Food Bioprocess Technol

https://doi.org/10.1007/s11947-018-2076-7

REVIEW

Current Scenario of Adsorbent Materials Used in Ethylene

Scavenging Systems to Extend Fruit and Vegetable
Postharvest Life
Marianela Hazel Álvarez-Hernández 1 & Francisco Artés-Hernández 2 &
Felipe Ávalos-Belmontes 1 & Marco Antonio Castillo-Campohermoso 3 &
Juan Carlos Contreras-Esquivel 1 & Janeth Margarita Ventura-Sobrevilla 4 &
Ginés Benito Martínez-Hernández 2

Received: 9 November 2017 / Accepted: 31 January 2018

# Springer Science+Business Media, LLC, part of Springer Nature 2018

Abstract Fruit and vegetables are much appreciated by con- supported onto silica gel or zeolite seems to be a promising tool
sumers due to their nutritional values and health-promoting to maintain fruit and vegetables quality attributes for long-term
compounds. However, different factors affect the postharvest storage. Although vermiculite and activated alumina are the
life of such products, in where ethylene is a major one, even at most commonly used materials to reach this goal, not promis-
low concentrations, besides temperature and relative humidity. ing results have been reported.
Therefore, high attention has been focused on the development
of effective tools to remove ethylene from the atmosphere sur- Keywords Shelf life . Postharvest losses . Scavengers .
rounding these products during storage or in transit. Potassium Ethylene scrubbers . Active packaging
permanganate scrubbers are one of the most used technologies
to remove ethylene from horticultural products. To facilitate
and improve the oxidation process, potassium permanganate
has been supported onto inert solid materials of a small particle Introduction
size. In this review, we aim to provide an outline of the most
common materials used as potassium permanganate supports Fresh fruit and vegetables (F&V) consumption has been asso-
on postharvest treatment and their respective effects on quality ciated with numerous health benefits as shown the existing
aspects of various fresh produce during postharvest life. related epidemiological studies which have been recently
Vermiculite, activated alumina, zeolite, silica gel, activated car- reviewed (van Berleere and Dauchet 2017). Such health ben-
bon and clays are the most popular materials that have been efits have been specifically linked to the F&V phytochemicals
used as a support of potassium permanganate-based ethylene (Rodriguez-Casado 2016). Accordingly, F&V are considered
scrubbers. The literature suggests that potassium permanganate as an important food group for a well-balanced diet
(Sivakumar and Bautista-Baños 2014). In that scenario,
F&V consumption has steadily augmented due to the increas-
* Ginés Benito Martínez-Hernández ing consumer profile interested in natural food products with
ginesbenito.martinez@upct.es
high health-promoting properties. Nevertheless, the product
1
selection by this consumer is primarily based on visual ap-
Faculty of Chemical Sciences, Universidad Autónoma de Coahuila,
25280 Saltillo, Coahuila, Mexico
pearance attributes, such as good colour, perfect shape and
2
size, together with taste, aroma and texture. However, F&V
Postharvest and Refrigeration Group, Department of Food
Engineering, Universidad Politécnica de Cartagena,
are perishable products and tend to lose their attractive appear-
30203 Cartagena, Murcia, Spain ance and nutritional value in a short time. It is important to
3
Agricultural Plastics Department, Centro de Investigación en
remember that after harvest, F&V quality can only be main-
Química Aplicada, CIQA-CONACYT, 25294 Saltillo, Coahuila, tained, not improved (Mahajan et al. 2017). It has been esti-
Mexico mated that roughly one third of food produced for human
4
Health Sciences, Universidad Autónoma de Coahuila, 26090 Piedras consumption is lost or wasted globally, corresponding 50%
Negras, Coahuila, Mexico of such food losses to F&V (Blanke 2014; FAO 2011).
 Food Bioprocess Technol

