio of the enzyme activity
after treatment to the activity before treatment. It is calculated using eq.
S. Pizarro-Oteíza and F. Salazar

3. Innovative Food Science and Emerging Technologies 80 (2022) 103097
3
1, in terms of percentage.
Enzyme activity (%) =
S
S0
*100 (1)
where S and S0 are Abs/min after heat and UV-LED treatment, and
control treatment (unprocessed), respectively.
2.4. Pectolytic inactivation in enzyme extracts
2.4.1. Heat treatments
The first conventional treatment performed was the “Hot Break”
(HB), which was carried out at a temperature of 90 ± 3 ◦
C for 5 min in a
thermoregulated water bath. The second conventional method, “Cold
Break” (CB), used a temperature of 60 ± 2 ◦
C for 5 min (Goodman et al.,
2002; Min et al., 2003).
To determine the enzymatic inactivity of the tomato juice, the
thermoregulated bath was previously heated for the respective treat­
ments (CB and HB), see Fig. 1. The center of the sample (2 mL) reached a
temperature of CB treatment after 10 min. Then, for 5 min it was
maintained at that temperature. With respect to the HB treatment, the
sample reached the temperature after 15 min and was maintained at this
temperature for 5 min. In addition, both treatments were constantly
agitated in the thermoregulated bath. Once these treatments were
finished, pectolytic activities were evaluated, according to the PME and
PG enzyme extraction and activity measurement protocols.
2.4.2. UV-LED irradiation process
The effect of the UV-LED irradiation process (UV-C: 278 nm) on the
pectolytic activity and quality features was evaluated for three different
time intervals (5, 10 and 15 min) in the tomato juice. Once the samples
were subjected to each processing time they were analyzed. The
experimental method used a miniature system for UV-LED irradiation
processing in a static regime with the quartz cell vertically placed
(Fig. 2). In addition, the average temperature of the UV-LED irradiation
process did not exceed 28.5 ± 2 ◦
C. Samples were irradiated in a
Spectrosil quartz cell (Starna Scientific Limited, Hainault, Essex, Starna
Scientific Limited, Hainault, Essex, England) with an effective volume of
1.8 mL and a path length of 1 mm. The diodes for UV-C: 278 nm (Vishay
Semiconductors, China) with a UV intensity of 10 mW were occupied at
70%.
On the other hand, to analyze the effectiveness of the UV-LED
treatment, the absorption coefficient of the juice was defined as an op­
tical property, according to Sew, Ghazali, Martín-Belloso, & Noranizan
(2014). The value of this parameter calculated from eq. 2 was 4.65
cm− 1
.
IX = I0exp(− αx)
(2)
Ix: Irradiance (mW/cm2
), I0: UV intensity, measured in the sample
solution (4 mW/cm2
), x: Distance between the UV source and the sensor
(0.5 cm) and α is the absorption coefficient of tomato juice (cm− 1
).
In addition, the tomato juice dose was calculated according to the
evaluated times of the UV-LED irradiation process using the eq. 3 (Sew
et al., 2014). These were for 5, 10 and 15 min of 117, 234 and 351
(mJ/cm2
), respectively.
Dosage
(
mJ
cm2
)
= Irradiance
(
mW
cm2
)
*time (s) (3)
Irradiance (mW/cm2
): UV intensity, measured by the sensor (mW) /
quartz cell area (18.1 cm2
).
2.5. Quality features
Tomato juice samples were centrifuged at 10143 ×g at 4 ◦
C for 20
min prior to physicochemical and bioactive compound analyses.
2.5.1. Physicochemical analysis
A hand-held refractometer was used to measure total soluble solids,
pH was determined with a pH meter calibrated at pH 4 and 7, and
percent total acidity is represented by g citric acid/100 g. All mea­
surements were carried out in triplicate, according to Anthon and Bar­
rett (2012).
