Vacuum Hermetic Fumigation: A review

Journal of Stored Products Research 71 (2017) 47e56

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Vacuum Hermetic Fumigation: A review Sunil Kumar*, Debabandya Mohapatra, Nachiket Kotwaliwale, Krishna Kumar Singh ICAR-Central Institute of Agricultural Engineering, Bhopal, 462038, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 October 2016 Received in revised form 12 January 2017 Accepted 20 January 2017 Available online 31 January 2017

Methyl Bromide and Phosphine are the most widely used chemical fumigants for insect control in stored grains. Ozone depletion, insect resistance, and residues on grain surface are the problems with the use of chemical fumigants. Zero tolerance for chemical residues under the international trade agreements require alternative solutions for safe and durable storage. Controlled atmosphere (CA)/modified atmosphere storage (MAS), temperature manipulation, hermetic storage, pressure manipulation (hyperbaric and hypobaric), safe fumigants of botanical derivatives and combination of these technologies have been practiced. Each method had certain merits and limitations restricting direct replacement for the existing chemical methods. This review explores chemical disinfection and physical methods with special emphasis on vacuum hermetic fumigation (VH-F). Modern hermetic storage systems utilize ultra-low oxygen and water permeability materials for storage of grains. Depletion of oxygen in the storage systems naturally or through the application of negative pressure (50e100 mm Hg) causes slower metabolic rate and finally cessation of basic metabolism and death of insects in a few days (up to 7 days). The efficacy of VH-F on the lethality of insects depends on vacuum level, stage and type of insects, temperature, CO2 level and exposure time. Suitability of vacuum hermetic storage systems for various agricultural produces as an alternative to chemical fumigation and the future scope of vacuum hermetic fumigation system are discussed. © 2017 Elsevier Ltd. All rights reserved.

Keywords: Vacuum Hermetic Fumigation (VH-F) Low-pressure storage Food protection Non-chemical insect control

Contents 1. 2. 3.

4. 5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Hermetic storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.1. Insect control and quality assurance under hermetic storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Vacuum hermetic fumigation (VH-F) system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.1. Insects control under VH-F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.2. Insects control under combination of VH-F and other techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Potentials and challenges in VH-F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

1. Introduction The world's population has already surmounted to 7 billion and it is expected to reach 8.1 billion in 2025, and 9.6 billion in 2050 (UN, 2014). Depleting and limited resources have drawn the

* Corresponding author. E-mail address: [email protected] (S. Kumar). http://dx.doi.org/10.1016/j.jspr.2017.01.002 0022-474X/© 2017 Elsevier Ltd. All rights reserved.

attention of researchers to move towards sustainable and precision agriculture, which aims for higher production with minimum utilization of resources to overcome the global threat of food security in the future (Lipinski et al., 2013; Mohapatra et al., 2015). Food production, distribution, and consumption are a series of events, which together forms a post-harvest system. In this whole series, an unfortunate attribute is associated, that is wastage of large amount of food grains both in field and during storage (Kiaya, 2014). In developing countries, about 10e15% of the total

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production is lost during harvesting, threshing, transport, storage and processing (Neethirajan et al., 2007). Lack of proper storage structure, pest damage during transport, improper handling and unscientific unit operations before reaching to consumers are the major reasons for food losses (Somavat et al., 2014). A survey conducted all over India, reveals that about 4.65e5.99% postharvest losses of cereals (wheat, paddy, maize, pearl millet and sorghum) occur during various unit operations. In India, storage losses for cereals was 0.75e1.21%, whereas the losses in pulses and oilseeds were observed to be in between 6.36-8.41% and 3.08e9.96%, respectively (Jha et al., 2015). In the past decades, major focus and investment were allocated to increase food production. 95% of the research expenditure of developing countries was invested in increasing the food productivity and rest in reducing the post-harvest losses (Kader, 2005). The stored product insects and pests are a global problem. Storage pests create both qualitative and quantitative losses in stored agricultural commodities (Neethirajan et al., 2007; Sharon et al., 2014). Losses could be classified as direct and indirect losses. The presence of open or concealed live and dead insects, their droppings and fragments are direct losses; whereas allergens, microorganisms, low market value and parasites transfer to human are categorized as indirect losses (Sahay and Singh, 2004). Two fumigants, Methyl bromide (MB) and phosphine (PH3) are globally used for disinfection in food grains storage. Methyl Bromide is a significant ozone depleting substance (ODS). Under Montreal Protocol, 2002, the use and production of methyl bromide was discontinued in developed countries by the year 2005 and worldwide by 2015 (UNEP, 2002). Continuous and discriminate use of phosphine has resulted in the evolution of chemical resistance in insects. Widespread experience has proven that repeated use of the single slow acting chemical in poorly sealed warehouses leads to develop strong resistance by the insects (Simmonds, 1989; Cao et al., 2003; Ahmad et al., 2013; Chadda, 2016). It diverted the focus of research towards development of residue free, organic and environment benign alternative technologies to protect stored produces (Simmonds, 1989; Darby and Caddick, 2007; Navarro, 2012; Kucerova et al., 2013). Physical measures are safer alternatives as it can be applied directly to stored food. Although a large number of potential alternative methods have been suggested; limitations of each prevent direct replacement of the chemical fumigants. The nonchemical alternatives in use today are not new technologies but it requires adequate monitoring and verification to ensure that treatment's efficacy and proper application (Dowdy, 2002). These methods include controlled atmosphere (CA)/modified atmosphere storage (MAS), hermetic storage, pressure manipulation, temperature manipulation, irradiation, microwave/Radiofrequency treatment, application of inert dust, and combinations of these technologies as hurdles to insect and pest (Das et al., 2013; Finkelman et al., 2004a,b,c; Kucerova et al., 2013; Mohapatra et al., 2015; Navarro, 2006; Subramanyam et al., 2011). The merits and demerits of most physical methods for insect control of stored food grains are listed in Table 1. The feasibility of using vacuum for safe post-harvest storage was first investigated by Back and cotton, (1925), Bare (1948) and later on by Calderon et al. (1966). Evolution of technologies enables to maintain low pressure in flexible plastic liner in place of massive and rigid vacuum chambers using a vacuum pump that started the abandoned work of vacuum storage of durable commodities (Finkelman et al., 2004a; Navarro et al., 2001, 2002a,b; Rindner et al., 2002). Consequently, a new term was originated for the sealed vacuum flexible container as Vacuum Hermetic Fumigation (VH-F), which is used for low-pressure storage of non-crushable agricultural produces in flexible bags (Finkelman et al., 2004c).

