La magia de los reflejos. Aproximaciones a las emociones: Tres perspectivas En este apartado se presentarán las emociones desde tres perspectivas que han sido centrales

According to The Konjac Association of Chinese Society for Horticultural Science (http://www�konjac�org/english/readnews�asp?rid=449), konjac, known also as elephant’s foot of devil tongue, represents a group of perennial herbal plants in

Amorphophallus genus of Araceae family� There are altogether about 170 species of konjac in the world, distributed mainly in Asia and Africa� China is rich in the resources of konjac germplasm and boasts of 20 odd species, of which 13 can be found only in this country�

Briefly, the process for making konjac glucomannan (KGM) involves the follow- ing steps: (1) the harvested fresh konjac tuber is first washed, cleaned, and peeled, followed by slicing; (2) drying is then achieved in a special type of oven dryer in which the konjac slices are subjected to high temperature to stabilized color, fol- lowed by low temperature drying; and (3) then the dried slices are broken and made into fine powder and the starch, fiber, and other impurities removed�

Konjac is grown in China, Korea, Taiwan, Japan, and Southeast Asia for its large starchy corms that are used to create a flour and jelly of the same name� It is also used as a vegan substitute for gelatin� KGM comprises 40% by dry weight of the roots, or corm, of the konjac plant� China and Japan are the main producing countries of konjac flour with annual output of 5000 ton (or 11 million pounds) and export of 2500 ton for China, and 3000–4000 ton for Japan (http://www�hnxcfood�com/cs2_e� asp)� Based on JECFA specifications, konjac has a MW of 200,000–2,000,000 Da; however, actual MW of KGM depends on the konjac variety, processing method, and storage time of the raw material�

Konjac is a heteropolysaccharide consisting of glucose and mannose monosac- charide units in the ratio of 5:8 (Shimahara et al� 1975b), connected by β-(1 → 4) glycosidic bonds (Figure 2�14)� Physical images, based on x-ray data revealed that the backbone conformation of the chain is a twofold helix stabilized by intramolecular O3…O5 hydrogen bonds (Yui et al� 1992)� This report is in agreement with KGM molecular chain parameters determined using the Mark–Houwink equation by Li et al� (2006)� This conclusion, however, is contrary to the molecular structure pro- posed for konjac mannan in earlier studies by Shimahara et al� (1975a), Kato (1973), and Kato and Matsuda (1980), which proposed slight branching on every 50–60

backbone sugar units� In addition, konjac mannan also contains approximately one acetyl ester group per 19 sugar residues (Maekaji 1978)� The MW of konjac man- nan depends on the species, or even variety, of Amorphophallus from which it is extracted and on the extraction method employed� Sugiyama et al� (1972) reported average MW of 0�67–1�9 million, depending on the Amorphophallus variety used, while Li et al� (2006) reported a average MW of 1�04 million Daltons� The idealized molecular structure of konjac is shown in Figure 2�14�

Konjac solution gels if it is heated after treatment or exposure to alkali� This gela- tion occurs as a result of the hydrolysis of the acetyl groups, which no longer hin- der intermolecular hydrogen bonding or association of the polymer chains (Maekaji 1978)� A further interesting characteristic of konjac gum lies in its synergy with other hydrocolloids� Takigami (2000) reported synergy between konjac mannan and xanthan such as the formation of an elastic gel and between konjac mannan– carrageenan and konjac mannan–agar as a significant increase in gel strength� Furthermore, konjac mannan is unique in that it produces a viscosity as high as 25,000 cP for a 1% solution, the highest viscosity ever reported for any nongelling gum� This is attributed to its extended or elongated twofold helix conformation, the absence of ionic charge on the molecule and its high MW� Konjac is a slow hydrat- ing gum and much less prone to lumping� In solution, konjac gum is also quite heat stable similar to xanthan�

HO HO HO HO HO H H H H H _HH H H H H H H H H H H H H H H H H H H H OH D-mannose D-mannose Konjac, 1.5%, 20 mil

