Impaginato 59 Adv. Hort. Sci., 2023 37(1): 59­66 DOI: 10.36253/ahsc­13872 Use of xanthan gum and calcium ascor­ bate to prolong cv. Butirra pear slices shelf life during storage E. Guccione (*), A. Allegra, V. Farina, P. Inglese, G. Sortino Department of Agricultural, Food and Forest Sciences, University of Palermo, Viale delle Scienze, 4, 90128 Palermo, Italy. Key words: Browning, edible coating, fresh­cut, pear, respiration. Abstract: After cut, pear fruit (Pyrus communis L.) during shelf life can be sub­ jected to color and flavor changes. To maintain flesh colour and firmness, dif­ ferent technologies could be employed during shelf life, such as chemical, phys­ ical and edible coating treatments. In the present study, the effects of two edi­ ble coating formulations containing xanthan gum and calcium ascorbate on fresh­cut pear fruit were investigated. After harvest, 200 fruits were cut and coated with Xanthan Gum (XAN) and distilled water or Xanthan gum + Calcium Ascorbate (ASC), respectively, while control (CTR) pear fruit slices were soaked in distilled water and lastly packed in polyethylene terephthalate (PET) pack­ ages sealed with a composite film (PP­PET). All samples were stored at 5±0.5°C with RH 90% for 10 days. Measurements were carried out at 3, 5, 7 and 10 days of storage evaluating visual quality score, browning index, color, total solid sol­ uble content (TSS), flavor, ascorbic acid content and total phenols content. The results showed that ASC treatment was the most efficient treatment in terms of color changes, ascorbic acid content, visual quality score and browning index, until the 7th day of storage. Moreover, ASC treatment reported lower mean values in terms of taste and flavor score if compared to CTR and XAN treatments. Untreated pear slices (CTR) kept good values concerning flavor score until the 3rd day of storage while on the 5th and 7th day off­flavor values were the same as treated samples. 1. Introduction ‘Butirra’ pear fruit is cultivated in southwestern Sicily and belongs to sicilian MIPAAF PATs (traditional agricultural products). After harvest, usually occurring between the second decade of July and the first decade of August, they must be consumed as they are easily rotten and are sub­ jected to fast decay. It’s easy to understand how fresh­cut ‘Butirra’ poor shelf­life is a key barrier to its commercialization especially for the fast weakening of tissues and surface’s browning that happens after cut due to the action of polyphenol oxidase (PPO) (Amiot et al., 1995; Hodges and Toivonen, 2008). Edible coatings are widely employed since they prevent the loss of quality acting like a selective barrier to gas exchanges between (*) Corresponding author: eugenia.guccione@unipa.it Citation: GUCCIONE E., ALLEGRA A., FARINA V., INGLESE P., SORTINO G., 2023 ­ Use of xanthan gum and cal‐ cium ascorbate to prolong cv. Butirra pear slices shelf life during storage. ­ Adv. Hort. Sci., 37(1): 59­66. Copyright: © 2023 Guccione E., Allegra A., Farina V., Inglese P., Sortino G. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 17 October 2022 Accepted for publication 24 January 2023 AHS Advances in Horticultural Science https://doi.org/10.36253/ahsc-13872 http://www.fupress.net/index.php/ahs/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2023 37(1): 59­66 60 food and external environment. Xanthan gum enhances all these properties and also controls the rheology of the final food product exhibiting pseudo­ plastic properties in solutions (Palaniraj and Jayaraman, 2011). As a generally recognized as safe (GRAS) molecule, xanthan gum is an exopoly­ saccharide produced by the fermentation of a carbo­ hydrate by cultures of Xanthomonas campestris. It is then refined by extraction with ethanol or 2­ propanol, dried, and powdered (FDA). Calcium ascor­ bate is the calcium salt of ascorbic acid that is widely used as an antioxidant whose reducing action against quinones and diphenols prevents browning of unprocessed fruit as it only produces colorless deriv­ atives; it is a reducing agent, capable of promoting the chemical reduction of the pigment precursors responsible for browning, acting by reducing o­ben­ zoquinone or dihydroxyphenol or irreversibly inacti­ vating PPO, promotes the regeneration of antioxi­ dants and acts synergistically with complexing