Postharvest quality of F&V is affected by several factors, KMnO4 supports and their respective effects on various fresh
e.g. physical damage, transportation, etc., being storage man- produce quality during storage. Physical characteristics such
agement a key factor to provide a product with excellent qual- as pore volume, pore size distribution and surface area of the
ity, and subsequently long shelf life, to the consumer. Storage materials are briefly described in this review.
management should take into account respiration rate, ethyl-
ene (C2H4) production and sensitivity of the product to several
critical parameters such as storage temperature and deter- Role of Ethylene on Postharvest Life of Fresh Fruit
mined gas concentrations (oxygen, carbon dioxide and and Vegetables
C2H4), while high relative humidity (RH) rates should be
maintained with the aim of extending F&V shelf life (Kader C2H4 is an important plant hormone regulating various es-
2005). sential processes during plant growth and development, in-
C2H4 concentration in product atmospheres is an important cluding ripening of F&V, like for example seed germina-
factor to be controlled since it often causes a faster degradation tion, cell elongation, flower development, senescence and
of fresh produce after harvesting, especially during their trans- defence against pathogens and response to external stress
portation and storage, leading to high product losses (Pathak factors, among others (Abeles et al. 1992; Saltveit 1999).
et al. 2017). Warton et al. (2000) measured the C2H4 level in Nevertheless, C2H4 presence around F&V is undesirable
the atmosphere of fresh commodities storage areas, founding since it negatively affects their postharvest life depending
C2H4 levels of 0.017–0.035 μL kg−1 in supermarket stores these undesirable effects of the product type.
and 0.06 μL kg−1 in wholesale markets and distribution cen- Based on the respiration behaviour and C2H4 production
tres. Based on the recorded levels, the latter authors indicated rates during the ripening process, fruit has been classified into
that the shelf life of C2H4-sensitive commodities may be re- climacteric and non-climacteric (Cherian et al. 2014; Paul
duced by 10–30% during distribution. et al. 2012). The first ones are those F&V characterised by a
The main sources of C2H4 in horticultural produce envi- peak in both respiration and C2H4 production during ripening
ronments are climacteric fruit (Pathak et al. 2017). (such as apple, mango, papaya, avocado, kiwifruit, banana,
Nevertheless, it should be considered that besides the pear, blueberry, broccoli, among others), whereas non-
C2H4 production of F&V tissues, there are anthropogenic climacteric fruit do not exhibit that dramatic change in respi-
and other biogenic sources of C2H4 (e.g. industrial pollution ration, remaining C2H4 production at basal levels (e.g. citrus
smoke, motor vehicle exhaust gases and that produced by fruits, pineapple, melon, peas, pepper, cacao, cucumber,
microbial activity) that can affect the produce along the food among others) (Paul et al. 2012). C2H4 concentrations ≤ 0.1–
chain (Morgott 2015). Therefore, high attention has been 0.2 μL kg−1 h−1 are registered in climacteric products during
focused on the development of effective postharvest tools the pre-climacteric period, increasing at least 10-fold during
to remove C2H4 from the atmosphere surrounding fresh ripening, while non-climacteric fruits usually do not produce
produce. more than 1 μL kg−1 h−1 at 20 °C (Kader 1980; Knee et al.
C2H4 can be removed from the environment through scav- 1985; Martínez-Romero et al. 2007; Saltveit 1999). In climac-
enging technologies by absorption, adsorption and/or oxida- teric fruit, C2H4 accelerates ripening causing excessive fruit
tion mechanisms to preserve a good quality of fresh F&V for softening, colour changes, sugar content alteration, texture
longer periods (Chopra et al. 2017). In this sense, C2H4 scav- changes and volatile aromas synthesis. Meanwhile, in non-
engers based on potassium permanganate (KMnO4) are the climacteric fruit, C2H4 stimulates senescence, often associated
best known and the most widely used technology in F&V with yellowing of green tissues by promoting chlorophyll
industry (Gaikwad and Lee 2017). KMnO 4 is an eco- degradation and hastens to toughen and wilting (Barry and
friendly and powerful agent that oxidises C2H4 to CO2 and Giovannoni 2007; Lelievre et al. 1997; Saltveit 1999).
H2O (Dash et al. 2009; Singh and Lee 2001). KMnO4-based Moreover, in both climacteric and non-climacteric fruit,
scrubbers are considered as a low-cost technology with easy C2H4 can induce chilling injuries and physiological disorders
application (Dash et al. 2009). They can be used in packaging (Wills 2015).
(as active packaging), storage facilities, transport vehicles and In addition, C2H4 may increase pathogen susceptibility by
domestic refrigerators (Keller et al. 2013). inhibiting the formation of antifungal compounds, and in
Since C2H4 is a gas and natural convection and diffusion some cases, it can even stimulate the growth of fungi such
are the only driving forces involved, KMnO4 is usually sup- as Botrytis cinerea on strawberries and Penicillium italicum
ported onto a porous inert material with a large surface area on oranges (Abeles et al. 1992; Kader 2003). C2H4 concen-
exposed with the aim to facilitate interaction between C2H4 trations higher than 0.1 μL L−1 strongly affect storage life of
and KMnO4 (Wills and Warton 2004). The materials used to fresh produce (Wills 2015). In that sense, a C2H4 concentra-
support KMnO4 are diverse. Therefore, we aim to provide in tion between 0.1 and 0.5 μL L−1 has been proposed as the
this review an outline of the most common materials used as threshold level to initiate ripening of banana, avocado,
Food Bioprocess Technol

honeydew melon and pear, while 0.03 μL L−1 has been Currently, it is well proven that KMnO4-based C2H4 scrub-
assigned to kiwifruit (Blanke 2014; Knee et al. 1985). C2H4 bers selectivity and reactivity can be improved by using small
concentrations higher than 4 μL L−1 at 20 °C has led to 30% particles which makes available a higher contact area
reduction of storage life of peach, avocado and tomato, where- (Shaabani et al. 2005; Spricigo et al. 2017). However, besides
as 0.029, 0.035, 0.043, 0.55, 0.113, 0.65 and 0.89 μL L−1 were the role played by the surface area size, the success of a scrub-
enough for banana, strawberry, lettuce, Chinese cabbage, ki- ber also depends on the material type and other physical char-
wifruit, custard apple and mango, respectively (Warton et al. acteristics such as shape and C2H4 adsorption ability. For ex-
2000; Wills et al. 2001). Therefore, it is important to remove ample, it has been reported that KMnO4-based C2H4 scrub-
C2H4 from fresh produce packaging and storage areas to avoid bers supported onto Al2O3 nanoparticles have higher C2H4
its negative effects. removal rate than scrubbers based on SiO2 nanoparticles
(Spricigo et al. 2017). Bhattacharjee and Dhua (2017) reported
better results in pointed gourd fruit (stored in polypropylene
(PP) bags at 29–33 °C, 68–73% RH) when C2H4 scrubbers of
The Importance of Support Materials KMnO4 supported onto celite were used instead of KMnO4-
in KMnO4-Based Scrubbers based scrubbers supported onto SiO2 gel (4–8 g scrubber kg−1
fruit). García et al. (2012) also evaluated the effect of different
KMnO4 oxidises C2H4 to CO2 and H2O (Fig. 1), releasing support materials (montmorillonite, kaolinite, vermiculite and
manganese dioxide (MnO 2 ) and potassium hydroxide zeolite) in KMnO4 scrubbers (17 g scrubber kg−1 fruit) on the
(KOH). The general stoichiometric oxidation reaction is: postharvest quality of baby banana (18 °C, 70–80% RH). The
best results were obtained when vermiculite was used, while
3C2 H4 þ 12KMnO4 þ 2H2 O H→
2O
6CO2 ð1Þ the worst results were obtained with kaolinite. Attending to
þ2H2 O þ 12MnO2 þ 12KOH support material shape, a study comparing C2H4 adsorption
capacity of granular, powered and fibred carbon activated was
carried out by Martínez-Romero et al. (2007). The best per-
As mentioned earlier, in order to facilitate the redox pro- formance was obtained with the granular shape (over 80%),
cess, it has been implemented adsorption of KMnO4 onto a followed by powered (over 70%) and finally fibred shape
porous inert material with a high surface area such as clays, (over 40%).
silica (SiO2) gel, zeolites, alumina (Al2O3), vermiculite and In addition, many other parameters also play a key role in
activated carbon (Fig. 2, Table 1). Furthermore, some of these the performance of a scrubber product, e.g. temperature and
materials can adsorb C2H4 creating an adsorption–oxidation RH (Gaikwad and Lee 2017; Keller et al. 2013). Spricigo
system, where the support material adsorbs C2H4 and perman- et al. (2017) carried out a study about the influence of par-
ganate (MnO4−) oxidises it (Pathak et al. 2017). ticle size (micro- versus nanoparticles), KMnO4 content
(2.5, 5 and 10% KMnO4) and RH (45, 60, 75 and 90%) on
the C2H4 removal rate of 0.3 g KMnO4-based C2H4 scrub-
bers supported onto two different materials: SiO2 and Al2O3
at 25 °C, under 1 h of exposure to 7.48 mL L−1 C2H4. The
latter authors reported that as the particle size of the scrub-
ber decreases and the KMnO 4 concentration increases,
C2H4 removal rate become higher, regardless of the used
material. Both nano- and micrometric SiO2particle sizes
showed the best performance with 10% KMnO 4 under
75% RH, resulting in 100 and 73% C2H4 removal, respec-
tively. However, there was observed a reduced C2H4 remov-
al rate under 60 and 90% RH for both particle sizes. In the
case of Al2O3, the effect of particle size reduction on C2H4
removal was more remarkable. Microparticles did not over-
come 50% C2H4 removal rate, while 45% was the lower
C2H4 removal rate of nanoparticles being C2H4 removal
efficiency increased as the RH and KMnO4 increased.
As observed, the intrinsic characteristics of the support ma-
terial highly influence the C2H4 removal efficiency. Therefore,
Fig. 1 Scheme of the ethylene oxidation reaction by potassium it is crucial to review the published studies, which addressed
permanganate this area.
 Food Bioprocess Technol

