Pullulan or HPMC?
1: What is pullulan:
Pullulan is naturally occurring, as a cell wall component for fungus Aureobasidium pullulans.
Pullulan is produced from starch by the fungus Aureobasidium pullulans.
As an edible, bland and tasteless polymer, the chief commercial use of pullulan is in the manufacture of edible films that are used in various breath freshener or oral hygiene products such as Listerine Cool Mint PocketPaks. As a food additive, it is known by the E number E1204.
Chemistry: CAS number [9057-02-7]; Molecular formula (C6H12O5)n
Pullulan is a polysaccharide polymer consisting of maltotriose units, also known as α-1,4- ;α-1,6-glucan. Three glucose units in maltotriose are connected by an α-1,4 glycosidic bond, whereas consecutive maltotriose units are connected to each other by an α-1,6 glycosidic bond.
2: Why pullulan:
We choose pullulan over HPMC, because of following factors:
1): Pullulan is more natural, involving no toxic chemicals, much less environment polluting in its production process
2): Pullulan possess more potential for price reduction when produced in mass, because the fermentation technology used is widely used and very mature.
3): Pullulan film is 250 times stronger oxygen barrier than HPMC film, 9 time stronger than gelatin film
4): Pullulan is much more inert than gelatin or HPMC, so there is no interaction with products it intended to deliver
How pullulan is made
4: What is HPMC (Chemical names: Propylene glycol ether of methylcellulose)
Hydroxypropyl methylcellulose is a methylcellulose modified with a small amount of propylene glycol ether groups attached to the anhydroglucose of the cellulose. The dry product contains 19 to 30 per cent of methoxyl (-OCH3) groups and 3 to 12 per cent. of hydroxypropyl (-OCH2CHOHCH3) groups.
5: How HPMC is made:
The cellulose ethers are manufactured by a reaction of purified cellulose with alkylating reagents (methyl chloride) in
presence of a base, typically sodium hydroxide and an inert diluent. The addition of the base in combination with water
activates the cellulose matrix by disrupting the crystalline structure and increasing the access for the alkylating agent and
promotes the etherification reaction. This activated matrix is called alkali cellulose (Kirk-Othmer, 1993). During the
manufacture of HPMC alkali cellulose reacts with methyl chloride to produce methyl cellulose and sodium chloride. Side
reactions of the methyl chloride and sodium hydroxide produce methanol and dimethyl ether by-products. The
methylcellulose is then further reacted with the staged addition of an alkylene oxide, which in the case of HPMC is
propylene oxide (Kirk Othmer, 1993; Dow, 2002).
After this reaction, MC and HPMC are purified in hot water, where they are insoluble. Drying and grinding completes the
6: Chemicals involved in manufacturing HPMC
RcellOH:NaOH + CH3Cl + NaCl +RcellOCH3 + x C H3CH –O CH2 + Rcel – OCH3 +O (OCH2 CHCH3)xOH.
Dangerous chemicals involved:
Methyl chloride (CH3Cl) is colorless gas with a faint, sweet odor that is not noticeable at dangerous concentrations.
Synthetic forms are a chlorinated hydrocarbon derived from petroleum, and a suspected carcinogen. (Lewis, 1992; NJ
Propylene oxide is also a petroleum derivative.
EPA – Clean Air Act Amendments – final rule for National emission standards for hazardous air pollution (NESHAP)
includes cellulose ethers production source category as including major sources of emissions of hazardous air pollutants.
(FR67:112: 40044) June 11, 2002.
7: Other chemicals used in making HPMC capsules
Hundreds of US, EU and Japanese patents have been granted to various combinations of HPMC and other ingredients
used as capsules. These include carageenan, potassium chloride, polyvinyl chloride, polyethylene glycol, ammonium ions, gelatin, catechin, mannan gums, locust bean gum, pectin, glycerin, acetic acid, calcium gluconate, sucrose fatty acid esters (Chiba 1990, Matsuura 1993, Tanida 1998, Yamamoto 2002, Yang 2002).