Total Phenolic Content (TPC)

Figure 4.4 shows the effect of different solvents on the total phenolic content extracted from BSG using soxhlet extraction.

Figure 4.4: TPC values for soxhlet extractions for water, acetone 80 % (v/v), ethanol 20 % (v/v)

The results shown in Figure 4.4 illustrates the TPC values for soxhlet extraction technique.

Soxhlet extraction method has been reported by Dhanani et al. (2017) to measure the maximum extractable polyphenols from natural herbs. Only free phenolic compounds are extractable by conventional solid-liquid extraction. However, due to higher extraction temperatures used in soxhlet extraction, both free and bound phenolics are recovered (Bonoli et al., 2004; Dvorakova et al., 2008). Since soxhlet extractions occurs at boiling point of the solvents, authors have found that the use of higher temperatures causes degradation of phenolic compounds thereby affecting antioxidant activity (Dorta et al., 2012). Extracts from water showed the highest TPC and this was in agreement with the results obtained for the global yield shown in Figure 4.2. The results also showed that ethanol 20 % (v/v) had a higher global yield than acetone 80 % (v/v) but the amount of TPC was less for ethanol 20 % (v/v). This indicates that soxhlet extraction might have released some undesired compounds which are not polyphenols when ethanol was used as a solvent resulting in a high global yield. Table 4.1 compares the results obtained in this research with the work done by Moreira, (2012) for soxhlet extractions. However, their work indicates that extracts obtained using acetone 70 % (v/v) solvent gives higher TPC than extracts obtained using water.

Table 4.1: TPC for BSG extracts obtained from soxhlet extraction method and literature data.

Values are expressed as mean ± standard deviation.

Solvent composition TPC (mg GAE/ g BSG)

Research work (Moreira, 2012)

Water 10,01 ± 0,9 4,3 ± 0,3

Acetone 80 % w/w 8,7 ± 0,1 11,6 ± 0,3¹

Ethanol 20 % w/w 7,6 ± 0,2 -

Figure 4.5 shows the effect of different solvents on the total phenolic content of extracts from BSG using maceration. The results show the influence of different solvent and solvent composition on the extraction. Moreira, (2012) reported that the nature of the extracting solvent used has got the greatest significance on the extract yields, the total phenolic content and the resulting antioxidant activities of the sample. In this work, the total phenolic content for all extracts obtained from maceration was highest for water, a more polar solvent.

Figure 4.5: TPC values for maceration extractions done using ethanol, acetone and their water mixtures

Acetone solvent had a different behaviour from ethanol solvent in the efficiency of extraction.

For acetone solvent, 60% v/v had the highest phenolic content whilst for ethanol solvent, the lesser the solvent in the mixture the greater the total phenolic content. This means that the highest amount of total phenols was obtained when there was no ethanol at all and it was only pure water. The results agree with those of Meneses et al., (2013a) as shown in Table

1 The value was a result of an extract done by Moreira, (2012) for Acetone 70 % w/w

4.2. They studied the influence of solvents on the extraction of polyphenols from BSG.

Meneses et al., (2013a) evaluated methanol, ethanol, acetone, hexane, ethyl acetate in different compositions of 100%, 80%, 60%, 40% and 20%), and water. They reported that TPC was higher for 60% acetone (v/v) than all other cases.

Table 4.2: TPC for BSG extracts obtained from Maceration extraction method. Values are expressed as mean ± SD

Solvent compositions (%) TPC (mg GAE/ g BSG)

Research work (Meneses et al., 2013a)

Water 14,86 ± 0,77 3,59 ± 0,46

Acetone

100 4,13 ± 0,85 5,66 ± 1,00

80 7,38 ± 0,11 5,37 ± 0,11

60 11,63 ± 0,28 9,90 ± 0,41

40 10,13 ± 1,49 6,26 ± 0,61

20 8,95 ± 0,68 5,94 ± 0,22

Ethanol

100 4,61 ± 0,23 4,60 ± 0,35

80 6,11 ± 0,70 5,54 ± 0,31

60 7,86 ± 0,69 7,13 ± 0,24

40 13,04 ± 0.084 6,18 ± 0,57

20 14,58 ± 0,14 4,26 ± 0,51

Meneses et al., (2013b) also reported that the more elevated total phenolic content was obtained when using 70% (v/v) acetone as compared to using water and ethanol. Their findings show that a less polar solvent (acetone) is able to recover higher amounts of phenolic compounds as compared to higher polar solvents such as water. The main reason for the verified differences may be due to the sample and type of origin or the differences in extraction procedures. The method of brewing and malting in the generation of the BSG may also be a contributor to the contrast findings in our results. Moreover, the application of aqueous acetone as solvent may lead to an unacceptable level of acetone residue in the extracts On the other hand our results are in agreement with several authors who reported the influence of the polarity of the extracting solvent as shown (Babbar et al., 2014; Roby et al., 2013; Zhao et al., 2006).

Roby et al., (2013) evaluated the influence of extracting solvents on the extraction of polyphenolic compounds from three aromatic plants (thyme, sage and marjoram) extracts.

They concluded that methanol and ethanol were better solvents in the extraction of polyphenols from thyme than ethyl acetate and hexane with a range of 8.1 mg GAE/g DW to 3.9 mg GAE/g DW. Although Roby et al. (2013) did not evaluate water as a solvent, their

materials than the less polar solvent. Dent et al. (2013) reported similar results to ours when they evaluated the effect of extraction solvent on the composition of polyphenols in Damlatian wild sage. They concluded that water was a greener and better solvent in extracting sage as compared to ethanol and methanol volume fractions in water.

Although our results do not agree with other authors in terms of the solvent with higher TPC, they have similarities in the trends exhibited by each solvent. The TPC values obtained in our results is lower than that observed by several authors which may again be attributed to the extraction procedure used. Our results showed that the amount of total phenolic content extracted from BSG is greatly influenced by the polarity of the solvent as shown by Dent et al., (2013) and Roby et al., (2013). However, this result was not in agreement with previous reports suggesting that binary solvent systems such as ethanol/water or acetone/water are more efficient than a mono-solvent system like water in the extraction of polyphenolic compounds in regards to their relative polarity (Moreira, 2012; Meneses et al., 2013a).