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Effect of Bioactive Components on Dough Rheology, Baking, and Extrusion

Effect of Bioactive Components on Dough Rheology, Baking, and Extrusion

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Fruit and Cereal Bioactives: Sources, Chemistry, and Applications

The increased recognition of the role food plays in disease prevention has necessitated a search for

strategies to improve the health profile of food. Food scientists and processors are constantly searching

for ways to increase the levels of beneficial dietary components in foods people consume every day.

Cereal grain is the single commodity group that is most widely and consistently consumed by humans

around the world, and thus present excellent opportunity to promote healthy eating. Additionally, whole

grain-based products have been associated with various health benefits (discussed in a separate chapter).

Unfortunately, most consumers prefer refined grain products that are of low nutritional quality. The challenge is thus to transform whole grain-based products into foods that meet consumer sensory expectations. An understanding of how the health-promoting whole grain components behave during processing

is key to optimizing their use in food products.

Effect of Bioactive Components on Dough Properties

As mentioned above, bioactives in cereal are a complex mixture of compounds. These compounds work

together in ways that are not fully understood to affect dough properties and final product quality. Among

the most prominent components of cereal bran that have been studied in isolation for their impact on processing are dietary fiber components and antioxidants. We will look at each of these components briefly

as they impact dough properties and product quality.

Despite the well-known health benefits of consuming whole or unrefined grain products and a generally well aware consumer base, whole grain consumption remains low. Most consumers prefer refined

cereal products primarily due to inferior sensory profiles of the whole grain products; especially a dull

appearance, firm or coarse/gritty texture, and harsh flavor. Food manufacturers are constantly struggling

to improve sensory profile of these products. Another problem food processors have to contend with is

that the whole grain constituents (e.g., dietary fiber) that are known to produce health benefits typically

also have a negative impact on product handling during processing. For example, whole wheat or wheat

bran fortified flour produces dough that is difficult to handle and process. Common problems include

altered water absorption, which can impact dough stickiness and stiffness, as well as reduced ability of

key ingredients, proteins and starch to form the desired network and consistency.

Dietary Fiber

The bulk of the undesirable characteristics of the whole wheat dough system can be attributed to soluble

and insoluble fiber components (mostly nonstarch polysaccharides) of the bran. Proper gluten network

formation via disulfide cross-linking during mixing is critical for the viscoelastic properties of the dough

that allows it to trap gases during proofing and produce the desirable texture of bread during baking.

Any ingredient that dilutes available gluten or alters its ability to cross-link will invariably affect dough

rheology and product quality. Bread and related systems are highly dependent on proper gluten network

formation for their quality, and are generally more adversely affected by bran components than other

products like cakes and cookies that do not require a strong gluten network.

An obvious effect of bran dietary fiber components on dough is the dilution of gluten, which reduces

effective gluten concentration and thus its ability to form a proper viscoelastic network during mixing.

However, research shows that the detrimental effect of bran fiber components on wheat dough rheology

and subsequent product quality (e.g., loaf volume) is generally higher than what would be expected of the

dilution effect on gluten alone (Lai, Hoseney, and Davis 1989). This indicates that the bran components

are involved in both physical and chemical interactions during processing.

Mechanisms by which Fiber Affect Dough Rheology and Product Texture

Insoluble Fiber Components

Effect of whole wheat dietary fiber is twofold. Insoluble fiber particles (mostly lignocelluloses) are fairly

rigid and do not hydrate easily thus can weaken dough by cutting gluten strands or interfering with their

Effect of Bioactive Components on Dough Rheology, Baking, and Extrusion


formation. As expected, the more coarse the fiber particles, the more they affect gluten network formation and products quality. Fine grinding of wheat bran has long been known to significantly improve its

functionality as an ingredient in baking (Lai, Hoseney, and Davis 1989); this may be partly due to an

increased surface area for more rapid hydration and thus improved pliability, as well as reduced ability

to physically interfere with gluten strands. The knowledge of improved functionality of finer particle size

bran was recently employed by major commercial bakers in the United States to produce the relatively

successful “whole wheat” white bread, which combined ultrafine grinding of wheat bran with improved

nonpigmented wheat varieties.

