The efficiency of the AiroFreshTM unit in replacement or reduction of chemical usage in long term storage of fruits
‘Cripps Pink’ apple has been extensively marketed under the name Pink Lady®. There are two mutations of ‘Cripps Pink’ called Rosy Glow and Lady in Red. These apples are a climacteric fruit, producing ethylene during ripening. Ethylene (C2H4) is a natural ripening (or “aging”) hormone (Keller, 2013) which is physiologically active at extremely low concentrations (parts per million – parts per billion, ppm – ppb). It acts positively as a ripening agent but it also causes fast deterioration of fresh produce and thus significant product losses during shipping and storage. In order to maximize fruit quality and shelf life, removing ethylene from the storage and handling environment is one of the main challenges in postharvest. Common storage tool used to reduce the sensitivity of fruits to ethylene is controlled atmosphere (CA) storage (Beaudry, 1999) where the concentrations of O2, CO2 and nitrogen, as well as the temperature and humidity of a storage room are regulated. Reducing the concentration of O2 in the storage atmosphere has been shown to reduce the sensitivity of apples to ethylene (Beaudry, 1999). As other plant hormones, ethylene binds to specific receptors to form a complex, which triggers the ripening processes (Watkins, 2006).
A commercial formulation of 1-methylcyclopropene (1-MCP; SmartFreshTM, Agrofresh Inc.), interacts with the ethylene receptors and thus inhibits the perception of ethylene and prevents ethylene-dependent responses (Watkins, 2006). In postharvest, 1-MCP successfully inhibits the ripening of apples, maintains firmness and colour, and thus extends their storage life (DeEll et al., 2005; Lafer, 2003; Watkins, 2006). Virtually, all postharvest diseases of fruit and vegetables are caused by fungi and bacteria. Apple trees are susceptible to fungal pathogens and in postharvest treatment, several fungicides can be used. However, many products formerly used postharvest in agriculture are no longer permitted because of concerns with residues and possible toxic effects. Other products are no longer as effective because of the development of resistance by the target pathogen. For example, intensive and continuous use of fungicides for control of blue and green mould on pome fruit and citrus has led to resistance by the causal pathogens of these diseases (Eckert, 1988). Resistance development continues to be a major problem and has resulted in the Fungicide Resistance Action Committee (FRAC), a cooperative effort among various producers of fungicides to delay resistance by recommending specific management guidelines (Why FRAC?, 2014).
Advanced oxidation processes (AOP) and photocatalytic oxidation (PCO) have been recently considered as highly promising and reliable technologies of ethylene removal, processes which chemically oxidize organic compounds into CO2 and water. They also assist in the control of biological agents such as bacteria, viruses and fungi (Goswami, 1997, Kűhn, 2003). The AiroFresh®, advanced oxidation processes, unit (NASAA certified organic) utilises photocatalytic and other oxidation methodologies in a closed atmosphere and has been shown to significantly reduce concentration of ethylene as well as fungi incidence, as detailed in the CRT Technology (Janovska, 2016) and the LaTrobe University report (Agriculture Research Division, 2016), respectively.
Aim of the study:
The aim of this study is to evaluate whether the advanced oxidation technology in the AiroFreshTM unit is efficient enough to replace or reduce the use of chemicals in long term storage of fruits, namely Lady Pink® apples.
Rosy Glow and Lady in Red (Pink Lady®) apples, mutations of ‘Cripps Pink’ (Malus domestica) trees were used. Apples were placed in 1 m3 plastic or wooden bins (Fig. 2). In total, 320 apple bins were arranged uniformly and randomly in a storage room to ensure adequate airflow and even distribution of air and storage conditions. The experimental apples were supplied by three different apple growers (Ashton Valley Fresh Pty Ltd, Ashton SA 5137; Filsell Apples, Deviation Rd, Forest Range SA 5139 and Graeme Schultz, Forest Orchards, Forest Range SA 5139). All participating orchards were located in the Adelaide Hills, South Australia, thus ensuring that the experimental fruits were harvested under the same climatic conditions (Fig. 1). The experiment took place at the Filsell Apples (Deviation Rd, Forest Range SA 5139, Australia) and the measurements were performed by the Flavell Fruit Sales Pty Ltd (Stentiford Rd, Forest Range SA 5139, Australia).
