Standardisation of Glycerinisation Technique for Fragile Foliages

Processing techniques in dry flower industry assume great significance in determining the final quality of dry flower products. Preserving plant materials by glycerinisation with glycols is experimented on fragile leaves. The treatment T 3 (Glycerine 30% followed Ethylene glycol 30%) resulted in enhancement of quality characteristics for Myrtus sp., Thuja orientalis, Eucalyptus glaucescens and Asparagus virgatus in terms of percentage of minimum moisture loss (34.22, 25.51, 26.81 and 9.15, respectively. The pigment concentration viz., chlorophyll ‘a’, ‘b’ and total chlorophyll contents (0.877, 1.726, 1.685 and 1.406 mg g -1 respectively were also superior. The leaves scored better for quality parameters viz. , texture and shape retention. As an improved glycerinisation technique 30 % Glycerine followed by 30 % Ethylene glycol resulted in soft near to natural leaves with minimum moisture loss and with maximum colour and shape retention.

In the present era of eco-consciousness, use of plant-derived natural products like dry flowers has become the premier choice of the masses in their life styles for interior decorations. Dried and preserved ornamental products offer a wide range of unique qualities which include novelty, longevity, aesthetic properties, flexibility and year round availability (Ranjan and Mishra, 2002). Many types of foliage can be preserved by variety of processes that impart longevity to the product. Common methods of preservation include air drying, dehydration by desiccants (silica gel, borax, sand), freeze drying, coating with polymer dispersions and systemic or immersion glycol treatments. Leaves are best preserved with glycols. More and more foliages have shown to respond very well to this manner of preservation.
Preserving plant materials with glycols is called glycerinisation or glycol preservation. Foliages commonly preserved by glycol treatment using hydrophilic chemicals help to maintain the suppleness of dried plant materials by attracting water vapour from the surrounding atmosphere. Accordingly preserved materials are less brittle than dried materials. Thus it is less prone to shattering and mechanical damage and more lifelike in appearance. Leonard Karel (1973) stated that among the various methods of preserving foliages, glycerinisation affords perhaps greatest satisfaction. Glycerinization improves pliability, retains natural shape and makes the dried products *Corresponding author email : visaarun@gmail.com last longer (Conder, 1979) . The merit of glycol preserving is replacing the volatile water in plant tissues with a non volatile liquid. If the internal moisture of plant parts are replaced with solvents like glycol to retain their original texture, shape and colour, the processed parts would look more natural than the air dried leaves (White et al., 2007). However, a wrong choice of solvent can considerably influence the texture of the final product. Use of low volatile solvents like glycerine causes bleeding while high volatize solvents like ethylene alcohol and propylene alcohol causes complete shrinkage (Joyce, 1998). Hence, an appropriate combination of these solvents can be a reasonable choice. Therefore, there is a need to reconsider appropriate solvents and their concentrations by improved methods to address the challenge of reducing bleeding but retaining texture and shape of the foliages. With this objective the current study was taken to standardize the advanced glycerinisation technique for fragile foliages.

Materials and Methods
Improved scientific glycerinisation study was carried out in the Tamil Nadu Agricultural University, Coimbatore during the year 2010 -13 under completely randomized design. Matured leaves of four species viz., Myrtus sp., Thuja orientalis, Eucalyptus glaucescen and Asparagus virgatus were sourced from Yercaud and Niligiris. Mixtures of Glycerine, Ethylene and Propylene glycol were prepared using warm distilled water (20 0 C). Treatment combinations were T1 -Glycerine 30% followed Glycerine 30%, T2 -Glycerine 25% followed Ethylene glycol 25%, T3 -Glycerine 30% followed Ethylene glycol 30%, T4 -Glycerine 25% followed Propylene glycol 25%, T5 -Glycerine 30% followed Propylene glycol 30%, T6 -Ethylene glycol 25% followed by Glycerine 25%, T7 -Ethylene glycol 30% followed by Glycerine 30% , T8 -Propylene glycol 25% followed by Glycerine 25%, T9 -Propylene glycol 30% followed by Glycerine 30%. To these mixtures, 0.1 per cent Sodium benzoate and 8 g of Apple green food dyes were added. The pH 4.0 was maintained 4.0 by adding citric acid. The systemic glycol preserving process adopted in this experiment is described below in different steps. Primary soaking -About 250 g each of mature fresh leaf stalks of the plant species were harvested and rinsed immediately in tap water. The leaf stalks were then given a slant cut of one inch with sharp knife without damaging the tissues, in order to ensure that air trapped inside is removed. The stalks were then placed quickly into the first step glycol preservative mixture as given in the treatment details in small mugs or jars. During the process of secondary soaking, the preserving durations were fixed as 2 days for Asparagus virgatus, 4 days for Myrtus sp., 4 days for Eucalyptus glaucescens and 8 days for Thuja orientalis. In the mid of preserving process (after completion of 50 % of the preserving duration), the foliages were removed and washed. The leaf stalks were again given a slant cut and immersed in the second step glycol preservative as mentioned in the treatment details. During both step at least 10 cm of the entire stem was totally immersed in the preservative solution with proper air circulation without overcrowding. The mugs were placed in dark room at ambient temperature (30±2 0C). Observations on percentage of moisture loss, pigment (chlorophyll) content and qualitative scores for texture and shape retention were measured. The percentage moisture loss was calculated by using the formula suggested by Ranganna (1977). The chlorophyll 'a', 'b' and the total chlorophyll contents in the preserved leaves were determined by using the method of Yoshida et al. (1971) and expressed in mgg-1 of preserved leaf sample. Sensory scoring was done for the quality characters texture and shape retention by a panel of 14 scientific persons including experts in dry flower technology on a 5 point Hedonic scale (Peryam , 1957). The data recorded were statistically analyzed for significance (Panse and Sukhatame, 1985).

