Journal of Applied Botany and Food Quality 94, 100 - 107 (2021), DOI:10.5073/JABFQ.2021.094.012 1Department of Plant Protection, Ministry of Agriculture, Palestine 2Department of Plant Production and Protection, Faculty of Agriculture and Veterinary Medicine, An-Najah National University, Palestine Effect of calcium chloride postharvest treatment in combination with plant natural substance coating on fruit quality and storability of tomato (Solanum lycopersicum) fruits during cold storage Fayez Sati1, Tawfiq Qubbaj2* (Submitted: September 8, 2020; Accepted: May 3, 2021) * Corresponding author Summary In this study, the impact of postharvest treatments with calcium chlo- ride (CaCl2) in-combination with postharvest coating treatments with plant natural substance arabic gum or cactus mucilage on the qua- lity and storage life of tomato fruits during cold storage (10 ± 1 °C, RH 85% ± 3) was evaluated. Results of dipping tomato fruits in 6% CaCl2 for 10 minutes combined with postharvest coating treatments with either 10% Arabic gum or 50% cactus mucilage for 3 minutes showed significant (p<0.05) higher value of fruit firmness, titratable acidity, reduce the percentage of weight loss and percent of decayed fruits. Treated fruits took longer to change color from pink to red compared with non-treated fruits. This study showed that dipping to- mato fruits in 6% CaCl2, or coating with different natural substances alone or in combination with CaCl2, enhances tomato fruits’ physical and chemical properties. Moreover, preserving tomato fruits can be preserved for a longer time compared with control fruits and main- tain the overall fruit quality. Keywords: Edible coating, arabic gum, cactus mucilage, storage life, physio-chemical properties, firmness, titratable acidity. Introduction Tomato (Solanum lycopersicum L.) of the Solanaceae family is one of the most grown and fresh consumed vegetables worldwide (AdAto et al., 2009). They have a high nutritional value of vitamins, minerals, natural antioxidant compounds and amino acids. In addition, several other beneficial health-related substances were found in tomatoes, such as carotenoids, lycopene and β-carotene, which have been cor- related with reducing risk of cancer and some cardiac diseases in humans (Borguini and torres, 2009). Tomato is classified as a climacteric and highly perishable fruit with a high respiratory peak associated with a high ethylene production rate after harvest (Ali et al., 2013), resulting in a short shelf life of usually one to two weeks (KApsiyA et al., 2015). During ripening, tomato’s physical properties and chemical composition change dramatically, affecting appearance, color, firmness, flavor, as well as the contents of phenolic, flavonoids and ascorbic acid (gArcíA et al., 2014; Ali et al., 2013). Therefore, susceptibility to substantial postharvest qua- lity reduction of tomato fruits during handling, transportation, stor- age and marketing is high (nAsrin et al., 2008). Several postharvest techniques have been applied to manage fruit ripening by reducing the respiration rate and associated ethylene synthesis, such as con- trolled atmosphere storage, modified atmospheric gas composition, temperature and humidity control. However, these techniques are expensive (BAldwin et al., 2000). Edible coatings have been considered as an eco-friendly and cost- efficient alternative technology to preserve quality and enhance agri- cultural commodities’ shelf life (HernAlsteens, 2020). Edible coat- ing of fruits provides several benefits, such as preserving the internal gas composition in tomato, mango, strawberry and guava (ZegBe et al., 2015; dHAll, 2013). They would form a semi-permeable bar- rier to gases, and water vapor on fruits surface, thus reducing weight loss, enabling the controlled release of bioactive compounds, enhanc- ing the antioxidant activity, total phenolic contents and leads to pre- serving the quality attributes of fruits during storage (HernAlsteens, 2020; Ali et al., 2010). Aloe vera, arabic gum, cactus mucilage and guar gum have been used on tomato (Ali et al., 2013; Ali et al., 2010; Al-JuHAimi, 2012; gArcíA et al., 2014). Arabic gum is dried gummy exudates from the stem and the branches of Acacia senegal (Ali et al., 2010) and is composed of a mixture of polysaccharides and glycol proteins. It is used in industries for film-forming and encapsulation (Ali et al., 2013). It was also used to delay fruit ripening, extend the shelf life, and reduce fruit browning in guava, strawberry and apple fruits (gurJAr et al., 2018; KAsHif and fAHAd, 2013; el-AnAny, 2009). Cactus mucilage is a complex hydrophilic polysaccharide found in Opuntia ficus-indica pads, that has the potential to create a barrier against water loss and gas exchange. Therefore, it could en- hance postharvest life of many fruits when applied as an edible coat- ing (gHeriBi and KHwAldiA, 2019). According to our best of knowledge, no records are showing the us- age of cactus mucilage as a coating substance on tomato fruits so far, while it has been tested on as an edible coating on strawberry (del- VAlle et al., 2005) and guava fruits (ZegBe et al., 2015). It has been demonstrated, that cactus mucilage has a positive impact on extend- ing shelf life, maintaining some quality parameters as firmness and delaying fruit skin color development. Postharvest application of calcium chloride on many fruits and vege- tables found to delay softening by increasing rigidity of the middle lamella and act as a binding agent in the cell wall to form calcium pectate, which helps conserve the quality and increases the storage life of fruits and make them firmer (meHmet et al., 2016; gAo et al., 2020). Several researchers reported the benefits of edible coating of fruits with natural substance and calcium chloride (CaCl2) treatment (ABBAsi et al., 2013; seneVirAtHnA and dAundAseKerA, 2010), but none of them used arabic gum or cactus mucilage in combination with CaCl2 as an edible coating for the preservation and extension of storage life of fresh tomato fruits. The current work aimed to study the effect of several novel combinations of edible coating substances as arabic gum or cactus mucilage and CaCl2 postharvest dipping treatments on tomato fruits’ physicochemical properties under cold storage. Material and method Plant materials and postharvest treatments Tomato fruits cultivar Izmir were harvested at breaker stage (i.e. the distal end of the fruits just turns yellowish ring) from a commer- cial farm in Tubas-City, the northern part of West Bank, Palestine. Immediately after harvesting, all fruits were transported and careful- Calcium chloride coating combined with natural substance 101 ly handled to the National Agricultural Researcher Center (NARC), Ministry of Agriculture in Qabatya, Palestine. Only firm and well- developed fruits with uniform medium size, free from disease, in- jures, and bruises, were selected for further use in the experiments. Dipping solutions preparation Calcium chloride CaCl2 6% (w/v) solution was prepared by dissolving 60 g of edible grade CaCl2 (Wei Bang Chemical Limited Company, Xiamen Ditai chemicals China) in 1000 ml distilled water. The solu- tion was constantly stirred using a magnetic stirrer (Model SP 18420- 26 Barnstead thermolyne USA) for 30 min until fully dissolved. Arabic gum solution 10% (w/v) was prepared by dissolving 100 g of arabic gum powder (Kapadia Gum Industries Pvt Ltd. MUMBAI - 400056, India) in 1000 ml distilled water. The solution had been stirred at a constant heat of 40 °C for 60 min on a magnetic stir- rer (model SP 18420-26 Barnstead thermolyne USA), then filtrated through cheesecloth and filter paper (pore size of 5 μm) to remove any undissolved material. The solution was allowed to cool to room temperature before use (ruelAs-cHAcón et al., 2017). Cactus mu- cilage extract (2/1) (w/w) was freshly prepared from Cactus opuntia ficus-indica pads harvested from plants in Tubas, Palestine. Pads were cleaned with 1% chloride, distilled water, then peeled and sliced into 1 cm cubes. Thereafter, squeezed by fruit juicers (GJE5437, 800wtt model Jepas, China) and diluted with distilled