**5. Unconventional sources of pectin: hulls or husks and seeds**

It is well known that the primary sources of pectin extraction are those obtained from citrus fruits or apples, due to their high yield and physicochemical properties that make them useful for various applications in the food and pharmaceutical industries. However, in recent years, new extraction sources have been sought that may represent alternatives to overexploited sources and that also have the advantage of allowing the use of organic by-products, such as the case of hulls or husks and seeds, from which pectins with specific physicochemical properties of high utility for multiple applications can be obtained.

**Table 2** shows current research work regarding unconventional sources for obtaining pectins, classified as hulls or husks that come from dry fruits (almonds, pistachios, walnuts, and cocoa), pods, and legume seeds (soy, peas, faba beans, and riang), cereal leaves (*Zea mays*) and seeds of different fruits (*Nicandra physaloides* Linn., Gaertn, papaya, jackfruit, creeping fig and sesame). In addition, its extraction methods and its most outstanding properties are also described.

The most widely used pectin extraction method for hulls or husk and seeds is the conventional one, which consists of acidifying the sample, for which different types of organic (citric and oxalic acid) and inorganic (HCl and HNO3) acids are used; the
