Postprandial effects of pecan nuts ingestion

ABSTRACT

Pecan nuts and walnuts are rich sources of polyphenolic compounds and nutrients, which have antioxidant capacity results in favorable reductions in plasma lipids and lipoproteins. However, the health benefits of these nuts may not be limited to blood lipid changes. There has been very little investigation into the contribution of bioactive components found in nuts to antioxidant protection. To assess the acute effect of treatment diet (75% of energy from pecan nuts) and control diet (habitual diet with no nut consumption) in healthy subjects on plasma total phenol content, antioxidant capacity and plasma lipid peroxidation.

Another setup compared the effect of another treatment diet (where 75% of energy from walnuts) and control diet. Twelve subjects participated in crossover design study. After an overnight fast, whole pecan, pecan smoothie, whole walnuts, walnut smoothie, and control diet will be consumed by study subjects. Each subject will participate on four occasions one week apart, consuming one of the diets each time. Blood samples will obtained at intervals up to six hours after consumption of the test meal.  It is expected that this proposal will provide baseline data needed to evaluate the protective effects of long-term pecan and walnut consumption.

 CHAPTER 1
INTRODUCTION

A. Statement of the Problem

Studies through the years have suggested the health benefits that can be derived from incorporating nuts in daily diet of humans. Pecans are rich sources of phytochemicals such as vitamin E, calcium, magnesium, potassium, zinc and fiber (Morgan, Bevwrly, & Clayshulte, 2000), as well as antioxidants that can have a unique effect on the body (Yochum, Folsom, & Kushi, 2000). Vitamin E in the form of tocopherol comes in different forms in pecan nuts, which protects fats from oxidation. The most abundant form is the gamma-tocopherol and an increase in concentration of gamma-tocopherol in the blood subsequently can reduce oxidation (Haddad, PJambazina, Tanzman, & Sabate, 2006). In addition gamma-tocopherol has a protective effect against prostate cancer and may protect the intestine. Pecans are also good sources of omega-3 fatty acids such as prevention of depression, which can interfere with brain function.

One study reported that pecans rank highest among all nuts and are among the top category of foods to contain the highest total anti-oxidant capacity (TCA) (Xianli et al., 2004). It is observed that 28.4 g (1 oz) of pecans had 5,095 TAC (Beans Blast Blueberries To Gain Antioxidant Crown, 2004), and a dietary fiber 9.00 g/100 g (Feldman, 2002). Plant sterols are also present in pecan nuts and these compounds are capable of lowering the cholesterol in the body. Pecan nuts contain about 95 milligrams plant sterols per 100 grams and most are in the form of beta-sitosterol. Beta-sitosterol lowers the level of blood cholesterol level through competing with cholesterol in the body. Thus, an increase in an intake of pecan nuts may also increase the amount of plant sterols in the body which in turn could benefit ones health (Eitenmiller, Rye, & Koehler, 2000).

Basically found in the majority of the world’s continents, walnuts are very abundant and are relatively popular among different peoples. This is a high lipid-containing nut that has antioxidative abilities. Walnuts are found to contain polyphenolic compounds such as ellagic and gallic acids that are very important in its function as a potential antioxidant. Like walnuts, pecans also contain a naturally class of phytochemicals which are known as natural polyphenols. Structurally polyphenols have one or more aromatic rings while functionally they help protect the plants against plant diseases and diseases associated with ultraviolet exposure Polyphenols also have an important role in preventing oxidation of cells hence it is one example of antioxidants.

Antioxidants prevent oxidation of compounds and in the process prevents the occurrence of an oxidative stress which is a condition wherein there is an excessive amount of species compounds reactive to oxygen (Scalbert, Johnson, & Saltmarsh, 2005). Biologically, oxidation may disrupt the integrity of cell membrane and may also interfere with the normal processing of DNA oxidative agents are considered as a potent danger to the body system. Natural polyphenols occur into different groups such as flavonoids, vitamins, phenolic acids, ellagic acid and many other others. An example of a polyphenol vitamin found among pecan nuts is gamma-tocopherol (Kim & Lee, 2004).