Since the review of VH-F is not available so far, this paper is an attempt to archive the research findings. The interstitial gas composition of a storage structure has dramatic effect on biotic components in a grain ecosystem. Insects, mold, grain, and microorganisms are aerobes, need oxygen for respiration. The biological activities help in depleting oxygen and generate a lethal high carbon dioxide (3e10%) atmosphere for insects (Abalone et al., 2011; Bartosik, 2012; Murdock et al., 2012; Subramanyam et al., 2012). The successful application of lethal atmosphere within a gastight container was used as commercial control tactic for insect infestation in many countries. Gas tightness has paramount importance for successful storage, so this technique was named as hermetic storage. Lack of gas tightness was a global challenge before the development of flexible plastic containers with zipper for hermetic storage. Adequate sealing in plastic containers is comparatively easy than rigid containers. Insect penetration, surface area/volume ratio, cost of sealing and permeability of plastic liner are bottlenecks in rendering the hermetic technology (Navarro, 2012). 2. Hermetic storage Successful storage is the placement of food grains in suitably sized containers which endowed protection from pests, insects, microbial and physical contamination as well as maintaining the nutritional and processing quality. Generation of modified atmospheres (MAs) inside hermetic bags thorough vacuum, inert gasses and respiration of commodity, have successfully replaced the use of fumigants for quality preservation and insect control of stored materials (Villers et al., 2008; Bartosik, 2012). There are three manners to use hermetic technology viz. Organic storage, Gas Hermetic Fumigation (G-HF) and Vacuum Hermetic Fumigation (VHF). Organic storage is a simple passive modified atmosphere storage technique, which developed the carbon dioxide enriched environment after a particular time. In G-HF and V-HF, the interstitial atmosphere is replaced by an inert gas (Carbon dioxide; Nitrogen) and vacuum respectively (Villers et al., 2006). Commercially, these terms are used by the USA based GrainPro® named company for their various solutions for hermetic storage. Ultimately the goal of all three manners to develop oxygen deficient (1e2%) ecosystem detrimental to insect and mold growth (Navarro et al., 2003; Villers et al., 2006; Jonfia-Essien et al., 2010). The oxygen concentration depends on insects, infestation level, type, and size of the storage system, stored commodity, the moisture content of commodity, environmental factors etc. It was reduced from 21% to less than 10% within a short period of time. Oxygen levels <10% curtailed the insect growth and germination of seed was above 85% for a period of up to 9 months, whereas nonchemical conventional storage in jute bags reduced germination down to 14% within 3 months (Villers et al., 2008; Bartosik, 2012). For bio-friendly and effective storage in tropical regions, sealed hermetic flexible silo bags are the efficacious solution for preserving moisture content without significant insect proliferation in stored grain (Anankware et al., 2012; Somavat et al., 2014). It is also known as “sealed storage” or “airtight storage” or “sacrificial sealed storage” or “hermetic silo storage” or “harvest bag” or “grain sausage” (Jonfia-Essien et al., 2010). These are available as small portable containers (60 kg to one ton) to large flexible storage structure (five tons to 30,000 tons capacity) (Villers et al., 2008). Storage systems based on the hermetic principle include the following: Bunker storage for conservation of large bulks (10,000e15,000 tons); storage cubes or “Cocoons™” (five to 1000 tons capacity); Silo Bags (200 tons capacity) for on-farm storage and small portable hermetic containers (25 kge2.5 tons), called “Super Grainbags™”, which are suitable for bagged and bulk

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Table 1 Physical methods of disinfestation with their merits and demerits. Sr.No. Physical Methods

Merits

Demerits

References

1

break-up of insect developing pockets, uniformity of temperature

labour and handling equipment requirement, time consuming, tedious work, chances of cross contamination, No post treatment protection, no effect on internal infestation. most effective in conditions of low humidity, Dusty to apply, Labour intensive to remove before processing, Decreased flowability, visible residues affect bulk density and grading. No post treatment protection, labour and handling equipment requirement, need extra structure, no effect on internal infestation, time consuming, tedious work, chances of cross contamination. Weather dependant, unhygienic conditions prevail in most traditional practices, requires prolonged exposure time Maintenance of safe moisture content, Storage in moisture impervious bag, require low humidity environment for long tern storage, Case hardening, moisture condensation and hot spots. Costly for low temperature maintenance, no post treatment protection, take hours to days, loss of viability on high temperature, temperature range 0e45
C, denaturing of intracellular proteins. Add extra cost in structure (Fan, ducts etc.), No post treatment protection. High cost of equipments, Slow fumigant, Need highly skilled labour for operation and maintenance of equipment. Anaerobic fermentation, need highly skilled labour; maintenance of airtightness, Slow process, Need safety from rodents, few reports of insect presence and moisture condensation. Applicable to sound sensitive insect and pests, Detection error due to external sound.

Banks, 1976; Jayas et al., 1994; Vincent et al., 2003

2

Physical Removal (Sieving, winnowing, cyclone separator) Inert dusts (Non-silica and Silica dusts)

Safe, low mammalian toxicity, chemically unreactive, inhibit insect behaviour, affecting movement and reproduction by blocking air spaces between grains and locally available. Pneumatic circulation or dropping from a certain height; kill insect effectively, Break-up of insect developing pockets, slight loss of heat during operation.

