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tions attributed to bioactive peptides, such as antimicrobial, immunomodulatory, enhancement of mineral, antihypertensive, opioid and antioxidant activities. The great complexity and

are theary enfunctrotein

Food Research International xxx (2013) xxxxxx

FRIN-04528; No of Pages 10

Contents lists available at SciVerse ScienceDirect

Food Research

e lsan increased interest in health-promoting functional foods, wherebyconsumers hold higher expectations of health-promoting benets be-yond basic nutrition. Dietary proteins provide a rich source of bioac-tive peptides, which are hidden in a latent state within the nativeprotein, requiring enzymatic proteolysis for their release. Biologicallyactive or functional peptides are food derived peptides that exert,beyond their nutritional value, a physiological, hormone-like effectin the body (Hebert, Saavedra, & Ferranti, 2010). Bioactive peptidesderive from a wide range of animal and vegetable proteins; such as

2. Production of bioactive peptides

Bioactive peptides are encrypted in the primary structure of ani-mal and plant proteins but they can be released by proteolysisin vitro, in vivo or a combination of both (Fig. 1, Hebert et al., 2010).The in vivo release of bioactive peptides involves the gastrointestinaldigestion (with digestive enzymes such as pepsin, trypsin, chymo-trypsin and peptidases from the intestinal brush border membranes)bovine and human milk, sh, egg, meat, soybcereals (Bouzerzour et al., 2012; Escudero, Ari& Toldra, 2012; Kussmann & Van Bladeren, 202012).

Corresponding author. Tel.: +54 3814310465; fax:E-mail addresses: [email protected] (L. Saavedra),

(E.M. Hebert), [email protected] (C. Minahk), fe

0963-9969/$ see front matter 2013 Published by Elhttp://dx.doi.org/10.1016/j.foodres.2013.02.034

Please cite this article as: Saavedra, L., et al.,national (2013), http://dx.doi.org/10.1016/j.s depends on the aminoanti-nutrients that can

ility. Nowadays, there is

biological activity of interest; and (iii) a QSAR-based in silico approachwas recently proposed for the prediction of food protein than can re-lease bioactive peptides (Gu et al., 2012; Udenigwe & Aluko, 2012).acid composition, the absence of co-existinglimit protein digestibility and absorptive ab1. Introduction

Proteins, carbohydrates and lipidsnutrients which provide the necessfunctions as well as the structural andganisms. Nutritionally, the quality of pof existing analytical methodologies. However, functional and comparative genomic studies as well as prote-omic approaches provide a wealth of knowledge in the way in which these lactic acid bacteria can use foodproteins releasing bioactive peptides.

2013 Published by Elsevier Ltd.

three classes of macro-ergy to maintain bodyional integrity of the or-

Food proteins are selected as sources of bioactive peptidesaccording to different criteria (Udenigwe & Aluko, 2012): (i) foodindustry by-products in order to reduce environmental contamina-tion and manufacture value-added products, for example whey pro-teins; (ii) proteins containing specic amino acid sequences for aGenomicMass spectrometrythe wide dynamic range of relative peptide abundance in these products severely challenge the capabilities

Proteomic absorption, antithromboticAn overview of omic analytical method

L. Saavedra a, E.M. Hebert a,, C. Minahk b, P. Ferrantia Centro de Referencia para Lactobacilos (CERELA-CONICET), Chacabuco 145, 4000 San Mib Instituto Superior de Investigaciones Biolgicas (CONICET-UNT) e Instituto de Qumica Bic Dipartimento di Scienza degli Alimenti, University of Naples Federico II, Parco Gussone, P

a b s t r a c ta r t i c l e i n f o

Article history:Received 29 October 2012Received in revised form 13 February 2013Accepted 20 February 2013Available online xxxx

Keywords:

Nowadays, there is an incrhigher expectations of heasource of bioactive peptidesproteolysis for their release.or food processing. Lactic afor the production of fermeof bioactive peptides from d

j ourna l homepage: www.ean, rice, sunower andstoy, Nishimura, Arihara,11; Senevirathne & Kim,

+54 [email protected]@unina.it (P. Ferranti).

sevier Ltd.

An overview of omic analytfoodres.2013.02.034pplied in bioactive peptide studies

de Tucumn, Argentinaica Dr. Bernabe Bloj UNT, Chacabuco 461, 4000 San Miguel de Tucumn, Argentinai I-80055, Italy

ed interest in health-promoting functional foods, whereby consumers holdpromoting benets beyond basic nutrition. Dietary proteins provide a richich are hidden in a latent state within the native protein, requiring enzymaticactive peptides can be produced during in vivo gastrointestinal digestion and/bacteria are among the most widely microorganisms used as starter culturesd foods, and through their proteolytic system, they contribute to the releasery proteins. In vitro and in vivo studies demonstrated several biological func-

International

ev ie r .com/ locate / foodresas well as enzymes derived from the human microbiota. On the otherhand, the in vitro production of bioactive peptides includes theenzymatic hydrolysis of the food protein by endogenous enzymespresent in the food matrix as well as proteolysis occurring duringfood processing or ripening by action of starter cultures or by en-zymes isolated from proteolytic microorganisms (e.g., Lactobacillushelveticus, Lactobacillus delbrueckii subsp. bulgaricus and L. delbrueckiisubsp. lactis, Espeche Turbay, de Moreno de LeBlanc, Perdigon, Savoy

ical methods applied in bioactive peptide studies, Food Research Inter-

2 L. Saavedra et al. / Food Research International xxx (2013) xxxxxxde Giori, & Hebert, 2012; Hebert et al., 2010). Therefore, certain lacticacid bacteria (LAB), mainly the strains belonging to the generaLactobacillus, are currently marketed as health-promoting culturesor probiotics (Kleerebezem et al., 2010; Saxelin, Tynkkynen, Mattila-Sandholm, & de Vos, 2005). Microbial fermentation is one of themajor processes to generate bioactive peptides, mainly in the dairyindustry where the lactobacilli cell envelope-associates proteinases(Prt) release peptides during milk fermentation (Espeche Turbay etal., 2012; Hebert et al., 2008, 2010).

