In the ingredients of Kombucha leathers, bacterial cellulose (BC) was harvested from a traditional fermented beverage called Kombucha “tea fungus”.
Cellulose was harvested in this fermentation called Kombucha-derived bacterial cellulose (KBC).
BC is an eco-friendly natural polymer that unique physicochemical and mechanical characterization such as a three-dimensional fibrillar structure, high elasticity, durability, porosity, a high degree of crystallinity, biodegradable, non- cytotoxic, high thermal stability, and great water holding capacit [36-39]. Table 2 and Fig. 4 revealed some main differences between the properties and structure of plant cellulose and bacterial cellulose. Obviously, BC has been described with superior physical properties, high purity, and good thermal stability [40-42].
Table 2. Properties comparison between plant cellulose and BC [40, 42].
Property Plant Bacterial Ref
cellulose cellulose
Tensile strength (MPa) 25-200 20-300 [43]
Young’s modulus (MPa) 25-200 Sheet: 20,000 [44]
Single fibre: 130,000
Water holding capacity (%) 25-35 >95 [45]
Size of fibers (nm) Micrometer 20-100 [46]
scale
Crystallinity (%) 40-85 74-96 [47]
Relative hydrophilicity (%) 20-30 40-50 [48]
Purity (%) <80 >99 [49]
Degree of polymerization 300—10,000 14,000-16,000 [50]
Lignin and hemicelluloses Co-exists Non-exists [42]
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(a)
Plant cellulose
Bacterial cellulose
Single microfiber Ribbon Glucan chain
aggregat ——*>
“nam cà)
Figure 4 Structure of (a) plant cellulose and (b) bacterial cellulose of Acetobacter xvlinum [41].
BC has been extensively applied in medicine as antimicrobial wound dressings [51], blood vessel regeneration [52], dental and oral implants, neural implants, urinary conduits, tympanic membrane [53, 54], bio-printing [55], cosmetic [56], fabric [57], leather [24, 27, 58], textile [59], paper [60], electronic
25
devices [61], environmental [62] and food packaging [63, 64]. At the present time, BC is considered a future green-material source due to its life cycle being completely possible easy to toward the sustainable production processes as shown in Fig. 5 [38].
‘Tissue engineering
Figure 5 The life cycle of BC towards sustainable production [38].
Over the last decade, BC biosynthesis was mainly studied via the fermentation of different microorganism groups including Achromobacter, Agrobacterium, Acetobacter, Gluconacetobacter, Rhizobium, Sarcina and Pseudomonas [42, 65, 66] or cell-free BC synthesis via control enzyme systems [67, 68]. Yeast extract, peptone, glycine, glucose, fructose, sucrose, mannitol in Hestrin and Schramm (HS) standard medium [69] or alternative media were metabolized by these microorganisms as the key nutrient sources to grow, develop, and form gel-like
26
cellulose [70-72]. Fig. 6 displayed a representatively schematic of BC synthesis by Komagatacibacter xilyrus E25 [13]
Microfiber - Nanotbee
ee COOOQ,
vn xe. fam Stoo Ghee
hee nie het el re Cnn .. se“ =
`. ilo ae ose ace —— wore
= i
xạ | ox
ơ MP apa
ay, Ì
oAZ“—————2 +
Figure 6 BƠ gmthests and carbon sources metabolism in Komagataeibacter xilynus
£25 [73].
In brief, in the BC synthesis pathway of Kemagataeibacter salynus, carbon sources are metabolized through the pentoses phosphate pathway (PPP) to Glucose-6-Phosphate. It is worth noting that glucose is partially oxidized in the periplasm to obtain reduction power and this oxidation product is gluconic acid (as one of the main agents causing decreased pH value of the fermentation medium leading to cellulose synthesis activity inhibition of used bacterial strain) Ethanol is dehydrogenized to Glucose-6-Phosphate by the tricarboxylic acid cycle (PCA) and gluconeogenesis (GNG) pathways, Glucose-6-Phosphate has then isomerized to Glucose-1 Phosphate by phosphoglucomutase (PGM) before
7
is subsequently transformed to Uridine-5-Phosphate (a cellulose precursor) by uridylyltransferase (UGPT). Upon activation by cyclic-di-guanosine monophosphatase (c-di-GMP), Uridine-5-Phosphate is polymerized into B-1,4- glucan chains and translocated to the periplasm as cellulose synthase subunits such as BesA, BesB, BesC, and BesD for the exportation to the nanofibrils cellulose. Other key enzymes attend in the process will be PGI:
phosphoglucoisomerase; PEPCK: phosphoenol pyruvate carboxykinase; OAA:
oxalacetate; PEP: phosphoenol pyruvate, 3PGA: 3-phosphoglycerate,; GA3P:
glyceraldehyde-3- Phosphate [66, 73, 74].
