Biomedical Engineering Reference
In-Depth Information
bulk and microcapsule with maltodextrin as a wall material. The oxidative stability in bulk
system increased with increasing the acyl chain length, whereas that in the microcapsule was
the highest at the acyl chain length of 10. The esterification of various polyunsaturated fatty
acids, such as linoleic,
α
- and
γ
-linolenic, dihomo-
γ
-linolenic, arachidonic, eicosapentaenoic,
docosahexaenoic and conjugated linoleic acids with ascorbic acid and subsequent
microencapsulation significantly improved their oxidative stability.
Keywords:
Acyl ascorbate; Immobilized lipase; Continuous production; Amphiphilic food
additive; Antioxidative emulsifier
Introduction
Oxidation of lipids has received much attention due to its involvement in food spoilage
and the relevance of lipid peroxidation
in vivo
to membrane damage, aging, heart disease and
cancer [1]. Lipid oxidation is a complicated process including the steps of initiation,
propagation and termination. Antioxidants may be used at very low concentrations to
lengthen the oxidation induction period [2]. They are usually phenolic compounds such as
BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene), propyl gallate and
tocopherols (vitamin E), and are used to inhibit free radical chain reactions. L-Ascorbic acid,
which is a water-soluble compound and called as vitamin C, is also used widely as an additive
in foods and cosmetics due to its strong reducing ability. Lipophilic derivatives of ascorbic
acid acylated with a long-chain fatty acid such as palmitic acid are also used as additives in
foods rich in lipid [3]. These esters, which are mainly synthesized by a chemical method [4],
would be edible surfactants because each substrate is eaten daily as a food component.
It has
been reported that 6-
O
-palmytoyl ascorbate has antitumor activity and metastasis-inhibitory
effects [5, 6]. The 6-
O
- and 2-
O
-monoesters of ascorbic acid and phosphate or fatty acid have
physiological activity equivalent to unmodified vitamin C [7]. It has been recognized that
medium-chain fatty acids or their glycerides enhance the absorption of hydrophilic substances
in the intestine [8]. Therefore, it is expected that an ester of ascorbic acid and medium-chain
fatty acid itself could be easily absorbed in the intestine with the physiological activity of
vitamin C or that the ester could facilitate the absorption of hydrophilic substances. In
addition, not only medium-chain fatty acid but also polyunsaturated fatty acid may be used as
a substrate for the synthesis of acyl ascorbate. Polyunsaturated fatty acid has important
physiological functions such as antithrombotic, cholesterol depressant and antiallergenic
properties [9, 10]. For example, arachidonic acid is one of n-6 polyunsaturated fatty acids and
the precursor of prostaglandins, leukotrienes and related compounds, which play important
roles in inflammation and in the regulation of immunity [11]. However, it is well known that
polyunsaturated fatty acid, especially high unsaturated fatty acid, is extremely susceptible to
the oxidation [12]. The oxidative stability of polyunsaturated fatty acid may be improved by
esterification of the acid with ascorbic acid.
Acyl ascorbate consists of ascorbyl moiety as a hydrophilic group and acyl residue as a
hydrophobic group, and therefore it seems to be promising emulsifiers with both surface-
activity and reductivity. However, 6-
O
-palmitoyl and stearoyl ascorbates, which are
commercially available, are practically so insoluble in water that they would be difficult to
use as an emulsifier for preparation of O/W emulsions. Acyl ascorbates with shorter acyl
chains would be more amphiphilic than palmitoyl and stearoyl ascorbates. The ascorbates