3. Main sources and target proteins involved in the production ofbioactive peptides

Cryptic bioactive peptides have been isolated and characterized froma variety of sources: soybean, sunower, corn, wheat, barley, rice, meat,sh, milk and its derivatives such as yogurt and cheese (Table 1,Bouzerzour et al., 2012; Escudero et al., 2012; Kussmann & VanBladeren, 2011; Senevirathne & Kim, 2012). Depending on their aminoacid sequence, bioactive peptides can exhibit diverse activities by bind-ing to a specic receptor in the gastrointestinal tract or in target organs

Fig. 1. Hydrolysis of food proteins by the proteolytic system of the lactic acid bacteria or bybioactive peptides.

Please cite this article as: Saavedra, L., et al., An overview of omic analytnational (2013), http://dx.doi.org/10.1016/j.foodres.2013.02.034and tissues after absorption into the bloodstream (Fig. 1, Table 1). Anti-microbial, immunomodulatory, anticarcinogenic, antitumoral, anti-thrombotic, opioid, and antioxidant activities; enhancement of mineralabsorption and/or bioavailability; and blood pressure-lowering effectare some of the biological activities attributed to food-derived peptides(Hebert et al., 2010). Furthermore, some peptides could play a role inprevention and treatment of metabolic syndrome via different mecha-nisms, for instance by decreasing body mass, regulation of blood pres-sure, insulinemia and cholesterolemia levels (Ricci-Cabello, Herrera, &Artacho, 2012). An exhaustive description of food bioactive peptides cur-rently known is outside the scopes of this review,which is instead aimedto give an overview of their main sources, in conjunction with the mostrepresentative in vitro and in vivo activities and of omic approaches fortheir characterization from food matrices.

3.1. Bioactive peptides: main food sources

A number of bioactive peptides were shown to be released fromsoy protein by means of microbial, gastric and pancreatic enzyme di-gestion of soybean proteins in the last decades (Kwon, Daily, Kim, &

several digestive enzymes during the digestion process, which results in the release of


Table 1Examples of bioactive peptides released from proteins derived from several food sources.

Food source Treatment(enzymes/microorganisms)

Primary structure or peptide fragment Activities displayed by bioactivepeptides

References

SoybeanPepsin, pancreatin Peptides from 1 to 13 kDa Antioxidant, improving muscle

glucose uptakeRoblet et al. (2012)

Endo-type protease frommicroorganism

KAVK

Reduced TG synthesis Inoue et al. (2011)

SY Reduced TG synthesisReduction of apoB secretion

Neutral and alkaline proteasefrom Bacillus amyloliquefaciens

Peptides from 200 to 3000 Da Stimulation of LDL-R transcription Cho et al. (2007)

Trypsin LPYP HMG-CoA reductase inhibitor Pak, Koo, Kasymova, & Kwon (2005)Pepsin IAVPGDVAPepsin and pancreatin SP-Sepharose fractions ACE inhibitor

Reactive oxygen speciesscavengers

Farzamirad & Aluko (2008)

De-fatted soy protein Thermolase XMLPSYSPY Anticancer Galvez, Chen, Macasieb, & deLumen (2001); Kim et al. (2000)

RiceAlcalase and simulatedgastrointestinal juices

EQRPR Anticancer Kannan et al. (2010)

Rice soluble protein Tryptic hydrolysis GYPMYPLPR Antimicrobial andileum-contracting activity

Takahashi et al. (1994)

CornTrypsin, thermolysin, GC 106 b1 kDa peptides ACE inhibitor Parris et al. (2008)

Defatted corn protein Flavourzyme Bile acid binding capacity Kongo-Dia-Moukala et al. (2011)

WheatAcid protease IAP ACE inhibitor Motoi & Kodama (2003)Proteolysis by lactobacillus strains MAPAAVAAAEAGSK, DNIPIVIR Antioxidant activity Coda et al. (2012)

MeatPorcine myosin Thermolysin MNPPK, ITTNP ACE inhibitor Arihara et al. (2001)

Peptic digestion VKKVLGNP ACE-inhibitor Katayama et al. (2007)Titin Pepsin and pancreatic proteases KAPVA ACE-inhibitor Escudero et al. (2010)Sarcoplasmic beefproteins

Synthetic peptides GFHI, DFHING, FHG, GLSDGEWQ Antimicrobial and anti-cancer Jang et al. (2008)

Fish and other aquatic organismsConger eel Tryptic hydrolysate LGLNGDDVN Antioxidants Ranathunga et al. (2006)Rotifer Pepsin LLGPGLTNHA

DLGLGLPGAHAntioxidants Byun et al. (2009)

Tuna Pepsin VKAGFAWTANQQLS Antioxidants Je et al. (2007)Pepsin GDLGKTTTVSNWSPPKYKDTP ACE-inhibitor Lee et al. (2010)

Oyster LLEYSL/I Antiviral (anti-HIV) Lee & Maruyama (1998)

Whey proteinsLactoferrin Pepsin Lactoferricin Antimicrobial Oo et al. (2010)-Lactalbumin Trypsin and chymotrypsin EQLTK, GYGGVSLPEWVCTTF ALCSEK,

CKDDQNPH ISCDKFBactericidal peptides Pellegrini et al. (1999)

-lactoglobulin Enzymatic hydrolysis IPA Inhibitor of dipeptidylpeptidase-4

Tulipano et al. (2011)

Milk whey Hydrolysis byL. helveticus LBK-16H

IPP, VPP Osteoblast proliferation Narva, Halleen, Vaananen, &Korpela (2004)

Caseins-casein Pepsin 4 to around 100 amino acids

No sequence availablePhosphopeptides Schmelzer et al. (2007)

Pepsin or trypsin andchymotrypsin

Neocasomorphin-6 (YPVEPF) Opiod properties Jinsmaa & Yoshikawa (1999)