water by adding half the weight to obtain cactus mucilage (2:1) (w/w) (ZegBe et al., 2015). Treatments and experimental work Selected fruits of the same size shape and free from visual damage or defects were randomly divided into six treatment groups. Each treatment was triple replicated and consisted of 90 fruits per repli- cate. A separate group of 15 fruits per treatment was used for weight loss assessment. Single coated postharvest fruit dipping treatments were applied as; (i) 6% CaCl2 for 10 min. (ii) 10% arabic gum (w/v) for 3 min. (iii) Cactus mucilage (2/1) (w/w) for 3 min. Double coated postharvest fruit dipping treatments were applied as; (i) 6% CaCl2 for 10 min, air-dried for 30 min at room temperature, then followed by another dipping in 10% arabic gum (w/v) for 3 min. (ii) 6% CaCl2 for 10 min, air-dried for 30 min at room temperature, then followed by another dipping in 50% Cactus mucilage (2/1) (w/w) for 3 min., (iii) distilled water for 3 min served as a control. Single and double- coated postharvest treated fruits were left to air-dried for 30 min at room temperature before storage. Treated fruits were packed in plas- tic boxes covered with polyethylene film and stored in a controlled walk-in cold storage room with relative humidity (RH) of 85% ± 3 and temperature at 10 ± 1 °C for 35 days. Postharvest fruit quality assessment Fruit quality parameters, such as flesh firmness, physical weight loss, total soluble solids (TSS) and titratable acidity (TA) were evaluated on the date of the experiment (zero-day) before treatments, and every four days post the experiment first date for 35 days. Three fruits were selected randomly from every replicate per treatment used for the assessment. Weight loss (%) The same fruit was weighed every four days and the difference in weight loss was expressed in percentage on a fresh weight basis fol- lowing the standard method; the percent of weight loss of tomatoes fruit sample was calculated using the following formula (pilA et al., 2010): Percent of weight loss = · 100%. Decay percentage Fruit decay was determined by visual observation. The various fruits peel spots and rotting development were observed, and the percent of decay was calculated for both treated and non-treated fruits follow- ing the formula (pilA et al., 2010). Percent of decay percentage = · 100%. Color development Colorimetric measurements of the tomato fruit skin colour were de- termined for three fruits per replicate per treatment from both sides of each fruit using a Chroma meter (KONICA MINOLTA) Hunter. ‘L’, ‘a’ and ‘b’ values measured light reflection and intensity from white to black, green to red and blue to yellow, respectively (Voss, 1992). Fruit firmness Fruit firmness was measured using a digital penetrometers device (Lutron FR-5120) with 6 mm steel tip head to measure the average amount of force needed to puncture the fruit’s flesh. The steel cy- linder tips were applied to opposite sides of each tomato fruit on an area with the skin removed to expose the fresh flesh (KumAH and olympio, 2011). Two fruits per replicate per treatment were random- ly selected. The results were measured in (N) force unit. Total soluble solid (TSS) Total soluble solid (TSS) was measured by a digital refractometer device (model Milwaukee MA871) (°Brix). TSS was calculated for each fruit as an average of two readings of the digital refractometer, and the result was recorded as a degree °Brix (pilA et al., 2010). The refractometer was calibrated using distilled water before readings were taken. Titratable acidity (TA) Titratable acidity (TA) in tomato fruit juice samples was quantified by titration method using 0.1 mol L-1 NaOH, and the endpoint was pH (8.1). 