Antioxidants primarily work through the donation of an electron to a free radical with an unpaired electron. This is highly unstable and has a very high kinetic energy. Due to the spontaneous reaction of these free radicals of seeking an electron in order to complete their valence electron, cellular systems are destroyed. Therefore antioxidants protect these cellular organelles from damage such as burst and oxidation. This would result to the reduction of free-radical amplification induced by oxidative stress. Naturally occurring antioxidants such as vitamin E and selenium, are less effective radioprotectors than synthetic thiols but may provide a longer window of protection against lethality and other effects of low dose, low-dose rate exposures (Landauer, 2007). Several plants have been used to treat free-radical-mediated ailments because of the presence of antioxidants and, therefore, it is logical to expect that such plants may also render some protection against other threats to cellular systems (Gupta et al., 2004).

In a certain study conducted to compare the effect of a pecan diet on blood level of gamma-tocopherol compared with that of AHA Step I diet, it was found out that pecan diet resulted into a greater increase in the serum blood level of the gamma-tocopherol (Haddad, PJambazina, Tanzman, & Sabate, 2006).. The AHA Step I diet is the diet designed by the American Heart Association as part of the treatment among patients with elevated levels of blood cholesterol.

Also in the same research it was found out that the pecan diet increased the percentage of fat in stool hence it was suggested that the structure of the lipid-storing granules and fiber components in the pecan nuts do not permit a ready and easy absorption. In another research study, it was discovered that the pecan diet can also control biomarkers of heart disease risk just as effective as the AHA Step 1 diet. Moreover, it was found out that the participants who took the pecan diet have a marked increase in the level of dietary fiber, thiamin magnesium, copper and manganese and the pecan diet even resulted into adequate levels of magnesium intake as compare to the AHA Step 1 diet (Barloon et al., 2001).

The significance of this research is to help elucidate the health benefits that can be derived from including pecan nuts and walnuts in the normal diets as humans. This will enlighten some key concepts and mechanisms involved as to why consumption of walnuts and pecan nuts have related health benefits particularly that of their antioxidative property as a product of their active components like polyphenols specifically gamma-tocopherol. This research proves to be a noteworthy undertaking since the health effects that can be derived from pecan nuts are in indeed very helpful especially in preventing circulatory-related diseases. Ultimately, this research may provide knowledge as to how the antioxidative properties of pecan nuts reduce or prevent progression of disease which develops as a result of cellular oxidation.

B. Purpose of the Study

This research primarily aims to provide a greater knowledge about the polyphenols and their role in helping the body maintain oxidative balance. Specifically, the mechanism by which polyphenols protect the body against disease progression through examining the effect of nut consumption on in vivo changes in lipid peroxidation and antioxidant markers will be answered. Secondly, this study will also examine the change in the bioavailability of polyphenols in pecans. Finally, time trend of plasma total polyphenol levels before and after ingestion of nut-containing meal in order to obtain plasma peak concentration will be investigated in this study.

C. Research Questions

1. After pecan consumption is there any increase in plasma polyphenol concentration? After walnut consumption? After regular food intake?
2. When is the peak concentration for polyphenols in plasma after consumption of pecan-containing meal? After walnut-containing meal? After a regular meal?
3. After nut consumption is there any increase in plasma antioxidant capacity?
D. Theoretical Justification [or Mechanisms]

The protective effect of nuts, pecan and walnuts, against oxidation is accounted for the presence of antioxidants. Pecans and walnuts contain various forms of vitamins in the form of tocopherols, gamma-tocopherol being the most predominant. Vitamins, in turn are one of the categories of natural polyphenols which are known for their antioxidative properties. It was thought before that polyphenols and other antioxidants scavenge free radicals thus protecting the cell against oxidation but this mechanism is thought to be oversimplified (Davies & Kelly, 2004).

