INTRODUCTION
People consume Beverages for their nutritional value, thirst-quenching properties,
stimulating effect and/or their medicinal values (Adegunloye
et al., 1996; Elmahmood and Doughari, 2007).
Tomato (Lycopericon esculentum Mill.) is one of the most popular and
demanding vegetables grown in Bangladesh. Tomato is popular because of its vitamin
C and valuable nutrients content. Recent statistics showed that tomato was grown
in 44275 acres of land with the production of approximately 190213 metric ton
in 2009-2010 (BBS, 2010). Tomato is highly water containing
perishable vegetables (Mahmud et al., 2009).
So, Tomatoes are processed in the form of various products such as Tomato juice,
puree, cocktail, paste, ketchup, sauce, jelly, soups, powder and tomato chutneys
etc.
Tomato juice is a ready to drink tomato product. Tomato juice or pulp is very
much susceptible to microbial spoilage (Mahmud et al.,
2009). Different types of chemical additives or preservatives can be used
for preservation of such food products. In juice preservation, chemical additives
or preservatives which are commercially used are Potassium Meta Bisulphate (KMS)
in the form of SO2, Sodium-benzoate and Sorbic acid (Tasnim
et al., 2010; Jatto and Adegoke, 2010).
As huge amount of tomato is produced during peak harvest season, large quantities
of this valuable vegetable is wasted due to limited storage life and improper
preservation (Ahmed and Ismail, 1995). It is important
to prepare products like juice which can be preserved for longer time. Keeping
in view this fact, this study was undertaken to know the effect of different
chemical preservatives namely Potassium meta-bisulphate, Na-Benzoate and sorbic
acid on the microbial and sensory quality of tomato juice stored at room temperature.
MATERIALS AND METHODS
The study was conducted in the laboratory of the Department of Food Technology and Rural Industries under the faculty of Agricultural Engineering and technology, Bangladesh Agricultural University, Mymensingh. The duration of this experiment was 1 year from July (2006) to June (2007).
Formulation of tomato juice: Tomato juice was prepared with the following formula.
| • |
Pulp 10% |
| • |
TSS 14% |
| • |
Acidity 0.35% |
| • |
Sugar 13.5% |
| • |
Preservative 350 ppm |
Dose distribution of preservatives
Preparation of tomato juice: Tomato juices were prepared according to
the method described by Mahmud et al. (2009).
Organoleptic observation: Organoleptic observations were done at every fifteen days interval. Off flavor, discoloration, sedimentation was recorded for each treatment.
Analytical methods: Tomato juices were analyzed at every fifteen days
interval for their moisture, vitamin C, total soluble solids, ash, reducing
sugar and non-reducing sugar. All the determinations were done in triplicate
and the results were expressed as average value. Moisture was determined adopting
AOAC (1984) method. TSS was measured directly by hand refractometer.
Total acidity was measured by titration with standard NaOH using phenolphthalein
indicator (Srivastava and Sanjeev, 2003). Vitamin C content
was determined by the method described by Ranganna (1979).
Ash was determined by AOAC method. Total sugar was determined by Lane
and Eynon (1923).
Microbiological test
Determination of total viable count: For total viable count of bacteria
present in the tomato juice, colony count method was used according to “Laboratory
Methods in Food Microbiology” (Harrigan, 1998). The
total number of viable bacteria per mL. of tomato juice was obtained by multiplying
the number of colony forming units (cfu) on the plate with respective dilution
factor and then was converted into logarithmic form.
Counting of yeast and mould: Yeast and mould count of tomato juices
were also determined according to the "Recommended method for the Microbiological
Examination of Food", published by American Public health Association (APHA,
1967).