Materials Used as KMnO4 Support on C2H4 the advantages of being low-cost production, great accessi-
Scrubbers bility, and has an excellent thermal and chemical stability,
and high specific surface area (up to 800 m2 g−1) (Jal et al.
Metal Oxides 2004; Polshettiwar et al. 2009).
In a recent study, it was reported that KMnO4 embedded
Silica Gel onto SiO2 crystals is a good tool to slow down the ripening and
senescence process of ‘Kajli’ pointed gourd fruit
The SiO2 gel is an amorphous material form of SiO2 with (Bhattacharjee and Dhua 2017). Fruit packed together with
mesopores (pores larger than 20 Å). SiO2 is a polymer of C2H4 scrubbers of KMnO4-SiO2 (8 g kg−1 of fruit) in PP bags
silicic acid with a surface rich in hydroxyl groups, or silanols at 29–33 °C (Table 2) showed lesser changes in sensory
(Si–O–H), which participate in adsorption as well as in properties and lowered chlorophyll content decrease
chemical modifications (Jal et al. 2004; Yang 2003). The compared to fruit without C2H4 scrubbers. A significant
SiO2 gel can be classified into two common types: low- reduction in weight loss and a decrease in the spoilage
density and regular-density SiO2 gels. The first one has a percent, as well as a higher disease reduction index was also
surface area of 300–350 m2 g−1 and an average pore diameter observed. Singh and Giri (2014) demonstrated that KMnO4
of 100–150 Å, whereas the regular density type has a surface embedded onto SiO2 crystals could prolong shelf life of guava
area 750–850 m2 g−1 and a pore diameter 22–26 Å, but some fruit (up to 7 weeks), under active packaging using low-density
materials can have higher surface areas (above 1000 m2 g−1) polyethylene (LDPE) film at 8 °C (Table 2). With the use of
and high pore volume (approximately 1 cm3 g−1) (Sneddon KMnO4-based C2H4 scrubbers supported onto SiO2, minor
et al. 2014; Yang 2013). Furthermore, SiO2 is a non-toxic changes in fruit firmness, total soluble solids content (SSC),
material, and it is generally recognised as safe (GRAS) prod- titratable acidity (TA) and colour were obtained. Furthermore,
uct by US Food and Drug Administration (FDA), with the a significant reduction in decay was reported. However, the
GRAS Notice (GRN) No. 298 and the Codex SNI No. 551 used of SiO 2 as support is not popular as observed in
(FDA 2009; FAO 2015). Spricigo et al. (2017) reported that Tables 1 and 2 being attributed to its low C2H4 removal capac-
0.3 g SiO2 nanoparticles with a surface area of 549.6 m2 g−1 ity. Eastwell et al. (1978) evaluated the C2H4 removal capacity
and an average pore size of 28.6 Å could reach a C2H4 of 20% (w/w) KMnO4 on the SiO2 gel with 5% (w/w) fuming
adsorption rate of 34 ± 8% after 1 h of exposure to sulphuric acid at 22 °C. After 10, 30 and 60 min of C2H4
7.48 mL L−1 C2H4 at 25 °C and 90% RH. SiO2 possesses flushing (0.02 μL L−1 C2H4 at a flow rate of 100 mL min−1),

Fig. 2 Different support

materials (scanning electron
microscope details) used in
potassium permanganate-based
scavengers
Table 1 Characteristics of support materials used in commercial potassium permanganate-based ethylene scrubbers