The metabolic processes in the body result in the formation of by-products, which could as free radicals. Among the reactive species that may be produced are hydroxyl radicals (.OH), superoxide anions (O2-), singlet oxygen (1O2), hydrogen peroxides (H2O2), organic peroxides (R-OOH), nitric oxide and peroxynitrite. These reactive molecules lack stability and are greatly reactive. Thus, they may disrupt the stability of lipid membranes the different organelles in side the cell even the DNA; they may also disrupt the integrity of the cell membrane. These reactive species may be acted upon by antioxidants through four ways: “(1) chain breaking; (2) reducing the concentration of reactive oxygen species; (3) scavenging initiating radicals, and (4) chelating the transition metal catalysts” (Fouad, 2005). Polyphenols such as gamma-tocopherol which is present in pecan nuts act by chain breaking reactions and they act in liquid phase to trap “ROD” radical (Fouad, 2005)..

Structurally, gamma-tocopherol does not possess one of the electron-donating methyl groups on its chromosomal ring making it a weaker antioxidant than alpha-tocopherol which is also present among pecan nuts. Gamma-tocopherol on the other hand is more efficient in trapping nitrogen-based free radicals called reactive nitrogen oxide species (RNOS) such as peroxynitrite and nitrogen dioxide.

Moreover, gamma-tocopherol can act against lipid peroxidation by donating a hydrogen atom to radicals. In addition, cells may react with polyphenols through reactions involving receptors or enzymes enabling signal transduction. In turn this results in modification of the redox status of the cell which may result into subsequent reactions of redox-dependent reaction (Halliwell, Rafter, & Jenner, 2005; Moskaug, Myhrstad, & Blomhoff, 2005; Rachmiel et al., 1996). This in turn may return the balance of the charge state of the cells thereby preventing the occurrence of oxidation such that of lipid peroxidation which is triggered by hydroxyl ions (Haddad et al., 2006).

Based from the study conducted by Haddad, Jambazina, Tanzman, & Sabate, 2006) which was previously mentioned above pecan-enriched diet increased the level of gamma-tocopherol. Measurement of the cholesterol-adjusted plasma gamma-tocopherol revealed a 10.1% increase among the blood samples of the participants after eating the pecan-enriched diet. This therefore proves the statement that pecan consumption can raise the plasma polyphenol level concentration since it was earlier mentioned that gamma-tocopherol is an example of polyphenol that falls under vitamin category (Haddad et al., 2006).

In the same study, the lipid oxidation was significantly reduced by 7.4% when compared with the Step 1 diet. Hence, this finding shows that after administration of the pecan-enriched diet can increase the plasma antioxidant capacity (Haddad et al., 2006).

E. Significance to Nutrition:

Advances in understanding the role of free radicals in the development of many chronic diseases suggest a potential health-promoting role of dietary antioxidants. Epidemiological studies have shown that consumption of phenol-rich foods such as fruits and vegetables correlates with reduced coronary heart disease mortality (Friedman & Kimball, 1986 and Knekt, Jarvinen, Reunanen & Maatela, 1996). In this study, we will extend the previous observations to polyphenols in nuts. Tree nut polyphenols might be effective inhibitors of lipid peroxidation and have antioatherogenic potential. Thus, the study results will serve as evidence that shows anti-oxidative effect of nuts in addition to their favorable lipid profile. Moreover, applications of this knowledge include recommendations by health professionals to encourage individuals to consume nuts in moderate amounts.

Essentially, the increased level of polyphenols in the blood such that of gamma-tocopherol present in pecan nuts may lead into many health benefits. On top of this is the prevention and protection against diseases which are eventually formed in consequence of oxidative stress. Through scientific studies it was known that pecan nuts may help prevent stroke by preventing formation of atherosclerosis which in turn is a consequence of oxidation of low density lipoprotein (LDL) (Yochum, Folsom, & Kushi, 2000).

Hence it has been associated with protective effects against cardiovascular-related diseases. Another health benefit that may be derived from pecan nuts may be protection against cancer since polyphenols are established to prevent oxidation of free radical which may trigger the formation of cancer. It was known from one study that polyphenols have anti-proliferative effects against growth of cancer cells in the breast (Damianaki & Bakogeorgou, 2000). Another study also reported that oral cavity-related cancer may as well be prevented by polyphenols (Sakagami & Oi, 1999). Still some studies assert the importance of polyphenol in achievement of normal brain function since it has been reported that Alzheimer’s disease may be associated with inadequacy of antioxidants.

