The average values for the physical parameters of fresh papaya were determined as follows: moisture content at 87.17% (wb), L value at 33.00, a value at 11.80, and b value at 18.80. On the biochemical front, the parameters for fresh papaya were recorded as total soluble solids at 13.5°Brix, ascorbic acid content at 250 mg/100 g, lycopene content at 1.65 mg/100 g, and total phenolic content at 54 mg/100 g.
Fitting the response surface model to significant independent variables
The results indicate that the response surface models were statistically significant (p < 0.05) for all responses, demonstrating a high coefficient of determination (R2 > 0.992). The contour plots, depicted in Figs. 1 and 2, illustrate the impact of OT, Osc, and Ot on the physico-chemical parameters of jaggery and honey osmosed papaya samples.
(a) The effect of OT, Osc and Ot on physical quality parameters of jaggery osmosed papaya. (b) The effect of OT, Osc and Ot on physical quality parameters of honey osmosed papaya.
(a) The effect of OT, Osc and Ot on biochemical quality parameters of jaggery osmosed papaya. (b) The effect of OT, Osc and Ot on biochemical quality parameter of honey osmosed papaya.
Effect of unconventional natural sweeteners on physical quality parameter of osmosed papaya
Total colour difference
Colour is a crucial visual indicator for evaluating the effects of heat treatment and predicting quality degradation from heat exposure. Tables 1 and 2 show that the total colour difference ranged from 9.1 to 25.9 for jaggery osmosed papaya and 11.7–24.3 for honey osmosed papaya. In jaggery osmosed papaya, the factors Osc, Ot, and the quadratic term OT significantly (p < 0.05) increased the total colour difference, while the quadratic term of Ot and all interaction terms significantly decreased it. The high F value for the main term of jaggery solution temperature indicates its significant influence on the total colour difference (Table 3). For honey osmosed papaya, the main terms OT and Ot, along with the interaction term of Ot and OT, significantly (p < 0.05) increased the total colour difference. Conversely, the factor Osc and all quadratic terms significantly decreased it. The high F value for Osc emphasizes its key role in influencing the total colour difference of honey osmosed papaya (Table 4). In the jaggery osmosed samples, the total colour difference increases with the rise in the concentration of the solution (Fig. 1a). Conversely, in honey osmo-solution, while there is a significant colour change with the increase in OT and time during the osmosis of papaya, the colour change diminishes with the increase in the solution concentration of honey (Fig. 1b). This phenomenon may be attributed to the fact that papaya tends to absorb the colour of the jaggery solution. Additionally, colour alteration can occur due to the micro-crystallization of the solute on the surface of the samples, as indicated by Tan et al.22. Comparable trends in colour change with an increase in osmo-solution concentration were also observed by Chauhan et al.23 in osmosed apple slices.
$${E_{JOP}} = + 16.56 – 0.94{{~}}A + 1.50B + 5.01{{~}}C – 0.38AB – 3.48AC – 0.87BC + 0.81{A^2} – 0.70{B^2} – 0.85{C^2}$$
$$\:{E}_{HOP}=+18.78- 2.15A-\:0.18B+3.17C\:-0.28AB\:-2.48AC+0.57BC\:-0.82{A}^{2}\:-0.73{B}^{2}\:-0.87{C}^{2}$$
Solid gain
Tables 1 and 2 reveal that the solid gain ranged from 8.23 to 16.62% for jaggery osmosed papaya and 6.97–17.47% for honey osmosed papaya. In jaggery osmosed papaya, the main factors OT and Osc, along with interaction terms (i.e. OT and Ot; Osc, and Ot) and the quadratic terms OT and Ot, significantly (p < 0.05) increased solid gain. Conversely, the main term Ot, the interaction term OT and Ot, and the quadratic term Osc significantly decreased solid gain. The high F value for the main term Ot underscores its predominant influence on solid gain in jaggery osmosed papaya (Table 3). For honey osmosed papaya, all main factors and the interaction term Ot and Osc, as well as the quadratic terms OT and Osc, significantly (p < 0.05) increased solid gain. Conversely, the interaction term OT, Ot, and Osc, and the quadratic terms Ot, significantly decreased solid gain. The high F value for the quadratic term Ot indicates its dominant role in affecting solid gain in honey osmosed papaya (Table 4). In jaggery osmosed papaya, there is an observed increase in solid gain as Ot decreases (Fig. 1a). On the other hand, in honey osmosed papaya, the solid gain increases with the rise in osmosis time (Ot), osmotic solution temperature (OT), and osmosis concentration (Osc) (Fig. 1b). This phenomenon may be attributed to the collapse of the cell membrane at higher temperatures, influenced by the high concentration difference between solids in the fruit and the syrup, particularly at elevated syrup concentrations. This collapse of the cell membrane is more pronounced at high temperatures, as discussed by Kaleemullah et al.24. A similar trend was noted by Kaur et al.25 in kiwifruit.