Trade name KMnO4 support Characteristics Physical properties Reference

(manufacturer)
Food Bioprocess Technol

Purafil Select Activated alumina Form: spherical Bulk density: 0.8 g mL−1 (± 5%) Purafil Inc. (2015a, b)
(Purafil Inc., GA, USA) Pellet diameter: 3.2 mm Moisture content: ≤ 35%
KMnO4 concentration: ≥ 8%
Ethysorb® Activated alumina Form: spherical Bulk density: 1.0 g mL−1 Molecular Products Limited (2009a, b)
(Molecular Products Ltd., UK) Particle size: 2.5–5.0 mm Relative density: 3.3 g mL−1
KMnO4 concentration: < 6%
Purafil Chemisorbant Activated alumina Form: spherical Bulk density: 0.8 g mL−1 (± 5%) Purafil Inc. (2015a, b)
(Purafil Inc., GEO, USA) Pellet diameter: 3.2 mm Moisture content: ≤ 35%
KMnO4 concentration: ≥ 4%
Multi-Mix® MM-1000 Activated alumina Form: spherical Bulk density: 0.88 g mL−1 Circul-Aire Inc. (2006)
(Circul-Aire Inc., Canada) Particle diameter: 3.2 mm Moisture content: 22%
Surface area: 250 m2 g−1
KMnO4 concentration: 4%
Sofnofil™ Activated alumina Form: spherical Bulk density: 0.8 g mL−1 Molecular Products Limited (2009a, b)
(Molecular Products Ltd., UK) Particle size: 2.5–5.0 mm Moisture content: 15–25%
KMnO4 concentration: < 6%
BrySorb™ 508 Activated alumina Form: spherical Bulk density: 0.85–0.90 g mL−1 Bry-Air (Asia), Pvt. Ltd. (2011)
(Bry-Air (Asia) Pvt. Ltd., India) Particle diameter: 2.5–3.5 mm Moisture content: > 18%
KMnO4 concentration: NS
Air Repair ™ Ethylene Gas Absorber Activated alumina Form: spherical NS Deltatrak (n.d.)
(DeltaTrack Inc., CA, USA) Particle diameter: NS
KMnO4 concentration: NS
Ozeano ETH Alumina Form: spherical Bulk density: 0.75–0.85 g mL−1 Ozeano Urdina (2013a, b)
(Ozeano Urdina S.L., Spain) Particle diameter: 3.0–5.0 mm Moisture content: ≤ 20%
Surface area: ≤ 150 m2 g−1
KMnO4 concentration: 7.5%
Ryan® Natural clays NS NS Sensitech Inc. (2013)
(Sensitech Inc., MA, USA)
Bi-On® Zeolite Form: cylindrical Bulk density: 0.84 g mL−1 (± 0.03) Bioconservación (2015)
(Bioconservación S.A., Spain) Pellet diameter: 2.3–4.0 mm Moisture content: 15–20%
KMnO4 concentration: 12%
Super Fresh Media Zeolite (clinoptilolite) Form: granules NS Ethylene Control Inc. (2015)
(Ethylene Control Inc., CA, USA) KMnO4 concentration: 4–6%
Extend-A-Life™ Zeolite Form: granules NS AgraCo Technologies International,
(AgraCo Technologies International KMnO4 concentration: 8% LLC (2014)
LLC., PE, USA)

NS not specified
Table 2 Overview of the use of support materials in potassium permanganate-based ethylene scrubbers used in fruits and vegetables

Produce KMnO4 Scrubber Dose Produce packaging Storage conditions Effects on produce quality Reference
support presentation

Apple Vermiculite Sachets 3 sachets (9 g of scrubber) Wrapped with LDPE 4 °C, 15 days + Reduced C2H4 concentration. Pulp firmness, Brackmann et al.
(Malus domestica per 18 kg of fruit (20 μm thick) and 20 °C, 3 days colour, TA and SSC were not affected (2006)
Borkh) packed in a carton
‘Gala’
Apple Zeolite Sachet 20 g of scrubber, weight Wrapped with craft 0 °C, Reduced pH increase and TA decrease. Sardabi et al.
‘Golden Delicious’ loss NS paper and placed 5 months Minimised SSC accumulation. Delayed (2014)
in a carton box (90% RH) degreening process and flesh firmness loss
Apples Alumina Bulk 100 and 80 g per 22 fruits Held in polyethylene 0.5 °C Reduced C2H4 and CO2 levels. Increased O2 Shorter et al.
‘Granny Smith’ bags (40 μm thick) 13 weeks or more level. Reduced bitter pit and superficial scald (1992)
Apricot Zeolite Filter NS Placed in a chamber 30 days Delayed TA and firmness value decrease, and Emadpour et al.
storage slowed pH, SSC and weight reduction (2009b)
Baby banana Vermiculite Sachet 5 g each of scrubber with Stored in LDPE bag 18 °C Delayed peel yellowing. Slowed SSC increase García et al.
(Musa AA Simmonds) KMnO4/vermiculite at 16 days and TA decrease. Reduced firmness loss and (2012)
1:1.5% based on fruit (70–80% RH) weight loss. Minimised SSC/TA ratio increase
weight
Banana Clay Sachet One sachet (30 g of Stored in a plastic bag 27–30 °C Delayed yellowing of peel and firmness loss. Santosa and
(Musa paradisiaca L. scrubber (at a rate of and then inside a 18 days Reduced weight loss. Slowed SSC and TA Widodo
AAB type) 7.5% w/w KMnO4)) carton increase. Pulp/peel ratio was not affected (2010)
‘Raja Balu’ per 0.42–0.67 kg of fruit
Banana ‘Kolikuttu’ Clay NS NS Packed in LDPE bags 25 °C Reduced C2H4 and CO2 levels and incresed O2 Illeperuma et al.
(75 μm thick) (85% RH) level. Slight changes in firmness and SSC (2000)
content were observed
Cabbage, Chinese Zeolite Filter NS Placed in a chamber 21 days Reduced texture firmness loss and minimised Kalaj et al.
(Brasica pekinensis) storage colour changes. Delayed weight loss, pH (2008)
reduction and tissue browning
Cantaloupe melon Vermiculite Sachet 12 sachets (2.5 g of Placed in a box with 3 °C, 14 days (85% Weight loss was not affected. Pulp/peel firmness, Sá et al. (2008)
(Cucumis melo L.) scrubber (at a rate of LDPE coating RH) + 23 °C, AT and pH were not affected
‘Vera Cruz’ 10% w/w KMnO4) 8 days
per kg of fruit
Cherry, black sweet Zeolite Filter NS Placed in a chamber 30 days Delayed firmness and weight loss. Reduced Emadpour et al.
‘Takdaneh Mashhad’ storage SSC increase and stem browning. Minimised (2009a)
TA reduction
Guava Silica crystal Sachet NS Packed using LDPE 8 °C Reduced changes in fruit firmness, SSC, TA Singh and Giri
(Psidium guajava L.) film (76.2 μm thick) and colour. Decay was reduced (2014)
Lettuce, iceberg Zeolite Filter NS Placed in a chamber 21 days Reduced texture firmness loss and minimised Kalaj et al.
(Lactuca sativa L.) storage colour changes. Delayed weight loss, pH (2008)
reduction and tissue browning
Mango Vermiculite Sachet 20 g of KMnO4 per kg fruit Placed in an acetate 13 °C Weight loss and pulp firmness were not affected. Jeronimo et al.
(Mangifera indica L.) tray with PVC film 20 days Delayed and minimised SSC/TA increase/ (2007)
‘Tommy Atkins’ (14 μm thick) (85–90% RH) decrease. Reduced ascorbic acid degradation
coating
Maxixe Vermiculite Sachet 4 g of KMnO4 and 6.5 g Placed in polystyrene 10 °C Delayed chlorophyll and vitamin C loss. Weigh Silva et al.
(Cucumis anguria) vermiculite, fruit weight trays with PVC film 10 days loss, carbohydrates, colour or chilling injury (2015)
NS coating (90% RH) were not effected
Nectarine Zeolite Filters 30 g of scrubber per 140 Placed in a chamber 0 °C Emadpour et al.
(Prunus persica) (clenoptelolite) fruits storage 36 days (2015)
Food Bioprocess Technol
Table 2 (continued)