15 ml of tomato juice were diluted with 85 ml of distilled water; 4 drops of phenolphthalein were added as an indicator for a color change to purple. The tomato fruit juice then titrated with 0.1 NaOH to pH (8.1) using the pH meter. The protocol was estab- lished by (gArner et al., 2003) from UC Davis, California, USA. Used with modifications to estimate the titratable acidity in the sam- ple. The result was expressed as a citric acid percentage using the follow- ing formula: Acid % = Mill equivalent factor = 0.0064 g Statistical analysis All statistical tests were performed using analysis of variance (ANOVA) using the SAS (SAS Institute Inc., 1998), Duncan multiple range test was used for evaluating mean separation at 5% level of probability, using sigma plot (version 8) in draw figure to show a significant difference. Result and discussion Weight loss In general, fruit weight loss was normally attributed to fruits senes- cence or desiccation (nAsrin et al., 2008); it was also used as a qua- lity index in the postharvest life of fruits. In this study, all samples initial weight - final weight initial weight decay fruit initial fruit (Mls NaOH used)·(0.1 N NaOH)·(Milliequivelent factor for tomato)·(100) grams of sample 102 F. Sati, T. Qubbaj showed a gradual loss of weight during storage, starting on day four of the experiment in both treated and non-treated fruits (Fig. 1, A). From day 8 until 16, no significant (P<0.05) differences were found between different coating treatments, except coating with 50% cactus mucilage. The control showed a significant (P<0.05) higher weight loss compared to all other coating treatments (Fig. 1, A). Furthermore, 6% CaCl2 in-combination treatments of either arabic gum or cactus mucilage postharvest coating effectively reduced weight loss after 20 days up to the end of the storage period (Fig. 1, B). The results are in agreement with previous studies, which reported that weight loss was reduced with natural substance postharvest coating treatment such as arabic gum in tomato (Ali et al., 2013), combined coating of arabic gum, chitosan with pectin in mango (cHien et al., 2007). Furthermore, arabic gum alone or combined with calcium chloride on mango (KHAliq et al., 2015). Meanwhile, gArcíA et al. (2014) found coating with pure aqueous extract of Aloe vera did not delay the weight loss in tomato. The loss of weight in fruits occurred during the transpiration pro- cess through the fruits’ surface, which is a normal metabolic pro- cess resulting in shriveling and deterioration of the fruit, depends on the gradient of water vapor pressure between the surrounding at- mosphere and the fruit tissue (BAldwin et al., 1999). In this study, the reduction in weight loss was probably due to the effects of the coating substance (arabic gum and cactus mucilage) and the CaCl2. Where, combination treatments act as a barrier against O2, CO2, lim- iting water transfer and solute movement, therefore, reducing respi- ration, water loss and oxidation reaction rates (BAldwin et al., 1999). Moreover, CaCl2 treatments found to delay ripening and extended storage life (irfAn et al., 2013), through reducing the concentration of O2 and increasing the concentration of CO2 in which help in delay senescence and ripening by reducing respiration and ethylene pro- duction rate in climacteric fruits as tomato fruits (pilA et al., 2010). Fruit decay During this study, the coating treatments had delayed decay symp- toms of fruits upto 20 days post-treatment compared with 12 days in non-treated control. At 24 days of cold storage, fruit decay started in all coating treatments and gradually increased in all fruits with storage time, but not in fruits coated with 6% CaCl2-treatments in- combination with 10% arabic gum (Fig. 2, A). Furthermore, the com- bination treatments of 6% CaCl2-treatments in-combination with 10% arabic gum or combination with 50% cactus mucilage showed the lower significant (p<0.05) decayed fruits compared to the alone treatment of each of 6% CaCl2, 10% arabic gum and 50% cactus mu- cilage postharvest treatments at day 28, and at the termination day of the experiment (day 35) (Fig. 2, B). Fruit decay is a natural phenomenon associated with the ripening process and postharvest diseases (KHAliq et al., 2015). The cur- rent results clearly indicate a significant role of coating substance and calcium chloride combined treatments in reducing fruit decay. Calcium chloride plays a major role