3

Turning and disturbance Method

4

Sun drying

Economical, wide spread, no need of skilled labour, use of renewable energy source, environmental friendly

5

Conventional Drying

6

Temperature Manipulation (Fluidized and sprouted beds) Aeration

Economical, widespread, Longer shelf life, reduction in cost involved for storage and handling, no need of skilled labour, use of local made components and conventional fuel. Use of Low (<14
C) or high (>40
C; Bake out technique) temperature, very effective, residue free, 100% kill, high quality of stored product, rapid than methyl bromide fumigation. Reduces temperature, off odour and moisture content, Delay infestation, uniform distribution of fumigants. 100% mortality of insects, High nutritional value, acceptability and safety.

7 8

9

10

11

12

Controlled Atmosphere Storage (CAS) Modified Atmosphere Storage (MAS)

Mortality of insects (Less than 1% (V/V) Oxygen), chemical free, High nutritional value, acceptability and safety; Environment Benign, Maintenance free and transportable. Ultra sound Kill the insect pest or produces changes in their behaviour, including reproductive behaviour. used in insect detection. IonizingUse of X ray and Gamma rays, cold sterilize, 100% Irradiation mortality, safer and easier to work, Fast start-up and shut-down (except isotopes), destroy internal and external infestation. Dielectric Heating Rapid action, Fast start-up and shut-down, precise (Radio Frequency process control, high thermal efficiency, safe and hygienic insect control, improved product quality, and Microwave) destroy internal and external infestation.

13

Infrared Radiation

14

Traps (Pheromone and Visual lures)

15

Hypobaric storage (Low pressure)

16

Hyperbaric storage (High Pressure)

Lale and Sastawa, 1996

Rahman and Perera, 1999; Vadivambal and Jayas, 2007. Jayas et al., 1994; Fields and White, 2002; Vincent et al., 2003; Wright et al., 2002. Jayas et al., 1994; Sahay and Singh, 2004. Jayas et al., 1994; Fields and White, 2002; Shejbal, 2012. Jayas et al., 1994; Simmonds, 1989; Jayas and Jeyamkondan, 2002; Bartosik, 2012 Jayas et al., 1994; Vincent et al., 2003

High initial investment, No immediate kill, Radiolysis of Fields and White, 2002; Vincent et al., 2003; Das products, poor consumer acceptability, high power consumption, large weight of machine and installations. et al., 2013.

Heat transfer behaviour depends upon thickness, geometry and dielectric properties of grain; nonuniformity in heating, poor penetrating power, no post treatment protection, Higher equipment cost; Hot spots and poor germination of seed. Above 99.5% mortality (65
C for less than a minute), Costly, slow than dielectric heating, Eggs and early High heating rate and energy efficient than conventional instars are most resistant stages of insects, no post treatment protection, Limited to research. methods. Does not heat the medium. Monitor insect populations or density, attract and kill Temperature, time, rainfall, and wind speed and certain flies, moths, and beetles within weeks. direction influence attractant release, Effective in certain indoor situations, pheromones are viable for three insects (R. domincia, T. castaneum, T. variabile). Disinfect the infested commodity, <100 mm Hg required Costly equipments and structure, regular inspection to for effective control, used on fruits and vegetables as prevent leakage, regular use of vacuum pump to well as cereals, pulses and oilseeds, can be used in maintain pressure <100 mm Hg, need of skilled labour to combination with essential oils, CO2, higher temperature operate etc. to reduce exposure time, on-farm storage, pesticide free. Environment friendly; can be used in combinations with Beetle require more pressure than moth; costly CO2, 5e20 min required for complete mortality at 30 kg/ equipment and structure, High initial investment, costly maintenance, need of skilled labour to operate cm2 with 98% CO2, used for Rapid disinfection of commodities, no significant effect on the germination of treated commodity.

commodities as well as seed storage (Villers et al., 2008; JonfiaEssien et al., 2010). Cocoons are fabricated from specially formulated flexible 0.83 mm thick PVC with permeability to oxygen of 400 cc/m2/day and to water vapor of 8 gm/m2/day (Jonfia-Essien et al., 2010). A type of Cocoon named the “MegaCocoon™” has been developed for large scale storage of up to 1050 tons (Villers et al., 2008, 2010). The Purdue Improved Crop Storage (PICS™) bag has demonstrated in controlling the losses in cowpeas, peanuts,

Jayas et al., 1994; Banks and Fields, 1995; Allen et al., 2001. Vincent et al., 2003 Jayas et al., 1994; Simmonds, 1989.

Gunasekaran, 1999; Vincent et al., 2003 Vadivambal and Jayas, 2007; Das et al., 2013. Mohapatra et al., 2014 Banks and Fields, 1995; Pan et al., 2008; Hansen et al., 2011. Vincent et al., 2003; Neethirajan et al., 2007.

Finkelman et al., 2004a; Navarro et al., 2002a; Mbata and Phillips, 2001

Caliboso et al., 1994; Nakakita et al., 2001.

maize, wheat, sorghum, and common beans due to insect and pests. The PICS bag is triple layer hermetic bagging technology. The 80 mm high-density polyethylene (HDPE) is used to make inner two layers and outer layer material is woven of polypropylene for safe handling. Research findings have proven up to 98% adult insect mortality after one month of storage period in PICS bags (Williams et al., 2014; Murdock and Baoua, 2014). Several researchers (Villers et al., 2008, 2010; Bartosik, 2012; De

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Bruin et al., 2012; Navarro et al., 2012) have advocated the use of hermetic grain storage technology as alternate methods of insect pest control to chemical fumigation, which are summarized as follows: i Hermetic bag can be used for durable and perishable commodities, ii. The hermetic bags can be stored indoor and outdoor in open atmosphere or farms. It saves the extra charge for shade. ii. No use of pesticides and insecticides for control of postharvest losses. iv. No need of regular inspection if sealed properly. v. Affordable price and maintenance free. vi. Preserves original moisture content and negligible pilferage loss. vii. Better utilization of space. vii. Corrosion free, Lightweight and Transportable. ix. Minimal waste.

