A Brief Study on Starch Based Bio-Plastics Produced From Staple Food Items

 

Shrushti Kothekar¹, Shivangi Shukla², Suneetha V³

 

ABSTRACT:

Increasing amounts of plastic contamination in the oceans leads to their ingestion by various organisms, causing suffocation by macro particles and bioaccumulation of micro-particles in smaller to larger organisms in the food chain, human beings at the very end of it (Racusin, Jacob Deva., and Ace McArleton, 2012, The Natural Building Companion: a Comprehensive Guide to Integrative Design and Construction. Chelsea Green Publishing). Hence, our food eats our own garbage. Bio-plastics have been a recent development, and are being considered for usage in medical and pharmaceutical industry too, apart from being the substitute to plastic which we normally use. In this paper we propose methods to produce bio-plastics from starch based, staple food items, which can not only biodegrade, but are also edible. We make a comparative study of bio-plastics produced from sources such as banana peel, corn and potato, amongst each other and against synthetic plastic, discuss their properties along with biodegradability from soil microbes, concluding the most apt bio-plastic to substitute the commonly used plastics.

 

 

 

INTRODUCTION:

Biodegradable and compostable plastic, especially from renewable resources, are essential innovations (Lörcks et.al, 1998)^[1].Many bio-plastics are biodegradable but not all degrade. Compared to petroleum based plastics, bio-plastics result in lower greenhouse gases. Poly-lactic acid (PLA)(Mol.wt.20.3x10⁴ g/mol)(Liu et.al., 2013)^[2] is one of the most common and best kind of bio-plastic till date, made from corn starch, wheat, sugarcane and tapioca roots. PLA is biodegradable, and has characteristics similar to PE (Polyethylene), PS (Polystyrene) and PP (Polypropylene). It’s production is cost effective as it can be produced from the equipment used in petroleum plastic based industries and biodegrades within 6 to 12 months.

 

Reasons for introducing biopolymer materials into the market are many, including innovations in development of material, preservation of fossil based raw materials, reduction in amount of waste, protection of climate, etc. From the very start, it has been kept in mind that bio plastics be developed in a manner which is pro-environment and inexpensive. They decrease the acute waste scenario in an ideal, environment-friendly manner; closing natural material cycles and being a great support in the explanation of many environmental and waste problems. Some of the properties of bio plastics are:

·       Compostable in accordance with DIN 54900

·       Can be processed using already existing production lines in plastic industries

·       High water-vapour permeability

·       Good oxygen barrier

·       Not electrostatically chargeable. (Lörcks et.al, 1998)^[1]

 

Polysaccharides such as cellulose and starch which are readily available, biodegradable and lower in costs to protein and synthetic additives, can be the natural alternatives to bio plastic synthesis(Gonzalez-Gutierrez et.al., 2010)^[3]. Starch is an inexpensive agricultural resource and consists of two macromolecules- amylose (linear starch chain) and amylo-pectin (branched starch chain)(Lörcks et.al, 1998)^[1].

 

Plasticizers are molecules used in starch synthesis, which are of low molecular weight and volatility, which increases polymer chain mobility by reducing intermolecular forces. Water, glycerol, propylene glycol and polyethylene glycol are some of the common plasticizers (Gonzalez-Gutierrez et.al. 2010)^[3]

 

Bio-plastics have been reported as the preferred material choice for application in tissue

engineering ,biomedical applications, sutures, implants, as they do not cause severe harm to

tissues or blood of the host, and are non-toxic and mostly biodegrade.

 

We have used starch as the bio-polymer in the production of bio-plastics. Since it has been made out of starch, it is edible.

 

Existing patents concerned with bio-plastics-

·       Envigreen Biotech India Private Ltd is India’s first company to produce 100% biodegradable substitute to plastics.

·       Floreon Transforming Packaging Ltd, a leading bio-plastic technology company has been granted a patent for Floreon, which is essential to extend the uses of bio plastics, owing to its toughness and ease of production. This is a polyester-based polymer blend with polylactic acid, or PLA.

·       French Carbios have got a patent in enzymatic bio-plastics manufacturing process to make Green PET (polyethylene terephthalate) from the petrochemical PET. The second patent covers a microorganism strain that was capable of degrading poly-lactic acid (PLA). This company aims to use enzymes for the conversion of plastics into their monomeric forms.

 

MATERIALS AND METHODS:

Collection of materials:

Collection of soil sample from VIT University, Vellore.

 

Soil sample was collected from a damp soil area, having partially degraded leaves.

·       Potato and banana had been procured from the grocery store, outside VIT University.