Subjective (sensory) evaluation of tomatoes: For statistical analysis
of sensory data, three different types of tomato juices were evaluated for color,
flavor, texture and overall acceptability by a panel of 10 testers (Hashimi
et al., 2007). All the testers were the students, teachers and laboratory
assistants of the Department of Food Technology and Rural Industries. Three
types of juices were presented to 10 panelists and randomly coded samples. The
test panelists were asked to rate the different juices presented to them on
a 9 point hedonic scale with the ratings of: 9 = like extremely; 8 = like very
much; 7 = Like moderately; 6 = Like slightly; 5 = Neither like nor dislike;
4 = Dislike slightly; 3 = Dislike moderately; 2 = Dislike very much and 1 =
Dislike extremely. The results were evaluated by Analysis of Variance (ANOVA)
and Duncan's Multiple Range Test (DMRT) procedures of the Statistical Analysis
System (SAS) software (SAS, 1985).
RESULTS
The tomato juice is a ready to drink juice prepared from tomato pulp, sugar, chemical additive and water. The effect of different chemical additives on acceptability and shelf life of tomato juice at room temperature was studied. The acceptability and shelf life were evaluated through organoleptic taste testing procedure along with chemical and microbiological analysis.
Nutritional aspects: Tomato pulp was used to formulate tomato juice.
The proximate composition of fresh pulp and processed juice was determined.
From the table it was observed that, moisture and pH declines slightly after
processing. Total soluble solid and total sugar level increased drastically
after processing. Vitamin C (L-ascorbic acid) content of processed tomato juice
was also gradually decreased from the fresh tomato juice. Ash content was unchanged
after processing. Nutritional composition of fresh pulp and processed tomato
juice is listed in Table 1. The content was more or less similar
to that obtained by Bose (1985).
Effect of chemical additives on shelf life of tomato juice: Chemical compositions of tomato juices were determined during the storage period at every 15 days interval. The results are discussed below.
Effect of different chemical additives on moisture content: Moisture
content reduced slightly in juices prepared with Na-benzoate and Potassium meta-bisulphate
(KMS). But in case of juice prepared with sorbic acid, moisture content reduced
significantly during storage.
Juice prepared with KMS contained 76.2% moisture content on the day of preparation
and 75.15% moisture content after 60 days storage period. Juice prepared with
Na-benzoate contained 76.2% moisture content on the day of preparation and 76.05%
moisture content after 60 days storage period. On the other hand, Juice prepared
with sorbic acid contained 76.2% moisture content on the day of preparation
and 72.85% moisture content after 60 days storage period. The effect of chemical
additives on moisture content of tomato juice has been shown in Fig.
1.
Effect of different chemical additives on acidity: According to results, Chemical additives have no significant effect on acidity though acidity of tomato juice with sorbic acid increased slightly during storage. Juice prepared with KMS contained 0.35% acidity on the day of preparation and 0.365% acidity after 60 days storage period. Juice prepared with Na-benzoate contained 0.358% acidity on the day of preparation and 0.361% moisture content after 60 days storage period. On the other hand, Juice prepared with sorbic acid contained 0.367% moisture content on the day of preparation and 0.44% moisture content after 60 days storage period. The effect of chemical additives on acidity of tomato juice has been shown in Fig. 2.
Effect of different chemical additives on total soluble solids (T.S.S.):
According to results, Chemical additives affect TSS content of the tomato juices.
Juice prepared with KMS contained 13% TSS on the day of preparation and 12.5%
TSS after 60 days storage period. Juice prepared with Na-benzoate contained
13% TSS on the day of preparation and 12.8% TSS content after 60 days storage
period. On the other hand, Juice prepared with sorbic acid contained 13% TSS
content on the day of preparation and 12% TSS content after 60 days storage
period. The effect of chemical additives on TSS content of tomato juice has
been shown in Fig. 3.
|
| Fig. 2: |
Effect of different chemical additives on acidity |
|
| Fig. 3: |
Effect of different chemical additives on T.S.S |
Effect of different chemical additives on pH: According to results, Chemical additives have differential effect on pH of the tomato juices. Juice prepared with KMS had pH value 3.60 on the day of preparation and 3.562 after 60 days storage period. Juice prepared with Na-benzoate had pH value 3.615 on the day of preparation and 3.610 after 60 days storage period. On the other hand, Juice prepared with sorbic acid had pH value 3.65 on the day of preparation and 3.58 after 60 days storage period. The effect of chemical additives on pH of tomato juice has been shown in Fig. 4.
