pH and acidity
Figure 1 shows the influence of storage and treatments on the pH and acidity of dilution syrup at 14 Brix. pH decreased up to 4 or less was an essential factor in preserving syrups against microbial spoilage. The pH value varied from 3.91 to 3.98 at zero time. The existing data showed that T2 and T3 had higher pH values. Throughout storing for 6 months, the pH value decreased, and the acidity increased in all treatments. T2 and T3 recorded the maximum pH value while T5 and T4 registered the minimum level compared with the other treatments.
Ascorbic acid
Changing in ascorbic acid content is shown in Fig. 2a. The thermal process during pasteurization effected on ascorbic acid retention in addition to storage periods. T1 recorded maximum ascorbic acid retention after preparation syrups and pasteurized. T1 was the highest ascorbic acid retention (98%) at zero time against 90% for the lowest one (T3). There was a gradual decrease in the level of ascorbic acid detected during storage. By storage ending, T1 and T2 had the maximum of vitamin C retention (71 and 60%) of the original amount at zero times.
Browning (non-enzymatic browning)
Figure 2b shows the development of polymerized color and browning. The browning varied from 0.025 to 0.045 at zero time for all treatments. The increasing amount of carrots had a positive relation with browning increasing. T5 has the lowest browning compared to the rest treatments at zero time. Browning increased gradually in syrups by increasing the time of storage progressively. T2 and T3 (0.113 and 0.120) had the lowest browning after the storage period, while the increase in browning of T5, T4, and T1 was more noticeable.
Total phenolics content (TP)
The differences between TP for different treatments were insignificant at zero time, as shown in Fig. 3a. During storage, the TP content dropped in all treatments. T2 and T3 recorded higher retention of TP with value (76% and 74%). The retention rate of the TP value of T5 was 55% compared to T4 and T1 (68% and 69%), respectively.
Carotenoids
The data regarding the influence of storage on carotenoid retention in diluted syrups are shown in Fig. 3b. The findings exhibit that the retention rate for all treatments varied from (98–99%) at zero time immediately after processing. All syrups had the same decreasing pattern in carotenoids through 6 months of the store. T1 and T2 recorded the highest β-carotene retention (88%) compared to T5 and T3 (82% and 79%) after 6 months of storage. T4 was the lowest retention rate of β-carotene after 180 days of an ambient store with a retention rate of 75%. By storage ending, samples containing 5 and 4% carrots were the most carotenoids maintained relative to sample comprising 6, 3, and 2% carrots in their composition.
Lycopene
The changes in lycopene syrups are presented in Fig. 4a. The lycopene retention in syrup samples had small changes at zero time, due to the constant percentage of the tomato pulp applied to the syrup composition of the five samples. The T2 lycopene retention rate equaled T5, and they recorded the maximum lycopene retention rate compared to the rest samples. The retention rate of lycopene decreased during storage to 65–88% compared to 96–98% at zero time, with losses varying from 10 to 31%, where T2 had the maximum rate of lycopene retention (88%) and T5 had the lowest retention rate (65%).
Antioxidant activity (AA)
Figure 4b shows the decrease in total antioxidant activity in different treatments during the storage period. The AA was ranged between 87 and 99% for the various treatments at zero time. T3 was the best treatment at zero time, which recorded the highest retention with total antioxidant activity, while T4 was the worst. As storage continued, the AA rate was reduced in different samples. The retention rate of AA ranged from 65–88% against 87–99% at zero time, with a loss rate of between 11 and 22%. T3 still recorded the maximum retention rate with AA (88%) compared with other treatments throughout storage.
Color evaluation
The surface color, L* or transparency (brightness to darkening), a* (redness), and b* (yellowness) values of diluted syrups were measured and are pointed in Fig. 5. The level of transparency, redness, and yellowness are linking to visual panel effects and shelf life dependent on color shifts. L* (transparency) values ranged from 42.2 to 45.9 at zero time. Transparency value increased (increase brightness) with increases in the content of sweet potatoes in the sample, while the transparency decreased (increase darkening) with an increase in the carrots percent.
The ratio of 2:6:2, T5 recorded the maximum transparency at zero time. Differences at a* (red color) were detected between different treatments at zero time. The value of b* (yellow color) is proportional to carotenoids so that more carotenoids responsible for yellow and orange contributed to an increase in yellowness or b*, which is a measurement of the color from yellow (100) to blue (− 100). The findings reveal that with a rise in carrots in syrups, the color rises to the orange color at zero time. The value of yellowness decreased from T1 to T5. During storage for 6 months, the values of transparency, redness, and yellowness of all diluted syrups decreased dramatically. Slightly darkening developed in the syrup as a result of a Millard reaction between sugars and amino acids. Higher carotenoids, lycopene, and brightness were reported (5:3:2, T2 and 4:4:2, T3). The findings showed that T2 and T3 syrups were a more suitable color compared with the rest syrups.
Sensory evaluation
Figure 6 illustrates the organoleptic features of various syrups at the start and end of the storage. Color, taste, odor, mouthfeel, and appearance are the most sensory attributes that influence the acceptability of syrups and customer approval or rejection. The highest overall acceptability score (9.1) was given by T1, which the panelists chose as more acceptable at zero time. T2 and T3 came out with scores after T1 (9.0 and 8.9). T4 and T5 (8.6) registered the lowest scores.
The mean score for color, odor, taste, mouthfeel, appearance, and total acceptance of various syrups continuously decreased significantly during storage under ambient storage, because of the production of the browning, the color score reduced, making the appearance of the product less desirable to the panelists. All syrups had a higher acceptance score even after the storage period. Finally, the most favorable sample by the panelists was the T2 followed by T3. Therefore, it is highly recommended using them for commercial production due to their attractive color and flavor. Further relationships between all analyses parameters confirmed the superiority of these two treatments, as shown in Fig. 7. These links are explained in discussion section. It is also clear from the influence of different treatments and storage period on the final quality of syrups.