Produce KMnO4 Scrubber Dose Produce packaging Storage conditions Effects on produce quality Reference
support presentation

‘Red Gold’ Reduced firmness and weight loss. Mantained

‘Songlu’ good appearance. Delayed SSC increase. pH
‘Independence’ and TA were not affected
Food Bioprocess Technol

Papaya Vermiculite Sachet One sachet (1.5 g scrubber) Wrapped in LDPE 10 °C Reduced CO2 level. Delayed peel colour index Silva et al. (2009)
(Carica papaya L.) per 3 fruits(289.9 ± 18.5 film (28 μm thick) 25 days change. Reduced fresh fruit matter loss,
‘Sunrise Golden’ g each) (90% RH) consistency decrease and pulp electrolyte
leakage increase
Peach Zeolite Filter 30 g of scrubber per Placed in a chamber 0 °C Reduced firmness and weight loss. Delayed pH Emadpour et al.
(Prunus persica (clenoptelolite) 140 fruits storage 36 days increase. Mantained good appearance. Slight (2015)
(L.) Stokes) effect on SSC and TA was observed
‘Red Top’
‘Anjiry’
Pointed gourd Silica gel NS 8 g of scrubber per Packed in PP bags 29.4–33.2 °C Reduced spoilage and disease index. Delayed Bhattacharjee and
(Trichosanthes dioica kg of fruit (50 μm thick) 8 days chlorophyll content loss Dhua (2017)
Roxb.) (68–73% RH)
‘Kajli’
Sapodilla Vermiculite Sachet 0.375 g of KMnO4 per Placed in styrofoam 25 °C Delayed pulp firmness loss and vitamin C de Souza et al.
(Manilkara zapota kg of fruit trays with PVC 5 days degradation (2017)
(L.) P. Royen) film coating (54% RH)
‘Itapirema-31’
Strawberry Activated Sachet 10 g of scrubber per Packed in punnets 20 °C Slightly reduced C2H4 and CO2 concentration. Wills and Kim
(Fragaria x ananassa) alumina and 250 g of fruit with PE film (50 2 days Increased storage life. Delayed quality (1995)
‘Torrey’ vermiculite μm thick) coating deterioration rate. Susceptibility to grey mould
was decreased
Tomato Zeolite Sachet KMnO4/zeolite at 1.5:1.5% Placed in TPT 18 °C Delayed weight loss. Slowed firmness loss and Salamanca et al.
(Solanum lycopersicum L.) based on fruit weight packaging 28 days SSC increase. TA was not affected (2014)
‘Chonto’ (85% RH)
Tomato Zeolite Sachets 20 g of scrubber, fruit NS 4 °C Reduced weight loss and increased TA decrease. Köstekli et al.
(Lycopersicon esculentum) (clinoptilolite) weight NS 25 days SSC was significant affected. Delayed (2016)
‘Cherry’ ascorbic acid degradation rate and antioxidant
‘Cherry pera’ capacity loss
‘Rama’
‘Raf’
‘Pera’

PE polyethylene, HDPE high density PE, LDPE low-density PE, PET polystyrene terephthalate, PVC polyvinylchloride, PP polypropylene, TPT thermoformed PE terephthalate, PS polystyrene, NS not
specified
 Food Bioprocess Technol