Orchard of Cripps Pink apples in the Adelaide Hills, Australia
Plastic bin with experimental Cripps Pink apples
The facility was a standard storage room, made from a corrugated iron, appropriately lined and sealed, with a total volume of 380 m3 and with a controlled atmosphere to reduce the sensitivity of apples to ethylene (Beaudry, 1999; Gorny and Kader, 1996). The oxygen level was reduced to 1.5 % – 3 %, the carbon dioxide was kept low with the use of absorber, hydrated lime, and monitored with an infrared CO2 meter (ANRI Instruments and controls, Victoria, Australia). Also, temperature 2 – 3 °C and relative humidity around 75 % in the room were regulated to maintain the optimum conditions for preservation.
To study the effect of the AiroFreshTM unit on apple quality during long-term storage, a standard AiroFreshTM 1000 unit (AiroFreshTM Pty Ltd., Fullarton SA 5063, Australia) was placed at height approx. of 1 m near the cool room door. The unit was 110 cm long and had 18 cm in diameter and the flow of air was 120 m 3/h. To enable constant airflow to feed the AiroFreshTM 1000 unit and to distribute cold air evenly through the storage room, a drum fan, approx. 90 cm in diameter, was installed and run continuously in the facility.
AiroFresh® 1000 unit (AiroFresh Pty Ltd.)
The apples were divided into 3 groups, according to their growers, and treated differently. Apples in the first group were treated once with two fungicides: Scholar in concentration 100ml/120 l (composed of 230 g/l of fludioxonil, Syngenta Australia) and Rovral® Liquid Fungicide in concentration 100 ml/100 l (composed of 250 g/l iprodione solvent : 332 g/l liquid hydrocarbons, FMC Australasia Pty Ltd.). In addition, 1-methylcyclopropene (1-MCP, SmartfreshTM, Agrofresh Inc.) gas was also released in 1 ppm concentration for 24 hours. Apples in the second group were treated either with fungicides and no MCP-1 (in plastic bins) or were not treated (in wooden bins). In this second group, Flavell Fruit Sales Pty Ltd assessed the apples treated with fungicides while the grower compared fungicides treated apples with non-treated apples independently. The third group was composed of only organic apples and therefore no chemical treatment was applied.
To compare the long-term effect of the AiroFresh® unit on inhibition of volatile organic compounds (VOCs; especially ethylene), fungi, bacteria and the overall quality of ‘Cripps Pink’ apples with the effect of chemical treatment, namely fungicides and MCP-1, all three groups of apples (treated and untreated) together with the AiroFreshTM unit were placed in the storage facility on 29/4/2016 which was then sealed. The room was again re-opened on 1/11/2016, after 6 months and 3 days of storage under CA.
Fruit quality assessments
Representative apple samples were taken from individual bins which were randomly selected according to assigned experimental groups of apples. Only samples free of any visible damage were used for the assessments. Apple samples were removed from the cool room, allowed to warm to 20°C and assessed for both visual quality and maturity.
To measure fruit maturity, total soluble solids (TSS) were evaluated. During apple maturation, sugars become the primary component of the soluble solids and consequently, the TSS gives a measurement of the sugar content in an aqueous solution. The TTS was measured in % or in degrees Brix (°Bx) as 1 degree Brix is equal to 1 gram of sucrose in 100 grams of solution. To measure the sugar content, a hand-held refractometer (Fisher Scientific, Pittsburgh) was used after it was calibrated at the 20°C ambient working temperature of the room.
As the fruit matures, fruit flesh becomes softer. The flesh firmness of ‘Cripps Pink’ apples were measured with a hand-held pressure tester (Effigi nc., Bologna, Italy). The penetrometer was equipped with an 11 mm tip. Each apple was tested once after its skin was removed. Firmness was measured in kg/cm2 and converted to newtons [N] using the following formula: N =kg/cm2 x 9.81.
All data are reported as means±S.E.M. Differences among groups were compared either by a one-way ANOVA or by an unpaired t-test after a normal distribution of a variable was confirmed by an Anderson-Darling test. Differences among groups were considered statistically significant if P≤0.05. All statistical analyses were performed using non-commercial Max-Stat statistical software for Windows.
Total soluble solids (sugar content):
The sugar content in the three experimental groups was as follows (mean±S.E.M.): 15.19±0.63 [%, °Bx], n=8 for group 1 (fungicides and MCP-1 treatment); 16.3 [%, °Bx] for group 2 (only fungicides) and 15.3 [%, °Bx] for group 3 (no treatment). Although the values for total soluble solids (sugar content, Brix) could not be statistically evaluated due to the absence of individual measurements in some experimental groups, it is obvious that the total sugar content was similar among the three groups (Fig. 4).
