Journal of Applied Botany and Food Quality 93, 130 - 135 (2020), DOI:10.5073/JABFQ.2020.093.017 1Szent István University, Department of Physics and Control, Budapest, Hungary 2Industrial University of Ho Chi Minh City, Institute of Biotechnology and Food Technology, Ho Chi Minh, Vietnam 3Szent István University, Department of Refrigeration and Livestock Product Technology, Budapest, Hungary 4Szent István University, Department of Postharvest Science and Sensory Evaluation, Budapest, Hungary Evaluation of precooling temperature and 1-MCP treatment on quality of ‘Golden Delicious’ apple László Baranyai1*, Lien Le Phuong Nguyen2,3, Mai Sao Dam2, Tamás Zsom4, Géza Hitka4 (Submitted: September 22, 2019; Accepted: January 17, 2020) * Corresponding author Summary The presented study simulates commercial practice and focuses on the effect of time gap between harvest and the beginning of cold storage. Apple fruit ʻGolden Delicious’ was harvested in Hungary and randomly separated into 3 groups for precooling at 1, 4 and 10 °C. After 7 d cold storage, groups were randomly split half to con- trol and the other half was subjected to gaseous 1-methylcyclopro- pene (1-MCP) treatment for 24 h on their cold storage temperature (1, 4 and 10 °C). All samples were stored for 6 months at 1 °C fol- lowed by 7 d shelf-life at ambient temperature. Ethylene production, firmness, total soluble solid content, surface color and disorder in- cidence were determined. Significant correlation was found between color parameters hue and normalized green with firmness, SSC and ethylene production. Precooling temperature and 1-MCP treatment significantly affected apple quality (p < 0.01). Initial storage at 10 °C and application of 1-MCP on this temperature had no clear effect on maintaining fruit quality compared to control after 6 months storage. On the other hand, 1 °C and 4 °C precooling and applied 1-MCP treatment could slow the softening of samples during 6 months stor- age and in the following shelf-life. Apple quality was observed to change faster for group of 10 °C precooling and slower for groups of 1 °C and 4 °C. According to the results, precooling of apple fruit at 1 °C can be recommended in case the 1-MCP treatment is delayed. Introduction Apple (Malus × domestica) is important fruit with annual produc- tion of 83 million tonnes (FAO, 2019). It is the second most con- sumed fruit after banana. The majority of apple production is used for fresh fruit consumption, therefore postharvest technology applied to maintain its best quality is important. Harvested apple is typi- cally stored for months in cold rooms of 0 - 5 °C using refrigerated air or controlled atmosphere (DeLong et al., 2004; Matthes and schMitz-eiberger, 2009). Postharvest technology subject apples to treatment before long term storage to keep both quality and commer- cial value. Controlled atmosphere of %CO2:%O2 of 1.5:1.5 and 5:3 were found to maintain apple firmness after long term storage and shelf-life the best among other combinations (Jeziorek et al., 2010). The controlled atmosphere of 1.5% O2 and 0.6-0.9% CO2 at 3 °C and 5 °C was applied on ‘Honyecrisp’ apple during 6 months storage (DeLong et al., 2004). Desired low O2 concentration was obtained by flushing N2 gas into storage chamber. Controlled atmosphere cold storage of 1.5 °C, 1.2% O2 and 2.5% CO2 was also reported to successfully maintain polyphenol content in apple (Matthes and schMitz-eiberger, 2009). Ripening of climacteric fruit can be controlled by 1-methylcyclo- propene (1-MCP) successfully (bLankenship and DoLe, 2003). The advantage of application of 1-MCP is its effect on respiration and ethylene production. As a result, 1-MCP treatment also affects ethy- lene induced postharvest disorders. gago et al. (2015) evaluated effect of harvest date and gaseous 1-MCP treatment on apple qua- lity during and after 6 months storage. It was observed that 1-MCP was able to maintain firmness, reduce electrolyte leakage and slow surface color change. During the experiments, apples from certain orchards developed bitter pit at higher rate as a result of 1-MCP treat- ment. Those fruit were found to have low Ca and high Mg content and therefore bitter pit is more affected by cultivation technique. Authors also concluded that optimal harvest date is essential, affect- ing both postharvest disorders and following shelf-life. MiLinkovic et