2.1. Insect control and quality assurance under hermetic storage Recently the hermetic bags are adopted in Asia, Africa, and Latin American countries for the storage of food grains for human consumption. Hermetic bags were used in more than 80 countries for storage of various commodities, including cereals, pulses, oilseeds, cocoa, and coffee as safe storage means for many months (Bartosik, 2012; Villers et al., 2010). Silo bags usage in Argentina has increased from 5 million tons in the year 2000 to 40 million tons in 2008 (Abalone et al., 2011; Bartosik, 2012). The quality can be maintained more easily (prevent aflatoxin and rancidity development) under hermetic storage. The airtight barrier between the dry grain (ERH below 67%) and the outside ambient atmosphere preserves the moisture content of the stored commodity for more than six months without losing nutritional and organoleptic quality (Bartosik, 2012). The respiration process of the biological agents (grain, insects, mites, and microorganisms) in grain ecosystem increases CO2 and reduces O2 concentrations (Bartosik, 2012; Subramanyam et al., 2012). This modified atmosphere results in cessation of the biotic activity (insect and molds) due to desiccation caused by enriched CO2 and depleted O2 concentrations (Murdock et al., 2012), aid in a suitable environment for grain conservation (Abalone et al., 2011; Bartosik, 2012). A similar work (Fig. 1) in India, reported germination percentages of stored wheat in hermetic bags was dropped to 84% from 93% after nine months’ storage. The germination percentage of grains stored in a metal bin dropped to 82% while in gunny bags fell more quickly and down to 73% in nine months (Kumar et al., 2015). Hermetic bags were observed to be able to save minimum standard germination (ISTA, 2011) for stored wheat seed even at high moisture content without using pesticides (Somavat et al., 2014). Depleted oxygen in the ecology of hermetically sealed bag naturally forces the insect to shift to anaerobic metabolism, resulting in accumulation of acids and lactates in the insect body. This leads to inactivity, cessation of population growth, desiccation, and eventual death of insects (Bartosik, 2012; Murdock et al., 2012). Storage of sound wheat in non-punctured bag reported to meet an equilibrium moisture limit (12%) as well as all processing quality parameters for 9e12 months (Darby and Caddick, 2007). Pasting characteristics play an important role in the baking industries. Peak viscosity, trough viscosity, Peak time, pasting temperature, breakdown viscosity, final viscosity, setback, and gelatinization temperature were maintained in hermetic storage of wheat in comparison with steel bin and gunny bags pile. Higher final viscosity and lowest pasting temperature were reported in hermetic bag storage of wheat (Kumar et al., 2015).

The PICS bag was effective in controlling the aflatoxin accumulation and mold growth in stored high-moisture maize. Triple layer bagging work as a barrier against the transmigration of gasses and moisture. Therefore, the PICS bags retained the original moisture content of the maize (Williams et al., 2014). A comparative study in between jute, woven polypropylene and PICS bag for 35 weeks has proven a good gas barrier, 1% weight loss, insignificant moisture change and insect infestation in stored maize under farmer storage conditions (Mutungi et al., 2016). 3. Vacuum hermetic fumigation (VH-F) system At the early stage of research on hermetic storage, low pressure could only be maintained in specially constructed rigid and expensive steel chambers. It needed a prohibitively expensive investment in construction and maintenance during operation of above-said steel chambers. A practical solution has been invented that uses a three-layer ultra-low permeability PVC based, sealed, flexible and transportable innovative storage system for vacuum fumigation with an air tight zipper (Navarro et al., 2001; Bartosik, 2012). The first two layers are white in color to alter UV rays and make the bag weatherproof. The third layer is black to keep out the sunlight (Bartosik, 2012). In these flexible systems, it was practical to obtain sufficiently low pressures (25e50 mm Hg) using a commercial vacuum pump for 17 days (Navarro et al., 2002a). A particular value of the vacuum could be maintained for indefinite periods of time by periodic operation of the vacuum pump (Navarro et al., 2001). It was recommended to use rotary vane, oil lubricated vacuum pump with oil type filter to avoid the problem of corrosive outgassing of vapors from stored commodity liable to contaminate the lubricating pump. The vacuum of 25e29 mm Hg was achieved in 15 m3 PVC system by continuous operation of 3HP vacuum pump for 21 min. The vacuum was maintained in between 25 and 29 mm Hg for 17 days. Commercially, these flexible PVC systems are now available in several countries as “Volcani Cubes™” and “GrainPro Cocoons™” for small scale and large scale VH-F applications (Navarro et al., 2001). It was incorporated with one directional valve and a quick release hose at the base or bottom of the chamber which was connected with rotary vane pump using 1.500 connecting pipes. The provision of using a single vacuum pump for more than one bag was also made using valves and fittings (Finkelman et al., 2002, 2004a,b,c). The bulk or bagged commodities were loaded over the bottom section on pallets inside the structure. Under vacuum, these flexible systems shrink over the periphery of stored product and shaped as material bulk (Finkelman et al., 2004c). Navarro et al., 2012 demonstrated that vacuum of 55 mm Hg at 30
C and 65% RH was similar to phosphine (7-day exposure) for disinfection of the commodities. System monitoring for vacuum level was necessary rather product monitoring (Navarro et al., 2012). The VH-F with the vacuum below 100 mm Hg was found effective in quarantine and pre-shipment (QPS) treatments of bagged or bulk agricultural produce for insect control. It could be used as an alternative to MB with similar exposure time for insect disinfection and control (Finkelman et al., 2002). 3.1. Insects control under VH-F The vacuum pump helps to remove the air from the system to make the negative pressure below 100 mm Hg. Vacuum reduce the partial pressure of O2 as well as the water vapor from the interstitial atmosphere. It causes the insect mortality because of hypoxia and dehydration due to O2 and water vapor deficit ecosystem respectively (Adler et al., 2000; Navarro et al., 2002a, 2003; Finkelman et al., 2004c). The insects are capable of living in >4.5% O2 content in the interstitial atmosphere of storage ecosystem. Low partial