in strengthening and thicken- ing the middle lamella of the cell wall, through increased formation and deposition of Ca-pectate in the cell wall (gArciA and HerrerA, 1996). During fruit ripening under long-term storage, fungi and bacteria were associated with some enzymatic change processes, which trig- ger damage to fruits and deteriorate the middle lamella, in particu- lar plant enzymes associated with the senescence process (ZApAtA et al., 2008). The current results agreed with sHArmA et al. (1996), who reported dipping apple fruits in calcium chloride reduced postharvest decay and delayed senescence compared to non-treated fruits. In addition, KHAliq et al. (2015) reported, coating mango fruits with arabic gum protected the fruits from pathogen infection and suggested coating forms a film on the mango surface. This film acts as a barrier to protect the fruits. Fruit color development Tomato fruit color is an important factor in determining fruit quali- ty. Additionally, it is the first sensory parameter for acceptance by consumers (nAsrin et al., 2008). Our results indicate a normal pat- tern of color development in non-treated and treated tomato fruits (Fig. 3, A). A significant (P<0.05) development of the red color oc- curred after 8 days in control (non-treated) fruits compared to other different treated fruits. The ‘a’ value is changed from a negative val- ue (green color) to a positive value (red color) (Fig. 3, B). No signifi- cant changes in color development were observed in other treatments as fruits were still predominately at the mature breaker stage (pink to light red). During the first 8 days, no significant changes were ob- served in ‘L’ and ‘b’ values among the treatments. The ‘L’ parameter is a sign of fruit from light to dark; all samples showed decrease ‘L’ values with progressing the storage times. Coating substance significantly reserved ‘L’ value compared with control (non-treated) fruits. However, no significant differences were observed among the other treatment at day 35 of storage (Fig. 3, A). The ‘b’ value also decreased with increasing the storage time in all fruits (Fig. 3, C). Coating treatments significantly (P<0.05) delayed color development of tomato fruits. Storage time(days) d4 d8 d12 d16 d20 F r W t L o s s (% ) 0 2 4 6 8 10 12 Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%CaCtus mucilage Figure(A) a a bb b b a b c c c c a b c cc c a b c ddd a b c c d d Storage time(days) d24 d28 d35 F r W t L o ss (% ) 0 20 40 60 control 6%CaCl2 10%Arabic gum 50%Cactus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage Figure(B) a b b c d d a b c c d d a b c c d d Fig. 1 (A, B): Effect of natural substance postharvest combination treatments with CaCl2 on the fruit weight loss of tomato fruits at cold storage. Means fol- lowed by the same letter are not significantly different (Duncan’s multiple range test, P > 0.05) Calcium chloride coating combined with natural substance 103 Fig. 2 (A, B): Effect of natural substance combination with CaCl2 on decay tomatoes fruit during cold storage at (10 °C). Means followed by the same letter are not significantly different (Duncan’s multiple range test, P > 0.05) Storage Time (days) d28 d35 D ec y P er ce nt (% ) 0 10 20 30 40 Control 6%CaCl2 10%Arabic gum 50%Cactus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage Figure (B)a a d c b e d c c dc b e Storage Time (days) d12 d16 d20 d24 D ec y P er ce nt (% ) 0 2 4 6 8 10 Control 6%CaCl2 10%Arabic gum 50%Cactus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage Figure (A) a a b b c c c a a Storage Time (days) d0 d4 d8 d12 d16 d20 d24 d28 d35 H un te r S ca le V al ue -15 -10 -5 0 5 10 15 20 Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a a a bc ab c a a a dc c a b b a b d c b c d bc c d e a d e c b b dc de c c d d c b dc d d d d Storage Time (days) d0 d4 d8 d12 d16 d20 d24 d28 d35 H un te r S ca le V al ue 16 18 20 22 24 26 28 a b abab a a a c ac b a b c b b b d a b ab bb a a a a c c bc ab a Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a Storage Time (days) d0 d4 d8 d12 d16 d20 d24 d28 