Soluble Fiber Components

The other major effect of dietary fiber on dough rheology is related to water absorption properties of the

soluble fiber components. One of the most obvious initial effects of bran addition to cereal dough systems is the increased demand for water to form workable dough. Cereal brans, depending on the source,

contain significant quantities of soluble fiber that is capable of binding large amounts of water relative to

its weight. For example, in commercial refined wheat flour the water soluble fiber components typically

constitute less than 1% by weight, but are believed to account for 20–30% of dough water absorption.

In whole grain flour or flour fortified with wheat bran where the soluble fiber proportion level is much

higher, the effect on dough water absorption is usually more pronounced.

On the surface, the dough water absorption problem should be easy to fix by just adding more water.

However, it is not this simple for two reasons: First, bran particles are difficult to finely grind and thus

tend to produce relatively large particles. The large bran pieces will absorb water relatively slowly; that

is, diffusion of water to the center of each particle will take a long time. Secondly, the soluble fiber

components, like highly branched arabinoxylans, or mixed linkage β-glucans (commonly designated

“β-glucans”) are usually part of a cell wall structure and are thus embedded in an insoluble cell wall

matrix; this further slows their rate of water absorption.

The consequence of the above scenarios is that if the theoretical correct amount of water (based on

known absorption potential of bran constituents) is added to flour at the beginning of mixing, the dough

will be very sticky and difficult to work and process since there is effectively too much free water in the

system that is not yet taken up by bran soluble fiber. On the other hand, the addition of less than the correct amount of water will lead to a dough that may be workable at the beginning, but will stiffen and feel

dry with time (e.g., during proofing) due to continued slow absorption of water by the bran soluble fiber.

The soluble fiber effectively competes with gluten for moisture and thus leads to the loss of viscoelastic

properties of gluten. An experiment by Lai, Hoseney, and Davis (1989) neatly demonstrated this concept

using bread dough as a model. These authors reported that when the slow water absorption property of

wheat bran was partially overcome by fine grinding and presoaking the bran for several hours in water,

the resulting loaf volume was significantly improved to a level equivalent to what would be expected of

inert fiber (i.e., by dilution effect alone). They further demonstrated that the effect of wheat bran on water

absorption was the biggest contributor to reduced loaf volume of bran fortified flour.

Similar effects are seen in most dough systems that involve substituting cereal endosperm with whole

grain or bran components. However, since different cereal grains have different soluble fiber composition, effects can vary widely. In general, the net effect of bran fiber components on gluten network will be

to impede extensibility of dough and its functionality during the baking process, which results in adverse

effects like reduced loaf volume, increased rate of firming of the bread, reduced flexibility of tortillas,

reduced spread in cookies, and so on. The bran fiber components may also impede starch swelling and

gelatinization by limiting available water, and also interfere with starch reassociation after baking, thus

further impacting texture.

Overcoming Negative Effects of Whole Grain Fiber

To overcome the above mentioned problems typically require the use of additional ingredients to improve

product quality. Gluten isolate can be used to partially overcome the diluting effect of whole grain/bran

components and also compensate for some of the lost functionality of flour gluten due to the presence of


Fruit and Cereal Bioactives: Sources, Chemistry, and Applications

fiber. Commercial hydrocolloids (water soluble polysaccharides) of known functionality (e.g., carboxymethylcellulose) are also commonly used to help overcome the problem of poor texture (e.g., crumbly

tortillas) and dry mouth feel of bran/fiber-enhanced grain products. These commercial soluble polysaccharides have advantage over whole grain soluble polysaccharides in that they are of known composition

and predictable functionality. But even more importantly, they are designed to solubilize rapidly and

thus can provide highly controlled functionality. The main effects include improving product moistness,

yield, softness, pliability, and so on, all of which are related to their ability to retain moisture.

