Effect of polyvinyl acetate (PVAc) based coating on quality characteristics of capsicum during storage

Abstract

The effect of PVAc (Polyvinyl acetate) coating on various characteristics of capsicum was determined during postharvest storage at room temperature (30 ± 1 °C) and refrigeration temperature (10 ± 1 °C). Food grade PVAc was used to make different coating formulations (2.5, 5, 7.5, 10 and 12.5%) by dissolving alcohol-water mixtures. After coating, the samples were stored at room temperature (30 ± 1 °C) and refrigeration temperature (10 ± 1 °C) for a comparative study. Various physicochemical parameters viz. weight loss, TSS, acidity, chlorophyll, pH, ascorbic acid, and color were analyzed every three days of storage till spoilage. Results revealed that the physicochemical characteristics and the quality of the bell peppers were improved by coating treatments at both the storage conditions. PVAc concentrations of 10 and 12.5% performed better than other PVAc coatings in retaining the chlorophyll and water content, which ultimately increased the shelf life of capsicum without significantly affecting its green color. The coating reduced the weight loss and color change, maintained total soluble solids, titratable acidity, pH over the storage period. About 40–50% less weight loss was observed in case of higher PVAc coating concentrations (10 and 12%). Therefore, the present study results suggested that PVAc coating can maintain postharvest storage quality of capsicum at 30 ± 1 °C and 10 ± 1 °C storage conditions.

Graphical abstract

Introduction

Capsicum (Capsicum annuum L., family Solanaceae) is a widely used vegetable and a commercial spice for the human diet used either in raw or processed form. The genus capsicum comprises more than 26 species, of which only 12, including some varieties, are used by humans. Only five species have been domesticated and cultivated (Reyes et al. 30). It has various bioactive compounds (flavonoids, phenols, etc.), which help prevent some types of cardiovascular diseases, cancers, atherosclerosis by extending the senescence process (Rao et al. 29). It has about 60–65% moisture during harvesting, which is not suitable for long-term storage (Chitravathi et al. 10). Its postharvest quality is affected by moisture loss and chilling injury (Ullah et al. 2017). Flaccidity, shriveling, wilting and decay hamper marketability and consumer acceptance (Lerdthanangkul and Krochta 19). These problems can be overcome by using a coating or film on the surface of the commodity (Rao et al. 29; Simonne et al. 34).

An outer layer applied to fruits and vegetables for covering the stomata, which reduces transpiration and respiration and consequently lowers weight loss, is called an edible coating (Salehi 33). Coatings improve the shelf life of fresh fruits and vegetables by providing a prominent barrier to gases and water through improving structural integrity (Ojagh et al. 23). Many researchers tried different coating materials on capsicum to extend its shelf life. It was found that chitosan–gelatin composite edible coating may extend shelf life up to 3 weeks in refrigeration storage, while 14 days on the shelf (Poverenov et al. 27). Researchers successfully used carboxymethylcellulose and steric acid-based coating to improve the sensory quality of capsicum (Capsicum annum L.) (Uquiche et al. 2002). Appropriate formulations of propolis and cinnamon oil-based coating were found to be effective in inhibiting the mycelial growth of Colletotrichum capsici which causes anthracnose in capsicums and also in delaying the ripening process (Ali et al. 2). Shellac can also be used to coat the capsicums to restrict metabolic activities, delay aging, and extend the shelf life by 12 days under ambient conditions (Chitravathi et al. 10).

Due to uncertainty of availability in the market and issues related to using natural resources, one cannot rely only upon these natural coatings. Therefore, people also tried synthetic coatings or packaging made from synthetic polymers for various fruits and vegetables. It may include polylactic acid (Muller et al. 20) and polypropylene, probable applications in food packaging.