Juice viscosity was measured using a viscometer (LV DVII+,
RT70354 Brookfield Engineering Laboratories, Inc., Stoughton, Mass,
USA) with a ULA adapter. Viscosity was determined at 25 ◦
C, 100 RPM,
torque 20% with 50 mL of juice placed in the ULA adapter, as described
by Mirondo and Barringer (2015) with some modifications.
Results were calculated by Wingather Brookfield software. Density
was determined using a pycnometer, which was weighed empty and
filled with distilled water up to the mark to determine its volume at
room temperature. Subsequently, it was filled in the same method with
tomato juice. All measurements were performed in triplicate as pro­
posed by (Evangelista, Sanches, de Castilhos, Cantú-Lozano, & Telis-
Romero, 2020) using approximately 50 mL tomato juice.
2.5.2. Bioactive compound analysis
The antioxidant capacity of the samples was measured using the
method proposed by Bhat (2016). DPPH radical scavenging activity
(measured at 517 nm) was calculated as shown in eq. 2.
DPPH (%) =
A0 − A1
A0
*100 (4)
where Ao = Absorbance of control treatment and A1 = Absorbance of
treated samples.
Total Phenolic Content (TPC) was measured spectrophotometrically
using the Folin-Ciocalteu (FC) reagent according to the methodology
described by Que, Mao, Fang, and Wu (2008) and Bhat (2016). Results
are expressed as mg gallic acid equivalents per L of tomato juice (mg
GAE/L).
All measurements were performed in triplicate. Total lycopene
content in tomato juice samples was determined according to the stan­
dard methods available (Bhat, 2016). Initially, 100 μL of tomato juice
was added to 7 mL of a 4:3 (v/v) ethanol-hexane mixture in a screw-
capped tube. The tube was vortexed and incubated in the dark for 1 h.
Then 1.0 mL of distilled water was added to each of the working sam­
ples. All samples were allowed to stand for 10 min to allow for phase
separation and the dissemination of air bubbles. The absorbance of the
separated hexane layer was read at 503 nm. The amount of lycopene in
the hexane extracts was calculated using eq. 3:
Total lycopene content (μg/g) = (A503
*
537*
2.7)/(0.1*
172) = A503
*
84.3
(5)
2.6. Statistical analysis
Mean and standard deviation were calculated for the Heat-treated
Fig. 1. Thermoregulated bath for heat treatments. Adapted of Akgün and
Ünlütürk (2017).
S. Pizarro-Oteíza and F. Salazar

4. Innovative Food Science and Emerging Technologies 80 (2022) 103097
4
and UV-LED-treated samples. A randomized design was performed with
analysis of variance (ANOVA) using Statgraphics Centurion XVI® soft­
ware, (StatPoint Technologies, Inc., Warrenton, VA, USA). In addition,
Duncan's multiple range test (MRT) was used to detect differences be­
tween means.
3. Results and discussion
3.1. Pectolytic activities
The activity of pectolytic enzymes in fruit juices leads to the for­
mation of precipitates, which affects the quality and consumer accep­
tance of the product. These precipitates are derived from the methyl
group esterification of galacturonic acid from pectin (Cervantes-Eliz­
arrarás et al., 2017). Pectolytic enzymes are found naturally in most
fruits bound to the cell wall and are released when juice is extracted.
Conventional thermal treatments are used to control and inactivate
these enzymes (Bhat, 2016; Boulekou et al., 2011; Min et al., 2003;
Polydera et al., 2004).
The values for residual PME and PG enzyme activity are shown in
Fig. 3. The percent residual PME activity for CB and HB treatment were
15.2 ± 1.68% and 10.19 ± 0.82%, respectively. Residual PG activity for
CB and HB treatment were 6.8 ± 0.88% and 13.1 ± 2.70%, respectively.