agents (Araújo, 2004). Furthermore, this cation can maintain cell wall structure by binding to pectins and forming calcium pectate (Vilas Boas et al., 2009). Calcium sta­ bilizes the membranes and cell walls, preserving their integrity and functionality and protecting them from being cleaved by hydrolytic enzymes that cause fruit softening (Poovaiah, 1986; Vilas Boas et al., 2009). Xanthan gum combined with antioxidant agents had positive effects on the reduction of weight loss and browning, preventing the loss of firmness, and the growth of psychotropic microorganisms, molds and yeasts in minimally processed apples and pears (Sharma and Rao, 2015; Allegra et al., 2022). The aim of the present study was to evaluate the effective­ ness of edible coating based on xanthan gum and xanthan gum enriched with calcium ascorbate on fresh­cut cv ‘Butirra’ pear fruit stored in passive atmosphere. 2. Materials and Methods The experiment was carried out in 2021. ‘Butirra’ pear fruit (Quince BA29 rootstock and intermediate ‘Butirra Hardy’ graft) were harvested during the sec­ ond week of august in a commercial orchard located in Zafferana Etnea (Catania, Italy), Italy, (730 m above sea level). The soil is a sandy clay loam (63% sand, 19% silt, 18% clay), with pH 6.9 and active carbonates lower than 5%, trees were trained as a free palmette. Fruits were hand­picked at an optimal ripening stage tested with Lugol solution. All trees received the same conventional cultural cares from planting until the end of the current experiment. After harvest, fruit were cold stored and transported at University of Palermo and stored at 5±1°C in cold room the night before the analysis. Experimental design Two hundred fruit were harvested from 20 trees and brought to the laboratory where they were dipped in chlorinated water (100 ppm of free chlo­ rine) for 360 s to sanitize them. Defective fruit were discarded and the remaining were sorted by firmness (4.1±1 kg/cm2) and average weight (120± 20.2 g). Quality indexes were calculated the first day of analy­ sis, particularly, color (CIELab), flesh compactness and total solid soluble content (TSS). Fruits were selected for weight, maturation index, caliber and absence or presence of defects and sani­ tized with OxVirin 200 ppm and H2O by soaking for 30 minutes. Then, they were peeled and cut. Edible coatings were applied by dipping and solutions were formulated as follows: i) Control (CTR): fruits were dipped in distilled water and used as control; ii) XAN: the solution was made by mixing 3% of xan­ than gum in distilled water using a magnetic stir­ rer; iii) ASC: the solution was made by mixing 3% of xan­ than gum and 2% of calcium ascorbate in distilled water using a magnetic stirrer. After treatments, fruit were packed in PET boxes, sealed with a composite PP­PET film and stored at 5±1°C with 95% relative humidity (RH) for 10 days. Trials were carried out at 3, 5, 7 and 10 days of stor­ age evaluating visual quality score, browning index, color, total solid soluble content (TSS), sensorial analysis, ascorbic acid content and total phenols con­ tent. Weight loss The following formula was adopted to determine weight loss during storage Weight loss (%) = [(W1­W2)/(W1)] x 100 Where W1 and W2 represent initial weight (T0) and measured weight at 3, 5, 7 and 10 days of storage with a precision balance (Gibertini, Italy), respec­ tively. At the beginning of trial period all boxes had homogeneous weight (100 ± 2.1 g). Color Flesh color was measured throughout the experi­ ment on the first day of analysis (0) and on the 3rd, Guccione et al. ‐ Xanthan gum and CA to prolong cv. Butirra shelf life 61 5th, 7th and 10th day of storage. Color was measured through a portable colorimeter (Chroma Meter CR 400, Konica Minolta Sensing Inc., Tokyo, Japan) equipped with an 8 mm measuring head and a C illu­ minant (6774 K). The white standard plate of the manufacturer was used for calibration. Chromatic dif­ ference (DE) was calculated using the following for­ mula to express the magnitude of difference between the non­aged pulp and stored samples: ΔE* = √ΔL*2 + Δa*2 + Δb*2 All trials were carried out in triplicate and data were reported as ± mean standard error (SE n=3). Browning index Browning index (BI) was determined following the equation of Ruangchakpet and Sajjaanantakul (2007): (BI)= [100 (x – 0.31)]/0.17 where x = (a* + 1.75 L*)/(5.645 L* + a* −0.3012b*). Firmness Fruit firmness was tested with a texture analyzer equipped with a 2.5 cm flat­tip (Instron 5564, MA, USA). The maximal force was expressed in kg/cm2 and slices were compressed with a speed of 5 mm/s to a depth of 4 mm. Total solid soluble Total solid soluble content was determined on pear fruit juice extracted from samples at each stor­ age time using a hand­held refractometer (ATAGO Palette PR­32). Total phenols content Total phenols content was quantified according to Sortino et al. (2022). 