The shelf life of the fresh and processed products be contingent on the moisture content. Higher the moisture content enhances the water activity of the products. Maximum moisture content was recorded at on the day of preparation for all the treated jelly. In this study, the moisture content was slightly decreased over the storage periods (0–8 months). Several similar findings have also been described by the Mehta & Bajaj [41]; Tripathi et al. [42] for candy preparation, those reported that the moisture content may decreased during the storage periods. The slight decrease in moisture content could be due to moisture loss by the process of evaporation, thus increasing the total solids of the jelly.
Herein, the study also confirmed that there was a highly significant relationship between the moisture content and aw (Fig. 2), i.e., the presence of low moisture in jelly may contribute to achieve lower aw (0.56). The aw was found in lower throughout the storage periods where it ranged from 0.60 − 0.56 in the standerdized natural jelly. The results indicating that the formulated jelly was within the range of aw, thus it generally inhibited to grow microorganisms, suggesting that the standardized jelly can be considered safe in terms of microbial stability and quality, and are shelf-stable up to 8 months. The decreased pH value after storage [43, 44] and the jelly prepared using bee honey acts as a prebiotic due to contained fructose and oligosaccharides which might be contributed to inhibition the growth of microorganisms [45]. Another reason, the diluted honey in jelly might be generated H2O2 by the process of oxidizes glucose to gluconic acid have been found to be more effective [14]. The antibacterial properties of honey was more effective due to its high sugar concentration, low moisture content, along with its acidic values that all the characteristics were present in the stored jelly to inhibit the growth of microbial loads. However, the antimicrobial properties of honey have been proven and fully agreement by the sevral researchers [14–19] those reported that honey acts against pathogenic bacteria, oral bacteria as well as food spoilage bacteria. Moreover, the microbial data obtained after 8 months of storage (Table 10), conclud that the lower aw and presence of honey in jelly can’t abolish the microorganism but can stop the activities of microorganisms like Aspergillus, Shigella, and E-coli within the acceptable range of limit (Table 10).
Ash content of a foodstuff represents inorganic residue remaining after destruction of organic matter [46]. It represents minerals like calcium, phosphorus and iron. When the jelly was stored for storage studies up to 8 months, the ash content was found to be increased significantly over the storage periods. The increase in ash content during storage has also been found in pitanga jam [47], conventional and light blackberry jam [48]. The increases of ash content indicate that the products were stable during the storage periods.
Water activity (aw) is only of limited use as an indicator for the storage life of foods with low water content. Minor changes in water content lead to major changes in aw [13]. In this study, the effect of aw in processing of jelly influenced the food compositions that are shown in Table 2 and Table 4. In Fig. 2, highly correlation was found between the aw and moisture content where the aw decreased, the moisture content was also decreased. Foods with aw values between 0.60 and 0.90 are largely protected against microbial spoilage. In this study the aw values were found between 0.60 and 0.63 after 8 months of storage, which was favorable to increase the storage life of the naturally treated jelly by the inactivation of Aspergillus, Shijella and E-cloi during the storage periods. However, the results obtained from the study disclose that the decreased aw between the range 0.60–0.63 retarded the growth of microbial activities (Table 10) through slowing down the enzymatic catalyzed reactions.
Total sugar, reducing and non-reducing sugar significantly increased from fresh sample to processed sample even during entire storage periods. An increase in sugar content was reported by several researchers for the guava jelly, fruit bar, and different fruit candies [37, 49–55]. The increasing of total sugar, reducing and non-reducing sugar content between the fresh and the processed samples might be due to variation of sugar content and the formulation variation among the samples. The increased total sugar content may be different in the samples because of insoluble polysaccharides and other starch converted into soluble sugars completely during the storage periods [3]. Another reason might be the increasing of total soluble solids (TSS) entire the storage periods (0 to 8 months) contributed to increase the sugar content in jelly sample [56].
In this study, the range of the TSS value was recorded from 67.10 ± 0.10 to 68.70 ± 0.02 ºB. Nurani et al.[57], reported that TSS of the prepared jam and jelly should be ranged from 50–70ºB, indicating that the TSS obtained from this study was within the range of the jelly. The substantial changes (P < 0.01) of TSS during storage might be for the degradation of polysaccharides into soluble compounds [41, 58]. Another reason might be due to additional sugar and other ingredients during the preparation of the jelly.