Fig. 4. Data are expressed as means±S.E.M where possible
The values for flesh firmness in the three experimental groups was as follows (mean±S.E.M.): 79.82±0.36 [N], n=18 for group 1 (fungicides and MCP-1 treatment); 73.35±3.82 [N], n=22 for group 2 (only fungicides) and 73.24±2.87 [N], n=28 for group 3 (no treatment). The flesh firmness in group 1 was significantly different (P≤0.05) from the other two experimental groups. There was no significant difference between group 2 and group 3 (Fig. 5).
Fig. 5. Data are expressed as means±S.E.M, *group one differs significantly from the other two groups (P≤0.05).
An independent comparison between apples treated with fungicide and non-treated with fungicide by the grower showed no significant difference in TSS (mean±S.E.M.): 15.52±0.21 [%, °Bx], n=13 (fungicides) and 15.75±0.07 n=13 [%, °Bx] (no treatment). The values for flesh firmness within the group 2 was as follows (mean±S.E.M.): 80.20±0.05 [N], n=13 (fungicides) and 70.63±0.77 [N], n=13 (no treatment). The flesh firmness was significantly different (P≤0.05) between fungicide treated and non-treated apples within experimental group 2. (Fig. 6).
Fig. 6. Data are expressed as means±S.E.M,*group differs significantly from the other group (P≤0.05).
The results showed no difference among experimental groups in sugar content. Surprisingly, it showed a higher FF in group one (1-MCP and fungicide treatment) when compared with other groups as well as higher FF for apples treated with a fungicide when compared with non-treated apples within group two. The explanation can be various, from a slightly different harvest day, different ‘Cripps Pink’ apple mutation or handling among growers to a possible effect of the fungicide treatment on the FF of fruit. Therefore, more than to the effect of fungicide itself, the difference in FF can be assigned to dissimilar handling of fruit during fungicide treatment. Apples are dipped into a solution containing fungicides when treated and this procedure can lead to an increased FF as ‘Berangan’ banana dipped in hot water at 50°Cm for 10 and 20 min retarded peel colour changes, slowed down fruit softening process and developed firmness characteristics, regardless of fungicide (Mirshekari, 2013). Therefore, these apples could retain higher firmness just because of their dipping in solvent (water) during the treatment procedure. Overall, in regards to maintaining high fruit quality, there is no distinct variation between apples chemically treated and organic apples during long-term storage if the advanced oxidation technology represented by AiroFreshTM is employed.
During apple maturation, starch is converted to sugars (Little and Holmes, 2000; Watkins, 2003) which then become the primary component of the soluble solids and, consequently, the TSS represents the sweetness of the fruit. Therefore, it is often used as a quality component and a minimum TSS is often required for export markets. Although ‘Cripps Pink’ apples were described as having a TSS between 12.5 % and 13.5 % (Cripps et al., 1993) for their export under the Pink Lady® name, a minimum TSS of 13 % and an average of 15 % is required (Hurndall and Fourie, 2003).
In our experiment, all groups had TSS level above 15 % thus demonstrating that all apples were good quality fruits and the grade was maintained even in organic apples where no chemical treatment was applied through the long-term storage, just proving the extensive effect of the AiroFreshTM unit on the fruit condition.
Flesh firmness (FF) is another quality measurement of apples and decreases during maturation as a result of the thinning of cell walls and of the action of pectinase enzymes during fruit ripening (Kays, 1991). Similarly to TSS, FF is a useful measure of consumer acceptance of apples as textural qualities of apples are often reported by consumers to be amongst the top requirements for acceptability (Harker et al., 2003). Cripps et al. (1993) also described the ‘Cripps Pink’ apples as ‘crisp and crunchy’ apples with firmness of 83 N at harvest. For their export as the Pink Lady®, the fruit is required to have a minimum flesh firmness of 66.7 N and an average flesh firmness of 68.6 N (Hurndall and Fourie, 2003). To be considered for a distribution via Coles (Coles Supermarkets Australia Pty Ltd, an Australian supermarket chain), i.e. as a good quality produce, the FF has to be above 61.8 N. All our experimental groups of apples showed FF above 70 N. Thus, as with the TSS, the need for a prominent quality, in this case of crispness, was entirely accomplished even in a fully organic way – just with the use of the AiroFreshTM unit during long-term storage.
Given the fact that no substantial difference between chemically treated and organic apples were found and that organic apples retained high sugar content and firmness and thus a high quality of products when only AiroFreshTM unit was employed during long-term storage, we can conclude that the advanced oxidation processes occurring in AiroFreshTM unit are capable of chemical reduction or even replacement. Besides having positive effects on human health due to the reduction of chemical consumption, this technology is low operation costs, mainly consisting of investment and energy costs, and maintenance costs which consist in the periodic replacement of active components.
Dr Alena Janovska
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