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Food and Beverage Chemistry/Biochemistry
Absorption of Ethylene on Membranes Containing Potassium Permanganate Loaded into Alumina Nanoparticle Incorporated Alumina/Carbon Nanofibers Ashkan Tirgar, Daewoo Han, and Andrew J. Steckl J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/ acs.jafc.7b05037 • Publication Date (Web): 11 May 2018 Downloaded from http://pubs.acs.org on May 13, 2018
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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
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Journal of Agricultural and Food Chemistry
ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
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#437
April 18, 2018
Absorption of Ethylene on Membranes Containing Potassium Permanganate Loaded into Alumina Nanoparticle Incorporated Alumina/Carbon Nanofibers Ashkan Tirgar, Daewoo Han, Andrew J. Steckl
∗
Nanoelectronics Laboratory Department of Electrical Engineering and Computer Science University of Cincinnati Cincinnati OH 45221-0030
∗
corresponding author:
[email protected] 1 ACS Paragon Plus Environment
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Abstract
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Ethylene is a natural aging hormone in plants, and controlling its concentration has long been a
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subject of research aimed at reducing wastage during packaging, transport, and storage. We
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report on packaging membranes, produced by electrospinning, that act as efficient carriers for
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potassium permanganate (PPM), a widely used ethylene oxidant. PPM salt loaded on membranes
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composed of alumina nanofibers incorporating alumina nanoparticles (ANPs) outperform other
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absorber systems and oxidize up to 73% of ethylene within 25 min. Membrane absorption of
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ethylene generated by avocados was totally quenched in 21 hours and a nearly zero ethylene
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concentration was observed for more than 5 days. By comparison, the control experiments
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exhibited a concentration of 53% of initial value after 21 hours and 31% on day 5. High surface
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area of the alumina nanofiber membranes provides high capacity for ethylene absorption over a
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long period of time. In combination with other properties, such as planar form, flexibility, ease of
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handling, and light weight, makes these membranes a highly desirable component of packaging
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materials engineered to enhance product lifetime.
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Key Words: Electrospinning, potassium permanganate, alumina nanoparticle, alumina fiber,
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ethylene absorption, ripening prevention.
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Introduction
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Climacteric fruits, like banana, tomato, avocado, kiwi, apples, apricots, and blackberries produce
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ethylene (C2H4) which regulates the plant growth and ripening process.1-19 The ripening process,
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normally described by flesh softening, color change and production of aromas, leads to the loss
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of eating quality in fruits and reduces their storage life. Even non-climacteric fruits like berries
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have shown acceleration in ripening process upon exposure to exogenous ethylene.20
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Previously, various methods and materials have been suggested to control the ethylene level.
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Sorbents, such as zeolite and carbon, have been successfully used to adsorb the ethylene 19, 21-23,
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but these materials only transfer it to another phase without any chemical destruction of ethylene.
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Use of catalytic materials, such as palladium and TiO2 nanoparticles, have been reported as an
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alternative ethylene control method. However, they are not favored in these applications because
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palladium is an expensive material and TiO2 requires UV light to react with ethylene. The most
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common ethylene control absorbent used in the fruit industry consists of strong oxidants, such as
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potassium permanganate (PPM) loaded on inert carrier materials, such as alumina
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diatomaceous earth 28.
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such as the absorber component of ethylene control systems31,
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antimicrobial agent in antiseptic products.33 Chemical leach study is recommended after
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developing any system containing PPM to select the right packaging material/structure that
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would not allow more than a ‘Do Not Use’ concentration of ~ 0.1 g PPM (for a 75-kg person)34
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in one exposure from contaminated fruits/produce. Our nanofiber membranes have an inherent
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advantage because they can be easily sandwiched between PPM-free (electrospun) membranes
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or any other desired packaging layers. Typically, an aqueous solution of the permanganate salt is
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loaded into/on the carrier substrate of interest to obtain an ethylene absorber system.
19, 29, 30
24-27
or
Potassium permanganate is extensively used in many applications
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water treatment32, and
, ,
In our
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manuscript, the term ‘absorption’ is used when ethylene molecules are hydroxylated by reacting
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with oxidants.