Enterococcus faecalis CECT 5727 LHLPLPLVYPFPGPIPNSLPQNIPP

Ace inhibitors Quiros et al. (2006)

s1-casein Pepsin, trypsin, chymotrypsin,and elastase

PQEVLNENLLR, VAPFPEVFGK MAP-kinase signaling cascadeactivation, cholesterol7-hydroxylase regulation

Nass et al. (2008)

Caseins (s1-casein,s2-casein, -casein)

Hydrolysis by L. helveticus PR4 LVYPFPGPIPNSLPQNIPP,FVAPFPEVFGKEKVNELSKDIGSE,LGTQYTDAPSFSDIPNPIGSENSEK,LVYPFPGPIPNSLPQNIPP,FVAPFPEVFGKEKVNELSKDIGSE,LVYPFPGPIPNSLPQNIPP

Ace inhibitorsAntimicrobial

Minervini et al. (2003)

Sodium caseinate L. acidophilus ATCC 4356 andLc. lactis subsp. lactis GR5

3 kDa-ultraltered peptide fractionNo sequence available

Immunomodulatory activity Stuknyte, De Noni, Guglielmetti,Minuzzo, & Mora (2011)

-Casein L. delbrueckii subsp. lactis CRL 581 No sequence available Anti-inammatory activity (colitis) Espeche Turbay et al. (2012)

3L. Saavedra et al. / Food Research International xxx (2013) xxxxxx

Please cite this article as: Saavedra, L., et al., An overview of omic analytical methods applied in bioactive peptide studies, Food Research Inter-national (2013), http://dx.doi.org/10.1016/j.foodres.2013.02.034

4 L. Saavedra et al. / Food Research International xxx (2013) xxxxxxPark, 2010). For instance, the sequential treatment with pepsin andpancreatin resulted in the generation of well-dened peptidesranging from approximately 13 kDa to less than 1 kDa, displayingimportant activities as antioxidants as well as in improving muscleglucose uptake (Roblet et al., 2012). Inoue et al. (2011) digestedsoy protein with endo-type protease from Bacillus sp., and twodipeptides that lowered triacylglycerols (Lys-Ala, Val-Lys) and,Ser-Tyr, that also reduces apoB secretion in a hepatoma cell line,were characterized (Inoue et al., 2011). Larger soy peptides displayedhypocholesterolemic activity, although by different mechanisms. Inthis regard, Cho, Juillerat, and Lee (2007) described peptides rangingfrom 200 to 3000 Da that stimulate LDL receptor transcription thusinducing a reduction in the levels of circulating LDL particles. Pak,Koo, Kwon, and Yun (2012) recently identied two soy bioactive pep-tides Leu-Pro-Tyr-Pro and Ile-Ala-Val-Pro-Gly-Asp-Val-Ala, whichinhibited the enzyme 3-hydroxy-3-methylglutaryl CoA reductase(HMGR) that catalyzes the rate-limiting step of cholesterol synthesis.Based on these sequences, they designed twelve peptides, one of whichdisplayed 14,500-fold increase inhibitory activity as compared to thenatural bioactive peptides (Pak et al., 2012). Other small bioactive pep-tides from soy were characterized as ACE inhibitors and reactive-oxygen species scavengers (Farzamirad & Aluko, 2008). In addition,the nonapeptide obtained by thermolase hydrolysis of de-fatted soyprotein, X-Met-Leu-Pro-Ser-Tyr-Ser-Pro-Tyr, was shown to arrestmouse monocyte macrophage cell line in G2/M phases (Kim et al.,2000). Up-to-date, evidence suggests that promising bioactive peptidescan be found elsewhere. In this regard, the pentapeptide Glu-Gln-Arg-Pro-Arg, isolated from heat stabilized de-fatted rice bran displayedanti-cancer property (Kannan, Hettiarachchy, Lay, & Liyanage, 2010).Another interesting example is the nonapeptide oryzatensin, Gly-Tyr-Pro-Met-Tyr-Pro-Leu-Pro-Arg, obtained by tryptic hydrolysis ofrice soluble protein which enhances the antimicrobial activity of leuko-cytes and it also displayed an ileum-contracting activity (Takahashi,Moriguchi, Yoshikawa, & Sasaki, 1994). Corn and wheat are otherplant sources of bioactive peptides. In fact, ACE inhibitors as well ashypocholesterolemic peptides were isolated from corn (Kongo-Dia-Moukala, Nsor-Atindana, & Zhang, 2011; Parris, Moreau, Johnston,Dickey, & Aluko, 2008). On the other hand, Ile-Ala-Pro tripeptide wasisolated from wheat gliadin, exhibiting a powerful ACE inhibitoryactivity (Motoi & Kodama, 2003). Interestingly, sourdough fermenta-tion of several cereal ours using Lactobacillus strains presented anti-oxidant activity due to the release of bioactive peptides from gliadinsranging from eight to fty-seven amino acids (Coda, Rizzello, Pinto, &Gobbetti, 2012).

In meat, short peptides commonly increase their concentrationsduring post-mortem storage even at low temperatures (Nishimura,Rhue, Okitani, & Kato, 1988). However, there is scarce information onthe formation of benecial bioactive peptides in such conditions,where ACE-inhibition is the most common activity found. For instance,two pentapeptides released from the heavy chain of porcine myosin bythermolysin were tested in vivo showing that they were very effectivein lowering blood pressure in animalmodel of spontaneously hyperten-sive rats (Arihara, Nakashima, Mukai, Ishikawa, & Itoh, 2001). On theother hand, pepsin also generated important ACE-inhibitors from thelight chain of porcine myosin, such as the octapeptide Val-Lys-Lys-Val-Leu-Gly-Asn-Pro, which was also effective in the same animalmodel (Katayama et al., 2007). Troponin and collagen are also impor-tant contributors to the bioactive peptide production (Katayama et al.,2008; Saiga et al., 2008). The ACE-inhibitor pentapeptide Lys-Ala-Pro-Val-Ala was released from titin after treatment of porcine musclewith a sequential digestion of pepsin and pancreatic proteases(Escudero, Sentandreu, Arihara, & Toldra, 2010). In addition, antioxi-dant, antimicrobial and anti-cancer peptides derived from meatwere also reported in the literature (Jang, Jo, Kang, & Lee, 2008; Li,Chen, Wang, Ji, & Wu, 2007; Ryan, Ross, Bolton, Fitzgerald, & Stanton,

2011).