Percentage of moisture content
All the parameters studied in the experiment were significantly differed by advanced glycerinisation technique. The glycerinisation of different foliages on percentage of moisture loss was presented in Table 1. Among different foliages employed in this study the minimum moisture loss  Chang, 1984). However, with the basic objective of reducing bleeding when the leaves were secondarily soaked in Ethylene glycol with two -OH groups, an optimal intermediate absorption isotherm is obtained (Mark Koch, 1995). Glycerinization of plant materials helps them to last longer apart from keeping them more pliable and retaining their natural shape. Further, it could be realized in the present study that, not only the choice of solvents, but also the sequence of solvents greatly influences the final quality of preserved botanicals. Improper choice of solvents and sequence of their usage can either cause bleeding or complete shrinkage of the plant materials. Hence, a combination of humectants with varied hygroscopic nature viz., Glycerine, Ethylene glycol, Propylene glycol seemed to be a reasonable choice, as already observed by Joyce (1998).
Moisture loss in the leaves by preservation influences the shape of leaves. Intermediate absorption isotherms obtained by combining glycols in the descending order of high rate uptake humectants viz., Glycerine > Ethylene Glycol enables softening of leaves, a capability resulting from its moisture retention capacity. This observation is in conformity with the view of White et al. (2007) who reported that treating foliages with glycols yields unique results that would enable plant parts to remain flexible and pliable indefinitely.
The treatment T8 (Propylene glycol 25% followed by Glycerine 25%) recorded the maximum percentage of moisture loss for Myrtus sp. (53.49 per cent), Asparagus virgatus (17.02 per cent), Eucalyptus glaucescens (48.46 per cent) and Thuja orientalis (38.19). Maximum moisture loss was recorded in treatments where plant materials were primarily soaked in propylene glycol and ethylene glycol followed by secondary soaking in glycerine. It may be due to the reason that primary soaking in solvents with only two -OH groups which are high volatile in nature, the water being evaporated easily results in drying and shrinkage of leaves (Morrison and Boyd, 1959). Though further soaked in glycerine, initial drying must have resulted in the high rate of senescence and death of cells prevent or slow down the absorption of solvent in the second step (Ito et al., 2010). Uptake of humectants in the transpiration stream characteristically slows markedly over the first few days; presumably as solute accumulation reflect progressive closure of an increasing proportion of the stomatal population. Thereafter, the sustained and relatively low rates of uptake observed could be indicative of humectants uptake and driven by transcuticular water loss (Joyce, 1998). The difference in performance of the foliage can be attributed to the difference in genetic makeup of the plants. Among the four different leaves, minimum moisture loss in Asparagus virgatus and maximum moisture loss in Myrtus sp. recorded might be due to the narrow and broad leaf structure of the leaves respectively. This is in accordance with findings of Guerfel et al. (2008) who reported that the morphological and structural characteristics of leaves influence their response to processing methods.
Qualitative criteria are centered around the visual look of the foliage, how it feels or how easy it is to work with as well as customer acceptance of the product. Visual scores were best for leaves preserved by primary soaking in Glycerine 30 % followed by secondary soaking in Ethylene glycol 30%. These leaves were associated with good texture and highest shape retention. Undoubtedly, the desirable quantitative criteria viz., less moisture loss and high pigment content might have naturally resulted in the high scores for the qualitative criteria.
Glycerinization of plant materials helps them to last longer apart from keeping them more pliable and retaining their natural shape. Further, it could be realized in the present study that, not only the choice of solvents, but also the sequence of solvents greatly influences the final quality of preserved botanicals. Improper choice of solvents and sequence of their usage can either cause bleeding or complete shrinkage of the plant materials. As an improved glycerinisation technique (T3) 30 per cent Glycerine followed by 30 per cent Ethylene glycol resulted in soft near to natural leaves with minimum moisture loss with maximum colour and shape retention.