Oxidative stress, which causes physical damage, can lead to heritable mutations that in the long-term can cause cancer, harm to reproduction and be potentially lethal for those affected. Therefore, protection from these harmful effects must be made. Walnuts and pecans are very common plants that comprise the human diet. Therefore exploring the possibility that they can effectively enhance human health is very essential. They contain polyphenolic compounds that are very important antioxidants.

They battle cellular damage due to oxidation and even promote cellular growth and repair. Research and experimentation on these compounds is very important, as these studies are precursors for the development of drugs combating existing and potential diseases such as cancer. Finding treatments against mutagenic substances will enhance the quality of life and will promote longevity. Thus with all of these benefits, antioxidants such as polyphenols are important parts of our diet in order to achieve a healthy system. Since it has been proven from one study the pecan nuts are indeed rich source of gamma-tocopherol it is therefore beneficial to include them as part of the daily diet.

Figure 1 The protective effects of pecan nuts and walnuts against oxidation

Figure 2 The role of metabolic processes in the body result in the formation of free radicals.

.OH

.OH

CHAPTER 2
REVIEW OF LITERATURE

According to a report of the American Diabetes Association (2002, p. 202), many experimental studies have shown that plasma LDL cholesterol levels can decline through a high carbohydrate low saturated fat diet. “Postprandial levels of plasma glucose, insulin, and triglycerides (ADA, 2002, p. 202) can be increased by this dietary design. This can also cause plasma HDL cholesterol decrease relative to results of “isocaloric high monounsaturated fat diets” (ADA, 2002, p. 202). Therefore, experts have suggested that there should be dietary interventions in order to promote the prevention of many kinds of diseases.

It is essential that alternative diets be formulated in order to impose effective blood lipid profile modification, which would lead to the reduction of risk towards serious ailments and diseases. One of the proposed methods is the introduction of nuts into the diets of individuals in order to protect them from diseases, such as coronary heart disease (Rajaram et al., 2001, p. 2275). According to different epidemiologic studies conducted, incorporation of nuts in human diet can decrease the levels of morbidity and mortality due to coronary heart disease. This is also applicable to other kinds of ailments and diseases. This advantage can be attributed to the effect that nuts induce where lipoprotein cholesterol levels are lowered (Kris-Etherton et al., 2001, p. 103).

Pecans are rich sources of phytochemicals such as vitamin E, calcium, magnesium, potassium, zinc and fiber (Morgan et al., 2000), as well as antioxidants that can have a unique effect on the body (Yochum et al. 2000). Pecans are also good sources of omega-3 fatty acids which plays several important roles in brain function. One of those roles may be to help prevent depression, which has a direct effect on brain function and the ability to think clearly. Pecans contain different forms of vitamin E – known as tocopherol which protects fats from oxidation. Pecans are especially rich in one form of vitamin E – gamma tocopherol. An increased level of gamma tocopherol concentrations in the blood subsequently reduces a marker of lipid oxidation (Haddad, et al., 2006).

Xianli Wu et al., (2004) reported that pecans rank highest among all nuts and are among the top category of foods to contain the highest total anti-oxidant capacity (TCA). It is observed that 28.4 g (1 oz) of pecans had 5,095 TAC (Vegparadise News Bureau, 2004), and a dietary fiber 9.00 g/100 g (Feldman, 2002). Plant sterols, widely researched and touted for their cholesterol-lowering ability are found naturally in pecans. They contain as much as 95 milligrams of plant sterols per 100 grams – 90 percent of which is in the form of beta-sitosterol. Beta-sitosterol as a food component competes with the absorption of cholesterol in the body, and thus has the ability to lower blood cholesterol levels. By increasing consumption of pecans (or peanuts), a person could easily raise the plant sterol levels in the diet to the point where health effects have been proven (Eitenmiller, 2000).

