Comparative Analysis of Vitamin C Levels in Selected Fruits: A Dual Approach Using Titration and UV-Visible Spectroscopy

Vitamin C is a pivotal antioxidant compound essential for human health. It plays a fundamental role in promoting immunity, aiding in iron absorption, and neutralizing free radicals. Since the human body cannot synthesize Vitamin C endogenously, dietary intake through fruits and vegetables is necessary to maintain optimal health. Various methods are employed to estimate Vitamin C content in food sources, with titration and UV-visible spectroscopy being two prominent techniques. Titration is a traditional, cost-effective method that offers reliable results but may lack precision in complex matrices. On the other hand, UV-visible spectroscopy offers higher accuracy, faster analysis, and the ability to detect lower concentrations. This research aims to compare the efficacy of these two methods by analyzing selected fruits known for their Vitamin C content. The study seeks to determine which method provides better accuracy, precision, and reproducibility, offering insights into the most suitable technique for nutritional assessments in food science.

2.MATERIALS AND METHOD

Instrument UV-Visible spectrophotometer (Double beam) having matched quartz cells of light path 1cm.
Model: Shimadzu 1800
Software: UV probe Version of software: 2.42
Electronic analytical weighing balance (REPTECH)
Volumetric flask (Borosilicate), Pipettes, Conical flask

METHODOLOGY

Materials and Chemicals

Fruit Samples: Grapes, Mango, Apple, Watermelon, Sweet Lemon (freshly collected)
Chemicals: 3% Metaphosphoric Acid (HPO3), 2,6-Dichlorophenol Indophenol (DCPIP), Bromine Water, 2,4-Dinitrophenylhydrazine (DNPH), 85% Sulfuric Acid (H2SO4), Standard Ascorbic Acid Solution
Glassware and Equipment: Volumetric flasks, pipettes, burettes, UV-Visible Spectrophotometer (521 nm), Analytical balance, Filtration apparatus

2.1Sample preparation

Fruit Juice Extraction:

Fresh fruit samples were washed, peeled (if required), and homogenized using a blender.
10 g of homogenized fruit pulp was diluted with 50 mL of 3% metaphosphoric acid to stabilize the ascorbic acid and prevent oxidation.
The mixture was filtered through Whatman filter paper No. 1 and diluted to 100 mL with distilled water.

3. Titrimetric Analysis (DCPIP Method)

Standard Ascorbic Acid Solution Preparation:
A 500 µg/mL ascorbic acid stock solution was prepared by dissolving ascorbic acid in 3% metaphosphoric acid.
Working solutions of 5 µg/mL, 10 µg/mL, and 15 µg/mL were prepared via serial dilution.

Titration Procedure:

10 mL of each fruit extract was titrated against DCPIP solution until a persistent pink endpoint was observed.
The volume of DCPIP consumed was recorded, and the Vitamin C content was calculated using the standard curve.

4.UV-Visible Spectrophotometric Analysis

Preparation of Standard Curve:

A series of standard ascorbic acid solutions (5 µg/mL to 15 µg/mL) were treated with 1 mL bromine water and 1 mL DNPH reagent.
The solutions were incubated for 15 minutes at 37°C, followed by the addition of 5 mL of 85% sulfuric acid.
The absorbance was measured at 521 nm using a UV-Visible spectrophotometer.

Sample Analysis:

10 mL of fruit extract was treated identically to the standard preparation and analyzed spectrophotometrically.

5. Calibration Curve for UV Method

The calibration curve was constructed by plotting absorbance values against standard ascorbic acid concentrations. The equation obtained from the curve was: y = 0.067x + 0.057
Where,
y = Absorbancex = Concentration of ascorbic acid (µg/mL)
The correlation coefficient (R²) value of 0.988 indicated excellent linearity.

6. Calculation Of Vitamin C Content

Vitamin C content was calculated using the equation:
C = (Asample / Astandard) × Cstandard
Where,
C = Vitamin C concentration in the sample (mg/100mL)
Asample = Absorbance of sample
Astandard = Absorbance of standard
Cstandard = Known concentration of standard ascorbic acid solution

3.RESULTS

Absorption Maxima of Vitamin C

The UV method consistently detected slightly higher Vitamin C levels due to enhanced sensitivity. The assay recovery values for both methods ranged between 95-105%, indicating the reliability and precision of the developed methods.

3.3.1 Titrimetric Results

Table 3.1 Vitamin C Content in Selected Fruits (mg/100mL)

3.3.2 UV Results