Food Biochemistry and Food Processing (2 edition)

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62 Part 1: Principles/Food Analysis

Table 4.2.(Continued)

Inhibition Targeted Toward the Enzyme Inhibition Targeted Toward the Substrate

Processing Enzymes Inhibitors Removal of Oxygen Removal of Phenols

Inhibition Targeted

Toward the Products

High pressure

(600–900 Mpa)

Honey (peptide∼600 Da

and antioxidants)

Supercritical carbon

dioxide (58 atm, 43◦C)

Proteases

Ultrafiltration Acidulants

Citric acid (0.5–2% w/v)

Malic acid

Phosphoric acid

Ultrasonication Chitosan

Employment of edible

coating

Source:Adapted from Marshall et al. 2000.

Morais 2001, Kaaber et al. 2002, Valverde et al. 2010); pre-

treatments employing sodium or calcium chloride and lactic

acid followed by conventional blanching (Severini et al. 2003);

combination of sodium chlorite and calcium propionate (Guan

and Fan 2010); high-pressure treatments combined with thermal

treatments and chemical anti-browning agents such as ascor-

bic acid (Prestamo et al. 2000, Ballestra et al. 2002) or natural

anti-browning agents like pineapple juice (Perera et al. 2010);

and UV-C light treatment of fresh-cut vegetables under nonther-

mal conditions (Manzocco et al. 2009) have been employed to

prevent enzymatic browning in foods.

The use of edible coating from whey protein isolate-beeswax

(Perez-Gago et al. 2003); edible coatings enriched with natu-

ral plant extracts (Ponce et al. 2008); oxygen-controlled atmo-

spheres (Jacxsens et al. 2001, Soliva-Fortuny et al. 2001, Duan

et al. 2009), and the use of active films (Endo et al. 2008) seem

to improve the shelf life of foods by inhibition of PPO.

Biotechnological approaches may be also employed for the

control of PPO (Rodov 2007). Transgenic fruits carrying an an-

tisense PPO gene show a reduction in the amount and activity of

PPO, and the browning potential of transgenic lines are reduced

compared with the non-transgenic ones (Murata et al. 2000,

Murata et al. 2001). These procedures may be used to prevent

enzymatic browning in a wide variety of food crops without the

application of various food additives (Coetzer et al. 2001).

NONENZYMATIC BROWNING

The Maillard Reaction

Nonenzymatic browning is the most complex reaction in food

chemistry because a large number of food components are able to

participate in the reaction through different pathways, giving rise

to a complex mixture of products (Olano and Mart ́ınez-Castro

2004). It is referred to as the Maillard reaction when it takes

place between free amino groups from amino acids, peptides,

or proteins and the carbonyl group of a reducing sugar. The

historical perspective showed by Finot (2005) shows the great

importance of Maillard reaction on food science and nutrition.

The Maillard reaction is one of the main reactions causing

deterioration of proteins during processing and storage of foods.

This reaction can promote nutritional changes such as loss of nu-

tritional quality (attributed to the destruction of essential amino

acids) or reduction of protein digestibility and amino acid avail-

ability (Malec et al. 2002).

The Maillard reaction covers a whole range of complex

transformations (Figure 4.4) that produces a large number

of the so-called Maillard reaction products (MRPs) such as

aroma compounds, ultraviolet absorbing intermediates, and

dark-brown polymeric compounds named melanoidins (Kim and

Lee 2008a). It can be divided into three major phases: the early,

intermediate, and advanced stages. The early stage (Figure 4.5)

consists of the condensation of primary amino groups of amino

acids, peptides, or proteins with the carbonyl group of reducing

sugars (aldose), with loss of a molecule of water, leading, via for-

mation of a Schiff’s base and Amadori rearrangement, to the so-

called Amadori product (1-amino-1-deoxi-2-ketose), a relatively

stable intermediate (Feather et al. 1995). The Heyns compound

is the analogous compound when a ketose is the starting sugar. In

many foods, theε-amino group of the lysine residues of proteins

is the most important source of reactive amino groups, but be-

cause of blockage, these lysine residues are not available for di-

gestion, and consequently the nutritive value decreases (Brands

and van Boekel 2001, Machiels and Istasse 2002). Amadori

compounds are precursors of numerous compounds that are im-

portant in the formation of characteristic flavors, aromas, and

brown polymers. They are formed before the occurrence of sen-

sory changes; therefore, their determination provides a very sen-

sitive indicator for early detection of quality changes caused by

the Maillard reaction (Olano and Mart ́ınez-Castro 2004).

The intermediate stage leads to breakdown of Amadori com-

pounds (or other products related to the Schiff’s base) and the

formation of degradation products, reactive intermediates (3-

deoxyglucosone), and volatile compounds (formation of flavor).