Surfactants like sodium stearoyl lactylate (SSL) will also generally improve dough handling and product texture by partially bonding with and “blocking” the water soluble NSP hydroxyl groups, creating

hydrophobic regions that limit the NSPs ability to cross-link via hydrogen bonds or to trap and retain

water. This mode of action of the surfactants also reduces the ability of gelatinized starch to retrograde

and form junction zones after baking, which contributes to the longer shelf life of whole wheat bread and

related products.

Resistant Starch

Another strategy that is becoming increasingly popular, is the use of resistant starch as an ingredient

to boost dietary fiber in baked products. Resistant starch obtained via physical (usually by annealing

or controlled temperature treatment) or chemical means (usually by cross-linking) have been shown in

limited studies to produce similar physiological effect as soluble dietary fiber. In terms of processing,

resistant starch offers a huge advantage over other forms of dietary fiber in that it is bland, very white,

and of fine particle size, thus physically near identical to refined wheat flour. Additionally, resistant

starch can be custom-made to behave like inert fiber (i.e., very limited water absorption capacity), and

thus will generally not produce any adverse effects in dough handling or baked product quality beyond

that expected from gluten-diluting effect. The diluting effect can be readily overcome by using stronger

gluten flour or adding gluten to the system as some studies indicate.

In the recent years, technology has allowed for the development of resistant starch that is virtually

100% dietary fiber (Woo, Maningat, and Seib 2009); this provides significant room for flexibility in terms

of level of incorporation to achieve desired dietary fiber level in the product. Some authors have reported

that products made with resistant starch can be of better quality (measured by textural profile and consumer acceptance) than products made with refined flour alone (Sharma, Yadav, and Ritika 2008). They

are thus becoming attractive as potential ingredients to “stealthily” boost dietary fiber intake and health

profile of refined cereal grain products.


Redox Status and Dough Rheology

The viscoelastic properties of wheat gluten make wheat a unique and hard to replace commodity utilized

in many cereal products. The viscoelastic properties of gluten are primarily due to the interaction of glutenin and gliadin fractions of the wheat protein. Development of the dough during mixing requires the

formation of disulfide bonds between thiol groups of cysteine residues of gluten. Disulfide bonds act to

stabilize the gluten network by enhancing protein folding and thus lowering its entropy. These bonds can

also enhance protein–protein hydrophobic interactions by enhancing local concentration of protein residues and thus lowering the effective local concentration of water molecules; this in turn lowers the ability

of water molecules to attack amide–amide hydrogen bonds and break up secondary protein structure.

The extent of disulfide cross-linking during dough development is enhanced in oxidizing environment, where the thiols are readily oxidized to disulfides as illustrated in Equation 16.1.

2 R-SH + Br2 → R-S-S-R + 2 HBr.


For this reason, oxidizing agents such as potassium bromate, calcium peroxide, and ascorbic acid are

often used to improve dough strength and loaf volume. In fact ascorbic acid (or more precisely its oxidized

form, dehydroascorbic acid) has long been recognized for its ability to strengthen dough and enhance

Effect of Bioactive Components on Dough Rheology, Baking, and Extrusion


loaf volume ( Melville and Shattock 1938; Meredith 1965). On the other hand, the disulfide bonds are

generally unstable in reducing the environment. Consequently reducing agents, such as sodium bisulfite

or cysteine can significantly reduce dough mixing tolerance and strength. The effect of reducing agents

on dough rheology is easy to demonstrate: the excess addition of cysteine to wheat dough formulation

will lead to a completely inelastic gooey mass after a relatively short period of mixing. This is because

the excess cysteine will readily reduce all disulfide linkages formed during mixing to form cystine residues and thus prevent the gluten from forming the viscoelastic network.

The reducing effect of cysteine is sometimes applied in tortilla manufacturing to slightly weaken the

gluten in the relatively strong bread flour commonly used in these formulations. Adding just the right

amount of reducing agent will ensure that only a limited number of the disulfide linkages are reduced

and so the dough will retain most of its elasticity. A slightly weakened gluten is important in tortilla processing to prevent the spring-back effect and produce a large diameter product. Spring-back is where the

dough tends to shrink back after being pressed into a disk, usually due to too much elasticity. An added

benefit of slightly weakening the gluten is that the product is less chewy.

