2.3.1. Microbiological and Physicochemical Analysis
At the end of storage, the total microbial count showed a significantly lower value (
p < 0.05) in the coated samples (approximately 2.8 Log CFU g
−1 in G-B and G-B + E) compared to the uncoated ones (3.0–3.25 log CFU g
−1 in B and T), as shown in
Table 3. Concerning mold counts, highly significant differences were measured at the final time between the samples, with a greater proliferation in the control sample T. The low presence of yeasts at time 0 does not appear to be critical data, also found in Patanè et al. [
18], as growth activity ceased during conservation. Contrary to what was reported by Patanè et al. [
2], the comparison of T and B shows that the type of packaging influences the level of bacterial proliferation as biodegradable packaging has allowed for levels to be kept lower, with a better effect attributed to the application treatment of the edible coating with guar gum as noted by Ruelas-Chacon et al. [
9].
Table 4 shows changes in CIEL*a*b* parameters between samples and over time. The L* values remain relatively stable over time for all treatments, with small variations only for some samples and sometimes reaching final values of around 41–42. Therefore, brightness does not seem to influence the type of preservation packaging or the presence of edible coating. The parameter a* showed a significant increase over time only in T and G-B, indicating intensification of the red color. Also, Ruelas-Chacon et al. [
9] observed the increase in red intensity during the storage time of tomatoes, linked to the normal ripening process. The parameter b* showed a slight increase over time in each sample. This result could be associated with an increase in β-carotene, the presence of which influences the yellow/orange color. The H° parameter highlights highly significant differences between the samples, with a considerable reduction over time indicating a tendency towards the red/orange color, except for the G-B + E sample for which the change over time is not significant (
p < 0.05). The saturation, expressed by the C* parameter, increases slightly over time but only T and G-B showed a considerable variation, with the highest values at the final time. In conclusion, we can therefore make a comparison between our samples: T (stored in PET trays) obtained slightly higher values than B (stored in biodegradable trays) in all colorimetric parameters with significant variation over time.
Consistently with what was stated in Korte et al. [
42], the type of packaging has a slight impact on the analysis results. In particular, cellulose trays internally covered with a PLA layer and with PLA lids were used in the study. García-García et al. [
43] showed how PLA-coated cardboard trays have better preservation characteristics for tomatoes compared with uncoated trays. The PLA coating absorbs part of the ethylene, delaying its maturation and positively influencing the a/b color parameter. The difference between the behavior of B and that of G-B and G-B + E, all packaged in biodegradable packaging, could be attributed to the guar gum coating, which created a modified atmosphere around the fruits, influencing the rate of respiration and the color change during the storage period itself [
9]. The maintenance or slight variation of the color coordinates in B, G-B, and G-B + E, with respect to T, showed a delay of the ripening process, related to the ethylene production and respiration rate in tomatoes, as shown in Zapata et al. [
44] on zein-coated tomato fruit.
Tomato fruit showed a significant increase (
p < 0.01) in weight loss in all samples as a function of storage time and treatment (
Figure 3). The uncoated samples, stored in conventional and biodegradable packaging, showed, at the final time, the greatest weight loss with values equal to 11.02 ± 0.77% and 9.65 ± 0.1% (
Table S1) respectively, highlighting the role of the application of the guar gum coating in the slow weight loss [
9]. Furthermore, the incorporation of a hydrophobic part in the coating increases the barrier characteristics by adding to the layer of wax with which the tomatoes are naturally covered, reducing weight loss as found by Adjouman et al. [
23] and Yang et al. [
45]. Also, Olawuyi et al. [
46] found a higher loss of weight due to transpiration phenomena in uncoated tomato than in tomato coated with polysaccharide film composites using mucilaginous polysaccharides and carboxymethylcellulose with extracts from okra leaf waste.
The values obtained for pH, ° Brix, and titratable acidity (TA%) in tomato fruits are represented in
Table 5. The analysis of the pH on the tomatoes highlighted increasing values over time in all the samples within a range from 4.1 to 4.4, underlining that the packaging and the use of the coating did not significantly influence the pH of the tomato, as well as also reported by Naeem et al. [
1].
Results of total soluble solids (° Brix) highlighted an increase over time, following the normal maturation process which sees the transformation of complex carbohydrates into simple sugars, with values around 5° Brix at 30 and 45 days of conservation. However, uncoated samples showed higher values in a shorter period. The effect of the guar gum coating is probably due to the formation of a semi-permeable barrier around the fruit which modifies the internal atmosphere by slowing down metabolic processes [
9].