75, 80 and 80% of residual C2H4 was obtained, respectively Layer Silicates and Zeolites
(percentage based on residual C2H4 of control).
Clays
Activated Alumina
Clay minerals are hydrous layered aluminosilicates composed
Activated Al2O3 is a semi-crystalline inorganic material com- of two layers: tetrahedral and octahedral layers (Bhattacharyya
posed mainly of aluminium oxide (Mallakpour and Khadema and Gupta 2008; Varma 2002). Tetrahedral layers consist of
2015). The raw material used, and the preparation and activa- sheets of Si4+, but Al3+ is also common, whereas the octahedral
tion methods determine the physicochemical and textural layers usually consist of Mg2+ or Al3+, although Fe2+, Ni2+,
properties of activated Al2O3 (Mallakpour and Khadema Li+, Fe3+, Cr3+ may also be present.
2015) . Activated Al 2 O 3 has a surface area from 50 to Clays are characterised by high surface area, high sorption,
500 m2 g−1 and pore size ranging from 60 to 150 Å (Leyva- swelling, and intercalation and cation-exchange with other
Ramos et al. 2008; Srivastava and Eames 1998). Nevertheless, ions without affecting the structure (Bhattacharyya and
the surface composition and pore structure of activated alumi- Gupta 2008). Moreover, they are eco-friendly, non-toxic, eco-
na can be modified, for example, by acid treatment (Yang nomical and recyclable. Therefore, it is useful to modified
2003). clays through ion exchange procedures with other positive
Alumina is often used as a desiccant similarly to SiO2, but charged atoms or organic ions (Avalos et al. 2008). In fact,
it is also used as a C2H4 scrubber. In fact, most commercial clays have a key role in the environment because they act as
KMnO4-based C2H4 scrubbers are made of activated alumina natural scavengers of contaminants by adsorption or ion-
as KMnO4 support (Table 1), which can be attributed to the exchange processes (Yagub et al. 2014).
physical and mechanical properties of the alumina particles. Smectite group is a kind 2:1 clay with an interlayer spacing
Alumina possesses high adsorption capacity and thermal sta- around 10 and 15 Å, where montmorillonite (MMT) is the
bility, being inexpensive and non-toxic (Mallakpour and most common member of this kind of clay (Varma 2002).
Khadema 2015). Spricigo et al. (2017) reported that 0.3 g MMT has an interlayer spacing of about 0.9 to 1.2 nm and
Al2O3 nanoparticles (93.59 m2 g−1 surface area and 20.6 Å great cation exchange capacity (Kaur and Kishore 2012).
average pore size) reached a C2H4 removal rate of 21% after MMT has been used as a KMnO4 support, but its applications
1 h when they were exposed to 7.48 mL L−1 C2H4 at 25 °C are mainly focused on adsorption of heavy metals, oxidation of
and 75% RH, but when these nanoparticles were impregnated alcohols and alkylarenes, among other organic compounds
with 5 and 10% KMnO4, they showed a C2H4 removal rate of (Abollino et al. 2003; Sen et al. 2012; Shaabani et al. 2004;
82 and 100%, respectively. In another study, it was reported a Shaabani et al. 2002). The KMnO4-MMT implementation for
90% C2H4 removal after 2.5 h when 1 g Al2O3 beads contain- the alkenes oxidation has been only reported by Choudary
ing 4% KMnO4 were exposed to 20 μL L−1 C2H4 at 20 °C et al. (1991). Nevertheless, the application of KMnO4-MMT
(60–70% RH) (Wills and Warton 2004). The high differences to extend postharvest life of fresh produce has not been report-
between the C2H4 removal rate of the scrubbers described in ed, although it should be noted that some studies do not indi-
the above-mentioned studies can be attributed to the particle cate the type of clay used (Table 2). For example, Santosa and
size differences since the last work stated that the activated Widodo (2010) evaluated the effect of KMnO4-based C2H4
alumina beads are 5 mm particle diameter before the modifi- scrubber using a clay as KMnO4 support on the quality attri-
cation with KMnO4. butes of banana. They observed that 30 g of scrubber per 0.42–
There are not many reports about the effect of KMnO4- 0.67 kg of fruit was enough to delay peel yellowing, reduced
based C2H4 scrubbers with Al2O3 as KMnO4 support on post- weight loss and firmness loss, and minimized the SSC and acid
harvest life of F&V to the best of our knowledge (Table 2). content increase up to 18 days at 27–30 °C. In another study
However, the study carried out by Wills and Kim (1995) carried out by Illeperuma et al. (2000), it was reported that the
showed good results when packed ‘Torrey’ strawberries green life of bananas packaged under modified atmosphere
(250 g) in punnets overwrapped with polyethylene (PE) film with KMnO4 supported on clay bricks was extended up to
and sachets containing activated Al2O3 and vermiculite im- 20 days at 25 °C in contrast to 4 days for fruit without C2H4
pregnated with KMnO4 (10 g). They found lower C2H4 and scavenger. Fruit showed little changes in firmness and SSC,
CO2 levels in the punnets with sachets, and a longer fruit lower C2H4 and carbon dioxide contents, and higher oxygen
storage life. Furthermore, Shorter et al. (1992) reported lower levels compared with fruit stored without C2H4 scavenger.
C2H4 and CO2 levels inside packages of Granny Smith apple
fruit stored in PE bags (0.5 °C, 2 weeks) with KMnO4-alumi- Vermiculite
na pellets scrubbers. At the end of storage, minor physiolog-
ical disorders (bitter pit and superficial scald) were observed in Vermiculite is a 2:1 layered silicate composed of two tetrahe-
apples stored with the mentioned C2H4 scrubber. dral sheets with a [T4O10]4− composition (where T can be Si4+,
Food Bioprocess Technol