$${\text{S}}{{\text{G}}_{{\text{JOP}}}}{\mkern 1mu} = {\mkern 1mu} + {\mkern 1mu} 10.76{\mkern 1mu} + {\mkern 1mu} 1.30{\text{A}}{\mkern 1mu} + {\mkern 1mu} 1.74{\text{B}}{\mkern 1mu} + {\mkern 1mu} 0.21~{\text{C}}{\mkern 1mu} + {\mkern 1mu} 1.13{\text{AB}}{\mkern 1mu} + {\mkern 1mu} 0.51{\text{AC}} – {\mkern 1mu} 1.00{\text{BC}}{\mkern 1mu} + {\mkern 1mu} 0.87{{\text{A}}^2}{\mkern 1mu} + {\mkern 1mu} 0.56{{\text{B}}^2} – {\mkern 1mu} 1.00{{\text{C}}^2}$$
$${\text{SG}}_{{\text{HOP}}} = + 11.47+ 2.45{\text{A}} + 2.90{\text{B}} +0.83{\text{C}} – 1.26{\text{AB}} – 0.09{\text{AC}} +0.02{\text{BC}}+0.46{{\text{A}}^{2}} – 0.80{{\text{B}}^{2}} + 0.03{{\text{C}}^{{2}}}$$
Water loss
In jaggery osmosed papaya, all quadratic terms and the interaction term OT and Ot significantly (p < 0.05) increased water loss. Tables 1 and 2 show that water loss ranged from 21.02 to 39.59% for jaggery osmosed papaya and 24.57–39.63% for honey osmosed papaya. Conversely, all main terms and the interaction terms (i.e., OT and Osc; Osc and Ot) significantly decreased water loss. The high F value for the quadratic term OT indicates its dominant influence on water loss in jaggery osmosed papaya (Table 3). For honey osmosed papaya, the main term Osc and the interaction term Ot, Osc significantly (p < 0.05) increased water loss. In contrast, the main term OT, the interaction terms OT, Ot, and Osc, and all quadratic terms significantly decreased water loss. The high F value for the interaction term Osc highlights its predominant role in influencing water loss in honey osmosed papaya (Table 4). In both jaggery and honey osmosed samples, water loss increased with the rise in Ot (Fig. 1a and b). Additionally, water loss during papaya osmosis increased with an increase in solution concentration. This can be attributed to the osmotic gradient that results from an increase in solution concentration, creating a higher driving force for water removal between the solution and the fruit, consequently leading to higher mass transfer rates. This trend aligns with findings reported by Shalini et al.26 in osmosed papaya, where water loss increased with an increase in Osc.
