Fruits (and, in some cases, vegetables) are sometimes covered with artificial waxing material. These waxing materials may be either natural or petroleum-based. Waxing are mainly done to prevent water loss making the fruits and to improve appearance. Dyes may be added to further enhance appearance. Thus the commercial producers use waxing to extend shelf life. In addition to fruit, some vegetables can usefully be waxed, vegetables commonly waxed are cucumbers.
The waxing materials used depend to some extent on regulations in the country of production and/or export / import. Both natural waxes (Candelilla wax, Beeswax and Carnauba) or petroleum-based waxes are used. In India as per the Government Act i.e Food Safety and Standard Act the natural waxes like Candelilla wax, Beeswax and Carnauba wax are the only permissible food waxes in different fruits and vegetables.
So here our aim of work to identify whether the waxing material is natural or petroleum based.
Principle of the design of the work
To identify the waxes , the physico-chemical property should be known e.g Carnauba wax is a natural wax. It comes from the leaves of the Copernicia prunifera palm grown only in Brazil. The wax is obtained by beating the wax off, of the dried palm fronds and then refining it for use. The pure wax is yellow in colour and consists of fatty acid esters (80-85%), fatty alcohols (10-16%), acids (3-6%) and hydrocarbons (1-3%). It is around 20% esterified fatty diols, 10% methoxylated or hydroxylated cinnamic acid, and 6% hydroxylated
Candelilla wax is a wax derived from the leaves of the small Candelilla shrub native to northern Mexico and the southwestern United States, Euphorbia cerifera and Euphorbia antisyphilitica, from the family Euphorbiaceae. It is yellowish-brown, hard, brittle, aromatic, and opaque to translucent and the wax consists of mainly hydrocarbons (about 50%, chains with 29–33 carbons), esters of higher molecular weight (20–29%), free acids (7–9%), and resins (12–14%, mainly triterpenoid esters).
The Beeswax is formed by worker bees Its main components are palmitate, palmitoleate, and oleate esters of long-chain (30–32 carbons) aliphatic alcohols. Beeswax can be classified generally into European and Oriental types.
Paraffin wax is a soft colourless solid, derived from petroleum, coal or oil shale, that consists of a mixture of hydrocarbon molecules containing between twenty and forty carbon atoms. Paraffin hydrocarbon, also called alkane, any of the saturated hydrocarbons having the general formula CnH2n+2, C being a carbon atom, H a hydrogen atom, and n an integer.
So in all the of the natural waxes the common functional group present is ester group which is absent in paraffin wax,
These functional group can be identified and well defined by a very well known authenticated technique known as FT-IR, where the functional groups are easily identified.
MATERIALS AND METHODS
Pure form of Candelilla wax, Beeswax, Carnauba and petroleum-based paraffin wax were purchased. Apples samples are collected from different locations and imported samples are also taken for the testing purpose.
Analysis & characterization
Analysis was done by taking the individual waxes on ATR of FT-IR, individual wave numbers are observed, From the Apple sample the wax coating was taken out by scratching and the wax found from it was also examined by FT-IR.
Different wax samples were finely grinded by using mortar pestle and placed over the ATR. A full IR range (i.e. 400-4000 c.m.-1) scan was done by using OMNIC software provided by Thermo Scientific.
The Thermo Scientific™ Nicolet™ iS™10 FT-IR Spectrometer was equipped with detector DTGS KBr with KBr beamsplitter which was used for this purpose. In one spectra compilation of 16 scan was performed. Diamond- Attenuated Total Reflectance (ATR) is used which is a powerful sampling technique that virtually eliminates sample preparation.
RESULTS AND DISCUSSION
A description of the chemical composition and characteristics spectra of the natural permitted waxes are observed at 1734-1740 c.m.-1 region.In the fig.1&3 beeswax and caranauba wax the observed wavenumber was 1735c.m.-1 whereas that for Candelilla wax the observed wavenumber value was 1734 c.m.-1(Fig–2) .
The observed spectra in this region was very strong in intensity and it was due to the C=O bond present in esters another C-O bending spectra is also observed at 1000-1030 c.m.-1 region. In case of parafin wax the peak in the region 1734-1740 c.m.-1 was completely absent but a strong band at 2847-3000 c.m.-1 region which is characteristic peak of C-H stretching (fig. 4)
So it is found that all the peaks lies within the the range of C=O bond present in esters group.Thus the permitted natural waxes are easily can be differentiated from the paraffin wax by identifying the ester groups which are present in all natural waxes.The fig 5 indicates clearly the the difference between the IR spectra of four different waxes.
Waxes of apple samples from different locations which are imported and also available in market are analyzed in FT-IR and found that all the apples under examination are waxed with permitted natural wax only.
FUTURE SCOPE OF WORK
The scope of work may be expanded by quantifying the edible waxes is apple / fruits samples by using FT-IR and also if possible, to develop a new technique/process that may be used to identify the individual permitted wax.
Contributed by Dr. Soumyadeep Mukhopadhyay, Ms. Payel Dey & Ms. Atrayee Saha