Al3+ or Fe3+), and an octahedral sheet formed by two planes of until 2004. After that, the surface area was enhanced with the
packed O2− and octahedral OH− anions with Mg2+ or Al3+ as introduction of zeolite-type metal-organic framework mate-
central cations (Valášková and Martynkova 2012). rials reaching surface areas up to 3000 m2 g−1 (Chae et al.
The interlayer space of vermiculite is between 1.49 and 2004). The pore size of zeolites is usually ranging from 3 to
1.53 Å, and the thickness of the structural unit (2:1 layer and 12 Å, with a manipulable size (Sneddon et al. 2014).
interlayer space) is approximately 1.4 nm, depending on the Structural and adsorption (selectivity and sorption rates) prop-
interlayer cations and interlamellar water content (Valášková erties of natural zeolites can be modified by fixing the type,
and Martynkova 2012). The vermiculite specific surface area number and location of exchangeable cations (Erdoğan 2013).
varies from 1.4 to 720 m2 g−1 (Maqueda et al. 2007; Temuujin Zeolite minerals have been widely studied for their ability
et al. 2003), but the highest specific surface area values can be in adsorption of many adsorbates, including C2H4 (Erdoğan
achieved when the material is subjected to an acid or mechan- 2013; Sneddon et al. 2014). A lot of studies are focused on the
ical treatment, or both (Reinholdt et al. 2013). It has a cation C2H4 removal capacity that can be achieved using modified
exchange capacity of 12.0–15.0 mEq kg−1 (Malandrino et al. zeolites. In this way, Erdoğan et al. (2008) evaluated the C2H4
2006). removal capacity of natural clinoptilolite and the modified
The effect of vermiculite impregnated with KMnO4 on the forms with Na+, K+, and Ca+2 ions. Among all the modified
quality parameters of produce has been widely studied zeolites, it was found that the K+ form had the highest C2H4
(Table 2), although not promising results have been reported. adsorption capacity (0.719 mmol g−1) at 20 °C, followed by
For example, sets of three papaya fruit were wrapped in low- the Na+ (0.069 mmol g−1) and Ca2+ forms (0.226 mmol g−1).
density PE films with sachets of KMnO4-based C2H4 scrub- The latter finding may be attributed to the electronegativity
bers supported onto vermiculite (one sachet containing 1.5 g value and atomic diameter of potassium. However, the highest
scrubber material) at 10 °C (90% RH). After 25 days, fruit C2H4 adsorption was obtained by the unmodified form
stored together with C2H4 scrubbers showed lower CO2 pro- (0.956 mmol g−1). The experiment was also performed with
duction, less fresh matter loss, reduced pulp consistency loss another zeolite from a different source being observed the
and less SSC increase in comparison with fruit without a same behaviour. In another study, Sue-aok et al. (2010) report-
scrubber, but peel colour index and electrolyte leakage did ed that the C2H4 adsorption capacity of the K+ modified form
not show a statistical difference between samples (Silva of NaY zeolite was also higher than that shown by Rb+ and
et al. 2009). The effect of KMnO4 supported on vermiculite Cs+ modified forms. The C2H4 adsorption on K+ modified
(0.375 g of KMnO4 per kg of fruit) was studied on different NaY zeolite was 102.5 cm3 g−1 at 0 °C, 98.5 cm3 g−1 on
quality parameters (firmness, appearance, colour, TA, SSC, Rb+-NaY zeolite and 90.15 on Cs+-NaY zeolite. Erdoğan
weight, among others) of sapodilla (packaged in a tray and (2013) found that it is possible to improve the C2H4 adsorp-
covered with PVC film) stored for 15 days at 25 °C (54% tion capacity of a clinoptilolite from 0.619 to 1.219 mmol g−1
RH). It was only observed beneficial effects on vitamin C (at 20 °C) by replacing the exchangeable cations with H+ ions
content and fruit firmness (throughout 5 days), but fruit using 0.5 M HCl. Nevertheless, higher HCl concentration may
showed similar softening to control fruit at the end of storage trigger crystalline loss and Al ions reduction. Zeolites have
(fruit packaged without C2H4 scrubbers) (de Souza et al. been widely used as material support in KMnO4-based C2H4
2017). Silva et al. (2015) reported higher vitamin C content scrubbers for active packaging for fresh F&V due to their
and less chlorophyll loss in maxixe fruit (packed in PE trays adsorption properties, high surface area, pore structures, cat-
with PVC film) with KMnO4-vermiculite sachets stored at ion exchange capacity and molecular sieve ability, as well as
10 °C (90% RH) after 10 days, but final weight loss, carbo- to their low cost and availability (Martínez-Romero et al.
hydrates content, fruit decay percent and chilling injury traits 2007; Yagub et al. 2014). Some products containing zeolite
were similar to control fruit. are available in the market for C2H4 control since zeolites have
great potential to remove C2H4. (Table 1).
Zeolite The effect of KMnO4-coated zeolite particles on the quality
characteristics of fresh fruit was evaluated in different studies
Zeolites are hydrophilic crystalline aluminosilicates with a (Table 2). Emadpour et al. (2015) reported that it was possible
negative framework charges that are balanced with alkali or to increase peaches’ and nectarines’ shelf lives (at 0 °C)
alkali earth ions (Patdhanagul et al. 2012). Zeolites can be preventing weight and firmness losses, as well as spoilage,
natural, or they can be synthesised in order to develop new using KMnO4-coated nano-zeolites filter in the storage cham-
materials with larger pores or channels and more catalytic bers. It was found lower weight loss, higher texture firmness
sites. A total of 234 zeolite framework types have been ap- and longer (≈ 20 days) iceberg and Chinese lettuces shelf lives
proved by the Structure Commission of the International when using KMnO4 and zeolite-based nano-molecular filters
Zeolite Association until today (IZA-SC 2017). It was consid- in the storage chambers (Kalaj et al. 2008). Similar results
ered that zeolite Y had the highest surface area (904 m2 g−1) were found when this filter system was evaluated on apricot
 Food Bioprocess Technol

