Efficacy of turmeric as a preservative on tomatoes

How does the ability of turmeric to act as a preservative for tomatoes (solanum lycopersicum), measured in terms of mass loss, pH and lycopene content depends on the percentage concentration (mass by volume) of the turmeric solution used and the type of tomato used-green tomato and red tomato ?

Use of turmeric as a preservative is a common practice in Indian kitchen. Turmeric has always been a common ingredient in almost all Indian recipes. As claimed by chefs and nutritionists, it is so because of the antibiotic and antiallergic therapeutic effects of turmeric. Being an inquisitive learner, the observation that made my interest about this more innate was the fact that I have seen applying turmeric and salt on fish and meats before they are refrigerated. I was more surprised to know that it is done to preserve the meat and fish for a longer time. I went through some research papers and came to know more about it and the biology behind it which will be explored further in the next section. However, the question that striked me was, will turmeric act as a potential preservative for vegetables as well ? Does the efficacy of a preservative depends on the type of the food substance preserved? In the current scenario of e-commerce, selling of packaged and processed foods contributes largely to the economy. To ensure health and safety, use of safe preservatives and their shelf life has become a major issue in food technology and preservation science genre. This finally brought me to the research question stated above.

Turmeric is a common tropical crop in Asia and Sub-Saharan regions(Shelef et al.). It has various medicinal as well as nutritional benefits. It belongs to the genus- “Curcuma longa” (Yarru et al.). The main ingredient of turmeric is curcumin which can acts as anti-oxidant. Moreover, it also shows abilities to produce vitamins through reductive degradation mechanism and can also acts as a precursor or co-factor of various other enzymes that are involved in the biological reactions happening during ripening of fruits and vegetables(Buch et al.). Curcumin can also degrades to form proteins and polyphenolic compounds which finally converts them to long chain fatty acids and can inhibit various diseases in plants due to deficiency of micro and macro nutrients (Almeida-Doria and Regitano-D’Arce).

Tomatoes of “solanum lycopersicum” is generally claimed to be a perennially grown vegetable albeit botanically it belongs to the class of berry fruit (Singh et al.). It is one of the most popular crop consumed worldwide which started it journey from South America and was then exported to Europe around the 15th century(OECD ). The main constituent of tomato is lycopene which has immense nutritional and medicinal benefits and is a pigment that offers the red colour to the fruit. Apart from this, tomato is also a major source of vitamins like – Vitamin B1 and Vitamin B3(Solanum Lycopersicum, Tomato: Life Cycle, Flower and Fruit Anatomy at GeoChemBio). The major part of tomato is carbohydrate and because of that it is a good source of calorie without unwanted fats for the dieticians (Stevens et al.)

Food preservation is a technique which is used to inhibit or delay the biochemical reactions in a fruit which may lead to the loss of nutritional benefits of the fruit accompanied by loss of texture, colour, aroma and turning rancid which eventually makes the fruit unsuitable for usage either in raw form or for cooking. There are multiple methods approved by the USDA (United States Department of Agriculture) for food preservation(“The Science Behind Food Preservation”). All of these or most of these methods aims to stop the growth of microorganisms and harmful bacteria in the fruits either by interfering with the conditions that are required for their growth or by adding chemicals or foreign substances named as preservatives which may kill the bacteria grown or inhibit their growth. The most popular methods of preservations are(“Science behind Food Preservation Methods”) - adding preservatives (chemical or natural), dehydrating (making the fruit stored in a moisture free condition), atmospheric canning (storing the fruit in a chamber or closed space filled with liquid nitrogen under high pressure), adding salts, adding acids to lower down the pH level that inhibits bacterial growth. In this investigation, use of turmeric a natural and homely method of preserving fruits will be discussed and its efficacy will be investigated.