Whole Grain Antioxidants and Dough Rheology

Among the most valuable bioactive compounds in whole grain cereals are the phenolic antioxidants.

The compounds, mostly concentrated in bran, are believed to contribute significantly to health benefits

reported for whole grain products, including promotion of cardiovascular health and chemoprotective

properties (discussed in a separate chapter). In wheat, like most commonly consumed cereal grains,

ferulic acid and its derivatives, is the most abundant phenolic compound, and probably the most widely

studied for its effect on dough properties. As stated earlier, the presence of wheat bran generally has a

negative effect on dough rheology and handling, which is partly due to the soluble and insoluble fiber.

However, another component of wheat bran that negatively affects dough handling is the phenolic group

of compounds, primarily ferulates.

Through their action as antioxidants, phenolic compounds have long been recognized for their reducing reaction on gluten disulfide cross-linkages, which induces dough breakdown during mixing, thus

reducing dough stability (Dahle and Murthy 1970; Weak et al. 1977). This in turn results in reduced loaf

volume and overall product quality. Other structurally different phenolic compounds, like flavonoids,

whether inherent in cereal grains or added to flour (e.g., catechin; Wang et al. 2006), have been shown to

negatively impact dough quality and loaf volume in a similar manner as the ferulates. This confirms that

the antioxidant mechanism that is beneficial from a health perspective is detrimental to dough properties

and product quality.

With the growing recognition of the importance of antioxidants in diet and the need to enhance antioxidant profile of cereal-based foods, considerable research has gone into devising mechanisms to reduce

the negative impact of antioxidants on dough rheology and product quality. One mechanism that has

been considered promising is the induction of new gluten cross-linkages that are independent of the

disulfide–sulfhydryl (disulfide–thiol) interchange reaction, and thus not sensitive to the redox state of

the system. The use of transglutaminase, an enzyme that catalyzes acyl-transfer reactions, producing

covalent cross-linking among proteins via the formation of inter- and intramolecular glutamyl and lysine

isopeptide bonds, has been considered in this regard. Even though this enzyme is widely used in the meat

industry as a protein binder (e.g., for making imitation crab meat), its use in the baking industry has not

been investigated very much.

Various reports have shown that the use of transglutaminase can strengthen dough and improve its

mixing properties in ways that are somewhat similar to the effect of oxidizing agents (Bauer et al. 2003).

In fact transglutaminase has been suggested as a modifier of protein functionality in gluten-free bread

(Moore et al. 2006). However, a recent study did not find any significant improvement in dough rheology

(mixing tolerance and elasticity) by transglutaminase when ferulic acid was also added as the antioxidant

at 250 ppm, even though the transglutaminase did seem to reduce dough stickiness (Koh and Ng 2009).

The resulting loaf quality (volume and rate of firming) were also not improved by transglutaminase. The

authors indicated that their transglutaminase use level might have been too low to produce the desired

effect. In fact other studies have indicated that a higher level transglutaminase than used by these authors


Fruit and Cereal Bioactives: Sources, Chemistry, and Applications

may be necessary to enhance dough quality (Bauer et al 2003). However, among the problems that will

need to be overcome in optimizing transglutaminase functionality is the fact that it tends to stiffen the

dough (reduces dough extensibility), which often can result in reduced loaf volume and rapid firming of


In dough systems that are less dependent on a proper gluten network formation for product quality

(e.g., in cookie dough), antioxidants generally have minimal effect on dough quality and product textural

properties (Nanditha, Jena, and Prabhasankar 2009). Such products would thus seem to be an easier

target for antioxidant fortification.