Polyvinyl acetate (PVAc) is also a synthetic polymer used in the food industry for various purposes. Polyvinyl acetate has been used for chewing gum manufacturing, cheese coating, sorbic acid carrier in margarine wrapper, cassava coating, an ingredient in sausage casings, and egg coatings (Hagenmaier and Grohmann 15). Apart from food, it has also been used in pharmaceuticals for controlled drug delivery without any adverse effects (Kolter et al. 17). Polyvinyl acetate has also been explored as a coating material for fruits and vegetables. It has been used for coating tomatoes without affecting their brightness (Cortez-Mazatán et al. 13) and Capsicum annum (Ortiz-Hernández et al. 24). Regulatory authorities like USFDA and FSSAI (GoI) have approved the the use of food grade PVAc as base material for the preparation of chewing gum and bubble gum. Polyvinyl acetate has also been approved by the Food Standards Australia and New Zealand (FSANZ) under the category of processing aids for the preparation of waxes for use in cheese and cheese products with maximum permissible level is as per GMP. During its toxicological study, histological analysis didn’t show any damage and recanalization in kidney of lab animal for even 6 months (Sadato et al. 32). PVAc, it has not been reported to be mutagenic, carcinogenic and a reproductive toxicant (Andersen 4). Furthermore, human body doesn’t show any toxic effect on exposure to polyvinyl acetate (Kaboorani et al. 16).

Considering the need for synthetic coating, properties of PVAc and the regulatory status of PVAc for food application, the present study was planned to reveal the effect of the PVAc coating on the physicochemical characteristics of capsicum throughout the storage period. During this study, a comparative analysis of the different concentrations of PVAc has been done for the shelf life enhancement of Capsicum annum in terms of weight loss, total soluble solids, titratable acidity, color, ascorbic acid, pH and chlorophyll for the first time. Also, the PVAc coating effect has been determined on capsicum stored on both low temperature and room temperature.

Materials and methods

Materials

Fresh capsicums (Capsicum annum) at the green stage (Commercial maturity) were procured from a local farm near Sonipat, Haryana, India, and then transported to the research laboratory. The capsicums were graded according to required uniformity in size, color, and shape. Capsicums without any blemishes and defects were chosen. These selected samples were surface disinfected by sodium hypochlorite solution (150 mg/Kg) for 2 min to inhibit the growth of unwanted and pathogenic microorganisms on the surface. After treatment, the capsicums were rinsed with distilled water and further air-dried. Polyvinyl acetate palates of a molecular weight of 25,000 Da were procured from Jubilant Agri and Consumer Products Limited (Greater Noida, India). The same was used for making coating solutions of various concentrations.

Reagents

Sodium hypochlorite (NaOCl), ethanol, 2, 6-dichlorophenol indophenol, sodium hydroxide (NaOH), phenolphthalein and acetone were used in the experiment, obtained from the Sigma Aldrich, India. All the chemicals were used in experiments were analytical grade.

Preparation of polyvinyl acetate (PVAc) coating formulations

Polyvinyl acetate coating solutions of concentrations 2.5, 5, 7.5, 10, and 12.5% were prepared by dissolving PVAc (w/v) in 95% Ethanol and 5% water. As per the literature, ethanol has been suggested to be the best solvent for PVAc. Five percentage of water was added because the PVAc solution made of pure ethanol tends to become turbid. Finally, the solution was stirred using a magnetic stirrer to prepare a coating solution.

Application of coating solutions

Capsicums were randomly distributed in six groups for each storage study (n = 3). Coating solutions were applied by dipping the capsicums for 15 s and then kept in trays for air drying. The coated samples along with uncoated (control) samples were then stored as a monolayer in trays at a refrigerated (10 ± 1 °C) and ambient temperature (30 ± 1 °C), respectively for studying the changes in various physicochemical properties of the samples.

Physicochemical analysis during storage

The physicochemical characteristics, such as weight loss, total soluble solids, titratable acidity, color, ascorbic acid, pH, and chlorophyll of the stored samples were analyzed at the interval of three days for both conditions.

Color

A colorimeter (CR-400, Konica Minolta Co., Japan) was used to measure the CIE Color parameters (L*, a*, and b*) of capsicum samples by triplicate samples. + L represents lightness and – L represents darkness, + a represents redness while − a represents greenness, + b represents yellow while − b represents blueness. Total color difference (∆E) was calculated by Eq. (1);

$$\mathrm{\Delta }\text{E}={\left[{\left(L_{1\ast }-L_{0\ast }\right)}^2+{\left(a_{1\ast }-a_{0\ast }\right)}^2+{\left(b_{1\ast }-b_{0\ast }\right)}^2\right]}^{1/2}$$ 1

where L_0*, a_0*, and b_0* were the color values of fresh capsicum without any treatments, and L_1*, a_1*, and b_1* represented the color values of hot peppers during storage (Qin et al. 28).