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Fig. 1. An experiment in CCS Haryana agricultural university, Hisar for comparison between hermetic bag and conventional methods (Somavat et al., 2014).

pressure of oxygen in the range of 1e2% causes the insect mortality (Fig. 2), while experimental evidence proved no significant function of the low pressure itself in insect mortality (Finkelman et al., 2004c). The species that develop outside grain kernels (external feeder or primary insect) are generally more susceptible to hypoxia than those living inside kernels (internal feeders or secondary insects) (Cao et al., 2010; Kucerova et al., 2013). The primary insects damage more to stored product in short term storage (Sarwar, 2015). The external feeder damages the outer surface of endosperm and left the grains for the internal feeder to eat starchy endosperm. The non-mobile developmental stages (eggs, pupae) generally took more exposure time for 99% mortality (LT99) than the mobile stages (larvae, adults) because of their lower O2 consumption and metabolic rate (Mbata and Phillips, 2001; Riudavets et al., 2009). Finkelman et al. (2002) showed in a laboratory trial with 1 Kg cocoa under 55 ± 10 mm Hg at 30
C and 55 ± 3% RH inside a 3 L desiccator would control all stages of E. cautella and T. castaneum. The lethal times needed to obtain 99% mortality (LT99) for all stages of insect development were shown in Table 2. The result showed that the egg stage was the most resistant stage in both species. The eggs of E. cautella and T. castaneum required an exposure time of 149.0 h and 96.0 h at 18
C temperature respectively. The temperature has a reverse influence on mortality of insects and the time for LT99 was reduced about one-third on increasing temperature from 18 to 30
C. The recorded exposure times for eggs of E. cautella and T. castaneum on 30
C was 41.0 h and 53.0 h respectively. Finkelman et al. (2002) also conducted a field trial with 15 m3 capacity of Volcani Cube™ for three and seven days on life stages of two major pests of cocoa beans: E. cautella and T. castaneum. Mainly the E. cautella is the most serious pest of the stored cocoa beans. The vacuum pump reduced the pressure to 23 mm Hg on the continuous operation for 55 min in two bags of 15 m3 capacity each. The

pressure was maintained at 23e75 mm Hg resulted in complete mortality in three days' exposure on 28 ± 0.5
C and 65% RH inside the cube. The insect infestation of every stage was controlled within three days of applying vacuum. In another field study by Finkelman et al., 2004c showed complete mortality of adult test insects within 5 days under the effect of 23e75 mm Hg vacuum using the 7.5 m3 and 34 m3 capacity bag on a number of agricultural commodities (oats, corn chips, cocoa beans, wheat, wheat flour, semolina, almonds, garden peas, chick peas, sunflower seeds and rice). The sensitivities of egg stages were tested in an experiment at two different temperatures (18 and 30
C) and 55 ± 3% RH on the eggs of six insects (T. castaneum, O. surinamensis, E. cautella, T. granarium, P. interpunctella, L. serricorne). At 30
C, the eggs of the L. serricorne required 91.1 h for complete mortality, whereas the T. castaneum required only 22.2 h (Table 2). Egg of the L. serricorne was the most resistant of all tested species (Navarro et al., 2004). Additional results proved that egg was the most resistant stage in all species of insects at lower temperatures or at higher relative humidity. Low temperature or high humidity prolonged the exposure times needed to achieve 99% mortality of insect (Mbata and Phillips., 2001; Finkelman et al., 2004a,c). In laboratory studies with L. serricorne exposed to low pressures (25 mm Hg) at 30
C, LT99 value for adults was 15.0 h and in the case of T. granarium larvae, 172.0 h exposure time was necessary for the most resistant species among insects under the same conditions. The larvae of T. granarium can hide in crevices of storage structure in the diapausing state for years. Stored cereals and oilseeds incur a great loss from T. granarium. The sensitivity of the most resistant stage of the most resistant insect species determined the treatment or exposure time to low pressure for complete insect control in stored produces (Navarro et al., 2003). Finkelman et al., 2004a used a test chamber filled with cocoa beans (1 kg) to test the mortality of three insects at 18
C and 55 ± 3%. Under a vacuum of 55 ± 5 mm Hg, they

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25

180 160

Oxygen (1.4-20.9 %) 20

140 120

Oxygen (11-159 mm Hg)

15

100 80

10

60 40

5

20 0

0 760

600

500

400

300

200

100

50

Vacuum, mm Hg Fig. 2. Atmospheric pressure and their equivalent partial pressure of oxygen expressed in mm Hg and in percentage (Finkelman et al., 2004c, Navarro, 2006).

