| dc.description.abstract | There is a close relationship between the susceptibility to disease and nutritional state, in the
sense that an adequate diet enhances resistance to disease. There is an increasing interest in this
beneficial relationship among scientists, food manufacturers and consumers. The trend is
moving towards functional foods and their specific health benefits.
The results of numerous epidemiological studies and recent clinical trials provide consistent
evidence that diets rich in fruits and vegetables can reduce the risk of chronic diseases. These
protective effects are mediated through multiple groups of beneficial nutrients contained in the
fruits and vegetables, one of these being polyphenol antioxidants. The intake of the polyphenols
plays an important role in the reduction and prevention of coronary heart disease (CHD),
cardiovascular disease and cancer, as a consequence of their associated antioxidant properties.
Fruits contain an array of polyphenols with antioxidant capacity. Polyphenols may be classified
in two broad groups namely: flavonoids and non-flavonoids. Flavonoid subgroups in fruits are
further grouped as catechins, anthocyanins, procyanidins and flavonol among others. Phenolic
acids occur as hydroxylated derivatives of benzoic acid and cinnarnic acid, and are classified as
non-flavonoids. Polyphenols have redox properties allowing them to act as reducing agents,
hydrogen donators and singlet oxygen quenchers, and thus contribute to the antioxidant capacity
of fruits and vegetables. Because of the numerous beneficial effects attributed to these
antioxidants, there is renewed interest in finding vegetal species with high phenolic content and
relevant biological activities.
In view of the importance of these substances towards health and food chemistry, this study will
focus on the polyphenol and Vitamin C characterisation and quantification of an indigenous
South African fruit, the Kei-apple (Dovyalis cafra), thought to have antioxidant properties. Due
to the fact that polyphenol content influences the colour, taste and possible health benefits of the
fruit / processed food product, this study will supply valuable information to industry in choosing
the best fruit processing methods to attain the desired end product. The exploitation of
indigenous South African fruits (Marula and Kei-apple) is receiving increasing prominence, not
only due to their health benefits, but also the opportunities these present to rural based
economics. Furthermore, this research will serve as a platform for further research on the Kei-apple
and other indigenous South African fruits with possible health benefits.
Aims: The overall aim of this study is the quantification and characterisation of various nutritionally
important antioxidants (polyphenols and ascorbate) in the Kei-apple fruit in its entirety, as well
as in its individual fruit components (peel, flesh and seeds). In addition, the total antioxidant
capacity of the entire fruit and the various fruit components will be determined in the
unfractionated and fractionated fruit extracts. Gas chromatography coupled mass spectrometry
(GC-MS) characterisation of the individual polyphenol components will also be analyzed in
order to speculate on possible specific health benefits which the Kei-apple may possess.
Methods: The study was designed to ensure that a representative fruit sample was collected.
Approximately 100 kg Kei-apples were picked in the month of November 2004 from the
Bloemhof area in South Africa. A sample of 50 fruits was rinsed and separated into the various
components (peel, flesh and seeds). An additional 50 fruits were randomly selected, cleaned and
used in their entirety for data representative of the entire fruit. The sample extracts were
prepared, after being grounded and lyophilized, by a method described by Eihkonen et al.
(1999) using 70% aqueous acetone. The C18-fractionation on the fruit and separated fruit
components resulted in four fractions containing (1) phenolic acids; (2) procyanidins, catechins
and anthocyanin monomers; (3) flavonols and (4) anthocyanin polymers.
The total polyphenol content of the fruit and fruit components as well as the above mentioned
C18-fractions were determined by Folin-Ciocalteu's method (Singleton & Rossi, 1965). Both
free and total ascorbate concentrations in these samples were determined as described by Beutler
(1984), in addition to total sugar content of these via standard methods. Apart from their
nutritional interest, both these measurements are necessary for the correction of the total
polyphenol concentrations. The total antioxidant capacity of the entire fruit and various fruit
components was determined by measuring the oxygen radical absorbance capacity (ORAC) and
ferric reducing antioxidant power (FRAP) of the unfractionated and fractionated extracts. Using
GC-MS analysis, the various individual polyhenol compounds contributing to the total
polyphenol content of the Kei-apple was separated, identified and quantified.
