Optimization, characterization and rheological behavior study of pectin extracted from chayote (Sechium edule) using ultrasound assisted method

Highlights

• Ultrasound-assisted extraction of pectin from chayote with higher yield be optimized.

• Chayote is a novel and alternative source for low-methoxyl pectin.

• Pectin with high Mw, water holding capacity and foaming capacity value be extracted.

• Chayote pectin solutions exhibited a pseudoplastic fluid behavior at 1%–5%.

Abstract

Pectin is one of high-value functional food ingredients. Better knowledge of properties of chayote pectin would help to promote the application of the chayote as a pectin source. In this study, ultrasound-assisted extraction (UAE) was used to extract chayote pectin. The extraction parameters were optimized by a Box-Behnken response surface design. The highest yield (6.19%) was obtained at a liquid/solid ratio of 50 mL/g, ultrasonic temperature of 70 °C and ultrasonic time of 40 min as optimized extraction conditions. The chemical properties, spectral information and rheological properties of pectin extracted with UAE under the optimum conditions (PEUO) were measured and the results indicated that the PEUO exhibited a low degree of esterification, high molar mass (2.47 × 10⁶ g/mol) and suitable foaming capacity. The PEUO featured a stronger antioxidant capacity compared to commercially apple pectin and the PEUO solutions (1%, 2%, 3% and 5%) showed a non-Newtonian behavior. Hence, PEUO may provide beneficial characteristics to find use in food industry.

Introduction

Chayote (Sechium edule) is a herbaceous perennial climbing plant belonging to the gourd family (Cucurbitaceae, subtribe Sicyinae) [1]. Chayote is native to Central America, Mexico and the Western Indies, and was introduced into China in the 19th century [2]. Almost all parts of the plant are edible, including the tuberous roots, shoots and fruits. The fruit is commonly known as chayote, christophene, vegetable pear, chuchu (Brazil) etc. [3]. As a raw fruit, the pulp has a firm and crisp texture that may feature a delicate and soft texture after cooking [4]. Chayote is widely consumed all over the world and the main producing countries include Mexico, Costa Rica, Brazil, Dominican Republic and China [5]. Nowadays, in the Guangdong Province, Sichuan Province, Yunnan Province and other areas in China, a large number of chayote cultivation facilities can be found.

Clinical and epidemiological studies showed that an inverse relationship between the consumption of chayote and the prevalence of chronic diseases exists [6,7]. These pharmacological properties depend on the bioactive compounds present in the composition of chayote, including flavonoids, phenols and vitamin C [[8], [9], [10]]. Further study to analyze the immunomodulatory effect of chayote pectin and results showed that crude chayote pectin has a cell protective effect [3]. Better knowledge of pectin composition and properties would help promote the use of the chayote fruit as a significant pectin source.

Pectin belongs to a family of complex polysaccharides that can be found in the primary cell walls and middle lamella of dicotyledons. Pectin as a high-value functional food ingredient is commonly used as a gelling, stabilizing, thickening and emulsifying agent in food industry [11]. In pharmaceutical industry, pectin features several applications and has been studied as a transmucosal delivery system [12]. Pectin involves a minimum of four different types of polysaccharides, such as homogalacturonan (HG), rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II), and in minor quantities xylogalacturonan [13]. HGs are liner homopolymers consisting of α-(1, 4) linked D-galacturonic acid residues. RG-I was found to feature a backbone containing diglycosyl repeat units of [→2)-α-L-Rhap-(1 → 4)-α-D-GalpA-(1→] featuring various side chains attached to the O-4 unit of the L-rhamnosyl residues [14,15].

Pectin is composed of a backbone of α-1, 4-galacturonic acid units which contain partially esterified carboxylic acid groups [16]. Based on these esterified carboxylic acid units, pectin can be classified into two categories: high methoxyl pectin (HMP, degree of esterification (DE) > 50%) and low methoxyl pectin (LMP, DE < 50%) [17]. Characteristics such as the chemical composition, molecular weight and rheological behavior of pectin are affected by the extraction method [18]. Existing extraction methods of pectin are mainly described as thermal methods at high temperature in acid solution including strong acids (e.g. HCl, HNO₃) and organic acids (e.g. malic, citric, and tartaric acid). The precipitation methods of pectin, including alcohol precipitation, metal precipitation, dialysis and membrane separation, represent other commonly used methods.

Furthermore, different non-conventional method ultrasound-assisted extraction (UAE) have been developed [19]. Due to the cavitation effect of ultrasound waves, the rate of mass transferring can be improved. Hosseini, Khodaiyan, Kazemi and Najari optimized the extraction process factors of pectin from sour orange peel using Box-Behnken design (BBD). The optimization process showed that the maximum extraction yield was 28.07 ± 0.67% in ultrasound power of 150 W, ultrasound time of 10 min and pH of 1.5 (as optimum conditions). The UAE yield of sour orange peel pectin was higher than aqueous extraction (17.95 ± 0.3%) in their optimum extraction conditions [20,21]. Therefore, UAE processing features a higher efficiency and yields pectin with a higher quality and a shorter extraction time [20]. Thus, UAE represents a suitable alternative to conventional extraction methods.

To the best of our knowledge, the data analysis available in research literature indicates a substantial lack in property studies of commercially available chayote pectin. Therefore, UAE and alcohol precipitation were used as methods to extract pectin from chayote. Then, optimized extraction variables based on a HCl solution-based extraction method were determined in an effort to obtain the highest pectin extraction yield. The response surface method (RSM) is a highly efficient statistical tool that can be used to determine optimized conditions for multifaceted processes [22]. In this study, RSM was used to optimize extraction efficiency of pectin from chayote. Finally, further studies reported herein focused on the production, characterization, antioxidant activity and rheological behavior of the extracted chayote pectin using UAE.