One important feature of storing jelly is the high acidity which usually prevents the growth of food poisoning bacteria and also helps maintain the color and flavor of most jelly, jamd and marmalade. In this study, the acidity of the fresh guava and pineapple were 0.31 ± 0.01% and 0.63 ± 0.01% but after processing into jelly the acidity was increased. The increasing trend of the acidity was also observed during storage periods from on the day of preparation to 8 months of storage. It has been reported by several researchers that the acidity augmented with the advancement of storage [50]. The increased acidity might be due to the combination of mixed fruit juice (guava and pineapple) used during the preparation of the jelly. The significant increase of the acidity with the advancement of storage periods might be due to the conversion of pectic constituents into soluble solids [2, 50]. There was inverse relationship between the acidity and the pH of the formulated jelly. The variation of pH and acidity might be occured due to the variation of the formulation of the manufacturing process and during processing the pH decrease and total acid content may increase [59]. pH of the treated jelly was gradually decreased with the advancement of storage periods. A decrease in pH thus may promote an inhibitory effect on the growth of microorganisms in the standardized jelly after 8 months of storage (although microbial data is not shown here). A small reductions in pH after 320 days of storage in pitanga jams reported by Tobal and Rodrigues [47] was also similar with the present findings. Reduction in pH during 90 days of storage also have been recorded by the Nachtigall et al. [48] those reported that these reductions might be associated to the processing conditions of jam.
Vitamin-C is present in all animals and plant foods, mostly in free from, and it is probably bound to protein as well. It is fully absorbed and distributed throughout the body with the highest concentration in adrenal and pituitary glands. The daily requirement of the vitamin-C for an adult is 100 mg/day. The intake of the vitamin-C is essential to recover the scurvy disease and lower level in blood plasma but in the opposite the high intake of vitamin-C can increase the oxalic acid level that may interrupt the kidney functions [13]. In this study, it is well reported the Vitamin-C content of fresh guava and pineapple fruits were recorded as 53.43 ± 1.64 mg/100 g and 39.49 ± 0.01 mg/100 g but after processing into jelly it was noted as 43.01 ± 0.00 and 34.13 ± 0.15 mg/100 g in the best combination of T2 and T3. The highest vitamin-C content obtained in fresh guava than the pineapple have been reported by the several researchers due to their fruit nature and environmental factors [3, 60, 61]. Apart from, the results indicating that the vitamin-C content dramatically decreased due to processing into jelly and after storage entire the storage priods (3–8 months). The decreased vitamin-C content during the entire storage periods might be due to thermal destructions during heat processing, leaching of vitamin-C into water during heating, and its subsequent oxidation during storage [51]. The loss of vitamin-C activates to reduce immediately after harvest and destroys steadily during storage and other processes. Similar results also has been found by the Singh and Harshal [62] for processing of leafy vegetables where they reported that the loss of Vitamin C in green leafy vegetables might be due to the processing method employed in its preparation and subjected to boiling and microwave heating as well as blanching.
Vitamins are required for the normal growth, maintenance and functioning of human body. Hence, their preservation during processing and storage in jelly is of far reaching importance. Vitamin A not occurs in plant origin foods, it occurs in animal tissue. But in plant originated food it is found as β-carotene. β-carotene is the major dietary precursor of vitamin A. Food processing and storage can lead to 5–40% destruction of β-carotene [13]. In this study, the ß-carotene was drastically lost from fresh to processing into jelly even entire the storage periods (0 to 8 months).The results obtained from this study are strongly supported with the findings of Jane et al. [49] those reported that 4053 % loss of ß-carotene might occur during the process of boiling lettuce and carrot. Hackett et al. [52] reported that the conversion of trans form into cis form could be the reason for the loss of ß-carotene during processing. The loss might be occurred due to absence of oxygen and at higher temperature during cooking, boiling and sterilization of jelly.
The lower L* and C* values for color measurement indicate that the color lightness and intensity of the jelly T2 and T3 were lowered gradually up to 8 months of storage. The decrease in L values might be due to the reduction of anthocyanin content (Table 7) and the occurrence of the Maillard reaction during the storage of the jelly. The findings are also supported by Maskan et al. [63], who showed that a* and b* values were improved and L* values were reduced during the processing and preservation of grape juice. The stored jelly (T2 and T3) finally faded out and turned into dark color after 8 months of storage. This might be due to an increase in water activity (0.57–0.60 and 0.60–0.63; Table 5), reduction of carotenoid (Table 7), and the development of browning compounds. Similar results were obtained by Rhim and Hong [64] while studying red pepper. They reported that the red color of the pepper paled and tarnished black due to an increase in aw and temperature.
H* value indicates Hue angel value of the stored jelly. The H* value was statistically significant and increased up to 6 months of storage. However, after 8 months, the value (H*) of the standardized jelly T2 and T3 was insignificantly increased as 120.90 ± 5.59 and 119.11 ± 5.89 respectively, indicating that the jelly is within 180° and 270° region and started to lose its initial color. Hue angle represents the overall colour of the sample. All the jelly samples were found to have decreased red color values (as the hue angle increased within 180° and 270° region). The decreased hue angle in this study are also fully agreement with the findings of Tijskenset et al. [65] those reported that the color change could be attributed to the air removal around the surface, the air expulsion between the cells and its replacement with water and cell juice that was released from the deteriorated membranes that occurred during storage. Anotherthing is, the color change could be attributed to enzymatic or non-enzymatic browning (Maillard reactions) [66]. In fact, the presence of a higher amount of reducing sugars after inversion of sucrose during cooking, and/or higher pH, could contribute to these browning reactions.