Please cite this article as: Saavedra, L., et al., An overview of omic analytnational (2013), http://dx.doi.org/10.1016/j.foodres.2013.02.034Fish and other aquatic organisms are also sources of bioactive pep-tides, including antioxidants such as the anionic nonapeptide Leu-Gly-Leu-Asn-Gly-Asp-Asp-Val-Asn from conger eel (Ranathunga, Rajapakse,& Kim, 2006) and two decapeptides from rotifer (Byun, Lee, Park, Jeon,& Kim, 2009). Antioxidant peptides were also reported from shes liketuna (Je, Qian, Byun, & Kim, 2007). In addition, pepsin digestion of tunaframe protein released a 21-mer cationic peptide that acted asACE-inhibitor (Lee, Qian, & Kim, 2010). Anti-coagulant (Jung & Kim,2009), anti-obesity (Cudennec, Ravallec-Pl, Courois, & Fouchereau-Peron, 2008), anticancer (Naqash & Nazeer, 2012), an anti-HIV activitieswere also reported. In the latter case, two hexapeptides from oyster,Leu-Leu-Glu-Tyr-Ser-Leu/Ile, proved to be highly effective at blockingHIV protease (Lee & Maruyama, 1998).

Bioactive peptides can also be released by hydrolysis with diges-tive enzymes from milk and dairy products. These peptides can bereleased from -, -, and -caseins and whey proteins such as-lactalbumin, -lactoglobulin, lactoferrin and immunoglobulins(Belem, Gibbs, & Lee, 1999; Fitzgerald & Murray, 2006). Lactoferricin,a 25 amino acid peptide derived from the digestion of the lactoferrinby pepsin, displayed an outstanding antimicrobial activity (Oo, Cole,Garthwaite, Willcox, & Zhu, 2010). Pepsin, trypsin or chymotrypsindigestion of -lactalbumin results in the production of peptideswith both, immunomodulatory and antimicrobial activities againstbacteria, viruses and fungi (Pellegrini, 2003; Pellegrini, Thomas,Bramaz, Hunziker, & von Fellenberg, 1999). Another interestingwhey-derived bioactive compound is the tripeptide Ile-Pro-Ala, re-leased from -lactoglobulin hydrolysis, which may act as inhibitorof dipeptidyl peptidase-4, reducing glucose levels and stimulate insu-lin (Tulipano, Sibilia, Caroli, & Cocchi, 2011). In the same trend, otherreports point out the possible role of whey peptides in reducing typeII diabetes as well as obesity (Jakubowicz & Froy, 2012).

Two peptides derived from s1-casein, released by enzymatictreatment, were found to be involved in the regulation of the choles-terol 7-hydroxylase expression i.e. the key enzyme of bile synthesis(Nass et al., 2008). -casein in turn was shown to release at least fourpotent ACE-inhibitors peptides from 3 to 11 amino acid length(Gomez-Ruiz, Ramos, & Recio, 2007).

3.2. Release of bioactive peptides by microorganisms

In milk, LAB undoubtedly have the greatest impact in releasingbioactive peptides. As milk contains only small amounts of aminoacids and short peptides, LAB depend on a complex proteolytic sys-tem to obtain essential amino acids from caseins during growth inmilk. This specialized proteolytic system comprises three major com-ponents (Fig. 2): (i) a cell envelope-associated proteinase (Prt) whichis involved in the rst step of casein degradation; (ii) peptide trans-port systems to allow uptake of the resulting peptides, and (iii) sever-al intracellular peptidases that degrade peptides into shorter peptidesand amino acids (Hebert et al., 2008; Lamarque et al., 2011; Liu,Bayjanov, Renckens, Nauta, & Siezen, 2010). This proteolytic systemis essential for bacterial growth, it also contributes to the develop-ment of avor and texture of fermented products and it can promotehuman health through the release of bioactive peptides duringmilk fermentation (Hebert et al., 2008, 2010; Savijoki, Ingmer, &Varmanen, 2006). Thus, certain Prts can release bioactive health-benecial peptides during milk fermentation (Hebert et al., 2008,2010; Savijoki et al., 2006). In fact, several immunomodulatory,hypocholesterolemic, antimicrobial, mineral-binding, opiod, and anti-hypertensive bioactive peptides have been isolated from fermenteddairy products (Fitzgerald & Murray, 2006; Hayes et al., 2007). How-ever, the antihypertensive activity is the main studied bioactivityproduced during milk fermentation (Fitzgerald & Murray, 2006).ACE-inhibitory peptides from dairy origin usually contain up to 10amino acids, being the strain selection one of the main factors that af-

