Effect of different drying methods on chemical composition and antimicrobial activity of bush tea (Athrixia phylicoides).
The effect of different drying methods; sun freeze shade and oven drying on total polyphenol content tannins total antioxidants and phytochemicals content of bush tea (Athrixia phylicoides DC.) were evaluated. Assessment of minimum inhibitory concentration (MIC) assay was also done on bush tea samples. Results showed that different drying processes significantly affected phytochemical compositions of bush tea. Highest total phenolic content (8.34 mg/100 g) sample was found on freeze and shade dried bush tea compared to less than (6.50 mg/100 g) in sun or oven dried samples. Similar response was shown in total antioxidants with shade (0.628 mol/g) and freeze (0.626 mol/g) drying having significantly highest content of total antioxidants as compared to sun (0.440 mol/g) and oven (0.444 mol/g) dried samples. MIC values falls within 3.1 to 6.3 mg/mL with gram-positive bacteria being more vulnerable to the inhibitory effect of extract regardless of bush tea drying method than gram-negative. Anti-microbial activities of bush tea observed in this study will be useful to develop tea extracts for deterrence of diseases causing microorganisms hence shade drying methods will provide easy drying bush tea samples which can be adopted by farmers for commercial purposes. Copyright 2014 Friends Science Publishers
Keywords: Antioxidants; Bush tea; Drying methods; Minimum inhibitory concentration; Phytochemicals
Bush tea (Athrixia phylicoides DC.) leaves contains 5- hydroxy-6783'4'5'-hexamethoxyflavon-3-ol (Mashimbye et al. 2006) 3-0-demethyldigicitrin 56783'4'- hexamethoxyflavone and quecertin (Mavundza et al. 2010) tannins (Mudau et al. 2007; Chabeli et al. 2008) total polyphenols (Mudau et al. 2006; Maudu et al. 2012) and total antioxidants (Maudu et al. 2010; Mogotlane et al.2007) compounds with antimicrobial activity (Mavundza et al. 2010; Nchabeleng et al. 2013). Indigenous South Africans have significant use of this plant as a traditional medicine (Roberts 1990; Van Wyk and Gericke 2000; Mbambezeli 2005).McGaw et al. (2007) reported that bush tea contains no caffeine as well as pyridoxine making it more appropriate as a healthy beverage. More so occurrence of antioxidants in bush tea has positive favourable health benefits (Mudau and Mariga 2012). According to Mudau et al. (2006) active chemical compounds present in herbal tea influence the quality of herbal tea. They also serve as the potential indicators of medicinal prospective due to their antioxidant activities (Mudau et al. 2006; MaKay and Blumberg 2007; Kokotkiewicz and Luczkiewicz 2009). However yield and chemical composition from herbalplants are related to a variety of factors which include the drying process (Rocha et al. 2011).Drying is an important part of tea post-harvest handling with the processing having impact on antioxidant content and appearance which all have effect on viability of the industry (Chong and Lim 2012). It is the most common and fundamental way to preserve quality of aromatic and medicinal plants (MA1/4ller and Heindl 2006; Rocha et al.2011). In other common herbal tea in South Africa Joubert and de Villiers (1997) reported that drying affects quality attributes on rooibos tea whilst in honeybush tea drying methods did not significantly influence the quality of tea (du Toit and Joubert 1998). In other herbal teas sun-drying resulted in deterioration of antioxidant properties (Chong and Lim 2012) and various drying methods have different effects on aromatic and medicinal plants (Stafford et al.2005; Rocha et al. 2011). Hence for viability of the bush tea production there is need to establish drying techniques for recommendations to producers.Data that describe the standard production protocol for drying bush tea have not been established. Thereforethe objective of this study was to compare effect ofdifferent bush tea drying methods on phytochemical composition and anti-microbial activities of bush tea extract.