Ascorbic acid

The ascorbic acid content was determined by 2, 6-dichlorophenol indophenol titration method as described in AOAC (5) and calculated using the following Eq. (2) and (3);

$$\text{Dye factor}=\frac{0.5}{\text{Titre}\text{Value}}$$ 2

$$\text{Ascorbic acid}\left(\text{mg}/100\text{ml}\right)=\frac{\text{Titre}\text{value}\times \text{dye}\text{factor}\times \text{Volume}\text{made}\text{up}\times 100}{\text{Aliqout}\times \text{Volume}\text{of}\text{juice}\text{sample}}.$$ 3

Weight loss

Every capsicum was weighed using a digital balance (BSA224S-CW, Sartorius). The weight was recorded for day 0 (after coating) and every three days. Weight loss (%) was calculated per the standard AOAC (AOAC 5) method below.

$$\text{Weight loss}\left(\%\right)=W_1-W_2/W_1\times 100$$ 4

where W₁ is the initial weight (g), W₂ is the weight loss under storage (g).

Total soluble solids

Total soluble solids (TSS) in °Brix (°Bx) were measured using a digital refractometer (Rx-7000i, ATAGO Instruments Pvt. Ltd. India) at 20 °C. The capsicum samples were crushed in mortar and pestle. The juice was extracted and filtered using the muslin cloth. One-two drops of transparent and clear juice of samples were kept on the surface of the prism, and the readings were recorded (Rao et al. 29).

pH

The pH of samples was determined by a digital pH meter (pH tutor, Eutech Instrument, Cyber scan, India) at 25 °C with an accuracy of 0.01 (Chaple et al. 9).

Titratable acidity

The titratable acidity of the treated and untreated bell peppers was estimated per the AOAC (5) standard titration methods using NaOH and phenolphthalein indicators. Each sample's prepared juice extract in a replicate of five was titrated against 0.01 N NaOH solution using phenolphthalein dye as an indicator. The acidity results were expressed as % citric acid present in the samples (Ullah et al. 2017). The titratable acidity was calculated using Eq. (5).

$$\text{Titratable acidity}\left(\%\text{as citric acid}\right)=\frac{\text{Equivalent}\text{weight}\text{of}\text{acid}\times \text{Normally}\text{of}\text{NaOH}\times 100}{\text{Sample}\text{weight}\text{or}\text{volume}\text{of}\text{a}\text{sample}\text{taken}\times 1000}$$ 5

Chlorophyll

Chlorophyll was determined as per the previously described method (Conforti and Ball 12). Capsicum sample of 1 g mixed with 15 ml acetone (cold) and homogenized for 2 min. The extracted fluid was collected. Extraction from residues was further done by 5 ml of 80% acetone. The whole volume of extracted juice was made to 30 ml using 80% acetone. These fluid samples were then analyzed by the spectrophotometric method at 645 nm and 663 nm. Total chlorophyll was calculated using the following Eq. (6).

$$\text{Total chlorophyll}\left(\text{mg}/\text{L}\right)=20.{\text{2A}}_{645}+8.0{\text{2A}}_{663}$$ 6

where, A₆₄₅ = absorbance at a wavelength of 645 nm; A₆₆₃ = absorbance at a wavelength of 663 nm.

Statistical analysis

Analysis of physicochemical parameters was performed in triplicates. The data were subjected to analysis of variance (ANOVA), and Duncan multiple range tests were used to compare differences between treatments at the 95% confidence level (IBM SPSS statistics 25 for windows).