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To be used as a PPM carrier, the material must be inert to chemical reaction with PPM and
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provide a porous structure with high surface area. To date, PPM carriers for absorbing ethylene
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have been developed in different forms of beads, films, and liners. Due to their physical form,
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the beads are placed inside small pouches made of gas permeable materials.
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Therefore, they can only provide ethylene absorption in a very limited area around the pouch.
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The self-supporting membranes demonstrated in our report can address this issue by serving as a
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PPM carrier that can be used as a packaging material for either individual fruits or the entire
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batch jet of fruits. In addition, since the natural convection and diffusion are the only driving
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forces displacing ethylene molecules, the efficiency of all different forms of absorption systems
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(bead, film, liner) would depend on their surface area where the contact and thus reaction
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between the ethylene and the oxidant occurs. A study of 21 different carrier materials has
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demonstrated that carriers with lower bulk densities and higher salt uptake capacity are more
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efficient in reducing ethylene levels. Our membranes provide a uniquely large surface area and
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are fabricated using fiber electrospinning, a simple but versatile technique that can be a cost-
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effective method for making PPM carriers.
19, 29, 30, 35-41
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Electrospinning42-44 is an extremely versatile technique for the fabrication of light and flexible
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free-standing porous fiber membranes made of a wide range and combinations of materials. The
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diameter of fibers produced by electrospinning ranges from tens of nanometers to micrometers
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depending on the solution parameters (viscosity, conductivity, vapor pressure, etc.) and process
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parameters (voltage, distance, flow rate, etc.). This technique has been also used for the
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fabrication of coaxial and triaxial fibers required in specific applications.45, 4 ACS Paragon Plus Environment
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The
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electrospinning setup is composed of a high voltage power supply connecting a spinneret and a
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collecting substrate that is grounded. The applied electric field provides a force for stretching a
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liquid out of the droplet at the tip of the nozzle. The liquid jet travels the distance between the
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spinneret and the collector while it undergoes whipping and bending instabilities that elongate
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the jet and eventually forms a nearly dry mesh of fibers, with high surface-to-volume ratio.
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Here, we report the first demonstration of using electrospun nanofiber membrane loaded with
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permanganate ethylene absorber to prevent food ripening. A summary of our approaches for
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making ethylene absorber membranes is illustrated in Fig. 1. ANP-incorporated carbon
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nanofibers after PPM casting are illustrated in Fig. 1a. These membranes were electrospun from
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an ANP-dispersed polyacrylonitrile (PAN) solution followed by a two-step carbonization process
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that converts PAN polymer fibers to carbon fibers. The carbonization step is necessary because
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PPM is a very strong oxidizing agent that will be inactivated by reduction upon contact with
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most polymers and solvents commonly used in electrospinning. Our second approach, illustrated
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in Fig. 1b, uses alumina nanofibers (ANF) fabricated by electrospinning a polymer solution
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containing aluminum acetate, followed by a calcination process in air to convert aluminum
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acetate to alumina. Alumina is widely in industrial compounds as an adsorbent, abrasive, water-
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proofing agent, and in lubricants.
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compounds is between 162 and 980 mg/kg.
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membranes and the concentration of alumina in them, they should not expose any risk to
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consumers health. Finally, Fig. 1c illustrates alumina nanofibers impregnated with ANPs to
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improve their efficiency as a PPM carrier. We have investigated the relationship between the
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ANP concentration and the ethylene absorption capacity of ANP-incorporated alumina
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nanofibers. The results indicate that the ethylene absorption capacity of our membranes can
47
The oral median lethal dose (LD50) value for aluminum 48
Hence, based on the weight of our developed
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outperform other well-known absorber systems, such as Blueapple absorber and PPM-loaded
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alumina beads. Further, the membrane absorption capacity can be easily tuned by controlling the
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amount of ANPs incorporated into the fibers. Furthermore, our membranes possess properties
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such as planar form, flexibility, ease of handling, and light weight that are attractive for many
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applications, enabling potential users to easily customize the absorption capacity and rate of
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absorption based on their needs.
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Experimental Section
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Materials
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Polyacrylonitrile (PAN, Mw = 150 kDa), polyvinylpyrrolidone (PVP, Mw = 360 kDa),
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aluminum oxide nanopowder (diameter