d35 H un te r S ca le V al ue 20 25 30 35 40 45 50 55 Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage Figure (A) L-Scale a b a a a d c b a ab bc d e dc a b e d d c a b e d c c a b e d c a b f c d e a d c b a d c b a Figure (B) A-Scale Figure (C) B-Scale Fig. 3 (A, B, C): Effect of natural substance combination with CaCl2 on the color development of tomatoes fruit stored at cold storage (10 °C). Means followed by the same letter are not significantly different (Duncan’s multiple range test, P > 0.05) Storage Time (days) d0 d4 d8 d12 d16 d20 d24 d28 d35 H un te r S ca le V al ue -15 -10 -5 0 5 10 15 20 Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a a a bc ab c a a a dc c a b b a b d c b c d bc c d e a d e c b b dc de c c d d c b dc d d d d Storage Time (days) d0 d4 d8 d12 d16 d20 d24 d28 d35 H un te r S ca le V al ue 16 18 20 22 24 26 28 a b abab a a a c ac b a b c b b b d a b ab bb a a a a c c bc ab a Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a Storage Time (days) d0 d4 d8 d12 d16 d20 d24 d28 d35 H un te r S ca le V al ue 20 25 30 35 40 45 50 55 Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage Figure (A) L-Scale a b a a a d c b a ab bc d e dc a b e d d c a b e d c c a b e d c a b f c d e a d c b a d c b a Figure (B) A-Scale Figure (C) B-Scale 104 F. Sati, T. Qubbaj The number of days required for treated tomato fruits to develop color from pink to full red was up to 16 days from harvest, compared to 8 days in control (non-treated) fruits (Fig. 3, B). A clear positive influence of postharvest coating by 6% CaCl2-treatments in-combi- nation with 10% arabic gum on delaying fruit ripening, as treated fruits required more time to develop red color (16 days), compared to other treatments which developed the red color stage in 12 days (Fig. 3 A, B and C). Color development in ripe tomato resulted of the de-novo synthe- sis of carotenoids, mainly lycopene and β-carotene associated with the change in fruit color from green to red as chloroplasts are trans- formed to chromoplasts (BAtHgAte et al., 1986). Coating substance was found to delay chlorophyll degradation and lycopene synthesis, as well as ripening processes compared to uncoated fruits (yAmAn and BAyoindirli, 2002). However, this delayed fruit color develop- ment could be attributed to the modified fruits surrounding atmo- sphere; reduced O2 concentration and increased CO2 concentration. This reduces the respiration and ethylene production rate in climac- teric fruits (pilA et al., 2010) and, therefore, helps in delay ripen- ing and the associated changes in fruit color development. It was reported that arabic gum coatings delayed colour changes in tomato (Ali et al., 2010; Al-JuHAimi, 2012) and guava (gurJAr et al., 2018), while calcium chloride delayed colour in fig fruits (irfAn et al., 2013). BArmAn et al. (2011) reported that combined application of putrescine and carnauba wax reduced colour changes and preserved pomegranate quality during storage. In this study, the delay in color changes in tomato fruits treated with 6% CaCl2-treatments combined with 10% arabic gum might have been resulted from decreased bio- synthesis of carotenoids and preservation of chlorophyll content. Firmness Tomato fruits’ coating by different natural substance (10% arabic gum and 50% cactus mucilage) in addition to 6% CaCl2-treatments showed a positive significant (P<0.05) effect on fruits firmness compared to control (non-treated) fruits (Fig. 4 A and B). During the time course of the experiments, high significant (P<0.05) values were found in 6% CaCl2-treatment in-combination with 10% arabic gum, or 50% cactus mucilage compared to other solo coating treatments and con- trol. Therefore, the in-combination treatments preserved tomatoes fruits’ firmness compared to other treatments (Fig. 4 A and B). Fruit texture is an important characteristic of fresh horticulture pro- duce. The current results indicted non-treated fruits are softening and lost textural quality rapidly compared to treated fruits. These changes are attributed to deterioration in cell structure, cell