Influence of Particle Size and Extraction Methods on Phenolic Content and Biological Activities of Pear Pomace

Abstract

The main goal of this research was to investigate how particle size influences the characteristics of pear (Pyrus Communis L.) pomace flour and to examine the impact of different pre-treatment methods on the phenolic content and associated bioactivities. Pear pomace flour was fractionated into different particle sizes, namely 1 mm, 710 µm, 180 µm, 75 µm and 53 µm. Then two extraction methods, namely maceration with methanol and two-step extraction with hexane via Soxhlet followed by ultrasound extraction with methanol, were tested. Total phenolic and total flavonoid contents ranged from 375.0 to 512.9 mg gallic acid/100 g DW and from 24.7 to 34.6 mg quercetin/100 g DW, respectively. Two-step extraction provided antioxidant activity up to 418.8 (in FRAP assay) and 340.0 mg Trolox/100 g DW (in DPPH assay). In order to explore various bioactive properties, this study assessed the inhibitory effects of enzymes, specifically α-amylase and β-glucosidase (associated with antidiabetic effects), as well as angiotensin-converting enzyme (linked to potential antihypertensive benefits). Additionally, the research investigated antibacterial potential against both Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria, revealing significant results (p < 0.05), particularly in the case of the two-step extraction method. This investigation underscores the substantial value of certain food industry wastes, highlighting their potential as bioactive ingredients within the framework of a circular economy.

Keywords: ACE; TFC; TPC; antidiabetic; antioxidant; pear pomace.

Figure 1

Total phenolic content (TPC) (a) and total flavonoid content TFC (b) of pear pomace flour. The data shown are mean values (n = 3) followed by an alphabet letter (for comparison between the different granulometric fractions subject to a two-step extraction), an alphabet letter and apostrophe (for comparison between the different granulometric fractions subject to maceration) or a Greek letter (when comparing extraction methods). Different letters mean significantly different results (p ≤ 0.05). DW: dry weight.

Figure 2

Antioxidant capacity of pear pomace flour measured via FRAP and DPPH assays. The data shown are mean values (n = 3) followed by an alphabet letter (for comparison between the different granulometric fractions subject to a two-step extraction), an alphabet letter and apostrophe (for comparison between the different granulometric fractions subject to maceration) or a Greek letter (when comparing extraction methods). Different letters mean significantly different results (Tukey’s HSD; p ≤ 0.05).

Figure 3

E. coli and S. aureus growth in the presence pear pomace powder at the same concentration of 5.0 mg/mL. The data shown are mean values (n = 3) followed by an alphabet letter (for comparison between the different granulometric fractions subject to a two-step extraction), an alphabet letter and apostrophe (for comparison between the different granulometric fractions subject to maceration). Different letters mean significantly different results (Tukey’s HSD; p ≤ 0.05).

Figure 4

Agglomerative hierarchical clustering (AHC) (A) and principal component analysis (PCA) (B) of phenolic compounds, biological activity and antibacterial activity of pear pomace flour. Active observations: 1A–5A—maceration (cluster 2—blue); 1B–5B—two-step extraction (cluster 2—green). Active variables: TPC—total phenolic content; TFC—total flavonoid content; FRAP—ferric reducing antioxidant power; DPPH –2,2-diphenyl-1-picryl-hydrazyl-hydrate; ACE—angiotensin-converting enzyme. Variables “α-amylase”, “β-glucosidase” and “ACE” mean inhibitory activity against those enzymes (according to Table 1). Variables of “E. coli” and “S. aureus” mean antibacterial activity against them (according to Figure 3).