Applications To Health Promotion And Disease Prevention

Cashew kernel testa (skin) is an important by-product obtained during the processing of cashew. With an annual global consumption of over 1,000,000 tonnes of cashew kernel, the resultant testa is a serious option for commercial exploitation. Although the various biochemical constituents of cashew kernels have been characterized (Nagaraja & Nampoothiri, 1986; Nagaraja, 1987a, 1987b, 1989), literature pertaining to the composition of cashew kernel testa is minimal.

Cashew kernel testa has been reported to be a good source of hydrolyzable tannins (Pillai et al., 1963). The tannin content of cashew kernel testa from various varieties of cashew samples has been quantified, and reported to be higher than that of almond skin testa. Cashew kernel testa from different varieties and industrial samples has also been analyzed for protein, sugar, starch, and phenols, and significant variation in the composition of testa among different released varieties and industrial samples has been reported. Chromatographic studies show that the main constituents are catechins (Subramanian & Nair, 1969) especially (+) catechin and (—) epicatechin, which account for about 6 and 7.5%, respectively, of the dried cashew kernel testa. Together, they represent more than 40% of the total polyphenols. In cashew kernel testa, as in most other plant products, the polymeric proanthocyanidins account for a little less than 40%. The monomeric proanthocyanidins are represented by two leukocya-nidins and two leukopelargonidins. Leukocyanidin was found to be the predominant leukoanthocyanidin (Mathew & Parpia, 1970). However, leukopelargonidin was found to occur in larger amounts than leukodelphinidin. Earlier, Kantamoni (1965) had reported the presence of gallic, caffeic, and quinic acids, as well as a catechin and leukocyanidin. Our

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Various extracts of cashew kernel testa have also been analyzed for protein, carbohydrate, and fiber content. Methanol-extracted cashew kernel testa was reported to contain higher protein, carbohydrate, and crude fiber contents, compared to cashew kernel testa. Methanol extraction of cashew kernel testa also resulted in a considerable decrease in tannin content, while it improved the water absorption capacity, and the in vitro digestibility of protein decreased considerably. The protein and carbohydrate contents of methanol-extracted cashew kernel testa were slightly higher than the reported values (Nagaraja, 2000). Crude fiber from cashew kernel testa had lower protein, sugar, and in vitro digestibility of carbohydrates, compared to methanol-extracted cashew kernel testa. Elemental analysis of cashew kernel testa has shown that it is also rich in phosphorus, potassium, and calcium. Hence, cashew kernel testa, after suitable treatment, could be a good source for developing mineral-, protein-, and crude fiber-rich foods/animal feed formulations.

Free radical scavenging activity of cashew kernel testa (skin) extract

In view of the chemical composition of the cashew kernel testa, we undertook investigations in our laboratory to establish the free radical scavenging activity of ethanolic extract of cashew kernel testa (Kamath & Rajini, 2007). Dried cashew kernel testa obtained from a local cashew nut processing industry was sun-dried, pulverized in a multi-mill, and passed through a 0.5mm sieve to obtain a fine powder. The testa powder was mixed with five parts of ethanol, and kept in a rotatory shaker for 3 hours at 37° C. The extracts were separated by centrifugation, and used for quantitation of total phenolic compounds and assessment of free radical scavenging activities, employing a battery of in vitro assay systems.

The cashew kernel testa powder yielded large amounts of extract (0.45 g/g powder). The total phenolic content of cashew kernel testa extract determined using Folin-Ciocalteu reagent revealed the presence of 245 mg gallic acid equivalent of phenolic compounds/g powder. The antioxidant rich extract of cashew kernel testa was resolved by silica thin layer chromatog-raphy, and an antioxidant spot was visualized by spraying b-carotene-linoleate solution. HPLC characterization of the antioxidant spot yielded a peak similar to that of standard epicatechin (Figure 36.1), suggesting its predominant role in the antioxidative potential of the extract.

We assessed the free radical scavenging ability of cashew kernel testa extract by employing ABTS (2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)) radical and superoxide anion radical scavenging, deoxyribose oxidation, the P-carotene-linoleate model, and lipid peroxidation assay systems. Significant scavenging of superoxide anion radicals by cashew kernel testa extract was evident in a concentration-dependent manner, suggesting that cashew kernel testa extract possesses the potential to neutralize superoxide anion radicals. Cashew kernel testa extract also exhibited concentration-dependent scavenging of hydroxyl radicals — a property which could confer its potential to inhibit lipid peroxidation (Figure 36.2). Potent antioxidant activity of cashew kernel testa extract was also evident, as cashew kernel testa extract prevented linoleate-radical mediated discoloration of P-carotene (Figure 36.3).