al. (2018) investigated 5 apple cultivars and did not find significant difference in their K:Ca ratio, but observed fluctuation of mineral content in consecutive years. ericsson and tahir (1996) evaluated possible factors on bruising of 3 cultivars. Pre cooling with cold air of 3 - 4 °C was found to make fruit more resistant to bruising, but treatment was less effec- tive for late harvested fruit. Harvest date affected bruising sensi- tivity significantly. Delay of 10 d could increase damage made by bruising with 20 - 40% in ‘Aroma’ and 12 - 25% in ‘Ingrid Marie’. The effect of harvest date was found to depend on cultivar. Timing is also important in application of postharvest treatments. DeLong et al. (2004) delayed cooling treatment with a warming period of 20 °C on ‘Honeycrisp’ apple in order to decrease soft scald and low temperature breakdown. It was found that delayed cooling of 7 d at 20 °C was beneficial and resulted in less disorder incidence during 4 - 6 months storage in case of early- and late harvested apple. Posi- tive effect of warming period and delay was confirmed by Watkins et al. (2004). They found that soft scald incidence can be decreased with higher storage temperature for sensitive cultivars. It was also highlighted that low production quantity of such sensitive fruit may not be enough to separate them and fill a storage facility to ensure different storage temperature. Delay before cooling was found to be effective, 1 d at 20 °C was able to prevent soft scald and soggy break- down disorders during storage at 0 and 0.5 °C. Common parameters measured to monitor apple quality are fruit firmness, soluble solid content and titratable acidity (Lu and Lu, 2016; Watkins et al., 2004). Nondestructive methods are offered by computer vision in wide range from color imaging of surface defects to hyperspectral imaging of quality based on spatial spectral infor- mation. Advanced techniques such as X-ray, MRI (magnetic reso- nance imaging) and CT (computed tomography) can detect internal structural changes, while diffuse reflectance showed its potential in firmness assessment (Lu and Lu, 2016). Surface color measurement with digital image processing is preferred in postharvest handling due to the high speed and ability to deploy in-line. More sophisti- cated and time consuming methods are utilized primarily in research. The main goal of the presented research was to simulate the com- mercial application of 1-MCP. During gradual loading of the storage facility, temperature fluctuates and fruit also have different tempera- ture according to the length of their prior storage. This may affect the efficiency of 1-MCP treatment. Therefore, this study evaluated the Apple response to precooling and 1-MCP treatment 131 effect of precooling temperature of 1, 4 and 10 °C as well as 1-MCP treatment on apple quality during 6 months storage. Another objec- tive of the experiment was to analyze relationship between quality indices and color parameters measured by digital image processing. Materials and methods Apple fruit and 1-MCP treatment Apple fruit (Malus × domestica) of ‘Golden Delicious’ cultivar have been collected from orchard in Hungary (at city of Ráckeve in Pest county). Samples were collected during middle of harvest season in September 2018. The experimental design was made to simulate whole harvesting procedure including the time gap between picking and long-term storage. The total amount of 900 fruit was selected for experiment and randomly split into 3 groups. Groups were subjected to 7 d cooling at 1 °C, 4 °C and 10 °C. After this initial precooling, groups were divided into two subgroups. Half was kept as control and another half was subjected to gaseous 1-MCP treatment at the pre- cooling temperature. After 1-MCP treatment, apple fruit were stored for 6 months at 1 °C. Forty fruit of each group was left at ambient temperature for 7 d to test their behavior during shelf-life right after the 1-MCP treatment. After long term storage of 6 months, all groups were withdrawn to ambient temperature for 7 d shelf-life. Experi- mental plan is introduced on flowchart (Fig. 1). Ethylene production Ethylene production was determined by an ICA-56 handheld ethyle- ne analyzer (International Controlled Atmosphere Ltd., UK). Apple was placed in a hermetically closed plastic container of 4 L for 1 h before measurement was performed. Measurement