fects the release of bioactive peptides in dairy fermentations (Hayes


a frorterpep

5L. Saavedra et al. / Food Research International xxx (2013) xxxxxxFig. 2. Schematic representation of the proteolytic system of lactic acid bacteria. (datcell-envelope associated proteinase (Prt), Opp oligopeptide permease, the Opt transpofor peptides, the intracellular endopeptidases (PepO, PepF, PepE/PepG), general aminoet al., 2007). ACE-inhibitory peptides have been mainly isolated fromdairy products fermentedwith L. helveticus (Hayes et al., 2007). Twopo-tent ACE-inhibitory peptides Val-Pro-Pro and Ile-Pro-Pro derivedfrom -casein, were isolated from milk fermented with L. helveticusCP790 (Takano, 2002) and sour milk fermented with L. helveticus andSaccharomyces cerevisiae (Nakamura et al., 1995). These peptides werealso identied in a -casein hydrolysate generated by L. delbrueckiisubsp. lactis CRL 581 (Hebert et al., 2008). Two commercial anti-hypertensive milk products containing Ile-Pro-Pro and Val-Pro-Pro,Ameal S and Evolus, fermented with L. helveticus are available inthe market (Fitzgerald & Murray, 2006). In addition, milks fermentedwith different strains of Enterococcus faecalis, L. helveticus, Lactobacillusrhamnosus, Lactobacillus animalis, Lactobacillus acidophilus, L. delbrueckiisubsp. bulgaricus and Lactococcus (Lc.) lactis subsp. cremorishave shownto present ACE inhibitory activity (Fitzgerald &Murray, 2006; Gobbetti,Ferranti, Smacchi, Goffredi, & Addeo, 2000; Hayes et al., 2007; Miguelet al., 2005; Yamamoto, Maeno, & Takano, 1999). ACE inhibitory pep-tides may also be released during fermentation of whey proteins byKluyveromyces marxiams varmarciams (Belem et al., 1999).

ACE inhibitors are thought to be competitive substrates for ACE.Although there is no apparent consensus on the peptide sequencefor the expression of ACE inhibitory activity, some common structuralproperties of ACE-inhibitory peptides are worth noting (Cheung,Wang, Ondetti, Sabo, & Cushman, 1980). The ACE binding is stronglyinuenced by the C-terminal tripeptide sequence of the substrate;ACE appears to prefer substrates or competitive inhibitors containinghydrophobic amino acids including aromatic amino acids such as Trp,Tyr, and Phe, or the amino acid Pro located at the three C-terminal po-sitions. In addition, the positive charge from Arg and/or Lys residuesmay increase the inhibitory activity (Pripp, Isaksson, Stepaniak, &Sorhaug, 2004).

(PepX, PepP, PepI, PepQ, PepR), tripeptidase (PepT), and dipeptidases (PepD and PepV) are

Please cite this article as: Saavedra, L., et al., An overview of omic analytnational (2013), http://dx.doi.org/10.1016/j.foodres.2013.02.034m Kunji et al., 1996; Savijoki et al., 2006; Lamarque et al., 2011; Liu et al., 2010). A, DtpT the ion-linked transporter for di- and tripeptides, and Dpp the ABC transportertidases (PepN, PepC), unique aminopeptidases (PepM, PepA, Pcp), proline peptidasesTheoretically, any food protein can be used as a potential source ofbioactive peptides. Several bioactive peptides are produced in vitro byenzymatic proteolysis or fermentation. A combination of enzymatic hy-drolysis by gastrointestinal digestion and fermentation of food proteinswith proteolytic starter cultures has been demonstrated to be effectivein producing short functional peptides (Hebert et al., 2010; Korhonen& Pihlanto, 2007). The choice of proteolytic enzymes ormicroorganismsused for food processing has a crucial impact on the composition of thereleased peptides (Panchaud, Affolter, & Kussmann, 2012). In this sense,the most important application of LAB is their use as starter cultures inthemanufacturing processes of various fermented food,mainly becausethey contribute to raw-material preservation due to acidication, butalso because of their contribution to the development of avor andtexture of fermented products (Canchaya, Claesson, Fitzgerald, vanSinderen, & O'Toole, 2006; Kleerebezem et al., 2010). The natural habi-tat of lactobacilli includes dairy, meat and vegetal material fermenta-tions to the gastrointestinal and genital tracts of humans and animals(Kleerebezem et al., 2010; Satokari et al., 2003; Vaughan et al., 2002).Therefore, any existing food proteins could be used as possible substratefor generating bioactive peptides.

4. Genomics as a tool for the prediction of proteolytic potentialof LAB

Beginning with the genome of Lactobacillus plantarum WCFS1 in2003 (Kleerebezem et al., 2003), currently public databases contain42 complete Lactobacillus genomes, while 105 more Lactobacillusgenome sequencing projects containing scaffolds or contigs areavailable on-line (http://www.ncbi.nlm.nih.gov/genome/browse/).The availability of microbial genomes and extensive comparativeanalyses of LAB genomes have allowed to reveal the genomic features

indicated.


6 L. Saavedra et al. / Food Research International xxx (2013) xxxxxxthat contribute to the ecological adaptability and examine theevolution of the species and their phenotypic diversities (Broadbentet al., 2012; Cai, Thompson, Budinich, Broadbent, & Steele, 2009;Canchaya et al., 2006; Kleerebezem et al., 2010; Liu et al., 2010;Makarova et al., 2006). Comparative analysis of several LAB genomesshowed that a combination of gene gain and gene loss occurred dur-ing the evolution of LAB with different ecological habitats (Broadbentet al., 2012; Cai et al., 2009; Canchaya et al., 2006; Kleerebezem et al.,2010; Liu et al., 2010; Makarova et al., 2006). Niche-specic genomicadaptations are reected within the genomes (Cai et al., 2009;Kleerebezem et al., 2010). Adaptation to the dairy niche has been as-sociated with a trend toward metabolic simplication. Thus, repre-sentative dairy LAB, L. delbrueckii subsp. bulgaricus and L. helveticus,contain many pseudogenes related to the utilization of several carbo-hydrates, reecting their dedication to growth on lactose (Cai et al.,2009). In addition, their genome lost amino acid biosynthetic and co-factor biosynthetic genes while an increased in genes for peptidetransport and proteolysis was observed, suggesting their adaptationto the protein rich dairy niche (Cai et al., 2009; Callanan et al.,2008; van de Guchte et al., 2006). Conversely, the lactobacilli com-monly associated with the gastrointestinal tract display a greatarray for transport of a diverse group of carbohydrates and specicextracellular enzyme complexes that could be involved in complexcarbohydrate degradation (Azcarate-Peril et al., 2008; Cai et al.,2009; Kleerebezem et al., 2010). These gastrointestinal lactobacilliencode other functions related with the gastric survival (e.g. genesencoding bile salt hydrolase) and with the intestinal mucosa interac-tions (e.g. mucus binding proteins).

