ANTIOXIDANTS IN BLACK CARROT ( Daucus carota L.) : PROCESSING STRATEGY FOR IMPROVED STABILITY AND FUNCTIONAL QUALITY
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Date
2008
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Abstract
Anthocyanins present in fruits and vegetables have potential beneficial health
effects such as reducing age-associated oxidative stress and possessing anti-
inflammatory properties. In addition, they have high potential for use as natural
colorant. Black carrots a grossly underutilized vegetable has high anthocyanin
content and antioxidant activity. The present study evaluates processing black carrots
for enhanced phytochemical content for food applications. Black carrot were found
to high total phenolic and flavonoid content of 270.74 mg GAE/100g and 94.38 mg
CE/100g fresh weight respectively. The anthocyanin pigment of black carrot
expressed as cyanidin 3- glucoside was 2430.45 mg/kg. Total antioxidant activity as
evaluated by FRAP and CUPRAC assay was 27.75 and 60.70 μmol Trolox/g
respectively. Exceptionally, high content of total phenolics, anthocyanin and
antioxidant activity equates them with high antioxidant fruits such as grapes and
blueberries. Results strongly point that black carrots, a underutilized vegetable is a
strong candidate in terms of its antioxidant composition and can be used as value
added ingredient for food applications.
Extraction temperatures and enzyme assisted processing (EAP) using cell
wall degrading enzyme pectinase (0.2%) remarkably improved the functional quality
of black carrot juice resulting in enhanced juice yield, levels of total phenols,
anthocyanin and total antioxidant activity. The total antioxidant activity in black
carrot juice extracted via EAP was 29.80 μmol Trolox/ml and 62.80 μmol Trolox/ml
in
in-vitro
FRAP and CUPRAC assay respectively. Colour values of black carrot
juice as expressed by CIELAB coordinates L* (lightness), a*, b*, hue angle and
C*(chroma) followed a definite trend in response to enzyme assisted processing.
With increasing pectinase concentration, there is a decrease in L*, b* hue and
increase in a*, chroma, ΔE va
lues of juice.
Drying temperatures (60-80°C) significantly affected the nutraceutical
composition of black carrot slices; there was significant reduction in the total
polyphenolics and total antioxidant activity. Highest retention of total phenolics and
flavonoids was observed at 60°C; content of 1616.16 and 131.84 mg/100g dwb.
Overall 54% of total phenolics was retained after drying. Irrespective of the drying
temperatures used, anthocyanins were found to be seriously degraded during drying
operations. Increasing temperature (60 to 80°C), degraded anthocyanins seriously
and 6% of original content was retained.
Predrying treatments (PDTs) significantly improved the total flavonoid
retention in dried black carrot slices. Promising results with use of n-acetyl cysteine
as a PDT prior to dehydration of black carrots corroborate the effectiveness of other
anti browning agents as alternatives to sulphites. The optimized value added powder
(VAP) has the potential to yield high anthocyanin rich extract (205 mg/L)
Black carrot anthocyanins showed remarkable high thermal stability at high
temperatures (50-100°C) in contrast to grape anthocyanins. Analysis of kinetic data
suggested a first-order reaction for the degradation of black carrot anthocyanins in all
food systems during both heating and storage. Coloring anthocyanin juices (black
grapes), non-anthocyanin containing juices (apple, white grape, pineapple, grape
fruit,) and RTS (guava and lime) colored with black carrot juice enhanced juice color
and stability of anthocyanins.
Technological implications
Black carrots with high anthocyanin content known to have health beneficial
effects have high potential value for vegetable growers as well as nutraceutical and
functional food market.
Valorization of black carrots can benefit the agricultural and food industries
by contributing valuable phytochemical constituents
Use of n-acetyl cysteine offers a viable alternative pre-drying treatment prior
to drying for improving the phytochemical retention in dried black carrots. This
becomes all the more important since sulphitation has been recently under critical
consideration with respect to allergen labelling of foodstuffs implemented by
European -Member States in November 2004.
For food industry looking for viable alternatives to synthetic colourants, black
carrot juice and VAP (value added powder) offer novel ingredients for increasing
functionality and consumer appeal of processed products