reported adults of O. surinamensis (164.1 h) were the most tolerant to the low pressure than E. cautella (76.7 h) followed by T. castaneum (29.9 h) (Table 2). The adults of T. castaneum and pupae of the E. cautella required lowest exposure time for the mortality. The T. granarium, L. serricorne, and O. surinamensis were used for a laboratory experiment in a treatment chamber with 1 kg of cocoa beans and pressure was reduced to 50 ± 5 mm Hg at 30
C and 55 ± 3% RH. The egg was most resistant in all stages to low pressure. The exposure times of 46.1, 91.1 and 32.4 h were required for mortality of eggs of T. granarium, L. serricorne and O. surinamensis respectively (Table 2). The adults of T. granarium and L. serricorne were more susceptible to low pressure than O. surinamensis in all stages (Finkelman et al., 2004b). 99% of the eggs and larva stages of Caribbean fruit fly (Anastrepha suspensa) were killed within 11 days’ treatment at 15e20 mm Hg, 13
C and >98% RH under quarantine of imported mangoes (Mangifera indica). The hypobaric prolonged the shelf life of the mangoes and ensures the freshness and eating quality (Davenport et al., 2006). Adler et al. (2016), in a laboratory experiment, kept 30 adults of S. granarius (L.) in vacuum bags (16  2 l capacity, Vacqpack Company) with 1.3 kg wheat for 3, 6, 9 and 12 months. One weevil out of 480 (30 insects  4 initial moisture content  4 oxygen content) was found alive after three months of storage. Particulars of oxygen content and initial moisture content of wheat were not mentioned for survival. However, no insects were found alive after 6, 9 and 12 months of storage. They had recommended 12.5% (w.b.) moisture content of wheat for vacuum storage on the basis of germination percentage, time to germinate, insect infestation and human sensory evaluation. Vacuum storage was found to be sufficient to control the already existent moderate infestation of dry grains. 3.2. Insects control under combination of VH-F and other techniques The combination of VH-F and other prevalent green techniques (High and very low temperature, botanical derivatives, RH etc.) are tested to reduce the exposure time of killing insects. Navarro et al., 2002a had investigated the combination of various treatments of CO2, and temperature along with vacuum to increase the effectiveness of treatment and concluded increasing CO2 concentration decrease the exposure time for LT99 (Table 2). Tests to check the influence of CO2 at 45
C on reducing the exposure time (LT99) values for diapausing larvae of T. granarium resulted that by increasing the CO2 concentration from 60% to 90% the exposure

time decreased to about 10.0 h. For E. cautella and O. surinamensis under the same conditions of CO2 and vacuum, the LT99 values were 3.0 h and 9.0 h for the most resistant and non-mobile (pupae and egg) stages respectively (Navarro et al., 2002a). Emekci and Ferizli (2016) observed that phosphine was ineffective against the egg stage of dried fruit pests in Turkey. Combinations of phosphine were tested with low pressure and complete mortality of eggs was achieved within 24.0 h of treatment (Table 2). E. cautella needed comparatively harsher treatment than O. surinamensis and Carpophilus hemipterus of low pressure and phosphine combinations. Kucerova et al., 2013 reported significant differences in the tolerance to low pressure (vacuum) between the adult stages of T. castaneum and S. granaries insects. Insects were enclosed in a package using the vacuum packaging machine at different temperatures and lethal times. S. granarius was approximately 10 times more tolerant to low pressure than T. castaneum. Since T. castaneum is the external feeder of the food grains so it required less exposure time to low pressure than internal feeders. Complete mortality of T. castaneum was obtained in one day, whereas S. granarius required 7e12 days’ exposure time depending on the temperature. Lethal exposure times (LT99) for adult T. castaneum were 15.1 h at 25
C and 30.8 h at 15
C. In the case of adult S. granarius LT99 were 160.1 h at 25
C and 274.0 h at 15
C. Higher temperatures under a constant vacuum (7.5 mm Hg) significantly shortens the exposure time (LT99) required to reach 100% mortality in the tested beetles (Kucerova et al., 2013). Mbata and Pascual-Villalobos, 2010 examined the combination of monoterpenoids with the vacuum on adults of T. castaneum and larvae of P. interpunctella. At 36.5 mm Hg, the exposure time of 24.0 h was required for adults of T. castaneum whereas the 48.0 h is required for larvae of P. interpunctella. This exposure time for 100% mortality was shortened to 3.0e24.0 h due to the toxic effect of monoterpenoids in combination with low pressure. Jiao et al. (2013) investigated the low pressure and low temperature (LPLT) combination as a disinfection method for the apples on all life stages of the codling moth. Under LPLT treatment, the apples were enclosed in a hypobaric chamber at 10
C and >98% RH under the vacuum of 10 mm Hg. 98% of mortality of moth was achieved in 12 days. LPLT was in found effective in quality maintenance and increase the shelf life of stored apples. A quarantine method of vacuum and CO2 in combination with high temperatures in “Volcani cube™” was examined by Navarro et al., 2002b on all life stages of three insects. Field trials revealed that the complete mortality of all life stages of T. castaneum and E. cautella was achieved in 3 days of exposure time. All life stages of E. cautella

S. Kumar et al. / Journal of Stored Products Research 71 (2017) 47e56

53

Table 2 Vacuum fumigation parameters for achieving LT99 in laboratory and field conditions. Test Insect (Stage)

Storage conditions CO2,%

T. granarium (larvae)

35
C 40
C 45
C 35
C 40
C 45
C 35
C 40
C 45
C 35
C 40
C 45
C 35
C 40
C 45
C 35
C 40
C 18,25,30
C

E. cautella (Egg)

E. cautella (Larva)

E. cautella (pupae)

E. cautella (adult)

O. surinamensis (Egg#Adult) L. serricorne (Adult) L. serricorne (Egg) L. serricorne (Larva) E. cautella (Egg) E. cautella (Larva) E. cautella (Pupae) E. cautella (Adult) T. castaneum (Egg) T. castaneum (Larva) T. castaneum (Pupae) T. castaneum (Adult) T. castaneum (Egg, Larvae, pupae, adults) E. cautella (Egg, Larvae, pupae, adults) O. surinamensis (Egg, Larvae, pupae, adults) T. granarium (Egg, Larvae, pupae, adults) L. serricorne (Egg, Larvae, pupae, adults) O. surinamensis (Egg, Larvae, pupae, adults) T. castaneum (Egg), O. surinamensis (Egg), E. cautella (Egg), T. castaneum (Egg), O. surinamensis (Egg), E. cautella (Egg), T. granarium (Egg), P. interpunctella (Egg), L. serricorne (Egg) Diapausing larvae of Khapra beetle (T. granarium) P. interpunctella (Eggs and Pupae) E. cautella (Pupae), T. granarium (Mixed) L. serricorne (Egg, Larvae, Pupae and Adult) O. surinamensis (Egg, Larvae, Pupae and Adult) T. granarium (Egg, Larvae, Pupae and Adult) C. hemipterus (Egg) and O. surinamensis (Egg) E. cautella (Egg),