These values were lower than the activity condition for this study within
the ranges established by other authors who have reported on the PME
and PG inactivation in different fruits (Aguiló-Aguayo, Soliva-Fortuny,
& Martín-Belloso, 2008; Anthon, Sekine, Watanabe, & Barrett, 2002;
Arbaisah, Asbi, Junainah, & Kennedy, 1997; Sentandreu, Carboneil,
Carboneil, & Izquierdo, 2005; Uemura, Kobayashi, & Takahashi, 2015).
In addition, authors such as Gupta, Balasubramaniam, Schwartz, and
Francis (2010) have proposed that HB treatment on crushed tomatoes is
sufficient to completely inactivate pectinmethylesterase (PME) and
approximately 4% polygalacturonase (PG) activity is retained. Mean­
while, protein contents of PME and PG were 89.22 ± 4.41 and 63.39 ±
5.83 (mg/L), respectively. Total protein content of the thermally pro­
cessed tomato juice was significantly reduced with respect to the control
sample, with a difference of 44.13% (p < 0.05). Residual activity and
protein concentration have a directly proportional relationship, since
the residual activity depends on the amount of active protein, and the
denaturation of enzymes by heat is often irreversible due to the breaking
of covalent bonds and/or the aggregation of denatured proteins (Ly-
Nguyen et al., 2003; Puppo et al., 2004).
The UV-LED irradiation treatment obtained significant differences in
residual enzymatic activity with respect to conventional pectolytic
inactivation treatments (p < 0.05). The residual PME activity of the UV-
LED treatment varied from 7.31 ± 0.89 to 16.2 ± 0.97% and the re­
sidual PG activity ranged from 6.25 ± 0.97 to 7.52 ± 1.11%. However,
the residual PME activity of samples subjected to UV-LED treatment for
5 min (117 mJ/cm2
) did not show significant differences from the CB
treatment (p < 0.05). In addition, the samples which underwent UV-LED
treatment for 15 min (351 mJ/cm2
) obtained the lowest residual PME
activity: 7.31 ± 0.89%, which was 28.3% lower than the residual PME
activity for the HB treatment (p < 0.05).
The residual PG activities from UV-LED treatment for 117, 234 and
Fig. 2. Miniature system for UV-LED irradiation process in static regime. 1. Computer (system control and data acquisition), 2. Power supply and control unit, 3.
Irradiation cuvette and sample, 4–7. UV-LEDs (UV-C: 278 nm).
0
20
40
60
80
100
120
Control 40 °C /1h CB HB UV-LED
(5 min)
UV-LED
(10 min)
UV-LED
(15 min)
Residual
activity
(%)
Treatments
Pectinmethylesterase (PME)
Polygalacturonase (PG)
c c
d
d
c
d
d
e
d e d
a a
b
b
Fig. 3. Residual activities of pectolytic enzymes in tomato juice treated with heat (CB and HB) and UV-LED.
S. Pizarro-Oteíza and F. Salazar

5. Innovative Food Science and Emerging Technologies 80 (2022) 103097
5
351 (mJ/cm2
) did not show a significant difference from those of the
conventional HB treatment, however they were 49% lower than the CB
treatment (p < 0.05). This data provides information on the effect of UV-
LED technology on the residual activities of pectolytic enzymes, showing
a significant decrease compared to thermal treatments for certain dosage
conditions (p < 0.05). In addition, the protein content in the UV-LED
treated tomato juice sample was 62.7% lower than the control sample
and 33.3% lower than the heat-treated samples. Residual activity and
protein concentration have a directly proportional relationship, and are
related to the composition and pH of the juice (Cervantes-Elizarrarás
et al., 2017).
Authors Akgün and Ünlütürk (2017) propose that UV-LED treatment
was able to reduce polyphenoloxidase (PPO) activity in juices and that
inactivation with UV-C depends on the juice matrix and its composition.
