Tomato is an important source of micronutrients, minerals like potassium and carboxylic acids, including ascorbic, citric, malic, fumaric and oxalic acids.1–2 Recent epidemiological studies have suggested that the consumption of tomatoes and tomato-based food products helps in reducing the risk of cardiovascular disease and cancer (oral cavity, pharynx, esophagus, stomach, rectum, colon, urinary bladder, prostate and breast) in humans as reported by, and this protective effect has been attributed to carotenoids, in particular lycopene and phenolic compounds which are considered as one of the major classes of phytochemicals in this fruit.6 As we know carotenoids are a family of compounds of over 600 fat-soluble plant pigments that provide much of the color we see in nature, by facilitating important nutritional benefits to human population owing to their pro vitamin A and antioxidant activities.7
Increasing demand and interest towards organically grown fruits and vegetables and its products imposed the need to study the quality and nutritional differences between organic and inorganic tomatoes. Some studies have shown higher number of bioactive compounds in organically produced tomatoes compared to conventional, 8–9–10 and are often linked in protecting the environment and having better quality in terms of taste with enhanced storage period.
Ultra Violet (UV) radiation is a surface sterilization treatment for increasing shelf life of fruits and vegetables that are highly susceptible to microbial spoilage. UV radiation is a promising non-thermal preservation method classified into UV-A (315-400 nm), UV-B (280-315 nm) and UV-C (200-280 nm) respectively. UV-C has the germicidal effect since it inactivates the microorganisms.11 Fresh fruits and vegetables exposed to low doses of UV induces anti-fungal compounds and delays ripening there by enhancing shelf-life.
Functional groups are specific group of atoms or bonds present within the molecules which are responsible for the characteristic chemical reactions of those molecules. The fresh and processed tomatoes contain volatile compounds falls under various chemical classes like ketones, aldehydes, alcohols, esters, ethers, hydro- carbons, sulfur, nitrogen and oxygen compounds, phenols, oxygen-containing heterocyclic compounds, free acids and lactones.12 FTIR is a powerful technique that can be used to obtain an infrared spectrum of absorption or emission of all states of matter (solid, liquid and gas). The morphological study becomes important in knowing the form and structure of any food material that can be achieved with the help of SEM. The present study focusses on analyzing and comparing the functional group and morphological differences between organic and inorganic tomatoes before and after UV treatment by using FTIR and SEM.
MATERIALS AND METHODS
Freshly harvested riped organic and inorganic tomatoes (Variety: Sivam) were procured from Coimbatore and Thanjavur, Tamil Nadu, India. Every effort was made in maintaining the quality of samples throughout the supply chain.
Preparation of sample: UV treatment and tray drying
A laboratory model of continuous UV-C system was used for the experiment consisting of conveying system, treatment chamber, control system and holding frame. Fresh tomato samples were subjected to UV treatment for 10-15 min (8x15W). Treated and untreated organic and inorganic tomato samples was sliced to 6-8 mm thickness and subjected to tray drying at 50°C for 14-16 hrs. Further, the dried slices were processed into fine powder by using a blender and passed through different sieves to achieve uniform particle size.
Functional group analysis
Fourier transform infrared spectrophotometer is an important tool for identifying the presence of different types of chemical bonds (functional groups) present in compounds. Dried powders of different sample specimen were loaded in FTIR Spectroscope by taking a small quantity to know the presence of functional groups in tomatoes (Shimadzu, IR Affinity1, Japan), with a scan range from 400 to 4000 cm-1 with a resolution of 4 cm-1 respectively.
RESULTS AND DISCUSSIONS
Quality attributes of fresh organic and inorganic tomatoes are presented in Table 1. Organic samples showed better results on confirming TSS (4.7 oBrix), vitamin C (22.5 mg/100g), lycopene (4.13 mg/100g), with reduced acidity (0.38%), pH was (4.2) indicating samples were more acidic. Whereas, inorganic tomatoes exhibited decreased amount of TSS, vitamin C and lycopene (4.1 oBrix, 20.2 mg/100g, 3.35 mg/100g), with increasing in acidity (0.43%).
Fourier transforms infrared spectroscopy (FTIR)
The FTIR spectroscopy was used to identify the functional groups of the active components present in organic and inorganic tray dried tomato powder in both control and UV treated condition based on the peak values in the region of IR radiation. The peak values of FTIR in all samples confirmed the presence O-H stretching, C-H stretching, C=O, C=C and C-OH groups respectively.
The study showed organic and inorganic tomato samples (control and treated), exhibited more or less same functional groups with considerable differences in peak values (Table 2 and Figure 1 to 4) which may be due to application of various pesticides, insecticides, fertilizers and other artificial chemicals, water source, soil condition and other residual effects in inorganic samples which varies in organic samples where some naturally occurring biological materials are used that influences direct or indirect changes in the functional groups. The presence of C-F group in inorganic untreated samples was found to be reduced considerably in UV treatment. Water treatment plants uses UV to disinfect water without any chemicals because of which taste, and other composition present may vary. Henceforth, UV showed positive results by retaining all functional compounds without losses.
FTIR spectra showed peak values at a 3290.12, 2924.72, 1611.61 and 1403.6 cm-1 in organic untreated, 3287.11, 2925.66, 1612.91 and 1402. 74 cm-1 in organic treated, 3289.47, 2925.76, 1619.26, 1407.24 cm-1 in inorganic untreated and 3289.42, 2925.34, 1616.31 and 1406.29 cm-1 in inorganic treated samples. The analyzed peak value results were found comparable with 15,16 respectively. IR spectrum between 3100 and 3600 indicates the presence of It was evident that tomatoes are rich in alcohols, phenols (phenolic acids and flavonoids), carboxylic acids (amino acids), amides, alkynes and alkenes, henceforth, considered as a health promoter.
Scanning Electron Microscopy (SEM)
The morphological changes of organic and inorganic treated, and untreated tomato powder were investigated by using Scanning Electron Microscope (Figure 5 to 8). The results of the work reveal no significant/ distinctive changes in both treated and untreated organic and inorganic samples. The surface structure of the images was almost similar in all cases; however, the effect of UV treatment was found to have a minimal effect on the structural changes of the tomato powder. Micrographs exhibited quite sticky surface with few spherical and elongated particles which may be due presence of moisture. Similar observations were noticed by, 17 on reporting the temperature and moisture content effects on cohesion and flow ability of dairy powder. Reports also showed some caking phenomena in tomato powder which is time-temperature dependent.18
FTIR and SEM are well-established simple, sensitive, non-destructive technique that helps in rapid determination of functional groups and morphology in agricultural food products with accuracy. The results of the study showed the presence of strong and broad absorption bands of water, alcohols, phenols and carboxylic acids along with alkenes and amide (O-H, C-H, C=O, C=C and C-OH) at higher peaks respectively. Functional groups help in knowing the quality properties of tomatoes that need to be taken care right from farm to fork and offers a platform in understanding organic and inorganic tomatoes subjected to various processing conditions respectively. In SEM analysis distinctive changes were not observed and concludes presence of moisture content, treatments, drying temperature and uniformity in particle size, variety are deciding factors that influences morphological changes in tomatoes.