$${\text{W}}{{\text{L}}_{{\text{JOP}}}}\,=\,+\,{\text{33}}.0{\text{7}}\,+\,{\text{1}}.{\text{65A}}\,+\,{\text{3}}.10{\text{B}}\,+\,{\text{4}}.56{\text{C}}\,+\,{\text{2}}.85{\text{AB}} – \,{\text{3}}.21{\text{AC}}\,+\,0.53{\text{BC}}\,+\,{\text{1}}.39{{\text{A}}^{\text{2}}}\,+\,{\text{3}}.0{\text{2}}{{\text{B}}^{\text{2}}} – 0.{\text{6}}0{{\text{C}}^{\text{2}}}$$
$${\text{W}}{{\text{L}}_{{\text{HOP}}}}\,=\,+\,{\text{31}}.12\,+\,{\text{1}}.81{\text{A}}\,+\,{\text{3}}.67{\text{B}}\,+\,{\text{1}}.17{\text{C}}\,+\,{\text{2}}.55{\text{AB}} – \,{\text{2}}.21{\text{AC}}\,+\,0.43{\text{BC}}\,+\,{\text{1}}.29{{\text{A}}^{\text{2}}}\,+\,{\text{3}}.11{{\text{B}}^{\text{2}}} – \,0.{\text{6}}0{{\text{C}}^{\text{2}}}$$
Weight reduction
Tables 1 and 2 show that weight reduction ranged from 11.99 to 27.66% for jaggery osmosed papaya and 16.31–28.07% for honey osmosed papaya. In jaggery osmosed papaya, all main terms and the interaction terms OT, Osc, and OT, Ot exhibited a significantly (p < 0.05) positive effect on weight reduction. Conversely, the interaction term Osc, Ot, and all quadratic terms had a significantly negative effect on weight reduction. The higher F value for the interaction term Ot indicates its dominant influence on weight reduction in jaggery osmosed papaya (Table 3). In honey osmosed papaya, the main terms Osc and Ot, the quadratic term Osc, and the interaction term Osc, OT showed a significant (p < 0.05) positive effect on weight reduction (Table 4). However, the main term OT, the quadratic terms OT and Ot, and the interaction terms OT, Ot, and Osc, Ot had a significant negative effect. The high F value for the interaction term Osc suggests its substantial impact on weight reduction in honey osmosed papaya. Figure 1a showed that weight reduction in jaggery osmosed samples increases with an increase in Ot, whereas in Fig. 1b showed that honey osmosed papaya, it increases as the concentration and time of osmosis increase. This may be attributed to the fact that weight reduction increases with the concentration of sugar, aligning with basic theories that posit the concentration and temperature of the osmotic solution as determinants of the driving force for osmotic mass transfer. Increased temperature and solute concentration lead to a higher osmotic pressure gradient, thereby enhancing mass transfer. Shalini et al.26 also found a comparable trend in the weight reduction of papaya during osmosis, and Kumar et al.27 quoted the same trend for papaya.
$${\text{W}}{{\text{R}}_{{\text{JOP}}}}\,=\,+\,{\text{22}}.{\text{12}}\,+\,0.{\text{35A}}\,+\,{\text{1}}.{\text{36B}}\,+\,{\text{4}}.35{\text{C}} – \,{\text{1}}.89{\text{AB}}\,+\,0.{\text{2}}0{\text{AC}}\,+\,0.{\text{88BC}} – \,0.{\text{32}}{{\text{A}}^{\text{2}}}\,+\,{\text{3}}.{\text{91}}{{\text{B}}^{\text{2}}} – \,0.{\text{69}}{{\text{C}}^{\text{2}}}$$
$${\text{W}}{{\text{R}}_{{\text{HOP}}}}\,=\,+\,{\text{19}}.24-0.63{\text{A}}\,+\,{\text{2}}.49{\text{B}} – \,{\text{1}}.38{\text{C}} – \,{\text{1}}.49{\text{AB}}\,+\,0.{\text{4}}0{\text{AC}}\,+\,0.{\text{87BC}} – \,0.{\text{22}}{{\text{A}}^{\text{2}}}\,+\,{\text{3}}.71{{\text{B}}^{\text{2}}} – \,0.{\text{79}}{{\text{C}}^{\text{2}}}$$
Effect of unconventional natural sweeteners on biochemical quality parameter of osmosed papaya
Ascorbic acid content (mg/100 g FW)
Tables 1 and 2 show that ascorbic acid content ranged from 84.09 to 180.29 mg/100 g FW for jaggery osmosed papaya and 12.02–93.75 mg/100 g FW for honey osmosed papaya. In jaggery osmosed papaya, the main terms Osc and Ot significantly (p < 0.05) increased ascorbic acid content, while the main term OT and all interaction and quadratic terms significantly decreased it. The higher F value for the quadratic term Osc highlights its dominant influence on ascorbic acid content in jaggery osmosed papaya (Table 3). For honey osmosed papaya, the main and quadratic terms OT, and the interaction term Osc, Ot, significantly increased ascorbic acid content (Table 4). Conversely, the main and quadratic terms Osc and Ot, and the interaction terms OT, Osc, and OT, Ot, significantly decreased it. The higher F value for the interaction term Osc indicates its substantial impact on ascorbic acid content in honey osmosed papaya. For both the samples, ascorbic acid content in papaya cubes decreased with the duration of osmosis due to leaching of organic acids in osmotic solution (Fig. 2a, b). However, in jaggery osmosed samples, a higher ascorbic acid content was observed at lower solution concentrations (Fig. 2a). This could be explained by the fact that the lesser concentration of the osmotic solution was unable to effectively coat the sample’s surface, leading to more ascorbic acid degradation. Similar results were reported by Islam et al.28 for osmotic dried papaya.