Result and discussion

Change in color parameters

Color is an important parameter when it comes to the consumer level. The color change is an indicator of ripening. In few capsicums, chlorophyll degrades and develops a red color during ripening. The red pigment which developed after chlorophyll degradation was capsanthin (Sabularse et al. 31; Ali et al. 2). Low temperature declined the enzymatic activity, and coating added extra protection from oxygen exposure, which prevents loss in greenness. Therefore, higher retention of green color was found at 10 ± 1 °C [Fig. 1a]. On the other hand, capsicum stored at room temperature (30 ± 1 °C) showed a gradual color change [Fig. 1b].

Fig. 1.

Effect of polyvinyl acetate on a* value at a 10 ± 1 °C and b 30 ± 1 °C and ascorbic acid content at c 10 ± 1 °C and d 30 ± 1 °C. Data shown are the means ± standard deviation

The use of PVAc coating had a significant (p ≤ 0.05) effect on the color parameters (L*, a*, b*) of capsicum stored under refrigerated conditions (10 ± 1 °C) and room temperature.

As the storage period increased, a* value also increased due to the transformation of green color to red in both the storage conditions. However, the transformation was observed in all samples (including control samples). While in the case of room temperature stored capsicum, succeeding 33 days of room temperature storage, a sharp decrease in a* value was observed. Comparative higher a* value observed in 12.5% coated capsicums. A similar trend was also reported by Panigrahi et al. (25). Figure 2 (located at the end) depicts the actual color change that occurred on the last day of storage at both temperatures i.e., at 10 ± 1 °C and 30 ± 1 °C.

Fig. 2.

Effect of polyvinyl acetate coating on skin color of green capsicum (Capsicum annuum L.) stored at a 10 ± 1 °C and b 30 ± 1 °C on 45th and 15th days respectively

The color change (∆E) is depicted in Tables 1 for capsicum stored at refrigeration and room temperature, respectively. In the case of refrigeration temperature, it was observed that the total color change (∆E) for higher coating concentration was minimal compared to lower concentrations. So, in the case of 12.5%, the color change was 34.36 ± 1.4 while 40.5 ± 1.4 for 2.5% after 45 days of storage. So, it can be concluded that the coating lowers the change in total color, especially in the case of 12.5% PVA concentration due to more retention of green color. In the case of room temperature, a similar kind of trend was observed. So, both the results show that coating favorably lowers the total color change during storage.

Table 1.

Effect of different PVAc concentrations on color change, acidity and chlorophyll of green capsicum stored at 10 ± 1 °C and 30 ± 1 °C