Vacuum, mm Hg LT99, h

60,70,90 25e29 60,70,80 60,70,80,90

e

25,30
C 18
C,30
C 55 ± 3% RH

25 50 100 50 55 ± 10

18
C 55% ± 3%RH

55 ± 10

30
C 55% ± 3%RH

50 ± 5

18
C 55 ± 3% RH 30
C 55 ± 3% RH

25
C, >70% RH 30
C, >70% RH 35
C, >70% RH 19.4e23.5
C 47.5e61.8% RH 30
C 55 ± 3% RH 20
C and 25
C 75% RH 30
C 75% RH

38.0, 29.0, 29.0 24.0, 28.0, 20.0 15.0, 17.0, 15.0, 10.0 23.0, 23.0, 17.0, 9.0 16.0, 12.0, 8.0, 5.0 9.0, 5.0, 3.0, 2.0 60.0, 27.0, 20.0 17.0, 9.0, 6.0, 6.0 5.0, 4.0, 2.0, 2.0 56.0, 37.0, 17.0, 17.0 36.0, 10.0, 8.0, 4.0 7.0, 4.0, 4.0, 3.0 20.0, 14.0, 6.0, 4.0 6.0, 5.0, 3.0, 2.0 3.0, 2.0, 2.0, 2.0 29.0, 25.0, 21.0, 9.0 # 26.0, 11.0, 8.0, 4.0 15.0, 7.0, 6.0, 6.0 # 12.0, 11.0, 6.0, 3.0 47.0, 46.0, 15.0 17.0, 43.0, 15.0 136.0, 75.0, 40.0 191.0, 49.0 148.8, 40.7 43.6, <28.0 26.2, <8.0 76.7, <10.0 96.3, 53.0 36.8, <28.0 71.8, <38.0 29.9, <28.0 96.3, 36.8, 71.8, 29.9 148.8, 43.6, 26.2, 76.7 76.9, 36.8, 128.2, 164.1 46.1, 41.0,34.6,5.8 91.1, 9.2, 29.6, 7.1 32.4, 6.5, 4.6, 6.0 96.3, 76.9, 148.8

References (Commodity) Navarro et al., 2002a (Lab Trial)

Finkelman et al., 2002 (Cocoa Beans)

Finkelman et al., 2004a (Cocoa Beans) Finkelman et al., 2004b (Cocoa Beans) Navarro et al., 2004 (Lab Trial)

22.2, 32.4, 44.8, 46.1, 49, 91.1

e

25, 50 and 100

e

25e29

e

45e55

1500 ppm PH3

250

required 3.0 h for complete mortality under 25 mm Hg at 45
C and 90% CO2 concentration, whereas at 35
C and 60% CO2 complete mortality was achieved in 60.0 h. They reported that the higher temperature and higher CO2 decrease the exposure time significantly. Vacuum storage was studied in combination with foliage powder of Peumus boldus mixed with lime for the adults of Sitophilus zeamais. It increased the insecticidal effect of powder with lime by 150 days at 20 ± 5
C without significant impact on the grain weight and germination percentage (Rivera et al., 2014). Toxicity of garlic emulsion (Sirinol) against the T. castaneum and R. dominica was examined to reduce the mortality time under low pressure. A period of 7.0 h was required for R. dominica for 100%

>360.0, >360.0 and > 360.0 172.0, 261.0 and > 360.0 145.0, 153.0 and > 360.0 3 Days and 3 Days 3 Days 10 Days 32.4, 6.5, 4.6 and 6.0 91.1, 9.2, 29.6 and 7.1 46.1, 41.0, 34.6 and 5.8 24.0

Navarro et al., 2001 (Lab Trial) Navarro et al., 2001 (cocoa beans) Finkelman et al., 2006 (cocoa beans) Emekci and Ferizli, 2016 (Lab Trial)

50

mortality and T. castaneum for 53.75% mortality at 50 mm Hg and 150 mL/L sirinol. The sirinol treatment shortened the exposure time significantly at 27 ± 2
C and 65 ± 5% RH (Jahromi et al., 2011). Laboratory experiment on eggs of E. cautella (Walker), P. interpunctella, R. dominica, and T. castaneum (Herbst) in a glass chamber were exposed to pressures of 50, 75, 100, 200, and 300 mm Hg at 5, 15, 22.5, 30, and 37.5
C for times ranging from 12.0 to 168.0 h. In all four species, the mortality of eggs increased with increasing exposure time and temperature. Low temperatures and high pressures were observed least effective conditions for killing eggs in all species investigated (Mbata et al., 2004). In a similar laboratory experiment by Mbata and Phillips (2001) on Eggs, larvae,