$${\text{A}}{{\text{A}}_{{\text{JOP}}}}\,=\,+\,{\text{84}}.11-{\text{14}}.42{\text{A}}\,+\,{\text{4}}.21{\text{B}} – \,{\text{4}}.81{\text{C}} – \,{\text{1}}.80{\text{AB}} – \,{\text{6}}.61{\text{AC}} – \,{\text{27}}.04{\text{BC}} – \,{\text{4}}0.58{{\text{A}}^{\text{2}}}\,+\,{\text{4}}.52{{\text{B}}^{\text{2}}}\,+\,{\text{35}}.{\text{77}}{{\text{C}}^{\text{2}}}$$
$${\text{A}}{{\text{A}}_{{\text{HOP}}}}\,=\,+\,{\text{48}}.23-{\text{21}}.04{\text{A}} – \,{\text{3}}.31{\text{B}} – \,{\text{5}}.71{\text{C}} – {\text{ 1}}.80{\text{AB}} – \,{\text{6}}.61{\text{AC}} – \,{\text{27}}.04{\text{BC}} – \,{\text{4}}0.58{{\text{A}}^{\text{2}}}\,+\,{\text{4}}.52{{\text{B}}^{\text{2}}}\,+\,{\text{35}}.77{{\text{C}}^{\text{2}}}$$
Lycopene content (mg/100 ml FW)
Tables 1 and 2 illustrate that lycopene content ranged from 0.011 to 0.106 mg/100 ml FW for jaggery osmosed papaya and 0.003–0.029 mg/100 ml FW for honey osmosed papaya. In jaggery osmosed papaya, the main term Ot and the quadratic term OT exhibited a significant (p < 0.05) positive effect on lycopene content. However, the main terms OT, Osc, and all interaction and quadratic terms involving Osc and Ot had a significant negative effect. The higher F value for the main term OT indicates its dominant influence on lycopene content in osmosed papaya (Table 3). For honey osmosed papaya samples, the main term Ot showed a significant (p < 0.05) positive effect on lycopene content. Conversely, the main terms OT, Osc, and all interaction and quadratic terms had a significant negative effect. The higher F value for the main term OT highlights its predominant role in affecting lycopene content in honey osmosed papaya (Table 4). The lycopene content of osmosed papaya increased with increasing Ot in honey osmotic solution, which contributed to overall solid gain and increased lycopene content in papaya samples (Fig. 2b). This is consistent with findings reported by Hempel et al.29 for peach palm fruit. However, in jaggery solution samples, the lycopene content of papaya samples decreased with an increase in osmo-solution concentration, Ot, and OT (Fig. 2a). This decrease in lycopene content is attributed to the increase in the temperature of the solution, causing a rise in the rate of cell breakdown and thermal degradation, ultimately leading to a decrease in lycopene content.