This led to adjustments in the absorption coefficient of the juice and
consequently the depth of UV-C light penetration. Moreover, Akgün and
Ünlütürk (2017) showed effective inactivation of the PPO enzyme in
apple juice. Utilizing UVC/UVA they reported a residual PPO activity of
32.6%, and when combining UVC/405 nm they produced a residual PPO
activity of 34.4%.The same effect evaluated Müller, Noack, Greiner,
Stahl and Posten (2014) with UV-C and concluded that the high
reduction of PPO activity at the dosage studied prevented further
browning of apple juice during the refrigerated storage. On the other
hand, Falguera, Pagán and Ibarz (2011), concluded that UV irradiation
of freshly squeezed apple juice was effective in inactivating poly­
phenoloxidase after 100 min, and peroxidase after only 15 min.
Conversely, Noci et al. (2008) found that UV-C light treatment had no
noticeable effect on enzymes such as pectinmethylesterase (PME) and
polyphenoloxidase in apple juice.
The mechanism of inactivation of pectolytic enzymes in tomato juice
with UV-C-LED treatment may be attributed to the fact that UV light is
absorbed by highly conjugated double bond systems. This absorption
modifies the structure of the enzymes due to the abundance of endog­
enous chromophores found in amino acid side chains and prosthetic
groups. In addition, enzymes have the additional ability to bind exog­
enous chromophores and react with other species in the excited state.
Consequently, a change in enzymatic properties is generated due to
backbone fragmentation, cross-linkage formation and oxidation of the
side chains (Davies, 2003; Davies & Truscott, 2001; Manzocco, Panozzo,
& Nicoli, 2013). In contrast, heat treatments that are greater than the
optimum temperature generate an exponential decrease in enzymatic
activity due to enzyme denaturation, suggesting first-order inactivation
kinetics (Moens, De Laet, Van Ceunebroeck, Van Loey, & Hendrickx,
2021).
3.2. Bioactive compounds analysis
Antioxidants are non-essential secondary metabolites formed during
the metabolism of plant tissues as a defense system. They are reported to
be able to react with cellular mediators and enzymes to help prevent
chronic diseases (Bochi, Godoy, & Giusti, 2015; Tan et al., 2021).
Passam and Savvas (2007) suggested that the antioxidant potential of
tomato comes from a mixture of biomolecules, such as ascorbic acid,
vitamin E, lycopene, phenols and flavonoids.
In this study, the DPPH assay was used to evaluate the antioxidant
capacity of tomato juice samples (Table 1). This method proposes that
the higher the percent inhibition, the higher the expected radical scav­
enging potency of a sample (Bhat & Stamminger, 2014). Results showed
that DPPH radical scavenging activity (%) for the heat treatments
decreased with respect to the unprocessed control sample (p < 0.05).
This is because antioxidant and polyphenolic compounds are not
completely stable during conventional food processing (Nayak, Liu, &
Tang, 2015; Vallverdú-Queralt et al., 2012). In this study the percent
DPPH inhibition values for UV-LED processing were lower than those of
the thermal treatments (p < 0.05). However, UV-LED treatment for 5
min (117 mJ/cm2
) did not show a significant difference from the CB
treatment. Furthermore, UV-LED treatment for 5 min (117 mJ/cm2
)
showed an increase of 5.3% over the HB treatment (p < 0.05). This
provides information that non-thermal UV-LED technology could be an
alternative to protect the antioxidant capacity in tomatoes. Authors such
as Bhat (2016) and Bhat, Ameran, Voon, Karim, and Tze (2011), stated
that the increase or reduction of antioxidant levels in fruit juice treated
with UV depends on factors such as the food matrix, maturity, exposure
time, dose administered, among others. Furthermore, they concluded
that changes in antioxidant compounds processed with this technology
are minimal compared to the untreated sample (p < 0.05).
Total Phenolic Content (TPC, mg GAE/L) of the untreated control
tomato juice, and with UV-LED and thermal processing are shown in
Table 1. The polyphenol group comprises important components in
fruits and vegetables and includes phenolic acids, tannins, flavonoids
and anthocyanins (Bhat & Stamminger, 2014). Quantification of phe­
nols provides vital information on antioxidant performance and some
functional properties (Baykuş, Akgün, & Unluturk, 2021; Kaur, George,
Jaggi, & Kapoor, 2007).