Comparative genome analysis of lactobacilli revealed that aminoacid biosynthetic pathways are decient in different degrees in LAB,being related with the adaptation to a specic-niche. Thus, dairy LABsuch as L. delbrueckii subsp. bulgaricus and L. helveticus have lost thema-jority of their amino acid biosynthetic genes (Cai et al., 2009; Callanan etal., 2008; van de Guchte et al., 2006). L. acidophilus and Lactobacillusgasseri, typical LAB found in the human gastrointestinal tract are auxo-trophic for 14 and 17 amino acids, respectively (Azcarate-Peril et al.,2008; Cai et al., 2009). L. plantarum and Lactobacillus casei, ubiquitousmicroorganisms, possesses enzyme for biosynthesis of all amino acidsexcept the branched-chain amino acids leucine, isoleucine, and valine(Cai et al., 2009).

Compensating for the inability of dairy-lactobacilli to synthesizemost amino acids, these genomes contain several genes related tothe proteolytic system that allows them to acquire amino acids fromproteins present in their environment. This proteolytic enzyme sys-tem is vital to obtain essential amino acids and likely provides theselactobacilli with a selective advantage in protein-rich environmentsdue to it is energetically favorable to obtain amino acids from envi-ronmental proteins than de novo synthesis (Cai et al., 2009; Hebertet al., 2008). As stated above, the proteolytic system of LAB consistsof a cell envelope-associated proteinase, transport systems to allowuptake of the resulting peptides, and several intracellular peptidases,which degrade peptides to amino acids (Fig. 2, Hebert et al., 2008;Savijoki et al., 2006). The Prt is the key enzyme of this system as itis involved in the rst step of casein degradation (Savijoki et al.,2006) and certain Prt can release bioactive health-benecial peptidesduring food fermentation (Hebert et al., 2008, 2010; Savijoki et al.,2006).

Liu et al. (2010) performed a genome comparison of the proteolyticsystem of 22 LAB, including Prt, peptide transporters and peptidases.The 22 LAB genomes analyzed included L. acidophilusNCFM, Lactobacillusjohnsonii NCC 533, L. gasseri ATCC 33323, L. delbrueckii subsp. bulgaricusATCC 11842, L. delbrueckii subsp. bulgaricus ATCC BAA365, L. plantarumWCFS1, Lactobacillus brevisATCC367, Lactobacillus sakei23 K, Lactobacillussalivarius UCC118, Oenococcus oeni PSU1, Pediococcus pentosaceus ATCC25745, LeuconostocmesenteroidesATCC 8293, L. caseiATCC 334, Lc. lactis

subsp. lactis IL1403, Lc. lactis subsp. cremoris MG1363, Lc. lactis subsp.

Please cite this article as: Saavedra, L., et al., An overview of omic analytnational (2013), http://dx.doi.org/10.1016/j.foodres.2013.02.034cremoris SK11, Streptococcus thermophilus CNRZ1066, St. thermophilusLMG18311, St. thermophilus LMD9, L. reuteri F275, L. helveticus DPC4571, and L. rhamnosus GG (Liu et al., 2010). The Prt enzyme, responsi-ble for the primary hydrolysis of food proteins, was only found in a fewLAB strains, such as on the chromosome of L. acidophilus, L. johnsonii,L. delbrueckii subsp. bulgaricus, L. casei, L. rhamnosus and S. thermophilusLMD9, as well as on the plasmid of Lc. lactis subsp. cremoris SK11 (Liu etal., 2010). With the exception of L. rhamnosus which presents two prtgenes, the other mentioned strains possess a single prt gene (Liu et al.,2010). On the other hand, essential peptidases such as PepC, PepN,and PepM, proline peptidases PepX and PepQ, and endopeptidasePepO and dipeptidase PepV were found in all LAB genomes whilemembers of both the PepE/PepG (endopeptidases) and PepI/PepR/PepL (proline peptidases) superfamilies are absent in lactococci andstreptococci (Liu et al., 2010).

Data about the distribution of the proteolytic system genes can beused to predict the proteolytic potential of the LAB strains. For exam-ple, L. delbrueckii subsp. bulgaricus and L. helveticus have a very broadset of proteolytic enzymes including proteinase (Prt), aminopepti-dases (PepC, PepN, PepM, PepA and Pcp), endopeptidases (PepO,PepF and PepG), dipeptidases (PepD and PepV), tripeptidase (PepT)as well as proline peptidases (PepX, PepI, PepR, PepP and PepQ).The presence of these enzymes agrees with the role of these bacteriain milk, L. delbrueckii subsp. bulgaricus serves as the proteolytic mi-croorganism in yogurt and L. helveticus is a cheese starter culturethat has been used to degrade bitter peptides in cheese. Vegetable or-igin LAB species such as L. plantarum, O. oeni, and Leuc. mesenteroidesencode less proteolytic enzymes in their genomes, which is consistentwith their habitat, a ber-rich with less proteins (Liu et al., 2010). Inaddition, this comparative genomic approach allowed exploring thediversity of proteolytic system genes in various strains of Lc. lactis,conrming the proteolytic diversity between the two Lc. lactis sub-species, i.e. subsp. lactis and subsp. cremoris.

Genomic approaches may allow the prediction of proteolytic andavor-forming potential of bacterial strains. In addition, this knowl-edge could be used to improve the functional properties of dairyand other fermented food products by supporting the strain selectionprocess.

5. Application of omic-based analytical strategies for thecharacterization of bioactive peptides in food andrelated challenges

Several aspects are important for determining the biological activ-ity of peptides including the enzymes used for hydrolysis, food pro-cessing conditions, and the size of the resulting peptides, whichinuences their absorption across the enterocytes and bioavailabilityin target tissues (Udenigwe & Aluko, 2012).