Pectin is the main factor to determine the the jelly consistency and its content and type have an effect on gel hardness [23, 67]. Thus, in this study, the texture profile of the storage jelly was investigated to evaluate the softness and hardness entire the storage periods as most of the consumer preferences high spreadable jelly. The results shown that T2 jelly found slight harder than the T3 jelly, could be due to the use of only guava juice which contains solid pectin, whereas T3 was diluted with pineapple juice. Thus, the presence of solid pectin in T2 might have worked as a gelling agent following different mechanisms during the storage periods. The softness of T3 jelly might be due to internal metabolism and enzymatic and non-enzymatic degradation of pectin [38, 67]. The hardness found by the T2 sample are consistent with the findings of Raj et al.[68] those reported that papaya jam gained more hardness throughout the storage periods due to gell properties nature and the capability of water retention. The gel strength deceased as well as softness gained by the T3 sample might be due to dilution to the extracted acidic pineapple fruit juice. These results are fully agreement with the findings of Morris et al.[69] and Korus et al.[70] those reported that the decreased gel strength could be due to the decomposition of pectin compounds by the presence of acids in gooseberry jam.
All the minerals were found to be decreased with increasing of storage periods. The minerals value Na, K, Ca and Mg was found to be highest in the sample T3 whereas Fe, Mn, Zn, B,Cu, P and S was found to be highest in the T2 sample. The variation of the T2 and T3 jelly could be due to their treatment effect using different concentration extracted juice. Similar variations had also been recorded by Mumtaz et al. [71] on different jams and jellies. The researchers determined Fe, Zn, Na, and K as 0.52–0.910 mg/100g, 0.02–0.09 mg/100g, 44.62-71.45mg/100g and 26.10-50.11 mg/100g, respectively; however, no Mn was detected in the their jelly, while the guava-pineapple natural jelly (T2 and T3) contained Mn in the range of 0.68 − 0.50 and 0.69-0.55ppm, respectively. The results indicate that the values (Fe, Zn, Na, and K) obtained by the Mumtaz et al. [71] were higher than the treated sample T2 and T3. It has been claimed that these variations could be due to the nature of the product, soil structure, soil fertility, orchard type, orchard geographical conditions, the method of processing and preservation (as their sample was collected from the market), and experimental error. T3 sample had the highest Na content followed by T2 sample. The results are similar to the apricot and buberry jam that was reported by Naeem et al. [72]. The differences in Na content between the samples might be associated with the presence of sodium citrate during jelly preparation. Sodium citrate is the sodium salt for citric acid and functions as an acidity regulator in jelly. The average daily requirement of Na intake for the male 3.30 g and female 2.50 g. From a nutritional stand point, the daily Na intake should be limited to 2.30 g (equivalent to 6 g NaCl). As the Na absorption in the human body is rapid and starts within 3–6 min after intake and is completed within 3 hrs, therefore its too much intake can result in serious disorders [13]. K, Ca and Mg content had significantly higher in the T3 sample whereas the lower was recorded by the T2 sample. The results are similar to the findings of Giampieri et al. [73]. The higher K, Ca and Mg content for T3 sample found in the present study could be attributed to the dilution of guava juice with pineapple juice during preparation of T3 sample jelly [74]. The intake of K, Ca and Mg in normal diet to be ranged from 2.0-5.9 g/day (minimum 782 mg), 0.80–1.50 g/day and 0.30–0.50 g/day respectively [13]. The highest Fe content of T2 sample have similar levels with blueberry and strawberry jams as reported by Naeem et al. [72]. The higher content of Zn in this study are similar to the grape and strawberry jams [72]. The higher Cu level of T2 sample found similar to the apricot jam [72]. Other minerals Mn, B, P and S found to be higher in T2 sample. The possible destruction of Fe, Cu, Mn, Zn, B, P and S found in the T3 sample might be caused by processing with different treatments, material separation, dilution and thermal heat treatment during processing of jelly [13]. The daily intake of Fe, Cu, Mn, Zn, B, S and P in normaldiet to be from 1.50–2.20 mg/ day, 1.00-1.50 mg/day, 2.00–5.00 mg/day, 5.00–10.00 mg/day, 1.30–4.30 mg/day, 0.80-1.00 mg/day and 0.80–1.20 mg/day respectively [13]. However, all the minerals were present more or less present in both jelly sample (T2 and T3). The identified 11 minerals obtained by this study not have only nutritional and physiological imporatance but also contribute to increase the food flavor and activate or inhibit the enzyme-catalyzed and other reactions in the jelly [13].