$${\text{L}}{{\text{C}}_{{\text{JOP}}}}\,=\,+\,0.0{\text{44}}-0.00{\text{4A}}\,+\,0.00{\text{6B}}-0.00{\text{6C}} – \,0.0{\text{1AB}}\,+\,0.0{\text{2AC}}-0.00{\text{5BC}} – \,0.0{\text{3}}{{\text{A}}^{\text{2}}} – \,0.0{\text{2}}{{\text{B}}^{\text{2}}}\,+\,0.00{\text{5}}{{\text{C}}^{\text{2}}}$$
$$\begin{aligned}{{\text{L}}{{\text{C}}_{{\text{HOP}}}}\,=\,+\,0.030\, – \,0.012{\text{ A}}\,+\,0.011{\text{B}}\,+\,0.014{\text{C}}\,+\,6.250{\text{E}}-003{\text{A}}{\text{B}}\,+\,7.000{\text{E}}-003{\text{A}}{\text{C}}} +\,4.500{\text{E}}-003{\text{B}}{\text{C}}\, \\ – \,0.020{{\text{A}}^{\text{2}}}\,-\,6.925{\text{E}}-003{{\text{B}}^{\text{2}}}\,+\,8.250{\text{E}}-004{{\text{C}}^{\text{2}}}\end{aligned}$$
Total phenolic content (mg/100 g)
Tables 1 and 2 demonstrate that weight reduction varied from 13.46 to 38.42 mg/100 g FW for jaggery osmosed papaya and 3.89–31.71 mg/100 g FW for honey osmosed papaya. In jaggery osmosed papaya, the main term OT and the interaction term Osc, Ot, along with the quadratic term Ot, significantly (p < 0.05) enhanced the total phenolic content. However, the interaction terms OT, Osc, and OT, Ot had a significantly negative effect on the total phenolic content of jaggery osmosed papaya. The higher F value for the quadratic term Ot suggests its predominant influence on total phenolic content in osmosed papaya (Table 3). Regarding honey osmosed papaya samples (Table 4), all main, interaction, and quadratic terms exhibited a significant negative effect (p < 0.05) on total phenolic content. The higher F value for the interaction term Ot and OT indicates its prominent impact on total phenolic content in honey osmosed papaya. In jaggery osmosed samples, phenolic content increased with increasing solution concentration (Fig. 2a). Conversely, in honey osmosed papaya samples, phenolic content increased with decreasing Osc, Ot, and OT (Fig. 2b). This can be attributed to the fact that the higher concentration of the osmotic solution effectively coated the samples during the osmosis process, resulting in a reduction in the degradation of phenolic content28.
$${\text{TP}}{{\text{C}}_{{\text{JOP}}}}\,=\,+\,{\text{29}}.00\,+\,4.35{\text{A}}\,+\,3.18{\text{B}} – \,{\text{8}}.00{\text{C}} – \,0.10{\text{AB}}\,+\,0.05{\text{AC}}\,+\,0.19{\text{BC}} – \,0.26{{\text{A}}^{\text{2}}} – \,0.14{{\text{B}}^{\text{2}}}\,+\,0.09{{\text{C}}^{\text{2}}}$$
$${\text{TP}}{{\text{C}}_{{\text{HOP}}}}\,=\,+\,{\text{17}}.58-0.09{\text{A}} – \,3.07{\text{B}} – \,1.71{\text{C}}\,+\,1.20{\text{AB}}\,+\,0.67{\text{AC}}\,+\,2.86{\text{BC}} – \,{\text{11}}.99{{\text{A}}^{\text{2}}}\,+\,1.02{{\text{B}}^{\text{2}}} – \,0.20{{\text{C}}^{\text{2}}}$$
Optimized condition
In the pursuit of achieving optimal product quality, the optimization strategy prioritizes the minimization of total colour difference and solid gain percentage, integral factors that significantly influence the visual appeal and textural characteristics of the end product. Simultaneously, the focus is on minimizing water loss percentage and maximizing weight reduction percentage to streamline processing efficiency and achieve an economically advantageous reduction in product weight. Additionally, the optimization objectives center around maximizing the concentrations of critical components, such as ascorbic acid, lycopene, and total phenolic content per unit weight, recognizing their pivotal roles in enhancing the nutritional profile and health-promoting attributes of the final product. The optimized operating conditions were found to be 49.46 °C, 40oBrix and 5 h for jaggery osmosed samples and 39.64 °C, 60°Brix and 4.92 h for honey osmosed samples (Table 5).
Kinetics study during osmosis at optimium condition
pH
The kinetic study investigated the relationship between pH and time, with pH measurements taken every 30 min. Figure 3 demonstrates that in both jaggery and honey solutions, the pH stabilized after 270 min. Overall, the pH of the osmotic solution decreased with time. This decline can be attributed to soluble acids from papaya leaching into the solution, causing the pH of the solution to shift from slightly acidic to moderately acidic30. The highest R2 values were obtained for the exponential model and polynomial (2nd order) model for honey (0.979) and jaggery (0.934) solutions, respectively. In contrast, the linear model had the lowest R2 value for both honey and jaggery solutions. Consequently, the exponential order was chosen for the kinetic study of pH in honey osmotic solution with respect to Os and the polynomial (2nd order) model for jaggery osmotic solution with respect to Os.