·       Vinegar, corn-starch, glycerin were purchased from the ALL MART store of VIT University.

 

 

 

 

Production of bio-plastics:

Corn-starch plastic:

 

Flowchart 1: synthesis of corn-starch plastic

 

·         Potato-starch plastic-

 

Flowchart 2: synthesis of potato-starch plastic

 

 

Corn and potato plastic:

We even combined corn-starch and potato starch, and made plastic using the same procedure.

 

Banana peel plastic:

 

Flowchart 3: synthesis of banana plastic

 

Potato, corn + potato and corn-starch plastic film is stronger and transparent compared to banana plastic film which is rough and fibrous.(Refer to figure 1)

 

Biodegradability test-:

We prepared media using LB HiMedia and Agar-agar, and made serial dilution up to 10^-6 of soil sample taken from our college, VIT University, Vellore district, TamilNadu.

 

In our first test,

·       We used the spread plate technique, using 10^-4 dilution factor, and let the microbial cultures grow in incubator at 37° C for a day (24 hours).

·       After obtaining colonies, we placed pieces of corn and potato plastic in separate plates to observe which one degraded the fastest.

·       We observed the degradation for a period of 15 days.

 

In our second test,

·       We used 10^-6 dilution factor, for obtaining bacterial cultures.

·       After getting isolated colonies, we placed 3-4 pieces of corn+potato, banana, corn and potato plastics in separate petri plates.

·       We observed the degradation for one day (24 hours).

 

(Refer Table 2, Table 3, Figure 2, Figure 3)

 

 

Table-1: Reported microbes capable of breakdown of plastic-

Sr.No.	Organism	Characterization	Properties
1.	Bacteria-Ideonellasakaiensis	Gram negative, aerobic, rod shaped bacteria	Uses PETase enzyme to break down PET plastics to terepthalic acid and ethylene glycol(Yoshida et.al, 2016)[4]
2.	Bacteria- Pseudomonas putida	Belongs to phylum Proteobacteria of the bacterial kingdom	Capable of converting styrene oil to biodegradable plastic PHA (Polyhydroxyalkanoates)(Raghavan et.al., 1999)[5]
3.	Bacteria- Brevibacillusborstelensis	Belongs to the division of Firmicutes of the Bacterial kingdom. It is gram positive, aerobic and rod shaped.	Capable of utilizing and degrading polyethylene as the sole source of carbon(Hadad et.al., 2005)[6]
4.	Bacteria- Alcaligenesfaecalis	Belongs to the phylum proteobacteria of the kingdom bacteria. It’s a gram negative, rod shaped bacteria	Emulsifying activity against different hydrocarbons and crude oil.(Bharali et.al, 2011)[7]
5.	Bacteria- Pseudomonas stutzeri	Belongs to the proteobacteria phylum of the bacterial kingdom. It’s a gram negative, rod-shaped, soil bacterium.	Uses PHA depolymerases to degrade PHA. Also, degrades carbon tetrachloride.(Lee et.al., 1999)[8]

 

                                                                 (a)                                             (b)                                           (c)                                           (d)

Figure 1(a to d) Bio-plastics: banana, (still wet in the pictures) potato, potato+ corn-starch, corn starch.

 

 

 

Table 2: Biodegradability Results (observed after 15 days)

 

Figure 2: (a)- corn starch plastic, figure (b)- potato starch plastic and figure (c)- potato starch plastic with orange food colouring

 

Table 3: Biodegradability Results (observed after 24 hours)

Figure 3: Biodegradability of (a)- corn + potato, (b)- banana, (c)- corn and (d)- potato bio-plastics in the bacterial cultures (in a duration of 24 hours

 

 

 (c)                                                           (d)

Figure 4: (a)- gram negative bacteria in 40X, (b)- shows the same in 100X, (c)- gram positive bacteria in 40X.Both these bacteria’s were observed to be acting upon corn-starch plastic (d)- bacteria which was inhibiting the growth of other bacteria

 

Characterization using Gram Staining of the bacteria responsible for degradation-:

·       On doing Gram staining for the bacteria responsible for bio-plastic degradation, we found gram positive and, gram negative bacteria, both in the same petri-plate.

·       Two different types of bacteria were observed which inhibited each other’s growth.(Refer Figure4)

 

Tensile Strength:

Test 2-Standard test using 100 gram weights:

·         We compared all our samples with synthetic plastic by applying weights of 100 grams.(Refer Figure 5)

 

 

(a)

 

(b)

Figure 5: (a) shows all the bio-plastics which tore easily,and (b) is the synthetic plastic which was the strongest.