30 grams of fresh tissue for each replication was homogenized with methanol on 1:10 ratio and then filtered through a Whatman grade N.1 filter, the application of reduced pressure allowed the concentration of methanolic extracts and the residue was then suspended in 50% aqueous methanol and used for phenolic content quantifica­ tion. Phenols content was determined through a spectrophotometrical analysis at the wave lenght of 700 nm and results were expressed in gallic acid equivalent (mg kg­1 fresh weight). Ascorbic acid Ascorbic acid content was analyzed at each sam­ pling date with the Megazyme kit (Bray Business Park, Bray, Co., Wicklow, Ireland) as reported by Allegra et al. (2015). Sensorial analysis Sensorial analysis was carried out by a panel of 12 specifically trained panelists (Sortino et al., 2017). All samples were subjected to a panel made up of 14 descriptors: external color uniformity (ECU), com­ pactness (COM), pulp color intensity (PCI), odor (O), herbaceous odor (HO), floral odor (FO), sweetness (SW), sourness (S), bitterness (B), juiciness (J), pear flavor (PF), herbaceous (HF) and floral flavor (FF) and overall rating (OR). The graduated scale went from 1 (absence of descriptor) to 9 (descriptor at its fullest intensity). Sensorial analysis was carried out from day 0 to day 10. Visual quality score Edible coatings effect on ‘Butirra’ fresh­cut slices was evaluated at each storage time on six slices used as single replicates, for each treatment. Six trained judges used a list of descriptors wrote down in pre­ liminary meetings. Descriptors involved the medium value of color, integrity and appearance on pear fruit slices as reported by Allegra et al. (2022). Descriptors were quantified using a 5 points hedonic scale where 5= very good, 4= good, 3= sufficient (limit of mar­ ketability), 2= poor (limit of usability) and 1= very poor (inedible). CO2 and O2 inside packaging O2 and CO2 content inside packages was analyzed at each sampling date using a PBI Dansensor Checkpoint O2­CO2 analyzer (Ametek Mocon, MS, USA) equipped with infrared detectors. Statistical analysis The experimental design consisted in two treat­ ments and one control, observed at 0, 3, 5, 7 and 10 days at 5°C after treatment. Nine slices were used as single replicates and analyzed at each sampling date. Analysis of variance was applied (Systat 13.0 for Windows was used as statistical software) and the significance of data (p≤0.05) was evaluated with Tukey’s test. 3. Results and Discussion Total solid soluble content Our results showed a general increase in TSS dur­ ing storage; control slices content increased about 29.03% during the 10 days of storage while XAN and ASC treatments scored an increase of 16.30% and 15.45%, respectively. CTR slices increase is probably Adv. Hort. Sci., 2023 37(1): 59­66 62 due to the greater water loss of the untreated sam­ ples, which also results in higher percentages of weight loss (Fig. 1). XAN and ASC treatments were more efficient than CTR in limiting the increase in TSS content, this phenomenon is due to ripening process­ es that result in the hydrolysis of starch into mono­ and disaccharides (Mahajan et al., 2004) and in the activation of respiration processes where sugars are the main substrate used (Dong et al. , 2004). Significant differences occurred between treatments on 5th and 7th day while on 10th day XAN and ASC treatment recorded the same value. closely linked, as previously discussed, with TSS con­ tent data. Color changes and browning index Color monitoring during cold storage showed a change in L*, a* and b* values in ‘Butirra’ in all treat­ ments (Table 1). A low decrease in L* values occurred in XAN treatment. Color changes are more limited in ASC treated