We employed a rat brain homogenate system subjected to Fe2+-H2O2 induced lipid peroxidation as a test to assess the ability of cashew kernel testa extract to prevent lipid peroxidation. Our results clearly demonstrate that cashew kernel testa extract significantly inhibited the formation of thiobarbituric acid reactive species (TBARS) in rat brain homogenate (Figure 36.4), suggesting its potential to inhibit lipid peroxidation. Employing the deoxyribose system, we successfully demonstrated the hydroxyl radical scavenging activity of cashew kernel testa extract. Therefore, inhibition of induced lipid peroxidation in rat brain homogenate by cashew kernel testa extract may be attributable to its ability to scavenge hydroxyl radicals. Since

Superoxide

Hydroxyl

Superoxide

Hydroxyl

CKT fog)

FIGURE 36.2

Superoxide and hydroxyl radical scavenging effect of cashew kernel testa extract. The percent radical scavenging versus concentration of cashew kernel testa in the extract revealed a concentration-related response in both the assay systems. Results are expressed as mean ± SEM of three determinations each.

CKT fog)

FIGURE 36.2

Superoxide and hydroxyl radical scavenging effect of cashew kernel testa extract. The percent radical scavenging versus concentration of cashew kernel testa in the extract revealed a concentration-related response in both the assay systems. Results are expressed as mean ± SEM of three determinations each.

Time (min)

FIGURE 36.3

Antioxidant activity of cashew kernel testa extract in b-carotene-linoleic acid system. p-carotene undergoes rapid discoloration in the absence of an antioxidant (control). The presence of cashew kernel testa extract (20 mg) hindered the b-carotene destruction.

Time (min)

FIGURE 36.3

Antioxidant activity of cashew kernel testa extract in b-carotene-linoleic acid system. p-carotene undergoes rapid discoloration in the absence of an antioxidant (control). The presence of cashew kernel testa extract (20 mg) hindered the b-carotene destruction.

FIGURE 36.4

Inhibition of lipid peroxidation by cashew kernel testa extract in rat brain homogenate.

Peroxidation was induced in rat brain homogenate by ferrous chloride (FeCl2)—hydrogen peroxide (H2O2), and the extent of protection offered by cashew kernel testa extract against induced lipid peroxidation (LPO) was monitored by measuring the formation of TBARS at 535 nm. A concentration-dependent protection was offered by cashew kernel testa extract against LPO. Values are expressed as mean ± SEM of three determinations each.

FIGURE 36.5

Ferrous ion chelating effect of cashew kernel testa extract.

Cashew kernel testa extract exhibited a concentration-dependent ferrous ion chelating effect although at higher concentrations. Values are expressed as mean ± SEM of three determinations each.

TABLE 36.1 EC50 of Cashew Kernel Testa Extract in Various Antioxidant Assay Systems

Antioxidant Assay EC50

Superoxide scavenging® 10.69 ± 1.13

Deoxyribose oxidation® 17.70 ± 0.05

Iron chelation5 6.00 ± 0.24

The EC50 value in each assay was determined by regression analysis of activity as a function of concentration of cashew kernel testa in the extract. Values are mean ± SEM of three determinations. ®mg/ml extract bmg/ml extract.

metal chelation is an important antioxidant property, we evaluated the ability of cashew kernel testa extract to compete with ferrozine for iron (II). The study revealed that cashew kernel testa extract exhibited relatively lower iron-binding capacity (Figure 36.5). Table 36.1 shows data from various in vitro assays depicted as EC50 values. The order of effectiveness of cashew kernel testa extract in antioxidant assays was as follows.

ABTS > superoxide > deoxyribose > inhibition of lipid peroxidation > iron chelation

Therefore, the antioxidant property of cashew kernel testa extract may be attributable to its radical scavenging activity due to the presence of free radical scavenging polyphenols.

With establishment of the radical scavenging potential of cashew kernel testa extract in vitro, it was of interest for us to investigate whether the antioxidant potential of cashew kernel testa could be exploited to abrogate oxidative stress in vivo. Organophosphorus insecticides (OPI) are neurotoxicants that primarily act by inhibiting acetylcholinesterase enzyme. Alterations in glucose homeostasis are another aspect of OPI toxicity, and oxidative stress is believed to be one of the mechanisms of OPI-induced alterations in glucose homeostasis. We investigated the possible role of oxidative stress in alterations in glucose homeostasis induced by dimethoate (OPI). The strategy of providing cashew kernel testa extracts supplements to dimethoate-treated rats confirmed involvement of oxidative stress dimethoate-induced alterations in glucose homeostasis, as cashew kernel testa extract offered protection against dimethoate-induced oxidative stress in rat pancreas as well as alterations in glucose homeostasis (Kamath et al., 2008). The above two lines of investigation clearly establish the usefulness of cashew skin extract as an antioxidant, the activity of which is predominantly attributable to the presence of polyphenols that confer on cashew kernel testa an ability to scavenge free radicals. Cashew kernel testa, with its chemical composition of potent bioactive phenolic compounds, could be of interest to food and pharmaceutical industries, where it might be used as an additive or a source of natural antioxidants.

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