D-mannose D-glucose D-glucose

OH O O O 1 1 1 6 4 4 4 1 1 6 4 3 4 O O O O O O O O O O C OH OH OH OH OH OH OH β β β β β CH2 CH2 CH2 CH3 CH2 CH2

FIGURE 2.14 Idealized structure of konjac mannan linear chain showing the repeating

units� (Adapted from Maeda, M�, Shimahara, H�, and Sugiyama, N� 1980� Agricultural and

Biological Chemistry, 44:245–252�) Other proposed repeating structural units are G-G-M-

M-M-G-M or G-G-M-G-M-M-M-M (Kato and Matsuda 1969) and G-G-M-M-G-M-M-M- M-M-G-G-M (Maeda et al� 1980; Takahashi et al� 1984)� Also shown is a konjac film, cast from a 1�5% solution and thickness of 20 mils (0�02 inches or 508 μm) measured across a 2�5- cm wide film strip using the TA�XT�PlusTexture analyzer, yielding tensile strength of ~805 g and puncture strength of ~630 g� (With kind permission from Springer Science+Business Media: Edible Films and Coatings for Food Applications, Structure and function of polysac- charide gum-based edible films and coatings, 2009, pp� 57–112, Nieto, M�)

Konjac, like other gums with a linear structure and high MW, produces strong film� The acetyl ester groups pose a steric hindrance that, in this case, serves to somehow open the molecule by acting as spacer between polymer chains, enabling the konjac powder to dissolve in RT water, although much slower compared to guar gum� This means that konjac can form film structure even without heating its solution but heating will be advantageous� As could be expected, the removal of acetyl ester groups will strengthen the intermolecular association of konjac molecules in solution and will result in the formation of a gel and stronger films, but this will also make konjac powder insoluble in RT water and would require heating to dissolve, similar to agar powder� A potential disadvantage of konjac mannan in film application is that it is too viscous� Optimally, the concentration of a gum polymer and other solids in a film application should be at least 25% for processing efficiency� Konjac, however, can only be dissolved in water at concentrations of 1�5% maximum before its solu- tion becomes too viscous to cast�

Wu et al� (2012) made edible blend films of KGM and curdlan by a solvent- casting technique using different ratios of the two polymers� The results showed formation of strong intermolecular hydrogen bonds between KGM and curdlan, and the interac- tion was much higher when the KGM content in the blend films was around 70 wt% with maximum tensile strength of 42�93 ± 1�92 MPa� Furthermore, the blend films displayed excellent moisture barrier properties�

2.5.2 ioniC gum PolymersWith extended, tWoFold helix struCtures Anionic gums exist as a polymers of sugar acids (e�g�, alginate); sugar units bio- synthesized with anionic substituents such as sulfate groups (e�g�, carrageenans); or carboxyl groups that are substituted through a chemical reaction (e�g�, CMC)� The presence of these anionic groups increases the polarity and water solubil- ity of gum polymers, though the inherent charge weakens intermolecular asso- ciations between polymer chains due to repulsion� However, these anionic gums are manufactured in the form of a salt, most commonly as sodium salt that pro- tonates and neutralizes the anionic charge� When cast and dried into film, they form films with superior clarity and decent tensile strength� The negative charge on molecules prevents gums from forming an excessively tight fiber structure in the dried state, which characteristic allows the polymers to imbibe water read- ily during the hydration process without foaming� Depending on the extent and distribution of charge on polymer molecules, the gum is either completely soluble in cold water, as in the case of alginate, λ-carrageenan and the highly substituted CMC; or only  partially soluble in water such as κ-carrageenan, ι-carrageenan, and pectin which are anionic gums but with threefold helix conformation that tend to aggregate; and therefore, require heat activation to fully hydrate the poly- mer molecules�

On the contrary, there are only few cationic gums that are currently produced and sold in commerce� Chitosan is one of them, a polymer of glucose amine where the amino group confers positive charge when the gum is dissolved in acidic solution� Several other grades of gums such as low methoxy, amidated pectin, and cationically modified guar that contain –NH2 groups are also available in the market�

2.5.2.1 Carboxymethylcellulose or Cellulose Gum (E466; CAS#:9004-32-4; 21CFR 182.1745)

Carboxymethylcellulose or CMC is first commercialized in 1946 by Hercules Inc� It is a cellulose ether produced by reacting the alkali cellulose with sodium mono- choroacetate, under controlled conditions� There are many degrees of substitution producing different properties of CMC; hence, many grades of CMC are in the market to perform different functions, that is, as an all purpose thickener, suspend- ing system, stabilizer, binder, and film former in a wide variety of uses� Average MW of commercial CMC grades ranges between 90,000 for the low viscosity and 700,000 for the high viscosity grade, corresponding to DP of 400–3200 (http://www� brenntagspecialties�com/en/downloads/Products/Multi_Market_Princpals/Aqualon/ Aqualon_CMC_Booklet�pdf). Viscosity grades ranging from 20–50 cP for a 2% concentration up to as high as 13,000 cP at 1% concentration in water are available, as measured at 30 RPM and 25°C� For general thickening applications, high viscos- ity grades are chosen for economic reasons, because it allows lower usage to achieve the same target viscosity� However, in other applications like flavored syrups, the rheology of high MW CMC and the presence of graininess or grit in solution due to unsubstituted and insoluble regions in the molecule are sufficient reasons to use lower viscosity grades which are less prone to this textural problem� In film applications, low viscosity CMC is also preferred over the viscous grades because higher gum concentrations can be achieved in casting solutions, which means less water to dry�

The CMC structure involves carboxymethyl substitution of the native cellulose polymer at the C2, C3, or C6 positions of anhydroglucose units (Figure 2�15)� The DS

O O– O– O– O– O– O HO HO HO HO H H H OH H _HH H H OH H H H H OH H _H H H H H H H H H H OH CMC, 3%, 60 mil CMC, 3%, 80 mil H O O O 4 4 4 O O O O O O O O O O O β1 β1 O O _O OH H H O OH OH β1 β1 CH2 H2C Na+ CH2 CH2 CH2 CH2 CH2 H2C H2C H2C Na+ Na+ Na+ Na+ β1

FIGURE 2.15 Idealized structure of carboxymethylcellulose showing five glucose units in

a twofold helix conformation with an average DS of 1�0 (the fourth glucose from the left having two substitutions and the fifth having 0)� Also shown is picture of its film cast from

a 3% solution with thicknesses of 60 mils (0�06 inch or 1524 μm) and 80 mils (0�08 inch

or 2032 μm)� Tensile strength measured across a 2�5-cm wide film strip using the TA�XT�

PlusTexture analyzer, yielding tensile strength of 1920 g and puncture strength of 1170 g� (With kind permission from Springer Science+Business Media: Edible Films and Coatings

for Food Applications, Structure and function of polysaccharide gum-based edible films and

is generally in the range of 0�65–0�95, but it can be as high as 1�2� Higher DS means higher solubility for CMC� However, the uniformity of the substitution along the cel- lulose backbone also influences the solubility or smoothness of CMC solutions� The glycosidic linkage of CMC is the same as the parent cellulose and is composed of β-(1 → 4) glucose linkages that assume a twofold helix, extended conformation with lengths varying depending on the MW� The carboxylate ends of the carboxymethyl groups are free and therefore, CMC is anionic� In addition to the free –OH groups remaining in the sugar residues, it is very polar and has good solubility in water� CMC is produced as sodium salt or NaCMC, and when it is dissolved in water, the –COONa groups ionize to Na+ _{and –COO}−_{, creating a negative charge on the gum molecule� At}

acidic pH levels of 3�0 or less, CMC becomes insoluble due to the protonation of the –COOH and loss of solubility� Figure 2�15 shows the structure of CMC and its film� It forms a clear film, water soluble with thickening property, but it does not heat seal�

Alyanak (2004) studied the film-forming properties of NaCMC and HPC and found that NaCMC film produced good mechanical properties but has a higher water vapor sorption capacities or low water vapor barrier properties� This is expected since CMC is anionic and more polar, whereas HPC is nonionic� If used in edible dissolvable packaging, this means that CMC film will dissolve faster when added to water or in the saliva when put in the mouth� Tongdeesontorn et al� (2011) studied the effect of CMC on properties of cassava starch films and found that CMC increased its tensile strength, reduced elongation at break, and decreased water solubility of the blended films� They further determined that FT-IR spectra indicated intermolecular interactions between cassava starch and CMC in blended films by shifting of car- boxyl (C = O) and OH groups� Shekarabi et al� (2014) made composite films based on plum gum and CMC plasticized with glycerol and found that WVP of the films increased when glycerol is increased from 5% to 20%, and decreased tensile strength but this improved flexibility of the films and elongation at break�

2.5.2.2 Sodium Alginate (E401; CAS#9005-38-3; 21CFR184.1724; FEMA 2015)

Alginate is present in the cell walls of brown algae as calcium, magnesium, and sodium salts of alginic acid� Commercially, alginate is mostly sold as sodium alginate although potassium alginate, ammonium alginate, or ammonium–calcium alginate grades are also produced to some extent� Alginic acid has limited function- ality and requires conversion to its salt form to improve its solubility and stability� Briefly, alginate processing starts with wet chopped seaweeds that are subjected to alkaline extraction, where the residue is removed and the alginate in solution is pro- cessed further to produce the final sodium alginate in two ways (http://www�fao�org/ docrep/006/y4765e/y4765e08�htm):

1� Alginic acid process: Acid is added to the alginate extract to form alginic acid which forms a gel� To remove excess water from the gel, alcohol is added to the alginic acid extract, followed by sodium carbonate which converts the alginic acid into sodium alginate� Sodium alginate does not dissolve in the mixture of alcohol and water and is therefore precipitated out, pressed to remove excess water, and then dried and milled to an appropriate particle size�

2� Calcium alginate process: In this method, calcium chloride is added to the alginate extract to form fibrous calcium alginate gels� The calcium algi- nate gel is then treated with acid to convert it to alginic acid� These fibrous alginic acid fibers are then reacted with sodium carbonate gradually, until all the alginic acid is converted to sodium alginate� The paste of sodium alginate is sometimes extruded into pellets that are then dried and milled� Annual production of alginate has not really increased much from 33 million tons in 2001 (http://www�fao�org/docrep/006/Y4765E/y4765e08�htm) to 38 million tons in 2008 (Helgerud et al� 2010)� Based on JECFA specification, commercial sodium alginate has average MWs ranging from 10,000 to 600,000 and these correspond to different viscosity grades�

Alginates are linear, unbranched polymers, containing _{β-(1 → 4)-linked d-man-} nuronic acid (M) and _{α-(1 → 4)-linked l-guluronic acid (G) units, and are therefore} highly anionic and very polar polymers� Alginates are not strictly random copolymers but are instead block copolymers� Based on the study by Haug et al� (1966, 1969), alginates consist of blocks of both similar (or homopolymeric) and alternating (or heteropolymeric) sugar units (i�e�, MMMMMM, GGGGGG, MG, and GM blocks) as shown in Figure 2�16, with each of these blocks having different conformation behaviors (Sabra and Deckwer 2005)� The G block forms a twofold helix with a pitch of 8�7 Å, which is 1�7 Å shorter than in cellulose or mannan (Atkins et al� 1973b)� The guluronic acid residues are in the 1_C

4 conformation and are, therefore, diaxially

linked along the polymer chain� This gives the structure of the G-block polymer a buckled, as opposed to flat, conformation� This helix is stabilized by O2…O61 hydro- gen bonds, and adjacent helices are bridged by water molecule which are present one

Alginate, 4%, 20 mil H O O α α α α β β β β O O O O O O O O O O O O O O O O O O O O O OH OH HO O O O O O O O O OH OH OH HO HO HO OH OH