UV-LED treatments (117, 234, 351 mJ/cm2
) showed a significant
decrease in TPC as compared to the CB treatment (p < 0.05). TPC was
25% higher for the CB treatment compared to the UV-LED treatment.
This could be interpreted as the CB treatment generated an increase in
the extraction of these compounds compared to the other treatments
(Baykuş et al., 2021).
TPC content for the UV-LED treatment (15 min) did not differ
significantly from the Hot Break treatment, and could be a non-thermal
alternative for preservation of these compounds (p < 0.05). Further­
more, TPC content of the sample treated by UV-LED (351 mJ/cm2
)
increased by 12.16% compared to the control sample (p < 0.05) and this
can be attributed to the fact that UV-LED processing generated an
accumulation of polyphenolic compounds as a means of defense against
the UV irradiation (Bhat, 2016; Gitz, Liu-Gitz, McClure, & Huerta,
2004). Authors such as Baykuş et al. (2021) suggested that an increase in
TPC in UV-LED treated samples could be attributed to the breakdown of
polyphenols into smaller phenolic components. Furthermore, it has been
reported that total phenols in fruit and vegetable juices are affected by
Table 1
Quality characteristics of tomato juice treated with UV-LED, heat treatment and unprocessed control: bioactive compounds (% Inhibition DPPH, Total Polyphenol and
Lycopene content) and physicochemical (pH, Total acidity, Total soluble solids, Density and Viscosity).
Quality Characteristic Control Heat treatment UV-LED (mJ/cm2
)
CB HB 117 (5 min) 234 (10 min) 351 (15 min)
DPPH (% inhibition) 66.22 ± 1.46 a
63.30 ± 5.31 ab
59.57 ± 3.02 bc
62.71 ± 1.31 ab
59.12 ± 1.13 bc
57.5 ± 2.60 c
Total Phenolic Content (mg GAE /L) 216.73 ± 1.26 c
285.36 ± 5.79 a
234.45 ± 5.79 b
217.18 ± 4.52 c
224.91 ± 6.43 c
243.09 ± 6.56 b
Total Lycopene Content (μg/g) 0.59 ± 0.12 b
0.62 ± 0.05 ab
0.56 ± 0.22 b
0.55 ± 0.30 b
0.89 ± 0.06 a
0.45 ± 0.05 b
pH 4.59 ± 0.03 a
4.57 ± 0.02 bc
4.56 ± 0.01 bc
4.54 ± 0.01 cd
4.54 ± 0.02 cd
4.51 ± 0.03 cd
Total Acidity (g Citric acid /100 g) 0.36 ± 0.01 a
0.25 ± 0.02 b
0.24 ± 0.01 b
0.24 ± 0.02 b
0.22 ± 0.03 b
0.22 ± 0.02 b
Total soluble solids (◦
Brix) 3.3 ± 0.06 c
3.3 ± 0.1 bc
3.4 ± 0.06 a
3.3 ± 0.06 c
3.4 ± 0.06 a
3.4 ± 0.06 a
Density (g/mL) 1.02 ± 0.002 a
1.01 ± 0.002 a
1.02 ± 0.001 a
1.02 ± 0.004 a
1.02 ± 0.002 a
1.01 ± 0.002 a
Viscosity (Cp) 1.19 ± 0.06 c
1.32 ± 0.05 b
1.52 ± 0.04 a
1.19 ± 0.06 c
1.21 ± 0.04 c
1.35 ± 0.07 b
Significant differences (p <0.05) in measurements from tomato juice with treated with UV-LED, heat treatment and untreated control are marked as a, b, and c, d.
S. Pizarro-Oteíza and F. Salazar

6. Innovative Food Science and Emerging Technologies 80 (2022) 103097
6
light and temperature (Alothman, Bhat, & Karim, 2009; Bhat, 2016;
Jagadeesh et al., 2009),which could also explain the behavior of these
results.