Trend for pH v/s time, total soluble solids v/s time and electrical conductivity v/s time.
Total soluble solids (°Brix)
The kinetic study explored the relationship between Total Soluble Solids (TSS) and time, revealing a gradual decrease in TSS of osmotic solutions from 0 to 180 min (Fig. 3). This decline could be attributed to osmosis causing an increase in solid gain. After a certain time period, the crop acts as a higher concentration medium, while the solution acts as a lower concentration medium, leading to reverse osmosis and an increase in the concentration of the solution31,32. In contrast, Osc decreased with time and became constant after 240 min, and Osc decreased with time and became constant after 270 min. This phenomenon may be due to an increase in the movement of solids from the osmotic solution to the samples31. The highest R2 values were obtained for the polynomial (2nd order) model for both honey (0.816) and jaggery (0.973) solutions, respectively, while the lowest R2 values were found for the exponential and linear models for honey and jaggery solutions, respectively. Consequently, the polynomial (2nd order) model was chosen for the kinetic study of TSS in honey osmotic solution with respect to Os and the polynomial (2nd order) model for jaggery osmotic solution with respect to Os.
Electrical conductivity (S/m)
The kinetic study examined the relationship between electrical conductivity and time. Electrical conductivity (EC) of honey osmotic solution exhibited an increase with time (Fig. 3). This rise in EC can be attributed to the increase in the moisture content of the solution. During the osmosis process, there is a transfer of moisture from the fruit to the solution. As a result, the moisture content of the solution increases, leading to an increase in electrical conductivity Rao et al.33. The highest R2 value was obtained for the polynomial (2nd order) model for honey (0.988) solution, while the lowest R2 value was found for the exponential model for honey solution. Notably, there was no electrical conductivity observed in the jaggery solution.
Drying of osmosed papaya at optimum condition using solar dryer
Total colour difference
Table 6 showed that the value of total colour difference was observed as 16.30 for jaggery osmosed papaya samples and 15.40 for honey osmosed papaya samples. It was observed that jaggery osmosed dried samples had maximum total colour difference from the fresh samples. This can be due to micro-crystallization of the solute on the surface of papaya samples that led to increase in the L value of solar dried samples2. Similar results were quoted by Chauhan et al.23 for apple, Kaur et al.4 for peas, Torres et al.34 for mango and Singh et al.35 for ber.
Ascorbic acid content
The maximum value of ascorbic acid content was observed in honey osmosed papaya samples (72.15 mg/100 g DW) and minimum value was for jaggery osmosed papaya samples (48.09 mg/100 g DW) (Table 6). It can be attributed to the increase in osmotic temperature, thermal degradation increases resulting degradation in ascorbic acid content28. Similarly, it was shown by Islam et al.28 for papaya, Nuñez-Mancilla et al.36 for strawberry, Choudhary et al.37 for pineapple slices.
Lycopene content
Table 6 showed that the value of lycopene content was observed as 0.028 mg/100 ml for jaggery osmosed papaya samples and 0.008 mg/100 ml for honey osmosed papaya samples. The value of lycopene content was maximum for jaggery osmosed samples. During the solar drying process, due to enzymatic reactions, the decomposition of pigments occurred Seerangurayar et al.38. Similar results were quoted by Seerangurayar et al.38 for dates, Mendelová et al.39 for tomato.
Total phenolic content
Table 6 showed that the value of total phenolic content was observed as 27.39 mg/100 g DW for jaggery osmosed papaya samples and 18.15 mg/100 mg DW for honey osmosed papaya samples. It was observed that honey osmosed dried samples had minimum total phenolic content. The decrease in total phenolic content can be due to the transfer of water during the application of these treatments which have caused nutrient loss Bozkir et al.40. Similar results were quoted by Minuye et al.41 in papaya, Bozkir et al.40 for persimmon, Guerra-Valle et al.42 for apple.