Currently, the high-cost of culture media and low-yield are still huge obstacles to limiting the commercial scalability of these BC green material sources [27, 75- 80]. Pineapple, apple, pomegranate, muskmelon, watermelon, tomato, orange fruits, coffee husk, sugarcane molasses, vinasse, distillery effluent from wastewater of noodle processing have been investigated as an efficient and comparatively low-cost nutrient source for BC production [64, 71, 78, 81-86].
Remarkably, BC has also been collected from Kombucha fermentation of a traditional fermented beverage which was known as kombucha-derived bacterial cellulose (KBC) [35, 39, 71, 79, 80, 84, 87, 88]. According to structural analysis, the produced KBC possessed similar characteristics to pristine plant cellulose or BC of HS standard medium and other alternative media. In addition, these KBC was also confirmed to be free from contaminants such as lignin or hemicellulose, and has demonstrated good biological compatibility without histologic and hematologic toxic effects on tissue and cells [89-91]. Table 3 and Fig. 7 displayed the list and a represented model of the use of the bio-waste sources as the nutrient media to produce BC/KBC with huge development and application potential via the abundance and simplicity of the procedures [92].
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Table 3. List of BC production using the bio-waste sources (author’s
elaboration).
Fermentation Bio-waste sources Incubation Dry Ref
microorganism period weight
(days) (g/L)
Gluconacetobacter Potato peel waste- 6 47 [93]
xylinus hydrolysate
Gluconacetobacter Carob and haricot bean 9 1.8 [94]
xylinus
Gluconacetobacter Crude sugar beet 14 45 [88]
xvlinus molasses
Cheese whey 3.5
pretreatmented with lactase
Gluconacetobacter Sour whey without 15 12.6 [29]
xylinus pretreatment
Waste apple juice 8.8
Brewers’ spent grain 7.6
Gluconacetobacter Waste apple juice 15 3.0 [95]
xylinus
Gluconacetobacter Cheese whey 3 6.2 [96]
sucrofermentans
Gluconacetobacter Corn steep liquor 10 9.6 [76]
hansenii
Gluconacetobacter Pecan nutshell 28 2.8 [97]
entanii
Gluconacetobacter Distillery effluent 14 8.5 [77]
oboediens
Komagataeibacter VInasse 10 0.3 [84]
xylinus
Komagataeibacter Molasses and corn steep 10 6.4 [83]
xylinus liquor
Komagataeibacter Cheese whey and date 10 18.8 [98]
xvlinus syrup
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Komagataeibacter Sugarcane molasses 7 3.9 [92]
saccharivorans
Komagataeibacter | Whey was diluted and 14 6.6 [99]
rhaeticus pretreatmented with B — Galactosidase
Apple juice diluted to 14 9.5 initial sugar
concentration of 20 g/L
Komagataeibacter Rotten bananas 7 5.0 [100]
medellinensis
Komagataeibacter Rotten mango juice 10 2.0 [101]
medellinensis Cheese whey 24
Rotten banana juice 48
Komagataeibacter The industrial side- 7 18.9 [102]
sucrofermentans stream of Corinthian currants finishing and cheese whey
Acetobacter Whey was 8 5.6 [103]
pasteurianus pretreatmented with B — Galactosidase
Enterobacter Orange juice 14 3.7 [104]
amnigenus incorporated HS medium
Pineapple juice 3.3
incorporated HS medium
Molasses incorporated 3.0
HS medium
Leifsonia soli Soy whey 6.0 [82]
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2 iy @ Agro-industrial wastes
| Ki Thermal scidie ci ‘extraction er
cổằ el Waste extracts
Assimilation of sugars and BNC
D-Glucose | |
BNC Production on glucose-free HS medium + waste extract
‘Komagataeibacter saccharivorans MD1
biosynthesis inside a model
Cultures of Komagataoibactor | saccharivorans MD1 after 7 days
BNC film
bacterial cell
ee Lk
BNC Nanoribbon Í -2-2+>
20-60 nm HAAR ANAL Ũ
| pres INC synthase ÿ-1,4glucanchains
ƒ Microfibrlls.
Figure 7 BC production process from the pre-treatment of wastes [92].