54

S. Kumar et al. / Journal of Stored Products Research 71 (2017) 47e56

and pupae of T. castaneum (Herbst), P. interpunctella (Hubner), and R. dominica at 32.5 mm Hg in glass chambers at 25, 33, 37, and 40
C for times ranging from 30 min to 144.0 h. Pupae stages of T. castaneum and R. dominica were more tolerant to vacuum than larvae. Higher temperatures and low pressure resulted in a further significant reduction in lethal time values. 1,8-Cineole is a toxic plant derivative of Eucalyptus spp. Against the insects. It was used in combination of low pressure (100, 150, 653 mm Hg) on two common insects named C. maculatus and T. Castaneum. 100 mm Hg reduced the amount of plant derivative to 27e41% for 50% mortality of insects in 12.0 and 24.0 h in comparison to 653 mm Hg. Low pressure significantly enhanced the susceptibility of insects against the plant derivatives (Abdolmaleki et al., 2010). The effect of RH and product moisture was investigated against the diapausing and nondiapausing larvae of P. interpunctella for weight loss and mortality at 50 mm Hg. Higher weight loss and mortality of larvae were recorded at lower RH. Diapausing larva was more resistant than non-diapausing larvae. Diapausing larvae required two times more exposure time of vacuum for complete mortality than nondiapausing larvae of P. interpunctella (Johnson, 2010). VH-F storage in flexible PVC structures has been demonstrated as a successful method for maintaining quality and quantity of stored agricultural produce. It extended the length of storage time of wheat, corn, beans, peas and sunflower by controlling insect and pests (Finkelman et al., 2002). It also had the potential for storage of high-value crops such as coffee, cocoa, nuts, and spices as the small application of VH-F flexible systems (Navarro et al., 2003; Johnson, 2010). The agricultural produces in bags or bulk are placed within the liner and the liner shrinks over the commodity on the application of vacuum. The liner took the shape as bulk or bag storage of a commodity. VH-F was used for quarantine purpose of high-value commodities since it is a nontoxic, residue free, environment benign and relatively quick. There is a scarcity of literature regarding the quality changes in stored commodities under VH-F condition. Finkelman et al., 2004c reported the complete mortality of adult test insects in 5 days under the effect of 23e75 mm Hg vacuum on oats, corn chips, cocoa beans, wheat, wheat flour, semolina, almonds, garden peas, chick peas, sunflower seeds and rice. The maintenance of vacuum below 100 mm Hg, low moisture content, temperature and RH, the ultra-low permeability of material are the only deciding factors for the success of vacuum hermetic storage of any non-crushable product. The “vacuum cube™” provide protection to cocoa beans from moisture loss or gain during storage, which prevents the test weight change of the stored product (Navarro et al., 2001; Finkelman et al., 2002). 4. Potentials and challenges in VH-F Unavailability of safe and economical fumigants as well as consumer awareness for health increases the demand of rapid, chemical free and safe method of grain storage. Under VH-F, the agricultural produce can be stored on-farm in commercially available Volcani cube™ and GrainPro Cocoons™ with no shade or costly infrastructure. Exposure time for QPS of imported and exported commodities using VH-F is shorter than the phosphine fumigation (Finkelman et al., 2006). VH-F can kill all stages of insects. Under vacuum, flexible liner shrinks over the stored commodity, so it becomes hard to bite by rodents. The commodities can be stored in bulk or bags as per the convenience of users. Gas tightness offers a small change in the moisture, preserving the test weight of commodity and other quality parameters. The mechanization for loading and unloading is another attraction to use VHF. Though VH-F sounds promising, but its application in the larger establishment is not without problems. Worldwide several companies manufacture flexible PVC bags is one of the major

impediments. The material should not allow moisture and air migration inside to outside environment and vice versa. Since the structures are meant for outdoor storage, UV-resistance nature of these materials is also important. By making moisture, water, and UV radiation resistant, the cost of structures escalates. Some companies are trying to make fungal resistant materials, which will protect the structures from microbes. However, it will also add to the cost. Adequate sealing of these structures is the backbone of hermetic technology. Though heat sealing, pressure tracks are used for hermetic storage structures; heat sealing makes the bag for once used item and pressure tracks for vacuum retention are prohibitively expensive. Moreover, there is a lack of time pressure data and combination testing data of VH-F regarding conventional methods, for different crops, which makes it difficult for the user to monitor and predict the insect activity and grain quality. On-farm storage needs electricity for operation of the vacuum pump. Availability of electricity at the farm level may not be feasible most times, especially in small and marginal farmers’ case. Most of the literature recommend 50e100 mm Hg vacuum application for complete mortality of insects of all stages, whereas practically it becomes cumbersome to maintain such a low level of vacuum in large establishments. This not only adds to the structural cost, but also adds to the operational and maintenance costs incurring from instrumentation, pipes, and fittings (Finkelman et al., 2006; Navarro, 2012). Since these structures are comprised of PVC, they are prone to external injuries by animals, human or natural disasters for which sufficient precautions are needed. The shelf life of these bags is usually 5e10 years, which are needed to be fumigated regularly as there is a scope of initial contamination of microbes and survived insect eggs, which may infect/infest the grain during storage considering that heat treatment of these bags will not be possible for eradicating microbes. All these challenges need to be addressed before embarking on this technology as most of the world pits for low cost, energy efficient technology for safe grain storage. 5. Conclusions The prospect of using low pressure or vacuum hermetic storage was found successful in prevention and disinfestations of insect infestation in stored commodity. It provides complete mortality in less time in comparison with phosphine fumigation in the same quantity. Residue free, non-hazardous to storage operator and nontarget organisms, high level of consumer acceptance, environment friendly and transportable vacuum storage are reasons which proved that vacuum hermetic fumigation has potential as a replaceable alternative for existing toxic chemical methods. This technology had been adopted over 40 countries for quantity and quality maintenance of durable and dry commodities. Research evidence showed the successful combinations of CO2, pressure, essential oils and higher temperature for 99% mortality (LT99) of insects and pests with minimum exposure time. Low pressure reduces the quantity of in combination ingredient like plant derivative, phosphine etc. for same mortality and exposure time. Exposure time for complete insect mortality was reduced by increasing carbon dioxide and temperature. It eliminates the need for chemical fumigation and other toxic means from the storage and promotes a “green” technology. The vacuum of 50 ± 10 mm Hg was maintained inside the hermetic bag using rotary vane vacuum pump. Egg stage of insects was the most resistant stage, which requires 46 h exposure time in T. granarium for 99% mortality (LT99) on 55% RH and 30
C interstitial condition. The time for LT99 in every stage (i.e. Egg, Larva, pupae, and adult) increase with a reduction in temperature up to a certain limit. Uses of VH-F technology is possible to expand even more rapidly in the future, as the

S. Kumar et al. / Journal of Stored Products Research 71 (2017) 47e56

more user will experience and understand the advantages of this environment benign technology on different commodities. Efficient patching of punctures on flexible bags need research work to render this technology on farm level. The quality analysis of stored produces, determination of economical, efficient and practical combinations in terms of temperature, safe fumigant, exposure time, carbon dioxide with vacuum for different commodities on a commercial scale are the future need of work under VH-F.

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