Effect of Anti-Obesity and Antioxidant Activity through the Additional Consumption of Peel from 'Fuji' Pre-Washed Apple

Abstract

There is limited information on the health effects of apple peel taken from 'Fuji' (Malus pumila Mill) apples washed with ozonated water. To clarify the health-promoting effects of peel, the triterpenoids (ursolic acid and oleanolic acid) were quantified with gas chromatograph-mass spectrometry. Anti-obesity effects of apple peel extract on the 3T3-L1 pre-adipocyte cell were compared with apple flesh, whole apple, and ursolic acid. The peel extract treatment with 3.30 ± 1.05 μM of ursolic acid significantly suppressed (p < 0.05) the lipid accumulation compared with the content in flesh, and a similar level was reached in the 5 μM ursolic acid positive control group. In the peel extract and ursolic acid treatment groups, the C16:0 concentration was significantly inhibited (p < 0.05), implying the anti-obesity effect of ursolic acid on the 3T3-L1 cell. Moreover, apple peel contributed 41% of the total flavonoids content and 31% of the phenolic contents of the whole apple, but only accounted for less than 10% of the whole apple (weight basis). This study's results offer basic data on pre-washed apple as a health functional food, offering information about the health benefits of apple peel, calculated based on the partial ratio in the whole apple.

Keywords: 3T3-L1; anti-obesity; apple peel; fresh-cut foods; pre-washed apple.

Figure 1

Antioxidant activities and compounds in different antioxidant assays comparing whole apple (peel + flesh) and flesh. NS, asterisk **, and asterisk *** indicate non-significant and significant differences between the peel and the flesh within the same assay, assessed by Student t-test at p > 0.05, p < 0.01, and p < 0.001, respectively. (A): Ferric-reducing antioxidant power; (B): DPPH radical scavenging activity; (C): total flavonoid contents; (D): total phenolic contents.

Figure 2

Triterpenoid contents of pre-washed apple peel, whole apple, and flesh. Different letters indicate significant differences (p < 0.05) among the tissues by Tukey’s HSD test (n = 3). Whole apple bioactive contents were calculated per peel and flesh portion.

Figure 3

3T3-L1 cell adipocyte images, observed and photographed using a microscope (×400) after cellular lipid accumulation was stained with Oil-Red O solution. The cells were from 70% methanol-treated extracts (1 μg dry powder in 1 mL of DMSO) of peel, flesh, and whole apple (peel + flesh) concentrated samples, or those treated with ursolic acid 5 μM. During the three repetitions of the treatments, a representative photograph was taken.

Figure 4

Lipid accumulation rate determined by Oil-Red O assay in 3T3-L1 cells treated with 70% methanol extract (1 μg dry powder in 1 mL of DMSO) from peel, flesh, and whole apple (peel + flesh) samples, or ursolic acid 5 μM-treated samples. The data are represented as % of lipid accumulation compared to control. The bar and error bar indicate mean and standard deviation (n = 3). Different letters indicate significant differences among the groups according to Tukey’s HSD test at p < 0.05.

Figure 5

Total triglyceride content determination from 3T3-L1 cells treated with 70% methanol extracts (1 μg dry powder in 1 mL of DMSO) from peel, flesh, and whole apple (peel + flesh) samples or ursolic acid 5 μM treated samples. The data represent the mean and standard deviation (n = 3). Different letters indicate significant differences among the groups according to Tukey’s HSD test at p < 0.05.