All samples underwent a significant decrease in titratable acidity (%) over time, starting from a range of approximately 0.5–0.6% citric acid and reaching values of approximately 0.4% citric acid without significant differences between treatments. The decrease in titratable acidity during storage time, both in samples coated with edible and non-edible coatings, was also observed by Ahmed et al. [
6] and Shakir et al. [
22]. Overall, it was reported that during tomato ripening the ° Brix degree increases and the acidity decreases; this follows the oxidation processes of organic acids and their conversion into sugars [
47]. pH, ° Brix, and, titratable acidity values found on tomatoes fall within the ranges reported in coated tomatoes with other natural polymers [
48].
The analyses of the lycopene content showed no differences between the various samples (
p > 0.05) up to time 45, with a slight variation for intermediate times only in B and C-B + E (
Table 6). As reported by Azali et al. [
49], lycopene variation during storage may be influenced by different factors including packaging, temperature, and oxygen. Furthermore, Barreto et al. [
50] also report a decrease in lycopene content in uncoated and coated cherry tomatoes during storage at room or cold temperature.
The analyses of the β-carotene content recorded a significant difference between the control sample, and the other three samples at the end of storage, recording a β-carotene value equal to 83.22 ± 0.94 mg kg−1, compared to values ranging from 52.96 ± 6.54 to 69.64 ± 1.99 mg kg−1 in B, G-B, and, G-B + E. Furthermore, sample T presented a significant variation over time, ranging from 18.49 ± 3.13 mg kg−1 at time 0 to 83.22 ± 0.94 mg kg−1 at time 45.
These results agree with Naeem et al. [
1], whose study highlighted the possible role of the edible coating made with guar gum in slowing down the synthesis of β-carotene, naturally synthesized during the ripening process of tomatoes through the transition of chloroplasts into chromoplasts where carotenoids are synthesized and accumulated through the conversion of geranylgeranyl pyrophosphate into phytoene and lycopene and the subsequent cyclization of lycopene with the production of α and β carotene [
51].
In addition, sample B showed a certain similarity with the coated samples, in particular G-B, and a highly significant difference with the sample packaged in conventional packaging, point to a possible role of biodegradable packaging in slowing down the synthesis processes of β-carotene. This could suggest the important role of packaging in maintaining quality, as confirmed by Azali et al. [
49].
2.3.3. Antioxidant Compound of Cherry Tomatoes
The results of the total phenolic content recorded a significant increase (
p < 0.01) in total polyphenols in all samples during storage (
Table 7), as a consequence of ripening, in accordance with what has been reported for different tomato cultivars and different storage conditions [
15].
Furthermore, the G-B + E sample recorded, already at time 0, the highest value (292.15 ± 10.83 mg GAE kg
−1) and maintained a highly significant difference at time 45 (421.17 ± 20.66 mg GAE kg
−1), compared to the other samples which recorded a total phenolic content within a range from 362.34 ± 6.96 to 388.8 ± 18.28 mg GAE kg
−1. This would suggest that the lemon pomace extract, used for coating enrichment, influences the phenolic composition of the fruit; this, in fact, increased the phenolic concentration in the tomato, as well as the coating, which probably created an environment around it, with conditions favorable to the synthesis and accumulation of phenolic compounds, as also reported by Kumar et al. [
21] and Barreto et al. [
50] where the pullulan/chitosan composite coating enriched with pomegranate peel extract enabled the preservation of phenolic compounds during storage at different temperatures.
Moreover, the results obtained are in agreement with what was stated by Shakir et al. [
22], whose study highlighted a lower phenolic content in the uncoated samples and an increase in the coated ones, which would suggest an important role on the part of the coatings in maintaining the integrity of the various substrates which normally come into contact during senescence processes and cause oxidation reactions, with a consequent drop in the concentration of phenolic compounds. Furthermore, the application of biodegradable packaging does not seem to particularly influence the concentration of the total phenolic content, as also found in Patanè et al. [
18] and Azali et al. [
49].
