Page 121 - Natural Antioxidants, Applications in Foods of Animal Origin

100 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir divided into different subclasses according to the degree of oxidation of the

heterocyclic ring: anthocyanins, flavonols, flavanones, flavanol, flavones,
and isoflavones (Scalbert & Williamson, 2000). Flavonols are the most ubiq-
uitous flavonoids in foods, and the main representatives are quercetin and
kaempferol. Onions, kale, broccoli, and blueberries are the richest sources.
Flavones are much less common than flavonols in fruit and vegetables.
Celery, parsley, wheat, millet, and skin of citrus fruits are important sources
of flavones. Anthocyanins are mainly found in red wine, certain leafy and
root vegetables, and are most abundant in fruits. Flavanols exist as catechins
or proanthocyanidins. Catechin and epicatechin are the main flavanols in
fruit, whereas gallocatechin, epigallocatechin, and epigallocatechin gallate
are found in certain seeds of leguminous plants, grapes, and more impor-
tantly in tea (Arts et al., 2000). Proanthocyanidins (condensed tannins) are
responsible for the astringent character of grapes, peaches, apples, pears,
berries, tea, wine, and bear. Flavanones are common in tomatoes, mint and
to a considerable extent in citrus fruit. Soya and its processed products are
the main source of isoflavones in the human diet. The importance of all these
antioxidant constituents of plant materials and other natural sources in the
maintenance of health and protection from coronary heart disease and cancer
is raising interest among scientists, food processors, and consumers as the
future trend is moving toward functional food with specific health effects.
The extraction of bioactive compounds is the first step in utilization of
natural antioxidants as additives in meat products. Generally the plant mate-
rial is cleaned, dried, and ground into fine powder followed by extraction.
The drying process has some undesirable effects on the constituent profile
of plant material; however, freeze-drying process retains higher levels of
phenolic content in plant samples than air-drying (Abascal et al., 2005).
There are many techniques to recover antioxidants from plants, such as
Soxhlet extraction, maceration, supercritical fluid extraction, subcritical
water extraction, and ultrasound assisted extraction but the solvent extrac-
tion process is the most commonly used procedure to prepare extracts from
plant materials due to their ease of use, efficiency, and wide applicability.
Table 3.1 represents the common solvents used for extraction of antioxi-
dant compound from different plant parts. Extraction efficiency is affected
by the chemical nature of phytochemicals, the extraction method used,
sample particle size, the solvent used, as well as the presence of interfering
substances (Stalikas, 2007) whereas the yield of extraction depends on the
solvent with varying polarity, pH, temperature, extraction time, and compo-
sition of the sample (Turkmen et al., 2006). Solvents, such as methanol,
ethanol, acetone, ethyl acetate, and their combinations have been used for