samples. At the end of cold storage period (T10), ΔE reached its highest in CTR samples and its lowest in ASC treated samples. Untreated ‘Butirra’ fruit slices recorded the highest browning values at each sam­ pling date, and it began to increase sharply from day five, while XAN and ASC treatments recorded the lowest values. Significant differences occurred between ASC and XAN treatments from 5th day of storage while no significant differences were record­ Fig. 1 ­ Total solid soluble content of untreated (CTR) and treat­ ed with Xanthan gum and Xanthan gum + calcium ascor­ bate (XAN and ASC) Pyrus communis L. cv. Butirra fruit slices at 0 time and after for 3, 5, 7, 10 days of storage at 5°C. At each sampling date, different letters indicate sig­ nificative differences between treatments. p≤0.05 was used in the Tukey’s test. The data are provided as the mean ± SE (n = 3). Weight loss and firmness Weight loss during cold storage showed an increase in all sample slices (Fig. 2). CTR samples showed a higher percentage of weight loss if com­ pared to other treatments. ASC treatment showed lower weight loss than XAN and control pear slices. The effectiveness of ascorbate calcium­can be attrib­ uted to the ability of calcium to preserve the com­ pactness of cell structures by limiting the action of pectolytic enzymes. In other work on fresh­cut pear the use of calcium ascorbate could be responsible of the maintenance of cellular wall structure since calci­ um maintains glycosidic bindings stable avoiding the collapse of cellular wall and the subsequent loss of liquids (Akhtar et al., 2010). Grant et al. (1973), on the other hand, showed that the maintenance of firmness in calcium­treated fruits may be due to its accumulation in cell walls, which facilitates the cross­ ing of pectic polymers by increasing wall strength and cell cohesion. Obtained results for weight loss are Fig. 2 ­ Weight loss (%) and firmness (kg/cm2) of untreated (CTR) and treated with Xanthan gum and Xanthan gum + calci­ um ascorbate (XAN and ASC) Pyrus communis L. cv. ‘Butirra’ fruit slices at 0 time and after for 3, 5, 7, 10 days of storage at 5°C. At each sampling date, different letters indicate significative differences between treatments. p ≤ 0.05 was used in the Tukey’s test. The data are provided as the mean ± SE (n= 3). Guccione et al. ‐ Xanthan gum and CA to prolong cv. Butirra shelf life 63 ed at 10th day between the two edible coatings for­ mulations (Fig. 3). A similar trend occurred in Sharma and Rao (2015) on fresh­cut pear treated with Xanthan gum for 8 days of cold storage. Sensorial analysis and visual quality score Sensorial analysis was carried out at each storage time and at harvest time high values were recorded for all descriptors except for bitterness, sourness, herbaceous and floral odor and flavor. A slower decrease in treated pear slices was recorded. All treatments recorded higher values than CTR one at each sampling time and no off­flavors or negative descriptors were found in edible coating treated sam­ ples until 10th day of storage. In fact, ‘Butirra’ pear slices treated with ASC and XAN recorded positive val­ ues for descriptors concerning sweetness, compact­ ness, external color uniformity, juiciness and pear fla­ vor during all storage time while, on the contrary, CTR samples recorded increasing values of negative descriptors such as bitterness and sourness as early as the 5th day of analysis. Overall rating was quite posi­ tive in treated samples until 10th day (Fig. 4). Visual quality score test enhanced that a decrease in mean values occurred in all treatments registering significant differences since the 3rd day of analysis (Fig. 5). Since day 3, CTR samples recorded mean val­ ues under 3 (limit of marketability). Instead, the judges evaluated ASC samples on 10th day at the limit of marketability (score=3). Xanthan coating had a positive effect on visual score of fresh­cut pear (Sharma and Rao, 2015) extending their marketability until the 10th day. Total phenols and ascorbic acid content No significant differences were showed between treatments on pear slices ascorbic acid content. During storage, total phenol content increases slowly in both CTR and XAN treatment. After 7 days a sharp increase was observed in treated and untreated sam­ ples and significant differences