There are in silico and in vitro approaches aimed at discovering andidentifying bioactive peptides in food matrix (Kussmann & VanBladeren, 2011). The in vitro method consists of the following steps(1) selection of an appropriate food protein source; (2) enzymatichydrolysis by selected enzymes, fermentation and/or gastrointestinaldigestion; (iii) in vitro screening for the potential bioactivity proper-ties; (iv) fractionation of the peptide mixture; (v) analysis of the pep-tide structure; and (vi) design of synthetic structural analogs orpeptide mimetic to validate bioactivity in vitro and in vivo (Fig. 3).

The newest omic approaches combine cell biology, immunology,biochemistry, synthetic chemistry, and the use of combinatoriallibrary with mass spectrometry to identify the patterns of peptideformation and the bioactivity of the peptides present in the sample.Typical protocol consists of sample purication, separation of pro-teins or peptides by 2D-PAGE or RP-HPLC, enzymatic digestion (inthe case of intact proteins) and identication by MS and MS/MS tech-niques. Using this methodology, the peptides naturally present in

human milk have been characterized (Picariello, Ferranti, Mamone,


7L. Saavedra et al. / Food Research International xxx (2013) xxxxxxRoepstorff, & Addeo, 2008), which allowed the detection of possiblebioactive sequences. The formation of angiotensin-converting enzyme-inhibitory sequences was monitored in milk (Gomez-Ruiz et al., 2007)and during Manchego cheese ripening (Hernandez-Ledesma, Amigo,Ramos, & Recio, 2004) using multiple reaction monitoring (MRM) de-tection technique.

Also MALDI-TOF-MS has become an important analytical tool inthe identication of peptides and evaluation of their role in biologicalprocesses. Unfortunately, this approach can be not exhaustive for theidentication of complex mixture of peptides, which is in most caseswhat is found in a food. Peptides in mixture may have either hydro-phobic or hydrophilic sections, in which case, the direct analysis ofsuch a mixture by MALDI-TOF-MS does not allow desorbing of allcomponents, due to the well-known suppression phenomena takingplace in the analysis of complex peptide mixtures. In these cases, se-quence coverage can be improved through the use of several matri-ces. Sinapinic acid (SA) is more suited for analysis of intact proteinsand large peptide fragments, whereas -cyano-4-hydroxycinnamicacid (HCCA) allows better detection of medium size peptides. Morerecent studies have proven the utility of using at least two matricesleading to a two-fold increase of the coverage of each protein. For in-stance, the use of HCCA in concert with the SA matrix has allowed toobtain a good coverage of hydrophilic proteins, and 2,5-dihydroxybenzoicacid (DHB) in concert with the SAmatrix to obtain a good coverage of hy-drophobic proteins (Gonnet, Lemaitre, Waksman, & Tortajada, 2003).

A further issue is the need for development of technologies toidentify low molecular weight (LMW) peptides with bioactivity. Thesimplest and most used approach is again based on MALDI-TOF-MS

Fig. 3. Food bioactive peptide analysis workow showing steps of production and pu

Please cite this article as: Saavedra, L., et al., An overview of omic analytnational (2013), http://dx.doi.org/10.1016/j.foodres.2013.02.034analysis, but matrix suppression often prevents detection of LMWcomponents, due in this case to matrix interference. A suitable methodfor analysis of small peptides in complex without extensive samplepre-treatment has been introduced recently (Nanostructure-AssistedLaser Desorption/IonizationNALDI). This method is a matrix-freemethod and therefore provided better signal intensity for LMW com-ponents compared with MALDI using matrix. This method has beensuccessfully applied to the study of bovine milk and colostrum(Nanostructure-Assisted LaserDesorption/Ionization (NALDI)) for anal-ysis of peptides in milk and colostrum (Ktt, Malbe, & Stagsted, 2001).

6. In vivo and in vitro omic studies on production and metabolismof food peptides

Despite of the extensive knowledge of the effects that food-derived peptides exert in vitro, data about the ability of the active pro-tein domains to be actually produced in vivo and to survive gastroin-testinal digestion are still scarce and contradictory due to the extremecomplexity of the peptide sets produced during digestion. Neverthe-less, these aspects are essential for potential bioactive peptides toperform their specic functions. Most biological activity assays formilk-, cereal- or soy-derived peptides, have been carried out on peptidefractions produced in non-physiological environments, using puriedenzyme and substrates, or enzyme extracts from LAB (Hartmann &Meisel, 2007; Hebert et al., 2008; Matar, Amiot, Savoie, & Goulet,1996) and yeast (Roy, Watanabe, & Tamai, 1999). Peptides can also bequantied from biological uids. For instance, blood levels of severalACE-inhibitor peptides were quantied in volunteers that have orally

rication integrated strategies for the structural and functional characterization.


8 L. Saavedra et al. / Food Research International xxx (2013) xxxxxxtaken up these peptides using LC-ESI-triple (van Platerink, Janssen,Horsten, & Haverkamp, 2006). Recently, Bouzerzour et al. (2012) ex-haustively studied in vivo, the kinetics of hydrolysis of a complexmatrixlike infant formula in the different compartments of the gut (proximaljejunum, median jejunum and ileum) using the piglet as a model;where some bioactive peptides were identied by nano-liquid chroma-tographyMS/MS.

Picariello et al. (2012) analyzed the human milk proteome byusing a gel-free shotgun proteomic analysis to overcome the limita-tions of the classical electrophoresis-based approach. Conventional2DE for descriptive proteomics shows some limitations that are par-ticularly critical for characterizing complex mixtures such as verylow-abundance proteins, as well as those with extreme isoelectricpoints or molecular weight values which can escape detection onthe gels. Briey, the shotgun proteomic strategy consisted of the re-duction of protein disulphide bridges and alkylation of cysteine resi-dues, following by the trypsin digestion and dephosphorylation, thislate step to prevent the missed detection of peptides due to phos-phorylation. To enlarge the proteome coverage, the peptides aresubjected to N-deglycosylation by PNGase F and analyzed separately.Finally, the complex mixture is analyzed by nanoow-high perfor-mance liquid chromatography (HPLC)/Fourier Transform-Ion Cyclo-tron Resonance (FT-ICR) mass spectrometry (MS) (Picariello et al.,2012).