Effect of Baking on Whole Grain Antioxidants

Even though much is known about how antioxidants affect dough rheology, what happens to the grain

antioxidants during baking is not clear. Most studies do indicate that the level of antioxidants is reduced

significantly by the baking process, the net reduction of which is dependent on the severity of the heat

treatment as well as the processes preceding the heat treatment (Awika et al. 2003b). However, the baking process, or any heat treatment for that matter, transforms the proteins, starch, and other components

of the food matrix in a way that completely alters extractability of most antioxidant molecules by common laboratory methods. The altered extractability may significantly confound measured antioxidant

activity in a product. For example some studies indicate that levels of phenolic acids, especially ferulic

acid and diferulate esters, and antioxidant activity of some whole grain products, including wheat products (Moore et al. 2009), increases after baking, probably due to the ability of heat to disrupt cellular

matrix and cell wall polysaccharide integrity leading to the release of ferulate esters and other bound

phenolic compounds. Such reports of increased antioxidant compounds after processing are also available for some vegetable products. On the other hand, other studies report a reduction or no change in

phenols or antioxidant activity due to processing (Alvarez-Jubete et al. 2010).

The separating effect of processing on the antioxidant molecules and effect of altered extractability

remains a challenge. For example, even though it is known that some phenolic compounds are heat labile

and will degrade over prolonged heating in model systems, such data has limited application in the true

food system, especially complex systems like cereal-based products. This is because in such systems

molecules will behave very differently due to their ability to interact with other molecules in ways that

can alter their structure or significantly influence their stability.

In general, available evidence suggests that altered extractability may account for a large part of the

reported change in antioxidant properties of cereal products after thermal processing. For example, in

comparing different baked products made with sorghum brans of different phenolic composition, Awika

et al. (2003b) reported that white sorghum with very low levels of extractable phenols and antioxidant

activity did show an increase in antioxidant activity after baking, whereas sorghum brans high in easily

extractable phenols (flavonoids) and antioxidants showed reduced activity after processing. They attributed the increase in antioxidant activity of white sorghum bran-enriched products to increased extractability of phenolic acids, the primary antioxidants in white sorghum. This supports other findings for

whole wheat (Moore et al. 2009), as well as other low antioxidant whole grain products. Thus it seems

measured phenol content and antioxidant activity in baked cereal products is dependent on a balance

between the enhanced release of bound phenolics and their breakdown by heat, as well as how the altered

food matrix affects their extractability. Another problem is that the measured in vitro extractability of

the phenolics or their antioxidant activity does not correlate with any known physiological properties.

Hence in vitro changes in cereal phenolics during processing may not predict their health benefits. There

is plenty of room for research in this arena.

Cereal Bioactive Compounds in Extrusion

Extrusion in the grain industry is mostly used to produce ready to eat snacks and related products.

Since snacks are traditionally among the least healthy food products (traditional extruded products

Effect of Bioactive Components on Dough Rheology, Baking, and Extrusion


are predominantly made from cereal endosperm or starches), significant research effort has gone into

transforming them into healthy products. The use of whole grain, as well as the incorporation of

fiber, antioxidants, and other health promoting components are among the popular strategies that have

been employed to enhance the health profile of extruded products. Socioeconomic factors have also

driven the research to increase the incorporation of fiber and antioxidants in extruded products. For

example, the recent spike in fuel oil prices necessitated a drive to develop alternative renewable energy

sources, the most popular of which has been ethanol derived from cereal grain fermentation. This

process creates significant quantities of spent brewers grain (also called distillers grain), which had

limited economic value but are rich in proteins, dietary fiber, and other health promoting compounds

associated with whole grain.

In general extrusion is largely dependent on extensive starch gelatinization and melting under high

heat and pressure, and then rapidly retrograding to form expanded structure when steam is released as

pressure is dropped. Thus any factors that dilute the starch or interfere with starch melting and reassociation will likely lead to a reduced product expansion (increased bulk density) and thus harder texture, which is undesirable in snacks. This has been observed in various studies that utilize whole grain

or spent brewers’ grain. Generally, the higher the level of substitution of the starchy component (e.g.,

endosperm) with a predominantly nonstarch component (e.g., bran) the lower the extrudate expansion.

However, the reduced expansion of a fiber enhanced product can be compensated somewhat by optimizing extrusion conditions. For example, increasing screw speed from 100 to 300 rpm was reported

to reduce bulk density of extruded snack fortified with 10–30% brewers spent grain by an average of

2.5 times (Ainsworth et al. 2007). Also, as observed in baking, fine grinding of bran before incorporation

can significantly reduce its negative effect on product expansion. This might be due to reduced ability of

fine bran pieces to cut through starch polymers and destroy their network, similar to an effect of bran on

the gluten network during baking.