wall composition and intracellular components during the ripening pro- cess under storage conditions (HArold et al., 2007) as it had been re- ported for a wide range of fruits, including tomato (ruelAs-cHAcon et al., 2017), mango (KHAliq et al., 2015; cHien et al., 2007) and plums (VAler et al., 2013). Postharvest application of calcium chloride was found to act as a binding agent in the cell wall to form calcium pectate, which increas- es the rigidity of the middle lamella and cell wall. It also inhibited cell wall activity degrading enzymes, so the outer membrane for the cell wall becomes more strength and rigid (KHAliq et al., 2015; pilA et al., 2010). Coating substances (arabic gum and cactus mucilage) in-combination treatments also helped create a modified atmosphere surrounding the fruit’s surface. Whereas elevating the CO2 and de- creased the fruit respiration rate (Ali et al., 2013), therefore limit the activity of softening related biochemical enzymes activity such as; hydrolases, pectin esterase, and polygalacturonase (ArAH et al., 2016; Ruelas-cHAcon et al., 2017). Therefore, the in-combination treatments of CaCl2 and coating substances retained significantly (P≤0.05) a higher firmness over the control fruits may be attributed to the thick coating, which created a modified atmosphere around the fruit surface, as a result, reduced changes in pectin substances and activity of cell wall degrading enzymes (KHAliq et al., 2015) in ad- dition to the role of Calcium in preserve cell wall structure by inter- acting with pectin in the cell wall to form calcium pectate complexes and reduce the activity of cell wall degrading enzymes. Total soluble solid (°Brix) In general, there was a gradual increase in total soluble solid (TSS) during the entire storage period (Fig. 5). No significant difference (p<0.05) was observed between control (non-treated) fruits and dif- ferent postharvest coating treatments from zero days (harvest day) until 12 days at cold storage (Fig. 5 A). While, after 16 days of stor- age up to the termination day of the experiments (day 35th), a higher significant (p<0.05) difference in total soluble solid was found in control (non-treated) fruits compared to 6% CaCl2-treatments in- combination with 10% arabic gum or 50% cactus mucilage coating treatments (Fig. 5 B). Fruit soluble solid concentration is a good index for determining fruit quality and maturity; it increases with maturity and ripening. Changes in the soluble solids content of tomatoes are correlated Fig. 4 (A, B): Effect of natural substance combination with CaCl2 on the firmness (N) of tomato fruits at cold storage (10 °C). Means followed by the same letter are not significantly different (Duncan’s multiple range test, P > 0.05) storage time (days) 0d 4d 8d 12d 16d F ir m n es s( N ) 0 10 20 30 40 Control 6%CaCl2 10%Arabic gum 50%Cactus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%CaCtus mucilage a a aaa a e a bc e c d a b cc e d b c e c d a c d d a b Figure (A) storage time (days) 20d 24d 28d 35d Fi rm ne ss (N ) 0 10 20 30 40 Control 6%CaCl2 10%Arabic gum 50%Cactus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%CaCtus mucilage c a b cc d a b c e c d a b c c e d a b dc e c d Figure (B) Calcium chloride coating combined with natural substance 105 Storage time (days) 0d 4d 8d 12d d16 °B ri x 4.1 4.2 4.3 4.4 4.5 4.6 Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a a a a a c d Figure (A) c ab bc b ab ab c c ab b bc d a Storage time (days) d20 d24 d28 d35 °B ri x 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 Control 6%CaCl2 10%Arabic gum 50%CaCtus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a a a d a c b Figure (B) ee f e d d d b c b b c c e Fig. 5 (A, B): Effect of natural substance combination with CaCl2 on the total soluble solid (°Brix) of tomato fruits at cold storage (10 °C). Means followed by the same letter are not significantly different (Duncan’s multiple range test, P > 0.05) with hydrolytic changes in polysaccharides (hemicellulose and pec- tin) during ripening (ruelAs-cHAcon et al., 2017). A similar to