Haddad, et al., (2006) reported that the pecan-enriched diets significantly reduced lipid oxidation (by 7.4 percent) versus the Step I diet, and the blood levels of tocopherols were higher after participants were on the pecan diet. Cholesterol-adjusted plasma gamma-tocopherol in the study participants blood samples increased by 10.1 percent (P < .001) after eating the pecan diet. Another key research finding was beyond the reduced level of blood lipid oxidation, the various phytochemicals found in pecans seem to be protective of the pecan’s high levels of unsaturated fat. All unsaturated fats in foods can be prone to oxidation themselves (which some may describe in foods as rancidity). Pecans, while high in unsaturated fat, are “self-protective” due to their vitamin E content (tocopherols) and relatively high content of complex phytonutrients, some of which have been identified as proanthocyanidins, or condensed tannins, which are recognized for their ability to slow the oxidation process.

Diets that are high in monounsaturated fat (MUFA) have been associated with reducing the risk of cardiovascular disease. According to this scientific statement from AHA’s Nutrition Committee, there is epidemiological evidence that dietary monounsaturated fats (MUFAs) have a beneficial effect on the risk of (CHD). Kris-Etherton et al., 1999 from epidemiological studies concluded, there is consistent evidence, that nuts have a strong protective effect against coronary heart disease (CHD). From the of clinical database studies it is evident that the cardio protective effect of nuts is due to their favorable effects on plasma lipids and lipoproteins, owing to their fatty acid composition when they replace dietary saturated fat and/or carbohydrates.

Rajaram et al., (2001) reported the effects of a pecan-rich diet on serum lipids and lipoproteins in 23 normocholesterolemic males and females. After a run-in period of 2 weeks on a “typical American” diet, subjects were fed for 4 weeks either the pecan diet or a Step 1 diet in a randomized, controlled, crossover design. The pecan diet was higher in total fat (42 vs. 30%); both diets had 8% long chain saturated fatty acid whereas the pecan diet was higher in MUFA (24 vs. 15%) and PUFA (10 vs. 7%). The pecan diet significantly lowered total cholesterol (11.3% compared with 5.2% on the Step I diet) and LDL cholesterol (16.5% compared with 6.7% on the Step I diet). In fact, the pecans doubled the cholesterol lowering ability of the Step I diet. The pecan diet increased HDL cholesterol levels whereas the Step I diet decreased HDL unfavorably. Triglycerides also were significantly lower with the pecan diet. Although the pecan diet contained more fat (39.6%) than the Step I diet (28.3%), participants did not gain weight.

Haddad et al., (2001) studied evaluated effects of a pecan-enriched diet on serum gamma tocopherol levels by using blood samples from the same research participants studied by Rajaram et al (2001). From the data it was concluded that the pecan-enriched diet significantly raised blood levels of gamma tocopherol compared to the AHA Step I diet. This is due to the high amounts of naturally occurring gamma tocopherol (a unique form of vitamin E) in the pecans.

The gamma tocopherol-to-cholesterol ratio was higher on the pecan-enriched diet compared to the control diet. According to Dr. Haddad, gamma tocopherol is an important antioxidant nutrient. Studies have shown that it may benefit intestinal health and have a protective effect against prostate cancer. They also observed that the pecan diet increased stool fat excretion. Stools were collected for 48 h in six subjects during each of the diet periods. Stool fat (25 g pecan, 6 g Step 1) and the percentage of fat in the stool (8% pecan, 3% Step 1) increased significantly with the pecan diet. These changes may explain, in part, why the added fat or calories in a nut-based diet do not lead to weight gain. The pecan fat may not have been as well-absorbed because of the structure of lipid-storing granules in nuts or the fiber components of the nuts.

Researchers at Texas A&M University discovered that a heart-healthy diet containing pecans can help control specific biomarkers of heart disease risk as effectively as the AHA Step I diet. Jessica Barloon et al., (2001) observed significantly increased levels of dietary fiber, thiamin, magnesium, copper and manganese in the participants by studying forty hypercholesterolemic men and women between the ages of 22 and 71, all of whom had already been eating a relatively low-fat diet. During the eight-week, randomized, controlled feeding trial, participants were placed on either the AHA Step I diet or an isocaloric but higher-fat, pecan-based diet. the pecan-rich diet significantly increased participants’ levels of dietary fiber, thiamin, magnesium, copper and manganese and actually changed dietary copper and magnesium intakes from inadequate (on the AHA diet) to adequate (on the pecan diet).