Materials and Methods
Fresh bush tea samples were collected from the wild at Muhuyu village (2253'60S and 3025'0E 724 m.a.s.l.) in Limpopo province South Africa. The fresh leaves of uniform shape color and size were selected and subjected to four different drying methods viz. sun freeze shade and oven drying. In sun drying bush tea leaves were placed in the sun/daylight. Midday temperature reached 35C for 5 days during the sun drying period. For freeze drying leaves were placed in freezer dryer. In shade drying leaves were placed in wooden trays and protected from direct sunlight. For oven drying leaves were placed in an oven tray and heated at a temperature between 45 to 65C overnight. All treatment were laid out in a completely randomized design (CRD) and replicated five times. Dry samples were thereafter analysed for chemical compositions. Assessment of minimum inhibitory concentration (MIC) assay was also done (Eloff 1988). Comparisons of total phenolic contents and antioxidant activities were made to the fresh bush tea extracts reported by Mavundza (2010).
Chemical Compositions Assays
Determinations of total polyphenol content were done using methods reported by Singleton and Rossi (1965) and modified by Waterman and Mole (1994). Tannins were determined using Vanillin HCL method described by Prince et al. (1978) and total antioxidants were determined using the method described by Awika et al. (2004).
The chlorophyll riboflavin niacin ascorbic acid carotenoid contents were determined using the standard AOAC methods (1984).
Minimum Inhibitory Concentration Assay
Gram-positive; Staphylococcus aureus (ATCC 12600) Bacillus cereus (ATCC 11778) B. subtilis B. pumilis (ATCC 21356) Enterococcus faecalis (ATCC 29212) and Gram-negative; Pseudomonas aeruginosa (ATCC 25922) Escherichia coli (ATCC 11775) Klebsiella pneumonia (ATCC 27736) microorganisms were used. The assays were carried out using micro-dilution methods on 96 well microplates (Eloff 1988).
Data were subjected to analysis of variance (ANOVA) using PROC GLM (General linear model) procedure of SAS version 9.2 (SAS Int 2011).
Drying of bush tea after harvesting had significant effect on the chemical composition of the extract with generally ahigher composition than in fresh samples which had 2.30 mg/100 g of total phenolic content. Total phenolics were higher in shade (8.34 mg/100 g) and freeze (8.34 mg/100 g) dried bush tea as compared to sun (6.42 mg/100 g) and oven (5.62 mg/100 g) dried samples (Table 1). The same response was shown in total antioxidants with shade (0.63 mol/g) and freeze (0.63 mol/g) drying having significantly highest content of total antioxidants as compared to sun (0.44 mol/g) and oven (0.44 mol/g) dried samples. However even though there was slightly more tannin content (0.4 mg/100 g) in freeze dried bush tea samples than in other drying techniques; the different drying approaches did not exhibit significant differences on tannin contents of bush tea leaves.Shade (83.4 mg/100 g) and freeze (83.4 mg/100 g) dried bush tea samples had significantly highest chlorophyll contents compared to sun (69.9 mg/100 g) and oven (68.3 mg/100 g) dried samples (Table 2). The difference between the highest and lowest contents was 14.1 mg/100 g of dried sample. The ascorbic acid niacin carotenoids and riboflavin contents of the sampled bush tea did not vary regardless of the drying method used. Average phytochemical compositions within the plant samples were76.3 mg/100 g 1.7 mol /g 1.5 mg/100 g 1.8 mg/100 g and 2.4 mg/100 g for chlorophyll ascorbic acid niacin carotenoids and riboflavin contents respectively.
Minimum Inhibitory Concentration
MIC values of extract on different microorganisms are shown in Table 3. The crude extract showed positive inhibitory activity against the entire gram-positive and gram-negative tested microorganism regardless of drying method subjected to the bush tea sample with MIC values ranging from 3.1 to 6.3 mg/mL. All the gram-negative microorganisms gave a MIC value of 6.3 mg/mL whilst the lowest MIC values of 3.1 mg/mL were obtained in gram- positive microorganisms except for B. cereus with MIC value of 6.3 mg/mL.