Concentrations	Days	Temperature	Color change (ΔE)	Acidity	Chlorophyll	Temperature	Color change (ΔE)	Acidity	Chlorophyll
Control	0	10 ± 1 °C	0a	0.15 ± 0.05a	1.34 ± 0.1b	30 ± 1 °C	0a	0.15 ± 0.05a	1.34 ± 0.10a
	15		17.08 ± 0.9b	0.25 ± 0.05c	2.46 ± 0.3c		23.09 ± 1.4b	0.26 ± 0.05b	1.55 ± 0.19b
	30		36.47 ± 2.2c	0.21 ± 0.01b	1.50 ± 0.06b		–	–	–
	45		50.2 ± 0.12d	0.21 ± 0.03b	0.51 ± 0.03a		–	–	–
2.50%	0		6.51 ± 1.2a	0.15 ± 0.05a	1.34 ± 0.1b		8.83 ± 1.5a	0.15 ± 0.05a	1.34 ± 0.10b
	15		15.14 ± 1.4b	0.64 ± 0.05c	1.55 ± 0.15b		21.57 ± 0.6b	0.19 ± 0.2b	0.89 ± 0.24a
	30		29.14 ± 0.7c	0.17 ± 0.01a	2.18 ± 0.11c		–	–	–
	45		40.5 ± 1.4d	0.18 ± 0.006bc	0.67 ± 0.026a		–	–	–
5%	0		5.61 ± 1.5a	0.15 ± 0.05ab	1.34 ± 0.1b		6.29 ± 1.2a	0.15 ± 0.05a	1.34 ± 0.10b
	15		16.85 ± 0.7b	0.66 ± 0.06c	2.14 ± 0.04c		17.45 ± 0.1b	0.35 ± 0.05b	1.02 ± 0.08a
	30		26.52 ± 1.4c	0.11 ± 0.01a	2.44 ± 0.04c		–	–	–
	45		37.49 ± 0.1d	0.25 ± 0.04b	0.44 ± 0.03a		–	–	–
7.50%	0		2.56 ± 1.6a	0.15 ± 0.05a	1.34 ± 0.1b		12.97 ± 2.3a	0.15 ± 0.05a	1.37 ± 0.05b
	15		17.27 ± 1.9b	0.3 ± 0.03c	1.26 ± 0.14b		22.59 ± 1.4b	0.3 ± 0.04b	0.89 ± 0.10a
	30		35.49 ± 0.8c	0.22 ± 0.02b	1.80 ± 0.04c		–	–	–
	45		48.18 ± 0.1d	0.27 ± 0.02b	0.48 ± 0.01a		–	–	–
10%	0		3.29 ± 1.5a	0.15 ± 0.05a	1.34 ± 0.1d		11.92 ± 1.1a	0.15 ± 0.05a	1.34 ± 0.10b
	15		15.79 ± 1.1b	0.19 ± 0.06b	1.11 ± 0.04c		17.89 ± 0.2b	0.26 ± 0.05b	0.54 ± 0.01a
	30		32.69 ± 1.8c	0.18 ± 0.01b	0.82 ± 0.1b		–	–	–
	45		43.2 ± 0.4d	0.24 ± 0.05c	0.24 ± 0.05a		–	–	–
12.50%	0		2.9 ± 1.8a	0.15 ± 0.05ab	1.34 ± 0.1b		8.11 ± 0.1a	0.15 ± 0.05a	1.34 ± 0.10b
	15		14.99 ± 1.1b	0.23 ± 0.03bc	1.18 ± 0.05a		17.62 ± 1.2d	0.7 ± 0.08b	0.22 ± 0.03a
	30		24.62 ± 1.4c	0.17 ± 0.01ab	1.60 ± 0.1c		–	–	–
	45		34.36 ± 1.4d	0.16 ± 0.02ab	1.30 ± 0.61b		–	–	–

Mean ± S.D. value with super script (a, b, c and…) showed significant difference (p ≤ 0.05) in the column with respect to storage days

Changes in ascorbic acid

Ascorbic acid (vitamin C) is an essential nutrient for humans. About 100 mg of ascorbic acid is provided by 100 g of fresh capsicum which is far more than RDA (recommended dietary allowances) (Qin et al. 28). Ascorbic acid is highly prone to oxidative loss. Figure 1c and d depict the ascorbic acid content in capsicum at 10 ± 1 °C and 30 ± 1 °C, respectively. Ascorbic acid is an important antioxidant that chelates free radicals and reactive oxygen species. It is a very delicate constituent than any other nutrient at storage and food processing and is also affected by oxidation. Ascorbic acid oxidase may decline its activity (Panigrahi et al. 25). In the present study, the ascorbic acid content of PVAc coated capsicum was found to be higher than the control [Fig. 3c and d]. Higher concentrations of PVAc coating proved to be better in preserving ascorbic acid levels. The ascorbic acid content in capsicum declined with the storage period. It was observed that the absence and low concentration of coating have a minimal effect on reducing the ascorbic acid loss rate of capsicum. Polyvinyl acetate coating beneficially influenced the ascorbic acid content of capsicum. A significant difference (p < 0.05) was observed in the ascorbic acid contents of coated and uncoated samples. The trend was quite similar to that reported by (Qin et al. 28). The 12.5% PVAc coated capsicum had the highest ascorbic acid value of 60 mg/100 g, while the lowest content was found in uncoated capsicum 45.1 mg/100 g in case of refrigerated storage condition while for room temperature stored samples, a 10% PVAc coated capsicum had the highest ascorbic acid value.

Fig. 3.

Effect of various concentrations of polyvinyl acetate coating on weight loss of freshly harvested green capsicum stored at a 10 ± 1 °C and b 30 ± 1 °C. Data shown are the means ± standard deviation

Avoidance of contact with oxygen delays the oxidation rate of ascorbic acid (Ayranci and Tunc 6). Oxidation is driven by oxygen, peroxides, light, heat, and enzymes like peroxidase responsible for ascorbic acid degradation (Chitravathi et al. 10). Also, enhanced respiration and conversion of acids to sugars by oxidation may reduce the ascorbic acid content (Ullah et al. 2017). Therefore, PVAc preserved the ascorbic acid content in capsicum better than non-coated in this study.