Alternating poly α-(1→4)-L-guluronic

acid-β-(1→4)-linked D-mannuronic acid

OH OH OH OH X Y Z OH O O H 1 1 1 1 1 1 1 1 H G G G G M M M M H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H 4 4 4 4 4 4 4 4

Poly α-(1→4)-L-guluronic acid Poly β-(1→4)-D-mannuronic acid

FIGURE 2.16 Idealized structure of alginate showing polyguluronic (G), polymannu-

ronic (M), and alternating guluronic–mannuronic (GM) fractions� Also shown is a picture

of its film, cast from a 4% solution and thickness of 20 mils (0�02 inch or 508 μm) mea-

sured across a 2�5-cm wide film strip using the TA�XT�PlusTexture analyzer, yielding tensile strength of ~1500 g and puncture strength of ~830 g� (With kind permission from Springer Science+Business Media: Edible Films and Coatings for Food Applications, Structure and function of polysaccharide gum-based edible films and coatings, 2009, pp� 57–112, Nieto, M�)

per guluronate residue (Rao et al� 1998)� The structure of the polymannuronic acid segments is very similar to that of cellulose and mannan, especially the O3…O5 hydrogen bonds (Atkins et al� 1973a,b)� The mannuronic acid residues are in the 4_C

1

conformation and consequently it is diequatorially linked but also assumes a twofold helix or extended conformation� The linkages give the polymer segments containing polymannuronic acid a flattened, ribbon-like structure� It has been proposed that this structure is further stabilized by the formation of hydrogen bond to atom O3 in one ring with the ring oxygen of an adjacent residue� Another hydrogen bond, between the carboxyl group’s hydroxyl and the oxygen atom attached to C3 of a parallel chain causes the polymannuronic acid chains to bond into sheets of anti-parallel residues� Regularly alternating poly(MG)n, on the contrary, has a sinusoidal conformation�

Although alginates from brown seaweed sources may exist predominantly as high G or high M, all three blocks are present within a single alginate molecule� For example, the M/G ratio of alginate from Macrocystis pyrifera is about 1�6:1, whereas that from Laminaria hyperborea is about 0�45:1� Alginates may also be prepared with a wide range of average chain lengths (50–100,000 DP) to suit the application� Commercial grades that are high in guluronic acid are usually labeled HG�

There are two structural blocks in alginate molecule that respond differently to calcium or bivalent ions, such as the G-block and M-block� The G-blocks respond to calcium cross-linking faster than the M-blocks, because of its three-dimensional “egg box” molecular conformation, which structure accommodates Ca2+ _{ions to}

form salt bridges� The M-blocks also associate through Ca2+ _{salt bridges, forming}

more elastic gels with good heat stability (Donati et al� 2005)� Different viscosity grades corresponding to varying MWs of either high G or high M alginates are com- mercially produced�

Sodium alginate forms a clear film as shown in Figure 2�16� It does not stretch and does heat seal like all polar gum films� Cross-linking the alginate with calcium increases the tensile strength of the resulting film, indicating that film structure forms better without the charge repulsion� Cross-linked calcium–alginate always yields a strong, clear film that is insoluble in water compared to sodium alginate film; this combination has been used to microencapsulate probiotics, such as Lactobacillus

acidophilus, to increase its survival under gastric conditions� Based on a study by Chandramouli et al� (2004), the viability of the bacterial cells within calcium–alginate microcapsules increased as both capsule size and alginate concentration increased�

One important film application for sodium alginate is sausage casing� As shown in Figure 2�17, the meat and alginate can be coextruded, where the meat is extruded in the inner tube and the alginate solution in the outer tube� As the sausage comes out of the tube, it showered immediately with calcium chloride solution to form the calcium–alginate casing� The use of alginate as sausage casing has attracted the attention of many sausage manufacturers and has already started commercial productions in the United States, Europe, and Canada� Other film applications for sodium alginate have been published� Russo et al� (2007) made three films of sodium alginate, with different amounts of guluronic fraction and found that increasing the fraction of guluronic units promoted chain-to-chain interaction through Ca2+ _cross-