Drying of bush tea resulted in a higher composition of chemical constituents. During drying cell membranes rapture and degrade thereby releasing compounds during extraction (Stafford et al. 2005). However freeze and shade drying proved to be more efficient in retaining the total polyphenols and antioxidants within the bush tea samples than oven and sun drying procedures. In most studies carried out on various aromatic and medicinal plant types (Yousif et al. 2000; Asami et al. 2003; Abascal et al.2005) freeze drying has been shown as mostly recommended method in retention of plant compounds. Similarly van Golde et al. (2004) reported that approximately 70% of polyphenols in red wine can be preserved through freeze drying. In grape peel losses of
Table1: Response of chemical composition to selected dying methods of bush tea
Drying methods Total polyphenols Total antioxidants Tannin contents
###content (mg/100 g) (mol/g)###(mg/100 g)
Significant level 0.0001###0.0001###0.5038
Table 2: Effect of drying on phytochemical compositions of bush tea
Drying###Chlorophyll Ascorbic Niacin###Carotenoids Riboflavin
methods###(mg/100 g) acid###(mg/100 g) (mg/100 g) (mg/100 g)
LSD 5% 4.2###1.6###1.0###1.1###0.9
Table 3: MIC values of the crude extract from bush tea dried irrespective of drying methods
Bacterial species###Gram +/-###Minimum###inhibitory
polyphenols tannins and antioxidants have been reported in oven dried samples at higher temperature (Laurrauri et al. 1997).Post-harvest processes like drying take authoritative impact on the quality of the product influencing its value (MA1/4ller and Heindl 2006) which is mostly shown on its appearance. The present study showed that sun and oven drying can reduce the chlorophyll content of bush tea adversely affecting the color. Mahanom et al. (1999) observed loss of chlorophyll in all oven dried medicinal plants leaves. Similar results were reported by Joubert and de Villiers (1997) in rooibos tea where less chlorophyll was present in sun-dried than in tea dried under controlled conditions. Ramana et al. (1988) suggested that such loss of colour must be minimized as it may adversely distance prospective customers due to possibility of below par processing. In addition to yielding extracts high in phenols and active ingredients; meadowsweet (Filipendula ulmaria) and willow (Salix alba) herbs developed an appropriate colour for fusion into a beverage when dried under temperatures of 30C compared to the 70C (Harbourne et al. 2009).Besides the benefits of antioxidants bush tea samples were also beneficial as antibacterial regardless of drying method used in this trial. According to Fabry et al. (1998) all plant extracts with MIC values below 8 mg/mL are considered to possess some antimicrobial activity. MIC values have demonstrated that the gram-positive bacteria appeared to be more susceptible than the gram-negative ones to the inhibitory effect of the extract. Similar resultswere reported by Tshikalange et al. (2005) who also notedthe antibacterial activities of other herbal plants. Thesedifference in susceptibility can be ascribed to the
morphological differences between the gram-positive and gram-negative bacteria (Palombo and Semple 2001; Tadeg et al. 2005) with the later having an outer phospholipidic membrane that carries structural lipopolysaccharidecomponents making the cell walls impermeable to lipophilic
solutes (Nostro et al. 2000).Benefits of tea extracts have been noted previously byToda et al. (1989) with the extract inhibiting enteric pathogens such as Staphylococcus aureus S. epidermis and Plassiomonas shigelloides. Amongst other things tea extracts have been found effective against Helicobacter pylori which are linked to gastric peptic and duodenal ulcer diseases (Diker and Hascelik 1994). Biological activities of the cariogenic streptococci can also be inhibited by polyphenols in green tea thereby preventing teeth from decaying (Sakanaka et al. 1996; Mitscher et al. 1997). According to Baydar et al. (2004) the extent of this inhibition can be attributed to phenolic composition within the plant with phenols as the predominant active compounds in medicinal plants (Rios and Recio 2004). This makes bush tea a very promising herbal tea as it is a rich source of phenols.In conclusion shade and freeze drying methods have shown to be more useful for retention of phytochemicals within bush tea samples. Crude extracts of bush tea had a broad spectrum in their actions on antibacterial activities of either gram positive bacteria or gram negative bacteria regardless of drying method subjected to the bush tea. Therefore sound processed bush tea could be used as accessible sources of natural antimicrobial and antioxidants.
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|Author:||Mudau, Fhatuwani N.; Ngezimana, Wonder|
|Publication:||International Journal of Agriculture and Biology|
|Date:||Oct 31, 2014|
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