Antimicrobial and Emulsifying Potential of Legumes
Legume is the fruit and grain seed of Fabaceae (or Leguminosae) family (Pina-P?rez and Ferr?s P?rez, 2019) which includes approximately 18000 species (Allaire and Brady, 2008). Moreover, legume provides high quality protein, fiber, and fat, especially in sub-Saharan Africa (SSA) where legume plays essential role in their diet (Odendo et al., 2011).
Proteins can be classified based on solubility, physiological role, and structure (Oomah et al.
, 2011). For legumes, proteins can be roughly classified into metabolic- and storage- types. Storage protein is the most abundant, reaching levels up to 80% of the total protein content (Guti?rrez-Uribe et al., 2015). Based on the solubility, Osborne (1916) defined the protein into albumin, globulin, prolamin, glutelin, and residue, which is the most efficient classification for protein in legume. For the storage protein, globulin is the most abundant (Oomah et al., 2011).
Among the most important legumes, haricot bean (Phaseolus vulgaris), chickpea (Cicer arietinum), lentil (Lens culinaris), garden pea (Pisum sativum), and soybean (Glycine max) are mainly discussed in this study.
For example, Silva et al. (2001) found that globulin (41.79%) is the most abundant protein in chickpea, followed by protein albumin (16.18%), glutelin (9.99%), and prolamin (0.48%). In addition, Gueguen and Barbot (1988) found that globulin and albumin accounted for up to 50-60% and 15-25% of the total protein in garden pea, respectively. Also, Gupta and Dhillon (1993) revealed that in lentil, globulin (49.0%) was mainly found, followed by albumin (16.8%), glutelin (11.2%), and prolamin (3.5%) (Boye et al., 2010).
Emulsion is the mixing of two immiscible liquids.
Legume protein is commonly used as emulsifier in baking products like meringue, whipped toppings, mousses, and cake batters. Aquafaba is generally defined as the wasted cooking water of chickpea, can also be broadly referred as the wasted cooking water of legumes. For instance, chickpea canning water (known as Aquafaba) exhibited higher EAI compared to egg white, along with increased stability of emulsion with increasing pH (Buhl et al., 2019). These results make aquafaba a potentially excellent novel emulsifier. Besides, Fiber as well as phytochemicals such as saponins and phenolics might also confer aquafaba emulsifying activity.
Legume exerts high antimicrobial activity within a wide range. Protein, phytochemical including saponins and phenolics, antinutrient like phytic acid, are mainly discussed for the antimicrobial activity. For legume protein, peptide such as defensin is mainly discussed in this study. Pina-P?rez and Ferr?s P?rez (2018) elucidated that proteins and peptides from legumes reveal high microbial growth inhibition between 91 and 97%. In addition, Legumes with antimicrobial activity comprises haricot bean, chickpea, lentil, garden pea, soybean, mung bean (Vigna radiata), pigeon pea (Cajanus cajan), and peanut (Arachis hypogeaea).
The objective of this essay is to elucidate the mechanisms of emulsifying and antimicrobial properties of legumes, correlating them to aquafaba effects on food quality.
Throughout the mixing of oil with protein solutions, protein molecules adsorb to the newly formed oil droplets which lowers the surface tension, during which the continuous formation of an oil-water interface and oil droplets results (Kiosseoglou & Paraskevopoulou, 2011). The
The emulsifying ability of the legume protein and the stability of legume protein-stabilized emulsions is defined as emulsifying activity index (EAI) (Pearce and Kinsella, 1978) and emulsifying stability index (ESI) (Aryee et al., 2018).
Phytochemicals are chemicals produced by plants. Various groups of phytochemicals exist in green tea, grains, seeds, legumes, fruits and vegetables (Vaclavik & Christian, 2013). In this study, phytochemical saponins and phenolics in legume and aquafaba are mainly discussed for emulsion and antimicrobial activity.
Saponins are glycosides that comprises a hydrophilic sugar moiety which linked to a lipophilic triterpene or steroid aglycone (Cornell University, 2019; Hostettmann & Marston, 2005). It has been reported to be found in many legumes such as chickpeas, lentils, peas, and various beans (Oomah et al, 2011). Due to the amphipathic characteristic, saponins are also presented in aquafaba.
3. Antimicrobial Activity
Among legumes with antimicrobial characteristic, chickpea and soybean processed the highest antimicrobial activity. For soybean, the long chain soy peptide IKAFKEATKVDKVVVLWTA acts on both gram-positive and gram-negative bacteria with a concentration of 37.2??M (Pina-P?rez and Ferr?s P?rez, 2018).
3.1 Antinutrient: Phytic Acid
Phytic acid (PA) is an antinutrient commonly found in legume cotyledon (Reddy, 2001). Recently it was found in the cooking water of legumes, especially yellow soybeans (data not published, FOOD 699 2018-2019). It contains a cyclic six-carbon ring with six reactive phosphate groups (Kim & Rhee, 2016).
