Its structure has a cis-trans structural isomer, which refers to a compound that has two isomers: geranial and neral . Citral is an essential oil component abundant in lemongrass and lemon balm and is used as a component of citrus fragrances because of its strong lemon-like scent. It is used as a flavoring agent in cosmetics and foods and as a raw material in the manufacture of other flavors and fragrances. The bioactivity of citral is reported to have antimicrobial, anti-inflammatory, analgesic, and sedative effects . Citral is easily oxidized under acidic and oxidative stress conditions, resulting in not only the loss of its lemon scent but also the production of undesirable off-flavors. In addition, citral gradually changes from a pale yellow to stronger yellowish color as it deteriorates. The mechanism of the formation of off-flavors in citral, as shown in Figure 2, is described as follows: First, p-menthadien-8-ol is formed by cyclization, which is then oxidized to p-cymen-8-ol, followed by the formation of p-methyl acetophenone via α- p-dimethyl styrene.
This p-methyl acetophenone has a lower threshold than the other products , a very strong deterioration odor, and is known to cause a signifificant quality loss in citrus products . The compound, p-menthadien-8-ol, has a lemon aroma, but compounds of the latter structures cause the deterioration of odors similar to p-methyl acetophenone.Isolation of Functional Compounds Used persimmons were obtained by separating the peel and flesh of each. Their immature persimmon was chopped by a commercial blender and homogenized after, finishing with a total volume of 3 L with water. Cold methanol was added to the water solution, and the mixture was allowed to stand 1 week in the dark to obtain crude extracts. The crude extracts were obtained by filtration and vacuum concentration. The crude extracts were extracted with hexane, then with 1-butanol to obtain hexane, 1-butanol, and water extracts. The isolation of 1-butanol extracts was performed by repeatEmulsions, which are thermodynamically metastable dispersion systems, are one of the forms of application of flavors in foods. Emulsions can change the rate of chemical reactions due to the presence of interfacial films that inhibit the reaction between the lipid and water phases .
The deterioration of citral may occur under both acidic and oxidative conditions, suggesting that the stability of citral may be improved by the formation of an emulsion. In this study, three types of alkanes , with citral mixed into them, were used for the oil phase, while SY-Glyster ML-750, an emulsifier, was used for the water phase. SY-Glyster ML-750 is a polyglyceryl fatty acid ester made by esterifying polyglycerin-10 and lauric acid. SY has been used as an excellent emulsifier in whipped cream, coffee whiteners, margarine, shortening, chocolate, milk drinks, and functional lipids. In this study, we investigated the optimal alkane and the inhibitory effect of citral deterioration caused by thinned persimmons in an emulsified form. Citral is a combination of the isomers geranial and neral. It is a lemon-scented aroma component that is widely used as a fragrance and flavoring in cosmetics and food. However, citral is susceptible to oxidation and deterioration, which causes the loss of its lemon scent, leading to the deterioration of food quality. Therefore, the addition of antioxidants is necessary. In this study, myrcenol and linalooloxide were detected as deteriorated substances using GC-MS, but other deteriorated substances were not tested. This formation route is thought to be caused by the effect of the SY-Glyster emulsifier .
Subsequently, we quantified citral, myrcenol, and linalooloxide. Then, in the water phase, the SY-Glyster ML-750 solution was used as an emulsifier, and TPA, a crude extract of the peel of Tone Wase persimmons, was added as an antioxidant, and gallic acid was added as a comparator substance at the respective concentrations. The control was prepared without the antioxidant TPA or GA. All of the abovementioned components were emulsified to produce emulsions, which were stored at 37 ◦C for 4 weeks, and the amounts of citral and deteriorated substances were measured and compared by gas chromatography every week. In this experiment, we investigated the oxidative stability of citral induced by the addition of antioxidants and the optimal combinations between the different types of alkanes and antioxidant concentrations.All the isolated compounds 1 to 12 showed higher activity than the positive control aminoguanidine in inhibiting the formation of AGEs. In particular, compounds 6 to 10 showed very high activity. These were catechins and procyanidins, which are polymers of catechin. Dicarbonyl compounds, such as glyoxal and methylglyoxal, are intermediates in the AGE formation route. It has been reported that catechins mainly trap dicarbonyl compounds through either the C6 or C8 position of the A-ring . Moreover, free radicals are also closely related to the formation of AGEs because their formation process generates a large number of free radicals .