An epidemiological study of food intake and health outcomes of 34,492 post-menopausal Iowa women conducted by Yochum et al., (2000) evaluated the relationship between antioxidant vitamins intake and stroke. The researchers found that death from stroke was 60 percent lower among those consuming the most vitamin E from foods when compared to those who consumed the least. These findings are of particular importance as the Recommended Daily Intake (RDI) for vitamin E was recently raised for both men and women. This population research suggest that eating foods like pecans – which are rich in a number of healthy nutrients, including vitamin E – helps increase levels of vitamin E in the diet. The higher intakes of vitamin E from foods (compared with lower intake from foods) may be associated with a lower risk of death from stroke. Vitamin E is a free radical scavenger and thus may help prevent oxidation of LDL, an important step in the atherosclerotic process.

Pecans are included in the American government’s newest dietary guidelines because of their high concentration of important nutrients and proteins(Dietary Guidelines for Americans, 2005). The monounsaturated fat in pecan is not only protective against heart disease but also controls diabetes (Franz et al., 2002). Thus intake of pecans reduces the risk factors and provides good health.

Walnuts are otherwise known as Juglans sp. that has a vast geographic range. It is found in America, Europe, Africa, and even Asia where its timber is much utilized for construction and furnishing projects (Das et al., 2001 p. 1). Walnuts are primarily part of the traditional diet of peoples found in the Mediterranean, South America, and Asia, where they are usually processed into ingredients of different kinds of food, including those created as sauces, stuffing, entrees, snacks, appetizers, and desserts. Since 7000 BC Persia, walnuts have always been present in the daily human food intake. Walnuts are nowadays used in the production of cereals, multigrain breads, and other food related products that are part of every person’s everyday life (Feldman, 2002, p. 1073S).

In comparison to other available monounsaturated fatty acid containing nuts, walnuts have the advantage of being enriched with n-6 (linoleate) and n-3 (linolenate) polyunsaturated fatty acids. Some of the other benefits that walnuts offer include its low lysine-arginine ratio, high arginine, folate, fiber, tannins, and polyphenol content. Despite the fact that walnuts are mainly composed of fatty acids, research studies have demonstrated that walnut intake does not result to a net gain weight when consumed to replace regular diet (Feldman, 2002, p. 1062S)

There are numerous historical medicinal uses of walnuts. During the times of American Indians, walnuts were used at laxatives and also as remedies for toothaches. The husks of walnuts are still used against inflammation and also against skin diseases. The juice from walnut husk is also used as treatment for ringworm while the bark is used for cure against dermatomycosis. Although it cannot synthesize any actual cure for any kind of disease, walnut pollen instead has a medical significance as a common allergen (Das et al., 1979 p. 1).

Walnuts are composed of different forms of molecules. According to the US Department of Agriculture, Agricultural Research Service (1999, p. 104), walnuts are have a very high fat content, and are therefore packed with much energy with high amounts of protein, potassium phosphorus, and folate, with adequate levels of fiber and vitamin E. Another nutritional value that walnuts have is that it contains potassium, with 441mg/100 g edible portion. Walnuts’ lipid contents mainly include oleic acid and linoleic acid, but it predominantly consists of palmitic and stearic acids. Also, essential to this study, walnuts are found to contain tocopherols. Unlike in other kinds of nuts, these tocopherols found in walnuts are distinctly enriched in gamma tocopherol. Also found in walnuts are two important polyphenols, namely gallic and ellagic acids. Studies have revealed that walnuts can potentially combat Alzheimer’s disease due to their content of the mentioned acids (Feldman, 2002, p. 1073S).