was repeated in triplicates. Results were expressed in microliter gas produced per kilogram of fruit in one hour (μL kg-1 h-1) calculated on fresh weight basis. Soluble solid content Soluble solid content (SSC, %) was determined by a hand-held tem- perature-compensated ATAGO PAL-1 digital refractometer (Atago Co. Ltd., Tokyo, Japan). Firmness measurement Fruit firmness was recorded with a handheld fruit firmness tester (FT 327, Italy). The instrument was mounted on a stand to make measurement more stable. Cylindrical probe of 10 mm diameter was penetrated into the tissue of peeled apple until 10 mm depth. The maximum force was measured at two opposite points on the external circumference. The average was recorded for each fruit. The instru- ment provided values in kg cm-2, what was transformed to the unit of N. Disorder incidence Fruit were visually tested for rot and bitter pit on the skin during storage period. The disorder was determined when a sign of those symptoms occurred. The incidence was calculated as percentage of the total number of fruit. Surface color Digital images of HD size (High Definition, 1920 × 1080 pixel) and 24 bit/pixel color depth were recorded with a camera (Samsung WB350F). The optical zoom of 4× was applied. Apples were placed on white paper and this background was used as white color refer- ence during processing. The ROI (region of interest) was selected based on saturation with the threshold of 0.2. Recorded color in- formation was transformed into HSL (hue, saturation, luminosity) space. Green color dominance was calculated as well, with linear normalization (Eq. 1). gn = G / (R + G + B) (1) where gn is the normalized green component, R, G and B are red, green, blue intensity values, respectively. Statistical analysis All data were subjected to statistical analysis with R version 3.6.0 (R Foundation for Statistical Computing, Austria) using analysis of variance (ANOVA). The effect of the factors of precooling tem- perature and storage time was evaluated. The ANOVA F value was used to compare effects to the natural variability of collected data. Tukey’s method was used as post-hoc test to compare selected groups with p<0.05. The results are reported on charts with mean and stan- dard deviation (SD). Figures were created using Microsoft Excel (Microsoft Co., USA). Results and discussion Effect of precooling on quality indices The comparison of initial readings with measurements after 7 d precooling (Tab. 1) showed that apple subjected to 10 °C precooling changed more than that of 1 °C and 4 °C. During the 7 d precool- Fig. 1: Experimental plan from harvest (H) with 7 d precooling, 6 months storage and 7 d shelf-life. Steps are simulating: short-term storage in orchard and transportation (7 d, 1-10 °C); long-term storage (6 months, 1 °C); storage in shop and household (7 d, 20 °C). The gaseous 1-MCP treatment was performed with commercial tab- lets (0.14% 1-MCP) as an application of the SmartFresh® system, provided by Rohm and Haas Polska Sp.z.o.o. (Warsaw, Poland). Measurements Measurements were performed at initial stage 0 d, at 7 d precooling, after 7 d shelf-life following 1-MCP treatment, at the end of 6 months storage and 7 d shelf-life following the 6 months storage. Starch in- dex was measured at 0 d and after 7 d precooling. The ethylene pro- duction, firmness, soluble solid content (SSC), disorder incidence, and surface color were measured at 20 °C during the experiment. Starch index Starch index was determined using Lugol’s solution (aqueous iodine) on half cut fruit and surface pattern was compared to starch index reference guide. 132 L. Baranyai, L.L.P. Nguyen, M.S. Dam, T. Zsom, G. Hitka ing after harvest, starch index and SSC increased while firmness de- creased. On the other hand, no significant difference was observed among fruit according to SSC and firmness. Regarding color attri- butes, Hue angle value decreased indicating that surface color started to change toward yellow. The green dominance was still similar after precooling, which means that fruit color changed within the green range. Ethylene production Ethylene measurements were conducted to evaluate the effect of precooling and 1-MCP application on postharvest life of apple. Precooling temperatures affected the ethylene production. Apples kept at 1 °C and 4 °C showed lower ethylene production during shelf-life both after 1-MCP