Effect of different chemical additives on vitamin C: According to results,
Chemical additives have significant effect on Vitamin C content of the tomato
juices. Juice prepared with KMS contained 3.05 mg/100 gm vitamin C on the day
of preparation and 2.98 mg/100 gm vitamin C after 60 days storage period. Juice
prepared with Na-benzoate contained 3.05 mg/100 gm Vitamin C on the day of preparation
and 3.01 mg/100 gm vitamin C after 60 days storage period. On the other hand,
Juice prepared with sorbic acid contained 3.05 mg/100 gm Vitamin C on the day
of preparation and 2.90 mg/100 gm Vitamin C after 60 days storage period. The
effect of chemical additives on Vitamin C content of tomato juice has been shown
in Fig. 5.
Vitamin C is light and heat sensitive, the concentration of Vitamin C follows
first order kinetics and thus storage time affects vitamin Content (Heldman
and Singh, 1981). However, Vitamin C is highly oxidized and may be oxidized
with the increase of storage period.
Microbiological load calculation: Microbial activity, its multiplication and load were calculated during 60 days storage period for the juices with three different chemical additives.
|
| Fig. 4: |
Effect of different chemical additives on pH |
|
| Fig. 5: |
Effect of different chemical additives on Vitamin C |
| Table 2: |
Growth of bacteria in tomato juices with three different
additives at room temperature |
 |
|
Bacterial growth: This study was performed by colony count method. After 48 h of incubation, colonies were counted. The total viable bacteria present in tomato juice were not uniform. Total viable bacterial count of the juice with KMS increased from 3.69 to 4.9 log cfu mL-1 after 60 days of storage at room temperature. Total viable bacterial count of the juice with sodium benzoate increased from 3.53 to 4.08 log cfu mL-1. Total viable bacterial count of the juice with sorbic acid increased from 3.65 to 4.80 log cfu mL-1 after 60 days of storage at room temperature. The total numbers of viable bacterial count in juices with different additives have been shown in Table 2.
| Table 3: |
Growth of Yeast and mold in tomato juices |
 |
| S1: Tomato juice with KMS, S2: Tomato
juice with Na benzoate, S3: Tomato juice with Sorbic Acid |
| Table 4: |
Mean score for color, flavor, texture and overall acceptability
of processed tomato juice |
 |
| S1: Tomato juice with KMS, S2: Tomato
juice with Na benzoate, S3: Tomato juice with Sorbic Acid |
The results showed that among the three juices stored at room temperature, juice with Na-benzoate contained least viable bacteria (log cfu mL-1) and juice with KMS contained highest viable bacteria (log cfu mL-1). From the above results, it is clear that the total viable bacterial count increased slightly with the increase of storage period. This may be due to the presence of preservatives in the juices.
Growth of yeast and mold: During the storage period there were no countable molds present in processed tomato juice. The juice was fermented due to the growth of yeast. The results have been shown in Table 3.
This result showed that, mold was not grown within 60 days but yeast count increased with time. This may occurred for either improper capping or improper pasteurization or faulty sterilization of the bottles or combination of these.
Sensory evaluation: The processed tomato juice was evaluated for its color, flavor, texture and overall acceptability through a taste testing panel. The panelists were asked to score the sample in ascending order of 1-9 points showing their degree of preference in respect of color, flavor, texture and overall acceptability of the juice sample. The responses were tabulated in Table 4.
A two way Analysis of Variance (ANOVA) was carried out for color preference and overall acceptability of processed tomato juices and the result showed that there were no significant differences among the three samples.
