CHAPTER 5 DISCUSSION
5.1 Raw ingredient total polyphenol content and TAC
CHAPTER 5
evaluated their radical scavenging activities against cation, peroxyl and hydroxyl radicals. For each spice extraction, the total phenolic content and chelating activity was also determined. The extracts of all the samples showed significant radial scavenging capacities and chelating abilities. Cinnamon had the highest natural phenolic content and the strongest antioxidant properties (Su et al., 2007:996). In contrast, the polyphenol content determined for parsley was 389 mg GAE/100 g in comparison to the USDA database reported polyphenol content of only 77 mg GAE/100 g for parsley. The polyphenol content of 178 mg GAE/100 g determined for tomato paste was the same as that reported for tomato paste in the USDA database. The USDA database reported a much higher polyphenol content (175 mg GAE/100 g) for lemon juice compared to the content determined in this study (44 mg GAE/100 g).
Previous studies (Velioglu, Mazza, Gao & Oomah, 1998:4113; Sevick, Kondrashov, Kvasnicka, Vacek, Hamouz, Jiruskova, Voldrich & Cizkova, 2009:171) as well as this study have shown a strong correlation between the total polyphenol content and the TAC. Cinnamon had a TAC of 120 923 µmole TE/100 g while in the USDA database the TAC for cinnamon was much higher at 267 536 µmole TE/100 g. Coarse black pepper had a TAC of 114 597 µmole TE/100 g while in the USDA database the TAC was far lower (27 618 µmole TE/100 g). Parsley had a TAC of 20 134 µmole TE/100 g while in the USDA database a TAC of only 1 301 µmole TE/100 g was reported. The TAC of the tomato paste was 15 656 µmole TE/100 g while in the USDA database the TAC was only 694 µmole TE/100 g. The analysed total polyphenol content and TAC of the herbs, spices and flavourings were either far lower or higher compared to the USDA’s total polyphenol content and TAC of the herbs, spices and flavourings. Although herbs and spices are used in small quantities in recipe formulation their contribution to the total polyphenol content and the TAC can be substantial.
The total polyphenol content of the four vegetables used across the soup recipe formulations is published in the USDA database. The different vegetable inclusions had varying polyphenol contents. Raw carrots had a polyphenol content of 8 mg GAE/100 g while in the USDA database the polyphenol content is recorded as 35 mg GAE/100 g. Raw potatoes had a polyphenol content of 39 mg GAE/100 g while in the USDA database the polyphenol content was higher (163 mg GAE/100 g). The USDA database also had a higher polyphenol content (111 mg GAE/100 g) for raw cauliflower compared to this study (69 mg GAE/100 g). However, for the raw onion the polyphenol content determined of 93 mg GAE/100 g was somewhat higher than that reported for raw onion in the USDA database (23 mg GAE/100 g). No polyphenol contents were reported in the USDA database for the other vegetable ingredients included in
the soup recipe formulations. Three of the four vegetable ingredients analysed had a lower total polyphenol content compared to the total polyphenol content published in the USDA database.
The lower total polyphenol contents in the analysed vegetables compared to the USDA database values is possibly due to different cultivars used for analysis and different environmental growing conditions (Volden et al., 2008:596). Different pre-preparation techniques could also possibly cause variances between the analysed values in this study compared to the USDA database values. Pre-preparation of fruits and vegetables such as peeling, cutting and slicing are expected to cause rapid enzymatic loss of several natural antioxidants (Nicoli et al., 1999:96). Cutting exposes the inner tissues to oxygen and light (Ruiz- Rodriguez & Marin, 2008:345).
A previous study reported on the phenolic content of five vegetables, raw and thermally processed (Ismail, 2004:581). Among all the fresh vegetables, spinach had the highest phenolic content, followed by swamp cabbage, kale, shallots and cabbage (Ismail, 2004:581). Spinach was not a vegetable ingredient used in the soup recipe formulations of the current study. Raw onion was the vegetable ingredient with the highest polyphenol content (93 mg GAE/100 g) in this study. The USDA database vegetable with the highest polyphenol content across the four vegetables used in the soup recipe formulations for which a polyphenol content was published, was raw cauliflower (111 mg GAE/100 g). Raw carrot was the vegetable ingredient with the lowest polyphenol content (8 mg GAE/100 g) in this current study. The USDA database vegetable with the lowest polyphenol content across the four vegetables used in the soup recipe formulations for which a polyphenol content was published, was raw onion (23 mg GAE/100 g).
The TAC of the six vegetables used in the current study across the soup recipe formulations is also published in the USDA database. Raw carrots had a TAC of 1 097 µmole TE/100 g while in the USDA database the TAC was 666 µmole TE/100 g. Raw cauliflower had a TAC of 1 444 µmole TE/100 g while in the USDA database the TAC for raw cauliflower was much lower (829 µmole TE/100 g). Raw celery had a TAC of 1 083 µmole TE/100g while in the USDA database the TAC was 497 µmole TE/100 g. Raw leeks had a TAC of 1 966 µmole TE / 100 g which was more than 200% higher than the USDA database TAC for raw leeks (490 µmole TE/100 g). The TAC for raw onions was 2 063 µmole TE100 g while in the USDA database the TAC was 1 034 µmole TE/100 g. Raw potatoes had a TAC of 1 100 µmole TE/100 g while in the USDA database the TAC was 1 058 µmole TE/100 g. Raw onion was the vegetable ingredient with the highest TAC (2 063 µmole TE/100 g) in this study. Onions have relatively high scavenging properties among the different vegetables (Pinilla et al., 2005:S60). The USDA database
vegetable with the highest TAC across the six vegetables used in the soup recipe formulations, for which a TAC was published, was raw potatoes (1058 µmole TE/100 g). Raw celery was the vegetable ingredient with the lowest TAC (847 µmole TE/100g) in this study. The USDA database vegetable with the lowest TAC across the six vegetables used in the soup recipe formulations for which a TAC was published, was raw leeks (490 µmole TE/100 g). The TAC of the six vegetables used in the current study across the soup recipe formulations were all higher compared to the TAC values published in the USDA database. The South African vegetable cultivation environment may be partly be responsible for this finding. A previous study (Stewart, Bozonnett, Mullen, Jenkins, Lean & Crozier, 2000:2668) found that tomatoes originating from warm, sunny climates such as Spain, Israel and South Africa have a far higher phenolic flavonol concentration than tomatoes originating from growing conditions with lower light and sunlight exposure, such as from greenhouses (Stewart et al., 2000:2668).
Split peas had an analysed total polyphenol content of 51 mg GAE/100 g, while in the USDA database the polyphenol content reported was somewhat higher (74 mg GAE/100 g). Split peas had a TAC of 1 553 µmole TE/100 g while in the USDA database split peas had a TAC of about a third of this capacity (524 µmole TE/100 g).