occurred between Table 1 ­ Color slices (CIELab index) and color variation (ΔE) of untreated (CTR) and treated with Xanthan gum and Xanthan gum + calci­ um ascorbate (XAN and ASC) Pyrus communis L. cv. Butirra fruit slices at 0 time and after for 3, 5, 7, 10 days of storage at 5°C At each sampling date, different letters indicate significative differences between treatments. NS = not significant. p ≤ 0.05 was used in the Tukey’s test. The data are provided as the mean ± SE (n= 3). Days of storage Treatments L* a* b* ΔE T0 CTR 63.89 ­13.57 36.94 ­ T3 CTR 64.64 a ­0.32 b 24.30 b 18.33 NS ASC 66.27 b ­0.38 b 24.98 b 17.96 XAN 64.82 a 0.61 a 26.16 a 17.84 T5 CTR 66.97 a ­0.03 c 20.82 NS 27.27 a ASC 63.96 b ­0.11 b 19.25 22.23 b XAN 57.51 c 0.51 a 19.25 23.50 b T7 CTR 65.12 a ­0.22 a 17.4 b 28.69 a ASC 63.02 b ­0.07 b 16.72 b 24.33 b XAN 52.39 c 0.01 b 20.02 a 24.55 b T10 CTR 45.53 c ­0.02 b 12.20 b 33.66 a ASC 62.65 b 0.03b 14.90 a 25.93 b XAN 65.24 a ­0.36 a 14.37 a 26.19 b Fig. 3 ­ Browning index of untreated (CTR) and treated with Xanthan gum and Xanthan gum + calcium ascorbate (XAN and ASC) Pyrus communis L. cv. Butirra fruit slices at 0 time and after for 3, 5, 7, 10 days of storage at 5°C. At each sampling date, different letters indicate significative differences between treatments. p≤0.05 was used in the Tukey’s test. The data are provided as the mean ± SE (n = 3). 64 Adv. Hort. Sci., 2023 37(1): 59­66 ASC and other treatments (Fig. 6). An increase of total phenol content is possible in stress conditions after cutting or in low temperature (Amodio et al., 2014). CO2 and O2 inside packaging A limited O2 consumption and CO2 production occurred during storage in both XAN and ASC treat­ ments while higher values were registered in CTR samples (Fig. 7). Significant differences occurred from the 3rd day between treated and untreated samples, particularly, CTR samples registered a value of 1.5 kPa for O2 and a value of 21 kPa for CO2 at 10th day of storage. Both XAN and ASC kept the two para­ meters more stable. Similar trends were observed on fresh­cut peach treated with calcium lactate and ascorbic acid and on breba fig fruit stored in passive atmosphere (Allegra and Colelli, 2015; Allegra et al., 2015). 4. Conclusions The two different formulations based on calcium ascorbate and Xanthan gum preserved pear slices of ‘Butirra’ during the 10­day storage at 5°C. Positive effects were observed on browning, weight loss and firmness up to the 10th day, furthermore, the two edible coating formulations preserved the sensory attributes of fresh cut ‘Butirra’. Our results showed that Xanthan gum with calcium ascorbate treatment improved the retention of firmness, browining and weight loss than control slices. This result was con­ firmed by the sensorial analysis in which positive descriptors showed positive values until the 10th day of storage while untreated samples began to develop off­flavor and off­color since day 3. Fig. 4 ­ Sensorial analysis of untreated (CTR) and treated with Xanthan gum and Xanthan gum + calcium ascorbate (XAN and ASC) Pyrus communis L. cv. Butirra fruit slices after cut (0) and at 3, 7 and 10 days of storage at 5°C. At each sampling date, * indicates substantial changes between treatments. At each sampling date, NS indicate no changes between treatments. p≤0.05 was used in the Tukey’s test. Legend: external color uniformity (ECU), compactness (COM), pulp color intensity (PCI), odor (O), herbaceous odor (HO), floral odor (FO), sweetness (SW), sour (S), bitter (B), juiciness (J), pear flavor (PF), herba­ ceous flavor (HF), floral flavor (FF) and overall rating (O). Fig. 5 ­ Visual quality score of untreated (CTR) and treated with Xanthan gum and Xanthan gum + calcium ascorbate (XAN and ASC) Pyrus communis L. cv. Butirra fruit slices at 0 time and after for 3, 5, 7, 10 days of storage at 5 °C. At each sampling date, different letters indicate significative differ­ ences between treatments. p≤0.05 was used in the Tukey’s test. The data are provided as the mean ± SE (n = 3). Fig. 6 ­ Total phenols content (mg kg­1 fw) of untreated (CTR) and treated with Xanthan gum and Xanthan gum + calci­ um ascorbate (XAN and ASC) Pyrus communis L. cv. Butirra fruit slices at 0 time and after storage for 3, 5, 7, 10 days at 5°C. 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