Effect of ultrasonic pretreatments on the characteristics of pectin extracted from Salustiana orange cultivated in Argentina

Abstract

The use of direct and indirect ultrasound pretreatments was evaluated for the extraction of pectin enriched fractions with citric acid (pH 2.3, 85°C) from the albedo and pulp of Salustiana orange. The extractive method that produced the highest yield was the one involving a pretreatment with direct high-power ultrasound (HPUS) (41 g isolated fraction/100 g albedo CM versus 30 g isolated fraction/ 100 g albedo CM for indirect treatment; 39 g isolated fraction/100 g pulp CM versus 26 g isolated fraction/100 g pulp CM for indirect treatment) and allowed extracting the highest amount of pectin from both albedo and pulp. The major neutral sugars found in all fractions were arabinose, galactose, and rhamnose. Pectins were obtained with weight average molecular masses of 566–729 kDa from the albedo and 663–739 kDa from the pulp. All fractions gelled in the presence of sucrose at acidic pH. Pretreatment with HPUS gave origin to the least elastic gels (albedo: G′ higher than 100 Pa, G″ higher than 20 Pa. Pulp: G′ higher than 70 Pa, G″ higher than 25 Pa), while indirect US produced fractions that formed more elastic gels (albedo: G′ higher than 1000 Pa, G″ higher than 250 Pa. Pulp: G′ higher than 500 Pa, G″ higher than 100 Pa). Ultrasound pretreatments allowed obtaining a variety of pectin enriched fractions with interesting characteristics for food formulation. Practical applications: Pectins are widely used as texture modifiers in the food industry. Commercial pectins are commonly obtained from waste from the citrus juice industry, using mineral acids at high temperatures, producing large amounts of polluting effluents. The study of the use of organic acids in combination with clean technologies such as ultrasound, which allow higher pectin yields to be obtained through less polluting processes, is of great interest as an environmentally friendly alternative. Likewise, it is important to demonstrate that the pectins obtained through such technologies are effectively useful for the industry as texture modifying additives. In this work it is proposed to study the effect of the use of indirect and direct ultrasound as pretreatments in the extraction with citric acid of Salustiana orange pectin.