(Emadpour et al. 2009b) and black sweet cherry (Emadpour and Barska (2017), an active packaging is a system that inter-
et al. 2009a). In another study, Golden Delicious apples were acts with the packed product, actively changes the conditions
wrapped in craft paper together with KMnO4-coated nano- of the packed food (internal atmosphere) by scavengers or
zeolite sachets and then stored at 0 °C (90% RH) for 5 months emitters and prolongs its shelf life while maintaining its qual-
(Sardabi et al. 2014). The latter authors observed lower pH ity. Although active packaging can offer marketable solutions
increase/TA decrease, firmness loss and Hue angle changes to the food industry, the market offer of such system is still
when apples were stored with C2H4 scrubbers comparing to poor. Accordingly, the share of advanced packaging repre-
fruit without the scrubbers. sents about 5% of the total packaging market value, of which
35% corresponds to active packaging, and, especifically, the
Activated Carbon market share of C2H4 scavengers represents 3% of the global
market value of gas removal packaging (Gaikwad and Lee
Activated carbon (AC) materials are non-crystalline porous 2017; Wyrwa and Barska 2017). The latter low presence of
forms of carbon obtained by pyrolysis of carbonaceous mate- active packaging in the market may be mainly be due to con-
rials (Ben-Mansour et al. 2016; Sneddon et al. 2014). The sumer acceptance, since consumers have a key role on food
activation step of carbon is carried out to create more pores packaging industry by their purchasing choice (Ghaani et al.
and change their volume, form and size, and it can be per- 2016; Werner et al.2017).
formed by physical and chemical methods (Yang 2003). Most Consumer acceptance of active packaging can be influenced
commercial grades of AC usually possess a pore volume be- by health and environmental safety concerns (risk perception)
tween 10 to 25 Å in diameter and a surface area ranging from and mistrust in new technologies, which is due to a lack of
300 to 4000 m2 g−1, but some of them can reach surface areas information about technologies involved (Eiser et al. 2002).
up to 5000 m2 g−1 (Martínez-Romero et al. 2007; Yang 2003). Attending the concerns about possible health damage that
AC can be granular, powdered or fibre, being the most could be caused by KMnO4, KMnO4-based scavengers are
preferred the granular form due to its easier regeneration and never used in direct food contact (Dainelli et al. 2008;
versatility. In addition, it has been reported that the best C2H4 Wyrwa and Barska 2017). KMnO4-based scrubbers are avail-
adsorption is performed by granular form (over 80%) in com- able in the form of sachets, tube filters, blankets, labels or
parison with powder (over 70%) and fibre forms (over 40%) films, with the most widely used form being sachets because
(Martínez-Romero et al. 2007). Bailén et al. (2006) evaluated they are suitable for individual packaging (Janjarasskul and
the effect of modified atmosphere packaging (using 20 μm Suppakul 2016) and easy to apply. Nevertheless, it is also
thickness PP bags) with sachets containing 5 g granular AC difficult to deal with consumer perception about the presence
(having a specific surface area of 226 m2 g−1) on ‘Beef’ to- of a non-edible artefact together with the food. According to
mato quality during postharvest storage at 8 °C (90% RH). Aday and Yener (2015), consumers do not want to see sachets
The authors observed that granular AC delayed the changes in or anything else apart from the desired food inside the pack-
colour, firmness and weight in tomato, while significantly aging due to fear of swallowing the device and to the risk of its
reduced the C2H4 levels inside packages up to 2 weeks accidental rupture, contamination of the packaged food and
(Bailén et al. 2006). AC can be combined or impregnated with ingestion of the content. Therefore, this issue is still a chal-
other compounds such as KMnO4 to increase its effectiveness. lenge with a constant search for solutions that allow scaven-
Nevertheless, there are scarce works about the C2H4 removal gers to be incorporated into the packaging without the nega-
capacity of AC-KMnO4 although its use as C2H4 scrubber is tive perception of the consumer.
widely mentioned in the literature (Brody et al. 2008; Gavara Consumers must be correctly informed about novel tech-
et al. 2009; Sen et al. 2012). AC shows advantages such as nologies and the active products should be adequately labelled
hydrophobic behaviour, high surface area, lightweight while to change conventional consumers’ perception gaining their
its production is relatively cheap (Ben-Mansour et al. 2016). trust. The packaging manufacturer must provide active sub-
Nevertheless, the KMnO4-AC combination results in active stances list together with chemistry, environmental and toxico-
MnO2, which is an insoluble and powerful oxidising agent logical data (Werner et al.2017). In the USA, the FDA regu-
due to a redox reaction (Ishii et al. 1998). lates food packaging and food ingredients by the Federal Food,
Drug and Cosmetic Act (FFDCA), which is codified in the
Title 21 of the United States Code (Chapter 9) (OLRC 2017).
Consumer Acceptance and Safety Aspects Meanwhile, in the European Union, conventional and active/
intelligent materials or other articles intended to come into
The KMnO4-based scavengers can be used as part of a con- contact with food are regulated by the European Parliament
trolled or modified atmosphere system to remove the accumu- Council (EC) No. 1935/2004 and the Commission
lated C2H4 inside a closed atmosphere (Keller et al. 2013), Regulation (EC) No. 450/2009 (European Parliament 2004,
being then known as an active packaging. Based on Wyrwa 2009).
Food Bioprocess Technol

Toxicology and Environmental Aspects selected support material in KMnO4 scrubbers providing then
a product with excellent quality to consumers. Vermiculite and
KMnO4 has been widely used in postharvest treatment as a activated alumina are the most commonly used materials to
disinfectant and auxiliary agent in the degradation of pesticide reach this goal, being activated alumina the most used in com-
and clinically as antiseptic and antifungal agent (Osman et al. mercial KMnO4-based C2H4 scrubbers. However, based on
2014; Soriano et al. 2000; WHO 2017). The KMnO4 may be the information described above, scrubbers using SiO2 gel or
lethal for humans at high doses of approximately zeolite as KMnO4 supports seem to be a promising tool to
142.9 mg kg−1 person. Nevertheless, KMnO4 intoxication is slow down the ripening process and prolong shelf life of
not common being necessary approximately 10 g of KMnO4 F&V. Although vermiculite impregnated with KMnO4 has
to produce lethal intoxication in a person of 70 kg according to been widely studied, not promising results have been founded.
the latter lethal dose (Cevik et al. 2012). For example, using More studies using activated Al2O3 and activated carbon are
KMnO4 contents of treated banana and cantaloupe melon needed. In general, the combination of nano-sized materials
(Table 2), and according to the KMnO4 lethal dose, a person with C2H4 oxidant agents can be considered as an ideal ap-
(70 kg) would need to consume approximately 2.5 kg of treat- proach for C2H4 removal and preservation of quality charac-
ed banana or 3.4 kg of treated melon to become lethally in- teristics of F&V under controlled or modified atmospheres.
toxicated as described by Santosa and Widodo (2010) and Sá
et al. (2008). Nevertheless, the latter product quantities may
Funding Information The authors express their gratitude to
depend of course of the KMnO4 content of the used scrubbers CONACYT (National Council of Science and Technology, Mexico) for
being used commonly between 4 and 6% of KMnO4 within a doctoral grant (No. 291212) to Marianela Hazel Álvarez-Hernández.
the commercial sachets. For example, de Souza et al. (2017)
used 0.375 g of scrubber per kg of sapodilla and Brackmann
et al. (2006) used 1.5 g per kg of apple, while Wills and Kim
(1995) applied 20 g of scrubber per kilogram of strawberry. References
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