the presented TSS change pattern was found in tomato fruits coated with arabic gum (Ali et al., 2010; Al-JuHAimi, 2012), or with Aloe vera (gArcíA et al., 2014) and mango fruits coated with arabic gum combined with calcium chloride (KHAliq et al., 2015). Coating with natural substances can reduce the respiration rate and may slow down the synthesis and use of metabolites resulting in lower TSS (Ali et al., 2013) that may explain the higher concentration of TSS in non-treated fruits. Titratable Acidity (TA) Titratable acidity (TA) is the most essential parameter for evaluating fruits quality during storage. Lower values in TA concentration in fruits; faster fruit induced senescence (KHAliq et al., 2015). In this study, TA values of coated and non-coated fruit during storage de- creased with storage time (Fig. 6). After 12 days of storage until the termination day of the experiments (day 35th), the total soluble solid values were significantly higher (P≤0.05) in 6% CaCl2-treatments in-combination with 10% arabic gum or with 50% cactus mucilage coating treatments compared to other coating treatments and control (non-treated) fruits (Fig. 6 A). While after 20 days a significantly (P≤0.05) higher value was found in 6% CaCl2 treatments of, coating with either 10% arabic gum or 50% cactus mucilage compared to control (non-treated) fruits (Fig. 6 B). Titratable acidity decreased progressively with fruit ripening, and the decline rate significantly affected by the coating treatments with 10% arabic gum or with 50% cactus mucilage coating combined with 6% CaCl2. The significant lower level of TA in control fruit compared to coated fruit suggested that, coating delayed ripening by providing modified atmosphere around fruit surface and creating a barrier against O2 and CO2, led to reduce respiration rate (rodrigueZ et al., 2006; Ali et al., 2010). Preservation of titratable acidity by fruit coating treatments has been reported previously for various fruits as tomato coated with arabic gum (Ali et al., 2010; Al-JuHAimi, 2012) or with Aloe vera (gArcíA et al., 2014) and mango fruits coated with arabic gum combined with calcium chloride (KHAliq et al., 2015). Conclusion This study indicated that coating tomato fruits with either 10% arabic gum or 50% cactus mucilage combined with pre-dipping in 6% CaCl2 positively affect the physical and chemical properties of 0+*"G3(A"M&M.: "+*"(A$"0('&(&K.$"&/3;"+," (+)&(+$4",'83("&("/+.;"4(+'&7$"O!Q+ q $'"&'$"*+("437*3H/&*(.5" ;3\ $'$*("O#8*/&*i4")8.0 " Storage time (days) d0 d4 d8 d12 d16 TA ( % ) 0.0 0.1 0.2 0.3 0.4 0.5 Control 6%CaCl2 10%Arabic gum 50%Cactus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a a aaaa a aaaaa a aaa aa aa a b c d b c b b e d Figure (A) Storage time (days) d20 d24 d28 d35 TA ( % ) 0.0 0.1 0.2 0.3 0.4 0.5 Control 6%CaCl2 10%Arabic gum 50%Cactus mucilage 6%CaCl2+10%Arabic gum 6%CaCl2+50%Cactus mucilage a e a e b c d e a a b d c d d d bbc bc c b d d Figure (B) c Fig. 6 (A, B): Effect of natural substance combination with CaCl2 on the titratable acid of tomatoes fruit at cold storage (10 °C). Means followed by the same letter are not significantly different (Duncan’s multiple range test, P > 0.05) 106 F. Sati, T. Qubbaj tomato fruits, thus maintaineing the overall quality of fruits. A sig- nificant delay in fruit weight loss, firmness, titratable acidity, soluble solids concentration and color development was found during storage at 10 ± 1 °C compared to uncoated control fruit. Further research is needed to investigate the influence of the coating on ripening physio- logical processes, postharvest microbes inhibition, and on tomato fruit quality attributes under ambient storage conditions. Acknowledgments This research was supported by An-Najah National University. The authors gratefully acknowledges the excellent technical assistance by the team of the National Agricultural Researcher Center (NARC), Ministry of Agriculture, Qabatya, Palestine. Conflict of interest No potential conflict of interest was reported by the authors. 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