Polyphenols possess a vast range of characteristics and properties that vary according to their structures. They coloration may be in “yellow, orange, red, or blue pigements, as well as various compounds involved in food flavor” (Cheynier, 2005, p. 227S). Vanillin and eugenol are two examples of polyphenols that have relative volatility. These two polyphenolic compounds are responsible for the smell of cloves, making them essential causes of odors in different plants. Although these are the odor associated with these two compounds, polyphenols in general are mainly related to tastes of bitterness and astringency. Other contributing benefits of polyphenols include their radical-scavenging ability, and capacity to react with proteins (Cheynier, 2005, p. 227S).

This group of chemical compounds function in protecting individuals from the hazardous effects of diseases. They also function in preventing or delaying the manifestations of aging. As antioxidative compounds, they maintain cellular systems and prevent their damage due to the action of free radicals (atoms that are highly reactive). An example of harmful oxidation effects is the action of oxygen when it reacts with low-density lipoprotein. When oxidation occurs, this cholesterol adheres to the body’s arteries, which leads to what is known as coronary heart disease. These compounds also have the ability to block enzymatic activities that enable the development of cancer. They have the capacity to deactivate and disable substances functioning for the promotion of metastasis of cancer cells. Epigallocatechin-3-gallate is the most associated polyphenol in cancer studies (Medicine Net, 1996).

Polyphenols are naturally occurring compounds that form a large family. These are highly distributed in human food intake, especially plants. There are different categories to which polyphenols are classified. The main divisions are phenolic acids, stilbenes and lignans, and flavonoids (Urquiaga and Leighton, 2000). These compounds compose the majority of the antioxidants humans incorporate in their diet. Since polyphenols have antioxidants that have potential abilities of preventing the occurrence of many forms of diseases, scientists have demonstrated much interests in studying this phytochemical group (Moskaug et al., 2005, p. 277S). The level of polyphenol consumption in human diet is between 200 mg up to 1 g. These figures are considered higher than the levels of other antioxidants that are also usual in foods that humans eat. Comparing this amount to levels of vitamin C and vitamin E, polyphenols are found to be more than 10 times and 100 times higher respectively. They are commonly found in plants, vegetables, coffee, and wine. All these are food sources that primarily comprise the human typical diet (Scalbert et al., 2005, p. 215S).

Majority of the polyphenols that humans take are flavonoids, while a major but less fraction belongs to phenolic acids. Phenolic acids are basically widely distributed among main food sources (Scalbert et al., 2000, p. 2074S). Caffeic acid, courmaric acid, and vanillin are all examples of phenolic acids. This is a highly diverse category, which includes hydroxybenzoic acid (p-hydroxybenzoic, gallic acid, and ellagic acid) and hydroxycinnamic acids (p-courmaric, caffeic acid, ferulic acid).

These are respectively found in forms of glucosides and simple esters respectively. Flavonoids are another subcategory of polyphenolic compounds that are highly distributed but in a non-uniform manner. Flavonoids are further divided depending on their degree of oxidation of oxygen heterocycle. Belonging to this subclass are anthocyanins, catechins, flavonols, flavones, Quercetin, Isoflavones and more (Sahelian, 2007). Stilbenes are not very common among plant foodstuffs. However, one of the compounds belonging to this class, reservatrol, is a plant with medicinal value that has manifested certain antimutagenic abilities. Lignans, like Stilbenes, are rare and are still relatively not intensively explored by scientists (Scalbert at al., 2000, p. 2075S).

Majority of the polyphenols found in plants are called anthocyanins. This includes colors red, purple, or blue. These species are intensely unstable, and therefore very reactive. Once they are exposed in water molecules, “the anthocyanin red flavylium cations are converted to several other forms” (Cheynier, 2005, p. 227S) with the mechanism of protonation and hydration.

Polyphenols, when consumed and have been directed into the digestive system, have a relatively high intestinal absorption. But after 10-100 mg consumption of a polyphenolic compound, an individual’s concentration of plasma seldom rises above one micromole. This measurement figure is an indication that there are higher amounts of phenolic compound present in unknown metabolite forms. They can either be produced within an individual’s tissues or through the aid of a colonic microflora (Scalbert at al., 2000, p. 2075S).