There are various analytical methods to monitor and assess the quality of tomatoes:

• Mass loss
  The dry mass of a vegetable or fruit is an indicator of its nutritional well-being and biological conditions. It is the most accurate measurement of the biomass of the sample. It measures the amount of matter accumulated within the species. Decrease in biomass indicates a decline in the biological content of the sample. Thus, to determine the best possible preservative, it is required to keep all the species in the preservative solutions and measure the dry mass. The case that gives the least decrease in dry mass must be considered as the most effective preservative. The ideal dry mass of a tomato ranges from 110 g to 90 g (H. et al.)
• pH
  pH is a measurement of the acidity or alkalinity of the species. pH is an analytical tool to measure the maturity and ripeness of tomatoes. Ideally, tomatoes are found to have a pH in between 4.2 to 4.6 (Determining Tomato Maturity by Measuring PH). As the fruit ripens or loses its nutritional value, the pH level decreases. Thus, more the decrease in the values of pH from the ideal value, lower the efficacy of the indicator that has been used.
• Lycopene content
  Lycopene is a long chain aromatic compound which can absorb electromagnetic radiations in the visible spectrum and thus imparts red colour to the tomatoes. This is the major nutritional ingredient of the tomatoes. Thus, as the quantity of lycopene decreases, the tomato becomes less suitable for consumption. Using Beer-Lambert law (Chemat-Djenni et al.) the concentration of lycopene can be monitored by measuring it’s absorbance at the wavelength at which it displays maximum absorbance. A UV-Visible spectrum of lycopene shows a peak at 667 nm indicating that lycopene absorbs the maximum amount of radiation in the visible region at 667 nm (Friedman et al.). Absorbance is a measure of the concentration of the sample. Thus, more the value of absorbance at 667 nm as indicated in a colorimeter, more the concentration of lycopene. As lycopene is a nutritional ingredient, decrease in the values of absorbance will indicate a decrease in the quantity of it. So, more the decrease of the value of absorbance of lycopene, lower the efficacy of the preservative the tomatoes were exposed to.

Null hypotheses (Ho): There is no correlation between the percentage concentration of the turmeric solution used and it’s efficacy as a preservative for tomatoes – green and red. Any correlation, if identified is an outcome of a methodological or a systematic error.

Alternate hypotheses (H1): There is a positive or negative correlation between the percentage concentration of the turmeric solution used and it’s efficacy as a preservative for tomatoes – green and red. Any correlation, if identified is an outcome of a methodological or a systematic error.

There are two independent variable in the investigation –

• percentage concentration (mass by volume) of the turmeric solution used as a preservative the genus of the tomato – green and red.

The percentage concentration has been chosen to understand if using more amount of turmeric increases the efficacy or not and thus determining the optimum concentration of turmeric solution that can be used. The percentage concentration was varied from 0.00% (control), 5.00%, 10.00%, 15.00%, 20.00% and 25.00%. The values of concentration are expressed as mass by volume. For example, a 5.00% solution of turmeric means 5.00 ± 0.01 g of turmeric was added to 100 cm³ of water. To understand if the effect of turmeric as a preservative depends on the genus or biological variety of the sample or not, two different types of tomatoes-green and red were chosen.

The dependent variable of this investigation is the efficacy of the turmeric solution as an indicator.

The efficacy of the indicator will be measured in terms of three quantitative aspects – pH, dry mass loss and lycopene content. Refer to the background information for more details. A pH probe will be used to measure the pH, a digital mass balance will be used to record the mass and a colorimeter will be used to record the absorbance while measuring the amount of lycopene colorimetricaly.

• A laboratory coat and safety gloves were used.
• Social distancing protocols were maintained.
• The solutions were made under the supervision of an expert technician.
• The instruments were handled with care.
• The work station was kept clean and organized.

All unused and waste materials were thrown into the disposal bin and disposed using standard safe procedures.

None of the materials were wasted and minimum possible amount of materials were used. Any toxic or prohibited materials were not used.

The experimental procedure has been self- procured by the experimenter in conjunction with references from laboratory manuals for “measuring pH using pH meters” (What Is a PH Meter? Introduction to Digital PH Meters), “making lycopene extract” (Chiu et al.) and “Using colorimeter in food industry” (Huang et al.)

Stage-1 - Preparing the turmeric solution

500.00 ± 0.01 g of turmeric was kept on a watch glass on a top pan digital mass balance and weighed using a spatula. The weighed turmeric was transferred into a clean and dry mixer grinder. The grinder was operated to obtain a fine powder of the turmeric. The powdered turmeric was kept in a 100 cm³ glass beaker.

For a 5.00% solution, 5.00 g of turmeric should be added to 100 cm³ of water.

Mass of turmeric powder for 500 cm³ of 5.00% solution = \(\frac{5.00}{100} × 500 = 25.00 \, \,g\)

25.00 ± 0.01 g of the turmeric powder was weighed on a top pan digital mass balance and using a watch glass and a spatula. The weighed turmeric was completely transferred to a 500 cm³ glass beaker. The beaker was filled with drinking water till the mark of 500 cm³ . A glass rod was used to stir the solution and dissolve the turmeric. Thus, a 5.00 % solution of turmeric powder was made.