treatment and after storage than those at 10 °C (Fig 2). Tab. 1: Quality parameters before and after precooling treatment (mean value ± SD) Parameter 0 d 7 d, 1 °C 7 d, 4 °C 7 d, 10 °C Starch index 6.51 ± 0.22a 7.15 ± 0.24ab 7.82 ± 0.21bc 8.75 ± 0.27c Soluble solid content, % 12.87 ± 0.22a 13.30 ± 0.16a 13.20 ± 0.16a 13.40 ± 0.16a Firmness, N 72.81 ± 2.52a 71.15 ± 2.52a 69.32 ± 1.89a 66.25 ± 1.89a Hue angle 108.24 ± 0.94a 105.12 ± 1.28ab 103.45 ± 1.19bc 100.25 ± 0.91bc Green dominance, % 44.79 ± 0.73a 43.59 ± 0.22a 43.71 ± 0.29a 44.12 ± 0.48a Different superscript letters in a row show significant difference at p<0.05. Fig. 2: Ethylene production during experiment (SL: shelf-life). Presented values are mean ± SD. The 1-MCP inhibited strongly the ethylene production. After 6 months of storage and during the following shelf-life, treated samples showed lower values than control but at different rate. Fruit of 1 °C and 4 °C precooling treated with 1-MCP had lower level in ethylene production than those of 10 °C. At the same time, all control fruit showed high ethylene production, with increasing value from 1 °C precooling temperature to 10 °C. Samples of 1 °C or 4 °C precooling were not significantly different in ethylene production. Firmness After 7 d of precooling, firmness decreased slightly for fruit kept at 1 °C and 4 °C, whereas apple from 10 °C had significantly lower values compared to the initial time (Tab. 1). Firmness declined dra- matically for all groups throughout shelf-life and storage. The results also showed that 1-MCP reduced the softening of apple for all tem- perature groups compared to control during the experiment but at different rates (Fig. 3). Fig. 3: Firmness during experiment (SL: shelf-life). Presented values are mean ± SD. Fig. 4: Soluble solid content during experiment (SL: shelf-life). Presented values are means ± SD. Precooling temperature influenced the efficiency of 1-MCP applica- tion. 1-MCP strongly affected only the fruit of 1 °C and 4 °C groups. There was no significant difference in firmness between 1 °C and 4 °C precooling either at storage or shelf-life, whereas 1-MCP treated fruit from 10 °C group were much softer. 1-MCP treatment did not show expected effect on apple of 10 °C since no significant differ- ence was detected between control and 1-MCP treated fruit using this precooling temperature. Soluble solid content Apple obtained similar SSC values after 7 d precooling in all groups (Fig. 4). However, it increased slightly during shelf-life before stor- age and after storage. Fruit subjected to 10 °C precooling had higher values in SSC af- ter 6 months of storage, then declined in the following shelf-life. Nonetheless, there were significant changes and significant differ- ences among groups throughout the experiment. Apple response to precooling and 1-MCP treatment 133 Bitter pit and rot The disorder of bitter pit was detected more frequently in 1-MCP treated samples than in control after storage (Tab. 2). After precool- ing and shelf-life before long term storage, no bitter pit symptom was observed. There were no significant differences in bitter pit occur- rence among groups at the end of storage and in the following shelf- life. The rot infection was detected less frequently for 1-MCP treated fruit than for control in all temperature. The symptom of fungal develop- ment only occurred after 6 months of storage. Samples of 1 °C and 4 °C precooling suffered less decay than those of 10 °C (Tab. 2). Fruit subjected to precooling at 1 °C showed the lowest level of bitter pit and rot, while at 10 °C it became very high. No significant difference was observed in bitter pit and rot occurrence between 1-MCP treated and control apples for group of 10 °C. Surface color The color development of apple surface was expressed by hue angle values. The surface color of apple continuously changed during the experiment according to the mean value of groups, but no significant difference was found between initial values and that of after 7 d pre- cooling. The hue angle decreased and standard deviation increased after storage for all groups (Fig. 5). The standard deviation was simi- lar for all groups after shelf-life following both precooling and long term storage. Correlation between parameters Pearson’s correlation coefficient was calculated between para- meter pairs (Tab. 3). The highest correlation was observed between hue angle and firmness (r = 0.9597). Similarly high correlation was found between firmness and starch index, but starch index is not in- cluded in the overall comparison because it was measured until the beginning of long term cold storage. Firmness was highly correlated (r = -0.7715) with ethylene production according to the expectations. Among quality parameters, firmness gained the highest correlation with color, r = 0.9597 for hue angle and r = 0.7721 for green domi- nance. Ethylene production and SSC obtained lower but still signifi- cant correlation values with color. 