The antioxidative ability of both walnuts and pecans can be attributed to their polyphenolic content. Epidemiological studies have revealed that increasing the consumption of foods containing polyphenolic compounds can protect cells from oxidative damage, and therefore prevent individuals from acquiring unwanted diseases (Urquiaga and Leighton, 2000). There is an extensive range of beneficial effects that polyphenols provide due to their antioxidant properties. According to Frankel et al. (1993), in vitro studies reveal that these compounds have the ability to inhibit the oxidation of LDL. In a separate research conducted by Fuhrman et al. (1995), providing subjects with polyphenol containing red wine also caused the reduction of oxidation susceptibility.

Based on these laboratory results, scientists believe that it is probable that polyphenolic compounds can also protect individuals from oxidative damage on DNA by preventing LDL oxidation (Urquiaga and Leighton, 2000). There are different kinds of polyphenols that demonstrate anticarcinogenic and antimutagenic effects. These polyphenolic molecules can disrupt the process of tumor development as it can inactivate carcinogenesis and inhibit mutant gene expression. Other studies have revealed that polyphenols can prevent cellular oxidation and therefore protect DNA and genetic expression by initiating and promoting mechanisms that combat the progression of tumors (Feldman, 2002, p. 1073S).

The presence of polyphenols allow for the prevention of oxidation. Being an antioxidant agent, polyphenols have the ability to scavenge free hydroxyl and peroxy radicals. And as metal-chelating compounds, they manage to decrease the superoxide-driven Fenton reaction. This said reaction is nowadays regarded as one of the most significant pathway to active oxygen radicals (Hosseinimehr et al., 2003). With these under consideration, scientists have found that oxidative stresses are prevented through exposure of cellular systems to antioxidants. One of the mechanisms proposed by scientist as how these agents accomplish their protective function is through Repair by Donation of Hydrogen Atoms (Casarette, 1968, p. 233). If a molecule (RH) is converted by radiation (either by direct or indirect mechanisms) into a free radical Ro

RH→ Ro + H
It may undergo a variety of reactions such as crosslinking
Ro + Ro → R-R
Or peroxidation.
Ro + O2 → RO2o
A protective agent may donate a hydrogen atom to the radical, restoring it to its original state
(Caserette, 1968, p. 234).
Ro + PH → RH + Po

Despite the fact that there are several proposed mechanism that would allow experts to explain the phenomena occurring through the functioning of polyphenols, much is yet to be discovered concerning this group of molecules. It has been established that intestinal microflora do metabolically process these polyphenols and allow the intestinal walls to absorb them. Other molecules, on the other hand, are not metabolized until the process of absorption is finish.

Therefore, scientists are yet to analyze the specificity and the localization of the metabolic activities of polyphenols. The metal-chelating functions of polyphenols are explored in a study conducted by Morel et al. (1998). But results are not conclusive and only lead to the question whether polyphenols participate in metal metabolism. The antioxidative properties of polyphenols are much acknowledged by experts. However, due to the relative addition that polyphenols give the overall antioxidant capacity of the blood plasma, there is an inadequate amount of information on the actual concentration of the polyphenolic molecules in circulation (Scalbert et al., 2005, p. 215S).

In a study conducted by Halliwell et al. (2005, p. 268S), the researches investigated whether polyphenols are actually antioxidants or not and whether they directly affect cellular systems. Scientists have always speculated that the health benefits of different foods and beverages are due to their phenolic content. The researchers argued that indeed, phenols are can directly cause an impact on an individual’s gastrointestinal tract in conditions where these compounds are high in concentration. These direct effects include the “binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases” (Halliwell et al., 2005 p. 268S). The researchers also affirmed that both tocoperhols and tocotrienols have health benefits on human digestive system. They also asserted that phenols have physiological benefits when returned to the digestive tract through the action of liver using bile.

Conclusion

In summary, although several in vitro and in vivo studies have been conducted on variety of polyphenol-rich foods, no in vivo study has been performed on nuts in particular. Plasma polyphenol levels, plasma antioxidant concentrations and inhibition of lipid peroxidation should be investigated in nuts.

References

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