The other solutions – 10.00%, 15.00%, 20.00% and 25.00% were made in the same way. For the control – 0.00%, drinking water was used and no turmeric was added.

Stage-2: Preserving the tomatoes in the turmeric solution and measuring pH and lycopene absorbance:

•  A 50 cm³ glass beaker was taken and labelled as – 5.00% Trial-1.
•  A clean and dry red tomato was taken and the mass of the tomato was recorded using a digital mass balance.
•  The tomato was kept inside the beaker.
• The beaker was filled with 5.00% turmeric solution till the mark of 50.00 cm³ .
•  After 3 days, the tomato was taken out of the beaker and allowed to dry in open air.
•  The mass of the dried tomato was recorded using a digital mass balance and a watch glass.
•  The tomato was cut into four equal pieces using a knife.
•  The cut pieces of tomato was transferred to a mixer grinder and the grinder was operated for a while until a smooth and uniform paste was obtained.
•  The tomato paste was then transferred to a 100 cm³ glass beaker.
•  The vessel of the grinder used to make the paste was washed with distilled water and the washings were collected in the same beaker to transfer the tomato paste completely.
•  50 cm3 of ethanol was added to the beaker followed by addition of 50cm³ of distilled water. A graduated measuring cylinder was used for this.
•  The beaker was placed on a heating mantle and the temperature was kept constant at 60.0^oC.
•  A thermometer was used to check the temperature of the content of the beaker and heating was continued until a temperature of 60.0^oC is obtained.
•  The content of the beaker was then filtered using a funnel and a filter paper. The residue was discarded and the filtrate was collected in a conical flask. This filtrate is the ethanolic-aqueous extract of tomato.
•  5.00 ± 0.05 cm³ of the filtrate was then transferred to a test tube.
•  The pH probe was taken and calibrated using a buffer solution of pH 10.00
•  The pH probe was inserted into the test tube and the pH of the ethanolic aqueous extract of the tomato was measured.
•  A digital photo colorimeter was taken and the wavelength was set at 667 nm.
•  A cuvette was taken and filled with a mixture of 1.00 ± 0.05 cm³ of ethanol and 1.00 ± 0.05 cm³ of distilled water.
• The absorbance of this mixture of ethanol and water was set at ±0.000 AU to calibrate the photo- colorimeter.
•  A clean and dry cuvette was taken and filled with the ethanolic aqueous extract of the tomato.
•  The absorbance of the solution was measured.
•  Steps 1-4 were repeated for two more times to collect data in triplicates.

The same process was repeated for all other % concentration of turmeric solutions – 0.00%, 5.00%, 10.00%, 15.00%, 20.00% and 25.00%. The same process was repeated for samples of green tomatoes.

• A change in the colour of the skin of the tomato was observed when they were kept immersed in the turmeric solutions. The colour of the red tomatoes started fading with the progress of time from darker shades of red to lighter shades. However, as the percentage concentration of turmeric solution was more, the fading of colour was less significant.
• For green tomatoes, it was observed that the colour of the skin started becoming greenish red from green with the progress of time. As the percentage concentration of turmeric increased, the change of colour was more significant.

Key

• Initial mass of the tomato (measured before putting it in turmeric solution) = m₁
• Final mass of the tomato (measured after taking it out from turmeric solution and drying) = m₂

Sample calculation

For Row-1: (0.00% turmeric solution)

For Trial-1, Change in mass (m) = Initial mass (m₁) – Final mass (m₂)

= 95.30 ± 0.01 g – 91.65 ± 0.01 g = (95.30-91.65) ± (0.01 + 0.01) g = 3.65 ± 0.02 g

Average change in mass (m) =\(\frac{(3.65±0.01)+(5.48±0.01)+(4.34±0.01)}{3}= 4.49 ± 0.01 \, \,g\)

Standard deviation (SD) = \(\frac{(4.49-3.65)^2+(4.49-5.48)^2+(4.49-4.34)^2}{3} = 0.92\)

Key

• Initial mass of the tomato (measured before putting it in turmeric solution) = m₁
• Final mass of the tomato (measured after taking it out from turmeric solution and drying) = m₂