The ABTS assay recorded high statistical significance among the samples already at time 0, in which G-B + E showed the highest antioxidant activity with 189.35 ± 5.41 µmol Trolox 100 g−1, probably thanks to the lemon pomace extract which provided a content of phenolic compounds, while T and B, both without coating, recorded the lowest antioxidant activity, with 139.00 ± 7.98 µmol Trolox 100 g−1 and 145.02 ± 7.83 µmol Trolox 100 g−1 respectively. Data confirmed by the determination of the correlation coefficient which, at time 0, highlights a high correlation between the antioxidant assay and the total polyphenol content (r = 0.883).
At time 45, there was a highly significant difference between the samples B, G-B, and G-B + E, and T. The first three samples recorded a similar antioxidant activity, within a range from 193.59 ± 2.75 to 200.98 ± 0.38 µmol Trolox 100 g−1, while the lowest antioxidant activity was observed in T, with a value equal to 157.82 ± 2.89 µmol Trolox 100 g−1. In this case, the correlation with the total polyphenol content is absent but the antioxidant activity seems to be correlated to the presence of other lipophilic and hydrophilic compounds such as lycopene (r = 0.908) and citric acid (r = 0.933) and not with polyphenols (r = 0.0)
The DPPH assay reported lower antioxidant activity values than the ABTS assay. No relevant differences were observed between the samples at the various monitoring times, except after 45 days in which the greatest antioxidant activity was expressed by the tomatoes coated and packaged in biopackaging. This suggests a possible role of biodegradable packaging in prolonging the shelf life of tomatoes, with consequent maintenance of their antioxidant activity, as also reported in Patanè et al. [
18].
The results obtained from the DPPH assay are in agreement with those obtained by Shakir et al. [
22], in which the antioxidant activity of the various tomato samples presented very similar values during the first days of storage, and then differentiated significantly thereafter. This could be caused by a slowdown of the ripening processes by the coating on tomato fruits, as also indicated by Tsague Donjio et al. [
54]. At the same time, however, sample B also showed the same trends in maintaining its antioxidant capacity, suggesting that this was possible thanks to biopackaging, thus requiring this aspect to be further investigated in future studies.
The role of organic acids, in particular citric and malic acid which represent the main acids present in tomatoes, is important in the quality and organoleptic characteristics of the fruit [
5]. The results obtained from the determination of the organic acid content did not show high statistical significance between the treatments for all acids up to time 45, except in citric acid content (
Table 8). In fact, a decreasing trend over time was observed with significant differences between samples. Specifically, after 45 days, B, G-B, and G-B + E showed higher contents than T; these values are in line with the normal metabolism of citric acid in tomatoes (tricarboxylic acid cycle), which tends to decrease with the advancement of cellular maturation and respiration processes; however, the higher levels of citric acid recorded on samples with edible coating would confirm the role of the latter in slowing down the aging processes of tomatoes [
1].
The determination of the oxalic acid content allowed us to record an increasing trend over time for all samples, but a significant one in B, G-B, and G-B + E; while the malic acid content was stable over time with a significant reduction only in G-B + E.
Generally, ascorbic acid levels can increase with ripening and decrease in the senescence phase [
5]; in this case, the ascorbic acid content of the tomato samples was stable for up to 45 days, showing no differences between the various treatments.
However, the organic acid values found fall within the ranges reported in the bibliography [
44].
2.3.4. Sensorial Analysis
The results of the sensory analysis at time 0 denote a positive absence of variation as a result of the treatments applied compared to the traditionally packaged tomato that is well accepted by the consumer (
Table 9). At time 45, we noted a general decrease in the various descriptors with, in particular, a greater effect found in the control sample T which is the most depreciated in storage, for example, with an overall appearance that from 8.5 ± 0.5 at initial time was judged with 4.4 ± 1.1 at final time.
Also, for the descriptor “surface uniformity,” sample T (PET packed) turns out to be the worst (4.2 ± 0.8), whereas the better results of B, G-B, and G-B + E could indicate that the presence of the biopackaging and coating is a positive barrier for the preservation of the physical characteristics of the product. Among the coated samples, the crispness of the G-B sample at time 45 was better, while G-B + E scored slightly lower; these results are confirmed by the color and texture analysis.
At the end of the storage, only sample T was not within the limit of 4.5, while sample B showed the best results for general appearance, color, crunchiness descriptors, and total consumer acceptability, followed then by sample G-B and G-B + E, stored in biodegradable packaging; therefore, at the sensory analysis, such packaging gave positive results. In addition, the presence of edible coatings on the samples had no significant negative effects on sensory characteristics, in particular, for the coating enriched with lemon pomace extract, no relevant citrus flavour was perceived.