Due to its antimicrobial property, PA was regarded as the natural antimicrobial agent in the food industry. For instance, Both Kim and Rhee (2016) and Zhou and collaborators (2019) found that PA at concentration between 0.2 to 0.16% (w/w) exerted excellent antimicrobial activity on both non-acidadapted and acid-adapted E. coli O157:H7 strains. Furthermore, PA is also effective in destroying cell membrane of gram-positive bacteria (Zhou et al., 2019). Lipopolysaccharide (LPS) on the outer membrane (OM) of pathogenic bacteria (such as E. coli and S. aureus) protect the cell from antimicrobial agents or antibiotics (Nikaido, 2003; Raetz & Whitfield, 2002; Zhou et al., 2019) whereas PA inhibits the growth of it through cell membrane damage by chelation of LPS. Both hydrogen ion and phytate ion can act on the OM-stabilizing divalent cations and disintegrate LPS on OM, through which the membrane integrity is disrupted. Furthermore, compared to the commonly used organic acids, PA exerts greater bactericidal effect at same working concentration (p24-hour inhibition). In addition, antimicrobial activity against different bacteria varies as well. Araya-Cloutier et al. (2017) demonstrated that legume saponins tested in the study presented longer inhibition time on L. monocytogenes than MRSA.
Defensin is a cysteine-rich antimicrobial peptide (AMP) (Broekaert, Terras, Cammue, and Osborn, 1995) ubiquitous in plants but also commonly found in legume seeds. It was established to have a wide spectrum of antimicrobial activity on Gram-positive, Gram-negative bacteria, fungi, and enveloped viruses (Broekaert, Terras, Cammue, and Osborn, 1995; Tiwari et al., 2009). However, the study about legume seed defensin is still obscure only a few of them were discovered and researched, including Lc-def (Finkina, Shramova, Tagaev, and Ovchinnikova, 2008) from lentil and Psd1 from pea (Tam, Wang, Wong, and Tan, 2015).
18.104.22.168 Lc-def defensin from lentil (Lens culinaris)
Lc-def, defensin discovered from the germinated lentil Lens culinaris seeds (Finkina, Shramova, Tagaev, and Ovchinnikova, 2008), was reported to be high in antifungal activity but no inhibitory effect on neither Gram-positive (such as Clavibacter michiganensis) nor Gram negative (such as Agrobacterium tumefaciens and Pseudomonas syringae) bacteria. The antifungal activity exhibited notable variation among different fungal species like other defensins. For instance, Shenkarev et al. (2014) found that Botrytis cinerea only required 9.25?M Lc-def to be 50 % inhibited while Aspergillus niger requires 18.5?M. The defensin suppressed hyphal growth and can induce fungus mycelium lysis at the concentration higher than 37 mM (Shenkarev et al., 2014). Hammami, Ben, Vergoten, and Fliss (2008) concluded that the role of lc-def plays in molecular function and biological process is lipid binding and lipid transport, respectively. Hence, we can postulate that Lc-def inhibit the growth of fungi through electrostatic interaction with anionic lipid components of fungal membranes (Shenkarev et al., 2014). The detailed mechanism of the antifungal activity remains to be further studied.
22.214.171.124 Psds defensin from garden pea (Pisum sativum)
Psd1 and Psd2, isolated from the seed of pea Pisum sativum (Almeida, Cabral, Zingali, and Kurtenbach, 2000), were reported to have high antimicrobial activity against some fungi and yeasts. Both Psds were found to be effective against Aspergillus versicolor and Neurospora crassa but have little effect on Fusarium moniliforme and Saccharomyces cerevisae (Almeida, Cabral, Zingali, and Kurtenbach, 2000). The antibacterial activity was mediated through inhibiting the K+ channel (Almeida, Cabral, Zingali, and Kurtenbach, 2002) on the cell membrane whereas for the antifungal activity was found to be related to its high affinity with membranes containing glucosylceramides (GlcCer) or ergosterol (Erg), of which GlcCer and Erg are features of fungi cell membrane (Amaral et al., 2019; Gon?alves et al., 2012). Moreover, both Amaral et al. (2019) and Gon?alves et al. (2012) also found that Psd1 adsorbed to the membrane at lower Kp whereas at higher Kp, Psd1 could be partially inserted into membrane. Since lc-def and Psds are water-soluble, there is a high potential to exert strong antimicrobial activity if sufficient amount was found in aquafaba. Furthermore,
3.3.2 Others (TBC)
Aquafaba of different legume presents various emulsion and antimicrobial activity for the disparity in the composition. Further study into aquafaba is required in the application as emulsifier and antimicrobial preservative.
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