Food Chemistry Husk Tomato (Physalis ixocarpa Brot.) Waste as a Promising Source of Pectin: Extraction and Physicochemical Characterization Blanca Elizabeth Morales-Contreras, Juan Carlos Contreras-Esquivel, Louise Wicker, Luz Araceli Ochoa-Mart´ ınez, and Juliana Morales-Castro Abstract: Husk tomato (Physalis ixocarpa Brot. var. Rendidora) waste was evaluated as a source of specialized pectin, and pectin extracted from this waste was characterized physicochemically. Fruit was blanched for 10 or 15 min and extracted in 0.1 N HCl for 15 to 25 min. Extracted pectin was subjected to physicochemical analysis. For all extraction conditions, the percentage of anhydrogalacturonic acid exceeded 60%, indicating that husk tomato was a good source of pectin. The degree of esterification of pectin molecules was 63% to 91%. The amount of extracted pectin decreased with increasing extraction time. The apparent viscosity of husk tomato pectin showed the characteristic behavior of pseudoplastic fluids. Neutral sugars were identified, and the amounts of 6 sugars (fucose, rhamnose, arabinose, galactose, glucose, and xylose) were quantified. Sugars identified in husk tomato pectin and present in the Rhamnogalacturonan I region, arabinose, galactose, and rhamnose suggest a highly branched structure, which will influence its future applications. Molecular weight values were 542 to 699 kDa, exceeding molecular weight values reported for commercial citrus pectins from 134 to 480 kDa. The extraction process significantly (P < 0.05) influenced the physicochemical properties of pectin. Up to 19.8% from the total amount of pectin in the husk tomato was extracted by 10 min of blanching and 20 min of a more heat treatment. Our findings indicate that husk tomato can be a good alternative source of pectin having highly distinctive physicochemical characteristics. Keywords: apparent viscosity, husk tomato, pectin, Physalis ixocarpa Brot., tomatillo Introduction Pectin is a complex polysaccharide that is found in plant cell walls (Voragen and others 1995). It is formed of 3 main domains: the linear homogalacturonan (HG) domain, the rhamnogalactur- onan I (RG-I) domain, and the rhamnogalacturonan II (RG-II) domain (Mohnen 2008; Voragen and others 2009). HG consists of α (1-4) linked-D-galacturonic acid, the most abundant component of pectin, which can be methoxylated at C-6 and/or acetylated at C-2 or C-3. Proportions of methyl and acetyl groups determine the pattern and DE of the HG domain. These features, together with the degree of polymerization, determine the functionality of pectin in food products (Willats and others 2006). The RG-I is one of the domains of the main structure of pectins. The proportion of RG-I domain depends on the source and extraction method of the pectin (O’Neill and others 1990). L-rhamnose residues may be attached to other neutral sugar side chains, such as arabinose and galactose. Compounds such as ferulic acid or coumaric acid may also be attached to this structure (Saulnier and Thibault 1999). Composition differences specific to pectins from different sources JFDS-2017-0186 Submitted 1/31/2017, Accepted 5/1/2017. Authors Morales- Contreras, Ochoa-Mart´ ınez, and Morales-Castro are with Dept. de Ingenier´ ıas Qu´ ımica y Bioqu´ ımica, TecNM/ Inst. Tecnol´ ogico de Durango, Blvd. Felipe Pescador 1830 Ote., Col. Nueva Vizcaya, 34080 Durango, M´ exico. Author Contreras- Esquivel is with Facultad de Ciencias Qu´ ımicas, Univ. Aut´ onoma de Coahuila, Ing J. C´ ardenas Valdez, Rep´ ublica, Saltillo, Coahuila, M´ exico. Author Wicker was formerly withDept. of Food Science and Technology, Univ. of Georgia, Athens, GA 30602- 7610, U.S.A. and is now withSchool of Nutrition and Food Sciences, Lousiana State Univ. Agricultural Center, Baton Rouge, LA, 70808, U.S.A. Direct inquiries to author Morales-Castro (E-mail: jmorales@itdurango.edu.mx). contribute to functional characteristics (such as gel-forming abil- ity), depending on which interactions are favored in the branched portion of the molecule (Round and others 2010). Global demand for pectins is estimated to be about 40000 tons per year, with an annual growth of about 5%. The food industry uses citrus waste and apple pomace to obtain pectin, but these sources are not sufficient to meet the market demand (Willats and others 2006; Ciriminna and others 2015). Innovation in food product development and the need for specialized hydrocolloids have driven the search for new ingredients and stabilizers. Pectin is commonly used as a gelling agent in different products, including bakery fillings and confectionary products in the food industry (Willats and others 2006). In recent years, its use has spread to other sectors, such as pharmaceuticals and cosmetics. The reported biological activity of pectins (Wang and others 2016), owing to the presence of proteins, ferulic acid, acetyl groups, and polyphenols, could further increase global demand for this product. Research has focused on identifying new sources of pectin and features that may confer new functional properties. Novel sources of pectin that have been studied include passion fruit (Kulkarni and Vijayanand 2010), banana peel (Gopi and others 2014), gold kiwifruit (Yuliarti and others 2015b), pomegranate peel (Pereira and others 2016), grapefruit (Wang and others 2016), tomato waste (Ninˇ cevi´ c Grassino and others 2016), Artocarpus heterophyllus waste (Moorthy and others 2017), and others. Husk tomato plants (Physalis ixocarpa Brot.) originated in Mexico but are grown in different countries. Its fruit, the tomatillo, as it is known in Latin America, is an important culinary fruit that has a distinctive flavor, both in raw and cooked form and it is added to sauces and salsas to increase consistency. Due to a husk tomato surplus or lower quality product, the fruit is discarded and food waste is generated; in C  2017 Institute of Food Technologists R  doi: 10.1111/1750-3841.13768 Vol. 00, Nr. 00, 2017  Journal of Food Science 1 Further reproduction without permission is prohibited