Finally, Total Lycopene Contents “TLC” (μg/g) of thermally pro­
cessed tomato juices, UV-LED processed, and the control, are shown in
Table 1. Lycopene is the pigment that contributes to the red color; it
constitutes almost 90% of the total carotenoids and has a high antioxi­
dant potential (Bhat, 2016). In this study, total lycopene levels in tomato
juice samples treated with HB do not show significant differences with
respect to the control sample (p < 0.05) and this may be attributed to the
fact that this compound is stable during traditional thermal processing
(Gupta et al., 2010; Lin & Chen, 2005). Furthermore, Qiu, Jiang, Wang,
and Gao (2006), reported that cis-lycopene is highly stable under pres­
sure and heat treatments, which could explain its minimal isomerization
under such processing conditions. UV-LED for 10 min (234 mJ/cm2
)
processing generated an increase in total lycopene content of 43.2%
more than CB and 57% more than the HB treatment (p < 0.05). This
provides relevant information on this emerging non-thermal UV-LED
technology as a method for increasing the amount of this compound.
However, Bhat (2016) reported that the TLC of tomato juice did not
change significantly compared to control samples after processing with
UV-C irradiation (p < 0.05). This could explain the results from our
study for the UV-LED treatment for 5 (117 mJ/cm2
) and 15 min (351
mJ/cm2
) compared to the control sample. Authors such as Jagadeesh
et al. (2009), mentioned that the lycopene content in tomatoes
decreased exposed to UV-C (dose of 370 mJ/ cm2
). Moreover, under
these conditions: 5 min (117 mJ/cm2
) and 15 min (351 mJ/cm2
), it is
possible that a protection by lycopene to chloroplast photooxidation
occurred. This photooxidation caused by ultraviolet irradiation gener­
ated a lycopene degradation (Battaglia & Brennan, 2000). On the other
hand, the loss of lycopene content is also attributed to processing modes
along with oxidation (Abushita, Daood, & Biacs, 2000; Anguelova &
Warthesen, 2000). In contrast, the 10 min treatment (234 mJ/cm2
) may
have caused UV light to trigger the production of reactive oxygen species
(ROS), increasing carotenoid production (Kang, Yang, Park, & Choi,
2020). Therefore, the UV-LED irradiation process at the conditions
evaluated did not generate a linear change tendency of TLC in our study.
However, further studies should be conducted to clarify this behavior, as
TLC depends on factors such as UV-C intensity, extraction type, matu­
rity, and tomato type (Bhat, 2016; Thompson et al., 2000).
3.3. Physicochemical analysis
Physicochemical metrics evaluated were total soluble solids, pH,
total acidity, viscosity and density in tomato juice treated with UV-LED,
control and CB an HB treatment (Table 1). The ◦
Brix value for the control
sample was 3.3 ± 0.06 and the average value of the treatments (thermal
and UV-LED) was 3.4 ± 0.03. However, although there was a small
significant increase with respect to the control sample (p < 0.05), we can
conclude that the possible reason for the reduction of soluble solids in
the untreated juice (control) is attributed to microbial activities. During
the fermentation process, these microbes utilize soluble solids and
change the ◦
Brix level (Bhat et al., 2011; Plaza et al., 2011). Therefore,
thermal and UV-LED treatments had an impact on the activity of mi­
croorganisms affecting the level of soluble solids. The HB treatment and
UV-LED (234 and 351 mJ/cm2
) were that increased this parameter and
can be attributed to the above explanation.