In case of flavor a two way Analysis of Variance (ANOVA) was carried out and the results showed that there were significant differences in flavor acceptance among the juices with different chemical additives as the calculated F value (5.3) was greater than the tabulated F value (3.6).
As shown in table, sample S2 was the most acceptable in flavor preference
among the samples securing the highest score (7.7) and ranked as "Like moderately".
This was followed by sample S1 and S3 securing 6.7 and
7.0, respectively and was equally acceptable. However, sample S1
and S3 can be ranked as “Like Slightly”.
| Table 5: |
Organoleptic observation of prepared tomato juice stored
at room temperature (25-30°C) |
 |
|
In case of texture of products there were significant differences among the
samples at 5% level of significance as calculated F (4.9) value was higher than
tabulated value of F (3.7).
As shown in the table there was no significant difference for texture preference between sample S1 and S3 securing 6.3 and 6.4, respectively. On the other hand sample S2 secured the highest score (7.6) and was significantly different from other samples. Results showed that sample S2 was the most acceptable in texture preference among the samples securing 7.6 out of 9 and ranked as “Like moderately”.
Organoleptic observation: Organoleptic observation of tomato juices with three different preservatives during storage period at room temperature were judged on the basis of color, flavor and sedimentation. The observations have been shown in Table 5.
From the Table 5, it was found that there was a slight variation in color among the three different tomato juices during 60 days storage period. All the three juices become turbid at the end of the storage period. Color of the juices was found reddish/ deep reddish on the day of preparation. The color faded and flavor deteriorated gradually with the increase of storage period at room temperature. Tomato juice with Na benzoate seems to be more stable as after 60 days of storage, it develops slight turbidity, off-flavor and sedimentation. Whereas, tomato juice with sorbic acid deteriorated after 30 days of storage and tomato juice with KMS deteriorated after 45 days of storage.
DISCUSSION
The experiment was conducted to compare the effect of three different chemical
additives on overall quality, acceptability and shelf life of tomato juice stored
at room temperature. Negligible change in chemical constituents except Vitamin
C was observed in the prepared juice throughout the 60 days storage period.
Similar results were found in the study of Mehmood et
al. (2008) where Vitamin C content decreases with the storage time in
apple juice preserved with potassium sorbate and sodium benzoate. Hashimi
et al. (2007) and Gupta et al. (2007)
observed that mango pulp preserved with potassium metabisulphate either individually
or in combination with other preservatives retains maximum overall acceptability,
maintains maximum nutrients stability and negligible microbes. There was variation
in color and flavor in prepared juice with three different chemical additives.
Temperature has an effect on storage quality of food products. Safdar
et al. (2010) showed that tomato paste with sodium benzoate as additive
remains acceptable for longer period when stored at lower temperature. On the
shelf life study, after about 40 days fermentation and sedimentation problem
occurs in the samples. This may be due to improper capping, coarse homogenization
etc. Sensory evaluation showed that there was no significant difference among
the juices with three different chemical additives considering color and overall
acceptability. In general, synergistics effect of physical conditioning in combination
with additives based minimal processing can give longer shelf life of tomato
juice (Chauhan et al., 2006). Chemical preservatives
can be replaced with natural preservatives such as Baicalin (Bruzewicz
et al., 2006), plant essential oils (Fazlara
et al., 2008), Azelaic acid (Moniharapon et
al., 2005), extracts of different plants such as Zingiber officinale
(Sunilson et al., 2009) etc. to obtain longer
shelf life with acceptable quality.
CONCLUSION
In this study, it is evident that Na-benzoate is better preservative than Potassium Meta bi-sulphate (KMS) and Sorbic acid for tomato juice. The quality of juice may be improved by fine homogenization, proper capping, proper pasteurization and using sterilized bottles. More detailed study is required for further improvement of quality characteristics of tomato juice.
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