By combining enzymes called pectin methylesterase (PMEs) from a fruit (Valencia orange) and a fungus (Aspergillus aculeatus), the Korean and American scientists report the formation of a “pectin gelation system [that] could provide a useful alternative to acid-sugar or calcium cross-linked gels in food and other industrial applications”.
Researchers from Sejong University, Hanyang University, and the USDA’s Agricultural Research Service report their findings in the journal Food Hydrocolloids.
The chemical structure of pectin is based on a chain of repeating galacturonic acid units. In very basic terms, galacturonic acid has a ring structure with a carboxyl (CO2-) group jutting out. In nature, a large portion of these carboxyl groups have methanol (CH3OH) bonded via a reaction called esterification.
A high degree of esterification, or many bonded methanol groups, produces a high methoxyl (HM) pectin, while a low degree of esterification gives a low methoxyl (LM) pectin.
The chemical structure, including the level of esterification, and nature of other ingredients determines the strength of the gel. For example, calcium plays a significant role in gelling and is needed for LM pectins for form a gel since the pectin lacks methoxy groups on the carboxyl parts, the calcium acts as a bridge to bind pectin molecules together.
The researchers used pectin methylesterases (PMEs) from Valencia orange (Sigma Aldrich) and Aspergillus aculeatus (Novozymes) with citrus pectin (Sigma Aldrich), in the presence of certain ionic salts, including potassium and sodium chloride.
According to their findings, pectin gels formed following the enzymatic de-esterification of HM pectin with the orange-derived enzyme. The fungal enzyme didn not result in gel formation, they said.
When used in combination, a more stable gel was formed. Regarding the effects of the salts, potassium chloride resulted in stronger gels, they said.
“These results indicated that the pectin gelation of our system would be enhanced both by using larger monovalent cation and by lowering the DE value, which would presumably be attributed to the different action patterns recognized for [orange-derived] and [fungus-derived] PMEs,” they said.
The hydrocolloids umbrella
Gelling agents fall under the hydrocolloids umbrella - ingredients used extensively by the food industry to texturise and stabilise food products from dressings to ice cream. Though these products are sensitive to spiralling raw material costs, the demand for hydrocolloids remains impressive.
The food industry's most frequently used hydrocolloids include: agar, alginates, arabic, carrageenan, Carboxy Methyl Cellulose (CMC), gelatin, konjac flour, locust bean gum (LBG), Methyl Cellulose and hydroxypropyl Methyl Cellulose (MC/HPMC), microcrystalline cellulose (MCC), pectin, starch and Xanthan.
Source: Food Hydrocolloids
Volume 23, Issue 7, Pages 1926-1929
“Characteristics of enzymatically-deesterified pectin gels produced in the presence of monovalent ionic salts”
Authors: S.-H. Yoo, B.-H. Lee, B.J. Savary, S. Lee, H.G. Lee, A.T. Hotchkiss