Weight loss of samples

Weight loss is a sign that the quality of fruits and vegetables is deteriorating, impacting their marketability (Nair et al. 21). Weight loss in fresh commodity yields declined shelf-life with economic value as well. Also, it has a strong influence on appearance due to shrinkage. Storage time, as well as temperature, contributed to increased weight loss in capsicum. Weight loss was increased in all the treated samples of both the storage conditions as the storage period progressed, as depicted in Fig. 3a and b for 10 ± 1 °C and 30 ± 1 °C, respectively. On the 45^th day, control samples were discarded, due to which further data is not available for the control sample in case of refrigerated storage samples. However, it was clearly shown that a 10% coated capsicum sample had the lowest weight loss than others at the end of the storage. The weight loss was observed due to water removal by transpiration and postharvest treatments, such as coatings that prevented weight loss compared to the control (Rao et al. 29). The similar trend of increase in weight loss was also found in (Ochoa-Reyes et al. 22), who reported the use of edible coating formulations using pectin, arabic, and xanthan gums for green bell pepper. There was increased amount of weight loss was observed in capsicum as compared to other fruits and vegetables because of its hollow, non-uniform shape with porous wall structure which found susceptible to weight loss (Guerra et al. 14). The result is obvious as coating provides hydrophobicity to the samples (Ayranci and Tunc 6). Weight loss for coated samples was significantly lower (p < 0.05) than controlled ones.

Changes in total soluble solids (TSS)

In control and coated capsicum, the TSS was increased as storage increased, as shown in Fig. 4a and b. The highest content of TSS was recorded in control or non-coated samples with values 9.5ºBx and 6.9ºBx for 10 ± 1ºC and room temperature storage, respectively. On the other hand, the lowest TSS at the 45 and 15 days for refrigerated and room temperature stored samples was recorded in 12.5% coated capsicum, while highest in the control sample, which indicates coating delays the softening process and starch degradation. There was a slowed-down of rising in TSS of capsicum that was observed in refrigeration storage sweet pepper (Ali et al. 1). As per the reports, due to slowing down respiration, the synthesis of new metabolites also slows down, which causes the slow conversion of carbohydrates to sugars. The loss of water during storage may also cause a rise in TSS (Panigrahi et al. 25). Because of the hydrolytic conversion of complex polysaccharides into simpler sugars, as well as the transformation of pectic components and juice concentration, the TSS behavior of the capsicums gradually increased with storage time (Kumar et al. 18). The similar trend was observed in green chili (Capsicum annuum L) stored at 5 °C with different formulations of starch coating (A’yun and Bintoro 7).

Fig. 4.

Effect of polyvinyl acetate on total soluble solids at a 10 ± 1 °C and b 30 ± 1 °C and pH at c 10 ± 1 °C and d 30 ± 1 °C. Data shown are the means ± standard deviation

Change in pH

pH is also one of the critical physicochemical parameters. pH was measured for both coated and non-coated samples during storage. The initial pH was 6.5 for all the samples. However, during the storage, pH was increased in all samples with different levels [Fig. 4a and b]. It was evident the impact of coating on the pH of capsicum. Comparatively reduced changes in pH values of coated samples were recorded, more rapid or sharp ones in case of control were observed. The trend of pH was similar to that reported by Srinivasa et al. (2006). Polyvinyl acetate coating was demonstrated to be one step ahead for keeping the pH low significantly (p < 0.05) during the storage at low temperature. Not only respiratory stimulated changes, such as physiological, biochemical, and structural, but also the accumulation of dry matter with defragmentation of higher sugars under refrigeration storage temperature might be responsible for rising pH (Ullah et al. 2017). A higher coating concentration (12.5%) maintained the low pH throughout the refrigerated storage of capsicum, while 10 and 12.5% coating for room temperature stored samples. An increase in the conversion of organic acids into sugars is responsible for rising pH levels (Amin et al. 3). Barzegar et al. (8) found that, there was increase in pH during storage of pepper. During the postharvest ripening process, carbohydrate and acid metabolism are strongly linked, raising the pH of the product.