Another component of whole grain, bran and spent brewers grain that has a major effect on extrusion,

is the lipid. Lipids can form complexes with starch during extrusion (De Pilli et al. 2008), which would

affect the ability of starch to reassociate and form junction zones immediately after expansion. Thus, all

other factors constant, high lipid content tends to cause a reduced expansion and harder texture in product. The effect of fat is usually much more evident in single screw extrusion than twin screw extrusion.

This is because single screw extrusion is more dependent on friction to generate the heat that will cause

starch to melt and plasticize. Lipids will tend to produce lubricity that reduces friction and the ability of

starch to melt.

Effect of Extrusion on Cereal Antioxidants

Data is mixed on how extrusion affects phenolic content and antioxidant activity. Some authors show a

decrease (Dlamini, Taylor, and Rooney 2007) while others show an increase or no change (Stojceska et

al. 2009) for both phenols and antioxidant activity. Again, the problem here is likely similar to what is

mentioned above for baked products; differences in the food matrix in question and types, levels, and

extractability of the antioxidants in the raw material will affect what is measured before and after extrusion. This may be illustrated by some experiments that have demonstrated those conditions that promote

extrudate expansion (e.g., increased screw speed or reduced moisture) generally result in reduced antioxidant activity in the product (Ozer et al. 2006). This hints at reduced extractability as a major contributor to the change in the antioxidant profile of extruded snacks.

Another experiment that demonstrates how types of phenols in raw material may affect the measured effect of extrusion was reported by Awika et al. (2003b). The authors reported that under similar

extrusion conditions, whole grain white sorghum extrudate had 18% higher antioxidant activity than

its raw material, whereas black (high in 3-deoxyanthocyanins) and tannin sorghums showed decrease

in antioxidant activity of 56 and 36% respectively (Table 16.1). Some reports also indicate that extrusion may partly depolymerize some high molecular weight polyphenols like proanthocyanidins into

lower MW forms (Awika et al. 2003a). These authors reported that monomers to tetramers of sorghum proanthocyanidins increased whereas the higher MW oligomers and polymers decreased during


Fruit and Cereal Bioactives: Sources, Chemistry, and Applications

Table 16.1

Effect of Whole Grain Extrusion on Phenol Content and

Antioxidant Activity of Different Sorghum Types



Sample Type

Phenol Content

(mg/g, db)

Antioxidant Activity

(µmol TE/g, db)


































Source: Adapted in part from Awika, J. M., Rooney, L. W., Wu, , X. L.,

Prior, R. L., and Cisneros-Zevallos, L., J. Agric. Food Chem.,

51(23), 6657–62, 2003.

Note: ORAC = both lipophilic and hydrophilic oxygen radical absorbance capacity; TEAC = Trolox equivalent antioxidant capacity

measured by the ABTS (2,2′-azinobis(3-ethylbenzothiazoline-6sulfonic acid) method.

the single screw extrusion process. How such change may affect bioactivity of the products remains



Ainsworth, P., S. Ibanoglu, A. Plunkett, E. Ibanoglu, and V. Stojceska. 2007. Effect of brewers spent grain addition and screw speed on the selected physical and nutritional properties of an extruded snack. Journal of

Food Engineering 81 (4): 702–9.

Alvarez-Jubete, L., H. Wijngaard, E. K. Arendt, and E. Gallagher. 2010. Polyphenol composition and in vitro

antioxidant activity of amaranth, quinoa buckwheat and wheat as affected by sprouting and baking. Food

Chemistry 119 (2): 770–8.

Awika, J. M., L. Dykes, L. W. Gu, L. W. Rooney, and R. L. Prior. 2003a. Processing of sorghum (Sorghum

bicolor) and sorghum products alters procyanidin oligomer and polymer distribution and content. Journal

of Agricultural and Food Chemistry 51 (18): 5516–21.

