Ultrasound-Assisted Extraction of Pectin from Malus domestica ‘Fălticeni’ Apple Pomace

Florina Dranca,Mircea Oroian

doi:10.3390/pr7080488

Abstract

The use of an ultrasonic treatment for the extraction of pectin from Malus domestica ‘Fălticeni’ apple pomace, its effects on extraction yield and galacturonic acid content, and degree of esterification of the extracted pectin were investigated. The optimization of the extraction process showed that the highest yield of 9.183% pectin, with a 98.127 g/100 g galacturonic acid content and 83.202% degree of esterification, was obtained at 100% amplitude, pH of 1.8, SLR of 1:10 g/mL, and 30 min. The pectin obtained in optimal extraction conditions was compared to commercial citrus and apple pectin in terms of chemical composition (determined by FT-IR), thermal behaviour (analyzed by differential scanning calorimetry), rheological properties, and morphological structure (analyzed by scanning electron microscopy). By comparison to commercial citrus and apple pectin samples, the FT-IR analysis of pectin extracted by ultrasound treatment confirmed the high degree of esterification and showed similarity to that of apple pectin (88.526%). It was found that the thermal behaviour of the pectin obtained by ultrasound-assisted extraction was influenced by the narrower distribution of molecular weights and the orderly molecular arrangement, while the rheological properties (high viscosity, G0, and G1) of this sample were influenced by the morphological structure and the galacturonic acid content. The correlation coefficient showed a strong positive relationship between viscosity and galacturonic acid content (r = 0.992**).

Highlights

Pectins have numerous applications in the food industry as technological adjuvants—the commercially available pectins are almost exclusively produced from citrus peel and apple pomace, two by-products of fruit juice manufacturing [1,2].Apart from these main sources, other raw materials such as banana peel [3,4], watermelon rind [5], mango peel [6,7], sisal waste [8], sunflower heads [9], pistachio green hull [10,11], and tomato waste [2] were used for extraction, and the resulting yield and the composition and properties of the obtained pectin were studied and reported
As a means to increase the economic viability of the apples from this hybrid variety, we previously reported on the first extractionof pectin from Malus domestica ‘Fălticeni’ apple pomace [28]
While no simultaneous major modification of galacturonic acid (GalA) content occurred, these results show that the de-esertification of pectin chains taking place in some conditions of the ultrasound treatment was not accompanied by changes in the main structural polygalacturonic chain of pectin, corroborating the conclusions regarding the effects of ultrasounds on the structure of apple pectin reported previously [45]

Summary

Introduction

Pectins have numerous applications in the food industry as technological adjuvants—the commercially available pectins are almost exclusively produced from citrus peel and apple pomace, two by-products of fruit juice manufacturing [1,2].Apart from these main sources, other raw materials such as banana peel [3,4], watermelon rind [5], mango peel [6,7], sisal waste [8], sunflower heads [9], pistachio green hull [10,11], and tomato waste [2] were used for extraction, and the resulting yield and the composition and properties of the obtained pectin were studied and reported. Because the overall process is time-consuming and the resulting yield can be limited, other non-conventional extraction techniques that include the use of microwave, ultrasound, subcritical water, and enzymes have been applied for the isolation of pectin [16]

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Conclusion