Changes in chlorophyll content

In the post coating application, a decline in chlorophyll content was recorded because of changes that may have occurred in the chloroplast. The loss in chlorophyll could be due to the chlorophyllase enzyme or photosynthesis reaction. There was a gradual decrease in chlorophyll content of coated and the control samples during the storage in both the storage conditions. It is proven that during ripening, chloroplast gets converted to chromoplast, which is accompanied by a decrease in chlorophyll content (Chitravathi et al. 11). From Table 1, it was evident that the coating delayed the transformation of chlorophyll compared to the control sample. During maturation, the green-colored chlorophyll of capsicum converts to red-colored capsicum due to the degradation of chloroplast and synthesis of carotenoid chromoplast and their subsequent esterification by fatty acids. But coating helped slow this change by reducing respiration, causing hindrance in the formation of carotenoids (Panigrahi et al. 25). It may be observed from Table 1 that a 12.5% PVAc coated capsicum retained more chlorophyll as compared to the control in both storage conditions. The results were supported by (Patel et al. 26). From Table 1, it can be seen that the 12.5% coating concentration delays the chlorophyll conversion. At the end of storage, it was observed that chlorophyll content was 1.3 ± 0.61 mg, which suggests that a higher coating concentration may delay the conversion of chlorophyll.

Changes in titratable acidity (TA)

Titratable acidity of capsicum was significantly affected by PVAc coating treatments and storage intervals. Results showed that capsicum samples stored at low and room temperature showed a similar trend in acidity but better retention was observed with increasing PVAc concentration of coating. Table 1 depicts the acidities of all the samples kept at room temperature and refrigerated storage, respectively. Coating delayed the respiring rate and slowed down the use of acid (Yaman and Bayoιndιrlι 2002). In coated and non-coated samples, titratable acidity depicts falling drift through the storage. However, at the same time, acidity was survived in a controlled manner in coated samples of both the storage conditions (Table 1). Coated samples showed the extended shelf life of 45 and 15 days in refrigerated and room temperature stored samples, respectively. The decline in titratable acidity value was instantaneous in the control sample compared to the steady reduction in the case of coated samples. It was observed that initial and final acidities were identical in the case of higher concentrations of PVAc coating i.e., 12.5%, which was 0.16%. The higher coating (12.5%) concentration delays the change in the case of refrigeration temperature storage.

This might be due to lesser metabolic activities in coated samples. Post harvesting, acids and other products are observed to have a decreased trend with a rise in respiration rate. Such respiration might be disturbed by coating, causing delaying the maturity (Panigrahi et al. 25).

Conclusion

The result of the present investigation revealed that the green capsicum coated with a higher concentration of PVAc coating solution, especially 12.5%, improved the physicochemical characteristics of capsicums in both storage conditions. As a result, the commercial use of PVAc (12.5%) can be considered to maintain the quality characteristics of capsicums during storage and merchandise. In the future, PVAc coating will have immense applicability in fruits and vegetables for postharvest preservation. Additional research should be done examining the toxicity of PVAc coating for their extended use and applications.

Abbreviations

PVAc

Polyvinyl acetate

RDA

Recommended Dietary Allowances

Authors’ contributions

AVC conducted the experiment and wrote the manuscript; AS conceptualized, reviewed, edited and supervised the MS; MK investigated about methodology and software use; RS conceptualized, reviewed and edited the manuscript; AHD reviewed and edited the manuscript; NAS edited the primary MS draft. All authors discussed the results and contributed to the final manuscript.

Funding

The authors are thankful to NIFTEM and UGC for providing the financial support for this research project under Ph.D. research Grant No. N/FS/L/2019/5. This research work was also funded by Jubilant Agri and Consumer Products Limited (India) (Grant No. N/FS/D/2019/17).

Declarations

Conflict of interest

The authors declare that they have no competing interests.

Availability of data and material

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.