Awika, J. M., L. W. Rooney, X. L. Wu, R. L. Prior, and L. Cisneros-Zevallos. 2003b. Screening methods to measure antioxidant activity of sorghum (Sorghum bicolor) and sorghum products. Journal of Agricultural

and Food Chemistry 51 (23): 6657–62.

Bauer, N., P. Koehler, H. Wieser, and P. Schieberle. 2003. Studies on effects of microbial transglutaminase on

gluten proteins of wheat. II. Rheological properties. Cereal Chemistry 80 (6): 787–90.

Dahle, L. K., and P. R. Murthy. 1970. Some effects of antioxidants in dough systems. Cereal Chemistry 47 (3):


De Pilli, T., K. Jouppila, J. Ikonen, J. Kansikas, A. Derossi, and C. Severini. 2008. Study on formation of starchlipid complexes during extrusion-cooking of almond flour. Journal of Food Engineering 87 (4): 495–504.

Dlamini, N. R., J. R. N. Taylor, and L. W. Rooney. 2007. The effect of sorghum type and processing on the

antioxidant properties of African sorghum-based foods. Food Chemistry 105 (4): 1412–9.

Koh, B. K., and P. K. W. Ng. 2009. Effects of ferulic acid and transglutaminase on hard wheat flour dough and

bread. Cereal Chemistry 86 (1): 18–22.

Lai, C. S., R. C. Hoseney, and A. B. Davis. 1989. Effect of wheat bran in breadmaking. Cereal Chemistry


Melville, J., and H. T. Shattock. 1938. The action of ascorbic acid as a bread improver. Cereal Chemistry


Effect of Bioactive Components on Dough Rheology, Baking, and Extrusion


Meredith, P. 1965. Oxidation of ascorbic acid and its improver effect in bread doughs. Journal of the Science

of Food and Agriculture 16 (8): 474–80.

Moore, J., M. Luther, Z. H. Cheng, and L. L. Yu. 2009. Effects of baking conditions, dough fermentation, and

bran particle size on antioxidant properties of whole-wheat pizza crusts. Journal of Agricultural and

Food Chemistry 57 (3): 832–9.

Moore, M. M., M. Heinbockel, P. Dockery, H. M. Ulmer, and E. K. Arendt. 2006. Network formation in glutenfree bread with application of transglutaminase. Cereal Chemistry 83 (1): 28–36.

Nanditha, B. R., B. S. Jena, and P. Prabhasankar. 2009. Influence of natural antioxidants and their carry-through

property in biscuit processing. Journal of the Science of Food and Agriculture 89 (2): 288–98.

Ozer, E. A., E. N. Herken, S. Guzel, P. Ainsworth, and S. Ibanoglu. 2006. Effect of extrusion process on the

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Impacts of Food and Microbial Processing on the

Bioactive Phenolics of Olive Fruit Products

Moktar Hamdi


Introduction............................................................................................................................................. 347

Olive Fruit Composition and Bioactive Phenolics Content.................................................................... 348

Effect of the Postharvest of Olive Fruit on the Phenolics....................................................................... 350

Effect of the Table Olive Processing on the Bioactive Phenolics............................................................351

Impact of Olive Oil Processing on the Bioactive Phenolics....................................................................353




The olive tree, Olea europea L., is the only species of the Oleacea with edible fruit. Cultivation began in

the Mediterranean countries more than 6000 years ago, developed in Andalucia by Arabs and was then

introduced to America. In the last decades, cultivations were promoted in Asia, Australia, and South

Africa. Among the 1500 olive cultivars catalogued in the world, only approximately 100 are classified as

a main cultivar producing varieties and classified according to the use of their fruits: oil extraction, table

olive processing, and dual use cultivars.

The oleicol olive world heritage counts more than 800 million olive trees that occupy about

8711 ­thousand acres. Of that land, 99% is located in the Mediterranean basin (Luchetti 1993). Olive oil

represents the main product of the olive tree, since 91% of harvested olives are destined to be pressed into

oil (Luchetti 1999). The Mediterranean area alone provides 98% of the total surface area for olive tree

culture and 97% of the total olive production. The largest olive oil producers are Spain, Italy, Greece,

Turkey, and Tunisia.