1 °C 4 °C 10 °C 0 40 80 120 Shelf-life-control Shelf-life-1-MCP Storage-control Storage-1-MCP Storage+SL – control Storage+SL – 1-MCP Precooling temperature H u e , d e g Tab. 2: Bitter pit and rot occurrence after 6 months storage and after shelf-life After storage After storage + 7 d shelf-life Precooling Treatment Bitter pit, % Rot, % Bitter pit, % Rot, % 1 °C Control 8.45 9.86 13.49 11.32 1-MCP 10.69 7.33 16.74 9.12 4 °C Control 8.96 10.45 14.22 12.29 1-MCP 11.85 7.84 17.48 9.43 10 °C Control 12.89 12.39 20.83 15.79 1-MCP 14.97 11.92 21.75 14.61 Tab. 3: Correlation between measured parameters Ethylene SSC Hue gn Firmness -0.7715** -0.3425 0.9597** 0.7721** Ethylene 1 -0.0256 -0.6733* -0.4829+ SSC 1 -0.5199* -0.3294 Hue 1 0.8198** ** significant at p < 0.001; * significant at p < 0.01; + significant at p < 0.05 Fig. 5: Hue angle value during experiment (SL: shelf-life). Presented values are means ± SD. Similar tendency was observed for green dominance. Less difference was found in green dominance before 6 months storage. Green color became less dominant after shelf-life following both precooling and long term storage. Together with decreasing hue angle, they indicate that color changed into the direction of yellow. Discussion Maturity stage is the most important factor influencing the efficiency of 1-MCP treatment. The efficacy of 1-MCP is low at advanced ma- turity stage (Jia et al., 2014; sozzi and beauDry, 2007). Our results also indicated that the effectiveness of 1-MCP treatment depends on fruit maturity, in agreement with the previous report (Jia et al., 2014). Application of 1-MCP on apple subjected to 10 °C precooling had a little effect in reducing ethylene production after 6 months storage, while 1-MCP treatment on fruit of 1 °C and 4 °C precooling was effective in suppressing the ethylene production. The reason for this behavior might be that samples of 10 °C precooling for 7 d reached the advanced maturity, therefore 1-MCP did not show the efficacy as strong as other groups. According to this observation, if delay in 1-MCP treatment cannot be avoided due to transportation or optimi- zation of bulk treatment, short-term cold storage at 1 °C is recom- mended. The decline in firmness during storage results in soft and mealy fruit decreasing the quality value of fruit (kaDer, 1999). In our work, the softening of fruit increased during the precooling period from 1 °C to 10 °C corresponding to the increase of starch index due to ad- vanced ripening (Tab. 1). 1-MCP treatment on fruit of 1 °C and 4 °C precooling delayed the softening of apple during storage and shelf- life, whereas the softening of control samples rose rapidly. Similar behavior was observed for pear using gaseous 1-MCP of 1.0 mL L-1 (gao et al., 2015). Less efficacy of 1-MCP at 10 °C precooling was found perhaps due to incomplete blocking of the ethylene receptors, 134 L. Baranyai, L.L.P. Nguyen, M.S. Dam, T. Zsom, G. Hitka thus ethylene could exert its action partly in ripening (bLankenship and DoLe, 2003; Watkins, 2008). Regarding to delayed 1-MCP treat- ment, previous reports also indicated that the applied treatments at earlier maturity stage increased the possible storage periods (kubo et al., 2003; Watkins and nock, 2005). Depending on the cultivar and circumstances of treatment, the 1-MCP treated fruit can have higher, lower, or same values of soluble solid content compared to control samples (gago et al., 2015). Our results showed that 1-MCP had small effect on SSC and SSC of fruit of 10 °C precooling was lower than those at 1 °C and 4 °C at the end of experiment, but not significantly different. Surface color was found to change gradually from green toward yellow. Hue angle decreased in this direction but green dominance measured by normalized green value did not change significantly. Apple color in control group changed more than groups of 1-MCP treatment. Similar results were found for ‘Red chief Delicious’ apples (Mir et al., 2001). Ethylene plays an important role in the ripening process. 