 

Solubility-:

We suspended bio-plastic pieces of equal dimensions in beakers containg 20 ml water each.We made two observations, one after 15 minutes and another after 7 hours. (Refer Figure 6)

 

 

Figure 6: Solubility test (From left to right): Corn, Corn + Potato, Banana, Potato plastic

 

RESULT AND DISCUSSION:

For biodegradability test1:

According to all these observations, we can state that corn-starch bio-plastic degrades the fastest, followed by banana plastic, then corn and potato bio-plastic, and then potato plastic.

 

Characterization using Gram Staining of the bacteria responsible for degradation-:

For tensile strength test:

Test1-approximation test:

Corn, potato and their mixture, all the three plastic films were strong, but banana peel plastic tore easily on applying force. The plastic obtained from corn-starch was the strongest, i.e., didn’t tear easily.

 

Test 2-Standard Test using 100 gram weights:

·       All the bio-plastics tore easily, but the synthetic plastic could sustain even more than 500 grams of weight.

·       Also, the more the starch was used, more stronger and thicker was the film

·       So, the bio-plastics can be made stronger by using more of starch and proper processing, plasticizers and by using strengthening substances, mentioned in the floreon technology.

 

For solubility test-

·       In the 15 min observation,potato plastic and corn+potato plastic had started to solubilize,whereas the other two were undisturbed.

·       After 7 hours,potato plastic had turned into a very thin layer,followed by corn+potato,and corn starch plastic had solubilized a little. The banana plastic remained unaltered.

·       In both of our readings we observed that potato plastic solubilized the fastest, followed by corn + potato and corn starch plastic at last.

 

CONCLUSION:

Corn starch plastic is stronger, and degrades faster by soil microbes, compared to the other bio-plastics. It is water soluble, transparent, and also edible since it’s made from starch. It can be used as a substitute to petroleum based plastics, provided, it is processed by adding strengthening agents. It is already a constituent of PLA(poly-lactic acid)which is considered as the best source for bio-plastics.

 

ACKNOWLEDGEMENT:

We are grateful to our Chancellor Mr. G Viswanathan , for providing us with such good labs and technical support in VIT. We thank, Dr.Suneetha V, a truly dedicated faculty and mentor, for guiding us, and giving us the opportunity to work under her. We would like to extend our gratitude to MTCC and DSD for providing us with cultures and chemicals.

 

REFERENCES:

1.      Lörcks, Jürgen.,“Properties and Applications of Compostable Starch-Based Plastic Material.” Polymer Degradation and Stability, 1998, vol. 59, no. 1-3, pp. 245–249

2.      Liu, Chenguang, et al., “Preparation of Higher Molecular Weight Poly (L-Lactic Acid) by Chain Extension.” International Journal of Polymer Science, 2013, vol. 2013, pp. 1–6.

3.      Gonzalez-Gutierrez, J., et al., “Development of Highly-Transparent Protein/Starch-Based Bioplastics.” Bioresource Technology, 2010, vol. 101, no. 6, pp. 2007–2013.

4.      Yoshida, Shosuke, et al.,  “A Bacterium That Degrades and Assimilates Poly(Ethylene Terephthalate).” Science, 2016, vol. 351, no. 6278, pp. 1196–1199.

5.      Raghavan, P.u.m, and M Vivekanandan,  “Bioremediation of Oil-Spilled Sites through Seeding of Naturally Adapted Pseudomonas Putida.” International Biodeterioration& Biodegradation, 1999, vol. 44, no. 1, pp. 29–32.

6.      Hadad, D., et al.,“Biodegradation of Polyethylene by the Thermophilic Bacterium BrevibacillusBorstelensis.” Journal of Applied Microbiology, 2005, vol. 98, no. 5, pp. 1093–1100

7.      Bharali, P., et al., “Crude Biosurfactant from ThermophilicAlcaligenesFaecalis: Feasibility in Petro-Spill Bioremediation.” International Biodeterioration & Biodegradation, 2011, vol. 65, no. 5, pp. 682–690.

8.      Lee, Chang-Ho, et al.,“Identification of an Extracellular Catalyst of Carbon Tetrachloride Dehalogenation from Pseudomonas Stutzeri Strain KC as Pyridine-2,6-Bis(Thiocarboxylate).” Biochemical and Biophysical Research Communications, 1999, vol. 261, no. 3, pp. 562–566.

 

 

 

 

 

 

Accepted on 11.07.2018           © RJPT All right reserved

Research J. Pharm. and Tech 2018; 11(11): 4878-4883.