A number of olive cultivars are being cultivated in the Mediterranean countries for processing as

table olives (IOOC 2000). Some Spanish and Italian cultivars such as Gordal Sevillana, Manzanilla de

Sevilla, and Ascolana have been exported to the other countries (including Argentina, Australia, United

States, and Israel) to produce table olives.

The world production of table olives is estimated to surpass 1.5 million tons per year, with the

Mediterranean countries being the main producers. There has been an increased demand for fermented

green and black table olives in recent years in all regions of the world because of their nutritional

and functional foods proprieties. The International Olive Oil Council statistical data for 1989/1990

and 2000/2001 shows that the production of table olives increased in the majority of countries during the

last decade (IOOC 2000). Spain and Turkey are the main producers of green olives and naturally black

olives, respectively.

The improvement in nutritional value of various plant food commodities, by increasing their content of biologically active polyphenolic and phytochemicals, has become a challenge for scientists and



Fruit and Cereal Bioactives: Sources, Chemistry, and Applications

technologists. Saija and Uccelle (2000) suggested that an understanding of olive growing and ­processing

technologies, and the measurement of extra virgin olive oil and table olives macrobio-, microbio-, and

techno-components behavior, after the raw material has been subjected to appropriate harvesting, milling, malaxation, extraction, and debittering treatments, is important in order to communicate the hedonic-sensory quality and functional quality of olive agrifood to consumers. The bioactive phenolic of

olive fruit and their concentrations in the olive fruit products depend on the olive cultivars, harvesting,

processing, and storage.

Olive Fruit Composition and Bioactive Phenolics Content

The cultivar, the region of production, the degree of drupe maturation, and the postharvest conditions determine the nutritional quality, the functional and technological potential of the olive fruit

(Figure 17.1). The olive tree gives an oval fruit, which is fleshy green drupe, and consists of a pulp and

a stone representing 70–90% of the olive weight and the pit is the other 10–30% (Fernández Diéz et

al. 1985; Rejano 1977). The pulp consists mainly of oil (10–25%) and water (60–75%). The oil fraction includes mainly triglycerides, diglycerides, monoglycerides, free fatty acids, sterol esters, terpenes

alcohol, and phospholipids. The olive fruit texture is attributed to the presence of fiber fraction (1–4%;

Gullen et al. 1992) and the pectic substances (0.3–0.6%; Minguez-Mosquera et al. 2002). Sugars and

polyols represent 20% of the fresh pulp weight. The green color of olives is attributed to chlorophylls

(1.8–13.5 mg/100 g fresh pulp) and carotenoid pigments (0.6–2.4 mg/100 g fresh pulp; MinguezMasquera and Garrido-Fernandez 1989; Roca and Minguez-Masquera 2001). The variations of concentrations of most nutrients are influenced by the type of cultivar, the growing conditions, and the degree

of ripeness. During ripening processes, the ratio between chlorophylls and carotenoids change because

the chlorophylls decrease.

In the development of the olive fruit, three phases are usually distinguished (Soler-Rivas et al.

2000): a growth phase, during which accumulation of oleuropein occurs; a green maturation

phase, coinciding with a reduction in the levels of chlorophyll and oleuropein; and a black maturation phase, characterized by the appearance of anthocyanins and during which the oleuropein levels

continue to fall. Saija and Uccelle (2000) summarized the phenolic compound structures that range

from quite simple compounds to highly polymerized substances such as the tannins. Their content

in olive fruit can vary between 1 and 2% and are represented mainly by the oleuropein. Indeed, the

bitter taste of olives is largely ascribed to the content of oleuropein (García et al., 2001; GutiérrezRosales et al., 2003). During maturation, oleuropein is partially converted into demethyloleuropein,

which becomes the major phenol in black olives (Romero et al. 2002). The most important changes

Figure 17.1  Olive fruit.

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Effect of Bioactive Components on Dough Rheology, Baking, and Extrusion

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