The pH of tomato juice, which is a quality indicator, showed minimal
significant differences between the control and UV-LED treated samples
(p < 0.05). Levels of pH ranged from 4.51 ± 0.03 to 4.59 ± 0.03, and for
UV-LED (117, 234, 351 mJ/cm2
) treated samples there was no evidence
of a significant difference (p < 0.05). However, decreased compared to
the control sample (p < 0.05). Ibarz, Pagán, Panadés, and Garza (2005)
reported minimal changes in pH in apple, peach and lemon juice treated
with UV-LED. Total acidity (g citric acid /100 g) measures the total
concentration of acids in a food, and it is also a vital quality parameter
that influences storage behavior for fruit juices and plays an important
role in flavor (Anthon & Barrett, 2008, 2012). UV-LED treatment (117,
234, 351 mJ/cm2
) showed no significant differences (p < 0.05).
Nevertheless, showed a decrease compared to the control sample (p <
0.05). This result is supported by previous studies on fruit juices treated
with this technology (Bhat, 2016; Bhat & Stamminger, 2014).
Finally, the density (g/ml) and viscosity (Cp) of the tomato juice
processed with heat treatment, UV-LED, and the unprocessed control are
recorded in Table 1. With respect to density, there were no significant
differences between the samples processed with UV-LED, thermally
processed, and control treatment (p < 0.05). Authors, such as Razi,
Aroujalian, Raisi, and Fathizadeh (2011), concluded the same for sam­
ples with thermal treatment and unprocessed samples. The viscosity for
the Hot Break treatment was 14.5% higher than CB treatment and 27.3%
higher than the unprocessed juice (p < 0.05). This is primarily because
pectin is crucial for controlling the viscosity of tomato juice and is
related to the pectolytic activity of the pectinases pectin methyl esterase
(PME) and polygalacturonase (PG). HB treatment induces the complete
inactivation of these pectinases and the product consequently shows an
increase in viscosity compared to the Cold Break treatment. Conse­
quently, CB treatment uses a low temperature, decreasing pectin
retention and consequently a lower viscosity (Aguiló-Aguayo et al.,
2008; Fang, Reuhs, & Xu, 2021; Goodman et al., 2002). The viscosity of
tomato juice processed with UV-LED irradiation (351 mJ/cm2
) did not
differ significantly from the CB treatment (p < 0.05). This provides new
information on the effect of UV-LED irradiation on the viscosity of to­
mato juice as an alternative to conventional treatment, as it could be
correlated with the inactivation of the pectinases.
4. Conclusion
This study investigated the effect of UV-LED irradiation on pectolytic
activity and quality features of tomato juice. The results showed that
UV-LED technology efficiently decreased the residual activity of PME
and PG enzymes. The residual amount of PME enzyme activity for the
UV-LED treatment (351 mJ/cm2
) was lower than for the HB and CB
treatments. Regarding residual PG enzyme activity, samples treated
with UV-LED had reduced residual activity compared to CB, and showed
no difference compared to HB treatment. Bioactive compounds such as
phenols (TPC) were higher in samples treated with UV-LED (351 mJ/
cm2
), but lower than samples treated with CB treatment. Looking at the
percent inhibition of DPPH, the UV-LED treated samples (117 mJ/cm2
)
did not show a difference from the CB, and inhibition was increased
compared to the HB treatment. Although there are a limited number of
peer-reviewed studies on the use of UV-LED for processing fruit and
vegetable juices, this research yields a significant breakthrough by
decreasing the residual activities of pectolytic enzymes, and improving
and preserving certain quality characteristics of tomato juice. Therefore,
UV-LED irradiation is a compelling alternative to conventional heat
treatments and could be explored industrially as a non-thermal method
of preserving these products. However, to generate a more complete
study of this technology on tomato juice, it is necessary to evaluate the
effect on pathogenic microorganisms, shelf life or even other methods
for pectolytic and antioxidant activity.
Declaration of Competing Interest
The authors declare that there are no conflicts of interest regarding
the publication of this paper.
Data availability
No data was used for the research described in the article.
S. Pizarro-Oteíza and F. Salazar

7. Innovative Food Science and Emerging Technologies 80 (2022) 103097
7
Acknowledgement
The authors acknowledge the Pontificia Universidad Católica de
Valparaíso by the postdoctoral fellowship program 2021-2022.
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