The characterization of food-derived peptides in vivo is complicat-ed by the large occurrence of endogenous polypeptides but wouldbe virtually faceable by using the available up-to-date strategies ofhigh-resolution separation coupled to MS/MS targeting of specicsequences. By this approach, the -casein macro-peptide and theN-terminal fragments of s1-casein have been identied in humanblood after ingestion of yogurt (Chabance et al., 1998). Similarly, pep-tides produced during in vivo digestion of milk cow caseins have beenidentied in rat.

The stability of peptides to gastric digestion also has toxicologicalimplications, as it is one of the criteria used to assess the functionaland immunogenic characteristics of food proteins. Therefore, theomic identication of food peptides surviving gastrointestinal diges-tion can provide a means to help in localizing bioactive peptides.

In order to identify the peptides generated from protein digestion,several model systems, reproducing the gastrointestinal digestion havebeen developed. Proteolytic systems simulating the physiological diges-tive enzyme pools including pepsin and chymotrypsin and pancreatinhave been used (Hernndez-Ledesma, Quirs, Amigo, & I., 2007).Agudelo et al. (2004) designed a pilot plant to perform the continuous re-moval of digestion products during in vitro proteolysis, in order to mimicthe in vivo process and follow the fate of potentially bioactive peptides. Adigestion model that mimics in vivo gastricpancreatic intestinal process-es has been also applied to identication of gluten immunogenic peptides(Mamone et al., 2004).

Identication of peptide sequences surviving digestion is only therst among required step to assess potential bioactivity in vitro. Pep-tides produced in the intestine must be absorbed before delivering totheir nal organ or tissue. The study of these processes requires devel-opment of efcient omic strategies which conjugate biochemical, cellu-lar andMS tools. Transport studies across Caco-2 monolayers representone of the most widely acceptedmodels of in vitro permeation of drugsand peptides as they well correlate, at least under a qualitative stand-point, with intestinal absorption in vivo (Artursson, Palm, & Luthman,2001). Combination of the Caco-2 monolayer adsorption with MALDIand ESI-LCMS/MS analysis of the pool of peptides produced andtranslocated has allowed important progress in this research eld. Inone recent study, human Caco-2 cell line has been used as a model ofthe gut epithelium to predict the physiological behavior and the uptakeof gluten peptides. The epithelial translocation of a canonical immuno-genic peptide 33-mer by transcytosis was observed in Caco-2 cells

(Schumann et al., 2008). Similarly, the permeability of toxic p3143

Please cite this article as: Saavedra, L., et al., An overview of omic analytnational (2013), http://dx.doi.org/10.1016/j.foodres.2013.02.034and p3149 across Caco-2 cell layer was also demonstrated (Lebretonet al., 2012; Rauhavirta et al., 2011). The same omic approach hasbeen used to investigate how in vitro digestion contributes to the pro-duction of antioxidant peptides from soybean -conglycinin and tomonitor their uptake. The entire panel of peptides produced by digestionhas been characterized by combining MALDI and HPLCESIMS/MS in-vestigation leading to identication of novel bioactive sequences andtheir precursor able to be produced and adsorbed (Amigo-Benavent etal., Molecular Nutrition and Food Research, 2013, in press).

In addition to this classical peptide discovery strategy, an in silicoprediction and discovery of bioactive peptides approaches havebeen developed (Grigorov & van Bladeren, 2007; Panchaud et al.,2012). These in silico methods, named reverse genome engineeringallow the prediction of bioactive peptides and their enzymatic releasefrom a target protein diminishing the number of bioactivity tests de-veloped (Grigorov & van Bladeren, 2007; Panchaud et al., 2012). Bio-informatics approaches together with the available protein andpeptide databases offer the possibility to simulate the hydrolysis ofa target animal of plant protein and predict the release of bioactivepeptides. Several plant and animal genomes are available such asrice, maize, soy and bovine. On the other hand, some industrial andprobiotic LAB are sequenced, being possible to predict the enzymatichydrolysis of food proteins based on the specic enzyme activity of aselected LAB. Thus, nowadays, it is possible the in silico prediction ofbioactive peptide produced by gastrointestinal digestion and/or foodprocessing, providing a rapid and cost-effective strategy for novel bio-active peptide discovery.

7. Conclusions

The importance attributed to food proteins and bioactive peptidesin nutrition and health is undeniable. Scientic evidence demonstrat-ed that peptides derived from enzymatic food protein hydrolysatespossess several activities such as antimicrobial, immunomodulatory,enhancement of mineral absorption, antithrombotic, antihyperten-sive, opioid and antioxidant activities, which have a positive impactin human health. These bioactive peptides can be produced duringin vivo gastrointestinal digestion and/or food processing. Lactic acidbacteria are among the most widely microorganisms used as startercultures for the production of fermented foods, and through theirproteolytic system, they contribute to the release of bioactive pep-tides from dietary proteins. Therefore, microbial fermentation espe-cially by LAB, acquires a major role, since the production of keybioactive peptides can be triggered as foods are being produced. Inthis sense, the genomic and proteomic analysis of new LAB strains ca-pable of releasing milk-derived bioactive peptides constitute the basisfor the development of novel and improved functional foods. Omicanalysis will help to improve our knowledge on food-derived pep-tides identifying those bioactive peptides that have a benecial effecton health.

Acknowledgments

This work was supported by grants from CONICET, ANPCyT andCIUNT.

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An overview of omic analytical methods applied in bioactive peptide studies1. Introduction2. Production of bioactive peptides3. Main sources and target proteins involved in the production of bioactive peptides3.1. Bioactive peptides: main food sources3.2. Release of bioactive peptides by microorganisms

4. Genomics as a tool for the prediction of proteolytic potential of LAB5. Application of omic-based analytical strategies for the characterization of bioactive peptides in food and related c...6. In vivo and in vitro omic studies on production and metabolism of food peptides7. ConclusionsAcknowledgmentsReferences

2 ..analytical methods applied in bioactive peptide studies

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