Numerous bioactive compounds compounds and antioxidant activities such as total phenolic, total flavonoid, total carotenoid, anthocyanin, antioxidant activity, DPPH free radical scavenging activity, ferric reducing antioxidant power, reducing power assay and IC50 have carriedout in the stnderdized jelly on the day of preparation and after storage. Results revealed that all the bioactive compounds decreased with increasing of strage periods. In case of anthocyanin, it pigments are very sensitive to temperature and heat treatment during processing of jelly might be contributed to greatly reduce the content of pigments in the jelly. Storage temperature is the another main factor for retention and destruction of anthocyanin content [67]. As the final jelly was stored at room temperature therefore, it might be contributed to decrease the anthocyanin content. Anthocyanin content depend on the degree of pectin esterification. In this study, a higher anthocyanin content was found in the lower degree of pectin and lower energy value of the sample T3.
Carotenoid has a crucial part in human nutrition and health, which can lessen the risks of cancer and heart diseases because of the activity of pro-vitamin A [75]. The carotenoids extremely present in the diet as β-carotene and α-carotene are involved in the reduction of the incidence of type 2 diabetes [76]. Here, the results obtained from this study indicates that T3 sample have been found with higher ß-carotene and total carotenoid content followed by T2. Almost similar observations were made by the Dars et al.[77], those reported that mango juice contain 578 µg/100 g and 1.95 mg/100 g of total carotenoid and ß-carotene content. The variation of the total carotenoids and β-carotene content observed in T2 and T3 sample might be affected by the heat processing and storage temperature. The highest total phenolic, flavonoid, carotenoid, ß-carotene, and anthocyanin content in the sample T3 probably be due to the use of a mixture of guava and pineapple fruit juice during preparation. On the other hand, the guava and pineapple fruits individually contain different bioactive compounds [78]. Vukoja et al. [79] calculated total phenolic content as 1.69 g GAE/kg (dw) and total anthocyanin content as 98.48 mgcya-3-glu/kg in cherry jam, whereas these contents were higher in the standardized jelly (T2 and T3). The presence of higher total phenolic and anthocyanin content in this standardized jelly was probably because of adding natural honey during the preparation. Besides, the experimental honey contained 201.78 mg GAE/100g of total phenolic content and 6.04 mg QE/g of total flavonoid content. Therefore, the findings confirm that the standardized jelly (T2 and T3) contain a great variety of bioactive compounds.
The maximum total antioxidant activity significantly present T3 sample might be due to the abundance of phenolic components highly present in T3 as compared to T2. T2 and T3 showed a sturdy capability to scavenge free radicals as their total antioxidant capacity values were found to be 105.84–104.40 µg AA/g and 109.11-107.88 µg AA/g respectively. The determination of IC50 is a generally well established technique to judge the antioxidant activity of foodstuff and its lower value indicates higher free radical quenching ability [80]. Results revealed that both T3 and T2 showed potential antioxidant capacity due to their lesser assessment of IC50 (17.98–16.65 and 15.53–14.19 µg/g, respectively). The less amount of IC50 present in the T3 and T2 sample contributed to gain maximum amount of total antioxidant activity that might be accredited to the existence of significant quantities of phenolic compounds and flavonoids. The presence of FRAP values in the sample T3 and T2 could donate an electron to decrease the yellow ferric complex to a blue ferrous complex. The high FRAP values of T3 and T2 indicate that phenolic composite is the leading provider of the high antioxidant ability of the standardized natural jelly.
Phenolic compounds are an important bioactive compounds that preserve against dissimilar lethal chemical responses and diseases, and their association in antioxidants rely on their structure [81]. The difference of phenolic acids in T2 and T3 depends on the food matrix and chemical structures, extraction techniques used, solvent used, and the solubility of individual phenolic acid [81]. However, the results indicate that the standardized natural jelly (T2 and T3) were a rich source of phenolic compounds which were decreased slightly with the advancement of storage periods. The slightly decreased phenolic acids still now remains unknown. But the possible reason might be due to the fluctuation of room temperature during the storage periods. Another reason might be oxidisability of the studied phenolic acids with fluctuation of room temperature. Reblova [82] reported that the acivity of phenolic acids for pork lard decreased with increasing temperature. They also found inverses linear correlation between the relative decrease in phenolic antioxidant activity with increasing temperature and the oxidisability of the studied phenolic acids.
The standardized natural jelly (T2 and T3) was the abundant source of bioactive compounds and antioxidant activities due to combined processing effect of natural honey and fresh lemon juice.The best combination of these natural ingredients thus contributed to impart the jelly with improved attractive color, flavor, and texture.