This quantitative data was captured and statistically analysed. The analysis of variation was
performed using the Tukey Honest Significant Difference test for post-hoc comparison. ORAC,
FRAP and polyphenol Pearson correlation analyses were performed using Statistics (Statsoft
Inc., Tulsa, Oklahoma, USA) with significance set at P ≤ 0.05.
Results and discussion: This study determined the presence of various nutritionally important antioxidants (polyphenols
and ascorbate), the total antioxidant capacity in the entire fruit as well as in the individual fruit
components (peel, flesh and seeds) and their polyphenol sub group fractions.
Total phenol content: The Kei-apple, in its entirety, has a polyphenol concentration of 943 ±
20.3 mg GAE/100g dry weight. Comparison of the individual fruit components showed the
seeds to have the highest total polyphenol concentration with 1990 ± 31.3 mg GAE/100g dry
weight, followed by that of the peel, 1126 ± 45.8 mg GAE/100g dry weight and then that of the
flesh, 521 ± 1.01 mg GAE/100g dry weight.
Total, L-ascorbic (ASC) and L-dehydroascobic (DHA) concentration: The total ascorbate of
Kei-apple fruit is 517 ± 0.92 mg/100g dry weight. In contrast to the polyphenol content, the
flesh of the Kei-apple had significantly the highest concentration of total ascorbate 778 ± 1.20
mg/100g dry weight, Gascorbic 241 ± 21.0 mg/100g dry weight, as well as Gdehydroascobic
537 ± 22.2 mg/100g dry weight. The ratio of Lascorbic acidltotal ascorbate for the flesh, entire
fruit, peel and seed is 0.31,0.43,0.49,0.95, respectively, indicating the seeds are the most stable
source of biologically active Vitamin C, with 95% of the total ascorbate occurring as G
ascorbate. This is also in line with the total polyphenol content of these components, confirming
a polyphenol sparing effect on ascorbate.
C18-fractionation extracts: Solid phase (C18) fractionation of the Kei-apple fruit and fruit
components showed that the fruit, peels and seeds consist predominantly of phenolic acids,
followed by procyanidin, catechin and anthocyanin monomers and thereafter varying amounts of
anthocyanin polymers and flavonols.
Antioxidant capacity: The antioxidant capacity of the entire fruit and individual fruit
components as determined by ORAC, (r=0.76) and FRAP, (r=0.95) significantly correlated with
the total polyphenol content, as well as to each other (r=0.88), indicating both to be good
predictors of antioxidant capacity.
GC-MS polyphenol characterisation of the Kei-apple: Caffeic acid and hydro-p-coumaric
acid were seen to be the phenolic acids occurring in the highest concentrations in the Kei-apple
fruit. The majority of these are concentrated in the flesh and in the case of caffeic acid, also in
the peel. The order of predominance of other major non-flavonoid components in the whole fruit
analysis are m-hydroxybenzoic acid > p-hydroxyphenyl acetic acid > 3-methoxy-4-
hydroxyphenylpropionic acid > p-coumaric acid. The peel of the Kei-apple, apart from caffeic
acid, has exceptionally high concentrations of ferulic acid and also serves as a source of
protocatechuic acid. Syringic acid was most prominent in the seeds. Although the total
flavonoid concentration in the Kei-apple was low, taxifolin and catechin were identified and the
seeds almost entirely accounting for these.
Conclusion: From this study it was concluded the Kei-apple is a rich source of antioxidant compounds
(polyphenols and ascorbate), with a strong antioxidant capacity, and hence may be associated
with health promotion properties, particularly in the prevention of cancer, cardiovascular disease,
and neurodegeneration. Additionally, due to the increased scientific and commercial interest in
this fruit, it is essential to take into consideration the various factors (agronomic, genomic, pre- and
post harvest condition and processing) and tissues. This might affect the chemical
composition of the final marketed product, which may play a significant role in determining the
polyphenol and ascorbate composition and bioactivity of these compounds during food
processing procedures. Hence, the polyphenol composition of the various fruit components
should be taken into consideration when selecting a method of fruit processing into the desired
end product. | |