1-MCP inhibited the ripening by occupying ethylene recep- tors, so that ethylene is unable to elicit its action (bLankenship and DoLe, 2003). Other fruit, including papaya and melon also showed similar results (bron et al., 2004; ergun et al., 2005). Color para- meters were found to correlate strongly with firmness, followed by ethylene production and SSC. The percentage of bitter pit was higher in 1-MCP treated fruit than control. In earlier reports, similar results were found for ‘Golden Delicious’ apple (gago et al., 2015), ‘Granny Smith’ apple (caLvo and canDan, 2010). The symptom of bitter pit related to the Ca, K, Mg concentration and cultural technique (gago et al., 2015). Rot is also one of the main problems during postharvest transport and storage. As shown in Tab. 2, fruit was more susceptible to decay at the end of experiment due to aging and senescence. In addition, am- bient temperature during shelf-life also favor the microbial growth (MiccoLis and saLtveit, 1995; yang et al., 2003). Conclusions Precooling treatment of 7 d was applied on apple fruit ‘Golden Delicious’ before gaseous 1-MCP treatment, simulating commercial practice. Results show that 1-MCP treatment successfully delayed fruit ripening, but differences were observed depending on the short- term storage temperature between harvest and treatment. Precooling temperature of 1 °C and 4 °C were more effective, while samples subjected to 10 °C did not respond sensitively to 1-MCP by means of ethylene production, firmness and surface color. The 1-MCP treat- ment should be applied as soon as possible to prevent progressed aging. In case transportation or optimization of bulk treatment make several days delay, short-term cold storage at 1 °C should be applied to maintain quality and effectiveness of 1-MCP treatment. Color parameters correlated significantly with fruit firmness, SSC and ethylene production. This observation suggests that surface color can follow changes during ripening. The normalized green color component shown similar behavior to hue angle offering another pa- rameter to use. Acknowledgements The Project is supported by the European Union and co-financed by the European Social Fund (grant agreement no. EFOP- 3.6.3-VEKOP-16-2017-00005). The Project is supported by the European Structural and Investment Funds (grant agreement no. VEKOP-2.3.3-15-2017-00022). This research was supported by the Ministry for Innovation and Technology within the frame- work of the Higher Education Institutional Excellence Program (NKFIH-1159-6/2019) in the scope of plant breeding and plant pro- tection researches of Szent István University. Conflict of interest No potential conflict of interest was reported by the authors. References bLankenship, s.M., DoLe, J.M., 2003: 1-Methylcyclopropene: a review. Postharvest Biol. Tec. 28, 1-25. DOI: 10.1016/S0925-5214(02)00246-6 bron, i.u., ribeiro, r.v., azzoLini, M., JacoMino, a.p., MachaDo, e.c., 2004: Chlorophyll fluorescence as a tool to evaluate the ripening of ‘Golden’ papaya fruit. Postharvest Biol. Tec. 33(2), 163-173. DOI: 10.1016/j.postharvbio.2004.02.004 caLvo, g., canDan, a., 2010: 1-Methylcyclopropene (1-MCP) affects physio- logical disorders in ‘Granny Smith’ apples depending on maturity stage. Acta Hortic 857, 63-70. 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DOI: 10.1016/j.postharvbio.2003.11.003 yang, b., shiping, t., hongXia, L., Jie, z., Jiankang, c., yongcai, L., Weiyi, z., 2003: Effect of temperature on chilling injury, decay and quality of Hami melon during storage. Postharvest Biol. Tec. 29(2), 229- 232. DOI: 10.1016/S0925-5214(03)00104-2 ORCID László Baranyai https://orcid.org/0000-0001-6177-7364 Lien Phuong Le Nguyen https://orcid.org/0000-0002-5975-9906 Mai Sao Dam https://orcid.org/0000-0002-3170-0785 Géza Hitka https://orcid.org/0000-0003-0942-8102 Adress of the corresponding author: E-mail: Baranyai.Laszlo@etk.szie.hu © The Author(s) 2020. This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creative- commons.org/licenses/by/4.0/deed.en). http://dx.doi.org/10.21273/JASHS.126.5.618 http://dx.doi.org/10.1016/j.postharvbio.2003.11.003 http://dx.doi.org/10.1016/S0925-5214(03)00104-2